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2 目录 一. 光学与工程 Collecting real-time data for material microstructural evolution during radiation exposure New technology could revolutionize 3-D printing Breakthrough curved sensor could dramatically improve image quality captured with digital cameras New plasmonic sensor improves early cancer detection Seeing through materials with visible light 'Scrambled light' wavemeter breakthrough Manufacturing hybrid silicon lasers for mass-produced photonic devices New laser technique identifies the makeup of space debris, from painted shards to Teflon Scientists turbocharge high-resolution, 3-D imaging D virus cam catches germs red-handed New screen coating makes reading in sunlight a lot easier the secret? Moth eyes One billion suns: World's brightest laser sparks new behavior in light The sharpest laser in the world: Physicists develop a laser with a linewidth of only 10 mhz A material that can switch between multiple phases that have distinct electronic, optical and magnetic properties 二. 光子学 Researchers create ultrafast tunable semiconductor metamaterial Group develops technique to shape pulses of intense infrared light Photonic 'hypercrystals' shed stronger light Optical communication at record-high speed via soliton frequency combs generated in optical microresonators Learning with light: New system allows optical 'deep learning' Using thermal light sources to take accurate distance measurements Camera captures microscopic holograms at femtosecond speeds The world's most powerful X-ray laser beam creates 'molecular black hole' 三. 电子工程 Researchers discover way to make solar cells more efficient Magnetoelectric memory cell increases energy efficiency for data storage 四. 纳米物理与材料 Three-dimensional graphene: Experiment at BESSY II shows that optical properties are tuneable Making flexible electronics with nanowire networks Breakthrough in thin electrically conducting sheets paves way for smaller electronic devices Chemists create 3-D printed graphene foam Researchers create very small sensor using 'white graphene' A way to engineer photoactive junctions in iron-chloride-intercalated graphene using a laser. 29

3 31. Scientists detect light-matter interaction in single layer of atoms Researchers measure light fields in 3-D A levitated nanosphere as an ultra-sensitive sensor Optical nanomotors: Tiny 'motors' are driven by light 五. 量子物理 Testing quantum field theory in a quantum simulator A stream of superfluid light Prototype device enables photon-photon interactions at room temperature for quantum computing 六. 技术与应用 New design improves performance of flexible wearable electronics World's smallest and most accurate 3-D-printed biopsy robot First atomic structure of an intact virus deciphered with an X-ray laser New prototypes for superconducting undulators show promise for more powerful, versatile X-ray beams... 39

4 简介 一. 光学与工程 收集辐射环境下材料微结构变化的实时数据... 1 简介 : 美国马萨诸塞工学院的研究人员用新技术研究辐射对材料的影响, 探索在辐射环境下材料微结构的演变及退化过程, 以便确定辐射环境下的工程材料能安全使用的寿命长短 他们的技术能保证持续监控材料的性能在辐射时间内的变化过程, 提供动态的实时信息 这一技术改进称作 瞬态光栅光谱 (TGS) 他们下一步的实验性工作是建造一个离子束加速器靶室系统, 可实时观察辐射下材料的变化过程 2. 新技术可革新 3-D 打印技术... 2 简介 : 美国劳伦斯利弗莫尔的研究人员进行了一项新的研究, 他们利用原有的国家点火装置技术进行金属物体打印, 其速度达到空前之快 这一新的方法 (DiAM) 使用了高能激光二极管阵列, 激光 Q 开关和一个特殊的激光调制器, 对整个金属层进行扫描打印, 取代了以往分层电子光栅打印技术 3. 曲面传感器改进成像质量的突破性研究... 3 简介 : 光学快讯 刊物上报导了微软研究人员一项新的成像方法, 其球面曲率是现有的成像传感器的三倍多, 而且可将这样的传感器置入标准的照相机内, 照相机能产生更高的成像分辨率 研究人员正致力于进一步提高传感器球面曲率的研究, 使其能在红外波长范围内进行操作, 这样就可以应用于望远镜 3-D 空间绘图 计量物理以及其它科学领域的应用 4. 新的等离子传感器用于早期癌症检测... 4 简介 : 美国伊利诺尹大学的研究人员研发一款新的等离子传感器, 此传感器可用来检测癌症的早期生物指标, 也可适用于其他疾病 实验证明这款传感器的可信度很高, 可检测到癌胚抗原最大值为每毫升 1 纳米克, 而大多数个体携带的癌胚抗原平均数为每毫升 3-5 纳米克 此项研究结果有助于医生在患者的癌细胞扩散前给予及早治疗 该传感器由两个传感途径组成, 一个是纳米杯阵列 3-D 多层纳米腔, 另一个是等离子传感装置 5. 用可视光给人体内部结构进行成像... 6 简介 : 美国密歇根大学的研究人员借助酸乳和碎玻璃材料用可见光给身体内部结构成像, 用这种材料聚焦光线更快 更简捷, 他们选择此材料的原因是它们的散光能力强, 是很好的皮肤模型, 这种成像方法不仅精确 方便, 而且速度快 研究人员预计五年内将首次见证可见光透过皮肤进行成像的技术 6. 新的波长计是测量技术领域的一大突破... 7 简介 : 英国圣安德鲁斯大学和一家激光器公司运用光的任意散射原理研制出新的激光波长计 这项研究是波长测量技术的一大突破 他们还演示了用此波长计稳定激光的波长 这项研究结果将加强英国工业与大学在量子技术和医疗方面的合作 7. 用于批量生产光子设备的复合硅激光器... 8 简介 : 长期以来, 在电子工业领域, 人们一直都期望能在硅片上生产出半导体激光器, 而事实证明这是一件很困难的事 现在 A *START 研究人员研究出一种新方法, 不仅能生产出这样的半导体激光器, 而且所生产出的激光器使用简单, 价格便宜, 还可以进行批量生产 这咱激光器应用范围广, 能用在短距离数据通信, 也可用于高速远距离光学传输 研究人员还演示了这个新装置系统本身以及它的集成工艺 8. 用新的激光技术检测太空残骸物... 8 简介 : 美国麻省理工大学的航天工程师研发出能进行密电译义的激光传感技术, 叫激光偏振仪, 能预测并判断太空残骸物的类型 大小 动力及潜在的破坏力 同时这一技术还能在现有的轨道监测系统中得以应用

