34. New LEDs may offer better way to clean water in remote areas Graphene plasmons reach the infrared... 34

Transcription

1

2 目录 一. 光学与工程 Full-circle viewing: 360-degree electronic holographic display Scientists manipulate surfaces to make them invisible Converting optical frequencies with 10^(-21) uncertainty Nanoantenna lighting-rod effect produces Making silicon-germanium core fibers a reality Fluorescent holography: Upending the world of biological imaging Laser researchers boldly go into uncharted THz territory Professor developing super-resolution microscopy techniques Lasers + anti-lasers: Marriage opens door to development of single device with exceptional range of optical capabilities First random laser made of paper-based ceramics Light detector with record-high sensitivity to revolutionize imaging Building a bright future for lasers Low-power tabletop source of ultrashort electron beams could replace car-size X-ray devices Capturing an elusive spectrum of light 二. 光子学 Scientists create most efficient quantum cascade laser ever Innovative technique for shaping light could solve bandwidth crunch Researchers demonstrate extension of electronic metrology to the multi-petahertz frequency range Move over, lasers: Scientists can now create holograms from neutrons, too Controlling electrons in time and space Optical clock technology tested in space for first time Molecular imaging hack makes cameras 'faster' New records set up with 'screws of light' Scientists fabricate a new class of crystalline solid A new way to image solar cells in 3-D 三. 电子工程 A phone that charges in seconds? Scientists bring it closer to reality Developing graphene microwave photodetector Fujitsu develops analysis technology to improve communication performance of virtual networks Unusual quantum liquid on crystal surface could inspire future electronics Thermoelectric paint enables walls to convert heat into electricity 四. 纳米物理与材料 Supersonic spray yields new nanomaterial for bendable, wearable electronics 'Exceptional' nanosensor architecture based on exceptional points New ultra-thin semiconductor could extend life of Moore's Law New solution for making 2-D nanomaterials... 32

3 34. New LEDs may offer better way to clean water in remote areas Graphene plasmons reach the infrared 五. 量子物理 Quantum computers: 10-fold boost in stability achieved New 3-D wiring technique brings scalable quantum computers closer to reality Subnatural-linewidth biphotons generated from a Doppler-broadened hot atomic vapor cell Scientists discover particles similar to Majorana fermions Novel light sources made of 2-D materials Breakthrough in the quantum transfer of information between matter and light 六. 技术与应用 VTT creates the world's first hyperspectral iphone camera Faster manufacturing of breath sensors... 40

4 简介 一. 光学与工程 度角全息电子显示器... 1 简介 : 韩国 5G 通信研究实验室和电子通信研究所的一个科学家研究团队设计出 360 度全方位可视 3-D 全息显示器, 设备体积小, 可放置在桌面上 这款新研发的电脑显示器系统能使多个观看者从不同角度看 3-D 全息影像, 无须戴专用眼镜 2. 科学家们通过操控设备表面达到抗反射效果... 1 简介 : 大多数透镜 眼镜 激光器等器件都镀有一层减反膜, 这些膜只在狭窄的波长范围内起作用 德国马克斯普朗克智能技术研究所的科学家为解决这一局限性, 研究出镀膜的替代技术, 无须在器件表面进行镀膜处理, 而直接操控器件的表面, 能在很宽的波长范围内达到抗反射效果, 极大地提高了表面光传输效率 未来这种纳米结构表面可改进高效激光器 触屏以及太阳能电池组件的输出效率 3. 光学频率转换的不确定性提高到 10^(-21) 精确度... 3 简介 : 光频梳的发明为光频分频器的研发工作铺平道路 2003 年光频转换不确定性的精确度是 10^(-19) 最近中国华东师范大学的研究团队在此基础上整合几个关键技术, 实现了低噪音 高精度的光频分频器的研究研发工作, 其不确定精确度可达 10^(-21) 4. 纳米天线避雷针启发新型光开关的研发... 4 简介 : 英国南安普顿大学的一个科学家研究团队基于金纳米相变技术, 研制出纳米级快速光学晶体管, 为光学开关及光学记忆开辟了新的研究方向, 将掀起新的光学应用浪潮, 包括微小光电路 光学材料平面光学设备等 5. 科学家把锗化硅的内核用作玻璃纤维... 5 简介 : 挪威科技大学的一个科研团队用单晶锗化硅的核研制出玻璃纤维, 他们所采用的生产工艺有助于研发高速半导体设备, 比如研发可增强内窥镜工作性能的设备等 6. 荧光显微镜的全息成像技术... 6 简介 : 美国科罗拉多州立大学的一个从事电学工程研究的科学家设计并建造了一个荧光探测显微镜 此显微镜结合了 3-D 高清成像工艺, 比同类显微镜的成像速度更快, 可用于生物医学, 能生成更加清晰的细胞组织 3-D 影像, 而且可以同时给多个细胞进行成像处理, 而传统的光学显微镜一次只能给一个细胞进行成像处理 7. 研究人员进军太赫兹激光器研究的未知领域... 7 简介 : 美国里海大学的一名研究人员进行太赫兹光频激光器的研究, 涉足这个研究领域的人很少, 该研究人员着力于前沿的太赫兹半导体量子级联技术的开发, 他与他的同事在高温条件下操作激光器方面的研究工作达到了世界领先水平 他们未来研究的目标是要研发出用于更广泛领域的一系列激光设备, 比如, 化学生物传感显微镜 光谱显微镜 爆炸物及走私物品检测仪 疾病诊断仪, 药品质量控制仪以及天文遥感设备等 8. 研发出新的超清显微镜技术... 8 简介 : 美国新墨西哥大学的教授研究出一个新的荧光显微镜技术, 为研究细胞的相互作用打开了新的视野 这项技术叫单物体光片照明显微镜技术, 是对现有的荧光显微镜进行的一项改进 研究人员将该显微镜产生的一片光与待成像的焦面匹配后, 再减少其照明及系统噪音, 这时的信号能使我们看见细胞内蛋白质组织的动态活动 他们下一步的工作是研发出下一代新的芯片技术 9. 新型集成设备具有非凡的激光和抗激光性能... 9

5 简介 : 美国伯克利国家实验室的科学家首次研制出激光 - 抗激光单台设备, 他们在电信光频内演示了同时具有这两种相反功能的设备 他们的研究为未来研发出可弹性操作的激光器 放大器 调谐器 减震器以及探测仪等集成设备奠定了基础 10. 世界上首例随机纸基陶瓷激光器 简介 : 罗马大学和慕尼黑技术大学的物理学家使用新的材料技术制成了世界上首例基于纸纤维素的随机可控激光器 这项研究工作具有很大的实际应用潜力, 比如用于结构可变化的微开关或者微探测仪等 11. 新型超感 高清光检测仪 简介 : 芬兰阿尔托大学的一个研究团队研发出一个新型光检测器, 能捕捉超过 96% 的光子, 包括可见波 红外波和紫外波 他们已经为此仪器申请了专利, 该仪器的模型正在测试中, 其成像技术可应用于药品和安全领域 研究人员正致力于研究开发此产品的新应用 12. 激光器的未来前景 简介 : 太赫兹激光器能产生频率为每秒 30 亿转的光子, 而大多数电子光学和红外激光器不容易达到这一太赫兹范畴 美国加州大学洛杉矶分校的研究人员在此项研究中取得了可喜的成果 他们研制出一款太赫兹量子级联激光器, 可是对其进行操作时, 科学们必须将激光器冷却至 77K 研究人员正探索设计可在室温条件下进行操作的量子级联激光器 13. 低功率超短电子梁的小型光源设备有望取代大型 X 射线设备 简介 : 美国麻省理工学院 德国加速器中心和德国汉堡大学的研究人员描述了他们用电子爆裂研究的新技术, 基于此技术, 他们研发出只有一只鞋大小的设备, 其所耗能量只需以往设备的一小部分, 而其威力却毫不逊色 此设备可对细胞的工作机制进行实时成像, 将来这种低功率超短电子设备有望取代现在汽车大小的 X 射线设备 14. 捕捉捉摸不定光谱光线的新技术 简介 : 瑞士联邦工学院的研究人员建造了一台超高质量的光学微腔, 用于捕捉捉摸不定的中红外光谱域, 为研发新的化学和生物传感器拓宽了道路, 其技术前景看好 可实际应用于分子光谱显微镜 化学传感以及生物检测等 二. 光子学 科学家制造出目前世界上效率最高的量子级联激光器 简介 : 美国中央佛罗里达大学的一个研究团队研发出兼容性强, 生产效率高的激光器工艺 用此激光器不仅使激光制造更加容易, 而且所生产出来的激光器是目前世界上效率最高的量子级联激光器, 其体积比一粒大米还小, 而其输出功率则比以往的激光器都要大, 还可调至很宽的红外波长, 并能在室温环境下使用 16. 新科技解决了光通信的带宽问题 简介 : 南非金山大学的研究人员研究出一个空间多元技术, 重塑激光束, 使每束激光形成多元模式, 而每个模式都能传输信息 此项技术解决了目前网络只用一个空间模式进行信息传输的局限性. 17. 电子度量衡达到了多皮赫兹频率值 简介 : 德国马克斯普朗克研究所的研究人员发现了一个新方法, 他们演示了绝缘体激光光诱导高速转换如何把导体状态与受到激光脉冲冲击的高频光发射连结起来, 其频率达到了 8 皮赫兹, 可应用于高速传输设备 他们期望这一技术能够使科学家们研究出新的方法来探索原子级动力学与凝聚态物质结构之间的相互作用关系 18. 科学家用中子梁生成固物全息图... 17

6 简介 : 美国国家标准技术研究所的科学家们首次用中子生成大固体物质的全息图, 揭示了物体内部的详细结构, 是一项普通光基可视激光全息技术所实现不了的技术 他们的这一发现为将来探索固体物质材料提供了新的方法 19. 在时空中控制电子 简介 : 奥地利维也纳技术大学和德国埃尔朗根纽伦堡大学合作研究出一个控制电子发射的新方法, 其精确度达到有史以来的最高水平 他们借助于两个激光脉冲, 在超短的时间尺度内开启和关闭电子流 此项新技术开启了控制 X 射线的新时代 20. 首次在太空中测试光学钟 简介 : 美国光学协会期刊 光学 发表了一项具有很大影响力的研究成果 - 新型光学钟 此款光学钟克服了火箭发射的极端条件, 完成了太空之旅并能在微重力下正常使用 这将最终导致基于 GPS 导航系统得以在太空中应用 研究人员计划在 2017 年底完成光学钟的改进版, 并在未来的研究工作中, 实现让光学钟克服宇宙辐射的恶劣条件并确保其在轨道正常使用几年的时间 21. 分子成像盒使照相机的成像速度更快 简介 : 美国莱斯大学的研究人员研究出新的分子成像技术, 其成像速度比大多数实验室用的照相机都要快, 帧速率快 20 倍 这项技术也就是超瞬时 超清晰显微镜技术 22. 螺旋光创立新记录 简介 : 奥地利维也纳大学的一个研究团队用扭曲光粒子进行实验, 打破了以往的研究记录, 使我们看到了一个单个光粒子所拥有的巨大信息能力, 为将来的实际应用提供了无限的可能性 实验证明把单个光子扭曲成螺旋结构, 其量子特性没有丧失, 仍可承载任意大量信息, 其传输距离可达 100 多公里, 这一发现为将来的量子技术研究工作开辟了新的道路 23. 科学家们研究出新型晶体 简介 : 美国里海大学的科学家与劳伦斯伯克利国家实验室的万研究人员合作研制出一类新型晶体, 他们演示了其研制过程 : 用激光加热技术诱导原子组成旋转晶格而不影响其可视固体形状 通过控制晶体旋转制造出具有超电子和光学性能的新型合成单晶体以及仿生材料 24. 用新方法对太阳能电池进行 3-D 成像 简介 : 美国劳伦斯国家实验室的科学家研究出一个用光学显微镜给薄太阳能电池吸收光子时成像的新方法 这一成像技术可用来给微米级材料内部动态活动进行光电成像, 为达到这一成像目的, 他们使用了高焦红外光子激光束穿透光伏材料的内部, 这一成像技术有助于科学家设计出更好的太阳能电池以及其他生活应用产品 三. 电子工程 25. 给手机快速充电新技术 简介 : 美国中央佛罗里达大学纳米科学技术中心的科学家研发一个制造柔性超级电容器的新工艺, 此电容器的储电能力更大, 可重复充电 多次, 而其充电能力却不减弱 这一革命性技术创新给手机和电驱车辆等带来了福音 26. 韩国研制出石墨烯微波光电探测仪 简介 : 韩国大邱庆北科学技术院的一个联合研究团队研制出低温微波光电探测仪, 比现有的探测仪的探测能力高出 倍, 这是目前世界上第一台用石墨烯制成的光电探测仪 27. 日本富士通改进虚拟网络通信功能的分析技术 简介 : 日本富士通公司通过研究出新的技术来改进对虚拟网络通信功能的分析方法 这项技术大概能提高两倍的虚拟网络速度并能保证较高的网络通信质量, 即使系统的结构或者使用条件不断变化也不影响其通信效果 28. 晶体表面不寻常的电子流启发未来电子设备的研究工作... 28

7 简介 : 美国普林斯顿大学和德克萨斯大学奥斯汀分校的研究人员首次通过实验在高磁场环境下直接给电子轨道成像, 他们演示了电子在低温条件下产生量子的行为, 并能在铋晶体表面沿着同一个椭圆形轨道运行, 从而形成量子流态 这项研究揭示了电子不寻常的集体行为, 这一发现意味着找到了操控带电粒子的新方法, 有望在将来研制出新的电子设备 29. 热电涂料能使墙壁把热转换成电 简介 : 韩国蔚山国家科技研究所的研究人员宣布了他们的一个新研究成果, 并演示了把热电涂料转换成电的过程, 即如何把捕捉到的涂料表面的废热转换成电能 这项研究可实际应用于 3-D 打印电子产品 电子绘画艺术等, 他们还计划进一步研究开发其他应用 四. 纳米物理与材料 新的用于可穿戴电子产品的纳米材料 简介 : 美国伊利诺伊大学和韩国高丽大学的一个国际合作研究团队用简单低能耗的方法研制出一种新的超薄透明而且具有高导电性能的薄膜 具体方法就是使用一个小喷射管以超声速度给银纳米线喷纳米粒子 此薄膜产品可变曲 可拉伸, 其应用潜力很大, 可用于可卷曲触屏显示器 可穿戴电子产品 柔性太阳能电池以及电子皮肤等 31. 新型超感纳米传感器 简介 : 美国加利福尼亚大学圣地亚哥分校的研究人员研究出设计小型 超感纳米传感器的新方法, 此传感器适用于可携带健康监测设备, 也可用于探测毒气及爆炸物等 他们正致力于研究如何将此传感器独立集成到芯片上 32. 新研发的超薄半导体拓展了摩尔定律的适用范围 简介 : 英国曼彻斯特大学和诺丁汉大学的研究人员研发出新的半导体材料, 硒化铟, 其厚度只有几个原子厚, 类似石墨烯, 却比石墨烯的能隙大, 其电子性能比硅高, 适用于下一代超快电子设备 这一新研制的 2-D 晶体材料因其结构 厚度和化学成份的不同而具有变化多样的性能 33. 制造 2-D 纳米材料的新方法 简介 : 英国伦敦大学的研究人员把层叠纳米材料进行液溶处理制造出 2-D 纳米材料, 不仅制造成本低, 而且这种材料能实现符合未来研究要求的应用价值 这一方法可扩展用在其他多种材料上, 包括那些具有半导体和热电电能的材料, 甚至可以制造出用于太阳能电池的 2-D 材料, 把废热转换成电能 34. 新的用于水净化的发光二极管 简介 : 美国俄亥俄州立大学的研究人员首次用轻重量的金属箔研制出发光二级管, 用于可携带紫外线灯 饮用水净化以及医学用消毒设备 他们目前正致力于研制更亮的纳米线发光二级管, 将研究材料扩展为普通的金属如钢和铝等 35. 石墨烯等离子能够与红外光谱相互作用 简介 : 石墨烯是很好的导体, 但是它却不能与光进行相互作用, 如果要想使其在电信方面得到应用, 只有光谱近红外区域的光子具有这种可能性 丹麦技术大学的研究人员首次演示了石墨烯如何有效强化吸收 2 微米波长光, 他们借助于纳米级石墨烯盘的等离子来实现这一目的 这一研究团队计划将来用电先通信号技术对石墨烯等离子进行调谐, 使其快速振动, 实现石墨烯在电信领域的更多应用 五. 量子物理 量子计算机的稳定时长延了 10 倍... 35

8 简介 : 澳大利亚新南威尔士大学的一个研究团队研究出新的量子比特, 其特点是叠加稳定时间比以住长了 10 倍, 可使未来硅量子计算机的计算时间延长 他们演示了这种新的量子比特是由自旋硅原子组成的, 并将其浸入电磁场中, 促使量子信息持续更长的时间, 为未来制造出超强量子计算机开辟了新的途径 37. 新的 3-D 布线技术使可伸缩量子计算机更接近我们的生活 简介 : 加拿大滑铁卢大学量子计算研究所的研究人员研发一种新的延长 3-D 布线技术, 能控制超导量子比特, 这标志着科学研究使我们向实现可伸缩量子计算机的目标向前迈进了关键的一步 38. 用多谱勒热原子气泡装置生成亚线宽双光子 简介 : 在过去的二十年, 科学家经常用激光冷却的办法来生成双光子, 但是用来生成双光子的设备又大又复杂 香港科技大学的一个科研团队用多谱勒 (530MH Z ) 热原子气泡生成亚自然线宽 (<6MH2) 双光子 这一方法在这一研究领域具有突破性意义, 极大地简化了窄频带双光子的生成工艺 39. 科学家发现类似马约纳拉 (Majorana) 费米子的粒子 简介 : 最近中科院量子信息重点实验室的一个研究团队的科学家们发现了一种特殊的准粒子, 具有马约纳拉费米子的特征, 他们用光学目标模拟器成功生成并控制了这种粒子 他们运用的方法为研究量子统计学 拓扑量子计算以及马约纳拉费米子的特征提供了新的方法, 为将来建立此领域的研究平台打下了基础 40. 用 2-D 材料制成新的光源 简介 : 德国维尔茨堡大学的物理学家设计出了发射光子对的光源, 特别适用于拍敲校验的加密技术, 实验的关键成份是半导体晶体和胶带, 这个称为单层光源的设备供给能量时能生成光, 此项技术有助于研制出新型激光器, 而且还可以用来研究量子效应 41. 光与物质之间量子信息传输的突破性研究 简介 : 加拿大蒙特利尔理工学院和法国国家科研中心的一个研究团队研制出硒化锌量子位, 硒化锌是一种半导体材料, 这一项研究的结果使量子物理主导的纳米级物质行为与光速信息传输之间建立起了接口, 为建立量子信息网络铺平了道路 六. 技术与应用 高光谱手机摄像头的诞生 简介 : 芬兰 VTT 技术研究中心研制出世界上首例高光谱移动设备 他们把手机摄像头转换成一种光学传感器, 为低成本光谱成像带来了新的可能性, 在实际的生活应用中能给消费者带来很大的方便, 可用它对食品质量进行传感, 实时监控健康饮食 43. 快速制造呼吸传感器 简介 : 日本大阪大学的一组研究人员成功研制出纳米结构气体传感器, 用于检测呼吸中的挥发性有机化合物, 制造此传感器所用的时间少于制造传统传感器的十分之一时间, 而且它与目前世界上正在使用的传感器都兼容, 非常适用于健康保健