5 9. 科学家提高了光学相干断层扫描仪的分辨率, 增强了 3-D 成像效果 简介 : 美国斯坦福大学的科学家用常备的器件对光学相干断层扫描仪进行翻新, 使其分辨率提高了好多倍, 能对视网膜和眼角膜的早期损伤以及初期肿瘤进行检查 此项技术解决了 25 年来未曾解决的难题, 提高了该扫描仪的诊断能力, 对预测疾病 防止疾病及治疗疾病具有实际的应用价值 10. 研发出新的病毒细菌 3-D 成像相机 简介 : 美国杜克大学的化学家建造了一个强大的显微镜, 它可以捕捉到微小细菌正在发炎的整个过程的影像 他们研发的这款新的 3-D 成像设备能实时监控微小病毒细菌的活动情况 他们未来的研究计划是设计出多功能 魔术相机 11. 新的抗反射屏保薄膜 简介 : 美国弗罗里达中央大学光学与光子学的研究人员受到具有纳米结构蛾眼的启示, 研发出一种新的抗反射薄膜, 它带有微小 统一形状的球表面凹痕, 每个凹痕直径大约 100 纳米 这种薄膜可用于柔性显示器, 如手机等 预期明年可以将其投入市场 目前研究人员正努力改进该抗反射膜的机械性能和光学效果 12. 激光的亮度达到了太阳表面光线亮度的十亿倍 简介 : 美国内布拉斯加林肯大学的物理学家通过观察光与物质可视情况下的相互作用变化, 研究出地球上最亮的光线, 其亮度是太阳光线亮度的十亿倍 这种独特的 X- 射线脉冲具有生成高分辨率的潜力, 可应用于医学 工程 科研及安全领域的成像技术 13. 只有 10mHz 线宽的激光 简介 : 德国联邦研究院和美国天体物理实验室的研究人员研究出只有 10 mhz 线宽的激光, 创造了新的世界纪录 这项研究成果有广泛的应用潜力, 如光学原子钟 精密光谱仪, 还可用于相对论的无线电天文学领域的研究 14. 新材料能进行多阶转化并具有明显的电子 光学和磁特性 简介 : 中国 英国 美国和日本的一个大型国际研究团队合作研发出一种新材料, 这种材料能在多阶性间进行转换, 而且具有明显的电子 光学和磁特性 他们在 自然 上发表论文描述了这种材料的制做方法 性能转换特点以及它的应用价值 二. 光子学 研究人员研制出可调谐半导体超材料 简介 : 俄罗斯莫斯科国立大学 美国桑地亚国家实验室 德国里西 - 席勒耶拿大学的一个国际合作研究团队设计出基于纳米粒子的可调谐超材料 他们先用等离子蚀刻术, 再使用电子束平版印刷术生产出砷化镓薄膜 这种新的光学超材料为纳米级超快信息传输研究铺平了道路 16. 研究人员研发出新的强红外光脉冲技术 简介 : 摄影师需要用快门和快闪技术在暗光环境下拍摄移动物体图像 激光物理学家受到这一原理的启发, 利用红外快速脉冲技术捕捉微观物体运动的影像, 从而研究出一个生成强中红外光脉冲的工艺, 运用这一工艺, 他们研制出强中红外宽带光源, 并能通过这一工具对分子内部结构进行研究, 这项研究可应用于生物 医学领域 17. 光子 超晶 在网络通信中更有优势 简介 : 美国普渡大学的一个电气计算机工程教授整合了两个光学材料概念, 形成 光子超晶 此项研究结果有助于减少网络黑客攻击 这位教授还与纽约城市大学的同仁们一起演示了超晶是如何实现大幅度增加发射率和强度的 这项研究将用于未来的 Li-Fi 技术, 比目前的 Wi-Fi 及其他高频通信系统更加有优势 18. 光孤子频率梳提高光的通信能力... 18

6 简介 :KIT 光子量子电子研究所和微结构技术研究所的研究人员演示了用光孤子生成具有各种光谱线特点的频率梳系统, 有效地实现了高频光学通信能力, 极大地增强了光通信中波长分流多路技术, 提高了设备的性能, 同时也极大地提高了其稳定性 19. 用光取代电子来提高光学 深度学习 能力 简介 : 麻省理工学院的一个研究团队研究出新的计算方法, 此方法用光取代电子, 能极大地提高计算速度和效率, 具有一定的深度学习计算能力 他们还演示了这一款概念性 基础性系统 研究人员认为一旦这一系统升级并完全发挥作用, 它将应用于很多方面, 比如数据中心或者安全系统, 也可用于自动车辆驾驶等 20. 用热光源对远距离物体进行精确的测量 简介 : 英国朴次茅斯大学 意大利巴里大学和美国的马里兰大学进行合作研究, 他们用简单的热光源首次对远距离物体的空间结构和位置进行比较, 这一传感技术为遥感应用铺平了道路 他们未来的工作重点是用纠缠光子引领高精计量学应用, 对信息处理及新的光学算法研究也有一定的应用潜力 21. 全息显微镜以飞秒速度进行成像 简介 : 俄罗斯圣彼得堡光机大学建造了一个光学全息成像显微镜装置, 能以飞秒速度记录像生物细胞这样微小物体的结构变化 他们根据激光脉冲通过样品时所产生的变形, 重建样品的相位拓扑 与电子显微镜相比, 这一设备无须任何药剂的介入就能对生物结构进行透明可视成像 22. 世界最强 X 射线激光束生成 分子黑洞 简介 : 美国能源部斯坦福国家直线加速器中心的科学家致力于世界最强 X 射线小分子激光器的研究, 他们惊奇地发现, 除了几个电子以外, 一个激光脉冲把分子中最大原子的其他电子从里到外都剥夺了, 只留一个空隙, 其他分子都被拉进此空隙中, 像一个黑洞吞咽一个螺旋状盘旋物一样 他们研究的目的是为了研发更先进的技术应用, 比如获取更高清的生物分子影像等, 为研发下一代相干光源提供技术支撑 三. 电子工程 发现了提高太阳能电池效率的新方法 简介 : 美国怀俄明州立大学的教授用增加锰原子的方法来改进太阳能电池的效率 他们惊奇地发现, 用这种方法能使太阳能电池的能量平均增加了三倍, 有的甚至增加了七倍 这一研究发现可用于未来农场对电力的需求, 对农作物及牲畜的生长很有价值, 同时还可用于大城市的车辆用电, 减少雾霾 24. 磁电存储电池增加数据存贮效率 简介 : 法国和俄罗斯的一个合作研究团队研发一种磁电随机存贮电池, 有提高功率效率的潜力, 能减少废热, 可用于瞬启电脑 近零损耗闪存盘以及数据存储中心等 四. 纳米物理与材料 实验显示 3-D 石墨烯材料的光学性能是可调谐的 简介 : 一个国际合作研究团队首次发现 3-D 纳米多孔石墨烯的光学性能是可调谐的 他们通过实验验证借助孔的大小和介入的原子杂质能对新材料中的等离子激子进行精确的控制 这一发现有助于生产高敏化学传感器 另外, 这一新材料还可用于研发太阳能电池 26. 用纳米线网制造柔性电子产品 简介 : 美国加利福尼亚大学的研究人员发明了新的智能触屏材料, 他们把微金属线编织成网格层, 形成金属纳米网, 可使智能手机等电子产品的触屏更柔软 更耐用, 而且清晰 轻巧, 也廉价, 使电子产品用起来更快捷 更方便

7 27. 薄电导片的突破性研究为小电子产品的研发铺平道路 简介 : 加拿大女皇大学的研究人员发现了一个新的生产超薄电导片的方法 它可能是微电子设备的一次革命, 有很多应用价值, 从智能电话到银行系统以及医疗技术 这是一种 2 D 薄片, 叫做磁畴壁, 存在于晶体材料中 这一发现意味着将来的电子产品, 无论大小都可以实现多种功能 28. 化学家研制出 3-D 打印石墨烯泡沫 简介 : 在最近的一项研究中, 美国莱斯大学的纳米技术专家和中国天津大学的一个纳米技术研究专家采用普通的 3-D 打印技术制造了指尖大小的石墨烯泡沫块, 整个过程都在室温条件下进行, 不需要模型, 而且使用的材料是糖和镍的粉末, 在快速打印以及 3-D 碳材料生产方面有很大的应用前景 29. 研究人员用 白石墨烯 生成超小传感器 简介 : 荷兰代尔夫特理工大学和英国剑桥大学合作研究发现了一个生产可伸缩小机械传感器的方法 他们把 2-D 六方氮化硼片, 即 白石墨烯 悬于硅基座上方的小孔, 从而制造出这种传感器 这一技术革新对未来生产超小的气体和压力传感器有重要的意义 30. 用激光对 FeC1 3 夹层石墨烯的光敏结进行工程处理 简介 : 英国埃克塞特大学和西班牙光子科学研究所的一个联合研究团队研制出一种材料, 能在像核反应堆这样不利的条件下拍摄照片, 相关论文发表在 科学进步 上, 并阐述了新材料的制作方法 新材料的性能及其将来的应用 研究人员借助激光照射, 用新方法对 FeC13 夹层石墨烯的光敏结进行工程处理, 其研究结果对设计超薄高清成像和传感光电检测仪具有推动作用 31. 科学家检测单层原子光与物质的相互作用 简介 : 美国弗罗里达中央大学的研究人员首次用石墨烯材料在单层原子层面演示了弹性散射 近场实验 从而研发了一个更好的检测原子级光与物质相互作用的新方法 这一发现将推进二维材料的研究工作, 也找到了控制光的新方法 32. 研究人员进行 3-D 光场测量 简介 : 德国格拉茨技术大学的研究人员首次展示了如何用 X- 射线断层摄影术重构 3-D 影像, 这个新的等离子 X 射线断层摄影术有助于科学测量等离子场以及更好地理解传感技术, 太阳能技术, 计算机存储等领域的应用, 还有可能因此产生新的技术 33. 悬浮纳米球用作超敏传感器 简介 : 苏黎世联邦理工学院的科学家演示了给纳米球增减元电荷的方法, 目的是用于测量极弱作用力 他们研发了一款高敏传感器, 期待能用此传感器在将来精确地测量微弱作用力或者电场 34. 激光 纳米发动机 : 微小的光驱 发动机 简介 : 近期关于原子级光与物质相互作用的研究工作有了一些进展和结果, 比如研究人员制造了激光牵拉光束仪 光钳子 涡流光束仪等 美国麻省理工学院的一个研究团队将此领域的研究又向前推进了一步, 他们首次研制出仿真系统, 此系统能用普通的光束对粒子进行操纵和控制 对他们来说, 这项研究工作才刚刚开始, 他们将进行更加深入而复杂的研究工作 五. 量子物理 用量子模拟器测试量子场 简介 : 奥地利维也纳量子科学技术中心的研究人员用新的实验方法来验证量子场理论 他们制造了一个量子系统, 这个系统由数以千计的冷原子组成 把这些冷原子存放在一个原子芯片的磁阱里, 这些原子云就可用作 量子模拟器, 能生成各种物理系统的信息以及为我们提供物理方面最基本问题的看法, 这些数据帮助我们更好地了解物理世界

8 36. 对超流光进行研究的意义 简介 : 当形成光波的光子能进行相互作用时, 在特殊条件下会出现光的 流体 特性 意大利莱切和加拿大蒙特利尔的研究人员通过给光 穿上 一层电子, 发现了一个更加引人注目的现象, 光变成超流体, 流经障碍物时呈现无摩擦流, 而且绕过障碍物后能重新自行连成一体, 不产生任何涟漪 对这一现象进行研究有助于设计出基于超流的光子设备 37. 研究光子与光子在室温条件下的相互作用对量子计算具有重大意义 简介 : 光子通常情况下不发生相互作用, 如果两个光子地真空中碰撞, 它们只是简单地彼此通过 让光子之间相互作用有可能为传统光学和量子计算打开新的视野 美国麻省工学院的研究人员描述了他们让光子和光子在室温条件下相互作用的新技术, 他们用硅晶体引入 非线性 技术对光信号进行传输 这项研究工作对未来的量子信息设备研究有重大意义 六. 技术与应用 新的设计改进了可佩戴电子产品的性能 简介 : 美国北卡罗莱纳州立大学的工程师们设计了一个热电俘能器, 它只用体热作为能量源, 其应用潜力和效果可与目前的可佩戴电子设备相媲美 他们未来的工作重点是用材料和技术来进一步消除仪器的寄生电阻, 改进仪器的使用效果 39. 世界上最小最精确的 3-D 打印活组织检查机器人问世了 简介 : 机器人 Stromram4 是用 3-D 打印塑料制成, 用空气压力驱动, 其优点是可用于 MRI 扫描, 在扫描时完成活组织检查, 其特点是精准 这是世界上最重要的大事之一, 实时扫描, 精确诊断, 这样的医用机器人在不久的将来, 会是标准的治疗程序 40. 用 X- 射线激光器首次揭密原子级病毒的完整结构 简介 : 一个国际合作团队的科学家首次用 X 射线自由电子激光器揭密原子级完整病毒颗粒的结构 他们的方法极大地减少了所使用病毒材料的数量并使研究进展比以前提速几倍, 为科研工作创造了更多的可能性 将来还可以用这种新的激光器来探索更多的应用潜力 研究人员正着力研发新一代芯片, 用于避免辐射带来的损害 41. 新的超导波动器生成强大的通用 X- 射线束 简介 : 美国能源部的劳伦斯国家实验室和阿贡国家实验室合作设计 建造并测试了两个设备, 这两个设备用不同的超导材料, 能使 X 射线激光器更加强大, 功能更多, 更耐用, 而且使用起来更简捷 这一设备模型叫超导波动器, 跟传统的同样大小的波动器相比, 能生成更加强大的磁场

9 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) 一. 光学与工程 1. Collecting real-time data for material microstructural evolution during radiation exposure This is a long-range exposure image of the researchers' optical arrangement in which they highlight some of the laser beam paths. It may be surprising to learn that much remains unknown about radiation's effects on materials. To find answers, Massachusetts Institute of Technology (MIT) researchers are developing techniques to explore the microstructural evolution and degradation of materials exposed to radiation. Today, most irradiated materials testing involves designing a material, exposing it to radiation, and destructively testing the material to determine how its performance characteristics change. Of particular interest are changes in mechanical and thermal transport properties with which researchers try to determine the lifetime for safe use of the material in engineering systems within radiation environments. One drawback with this testing method, affectionately known as "cook and look," is that it's slow. MIT researchers report a more dynamic option this week in Applied Physics Letters, to continuously monitor the properties of materials being exposed to radiation during the exposure. This provides real-time information about a material's microstructural evolution. "At MIT's Mesoscale Nuclear Materials Lab, we've been developing improvements to a technique called 'transient grating spectroscopy' (TGS), which is sensitive to both thermal transport and elastic properties of materials," said Cody Dennett, the paper's lead author and a doctoral candidate in nuclear science and engineering. "To use this type of method to monitor dynamic materials changes, we first needed to show via developing and testing new optical configurations that it's possible to measure material properties in a time-resolved manner." TGS relies on inducing and subsequently monitoring periodic excitations on material surfaces using a laser. "By pulsing the surface of a sample with a periodic laser intensity pattern, we can induce a material excitation with a fixed wavelength," Dennett said. "These excitations manifest themselves in different ways in different systems, but the type of responses we observed for pure metallic materials are