9 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) 一. 光学与工程 1. Full-circle viewing: 360-degree electronic holographic display Schematic of the design of 360-degree tabletop electronic holographic display, the design concept of which allows several persons to enjoy the hologram contents simultaneously. In the original 'Star Wars' movie, the inviting but grainy special effects hologram might soon be a true full-color, full-size holographic image, due to advances by a South Korean research team refining 3-D holographic displays. The team described a novel tabletop display system that allows multiple viewers to simultaneously view a hologram showing a full 3-D image as they walk around the tabletop, giving complete 360-degree access. The paper was published this week in the journal Optics Express. To be commercially feasible in a range of applications from medicine to gaming to media the hologram challenge is daunting. It involves scaling an electronic device to a size small enough to fit on a table top, while making it robust enough to render immense amounts of data needed to create a full-surround 3-D viewing experience from every angle without the need for special glasses or other viewing aids. "In the past, researchers interested in holographic display systems proposed or focused on methods for overcoming limitations in the combined spatial resolution and speed of commercially available, spatial light modulators. Representative techniques included space-division multiplexing (SDM), time-division multiplexing (TDM) and combination of those two techniques," explained Yongjun Lim, of the 5G Giga Communication Research Laboratory, Electronics and Telecommunications Research Institute, South Korea. Lim and his team took a different approach. They devised and added a novel viewing window design. To implement such a viewing window design, close attention had to be paid to the optical image system. "With a tabletop display, a viewing window can be created by using a magnified virtual hologram, but the plane of the image is tilted with respect to the rotational axis and is projected using with two parabolic mirrors," Lim explained. "But because the parabolic mirrors do not have an optically-flat surface, visual distortion can result. We needed to solve the visual distortion by designing an aspheric lens." Lim further noted, "As a result, multiple viewers are able to observe 3.2-inch size holograms from any position around the table without visual distortion." Building on these advances, Lim's team hopes to implement a key design feature of strategically sizing the viewing window so it is closely related to the effective pixel size of the rotating image of the virtual hologram. Watching through this window, observers' eyes are positioned to accept the holographic image light field because the system tilts the virtual hologram plane relative to the rotational axis. To enhance the viewing experience the team hopes to design a system in which observers can see 3.2-inch holographic 3-D images floating on the surface of the parabolic mirror system at a rate of 20 frames per second. Test results of the system using a 3-D model and computer-generated holograms were promising though right now still in a monochrome green color. Next, the team wants to produce a full-color experience and resolve issues related to undesirable aberration and brightness mismatch among the four digital micromirror devices used in the display. "We are developing another version of our system to solve those issues and expect to have the next model in the near future, including enhancement of the color expression," said Lim. "Many people expect that high quality holograms will entertain them in the near future because visualizations are increasingly sophisticated and highly imaginative due to the use of computer-aided graphics and recently-developed digital devices that provide augmented or virtual reality." And the Princess Leia hologram? That old miniature was a motivating experience of their work, Lim explained. e-electronic-holographic.html 2. Scientists manipulate surfaces to make them invisible Image of the Greek goddess Minerva as seen under a fused silica substrate with 450 nm nanopillars on both sides (left) compared to an unstructured reference (right). Each substrate 1

10 光学与工程 has a diameter of 25 mm, matching the size of the drawing. The top set of images were taken at an observation angle of 0, the bottom set of images at an observation angle of 30. Most lenses, objectives, eyeglass lenses, and lasers come with an anti-reflective coating. Unfortunately, this coating works optimally only within a narrow wavelength range. Scientists at the Max Planck Institute for Intelligent Systems in Stuttgart have now introduced an alternative technology. Instead of coating a surface, they manipulate the surface itself. By comparison with conventional procedures, this provides the desired anti-reflective effect across a wider wavelength range. But more than this, it largely increases the light transmittance through surfaces. In the future, the nanostructured surfaces may improve high-energy lasers as well as touchscreens and the output of solar modules. Researchers at the Max Planck Institute for Intelligent Systems took a page out of the design book for moth cornea. The corneas of these mostly nocturnal insects reflect almost no incoming light. There is no glow of light bouncing off the moth's eyes to betray their presence to potential predators. Less reflected light also means that moths are able to use practically all the scarce night-time light to see. This magic from the world of insects inspired scientists to try the same tactics for the design of optical components. Like the corneas of moths, the components must allow light to pass through while light reflection is of little use. So far, component designers apply anti-reflective coating to lenses, display screens, monitors and laser components. However, these coatings have disadvantages. Most of them work only in a narrow wavelength range, and they produce lens errors dependent on the angle of light incidence. Applying the moth cornea principle will put an end to these problems. Scientists at the Max Planck Institute for Intelligent Systems, Department for New Materials and Biosystems, under the guidance of Director Joachim Spatz had a good look at their natural model. Physicist Zhaolu Diao explains nature's design: "The eye surface is densely covered with column-like structures. They are only a few hundred nanometres high and taper conically toward the tip". The columns look like regularly spaced stalagmites on a cavern floor. As the light passes through this boundary layer, its refractive index changes continuously, starting from the ambient air to the materials of the outer moth eye layers. This gradual refractive index change has the effect that the layer hardly reflects any of the incoming light. Instead, almost all incoming light penetrates into the eye. By contrast, when incoming light hits a smooth surface, the refractive index will change abruptly. Based on the laws of physics, this will cause light reflection. Diao adds another important prerequisite: "To make the system work, the distances between individual columns must be significantly smaller than the wavelength of the incoming light." To imitate the moth eye principle, the scientists needed to find a way of turning smooth surfaces into nano-column landscapes. To accomplish this they developed a two-step process. In the first step, they deposited gold particles in a regular honeycomb pattern on a large surface. In this regular honeycomb pattern, the gold particles settle in the points of crossroad. In the second step, the gold-studded crossroads serve as mask in a chemical etching process. As a result, no material is etched away underneath the gold-studded crossroads, and the desired upright column-like structures remain. The structured surfaces covered as much as two by two centimetres. The column height is of the essence While this technique registered first successes in the past, it has so far only worked for short wave UV radiation and visible light. However, the same was not the case for the longer wavelengths of near infrared light (NIR). The reason for this was the column size. Until then, the columns etched out of the surface were at most 500 nanometres high. The columns are not high enough to reach the 99.5 per cent or higher light transmittance for the wavelengths in the NIR range. "The longer the light waves, the higher we must build the nanostructures", explains Diao. The group fine-tuned their procedures and found a way to increase the size of the deposited gold particles. "This made it possible for us to etch deeper into the material", reports Diao. The scientists were now able to etch out columns as high as 2,000 nanometres or two micrometres, four times as high as before. The new techniques also allow the scientists to influence the shape of the nano-columns. They control the way in which the columns taper from the bottom to the top and how narrow they are on the top. In the process, they learned that evenly tapered columns will permit the highest transmittance rates. The scientists experimented with various column heights and confirmed that they achieved the best transmittance values for different wavelengths with different heights they made the columns. For 1.95 micrometre high columns, the transmittance maximum was 99.8 %, clearly in the NIR at almost 2.4 micrometres. With increasing column height the range of wavelengths with high transmittance widened. For 1.95 micrometre high column layers, the high transmittance rates of 99.5 % or higher covered about 450 nanometres of the spectrum. For smaller column structures, the high-transmittance window was only 250 nanometres wide. High transmittance rates together with much reduced light reflection are the basis for possible 'stealth applications' because the surface-treated materials are optically indistinguishable from their environment. After column etching a piece of quartz glass, people did not see the outlines of the piece of quartz glass in front of them, and a camera did not record them. But when the 2

11 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) Max Planck scientists covered an image with a piece of quartz glass with column-studded surface, the image remained clearly visible even if viewed at an acute angle and from the upper edge (see illustration). In contrast, quartz glass with unmodified surface reflected the incoming light so much that onlookers no longer recognized anything at an angle of only 30. Still more output from high-energy lasers In the first experimental phase, the scientists tested their hypotheses using quartz glass. Future plans include testing the techniques on optical lenses and sapphires. As soon as the techniques have proven applicable to the new materials, the scientist will be eager to test the many possible applications. Many applications could certainly benefit from the use of components with next to no reflection across a wide range of wavelengths and up to 99.8 per cent transmittance of incoming light. "One important field would be high-energy lasers operating in the infra-red range", asserts Diao. Especially in certain laser systems, in which the light is amplified while it passes through the same optical components again and again, small losses through reflection will add up to noticeable energy losses. "Twenty three percent of the energy will be lost after the same light beam hits the same boundary fifty times at a transmittance of 99.5 per cent", points out Zhaolu Diao. At 99.8 per cent transmittance, the total energy loss after 50 passages would be only ten per cent. Furthermore, in field tests, the nanostructured surfaces are far more resilient against the high laser energy than anti-reflective coatings. This is another advantage especially for laser applications. Other feasible applications could be lenses, objectives or touchscreens. Nanostructured surfaces offer yet another advantage. Diao points out: "The technique is not only suitable for level, but also for curved surfaces. That would be beneficial especially for camera or microscope lenses. Before the technique can help improve touchscreens, a solution must be found for the problem of contamination via touch. Experiments have shown that touch by human hands will leave obvious traces. Over time, this will seriously impair the surface and lead to significantly reduced transmittance. On the bright side, the scientists were also able to show how easily touchscreen users can wipe away such contamination with a little laboratory alcohol as easy as from a glass surface. Still for touchscreen applications, the scientists still expect to find a more elegant solution. ble.html 3. Converting optical frequencies with 10^(-21) uncertainty Diagram of an optical frequency divider. Frequency synthesizers from audio frequency to the microwave region have been widely used in daily life, high technology and scientific research. Those frequency synthesizers can output a signal with frequency related to the input light frequency (fin) as fin/r. Meanwhile, the phase coherence, frequency stability and accuracy of the output signal inherit from the input signal. While in the optical region, there was no such a device. Since the invention of lasers, scientists are able to realize optical frequency conversion with nonlinear optical process. For example, second harmonic generation can convert optical frequencies as fout = fin/0.5, where fout is the output light frequency. However, optical frequency conversion with arbitrary ratios has not been realized for a long time. The invention of optical frequency comb paved the way for optical frequency divider. In 2003, international comparison among four optical frequency combs from East China Normal University (ECNU, China), National Institute of Standards and Technology (NIST, USA) and International Bureau of Weights and Measures (BIPM) was performed, which demonstrated that the frequency synthesis uncertainty of optical frequency combs based on different types of femtosecond lasers was at the 10^(-19) level (Long-Sheng Ma, et. al, Science, Vol. 303, page.1843, 2004). Recently, the group from ECNU has realized a low noise, accurate optical frequency divider by combining several key techniques of an optically-referenced frequency comb, a collinear self-referencing interferometer for detecting the comb carrier-envelope offset frequency, an optically-referenced RF time base, and the transfer oscillator scheme. By comparing against the frequency ratio between the fundamental and second harmonic of a 1064 nm laser instead of a second copy of the identical optical frequency divider, the division uncertainty is demonstrated to be ^(-21). The optical frequency divider can accurately divide an optical frequency with an arbitrary preset ratio to several different wavelengths. Scientists are able to measure optical frequency ratios directly from the division ratios of the optical frequency dividers when the output and input light of the optical frequency dividers correspond to clock frequencies. Optical frequency divider will be instrumental in the applications of optical clocks. "Recent progress in optical atomic clocks demonstrates record fractional frequency instability and uncertainty at the 10^(-18) level. The unprecedented accuracy is fostering a revolution in science and technology. Using optical 3

12 光学与工程 clocks, searches for possible variations of fundamental constants are carried out in laboratories by precisely measuring the frequency ratios of two different atomic transitions of optical clocks over time. In relativistic geodesy, long-distance geopotential difference will be accurately measured by comparing the frequencies of remotely-located optical clocks linked with optical fibers, where the frequencies of optical clocks have to be accurately converted to the fiber telecom band for long-distance transmission. In metrology, the fundamental unit for time, the second, in the International System of Units (SI) will be redefined based on optical atomic clocks. Frequency comparisons between optical clocks based on different atom species have to be performed in order to affirm the agreement between optical clocks with uncertainty beyond the current SI second, as well as to demonstrate the frequency reproducibility of optical clocks. Moreover, in atomic and molecular precision spectroscopy hopes are high that accurate and stable clock light can be transferred to wider spectral range. All those applications rely on accurate frequency ratio measurement between spectrally-separated optical clocks or frequency conversion of optical clocks." In a research article published in the Beijing-based National Science Review, Yao et. al. introduce an optical frequency divider with division uncertainty at the 10^(-21) level. The division uncertainty induced by the optical frequency divider is therefore three orders of magnitude better than the most accurate optical clocks, promising optical frequency division without degrading the performance of optical clocks. They hope this type of optical frequency divider will be also instrumental in precision measurement. Diagram of performance measurement. An optical frequency divier (OFD) is used to connect the optical frequencies of a cavity-stabilized laser light at 1064 nm (f1064-1) and the light second-harmonic generated from a second independent 1064 nm laser light (f1064-2) as f532 = f1064-1/rx. The value of Rx is obtained by measuring the beat frequency (fb) between f and f on an RF frequency counter with a self-referenced time base of f1064-1/k. rtainty.html 4. Nanoantenna lighting-rod effect produces Otto Muskens. A team of scientists, led by the University of Southampton, have produced a fast nanoscale optical transistor using gold nanoantenna assisted phase transition. The work, published in the journal Light: Science and Applications, opens up new directions in antenna-assisted switches and optical memory. Small nanostructures that can interact strongly with light are of interest for a range of emerging new applications including small optical circuits and metasurface flat optics. Nanoantennas are designed to have strong optical resonances where energy is concentrated far below the diffraction limit, the smallest scale possible using conventional optics. Such extreme concentration of light can be used to enhance all kinds of effects related to localised energy conversion and harvesting, coupling of light to small molecules and quantum dots, and generating new frequencies of light through nonlinear optics. Next to precise tuning of these antennas by design, an ability to actively tune their properties is of great interest. Lead author Professor Otto Muskens, from the University of Southampton, said: "If we are able to actively tune a nanoantenna using an electrical or optical signal, we could achieve transistor-type switches for light with nanometer-scale footprint for datacommunication. Such active devices could also be used to tune the antenna's light-concentration effects leading to new applications in switchable and tuneable antenna-assisted processes." The Southampton team used the properties of the antenna itself to achieve low energy optical switching of a phase-change material. The material used to achieve this effect was vanadium dioxide. Vanadium dioxide is a special material with properties that can be switched from an insulator to a metal by increasing the temperature above the phase transition point (68 C). Fabrication of this material is challenging and was produced by a team at the University of Salford, who specialise in thin-film deposition and who were able to grow very high quality films of this material. Gold nanoantennas were fabricated on top of this thin film and were used to locally drive the phase transition of the vanadium dioxide. 4

13 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) Professor Muskens explained: "The nanoantenna assists the phase transition of the vanadium dioxide by locally concentrating energy near the tips of the antenna. It is like a lightning-rod effect. These positions are also where the antenna resonances are the most sensitive to local perturbations. Antenna-assisted switching thus results a large effect while requiring only a small amount of energy." The theoretical modelling was done by a team from the University of the Basque Country in San Sebastian, Spain. Their detailed calculations revealed that the nanoantennas provided a new pathway by local absorption around the antenna. The antenna-assisted mechanism resulted in a much lower switching energy compared to just the VO2 film, corresponding to picojoule energies and a calculated efficiency of over 40 per cent. d-effect-fast-optical.html 5. Making silicon-germanium core fibers a reality Ursula Gibson, a professor of physics at the Norwegian University of Science and Technology, holds a glass fiber with a semiconductor core. Rapid heating and cooling of this kind of fiber allows the researchers to make functional materials with applications beyond traditional fiber optics. Glass fibres do everything from connecting us to the internet to enabling keyhole surgery by delivering light through medical devices such as endoscopes. But as versatile as today's fiber optics are, scientists around the world have been working to expand their capabilities by adding semiconductor core materials to the glass fibers. Now, a team of researchers has created glass fibers with single-crystal silicon-germanium cores. The process used to make these could assist in the development of high-speed semiconductor devices and expand the capabilities of endoscopes says Ursula Gibson, a physics professor at the Norwegian University of Science and Technology and senior author of the paper. "This paper lays the groundwork for future devices in several areas," Gibson said, because the germanium in the silicon core allows researchers to locally alter its physical attributes. The article, "Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres," was published in Nature Communications on October 24. Melting and recrystallizing To understand what the researchers did, you need to recognize that silicon and germanium have different melting points. When the two substances are combined in a glass fiber, flecks of germanium-rich material are scattered throughout the fiber in a disorderly way because the silicon has a higher melting point and solidifies, or "freezes" first. These germanium flecks limit the fiber's ability to transmit light or information. "When they are first made, these fibers don't look very good," Gibson said. But rapidly heating the fiber by moving it through a laser beam allowed the researchers to melt the semiconductors in the core in a controlled fashion. Using the difference in the solidification behavior, the researchers were able to control the local concentration of the germanium inside the fiber depending upon where they focused the laser beam and for how long. "If we take a fibre and melt the core without moving it, we can accumulate small germanium-rich droplets into a melt zone, which is then the last thing to crystalize when we remove the laser slowly," Gibson said. "We can make stripes, dots... you could use this to make a series of structures that would allow you to detect and manipulate light." An interesting structure was produced when the researchers periodically interrupted the laser beam as it moved along their silicon-germanium fibre. This created a series of germanium-rich stripes across the width of the 150-micrometer diameter core. That kind of pattern creates something called a Bragg grating, which could help expand the capability of long wavelength light-guiding devices. "That is of interest to the medical imaging industry," Gibson said. Rapid heating, cooling key Another key aspect of the geometry and laser heating of the silicon-germanium fibre is that once the fibre is heated, it can also be cooled very quickly as the fibre is carried away from the laser on a moving stage. Controlled rapid cooling allows the mixture to solidify into a single uniform crystal the length of the fibre which makes it ideal for optical transmission. Previously, people working with bulk silicon-germanium alloys have had problems creating a uniform crystal that is a perfect mix, because they have not had sufficient control of the temperature profile of the sample. "When you perform overall heating and cooling, you get uneven composition through the structure, because the last part to freeze concentrates excess germanium," Gibson said. "We have shown we can create single crystalline silicon-germanium at high production rates 5

14 光学与工程 when we have a large temperature gradient and a controlled growth direction." Transistors that switch faster Gibson says the laser heating process could also be used to simplify the incorporation of silicon-germanium alloys into transistor circuits. "You could adapt the laser treatment to thin films of the alloy in integrated circuits," she said. Traditionally, Gibson said, electronics researchers have looked at other materials, such as gallium arsenide, in their quest to build ever-faster transistors. However, the mix of silicon and germanium, often called SiGe, allows electrons to move through the material more quickly than they move through pure silicon, and is compatible with standard integrated circuit processing. "SiGe allows you to make transistors that switch faster" than today's silicon-based transistors, she said, "and our results could impact their production." 6. Fluorescent holography: Upending the world of biological imaging Field and other optics scientists work in a world of tradeoffs. For example: an advanced deep-tissue imaging technique called multiphoton fluorescence microscopy employs a short, bright laser pulse focused tight to one spot, and the fluorescence intensity from that one spot is recorded. Then, the laser moves to the next spot, then the next, to build up high-resolution 3D images. The technique offers subcellular detail, but it's relatively slow because it illuminates only one tiny spot at a time. Other techniques, like spinning disk confocal microscopy, are faster because they shine light on multiple spots, not just one, and they scan simultaneously over a larger area. But unlike multiphoton, these techniques require collecting an image with a camera. As a result, fluorescent light emitted from the specimen is blurred on the camera, leading to loss in resolution, and with it, subcellular detail. Call them greedy, but Field and colleagues want it all. Spatiotemporal modulations of illumination intensity in the CHIRPT microscope are achieved by imaging a spinning modulation mask to the focal plane of the microscope. A spatial filter placed in the pupil plane of the objective lens allows illumination intensity to form by the interference of two beams in the object plane. The microscope and illumination intensity are shown here at a snapshot in time. Optical microscopy experts at Colorado State University are once again pushing the envelope of biological imaging. Jeffrey Field, a research scientist in electrical engineering and director of CSU's Microscope Imaging Network, has designed and built a fluorescence-detection microscope that combines three-dimensional and high-resolution image processing that's also faster than comparable techniques. The work, with co-authorship by Randy Bartels, professor of electrical and computer engineering, and former postdoctoral researcher David Winters, has been published in Optica, the journal of the Optical Society of America. They named their new microscope CHIRPT: Coherent Holographic Image Reconstruction by Phase Transfer. Imaging tradeoffs CHIRPT and confocal imaging of fluorescently labelled mouse intestine slices. (a) and (b) are digitally refocused CHIRPT images. (c) and (d) are conventional confocal images. In all four, features in focus are denoted by arrows. Breaking established boundaries Their goal is working around each of these limitations - speed, resolution, size of field - to break through established boundaries in light microscopy. Field and Bartels' new microscope builds upon a previously published technique, and permits digital re-focus of fluorescent light. It illuminates not one point, but multiple points by harnessing delocalized illumination spread over a large area. The physical principles they are using are similar to holography, in which scattered light is used to build a 3-D image. Using a large illumination field, followed by back-end signal processing, the microscope can define distinct light modulation patterns of many points within the field of view. It builds up a 3-D image by combining the signals from all those distinct patterns. "The idea is that you have a fluorophore at any point in the specimen, and the temporal structure of its fluorescence will be distinguishable from all others," Field said. "So you can have this huge array of fluorophores, and just with this single-pixel detector, you can tell where every one of them is in that 2D field." 3D, deep-tissue images 6

15 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) So what does this new technique allow? Deep-tissue images in three dimensions, with better depth of field than comparable techniques. Depth of field, like in photography, means background images are in sharp focus along with the main image. And the CSU researchers can work at 600 frames per second, which is many times faster than established techniques. With their new microscope, images can also be post-processed to remove aberrations that obscure the object of interest. It's akin to being able to focus a picture after it's been taken. The CHIRPT microscope could allow biomedical researchers to produce sharp, 3-D images of cells or tissue over a much larger volume than conventional fluorescence microscopy methods allow. It could lead to things like imaging multicellular processes in real time that, with a conventional light microscope, could only be seen one cell at a time Laser researchers boldly go into uncharted THz territory In this illustration of a terahertz plasmonic laser, the laser cavity is enclosed between two metal films (with periodic slits on the top film). The colors represent coherent SPP light waves. One wave is confined inside the 10-micron-thick cavity. The other, with a large spatial extent, is located on top of the cavity. Once the preferred weapon of B-movie madmen and space-fiction heroes alike, the laser a device that generates an intense beam of coherent electromagnetic radiation by stimulating the emission of photons from excited atoms or molecules has grown a bit domesticated of late. These days, it has a steady job in industry, and spends its spare time printing documents in home offices and playing back movies in home theaters. Here and there it pops up in medical journals and military news, but it's basically been reduced to reading barcodes at the grocery checkout a technology that's lost its mojo. But lasers are still cool, insists Sushil Kumar of Lehigh University, with vast potential for innovation we've just begun to tap. And with support from the National Science Foundation (NSF), he's on a mission to prove it. Kumar, an associate professor of electrical and computer engineering, focuses specifically on lasers that arise from a relatively unexploited region in the electromagnetic spectrum, the terahertz (THz), or far infrared, frequency. A researcher at the forefront of THz semiconductor 'quantum-cascade' laser technology, he and his colleagues have posted world-record results for high-temperature operation and other important performance characteristics of such lasers. His goal is to develop devices that open up a wide array of possible applications: chemical and biological sensing, spectroscopy, detection of explosives and other contraband materials, disease diagnosis, quality control in pharmaceuticals, and even remote-sensing in astronomy to understand star and galaxy formation, just to name a few. (Pretty cool stuff... the folks back at the checkout line would be impressed.) Yet despite the known benefits, Kumar says that terahertz lasers have been underutilized and underexplored; high cost and functional limitations have stymied the innovation that would lead to such usage. Kumar, however, believes he's on track to truly unleash the power of THz laser technology; he recently received a grant from the NSF, Phase-locked arrays of high-power terahertz lasers with ultra-narrow beams, with a goal of creating THz lasers that produce vastly greater optical intensities than currently possible and potentially removing barriers to widescale research and commercial adoption. Focusing on a solution According to Kumar, the terahertz region of the electromagnetic spectrum is significantly underdeveloped due to lack of high-power sources of radiation. Existing sources feature low output power and other undesired spectral characteristics which makes them unsuitable for serious application. His current project aims to develop terahertz semiconductor lasers with precise emission frequency of up to 100 milliwatts of average optical power an improvement of two orders of magnitude over current technology in a narrow beam with signifcantly less than five degrees of angular divergence. Kumar works with quantum cascade lasers (QCLs). These devices were originally invented for emission of mid-infrared radiation. They have only recently begun to make a mark at THz frequencies, and in that range they suffer from several additional challenges. In this cutting-edge environment, Kumar's group is among a select few in the world making progress toward viable and low-cost production of these lasers. Kumar's intended approach will significantly improve power output and beam quality from QCLs. A portable, electrically-operated cryocooler will provide the required temperature-cooling for the semiconductor laser chips; these will contain phase-locked QCL arrays emitting at a range of discrete terahertz frequencies determined by the desired application. In previous work, Kumar and his group showed that THz lasers (emtting at a wavelength of approximately 7

16 光学与工程 100 microns) could emit a focused beam of light by utilizing a technique called distributed feedback. The light energy in their laser is confined inside a cavity sandwiched between two metallic plates separated by a distance of 10 microns. Using a box-shaped cavity measuring 10 microns by 100 microns by 1,400 microns (1.4 millimeters), the group produced a terahertz laser with a beam divergence angle of just 4 degrees by 4 degrees, the narrowest divergence yet achieved for such terahertz lasers. Kumar believes most companies that currently employ mid-infrared lasers would be interested in powerful, affordable terahertz QCLs, and that the technology itself will spawn new solutions. "The iphone needed to exist before developers could write the 'killer apps' that made it a household product," he says. "In the same way, we are working toward a technology that could allow future researchers to change the world in ways that have yet to even be considered." light that degrades the image quality and leads to cell damage through photo-toxicity. "What light-sheet microscopy does is allow us create a sheet of light that is matched exactly to the focal plane that we're imaging," he explained. "We reduce light exposure and we reduce background noise in the system, so in living cells that allows us to see fluorescent proteins with enough signal to look at the dynamics of those proteins." A new approach to this technique, developed by Lidke, his research group and collaborators at Sandia National Laboratories, overcomes these prominent issues and allows light-sheet microscopy to be performed using common microscopes found in most cell biology laboratories. hz-territory.html 8. Professor developing super-resolution microscopy techniques HeLa cells were imaged using the light-sheet illumination technique. The Lidke group worked with Sandia National Labs to develop microfluidics chips that contain an integrated mirror to allow their light-sheet technique to work. For scientists developing life-saving medicines, knowing how cells interact and communicate with one another is an important part of the puzzle. The problem is, being able to see those interactions through a microscope hasn't always been possible. But now, thanks to University of New Mexico Associate Professor Keith Lidke, a new technique has opened the door to allow researchers a better view of cellular interactions. The technique, published this year in Biomedical Optics Express, is called single objective light-sheet microscopy and improves on an existing method of fluorescence microscopy. According to Lidke, who works in UNM's Department of Physics & Astronomy, traditional fluorescence microscopy techniques can only provide researchers a very limited view of the cells they're looking at and exposes the sample to an abundance of While Lidke's technique is still in its early stages, he has already received a lot of interest from researchers at UNM and across the country because of the unique view the equipment can provide. According to Lidke, cells function through signaling pathways which are a series of protein-protein interactions. But, exactly how those interactions work isn't clear due to a lack of technology available to see those events happen in living cells. "What we're trying to do is to develop this light-sheet technology to see these interactions in living cells," said Lidke. "And, if we can understand how that's working then somebody may be able to target a therapy to a dysregulated signaling pathway." Essentially, the technique has the ability to help answer questions about how cells communicate and work internally, making it possible for researchers to develop medicine or therapies that utilize these interactions. "Knowing that our work has a potentially valuable application really makes what we're doing everyday feel extremely important," Lidke said. 8

17 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) UNM Associate Professor Keith Lidke (center) is working at an optics table with post-doctoral student Marjolein Meddens (l.) and graduate student Hanieh Mazloom-Farsibaf (r.). The new technique is made possible through two different components; a specialized optics attachment that creates the light-sheet and a highly engineered microfluidics chip that holds the sample. Lidke's group is responsible for creating the optics component which was developed as an attachment to most epi-fluorescent microscopes as a way to make the technique usable for a large audience. Collaborators at Sandia National Labs worked with the group to develop the microfluidics chip which has an integrated mirror in it that allows them to create the light-sheet using a single objective lens. Together, these two pieces give researchers the opportunity to see cellular interaction on an entirely new level. Right now, Lidke says he's working with the team at Sandia to develop an improved, next-generation chip that he expects to be made commercially available to researchers. n-microscopy-techniques.html 9. Lasers + anti-lasers: Marriage opens door to development of single device with exceptional range of optical capabilities Schematics above show light input (green) entering opposite ends of a single device. When the phase of light input 1 is faster than that of input 2 (left panel), the gain medium dominates, resulting in coherent amplification of the light, or a lasing mode. When the phase of light input 1 is slower than input 2 (right panel), the loss medium dominates, leading to coherent absorption of the input light beams, or an anti-lasing mode. Bringing opposing forces together in one place is as challenging as you would imagine it to be, but researchers in the field of optical science have done just that. Scientists at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have for the first time created a single device that acts as both a laser and an anti-laser, and they demonstrated these two opposite functions at a frequency within the telecommunications band. Their findings, reported in a paper to be published Monday, Nov. 7, in the journal Nature Photonics, lay the groundwork for developing a new type of integrated device with the flexibility to operate as a laser, an amplifier, a modulator, and an absorber or detector. "In a single optical cavity we achieved both coherent light amplification and absorption at the same frequency, a counterintuitive phenomenon because these two states fundamentally contradict each other," said study principal investigator Xiang Zhang, senior faculty scientist at Berkeley Lab's Materials Sciences Division. "This is important for high-speed modulation of light pulses in optical communication." Reversing the laser The concept of anti-lasers, or coherent perfect absorber (CPA), emerged in recent years as something that reverses what a laser does. Instead of strongly amplifying a beam of light, an anti-laser can completely absorb incoming coherent light beams. While lasers are already ubiquitous in modern life, applications for anti-lasers first demonstrated five years ago by Yale University researchers are still being explored. Because anti-lasers can pick up weak coherent signals in the midst of a "noisy" incoherent background, it could be used as an extremely sensitive chemical or biological detector. A device that can incorporate both capabilities could become a valuable building block for the construction of photonic integrated circuits, the researchers said. "On-demand control of light from coherent absorption to coherent amplification was never imagined before, and it remains highly sought after in the scientific community," said study lead author Zi Jing Wong, a postdoctoral researcher in Zhang's lab. "This device can potentially enable a very large contrast in modulation with no theoretical limits." The researchers utilized sophisticated nanofabrication technology to build 824 repeating pairs of gain and loss materials to form the device, which measured 200 micrometers long and 1.5 micrometers wide. A single strand of human hair, by comparison, is about 100 micrometers in diameter. The gain medium was made out of indium gallium arsenide phosphide, a well-known material used as an amplifier in optical communications. Chromium paired with germanium formed the loss medium. Repeating the pattern created a resonant system in which light bounces back and forth throughout the device to build up the amplification or absorption magnitude. Scanning electron microscope image of the single device capable of lasing and anti-lasing. Indium gallium arsenide phosphide (InGaAsP) material functions as the gain medium, 9

18 光学与工程 while the chromium (Cr) and germanium (Ge) structures introduce the right amount of loss to satisfy the condition of parity-time symmetry that is required for lasing and anti-lasing. If one is to send light through such a gain-loss repeating system, an educated guess is that light will experience equal amounts of amplification and absorption, and the light will not change in intensity. However, this is not the case if the system satisfies conditions of parity-time symmetry, which is the key requirement in the device design. Balance and symmetry Parity-time symmetry is a concept that evolves from quantum mechanics. In a parity operation, positions are flipped, such as the left hand becoming the right hand, or vice versa. Now add in the time-reversal operation, which is akin to rewinding a video and observing the action backwards. The time-reversed action of a balloon inflating, for example, would be that same balloon deflating. In optics, the time-reversed counterpart of an amplifying gain medium is an absorbing loss medium. A system that returns to its original configuration upon performing both parity and time-reversal operations is said to fulfill the condition for parity-time symmetry. Soon after the discovery of the anti-laser, scientists had predicted that a system exhibiting parity-time symmetry could support both lasers and anti-lasers at the same frequency in the same space. In the device created by Zhang and his group, the magnitude of the gain and loss, the size of the building blocks, and the wavelength of the light moving through combine to create conditions of parity-time symmetry. When the system is balanced and the gain and loss are equal, there is no net amplification or absorption of the light. But if conditions are perturbed such that the symmetry is broken, coherent amplification and absorption can be observed. In the experiments, two light beams of equal intensity were directed into opposite ends of the device. The researchers found that by tweaking the phase of one light source, they were able to control whether the light waves spent more time in amplifying or absorbing materials. Speeding up the phase of one light source results in an interference pattern favoring the gain medium and the emission of amplified coherent light, or a lasing mode. Slowing down the phase of one light source has the opposite effect, resulting in more time spent in the loss medium and the coherent absorption of the beams of light, or an anti-lasing mode. If the phase of the two wavelengths are equal and they enter the device at the same time, there is neither amplification nor absorption because the light spends equal time in each region. The researchers targeted a wavelength of about 1,556 nanometers, which is within the band used for optical telecommunications. "This work is the first demonstration of balanced gain and loss that strictly satisfies conditions of parity-time symmetry, leading to the realization of simultaneous lasing and anti-lasing," said study co-author Liang Feng, former postdoctoral researcher in Zhang's Lab, and now an assistant professor of electrical engineering at the University of Buffalo. "The successful attainment of both lasing and anti-lasing within a single integrated device is a significant step towards the ultimate light control limit." ge-door-device.html 10. First random laser made of paper-based ceramics The team used conventional laboratory filter paper as a structural template due to its long fibers and the stable structure. Working with physicists from the University of Rome, a team led by Professor Cordt Zollfrank from the Technical University of Munich (TUM) built the first controllable random laser based on cellulose paper in Straubing. The team thereby showed how naturally occurring structures can be adapted for technical applications. Hence, materials no longer need to be artificially outfitted with disordered structures, utilizing naturally occurring ones instead. Material synthesis that is inspired by biology is an area of research at TUM's Chair of Biogenic Polymers at the Straubing Center of Science. It utilizes models from nature and biogenic materials to develop new materials and technologies. The latest issue of the publication Advanced Optical Materials features a basic study by a joint team from Straubing and Rome who succeeded in "using a biological structure as a template for a technical random laser," according to scientist Dr Daniel Van Opdenbosch. Two components are necessary for a laser: First of all, a medium which amplifies light. And secondly, a structure which retains the light in the medium. A classic laser uses mirrors to order and shine light in a single direction in a targeted, uniform fashion. This also takes place uniformly in the microscopic structure of a random laser, but in different directions. Although the development of the random laser is still in its infancy, in 10

19 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) the future it could result in lower-cost production. This is because random lasers have the advantage that they are direction-independent and function with multiple colors, just to name a few benefits. Disordered structure deflects light in all directions "The prerequisite for a random laser is a defined degree of structural chaos on the interior," Van Opdenbosch explained. The light in a random laser is therefore scattered at all manner of angles along random paths, which are determined by an irregular structure in the interior of the medium. The team led by Professor Zollfrank from the Chair of Biogenic Polymers in Straubing used conventional laboratory filter paper as a structural template. "Due to its long fibers and the resulting stable structure, we deemed it to be suitable for this purpose," said Van Opdenbosch. In the laboratory, the paper was impregnated with tetraethyl orthotitanate, an organometallic compound. When it is dried and the cellulose burned off at 500 degrees Celsius, it leaves behind the ceramic titanium dioxide as residue the same substance generally used in sunblock to provide protection from the sun. "This effect in sunblock is based on titanium dioxide's strong light scattering effect," said Van Opdenbosch, "which we also utilized for our random laser." And "our laser is 'random' because the light which is scattered in different directions due to the biogenic structure of the laboratory filter paper can also be scattered in the opposite direction," he added, explaining the principle. Random laser not that random after all However, the light waves can still be controlled despite their random nature, as the team led by Claudio Conti of the Institute for Complex Systems in Rome discovered, with whom Daniel Van Opdenbosch and Cordt Zollfrank collaborated. With the help of a spectrometer, they were able to differentiate the various laser wavelengths generated in the material and localize them separately from one another. Van Opdenbosch described the procedure: "The test setup used to map the samples consisted of a green laser whose energy could be adjusted, microscope lenses, and a mobile table which allowed the sample to be moved past. That way, our colleagues were able to determine that at different energy levels, different areas of the material radiate different laser waves." In light of this analysis, it is possible to configure the laser in any number of ways and to determine the direction and intensity of its radiation. This knowledge puts potential practical applications within reach. "Such materials could, for example, be useful as micro-switches or detectors for structural changes," said Van Opdenbosch. d-ceramics.html 11. Light detector with record-high sensitivity to revolutionize imaging Structure and performance of the novel photodetector. The research team led by Professor Hele Savin has developed a new light detector that can capture more than 96 percent of the photons covering visible, ultraviolet and infrared wavelengths. "Present-day light detectors suffer from severe reflection losses as currently used antireflection coatings are limited to specific wavelengths and a fixed angle of incidence. Our detector captures light without such limitations by taking advantage of a nanostructured surface. Low incident angle is useful especially in scintillating x-ray sensors", Savin explains. "We also addressed electrical losses present in traditional sensors that utilize semiconductor pn-junctions for light collection. Our detector does not need any dopants to collect light - instead we use an inversion layer generated by atomic layer deposited thin film." The new concept for light detection kindled from the team's earlier research on nanostructured solar cells. Indeed, the nanostructure used in the light detector is similar to that used by the team a couple of years ago in their record-high efficiency black silicon solar cells. The team has filed a patent application for the new light detector. The prototype detectors are currently being tested in imaging applications related to medicine and safety. The team is also continuously seeking new applications for their invention, especially among the ultraviolet and infrared ranges that would benefit from the superior spectral response. The research results are published in Nature Photonics. itivity-revolutionize-imaging.html 12. Building a bright future for lasers Professor Benjamin Williams, at left, and 2016 Ph.D. graduate Benjamin Burnett at work in the Terahertz Devices and Intersubband Nanostructures Laboratory. 11