primarily standing surface acoustic waves." The approach is generally referred to as a transient grating technique. To help visualize this, Dennett offered the imagery of flicking a drumhead, but in this case, on a solid surface where the laser does the "flicking." The "drum's" response depends on the condition of its structure and can therefore reveal changes in structure. "These excitations' oscillation and decay are directly related to the material's thermal and elastic properties," Dennett said. "We can monitor these excitations by using the material excitations themselves as a diffraction grating for a probing laser. Specifically, we monitor the first-order diffraction of the probing laser because its intensity and oscillation directly reflect the amplitude and oscillation of the material excitation." The signal the researchers are trying to detect is very small so it must be amplified by spatially overlapping a reference laser beam that doesn't contain the signal of interest, which is a process called heterodyne amplification. "Most complete measurements are made by collecting multiple measurements at different heterodyne phases (a measure of the path length difference) between the signal and reference oscillator to remove any systematic noise," he said. "So we've added an additional probing laser path in the same compact optical configuration that allows us to collect measurements at multiple heterodyne phases concurrently." This allows the researchers to make complete measurements in a manner constrained only by the system repetition, detection rate and desired signal-to-noise ratio of the overall final measurement according to Dennett. "Previously, complete measurements of this type required actuation between measurements at different heterodyne phases," he said. "With this method in hand, we're able to show that time-resolved measurements of elastic properties on dynamic materials are possible on short timescales." The group's experimental method is called Dual Heterodyne Phase Collection Transient Grating Spectroscopy (DH-TGS). It's a significant advance because it can be used for dynamically monitoring the evolution of material systems. "Our technique is sensitive to elastic and thermal transport properties, which may be indicative of microstructural changes within the material systems being monitored," Dennett said. It's also both nondestructive and noncontact, meaning that as long as optical access to a sample with sufficient surface quality is established, it can be used to monitor real-time property changes as a result of any "external forcing" such as temperature, voltage or irradiation. Because DH-TGS is a nondestructive material diagnostic, Dennett said there are many systems one might envision studying as microstructural evolution is taking place. "We're interested in the radiation damage 1

10 光学与工程 case in particular, but other applications might include studying low-temperature phase change materials, or real-time monitoring of oxide layer formation on steel alloys," he said. "[W]e're trying to enable real-time, nondestructive monitoring of dynamic materials systems," said Dennett. "But another goal of ours is to disseminate the abilities of this type of methodology more widely. We have particular applications in mind for our next steps, but the relative ease of implementation should make it interesting to a wide range of materials scientists." Their next experimental iteration involves constructing a target chamber for an ion beam accelerator so they can watch materials evolve in real time during exposure. "The work we presented in Applied Physics Letters was the last piece in the puzzle standing between us and realizing the overarching motivation for the project," Dennett said. ostructural-evolution-exposure.html 2. New technology could revolutionize 3-D printing By using high-powered arrays of laser diodes and a specialized laser modulator developed for the National Ignition