20 光学与工程 Invisible to the human eye, terahertz electromagnetic waves can "see through" everything from fog and clouds to wood and masonry an attribute that holds great promise for astrophysics research, detecting concealed explosives and many other applications. Terahertz lasers can produce photons with frequencies of trillions of cycles per second energies between those of infrared and microwave photons. These photons, however, are notoriously difficult to generate and that's where UCLA associate professor of electrical engineering Benjamin Williams comes in. He and his research group at the UCLA Henry Samueli School of Engineering and Applied Science are hard at work exploring "one of the last frontiers of the electromagnetic spectrum," as Williams describes it. Most optical and infrared lasers operate by electrons transitioning between two energy levels in a semiconductor crystal and emitting a photon. However, this process is not so easily extended to the terahertz range. "If you want to make terahertz radiation, you need a very low-energy photon, so you need two energy levels that are very close together, and that's hard to do with the semiconductors that nature gives us," said Williams. He and his collaborators at the Terahertz Devices and Intersubband Nanostructures Laboratory instead produce terahertz photons by engineering artificial materials that mimic the energy levels of atoms. These so-called "quantum cascade lasers" are made by arranging different semiconductors in layers some only a few atoms thick to form quantum wells. Quantum wells are like tiny "boxes" that confine electrons to certain energy levels chosen by design. As an electron transitions between different energy levels, it emits photons. A single electron can cascade between the many quantum wells in a quantum cascade laser and trigger the emission of multiple terahertz photons, thereby producing a powerful laser beam. Another advantage of quantum cascade lasers is that the frequency of the emitted photons can be modulated. "Instead of being limited to the band gap that nature gives you, we can change the width of these quantum wells to choose the effective band gap [and change the photons' frequency]. That's a very powerful concept," said Williams. While quantum cascade lasers are both powerful and tunable in frequency, a significant disadvantage has been their low beam quality. "Think of a laser pointer, which has a very nice beam, "Williams said. "The beam goes where you want it, and it looks like a nice spot. You're not wasting the light." Terahertz lasers, on the other hand, often have beams that are highly divergent, meaning that the light beam spreads out and accordingly becomes less powerful. In some cases, the beam of a terahertz laser diverges so much that only 0.1 percent of it ends up where it was initially intended to go. A major achievement of Williams' lab has been creating a type of terahertz quantum cascade laser that possesses both an excellent beam pattern and high power. "Our innovation was to make an artificial surface that's made up of lots of little laser antennas [metal structures that each function like a quantum cascade amplifier]. The net effect is a mirror that reflects terahertz light as it amplifies and focuses it at the same time," said Williams. "We believe that this ability will allow us to create lasers with control of nearly all of the properties of the light its wavelength, amplitude, phase, and polarization." Williams and his team are also exploring how quantum cascade lasers can be designed to operate at room temperature. Currently, scientists must cool their lasers down to 77 Kelvin (-321 F), a step that limits the lasers' use outside of a laboratory. Now, Williams is investigating building those lasers using quantum dots instead of quantum wells. While quantum wells confine electrons' motion in only one dimension, quantum dots restrict their motion in all three dimensions. The extra confinement in quantum dots is predicted to drastically reduce how much the electrons scatter, which would allow these lasers to work at room temperature. "We're currently working with Diana Huffaker [professor of electrical engineering at UCLA], who grows quantum dots," said Williams. "[Her work] would allow us to do the same kinds of quantum engineering with quantum dots that we presently do with quantum wells." Low-power tabletop source of ultrashort electron beams could replace car-size X-ray devices This illustration shows a miniature electron gun driven by terahertz radiation. A UV pulse (blue) back-illuminates the gun photocathode, producing a high-density electron bunch inside the gun. The bunch is immediately accelerated by ultra-intense terahertz pulses to energies approaching 1 kiloelectronvolt. These high-field optically-driven electron guns can be utilized for ultrafast electron diffraction or injected into the accelerators for X-ray light sources. Ultrashort bursts of electrons have several important applications in scientific imaging, but producing them has typically required a costly, power-hungry apparatus about the size of a car. 12

21 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) In the journal Optica, researchers at MIT, the German Synchrotron, and the University of Hamburg in Germany describe a new technique for generating electron bursts, which could be the basis of a shoebox-sized device that consumes only a fraction as much power as its predecessors. Ultrashort electron beams are used to directly gather information about materials that are undergoing chemical reactions or changes of physical state. But after being fired down a particle accelerator a half a mile long, they're also used to produce ultrashort X-rays. Last year, in Nature Communications, the same group of MIT and Hamburg researchers reported the prototype of a small "linear accelerator" that could serve the same purpose as the much larger and more expensive particle accelerator. That technology, together with a higher-energy version of the new "electron gun," could bring the imaging power of ultrashort X-ray pulses to academic and industry labs. Indeed, while the electron bursts reported in the new paper have a duration measured in hundreds of femtoseconds, or quadrillionths of a second (which is about what the best existing electron guns can manage), the researchers' approach has the potential to lower their duration to a single femtosecond. An electron burst of a single femtosecond could generate attosecond X-ray pulses, which would enable real-time imaging of cellular machinery in action. "We're building a tool for the chemists, physicists, and biologists who use X-ray light sources or the electron beams directly to do their research," says Ronny Huang, an MIT PhD student in electrical engineering and first author on the new paper. "Because these electron beams are so short, they allow you to kind of freeze the motion of electrons inside molecules as the molecules are undergoing a chemical reaction. A femtosecond X-ray light source requires more hardware, but it utilizes electron guns." In particular, Huang explains, with a technique called electron diffraction imaging, physicists and chemists use ultrashort bursts of electrons to investigate phase changes in materials, such as the transition from an electrically conductive to a nonconductive state, and the creation and dissolution of bonds between molecules in chemical reactions. Ultrashort X-ray pulses have the same advantages that ordinary X-rays do: They penetrate more deeply into thicker materials. The current method for producing ultrashort X-rays involves sending electron bursts from a car-sized electron gun through a billion-dollar, kilometer-long particle accelerator that increases their velocity. Then they pass between two rows of magnets known as an "undulator" that converts them to X-rays. In the paper published last year on which Huang was a coauthor the MIT-Hamburg group, together with colleagues from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg and the University of Toronto, described a new approach to accelerating electrons that could shrink particle accelerators to tabletop size. "This is supposed to complement that," Huang says, about the new study. Franz Kärtner, who was a professor of electrical engineering at MIT for 10 years before moving to the German Synchrotron and the University of Hamburg in 2011, led the project. Kärtner remains a principal investigator at MIT's Research Laboratory of Electronics and is Huang's thesis advisor. He and Huang are joined on the new paper by eight colleagues from both MIT and Hamburg. Subwavelength confinement The researchers' new electron gun is a variation on a device called an RF gun. But where the RF gun uses radio frequency (RF) radiation to accelerate electrons, the new device uses terahertz radiation, the band of electromagnetic radiation between microwaves and visible light. The researchers' device, which is about the size of a matchbox, consists of two copper plates that, at their centers, are only 75 micrometers apart. Each plate has two bends in it, so that it looks rather like a trifold letter that's been opened and set on its side. The plates bend in opposite directions, so that they're farthest apart 6 millimeters at their edges. At the center of one of the plates is a quartz slide on which is deposited a film of copper that, at its thinnest, is only 30 nanometers thick. A short burst of light from an ultraviolet laser strikes the film at its thinnest point, jarring loose electrons, which are emitted on the opposite side of the film. At the same time, a burst of terahertz radiation passes between the plates in a direction perpendicular to that of the laser. All electromagnetic radiation can be thought of as having electrical and magnetic components, which are perpendicular to each other. The terahertz radiation is polarized so that its electric component accelerates the electrons directly toward the second plate. The key to the system is that the tapering of the plates confines the terahertz radiation to an area the 75-micrometer gap that is narrower than its own wavelength. "That's something special," Huang says. "Typically, in optics, you can't confine something to below a wavelength. But using this structure we were able to. Confining it increases the energy density, which increases the accelerating power." Because of that increased accelerating power, the device can make do with terahertz beams whose power is much lower than that of the radio-frequency beams used in a typical RF gun. Moreover, the same laser can generate both the ultraviolet beam and, with a few additional optical components, the terahertz beam. According to James Rosenzweig, a professor of physics at the University of California at Los Angeles, that's one of the most attractive aspects of the 13

22 光学与工程 researchers' system. "One of the main problems you have with ultrafast sources like this is timing jitter between, say, the laser and accelerating field, which produces all sorts of systematic effects that make it harder to do time-resolved electron diffraction," Rosezweig says. "In the case of Kärtner's device, the laser produces the terahertz and also produces the photoelectrons, so the jitter is highly suppressed. You could do pump-probe experiments where the laser is the driver and the electrons would be the probe, and they would be more successful than what you have right now. And of course it would be a very small-sized and modest-cost device. So it might turn out to be very important as far as that scenario goes." e-ultrashort-electron.html 14. Capturing an elusive spectrum of light A microresonator crystal used in this study. Researchers led by EPFL have built ultra-high quality optical cavities for the elusive mid-infrared spectral region, paving the way for new chemical and biological sensors, as well as promising technologies. The mid-infrared spectral window, referred to as "molecular fingerprint region," includes light wavelengths from 2.5 to 20 μm. It is a virtual goldmine for spectroscopy, chemical and biological sensing, materials science, and industry, as it is the range where many organic molecules can be detected. It also contains two ranges that allow transmission of signals through the atmosphere without distortion or loss. A way to harness the potential of the mid-infrared spectral window is to use optical cavities, which are micro-devices that confine light for extended amounts of time. However, such devices are currently unexplored due to technological challenges at this wavelength. Researchers led by EPFL have taken on this challenge and successfully shown that crystalline materials can be used to build ultra-high quality optical cavities for the mid-infrared spectral region, representing the highest value achieved for any type of mid-infrared resonator to date and setting a new record in the field. T his unprecedented work is published in Nature Communications. Caroline Lecaplain and Clément Javerzac-Galy from Tobias J. Kippenberg's lab at EPFL led the research effort, together with colleagues from the Russian Quantum Center. To make these ultra-high quality microcavities, the scientists used alkaline earth metal fluoride crystals that they polished manually. They developed uncoated chalcogenide tapered fibers to efficiently couple mid-infrared light from a continuous wave Quantum Cascade Laser (QCL) into their crystalline microcavities. Finally, cavity ring-down spectroscopy techniques enabled the team to unambiguously demonstrate ultra-high quality resonators deep in the mid-infrared spectral range. Equally important, the scientists also show that the quality factor of the microcavity is limited by multi-phonon absorption. This is a phenomenon in which phonons quasiparticles made of energy and vibrations in the cavity's crystal simultaneously interact and disrupt light confinement. This work marks a milestone in the field of mid-infrared materials as it opens for the first time access to ultra-high resonators. It is a significant step toward a compact frequency-stabilized laser in the mid-infrared, which could have a major impact on applications such as molecular spectroscopy, chemical sensing and bio-detection. m.html 二. 光子学 15. Scientists create most efficient quantum cascade laser ever Assistant Professor Arkadiy Lyakh of UCF's NanoScience Technology Center has developed the most efficient Quantum Cascade Laser ever. A team of UCF researchers has produced the most efficient quantum cascade laser ever designed - and done it in a way that makes the lasers easier to manufacture. Quantum cascade lasers, or QCLs, are tiny - smaller than a grain of rice - but they pack a punch. Compared to traditional lasers, QCLs offer higher power output and can be tuned to a wide range of infrared wavelengths. They can also be used at room temperature without the need for bulky cooling systems. 14

23 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) But because they're difficult and costly to produce, QCLs aren't used much outside the Department of Defense. A University of Central Florida team led by Assistant Professor Arkadiy Lyakh has developed a simpler process for creating such lasers, with comparable performance and better efficiency. The results were published recently in the scientific journal Applied Physics Letters. "The previous record was achieved using a design that's a little exotic, that's somewhat difficult to reproduce in real life," Lyakh said. "We improved on that record, but what's really important is that we did it in such a way that it's easier to transition this technology to production. From a practical standpoint, it's an important result." That could lead to greater usage in spectroscopy, such as using the infrared lasers as remote sensors to detect gases and toxins in the atmosphere. Lyakh, who has joint appointments with UCF's NanoScience Technology Center and the College of Optics and Photonics, envisions portable health devices. For instance, a small QCL-embedded device could be plugged into a smartphone and used to diagnose health problems by simply analyzing one's exhaled breath. "But for a handheld device, it has to be as efficient as possible so it doesn't drain your battery and it won't generate a lot of heat," Lyakh said. The method that previously produced the highest efficiency called for the QCL atop a substrate made up of more than 1,000 layers, each one barely thicker than a single atom. Each layer was composed of one of five different materials, making production challenging. The new method developed at UCF uses only two different materials - a simpler design from a production standpoint. Lyakh came to UCF in September 2015 from Pranalytic, Inc., a California-based tech company, where he led QCL development and production. His research team at UCF included graduate students Matthew Suttinger, Rowel Go, Pedro Figueiredo and Ankesh Todi, and research scientist Hong Hsu. um-cascade-laser.html 16. Innovative technique for shaping light could solve bandwidth crunch Researchers used more than 100 spatial modes of light to transmit an image pixel by pixel over a lab-based free-space optical network As data demands continue to grow, scientists predict that it's only a matter of time before today's telecommunication networks reach capacity unless new technologies are developed for transporting data. A new technique could help avert this bandwidth crunch by allowing light-based optical networks to carry more than one hundred times more data than is possible with current technologies. Laser light comes in many different shapes, or spatial modes. However, today's optical networks use just one spatial mode to carry information, limiting the amount of data that can be transmitted at one time. Researchers led by Andrew Forbes, a professor at the University of Witwatersrand, South Africa, developed a technique known as spatial multiplexing that reshapes a laser beam into many spatial modes that can each carry information. In a paper presented at the OSA Laser Congress in Boston, the researchers demonstrate optical communication with more than 100 spatial modes by combining their new spatial multiplexing approach with wavelength division multiplexing (WDM), which uses different wavelengths of light to carry information. "We created 35 spatial modes encoded in three different wavelengths, producing 105 total modes," said Carmelo Rosales-Guzmán, research fellow and first author of the paper. "Our new method might serve as the basis for future communication technologies." The researchers demonstrated that their technique can transmit data with 98 percent efficiency in a laboratory free-space optical network, which uses light to transmit information over the air. The scientists say the approach should also work in optical fibers, the basis for fiber-optic communications. Increasing bandwidth with more light modes The new technique makes use of light with an orbital angular momentum, which gives it a twisted, or helical, shape. Different spatial modes can be created by varying the number of twists, known as the azimuthal degrees of freedom. While other scientists have been exploring the use of azimuthal degrees of freedom for increasing bandwidth, recent research showed that even though, in theory, the set of modes with orbital angular momentum is infinite, in practice there aren't enough modes available to make significant improvements. Forbes' team solved this problem by using the azimuthal degrees of freedom plus another variable known as a radial degree of freedom. Each azimuthal degree of freedom can have, in theory, an infinite amount of radial degrees of freedom, but there are practical limitations that restrict this number. Because all the modes are orthogonal to each other, the signals don't get mixed up as they travel and can be separated upon arrival at their destination. The researchers say that 15

24 光子学 this is the first time two spatial degrees of freedom have been used to optically encode information. Key to this new approach is an optical device known as a spatial light modulator. The researchers used one spatial light modulator to shape the laser light into the various modes and another to reverse the process on the receiving end. "One of the advantages of our approach is that we only need a single detector to demultiplex all the spatial modes to recover all the information," said Rosales-Guzmán. "This is faster than other approaches for increasing bandwidth that need multiple detectors." Sending pictures pixel by pixel To test the new technique, the researchers used it to encode a grayscale and color image. Each image was sent across a communication link pixel by pixel and then each pixel was recovered to reconstruct the image. For the grayscale image, each gray level was linked to a separate spatial mode, allowing transmission of 105 gray levels. "In this demonstration, sending a 10,000-pixel image took 5 to 7 minutes," said Rosales-Guzmán. "However we could increase that speed by sending two or four pixels at the same time or by using many more wavelengths." Real-world free-space optical networks which can transfer information between buildings, for example come with many challenges that aren't present in the lab. As a next step, the researchers are partnering with experts in free-space communication to adapt their technique for practical applications. "We are working with a company in South Africa that already makes a device that has the ability to use different spatial modes for free space communication," said Rosales-Guzmán. "We are interested in trying to increase the bandwidth of their device to four times what it is capable of now." nch.html 17. Researchers demonstrate extension of electronic metrology to the multi-petahertz frequency range Attosecond pulse metrology in bulk SiO 2. A team of researchers with the Max-Planck-Institut für Quantenoptik has found a way to link previously demonstrated laser light-induced high-speed switching of an insulator between conducting states and high-frequency light emissions from insulators blasted with laser pulses. In their paper published in the journal Nature, the team describes the techniques they used to pull off this feat. Michael Chini with the University of Central Florida offers a News & Views piece on the work done by the team in the same journal issue, and explains what hurdles still need to be overcome before devices making use of the technology can be developed. As Chini notes, huge strides have been made over the past few decades in using light to convey information, while at the same time, electronic devices have continued to be limited by the upper frequency limits at which electric currents can be driven. As he also notes, prior research has shown that it is possible to use light in the form of laser pulses to drive electrons through a bulk insulator at much higher than normal frequencies, but until now, there was no way to measure the oscillations of those electrons, a necessary part of applying them in a high-speed device. In this new effort, the researchers took advantage of the fact that when electrons speed up, they emit what are known as high-order harmonics, which just happen to be a direct reflection of the motion of those electrons. They used an attosecond streak camera to measure these harmonics in a silica nanofilm and noted that the light was emitted in bursts lasting less than 500 attoseconds. These findings suggest that it should be possible to build devices that use lasers to push the oscillating frequency of electrons up to 100 times that of devices currently used to test the limit (into the multi-petahertz range). Currently, Chini notes, more work still needs to be done subtle variations that occur in the process will have to be removed, for example, and testing will have to be done to see if the same results can be obtained with materials other than silica. Also, it is still not clear if the laser-pulsed approach causes any negative impact on current production. Abstract The frequency of electric currents associated with charge carriers moving in the electronic bands of solids determines the speed limit of electronics and thereby that of information and signal processing1. The use of light fields to drive electrons promises access to vastly higher frequencies than conventionally used, as electric currents can be induced and manipulated on timescales faster than that of the quantum dephasing of charge carriers in solids2. This forms the basis of terahertz (1012 hertz) electronics in artificial superlattices2, and has enabled light-based switches3, 4, 5 and sampling of currents extending in frequency up to a few hundred terahertz. Here we demonstrate the extension of electronic metrology to the multi-petahertz (1015 hertz) 16

25 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) frequency range. We use single-cycle intense optical fields (about one volt per ångström) to drive electron motion in the bulk of silicon dioxide, and then probe its dynamics by using attosecond (10 18 seconds) streaking6, 7 to map the time structure of emerging isolated attosecond extreme ultraviolet transients and their optical driver. The data establish a firm link between the emission of the extreme ultraviolet radiation and the light-induced intraband, phase-coherent electric currents that extend in frequency up to about eight petahertz, and enable access to the dynamic nonlinear conductivity of silicon dioxide. Direct probing, confinement and control of the waveform of intraband currents inside solids on attosecond timescales establish a method of realizing multi-petahertz coherent electronics. We expect this technique to enable new ways of exploring the interplay between electron dynamics and the structure of condensed matter on the atomic scale. rology-multi-petahertz-frequency.html 18. Move over, lasers: Scientists can now create holograms from neutrons, too Interference pattern created by neutron holography. For the first time, a team including scientists from the National Institute of Standards and Technology (NIST) have used neutron beams to create holograms of large solid objects, revealing details about their interiors in ways that ordinary laser light-based visual holograms cannot. Holograms flat images that change depending on the viewer's perspective, giving the sense that they are three-dimensional objects owe their striking capability to what's called an interference pattern. All matter, such as neutrons and photons of light, has the ability to act like rippling waves with peaks and valleys. Like a water wave hitting a gap between the two rocks, a wave can split up and then re-combine to create information-rich interference patterns (link is external). An optical hologram is made by shining a laser at an object. Instead of merely photographing the light reflected from the object, a hologram is formed by recording how the reflected laser light waves interfere with each other. The resulting patterns, based on the waves' phase differences (link is external), or relative positions of their peaks and valleys, contain far more information about an object's appearance than a simple photo does, though they don't generally tell us much about its hidden interior. Hidden interiors, however, are just what neutron scientists explore. Neutrons are great at penetrating metals and many other solid things, making neutron beams useful for scientists who create a new substance and want to investigate its properties. But neutrons have limitations, too. They aren't very good for creating visual images; neutron experiment data is usually expressed as graphs that would look at home in a high school algebra textbook. And this data typically tells them about how a substance is made on average fine if they want to know broadly about an object built from a bunch of repeating structures like a crystal (link is external), but not so good if they want to know the details about one specific bit of it. But what if we could have the best of both worlds? The research team has found a way. The team's previous work, performed at the NIST Center for Neutron Research (NCNR), involved passing neutrons through a cylinder of aluminum that had a tiny "spiral staircase" carved into one of its circular faces. The cylinder's shape imparted a twist to the neutron beam, but the team also noticed that the beam's individual neutrons changed phase depending on what section of the cylinder they passed through: the thicker the section, the greater the phase shift. Eventually they realized this was essentially the information they needed to create holograms of objects' innards, and they detail their method in their new paper. The discovery won't change anything about interstellar chess games, but it adds to the palette of techniques scientists have to explore solid materials. The team has shown that all it takes is a beam of neutrons and an interferometer a detector that measures interference patterns to create direct visual representations of an object and reveal details about specific points within it. "Other techniques measure small features as well, only they are limited to measuring surface properties," said team member Michael Huber of NIST's Physical Measurement Laboratory. "This might be a more prudent technique for measuring small, 10-micron size structures and buried interfaces inside the bulk of the material." ms-neutrons.html 19. Controlling electrons in time and space 17

26 光子学 In an electron microscope, electrons are emitted by pointy metal tips, so they can be steered and controlled with high precision. Recently, such metal tips have also been used as high precision electron sources for generating X-rays. A team of researchers at TU Wien (Vienna), together with colleagues from the FAU Erlangen-Nürnberg (Germany), have developed a method of controlling electron emissions with higher precision than ever before. With the help of two laser pulses, it is now possible to switch the flow of electrons on and off on extremely short time scales. It's Just the Tip of the Needle "The basic idea resembles a lightning rod," says Christoph Lemell (TU Wien). "The electrical field around a needle is always strongest right at the tip. That's why the lightning always strikes the tip of a rod, and for the same reason, electrons leave a needle right at the tip." Extremely pointy needles can be fabricated with the methods of modern nanotechnology. Their tip is just a few nanometres wide, so the point at which the electrons are emitted is known with very high accuracy. In addition to that, it is also important to control at which point in time the electrons are emitted. This kind of temporal control has now become possible using a new approach: "Two different laser pulses are fired at the metal tip," explains Florian Libisch (TU Wien). The colours of these two lasers are chosen such that the photons of one laser have exactly twice the energy of the other laser's photons. Also, it is important to ensure that both light waves oscillate in perfect synchronicity. With the help of computer simulations, the team from TU Wien was able to predict that a small time delay between the two laser pulses can serve as a "switch" for electron emission. This prediction has now been confirmed by experiments performed by Professor Peter Hommelhoff's research group at FAU Erlangen-Nürnberg. Based on these experiments, it is now possible to understand the process in detail. Absorbing Photons When a laser pulse is fired at the metal tip, its electrical field can rip electrons out of the metal that is a well-known phenomenon. The new idea is that a combination of two different lasers can be used to control the emission of the electrons on a femtosecond time scale. There are different ways an electron can gain enough energy to leave the metal tip: It can absorb two photons from the high-energy laser or four photons from the low-energy laser. Both mechanisms lead to the same result. "Much like a particle in a double-slit experiment, which travels on two different paths at the same time, the electron can take part in two different processes at the same time," says Professor Joachim Burgdörfer (TU Wien). "Nature does not have to pick one of the two possibilities both are equally real and interfere which each other." By carefully tuning the two lasers, it is possible to control whether the two quantum physical processes amplify each other, which leads to an increased emission of electrons, or whether they cancel each other, which means that hardly any electrons are emitted at all. This is a simple and effective way of controlling electron emission. It is not just a new method of performing experiments with high energy electrons, the new technology should open the door to controlled X-ray generation. "Innovative X-ray sources are already being built using arrays of narrow metal tips as electron sources," says Lemell. "With our new method, these nano tips could be triggered in exactly the right way so that coherent X-ray radiation is produced." Optical clock technology tested in space for first time This view of Earth from the research rocket shows the detachment of the last booster -- the moment when the optical clock began operating under microgravity. For the first time, an optical clock has traveled to space, surviving harsh rocket launch conditions and successfully operating under the microgravity that would be experienced on a satellite. This demonstration brings optical clock technology much closer to implementation in space, where it could eventually allow GPS-based navigation with centimeter-level location precision. In The Optical Society's journal for high impact research, Optica, researchers report on a new compact, robust and automated frequency comb laser system that was key to the operation of the space-borne optical clock. Frequency combs are the "gears" necessary to run clocks ticking at optical frequencies. "Our device represents a cornerstone in the development of future space-based precision clocks and metrology," said Matthias Lezius of Menlo Systems GmbH, first author of the paper. "The optical clock 18

27 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) performed the same in space as it had on the ground, showing that our system engineering worked very well." Using time for location Phones and other GPS-enabled devices pinpoint your location on Earth by contacting at least four satellites bearing atomic clocks. Each of these satellites provides a time stamp, and the system calculates your location based on the relative differences among those times. The atomic clocks used on today's satellites are based on natural oscillation of the cesium atom a frequency in the microwave region of the electromagnetic spectrum. Optical clocks use atoms or ions that oscillate about 100,000 times higher than microwave frequencies, in the optical, or visible, part of the electromagnetic spectrum. The higher frequencies mean that optical clocks "tick" faster than microwave atomic clocks and could thus provide time-stamps that are 100 to 1,000 times more accurate, greatly improving the precision of GPS. Frequency combs are an important component of optical clocks because they act like gears, dividing the faster oscillations of optical clocks into lower frequencies to be counted and linked to a microwave-based reference atomic clock. In other words, frequency combs allow the optical oscillations to be precisely measured and used to tell time. Until recently, frequency combs have been very large, complex set-ups only found in laboratories. Lezius and his team at Menlo Systems, a spin-off company of Nobel Laureate T.W. Hänsch's group at the Max Plank Institute for Quantum Optics, developed a fully automated optical frequency comb that measures only 22 by 14.2 centimeters and weighs 22 kilograms. The new frequency comb is based on optical fibers, making it rugged enough to travel through the extreme acceleration forces and temperature changes experienced when leaving Earth. Its power consumption is below 70 watts, well within the requirements for satellite-based devices. Traveling to space The researchers combined their new frequency comb with an atomic cesium clock for reference and a rubidium optical clock developed by research groups at Ferdinand Braun Institute Berlin and Humbold University Berlin as well as a group from Hamburg University that recently moved to Mainz University. Airbus Defense & Space GmbH was involved in the construction, interfacing, and integration of the payload module that went into space and also provided support and equipment during the flight. In April 2015, the entire system was flown on a research rocket for a 6-minute parabolic flight into space as part of the TEXUS program that launches from the Esrange Space Center in Sweden. Once microgravity was achieved, the system started measurements automatically and was controlled from the ground station via a low-bandwidth radio link. "The experiment demonstrated the comb's functionality as a comparative frequency divider between the optical rubidium transition at 384 THz and the cesium clock providing a 10 MHz reference," said Lezius. Although the optical clock used in the demonstration had about one tenth the accuracy of atomic clocks used on GPS satellites today, the researchers are already working on a new version that will improve accuracy by several orders of magnitude. Global sensing from space The highly accurate measurements made possible with frequency combs could be useful for many applications. For example, space-based frequency combs could improve the accuracy of global remote sensing of greenhouse gases from satellites and could be used for space-based gravitational wave detectors. "Applications based on frequency combs are quite important for future space-based optical clocks, precision metrology and earth observation techniques," said Lezius. "The space technology readiness of frequency combs is developing at a fast pace." The researchers plan to fly an improved version of the optical clock into space at the end of In that experiment, the frequency comb module will not fly under a pressurized dome in order to test how well it works in the vacuum conditions that would be experienced on a satellite. The researchers also seek to further improve the system's resistance to harsh cosmic radiation to ensure that it can operate for several years in orbit. Within a few years, Lezius and his team aim to have a space-qualified frequency comb module that the space community can use in future missions and applications. They are aiming for a device with a volume of about 3 liters that weighs a few kilograms and has a power consumption of approximately 10 watts Molecular imaging hack makes cameras 'faster' A schematic shows a Rice University technique called super temporal resolution microscopy, which acquires faster molecular movies without needing a faster camera. A spinning "double helix" phase mask turns the single-point image of a molecule into barbell-shaped lobes that change angle depending on the time the 19

28 光子学 image is captured. A molecule may be captured multiple times in a single image. A new Rice University technique grabs images of chemical processes that happen faster than most laboratory cameras are able to capture them. The technique, super temporal resolution microscopy (STReM), allows researchers to view and gather useful information about fluorescing molecules at a frame rate 20 times faster than typical lab cameras normally allow. The work by Rice chemist Christy Landes and her team, along with Rice electrical engineer Kevin Kelly, appears in the American Chemical Society's Journal of Physical Chemistry Letters. The Rice researchers start with a Nobel-winning microscopy technique that views objects like molecules at "super resolution" - that is, things below the diffraction limit that are smaller than most microscopes are able to see. "Super-resolution microscopy lets us image things smaller than about half of visible light's wavelength - around 250 nanometers," Landes said. But she noted a barrier: "You couldn't take pictures of anything faster than your frame rate," she said. The Rice lab's new enhancement, which uses a rotating phase mask to encode fast dynamics in each camera frame, will help researchers understand processes that occur at interfaces like adsorption and desorption of proteins or molecules' trajectories as they move along two-dimensional surfaces. Rice University chemist Christy Landes, left, works with postdoctoral researcher Hao Shen to adjust lasers for the lab's super temporal resolution microscope. The lab invented a technique to acquire better data about molecules that move faster than a standard lab camera can capture. Typical charge-coupled device (CCD) cameras max out at frame rates of 10 to 100 milliseconds, Landes said. While other techniques like electron microscopy can see materials at the subnanoscale, super-resolution microscopy has a distinct advantage for fragile samples like biomolecules: It doesn't destroy them in the process. The technique manipulates the phase of light to give the image at the detector a more complicated shape. This process had previously been used by other researchers to encode where the object is in three-dimensional space within an otherwise two-dimensional image. The Rice lab's contribution was to note that by manipulating the phase over time, it would also be possible to encode faster time resolutions within a slow image frame. Thus, the group designed and built a spinning phase mask. The resulting images capture dynamic events that happen faster than the camera's intrinsic frame rate. The shape of each image within a frame effectively gives it a unique time stamp. The technique takes advantage of a characteristic of microscopy familiar to anyone who's ever taken a blurry picture. Point spread functions are a measure of the shape of images both in and out of focus. When the subjects are as small as single molecules, shifting in and out of focus happens easily, and the size and shape of the resulting blur can tell researchers how far from the focal plane the subject is. Phase-mask engineering makes it possible to make focus-dependent blur easier to detect by introducing distinct point spread functions. On film they look like the lobes of a barbell and rotate with respect to focus. STReM uses point spread function changes from the spinning mask to collect temporal information, Landes said. With the new technique, changes in the lobes' angles reveal the time an event has occurred within each frame. "The purpose is to allow scientists to study fast processes without the need to buy faster and much more expensive cameras," said Rice graduate student Wenxiao Wang, lead author of the paper. "This involves extracting more information from single images." Landes, who recently won ACS's prestigious Early Career Award in Experimental Physical Chemistry for her work to integrate super-resolution microscopy with information theory to understand protein separations, said designing and building the mechanism cost the lab only a few hundred dollars, a fraction of the cost of buying a faster camera. The phase mask is based on work by Kelly, who drew upon his contributions to Rice's single-pixel camera to design what amounts to a piece of plastic with variable thickness that distorts light en route to the CCD. "Like the single-pixel camera, we're doing compressive analysis," Landes said. "With the static phase mask, three-dimensional information is compressed into a 2-D image. In this particular case, we have compressed faster information into a slower camera frame rate. It's a way to get more information in the pixels that you have." Co-authors are postdoctoral research associates Hao Shen and Lawrence Tauzin; graduate students Bo Shuang, Benjamin Hoener and Nicholas New records set up with 'screws of light' 20

29 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) Camera image of a laser beam in false color, which consists of photons in a superposition with quantum numbers between +10,000 and -10,000. After zooming in twice, the enormous complexity of the structure can be revealed. Credit: IQOQI Vienna / Robert Fickler University of Vienna research team has succeeded in breaking two novel records while experimenting with so-called twisted particles of light. These results, now published in the journal PNAS, are not only of fundamental interest but also give a hint towards the enormous information capacity a single particle of light may offer in future applications. Twisted light Time and again, properties of the light surprise the research world. For example, light can be brought into a corkscrew-like form in order to produce so-called "screws of light", as Anton Zeilinger, quantum physicist at the University of Vienna, describes. The amazing fact is that one can in principle impose any number of windings on each individual light particle - called photons. The larger the number of windings, the larger the so-called quantum number with which the photon is described. The Viennese scientists results of the Vienna Center for Quantum Science and Technology (VCQ) at the University of Vienna and the Institute of Quantum Optics and Quantum Information Vienna (IQOQI Vienna) at the Austrian Academy of Sciences have now made use of this feature in two papers, breaking previous records on the transmission distance and the magnitude of the quantum number. Twisted light transmitted message over 143 kilometers In principle, twisted light can carry an arbitrary large amount of information per photon. This is in contrast to the polarization of light, which is limited to one bit per photon. For example, data rates of up to 100 terabits per second, which correspond to about 120 Blu-Ray discs per second, have already been achieved under laboratory conditions. The transmission under realistic conditions, however, is still in its infancy. In addition to transmission over short distances in special fiber optics, transmission of such light beams over free space, required for instance for satellite communication, was limited to three kilometers so far; achieved by the same Viennese team two years ago. Screw of light on the 143 km long way between the canary islands of La Palma and Tenerife. In the current study, the research team around Anton Zeilinger and Mario Krenn show that information encoded in twisted light can still be reconstructed even after more than 100 kilometers. The experiment has been conducted between the canary islands of La Palma and Tenerife, which is 143 kilometer away. "The message 'Hello World!' has been encoded onto a green laser with an optical hologram, and reconstructed with an artificial neural network on the other island", explains Krenn, PhD-student in Zeilinger's group. Having shown that these light properties are in principle maintained over long distances, they now have to be combined with modern communication technologies - a task which already several groups around the world are starting to address. Quantum entanglement with 5-digits quantum numbers Together with the research group of Ping Koy Lam in Canberra, Australia, the Viennese group of Anton Zeilinger also investigated how strongly single photons can be twisted into the screw-like structure without losing distinct quantum features. In other words, does quantum physics still hold in the limit of large quantum numbers or is classical physics and everyday experience taking over again? For this purpose, the researchers took advantage of a novel technique developed by their colleagues in Australia. There, they have established a technique to fabricate so-called spiral phase mirrors to twist photons in an unprecedented strong manner and thus increase the quantum numbers to huge values. The mirrors, custom-made for the experiment in Vienna, allow the generation of screw-like photons with quantum numbers of more than 10,000, which is a hundred times larger than in previous experiments. 21

30 光子学 Image of the screw of light on the wall of the Optical Ground Station telescope of the ESA in Tenerife, Canary Island, after being transmitted over more than 100 km. The ring-like structure, a signature of screws of light, is still clearly visible. At first, the Viennese researchers generated entangled photon pairs, i.e. two particles of light that are seemingly connected despite being separated by an arbitrary distance. Entanglement is the distinct phenomena in quantum physics, which Einstein described as "spooky action at a distance". After completion of this initial step, the researchers then twisted one of the photons with the Australian mirrors without destroying the entanglement, thus demonstrating that quantum physics even holds if 5-digit quantum numbers are entangled. Although driven by foundational questions, future applications can already be anticipated. "The enormous complexity of the light's structure is fascinating and can be seen as an intuitive indication about how much information should fit on a single photon", explains Robert Fickler, lead author of the study and currently working as a postdoctoral fellow at the University of Ottawa, Canada. Hence, in both studies the researchers set up novel records with "screws of light" to investigate foundational questions as well as pave the way to possible future technologies. html 23. Scientists fabricate a new class of crystalline solid This image shows the results of scanning X-ray microdiffraction ( 渭 SXRD) with submicron spatial resolution. Lauediffraction (a) from an unconstrained Sb2S3 single crystal (top) and laser fabricated RLS crystal Sb2S3 (bottom).magnified images (b) of selected reflection (852) extracted from Laue patterns (a, bottom) obtained for differentpoints of the RLS crystal (c). Scientists at Lehigh University, in collaboration with Lawrence Berkeley National Laboratory, have demonstrated the fabrication of what they call a new class of crystalline solid by using a laser heating technique that induces atoms to organize into a rotating lattice without affecting the macroscopic shape of the solid. By controlling the rotation of the crystalline lattice, the researchers say they will be able to make a new type of synthetic single crystals and "bio-inspired" materials that mimic the structure of special biominerals and their superior electronic and optical properties as well. The group reported its findings today (Nov. 3) in Scientific Reports, a Nature journal, in an article titled "Rotating lattice single crystal architecture on the surface of glass." The paper's lead author is Dmytro Savytskii, a research scientist in the department of materials science and engineering at Lehigh. The other authors are Volkmar Dierolf, distinguished professor and chair of the department of physics at Lehigh; Himanshu Jain, the T.L. Diamond Distinguished Chair in Engineering and Applied Science and professor of materials science and engineering at Lehigh; and Nobumichi Tamura of the Lawrence Berkeley National Lab in Berkeley, California. The development of the rotating lattice single (RLS) crystals follows a discovery reported in March in Scientific Reports in which the Lehigh group demonstrated for the first time that a single crystal could be grown from glass without melting the glass. In a typical crystalline solid, atoms are arranged in a lattice, a regularly repeating, or periodic three-dimensional structure. When viewed from any angle left to right, up and down, front to back a crystal-specific periodicity becomes evident. Glass, by contrast, is an amorphous material with a disordered atomic structure. Because they have no grain boundaries between interconnecting crystals, single-crystal materials often possess exceptional mechanical, optical and electrical properties. Single crystals give diamonds their brilliance and jet turbine blades their resistance to mechanical forces. And the single crystal of silicon of which a silicon chip is made gives it superior conducting properties that form the basis for microelectronics. The periodicity, or repeating pattern, in a rotating lattice single crystal, said Jain and Dierolf, differs from the periodicity in a typical single crystal. "We have found that when we grow a crystal out of glass," said Jain, "the periodicity does not result the some way. In one direction, it looks perfect, but if you turn the lattice and look at it from a different angle, you see that the whole structure is rotating." "In a typical single-crystal material," said Dierolf, "once I figure out how the pattern repeats, then, if I know the precise location of one atom, I can predict the precise location of every atom. This is possible only because single crystals possess a long-range order. "When we grow an RLS crystal out of glass, however, we have found that the periodicity does not result the some way. To predict the location of every atom, I have to know not just the precise location of a particular atom but the rotation angle of the lattice as well. "Thus, we have to slightly modify the textbook definition of single crystals." 22

31 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) The rotation, said Jain, occurs at the atomic scale and does not affect the shape of the glass material. "Only the string of atoms bends, not the entire material. We can see the bending of the crystal lattice with x-ray diffraction." To achieve this rotation, the researchers heat a very small portion of the surface of a solid glass material with a laser, which causes the atoms to become more flexible. "The atoms want to arrange in a straight line but the surrounding glass does not allow this," said Jain. "Instead, the glass, being completely solid, forces the configuration of the atoms to bend. The atoms move and try to organize in a crystalline lattice, ideally in a perfect single crystal, but they cannot because the glass prevents the perfect crystal from forming and forces the atoms to arrange in a rotational lattice. The beauty is that the rotation occurs smoothly on the micrometer scale. "Our laser imposes a degree of asymmetry on the growth of the crystal. We control the asymmetry of the heating source to impose this rotational pattern on the atoms." The group's ability to control the amount of heating is critical to the formation of the rotating lattice, said Jain. "The key to the creation of the rotating atomic lattice is that it occurs without melting the glass. Melting allows too much freedom of atomic movement, which makes it impossible to control the organization of the lattice. "Our subtle way of heating the glass overcomes this. We heat only the surface of the glass, not inside. This is very precise, very localized heating. It causes only a limited movement of the atoms, and it allows us to control how the atomic lattice will bend." Rotating lattices have been observed in certain biominerals in the ocean, said Jain and Dierolf, and it may also occur on a very small scale in some natural minerals as spherulites. "But no one had previously made this on a larger scale in a controlled way, which we have accomplished with the asymmetrical imposition of a laser to cause the rotating lattice," said Jain. "Scientists were not able to understand this phenomenon before because they could not observe it on a large enough scale. We are the first group to induce this to happen on an effectively unlimited dimension with a laser." Jain and Dierolf and their group are planning further studies to improve their ability to manipulate the ordering of the atoms. The researchers performed the laser heating of the glass at Lehigh and characterized the glass with micro x-ray diffraction on a synchrotron at the Lawrence Berkeley National Lab. They plan to perform further characterization at Berkeley and with electron microscopy at Lehigh. The project has been funded for six years by the U.S. Department of Energy. "This is a novel way of making single crystals," said Dierolf. "It opens a new field by creating a material with unique, novel properties." A new way to image solar cells in 3-D The Molecular Foundry s Edward Barnard is part of a team of scientists that developed a new way to see inside solar cells. Next-generation solar cells made of super-thin films of semiconducting material hold promise because they're relatively inexpensive and flexible enough to be applied just about anywhere. Researchers are working to dramatically increase the efficiency at which thin-film solar cells convert sunlight to electricity. But it's a tough challenge, partly because a solar cell's subsurface realm where much of the energy-conversion action happens is inaccessible to real-time, nondestructive imaging. It's difficult to improve processes you can't see. Now, scientists from the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a way to use optical microscopy to map thin-film solar cells in 3-D as they absorb photons. The method, reported Nov. 15 in the journal Advanced Materials, was developed at the Molecular Foundry, a DOE Office of Science user facility located at Berkeley Lab. It images optoelectronic dynamics in materials at the micron scale, or much thinner than the diameter of a human hair. This is small enough to see individual grain boundaries, substrate interfaces, and other internal obstacles that can trap excited electrons and prevent them from reaching an electrode, which saps a solar cell's efficiency. So far, scientists have used the technique to better understand why adding a specific chemical to solar cells made of cadmium telluride (CdTe) the most common thin-film material improves the solar cells' performance. "To make big gains in photovoltaic efficiency, we need to see what's happening throughout a working photovoltaic material at the micron scale, both on the surface and below, and our new approach allows us to do that," says Edward Barnard, a principal scientific engineering associate at the Molecular Foundry. He led 23