Facility, researchers could potentially 3D print large metal objects in a fraction of the time needed for metal 3D printers on the market today, according to a new study by LLNL researchers. A technology originally developed to smooth out and pattern high-powered laser beams for the National Ignition Facility (NIF) can be used to 3-D print metal objects faster than ever before, according to a new study by Lawrence Livermore researchers. A team of Lab scientists report the findings in the latest issue of Optics Express, published online on May 15. This new method Diode-based Additive Manufacturing (DiAM) uses high-powered arrays of laser diodes, a Q-switched laser and a specialized laser modulator developed for NIF to flash print an entire layer of metal powder at a time, instead of raster scanning with a laser across each layer, as with conventional laser-based powder-bed fusion additive manufacturing (PBFAM) systems. The result, researchers said, is the possibility that large metal objects could be printed in a fraction of the time needed for metal 3-D printers on the market today, expanding possibilities for industries requiring larger metal parts, such as aerospace and automotive. The combination of speed and degree of design flexibility afforded through the DiAM method, the team concluded, is potentially "far beyond" that of current powder-bed fusion-based systems. "By cutting the print time and having the ability to upscale, this process could revolutionize metal additive manufacturing," said Ibo Matthews, an LLNL scientist heading the research and the paper's lead author. "The illumination time savings, we estimate, is such that a one cubic meter build that would require 10 years of raster-scanned illumination to make would require only a few hours with DiAM, because you can image each layer at once. Printing with a gray-scaled image may also allow you to reduce residual stress because you can tailor the thermal stresses spatially and temporally." The "magic" of the process, Matthews said, is the implementation of a customized laser modulator called an Optically Addressable Light Valve (OALV), which contains a liquid crystal cell and photoconductive crystal in series. Much like a liquid crystal-based projector, researchers explained, the OALV is used to dynamically sculpt the high-power laser light according to pre-programmed layer-by-layer images. But unlike a conventional liquid crystal projector, the OALV is un-pixelated and can handle high laser powers. The technology was originally designed for and installed in NIF as part of the LEOPARD (Laser Energy Optimization by Precision Adjustments to the Radiant Distribution) system, which was deployed in 2010 and won an R&D 100 award in In NIF, the OALV is used to optimize the profile of the laser beams and locally shadow and protect optics subjected to higher intensities and fluences (or energy density the amount of laser energy for a given unit area). With LEOPARD, NIF electronically protects regions of its beams containing potentially threatening flaws on its final optics, as identified by the Final Optics Damage Inspection (FODI) system. This enables NIF to continue firing until the schedule allows those optics to be removed, repaired and reintroduced into the beamline. The team that first demonstrated the light valve could be used for printing parts was initially led by James DeMuth, a former LLNL researcher. John Heebner, the LLNL scientist that led the development of the OALV described its use in metal 3-D printing as a "natural synergy." "The DiAM project marries two technologies that we've pioneered at the Lab - high-power laser diode arrays and the OALV," Heebner said. "Given that we put all this time and development into this light valve, it became a natural extension to apply it to this project. We went through some calculations and it was clear from the outset that it would work (with 3-D printing). The ability to change a serial process to a parallel process is critical to ensuring that as parts increase in complexity or size that the patterning process speed can be increased 2