32 光子学 the effort with James Schuck, the director of the Imaging and Manipulation of Nanostructures facility at the Molecular Foundry. The imaging method is born out of a collaboration between Molecular Foundry scientists and Foundry users from PLANT PV Inc., an Alameda, California-based company. While fabricating new solar cell materials at the Molecular Foundry, the team found that standard optical techniques couldn't image the inner-workings of the materials, so they developed the new technique to obtain this view. Next, scientists from the National Renewable Energy Laboratory came to the Molecular Foundry and used the new method to study CdTe solar cells. To develop the approach, the scientists modified a technique called two-photon microscopy (which is used by biologists to see inside thick samples such as living tissue) so that it can be applied to bulk semiconductor materials. The method uses a highly focused laser beam of infrared photons that penetrate inside the photovoltaic material. When two low-energy photons converge at the same pinpoint, there's enough energy to excite electrons. These electrons can be tracked to see how long they last in their excited state, with long-lifetime electrons appearing as bright spots in microscopy images. In a solar cell, long-lifetime electrons are more likely to reach an electrode. In addition, the laser beam can be systematically repositioned throughout a test-sized solar cell, creating a 3-D map of a solar cell's entire optoelectronic dynamics. The method has already shed light on the benefits of treating CdTe solar cells with cadmium chloride, which is often added during the fabrication process. Scientists know cadmium chloride improves the efficiency of CdTe solar cells, but its effect on excited electrons at the micron scale is not well understood. Studies have shown that the chlorine ions tend to pile up at grain boundaries, but how this changes the lifetime of excited electrons is unclear. Thanks to the new imaging technique, the researchers discovered the cadmium chloride treatment increases the lifetime of excited electrons at the grain boundaries, as well as within the grains themselves. This is easily seen in 3-D images of CdTe solar cells with and without the treatment. The treated solar cell "lights up" much more uniformly throughout the material, both in the grains and the spaces in between. "Scientists have known that cadmium chloride passivation improves the lifetime of electrons in CdTe cells, but now we've mapped at the micron scale where this improvement occurs," says Barnard. The new imaging technique could help scientists make more informed decisions about improving a host of thin-film solar cell materials in addition to CdTe, such as perovskite and organic compounds. "Researchers trying to push photovoltaic efficiency could use our technique to see if their strategies are working at the microscale, which will help them design better test-scale solar cells and eventually full-sized solar cells for rooftops and other real-world applications," he says. 三. 电子工程 25. A phone that charges in seconds? Scientists bring it closer to reality A thin, flexible supercapacitor developed at the University of Central Florida boasts high energy and power densities. A team of UCF scientists has developed a new process for creating flexible supercapacitors that can store more energy and be recharged more than 30,000 times without degrading. The novel method from the University of Central Florida's NanoScience Technology Center could eventually revolutionize technology as varied as mobile phones and electric vehicles. "If they were to replace the batteries with these supercapacitors, you could charge your mobile phone in a few seconds and you wouldn't need to charge it again for over a week," said Nitin Choudhary, a postdoctoral associate who conducted much of the research published recently in the academic journal ACS Nano. Anyone with a smartphone knows the problem: After 18 months or so, it holds a charge for less and less time as the battery begins to degrade. Scientists have been studying the use of nanomaterials to improve supercapacitors that could enhance or even replace batteries in electronic devices. It's a stubborn problem, because a supercapacitor that held as much energy as a lithium-ion battery would have to be much, much larger. The team at UCF has experimented with applying newly discovered two-dimensional materials only a few atoms thick to supercapacitors. Other researchers have also tried formulations with graphene and other two-dimensional materials, but with limited success. "There have been problems in the way people incorporate these two-dimensional materials into the existing systems - that's been a bottleneck in the field. We developed a simple chemical synthesis approach so we can very nicely integrate the existing materials with 24

33 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) the two-dimensional materials," said principal investigator Yeonwoong "Eric" Jung, an assistant professor with joint appointments to the NanoScience Technology Center and the Materials Science & Engineering Department. Jung's team has developed supercapacitors composed of millions of nanometer-thick wires coated with shells of two-dimensional materials. A highly conductive core facilitates fast electron transfer for fast charging and discharging. And uniformly coated shells of two-dimensional materials yield high energy and power densities Developing graphene microwave photodetector Senior researcher Jeong Min-kyung. Illustration represents the novel design of the supercapacitor developed at the University of Central Florida. Scientists already knew two-dimensional materials held great promise for energy storage applications. But until the UCF-developed process for integrating those materials, there was no way to realize that potential, Jung said. "For small electronic devices, our materials are surpassing the conventional ones worldwide in terms of energy density, power density and cyclic stability," Choudhary said. Cyclic stability defines how many times it can be charged, drained and recharged before beginning to degrade. For example, a lithium-ion battery can be recharged fewer than 1,500 times without significant failure. Recent formulations of supercapacitors with two-dimensional materials can be recharged a few thousand times. By comparison, the new process created at UCF yields a supercapacitor that doesn't degrade even after it's been recharged 30,000 times. Jung is working with UCF's Office of Technology Transfer to patent the new process. Supercapacitors that use the new materials could be used in phones and other electronic gadgets, and electric vehicles that could benefit from sudden bursts of power and speed. And because they're flexible, it could mean a significant advancement in wearable tech, as well. "It's not ready for commercialization," Jung said. "But this is a proof-of-concept demonstration, and our studies show there are very high impacts for many technologies." In addition to Choudhary and Jung, the research team included Chao Li, Julian Moore and Associate Professor Jayan Thomas, all of the UCF NanoScience Technology Center; and Hee-Suk Chung of Korea Basic Science Institute in Jeonju, South Korea. A joint team has developed cryogenic microwave photodetector which is able to detect 100,000 times smaller light energy compared to the existing photedetectors. The significance is DGIST have developed the world's first microwave photodetector using graphene device. Daegu Gyeongbuk Institute of Science and Technology (DGIST), South Korea, announced that a senior researcher Jung Min-kyung at Division of Nano and Energy Convergence Research has developed cryogenic microwave photodetector which is able to detect 100,000 times smaller light energy compared to the existing photedetectors. The senior researcher Jung Min-kyung and a team at the Department of Physics of University of Bazel in Switzerland conducted a joint research and realized microwave photodetection in a fully suspended and clean graphene p-n junction. This study is worth spotlighting as graphene, the single layer carbon based material, has shown a great number of electrical, mechanical, and thermal properties. With its innumerable application potential, gaphene is called dream material and researches are underway not only in basic sciences but also in application science area such as flexible display, wearable devices, next-generation solar energy, etc. Graphene has attracted attention as a next-generation photonic device such as a photodetector because its gapless band structure allows electron-hole pairs to be generated over a broad energy spectrum, unlike general semiconductors. So far, graphene photodetectors have only been demonstrated for optical wavelengths, from near-inflared to ultraviolet. However, Photodetection in 25

34 电子工程 the microwave range has not yet been studied as it was impossible to measure the microwave on the detector because it has much smaller energy than the surface potential difference caused by the surrounding environment as well as the residues on the surface of graphene created in the device process. To increase the light energy absorption rate of microwave region, the senior researcher Jeong Min-kyung separated the graphene p-n junction device from the substrate, made bridge forms as if they are bridges floating in the air and created a clean electronic system in which the electrons can move far distance without residues or dispersion. Through the process, the team confirmed that sufficient electron-hole pairs are generated in the microwave region by shifting the Dirac point of graphene close to Fermi energy. They succeeded in realizing the graphene photodetector in the microwave region by measuring the flow of the photocurrent due to the temperature difference between both electrodes as the temperature of the p-n junction increases due to the electron-hole pairs generated in the graphene p-n junction. The graphene microwave photodetector developed in this study is superior in sensitivity compared to the existing graphene photodetectors and is expected to improve the performance of various optical sensors used in high resolution smart phones, high efficiency solar cells, etc. DGIST's senior researcher Jeong Min-kyung at Division of Nano-Energy Convergence Research said, "The significance of this study is that we have developed the world's first microwave photodetector using graphene device. We will carry out further research to improve the performance of wearable devices and flexible displays by developing new application device such as a large-area microwave photodetector using a single device based graphene." The research findings were published on November 9, 2016 in Nano Letters, the international academic journal of published by the American Chemical Society (ACS). todetector.html 27. Fujitsu develops analysis technology to improve communication performance of virtual networks Figure 1: Summary of the newly developed technology Fujitsu Laboratories today announced the development of an automatic analysis technology to improve communications performance and quality in virtual networks. With the spread of virtualization technologies, such as the cloud, software defined networking (SDN), and network functions virtualization (NFV), there is demand for the ability to flexibly set up and operate high performance virtual infrastructure. In order to set up and operate virtual infrastructure for operations that require high performance, it is necessary for experts with knowledge of both hardware and software to take time to analyze bottlenecks and set up the virtual infrastructure appropriately. This results in high operating costs with frequent changes to the system structure or usage situation. Now Fujitsu Laboratories has developed a technology that, with a low load, captures communications packets passing through virtual infrastructure, as well as a technology which uses this information to identify communication bottlenecks and automatically recommend configurations to improve communications speed and to reduce packet loss and other measures to raise virtual network quality. These technologies have been confirmed to roughly double communication speeds of virtual networks. With this technology, high communication performance and quality can be maintained, even in environments where the system structure and usage situation frequently change, such as virtual infrastructure for the cloud or telecommunications carriers. This technology will be exhibited at Fujitsu Forum 2016 Munich, to be held from November With the spread of virtualization technologies like the cloud and NFV, the importance of virtual network technologies for rapidly and flexibly connecting multiple systems is increasing. In current virtual networks, there are issues with degradations of communication performance and quality, particularly at high load times, so there has been a demand for technology to improve them for applications which 26

35 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) require high communications performance and quality, such as telecommunications carriers. Figure 2: Load-reducing capture technology in virtual networks In order to improve the communications performance of virtual networks, it is necessary to identify the locations and causes of bottlenecks, and then, based on those results, to eliminate the bottleneck by appropriately configuring the hardware and software. This can be done by expanding the buffer between processes that are communicating with each other in significant volumes, for example, or by changing deployment such that the processes communicating with each other are handled on processors with shorter communication routes. In order to identify bottlenecks, it was necessary for an expert who is well versed in in the methods of configuring both hardware and software, and familiar with their characteristics, to spend time investigating the bottlenecks. In addition, as the system structure and usage situation frequently change with virtual infrastructure, it was necessary to analyze communications bottlenecks with every change and reconfigure the virtual infrastructure, resulting in higher operating costs. Now Fujitsu Laboratories has developed technologies that automatically recommend configurations to eliminate communications bottlenecks by automatically analyzing a virtual network's communications (Figure 1). These newly developed technologies enable operators to quickly and appropriately configure virtual infrastructure to suit conditions. Features of the technologies are as follows. Technology that captures communications packets on the virtual network with low load Previously, in order to capture the communication packets flowing through a virtual network, it was necessary to copy the communication packets' data to a packet analysis virtual machine (VM). This process added to the system's load, inviting deterioration in communication performance and quality. Now, by setting up a shared buffer that can be accessed from multiple VM s in switches on the virtual network (vswitches), it is possible to capture communications packets with low load, without copying the data of communication packets. Figure 3: Technology that analyzes bottlenecks from packet analysis and infrastructure information and recommends configurations Technology that recommends configurations to eliminate bottlenecks Compared with physical networks, virtual networks more often experience packet loss, particularly under high load conditions, which worsens communication performance and quality. With monitoring information that could be gathered in operating previous virtual infrastructure, only a portion of packet loss could be detected, making it difficult to identify the causes of bottlenecks. With this newly developed technology, by analyzing the behavior of captured communication packets, packet loss that occurs in virtual infrastructure can be thoroughly detected. This includes loss caused by hypervisors or VMs, which was previously difficult to detect. Based on this information, the technology correlates packet loss trends and infrastructure resource usage information to analyze bottlenecks and display configurations to eliminate them. Effects In a trial based on a communications environment with high volumes of traffic, one in which file-transfers and other bandwidth intensive activity is taking place, Fujitsu Laboratories confirmed that using the same hardware with the configuration recommended by this technology roughly doubled communications performance. A decreased packet loss rate and other factors also enhanced communications quality by approximately ten times. In addition, with this bottleneck analysis and optimal configuration generation technology, it has become possible to quickly and optimally configure a virtual network without an expert, which is also expected to reduce operating costs. With this technology, it is possible to operate stable services using virtual infrastructure, even in applications where virtualization technology could not previously be applied because of communications performance and quality problems, such as in a telecommunications carrier's networks, which require flexible changes in network structure. Fujitsu Laboratories will continue research and development on this technology with objectives such heightening the ability to solve detectable bottleneck events that currently prove problematic, and improving the accuracy of the analysis. This technology will be incorporated in operations management products, 27

36 电子工程 beginning with FUJITSU Software ServerView Infrastructure Manager, in fiscal gy-virtual-networks.html 28. Unusual quantum liquid on crystal surface could inspire future electronics Strange electron orbits form on the surface of a crystal in this image created using a theoretical data model. These orbits correspond to the electrons being in different 'valleys' of states, yielding new insights into an area of research called 'vallytronics,' which seeks alternative ways to manipulate electrons for future electronic applications. For the first time, an experiment has directly imaged electron orbits in a high-magnetic field, illuminating an unusual collective behavior in electrons and suggesting new ways of manipulating the charged particles. The study, conducted by researchers at Princeton University and the University of Texas-Austin was published Oct. 21, in the journal Science. The study demonstrates that the electrons, when kept at very low temperatures where their quantum behaviors emerge, can spontaneously begin to travel in identical elliptical paths on the surface of a crystal of bismuth, forming a quantum fluid state. This behavior was anticipated theoretically during the past two decades by researchers from Princeton and other universities. "This is the first visualization of a quantum fluid of electrons in which interactions between the electrons make them collectively choose orbits with these unusual shapes," said Ali Yazdani, the Class of 1909 Professor of Physics at Princeton, who led the research. "The other big finding is that this is the first time the orbits of electrons moving in a magnetic field have been directly visualized," Yazdani said. "In fact, it is our ability to image these orbits that allowed us to detect the formation of this strange quantum liquid." Fundamental explorations of materials may provide the basis for faster and more efficient electronic technologies. Today's electronic devices, from computers to cellphones, use processors made from silicon. With silicon reaching its maximum capacity for information processing, researchers are looking to other materials and mechanisms. One area of progress has been in two-dimensional materials, which allow control of electron motion by breaking the particles away from the constraints of the underlying crystal lattice. This involves moving electrons among "pockets" or "valleys" of possible states created by the crystal. Some researchers are working on ways to apply this process in an emerging field of research known as "valleytronics." In the current work, the strange elliptical orbits correspond to the electrons being in different "valleys" of states. This experiment demonstrates one of the rare situations where electrons spontaneously occupy one valley or another, the researchers said. The team at Princeton used a scanning tunneling microscope to visualize electrons on the surface of a bismuth crystal at extremely low temperatures where quantum behaviors can be observed. Because electrons are too small to be seen, the scanning tunneling microscope has a miniscule electrically charged needle that detects electrons as it scans the crystal surface. Co-first authors Benjamin Feldman, an associate research scholar in Princeton's Department of Physics; Mallika Randeria, a graduate student in physics; and András Gyenis, a postdoctoral research associate in the Department of Electrical Engineering, conducted the experiments at Princeton. Huiwen Ji, a postdoctoral research associate in the Department of Chemistry, working with Robert Cava, Princeton's Russell Wellman Moore Professor of Chemistry, grew the exceptionally pure bismuth crystal. Using a microscope capable of detecting electrons, researchers at Princeton imaged strange elliptical orbits of electrons on the surface of a crystal of bismuth (pictured). Bismuth has relatively few electrons, which makes it ideal for watching what happens to a flow of electrons subjected to a high magnetic field. Despite its purity, the crystal Ji and Cava grew contained some defects. Roughly one atom was slightly out of place for every tens of thousands of atoms. Normally, in the absence of the magnetic field, electrons in a crystal will flit from atom to atom. Applying a strong magnetic field perpendicular to the flow of electrons forces the electrons' paths to curve into orbit around a nearby defect in the crystal, like planets going around the sun. The researchers found that they could measure the properties, or wave functions, of these orbits, giving them an important tool for studying the two-dimensional soup of electrons on the surface of the crystal. Due to the crystal's lattice structure, the researchers expected to see three differently shaped elliptical orbits. Instead the researchers found that all the electron orbits spontaneously lined up in the same direction, or 28

37 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) "nematic" order. The researchers determined that this behavior occurred because the strong magnetic field caused electrons to interact with each other in ways that disrupted the symmetry of the underlying lattice. "It is as if spontaneously the electrons decided, 'It would lower our energy if we all picked one particular direction in the crystal and deformed our motion in that direction,'" Yazdani said. "What was anticipated but never demonstrated is that we can turn the electron fluid into this nematic fluid, with a preferred orientation, by changing the interaction between electrons," he said. "By adjusting the strength of the magnetic field, you can force the electrons to interact strongly and actually see them break the symmetry of the surface of the crystal by choosing a particular orientation collectively." Spontaneous broken symmetries are an active area of study thought to underlie physical properties such as high-temperature superconductivity, which enables electrons to flow without resistance. Prior to directly imaging the behavior of these electrons in magnetic fields, researchers had hints of this behavior, which they call a nematic quantum Hall liquid, from other types of experiments, but the study is the first direct measurement. "People have been looking at these states in a bunch of different contexts and this experiment represents a new way of observing them," said Allan MacDonald, a professor of physics at the University of Texas-Austin who contributed theoretical understanding to the study along with graduate student Fengcheng Wu, who is now at Argonne National Laboratory. "I'd done some work on a similar system together with former graduate students, Xiao Li, who is now at the University of Maryland, and Fan Zhang, now at the University of Texas-Dallas. When Yazdani's group showed me what they saw, I immediately recognized that they had identified a state that we had predicted, but in a completely unexpected way. It was quite a happy surprise." The study gives experimental evidence for ideas predicted over the past two decades, including theoretical work by Princeton Professor of Physics Shivaji Sondhi and others. Eduardo Fradkin, a professor of physics at the University of Illinois at Urbana-Champaign, contributed, along with Steven Kivelson, a professor of physics at Stanford University, to early predictions of this behavior in a paper published in Nature in "What Yazdani's experiments give us is a more quantitative test to explore the collective property of the electrons in this material," said Fradkin, who was not involved in the current study. "This is something we made arguments for, and only now has it been confirmed in this particular material. For me, this is very satisfying to see." Thermoelectric paint enables walls to convert heat into electricity Thermoelectric paint being applied to an alumina hemisphere. The paint provides closer contact with the heat-emitting surface than conventional planar thermoelectric devices do. Paint these days is becoming much more than it used to be. Already researchers have developed photovoltaic paint, which can be used to make "paint-on solar cells" that capture the sun's energy and turn it into electricity. Now in a new study, researchers have created thermoelectric paint, which captures the waste heat from hot painted surfaces and converts it into electrical energy. "I expect that the thermoelectric painting technique can be applied to waste heat recovery from large-scale heat source surfaces, such as buildings, cars, and ship vessels," Jae Sung Son, a coauthor of the study and researcher at the Ulsan National Institute of Science and Technology (UNIST), told Phys.org. "For example, the temperature of a building's roof and walls increases to more than 50 째 C in the summer," he said. "If we apply thermoelectric paint on the walls, we can convert huge amounts of waste heat into electrical energy." The thermoelectric paint looks very different than conventional thermoelectric materials, which are typically fabricated as flat, rigid chips. These devices are then attached to irregular-shaped objects that emit waste heat, such as engines, power plants, and refrigerators. However, the incomplete contact between these curved surfaces and the flat thermoelectric generators results in inevitable heat loss, decreasing the overall efficiency. In the new study published in Nature Communications, Sung Hoon Park et al., from UNIST, the Korea Institute of Science and Technology (KIST), and the Korea Electrotechnology Research Institute, have addressed this issue of incomplete contact by demonstrating that the thermoelectric paint easily adheres to the surface of virtually any shape. The thermoelectric paint contains the thermoelectric particles bismuth telluride (Bi2Te3), which are commonly used in conventional thermoelectric devices. 29

38 电子工程 The researchers also added molecular sintering aids which, upon heating, cause the thermoelectric particles to coalesce, increasing the density of these particles in the paint along with their energy conversion efficiency (the ZT values are up to 0.67 for n-type and 1.21 for p-type particles). The researchers demonstrated that the thermoelectric paint can be painted onto a variety of curved heat-emitting surfaces. After sintering for 10 minutes at C, the painted layers form a uniform film about 50 micrometers thick. Tests showed that the devices painted with the thermoelectric paint exhibit a high output power density (4 mw/cm2 for in-plane type devices and 26.3 mw/cm 2 for through-plane type devices). These values are competitive with conventional thermoelectric materials and better than all thermoelectric devices based on inks and pastes. Besides the traditional thermoelectric applications, the researchers expect that thermoelectric paint have the potential to be used as wearable thermoelectric energy harvesters. The technology developed here could also be used in 3D printed electronics and painted electronic art. The researchers plan to further pursue these applications in the future. "We are planning on developing room-temperature-processable, air-insensitive, and scalable thermoelectric paint and painting processes for practical applications," Son said. alls-electricity.html 四. 纳米物理与材料 30. Supersonic spray yields new nanomaterial for bendable, wearable electronics Left, photograph of a large-scale silver nanowire-coated flexible film. Right, silver nanowire particles viewed under the microscope. A new, ultrathin film that is both transparent and highly conductive to electric current has been produced by a cheap and simple method devised by an international team of nanomaterials researchers from the University of Illinois at Chicago and Korea University. The film is also bendable and stretchable, offering potential applications in roll-up touchscreen displays, wearable electronics, flexible solar cells and electronic skin. The results are reported in Advanced Functional Materials. The new film is made of fused silver nanowires, and is produced by spraying the nanowire particles through a tiny jet nozzle at supersonic speed. The result is a film with nearly the electrical conductivity of silver-plate and the transparency of glass, says senior author Alexander Yarin, UIC Distinguished Professor of Mechanical Engineering. "The silver nanowire is a particle, but very long and thin," Yarin said. The nanowires measure about 20 microns long, so four laid end-to-end would span the width of a human hair. But their diameter is a thousand times smaller and significantly smaller than the wavelength of visible light, which minimizes light scattering. The researchers suspended the nanowire particles in water and propelled them by air through a de Laval nozzle, which has the same geometry as a jet engine, but is only a few millimeters in diameter. "The liquid needs to be atomized so it evaporates in flight," Yarin said. When the nanowires strike the surface they are being applied to at supersonic speed, they fuse together, as their kinetic energy is converted to heat. "The ideal speed is 400 meters per second," Yarin said. "If the energy is too high, say 600 meters per second, it cuts the wires. If too low, as at 200 meters per second, there's not enough heat to fuse the wires." The researchers applied the nanowires to flexible plastic films and to three-dimensional objects. "The surface shape doesn't matter," Yarin said. The transparent flexible film can be bent repeatedly and stretched to seven times its original length and still work, said Sam Yoon, the corresponding author of the study and a professor of mechanical engineering at Korea University. Earlier this year, Yarin and Yoon and their colleagues produced a transparent conducting film by electroplating a mat of tangled nanofiber with copper. Compared to that film, the self-fused silver nanowire film offers better scalability and production rate, Yoon said. "It should be easier and cheaper to fabricate, as it's a one-step versus a two-step process," said Yarin. "You can do it roll-to-roll on an industrial line, continuously." aterial-bendable-wearable.html 31. 'Exceptional' nanosensor architecture based on exceptional points 30

39 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) (L-R): Boubacar Kanté and Ashok Kodigala. Researchers from the University of California San Diego have developed a novel design for a compact, ultra-sensitive nanosensor that can be used to make portable health-monitoring devices and to detect minute quantities of toxins and explosives for security applications. The study addresses one of the major challenges of nanosensor design: how to increase sensitivity while reducing size. The nanosensor design presented in this study combines three-dimensional plasmonic nanoparticles with singularities called exceptional points a combination that's being demonstrated for the first time. "The new physics implemented here could potentially outcompete the plasmonic technologies currently in use for sensing," said Boubacar Kanté, electrical engineering professor at the UC San Diego Jacobs School of Engineering and senior author of the study. Kanté and his team published their novel design Nov. 8 online in the rapid communication section of the journal Physical Review B. Singularities, such as exceptional points, are fundamental in physics due to their uncanny ability to induce a large response from a small excitation, Kanté explained. Singularities occur when a quantity is undefined or infinite, such as the density at the center of black hole, for example. Exceptional points occur when two waves become degenerate, meaning that both their resonant frequencies and spatial structure merge as one. "Exceptional points have been highly sought after for sensors and enhanced light-matter interactions," said Ashok Kodigala, a PhD student in Kanté's lab and first author of the study. "The possibility to demonstrate exceptional points in systems that are simultaneously sub-wavelength and compatible with small biological molecules for sensing has remained elusive until now." Nanosensors operate based on a phenomenon called frequency splitting, meaning that the presence of a substance perturbs the degeneracy between two resonant frequencies and causes a detectable split. In an exceptional-point-based nanosensor, resonant frequencies would split much faster than they do in traditional nanosensors, giving rise to enhanced detection capabilities. By combining exceptional points and plasmonics, researchers formulated a design for a nanosensor that is both compact and ultra-sensitive. "We believed that designing such a nanosensor requires not just a gradual improvement of existing devices, but a conceptual breakthrough. That is why we chose to focus on exceptional-point-based-nanosensors," Kodigala said. In this study, researchers proposed what Kodigala calls "a general recipe to obtain exceptional points on demand." The method involves controlling the interaction between symmetry-compatible modes of the plasmonic system. The nanosensor design has only been demonstrated computationally so far. The team is working on integrating the exceptional-point-based nanosensors on a chip. "Once we optimize some of the main parameters of this system to minimize ohmic and radiative losses, we can start transitioning this research from the theoretical stage to a commercially relevant product," Kanté said. The team has filed a patent on the technology New ultra-thin semiconductor could extend life of Moore's Law Following a decade of intensive research into graphene and two-dimensional materials a new semiconductor material shows potential for the future of super-fast electronics. The new semiconductor named Indium Selenide (InSe) is only a few atoms thick, similarly to graphene. The research was reported in Nature Nanotechnology this week by researchers of The University of Manchester and their colleagues at The University of Nottingham. Graphene is just one atom thick and has unrivalled electronic properties, which has led to widely-publicised suggestions about its use in future electronic circuits. For all its superlative properties graphene has no energy gap. It behaves more like a metal rather than a normal semiconductor, frustrating its potential for transistor-type applications. The new research shows that InSe crystals can be made only a few atoms thick, nearly as thin as graphene. InSe was shown to have electronic quality higher than that of silicon which is ubiquitously used in modern electronics. Importantly, unlike graphene but similar to silicon, ultra-thin InSe has a large energy gap allowing 31

40 纳米物理与材料 transistors to be easily switched on and off, allowing for super-fast next-generation electronic devices. Combining graphene with other new materials, which individually have excellent characteristics complementary to the extraordinary properties of graphene, has resulted in exciting scientific developments and could produce applications as yet beyond our imagination. Sir Andre Geim, one of the authors of this study and a recipient of the Nobel Prize in Physics for research on graphene, believes that the new findings could have a significant impact on development of future electronics. "Ultra-thin InSe seems to offer the golden middle between silicon and graphene. Similar to graphene, InSe offers a naturally thin body, allowing scaling to the true nanometre dimensions. Similar to silicon, InSe is a very good semiconductor." The Manchester researchers had to overcome one major problem to create high-quality InSe devices. Being so thin, InSe is rapidly damaged by oxygen and moisture present in the atmosphere. To avoid such damage, the devices were prepared in an argon atmosphere using new technologies developed at the National Graphene Institute. This allowed high-quality atomically-thin films of InSe for the first time. The electron mobility at room temperature was measured at 2,000 cm2/vs, significantly higher than silicon. This value increases several times at lower temperatures. Current experiments produced the material several micrometres in size, comparable to the cross-section of a human hair. The researchers believe that by following the methods now widely used to produce large-area graphene sheets, InSe could also soon be produced at a commercial level. Co-author of the paper Professor Vladimir Falko, Director of the National Graphene Institute said: "The technology that the NGI has developed for separating atomic layers of materials into high-quality two-dimensional crystals offers great opportunities to create new material systems for optoelectronics applications. We are constantly looking for new layered materials to try." Ultra-thin InSe is one of a growing family of two-dimensional crystals that have a variety of useful properties depending on their structure, thickness and chemical composition. Currently, research in graphene and related two-dimensional materials is the fastest growing field of materials science that bridges science and engineering. A laser shines through a solution of still dissolving 2-D nanomaterial showing there are particles within the liquid (left). When a drop of the solution is dried, the still dissolving nanosheets stack into different tiled shapes (right). When left to fully dissolve, only single layer sheets are found. Two-dimensional (2D) nanomaterials have been made by dissolving layered materials in liquids, according to new UCL-led research. The liquids can be used to apply the 2D nanomaterials over large areas and at low costs, enabling a variety of important future applications. 2D nanomaterials, such as graphene, have the potential to revolutionise technology through their remarkable physical properties, but their translation into real world applications has been limited due to the challenges of making and manipulating 2D nanomaterials on an industrial scale. The new approach, published today in Nature Chemistry, produced single layers of many 2D nanomaterials in a scalable way. The researchers used the method on a wide variety of materials, including those with semiconductor and thermoelectric properties, to create 2D materials that could be used in solar cells or for turning wasted heat energy into electrical energy, for example. "2D nanomaterials have outstanding properties and a unique size, which suggests they could be used in everything from computer displays to batteries to smart textiles. Many methods for making and applying 2D nanomaterials are difficult to scale or can damage the material, but we've successfully addressed some of these issues. Hopefully our new process will help us realise the potential of 2D nanomaterials in the future," explained study director Dr Chris Howard (UCL Physics & Astronomy). For the study, funded by the Royal Academy of Engineering and the Engineering and Physical Sciences Research Council, the scientists inserted positively charged lithium and potassium ions between the layers of different materials including bismuth telluride (Bi2Te3), molybdenum disulphide (MoS2) and titanium disulphide (TiS2), giving each layer a negative charge and creating a 'layered material salt'. -life-law.html 33. New solution for making 2-D nanomaterials 32

41 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) As the still dissolving 2-D nanomaterial solution is dried, the nanosheets stack into different tiled shapes (right). When left to fully dissolve, only single layer sheets are found. These layered material salts were then gently dissolved in selected solvents without using chemical reactions or stirring. This gave solutions of 2D nanomaterial sheets with the same shape as the starting material but with a negative charge. The scientists analysed the contents of the solutions using atomic force microscopy and transmission electron microscopy to investigate the structure and thickness of the 2D nanomaterials. They found that the layered materials dissolved into tiny sheets of clean, undamaged, single layers, isolated in solutions. The team from UCL, University of Bristol, Cambridge Graphene Centre and École Polytechnique Fédérale de Lausanne, were able to demonstrate that even the 2D nanomaterial sheets, comprising millions of atoms, made stable solutions rather than suspensions "We didn't expect such a range of 2D nanomaterials to form a solution when we simply add ed the solvent to the salt - the layered material salts are large but dissolve into liquid similar to table salt in water. The fact that they form a liquid along with their negative charge, makes them easy to manipulate and use on a large scale, which is scientifically intriguing but also relevant to many industries," said first author Dr Patrick Cullen (UCL Chemical Engineering). "We've shown they can be painted onto surfaces and, when left to dry, can arrange themselves into different tiled shapes, which hasn't been seen before. They can also be electroplated onto surfaces in much the same way gold is used to plate metals. We're looking forward to making different 2D nanomaterials using our process and trying them out in different applications as the possibilities are near endless," he concluded. UCL Business PLC (UCLB), the technology commercialisation company of UCL has patented this research and will be supporting the commercialisation process New LEDs may offer better way to clean water in remote areas Ohio State University researchers have developed a technique to create light emitting diodes on metal foil. For the first time, researchers have created light-emitting diodes (LEDs) on lightweight flexible metal foil. Engineers at The Ohio State University are developing the foil based LEDs for portable ultraviolet (UV) lights that soldiers and others can use to purify drinking water and sterilize medical equipment. In the journal Applied Physics Letters, the researchers describe how they designed the LEDs to shine in the high-energy "deep" end of the UV spectrum. The university will license the technology to industry for further development. Deep UV light is already used by the military, humanitarian organizations and industry for applications ranging from detection of biological agents to curing plastics, explained Roberto Myers, associate professor of materials science and engineering at Ohio State. The problem is that conventional deep-uv lamps are too heavy to easily carry around. "Right now, if you want to make deep ultraviolet light, you've got to use mercury lamps," said Myers, who is also an associate professor of electrical and computer engineering. "Mercury is toxic and the lamps are bulky and electrically inefficient. LEDs, on the other hand, are really efficient, so if we could make UV LEDs that are safe and portable and cheap, we could make safe drinking water wherever we need it." Nanowires were grown on titanium foil at The Ohio State University. He noted that other research groups have fabricated deep-uv LEDs at the laboratory scale, but only by using extremely pure, rigid single-crystal semiconductors as substrates a strategy that imposes an enormous cost barrier for industry. Foil-based nanotechnology could enable large-scale production of a lighter, cheaper and more environmentally friendly deep-uv LED. But Myers and materials science doctoral student Brelon J. May hope that their technology will do something more: turn a niche research field known as nanophotonics into a viable industry. "People always said that nanophotonics will never be commercially important, because you can't scale them up. Well, now we can. We can make a sheet of them if we want," Myers said. "That means we can consider nanophotonics for large-scale manufacturing." In part, this new development relies on a well-established semiconductor growth technique known as molecular beam epitaxy, in which vaporized 33

42 纳米物理与材料 elemental materials settle on a surface and self-organize into layers or nanostructures. The Ohio State researchers used this technique to grow a carpet of tightly packed aluminum gallium nitride wires on pieces of metal foil such as titanium and tantalum. The individual wires measure about 200 nanometers tall and about nanometers in diameter thousands of times narrower than a human hair and invisible to the naked eye. In laboratory tests, the nanowires grown on metal foils lit up nearly as brightly as those manufactured on the more expensive and less flexible single-crystal silicon. The researchers are working to make the nanowire LEDs even brighter, and will next try to grow the wires on foils made from more common metals, including steel and aluminum Graphene plasmons reach the infrared Probing graphene plasmon in nanodisks by FTIR. Graphene's unique properties can be both a blessing and a curse to researchers, especially to those at the intersection of optical and electronic applications. These single-atom thick sheets feature highly mobile electrons on their flexible profiles, making them excellent conductors, but in general graphene sheets do not interact with light efficiently. Problematic for shorter wavelength light, photons in the near infrared region of the spectrum, where telecommunication applications become realizable. In a paper published this week in the journal Optics Letters, from The Optical Society (OSA), researchers at the Technical University of Denmark have demonstrated, for the first time, efficient absorption enhancement at a wavelength of 2 micrometers by graphene, specifically by the plasmons of nanoscale graphene disks. Much like water ripples arising from the energy of a dropped pebble, electronic oscillations can arise in freely moving conduction electrons by absorbing light energy. The resulting collective, coherent motions of these electrons are called plasmons, which also serve to amplify the strength of the absorbed light's electric field at close proximity. Plasmons are becoming increasingly commonplace in various optoelectronic applications where highly conductive metals can be easily integrated. Graphene plasmons, however, face an extra set of challenges unfamiliar to the plasmons of bulk metals. One of these challenges is the relatively long wavelength needed to excite them. Many efforts taking advantage of the enhancing effects of plasmons on graphene have demonstrated promise, but for low energy light. "The motivation of our work is to push graphene plasmons to shorter wavelengths in order to integrate graphene plasmon concepts with existing mature technologies," said Sanshui Xiao, associate professor from the Technical University of Denmark. To do so, Xiao, Wang and their collaborators took inspiration from recent developments at the university's Center of Nanostructured Graphene (CNG), where they demonstrated a self-assembly method resulting in large arrays of graphene nanostructures. Their method primarily uses geometry to bolster the graphene plasmon effects at shorter wavelengths by decreasing the size of the graphene structures. Using lithographic masks prepared by a block copolymer based self-assembly method, the researchers made arrays of graphene nanodisks. They controlled the final size of the disks by exposing the array to oxygen plasma which etched away at the disks, bringing the average diameter down to approximately 18 nm. This is approximately 1000 times smaller than the width of a human hair. The array of approximately 18 nm disks, resulting from 10 seconds of etching with oxygen plasma, showed a clear resonance with 2 micrometer wavelength light, the shortest wavelength resonance ever observed in graphene plasmons. An assumption might be that longer etching times or finer lithographic masks, and therefore smaller disks, would result in even shorter wavelengths. Generally speaking this is true, but at 18 nm the disks already start requiring consideration of atomic details and quantum effects. Instead, the team plans to tune graphene plasmon resonances at smaller scales in the future using electrical gating methods, where the local concentration of electrons and electric field profile alter resonances. Xiao said, "To further push graphene plasmons to shorter wavelengths, we plan to use electrical gating. Instead of graphene disks, graphene antidots (i.e. graphene sheets with regular holes) will be chosen because it is easy to implement a back-gating technique." There are also fundamental limits to the physics that prevent shortening the graphene plasmon resonance wavelength with more etching. "When the wavelength becomes shorter, the interband transition will soon play a key role, leading to broadening of the resonance. Due to weak coupling of light with graphene plasmons and this broadening effect, it will become hard to observe the resonance feature," Xiao explained. 34