11 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) to catch up." Besides the ability to potentially produce larger parts, using such a valve results in imaging quality that rivals and could exceed today's metal 3-D printers, and the ability to fine-tune gradients in the projected image means better control over residual stress and material microstructure, researchers said. With DiAM printing, the laser light is sourced by a set of four diode laser arrays and a nanosecond pulsed laser. It passes through the OALV, which patterns an image of a two-dimensional "slice" of the desired 3-D part. The images go from a digital computer file to the laser in a two-stage liquid crystal modulation process. In the first stage, the images are sourced from a digitized CAD model and imprinted on a low-power blue LED source using an ordinary, pixelated liquid crystal projector. In the second stage, the blue images activate the OALV's photoconductive layer creating local conductive patches (where blue light is present) that transfer voltage to its liquid crystal layer. This enables the low power blue images to modulate the high-power laser beam. The beam is then directed onto a build plane, printing the entire metal layer at once. For the study, the researchers used tin powder, successfully demonstrating the printing of two small 3-D models, an impeller (a small turbine blade structure) and LLNL logo. While speeding up the metal additive process was a main driver for pursuing the technology at LLNL, the larger build size could potentially have significant value for the Lab's core mission of stockpile stewardship, the researchers said. The laser diodes - which provide most of the energy compared to the pulsed laser system - are also cheap to purchase, so such a system would be more cost-effective than fiber laser-based machines on the market today. e-d.html 3. Breakthrough curved sensor could dramatically improve image quality captured with digital cameras Researchers developed a way to create spherically curved image sensors by three-dimensionally bending off-the-shelf image sensors. When incorporated into prototype cameras, the curved sensors produced greatly improved image quality compared to high-end commercial cameras. If you've ever tried to take a picture in a dark restaurant, you know that it is difficult to get a clear, quality image. In the future, cameras might not struggle under these conditions thanks to a newly developed method for spherically curving the flat image sensors found in today's digital cameras. "Our approach to curving commercially available image sensors could make it possible to have a new class of camera that would be very small, but have image quality that would be comparable to image sensors found in much larger cameras," said Brian Guenter, leader of the Microsoft Research team. "In addition to improving consumer cameras, curved sensors could be used to create better cameras for surveillance, head-mounted displays and advancements in autonomous vehicle navigation. Most of today's cameras use lenses made of multiple optical elements that correct for various optical errors, or aberrations, and that also manipulate the image so that it can be detected by a flat sensor. Using a curved, rather than flat, image sensor means the optical elements have to do less work to correct and flatten the image, making it possible to use fewer optical elements. This not only translates to smaller, faster and less expensive lenses but also makes it easier to improve other properties of the optical components. "When using curved sensors, it is possible to correct aberrations in a much more efficient way, making it easier to create very wide angle lenses that produce sharp images across the entire field of view or to create fast lenses that produce better images in low light," said Neel Joshi, a member of the research team. "It is also more straightforward to make cameras that exhibit uniform illumination across the entire image." In The Optical Society journal Optics Express, researchers from Microsoft Research and research-and-development laboratory HRL Laboratories LLC, report that their new method can create image sensors with three times more spherical curvature than reported previously. They have been able to incorporate one of the sensors into a prototype camera. Compared to today's high-end commercial single-lens reflex camera (SLR) cameras, the camera with the new sensor produced higher resolution images across the entire field of view. "Although the benefits of using curved sensors have been known for some time, our work now makes it practical to create cameras with curved sensors," said Richard Stoakley, a member of the research team. "Adding spherical curvature to an off-the-shelf image sensor can be done for a reasonable cost and in a way that shows significant benefits." Creating the ideal camera The new approach for creating curved sensors grew out of a question the researchers asked themselves about seven years ago: "What would an ideal camera be like?" They decided such a camera would take pictures under very low light, be very small, and produce extremely 3

12 光学与工程 sharp pictures. "At the time, it wasn't possible to make a camera like that," said Guenter. "We thought that if we could improve a camera's optics by creating a faster lens, we could potentially use a smaller sensor while still gathering enough light to get a good picture. That motivated us to begin investigating curved sensors as a way to potentially achieve breakthrough performance." To make curved sensors, the researchers placed individual sensors cut from a thinned CMOS image-sensor wafer into custom-made molds and then used pneumatic pressure to push each sensor down into the mold. Other attempts at curving a sensor have typically involved gluing the edges down and trying to push on the center of the sensor. However, this creates points of high stress that cause the sensor to shatter before it reaches the target level of curvature. The researchers coaxed significantly more curvature out of the sensors by letting them float freely during the bending process, which allowed stresses to dissipate gradually. They also used a specially shaped mold that very slowly builds stress around the chip's edges as it is pressed into the mold. Microsoft contracted HRL Laboratories, which has semiconductor fabrication capabilities and equipment, to help solve some of the specific physics challenges involved in bending the sensors. "This work involved extensive amounts of experimentation," said Joshi. "Every single surface involved has to be carefully treated to exhibit the exact properties necessary for the sensor to end up with the right amount of stress without breaking." Tests showed that curving the sensors did not change any of their electrical or imaging characteristics. When used in a prototype camera with a specially designed f/1.2 lens, a curved sensor exhibited a resolution more than double that of a high-end SLR camera with a similar lens. Toward the edges of the image, the curved sensor was about five times sharper than the SLR camera. Although most cameras exhibit decreased light detection around the corners of the imaging sensor, the researchers showed that the curved sensors lost almost no light. This was a significant improvement compared to the decrease of around 90 percent measured for the commercial SLR camera. "We showed that you can take an off-the-shelf sensor, curve it and dramatically improve the performance of the optical system," said Guenter. "This can be done with relatively low costs and effectively no downside." Curved sensors for mobile phones Although the prototype camera reported in the paper is about the size of a small consumer camera, the