43 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) red.html 五. 量子物理 36. Quantum computers: 10-fold boost in stability achieved Computation & Communication Technology (CQC2T) at UNSW. "Our decade-long research program had already established the most long-lived quantum bit in the solid state, by encoding quantum information in the spin of a single phosphorus atom inside a silicon chip, placed in a static magnetic field," he said. Artist''s impression of a single-atom electron spin, hosted in a silicon crystal and dressed by an oscillating electromagnetic field. Australian engineers have created a new quantum bit which remains in a stable superposition for 10 times longer than previously achieved, dramatically expanding the time during which calculations could be performed in a future silicon quantum computer. The new quantum bit, made up of the spin of a single atom in silicon and merged with an electromagnetic field - known as 'dressed qubit' - retains quantum information for much longer that an 'undressed' atom, opening up new avenues to build and operate the superpowerful quantum computers of the future. The result by a team at Australia's University of New South Wales (UNSW), appears today in the online version of the international journal, Nature Nanotechnology. "We have created a new quantum bit where the spin of a single electron is merged together with a strong electromagnetic field," said Arne Laucht, a Research Fellow at the School of Electrical Engineering & Telecommunications at UNSW, and lead author of the paper. "This quantum bit is more versatile and more long-lived than the electron alone, and will allow us to build more reliable quantum computers." Building a quantum computer has been called the 'space race of the 21st century' - a difficult and ambitious challenge with the potential to deliver revolutionary tools for tackling otherwise impossible calculations, such as the design of complex drugs and advanced materials, or the rapid search of massive, unsorted databases. Its speed and power lie in the fact that quantum systems can host multiple 'superpositions' of different initial states, which in a computer are treated as inputs which, in turn, all get processed at the same time. "The greatest hurdle in using quantum objects for computing is to preserve their delicate superpositions long enough to allow us to perform useful calculations," said Andrea Morello, leader of the research team and a Program Manager in the Centre for Quantum Scanning electron microscope image of a device, similar to the one used. Highlighted are the positions of the tuning gates (red), the microwave antenna (blue), and the single electron transistor used for spin readout (yellow). What Laucht and colleagues did was push this further: "We have now implemented a new way to encode the information: we have subjected the atom to a very strong, continuously oscillating electromagnetic field at microwave frequencies, and thus we have 'redefined' the quantum bit as the orientation of the spin with respect to the microwave field." The results are striking: since the electromagnetic field steadily oscillates at a very high frequency, any noise or disturbance at a different frequency results in a zero net effect. The researchers achieved an improvement by a factor of 10 in the time span during which a quantum superposition can be preserved. Specifically, they measured a dephasing time of T2*=2.4 milliseconds - a result that is 10-fold better than the standard qubit, allowing many more operations to be performed within the time span during which the delicate quantum information is safely preserved. "This new 'dressed qubit' can be controlled in a variety of ways that would be impractical with an 'undressed qubit',", added Morello. "For example, it can be controlled by simply modulating the frequency of the microwave field, just like in an FM radio. The 'undressed qubit' instead requires turning the amplitude of the control fields on and off, like an AM radio. "In some sense, this is why the dressed qubit is more immune to noise: the quantum information is controlled by the frequency, which is rock-solid, whereas the amplitude can be more easily affected by external noise". Since the device is built upon standard silicon technology, this result paves the way to the construction of powerful and reliable quantum processors based upon the same fabrication process already used for today's computers. The UNSW team leads the world in developing quantum computing in silicon, and Morello's team is 35

44 纳米物理与材料技术与应用量子物理 part of the consortium of UNSW researchers who have struck a A$70 million deal between UNSW, the researchers, business and the Australian government to develop a prototype silicon quantum integrated circuit - the first step in building the world's first quantum computer in silicon. A functional quantum computer would allow massive increases in speed and efficiency for certain computing tasks - even when compared with today's fastest silicon-based 'classical' computers. In a number of key areas - such as searching large databases, solving complicated sets of equations, and modelling atomic systems such as biological molecules and drugs - they would far surpass today's computers.they would also be enormously useful in the finance and healthcare industries, and for government, security and defence organisations. Quantum computers could identify and develop new medicines by greatly accelerating the computer-aided design of pharmaceutical compounds (and minimising lengthy trial and error testing), and develop new, lighter and stronger materials spanning consumer electronics to aircraft. They would also make possible new types of computational applications and solutions that are beyond our ability to foresee. lity.html 37. New 3-D wiring technique brings scalable quantum computers closer to reality Researchers from the Institute for Quantum Computing at the University of Waterloo led the development of a quantum socket, representing a significant step towards to the realization of a scalable quantum computer. Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer. "The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD candidate with IQC and the Department of Physics and Astronomy at Waterloo. He and Thomas McConkey, PhD candidate from IQC and the Department of Electrical and Computer Engineering at Waterloo, are lead authors on the study that appears in the journal Physical Review Applied as an Editors' Suggestion and is featured in Physics. "The technique connects classical electronics with quantum circuits, and is extendable far beyond current limits, from one to possibly a few thousand qubits." One promising implementation of a scalable quantum computing architecture uses a superconducting qubit, which is similar to the electronic circuits currently found in a classical computer, and is characterized by two states, 0 and 1. Quantum mechanics makes it possible to prepare the qubit in superposition states, meaning that the qubit can be in states 0 and 1 at the same time. To initialize the qubit in the 0 state, superconducting qubits are brought down to temperatures close to -273 degrees Celsius inside a cryostat, or dilution refrigerator. To control and measure superconducting qubits, the researchers use microwave pulses. The pulses are typically sent from dedicated sources and pulse generators through a network of cables connecting the qubits in the cryostat's cold environment to the room-temperature electronics. The network of cables required to access the qubits inside the cryostat is a complex infrastructure and, until recently, has presented a barrier to scaling the quantum computing architecture. "All wire components in the quantum socket are specifically designed to operate at very low temperatures and perform well in the microwave range required to manipulate the qubits," said Matteo Mariantoni, a faculty member at IQC and the Department of Physics and Astronomy at Waterloo and senior author on the paper. "We have been able to use it to control superconducting devices, which is one of the many critical steps necessary for the development of extensible quantum computing technologies." The paper, Three-Dimensional Wiring for Extensible Quantum Computing: The Quantum Socket, is a collaborative effort of researchers at INGUN Prüfmittelbau GmbH, Germany, INGUN USA, and Google in the United States, plus the following researchers from IQC and Waterloo: Jeremy Béjanin, Thomas McConkey, John Rinehart, Carolyn Earnest, Corey Rae McRae, Daryoush Shiri, James Bateman, Yousef Rohanizadegan and Matteo Mariantoni. ble-quantum.html 36

45 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) 38. Subnatural-linewidth biphotons generated from a Doppler-broadened hot atomic vapor cell Experimental configuration for generating narrowband entangled photon pairs from a hot Rb87 vapor cell. Entangled photon pairs, termed as biphotons, have been the benchmark tool for experimental quantum optics. The quantum-network protocols based on photon-atom interfaces have stimulated a great demand for single photons with bandwidth comparable to or narrower than the atomic natural linewidth. In the past decade, laser-cooled atoms have often been used for producing such biphotons, but the apparatus is too large and complicated for engineering. Led by Shengwang Du, Associate professor of physics at the Hong Kong University of Science and Technology (HKUST), a group of scientists were able to produce subnatural-linewidth (<6MHz) biphotons from a Doppler-broadened (530 MHz) hot atomic vapour cell. This method marks a significant breakthrough in the field, as it greatly simplifies production process of narrowband biphotons. Their findings were published in Nature Communications on Sep 23, "Subnatural-linewidth biphotons with controllable waveforms have used to be produced from spontaneous four-wave mixing in cold atoms at a temperature of about 10 μk assisted with electromagnetically induced transparency or cavity," said Du. "But such systems require expert knowledge in laser cooling and trapping. A cold-atom apparatus is not only expensive, but also large and complicated in its vacuum-optical-electronic-mechanical configuration. Moreover, operating cold atoms for producing paired photons requires a complex timing control." "In our study, we find a novel way to use a hot paraffin-coated 87Rb vapour cell at 63 C to successfully produce biphotons with controllable bandwidth ( MHz) and coherence time (47-94ns). This is the best result in the world so far for generating narrowband biphotons from a hot vapor cell." Du continued. The two key elements to make narrowband biphoton generation feasible are the paraffin coating and the spatially separated optical pumping. The long ground-state coherence time preserved by the paraffin coating enables efficient optical pumping for the flying atoms, which is spatially separated from the biphoton generation volume. Du said, "Hot atomic vapour cell is simple in configuration, operation and maintenance, and it is a continuous biphoton source. This result may lead towards miniature narrowband biphoton sources for practical quantum applications and engineering." hotons-doppler-broadened-hot-atomic.html 39. Scientists discover particles similar to Majorana fermions The braiding of Majorana zero modes is shown. Majorana fermions were first proposed by the physicist Ettore Majorana in They are fermion particles that are also their own antiparticles. These fermions are vital to the research of superconducting materials and topological quantum computation. However, 80 years later, scientists have not found a Majorana elementary particle. Though it is hypothesized that neutrinos are Majorana fermions, there is still no evidence to support this conjecture. In condensed matter physics, scientists found that a particlular kind of quasiparticle Majorana zero modes (MZMs) have characteristics similar to Majorana fermions. Recently, a research team from the Key Laboratory of Quantum Information of the Chinese Academy of Sciences achieved the fabrication and manipulation of MZMs in an optical simulator. The team led by Professors LI Chuangfeng, XU Jinshi, and HAN Yongjian implemented the exchange of two MZMs such that the non-abelian statistics of MZMs are supported. This work is published in Nature Communications on October 25th. Generally, the statistics of the identical particles can be determined by their exchange characteristics. For example, the internal quantum states remain the same when two bosons are exchanged, and are imposed by a pi phase when two fermions are exchanged. The bosons and fermions belong to particles with more general statistics, called Abelian anyons. A global phase (not necessarily 0 or pi) is gained after the exchange of two identical Abelian anyons. Moreover, there may exist some exotic particles, called non-abelian anyons, which undertake a unitary transformation (not just a global phase) after exchange. The Majorana fermions with their own antiparticles are widely believed to be non-abelian particles. 37

46 技术与应用量子物理 The research team took advantage of the quantum simulation approach: While the simulated system is not experimentally accessible with current technology, the quantum simulator and its measurement results provide information about the simulated system. In their work, they designed a set of dissipative processes that can effectively create and transfer the MZMs supported in the Kitaev model. The researchers then completed the exchange of two MZMs. The Berry phase the researchers measured during the exchange process supports the non-abelian statistics of MZMs. Furthermore, they demonstrate that the information encoded in the MZMs is immune to local noises in the linear optical system. The method established here provides a novel way to study quantum statistics, topological quantum computation and the characteristics of MZMs. Moreover, this achievement establishes a promising platform to investigate the properties of the MZMs in complex architectures and topological quantum computation based on MZMs. r-majorana-fermions.html 40. Novel light sources made of 2-D materials Artistic representation of a two-photon source: The monolayer (below) emits exactly two photons of different frequencies under suitable conditions. They are depicted in red and green in the picture. Physicists from the University of Würzburg have designed a light source that emits photon pairs, which are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal and some sticky tape. So-called monolayers are at the heart of the research activities. These so-called "super materials" have been surrounded by hype over the past decade. This is because they show great promise to revolutionise many areas of physics. In physics, the term "monolayer" refers to solid materials of minimum thickness. Occasionally, it is only a single layer of atoms thick; in crystals, monolayers can be three or more layers. Experts also speak of two-dimensional materials. In this form, monolayers can exhibit unexpected properties that make them interesting for research. The so-called transition metal dichalcogenides (TMDC) are particularly promising. They behave like semiconductors and can be used to manufacture ultra-small and energy-efficient chips, for example. Moreover, TMDCs are capable of generating light when supplied with energy. Dr. Christian Schneider, Professor Sven Höfling and their research team from the Chair of Technical Physics of the Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, have harnessed exactly this effect for their experiments. Experiments started with sticky tape First, a monolayer was produced using a simple method. The researchers used a piece of sticky tape to peel a multi-layer film from a TMDC crystal. Using the same procedure, they stripped increasingly thin layers from the film, repeating the process until the material on the tape was only one layer thick. The researchers then cooled this monolayer to a temperature of just above absolute zero and excited it with a laser. This caused the monolayer to emit single photons under specific conditions. "We were now able to show that a specific type of excitement produces not one but exactly two photons," Schneider explains. "The light particles are generated in pairs, so to speak." Such two-photon sources can be used to transfer 100 percent tap-proof information. For this purpose, the light particles are entangled. The state of the first photon then has a direct impact on that of the second photon, regardless of the distance between the two. This state can be used to encrypt communication channels. Monolayers enable novel lasers In a second study, the JMU scientists demonstrated another application of exotic monolayers. They mounted a monolayer between two mirrors and again stimulated it with a laser. The radiation excited the TMDC plate itself to emit photons. These were reflected back to the plate by the mirrors, where they excited atoms to create new photons. "We call this process strong coupling," Schneider explains. The light particles are cloned during this process, in a manner of speaking. "Light and matter hybridise, forming new quasi particles in the process: exciton polaritons," the physicist says. For the first time, it is possible to detect these polaritons at room temperature in atomic monolayers. In the short term, this will open up interesting new applications. The "cloned" photons have properties similar to laser light. But they are manufactured in completely different ways. Ideally, the production of new light particles is self-sustaining after the initial excitation without requiring any additional energy supply. In a laser, however, the light-producing material has to be excited energetically from the outside on a permanent basis. This makes the new light source highly energy efficient. Moreover, it is well suited to study certain quantum effects. 38

47 光电技术情报 2017 年第 1 期 ( 总第 26 期 ) Breakthrough in the quantum transfer of information between matter and light From stationary to flying qubits at speeds never reached before. This feat, achieved by a team from Polytechnique Montréal and France's Centre national de la recherche scientifique (CNRS), brings us a little closer to the era when information is transmitted via quantum principles. A paper titled "High-Fidelity and Ultrafast Initialization of a Hole-Spin Bound to a Te Isoelectronic Centre in ZnSe" was recently published in the prestigious journal Physical Review Letters. The creation of a qubit in zinc selenide, a well-known semi-conductor material, made it possible to produce an interface between quantum physics that governs the behaviour of matter on a nanometre scale and the transfer of information at the speed of light, thereby paving the way to producing quantum communications networks. Classical physics vs. quantum physics In today's computers, classical physics rules. Billions of electrons work together to make up an information bit: 0, electrons are absent and 1, electrons are present. In quantum physics, single electrons are instead preferred since they express an amazing attribute: the electron can take the value of 0, 1 or any superposition of these two states. This is the qubit, the quantum equivalent of the classical bit. Qubits provide stunning possibilities for researchers. An electron revolves around itself, somewhat like a spinning top. That's the spin. By applying a magnetic field, this spin points up, down, or simultaneously points both up and down to form a qubit. Better still, instead of using an electron, we can use the absence of an electron; this is what physicists call a "hole." Like its electron cousin, the hole has a spin from which a qubit can be formed. Qubits are intrinsically fragile quantum creature, they therefore need a special environment. Zinc selenide, tellurium impurities: a world first Zinc selenide, or ZnSe, is a crystal in which atoms are precisely organized. It is also a semi-conductor into which it is easy to intentionally introduce tellurium impurities, a close relative of selenium in the periodic table, on which holes are trapped, rather like air bubbles in a glass. This environment protects the hole's spin our qubit and helps maintaining its quantum information accurately for longer periods; it's the coherence time, the time that physicists the world over are trying to extend by all possible means. The choice of zinc selenide is purposeful, since it may provide the quietest environment of all semiconductor materials. Philippe St-Jean, a doctoral student on Professor Sébastien Francoeur's team, uses photons generated by a laser to initialize the hole and record quantum information on it. To read it, he excites the hole again with a laser and then collects the emitted photons. The result is a quantum transfer of information between the stationary qubit, encoded in the spin of the hole held captive in the crystal, and the flying qubit - the photon, which of course travels at the speed of light. This new technique shows that it is possible to create a qubit faster than with all the methods that have been used until now. Indeed, a mere hundred or so picoseconds, or less than a billionth of a second, are sufficient to go from a flying qubit to a static qubit, and vice-versa. Although this accomplishment bodes well, there remains a lot of work to do before a quantum network can be used to conduct unconditionally secure banking transactions or build a quantum computer able to perform the most complex calculations. That is the daunting task which Sébastien Francoeur's research team will continue to tackle. tml 六. 技术与应用 42. VTT creates the world's first hyperspectral iphone camera VTT Technical Research Centre of Finland has created the world's first hyperspectral mobile device by converting an iphone camera into a new kind of optical sensor. This will bring the new possibilities of low-cost spectral imaging to consumer applications. Consumers will be able to use their mobile phones for example to sense food quality or monitor health. Hyperspectral cameras, which are traditionally expensive, have been used for demanding medical and industrial, space and environmental sensing. The cost-effective optical MEMS (Micro Opto Electro Mechanical Systems) spectral technology enables the development of new mobile applications for environmental sensing and observation from vehicles and drones. Other applications include health monitoring and food analysis. All of this forms part of an environment combining smart sensors with the Internet. "Consumer benefits could appear in health applications, such as mobile phones that are able to check whether moles are malignant or food is edible. They could also verify product authenticity or identify users based on biometric data. On the other hand, driverless cars could sense and identify environmental features based on the representation of the full optical spectrum at each point of an image," explains Anna Rissanen, who is heading the research team at VTT. VTT has already developed a wide range of new applications for the innovative hyperspectral cameras. These include the diagnosis of skin cancer, environmental sensing based on nanosatellites, various drone applications for precision agriculture and forest 39

48 技术与应用量子物理 monitoring, and projects underway for the remote measurement of vessel emissions. Spectral imaging everywhere Optical spectral imaging offers a versatile way of sensing various objects and analysing material properties. Hyperspectral imaging provides access to the optical spectrum at each point of an image, enabling a wide range of measurements. The adjustable tiny MEMS filter is integrated with the camera lens and its adjustment is synchronised with the camera's image capture system. "Today's smart devices provide huge opportunities for the processing of image data and various cloud services based on spectral data. Mass-produced sensor technology will enable the introduction of hyperspectral imaging in a range of devices in which low-cost camera sensors are currently used," Rissanen comments. VTT Technical Research Centre of Finland aims to cooperate with companies to commercialise the technology and bring new, innovative optical sensor products to the market. phone-camera.html 43. Faster manufacturing of breath sensors a. Photo figure of the gas sensor device, b. Cross-sectional FE-SEM image of the MoO3 nanorod arrays. A group of researchers at Osaka University, succeeded in producing nanostructured gas sensor devices for detecting volatile organic compounds (VOC) in breath for the purpose of healthcare in time equivalent to or shorter than one tenth of the time required for manufacturing conventional gas sensors. This group improved conventional complicated production methods, developing a simple production method of just sintering substrates applied with materials. This gas sensor's sensing response was comparable to the top-of-the-line sensors reported all over the world. Research leading detection of low concentrations of gas present in exhaled human breath to health checkups and early detection and treatment of serious diseases is being performed. As gas sensors using nanomaterials can detect various gases even at low concentrations, installing such sensors in electronic healthcare devices is sought after, and research and development are being actively conducted. Semiconductor gas sensors detect gas through reduced electrical resistance due to gas molecules attached to the surface of crystalline semiconductor materials. For this, gas sensors need a specific surface area of nanomaterials. In order to use nanomaterials for conventional gas sensors, a complicated flow was necessary, from nanomaterials synthesis to cleansing, uniform dispersion of solvent, applying on substrates, and sintering. Thus, there is a concern that manufacturing technology of such gas sensors requires significant time and labor, increasing cost. A group of researchers led by Assistant Professor Tohru Sugahara (SUGANUMA Lab.) at The Institute of Scientific and Industrial Research, Osaka University, succeeded in producing nanostructured gas sensor devices for detecting volatile organic compounds (VOC) in breath for the purpose of healthcare in time equivalent to or shorter than one tenth of the time required for manufacturing conventional gas sensors. This group improved conventional complicated production methods, developing a simple production method of just sintering substrates applied with materials. This gas sensor's sensing response was comparable to the top-of-the-line sensors reported all over the world. Since demand in healthcare products is on the rise, there is a lot of activity in research and development of sensors for checking health and disease by examining the gas components of a person's breath. Breathalyzers for finding out who is driving drunk have already been commercialized. Recently, breath sensors for early detection of life-style diseases such as cancer and diabetes have been developed, but most of them are large, bulky and expensive. If gas sensors with high sensitivity are produced thanks to this group's research results, portable breath sensors enabling early detection of diseases will gain popularity. 40