researchers say that the lenses could be made small enough for mobile phones and tablets. It should also be possible to build machines that could mass produce these curved sensors, allowing the additional processing to be incorporated into existing sensor manufacturing in a way that would amortize well in volume production. The researchers are now working to see if further improvements might produce sensors with even more curvature. They also want to experiment with curving sensors that operate in infrared wavelengths, which could be useful for telescopes, 3D spatial mapping, biometric authentication and various scientific applications. Although they caution that it is unlikely that commercial products featuring the curved sensors will be available soon, they are interested in working with other companies to further improve the sensors and to perform the strenuous robustness testing that would be needed to prepare for mass production. "I think we have opened the door for an entirely new class of lenses," said Stoakley. "I'm excited to see how our group and others use curved sensors to achieve even more improvements in camera quality through innovative lens design." age-quality-captured.html 4. New plasmonic sensor improves early cancer detection A plasmonic nanocup metal-insulator-metal cavity design used to detect the cancer biomarker CEA. The nanocavity leads to optical energy storage which is out-coupled to the far field by a refractive index increase. Therefore, CEA binding to its immobilized antibody leads to a sensitive increase in the transmission intensity at the resonance wavelength with no spectral shift. A new plasmonic sensor developed by researchers at the University of Illinois at Urbana-Champaign will serve as a reliable early detection of biomarkers for many forms of cancer and eventually other diseases. The sensor has been proven reliable to detect the presence of the cancer biomarker carcinoembryonic antigen (CEA) to the magnitude of 1 nanogram per milliliter. Most humans carry at least some amounts of CEA with an average range of 3-5 nanograms per milliliter. The researchers chose to focus on CEA because its presence in higher concentrations is an early indicator of many forms of cancer, including lung and prostate cancers. "Cancer is one of the major causes of death in the United States as more than half of the new patients are diagnosed after it has already spread," Ameen explained. 4

13 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) "This shows the gravity with which this problem needs to be addressed and this new design of a plasmonic sensor helps to detect the lower concentration of CEA at an earlier state." The plasmonic sensor is an improvement of the current state-of-the-art method for a few reasons. First, it was able to improve the limit of detection by at least two orders of magnitude. In fact, most methods aren't able to accurately detect the presence of CEA until it reaches a higher concentration. Secondly, because it works with much less instrumentation, it is less expensive and more portable and doesn't require nearly the expertise to make a reading. It also means instead of needing a vial of blood for a test, a simple finger prick will do. This aspect will be especially important for those who don't live close to an advanced medical facility, including those in developing nations. The research team was led by Logan Liu, and Lynford Goddard, associate professors of electrical and computer engineering with students Abid Ameen and Lisa Hackett carrying out the project. The team published its results in Advanced Optical Materials as a cover article. no light transmitted. However if you put a periodic array of nanoholes, or in our case a nanocup structure, then what you see is a resonance condition where at a certain wavelength, you will have a peak in the transmission through this device." Because the resonance is changing at a single wavelength and because the spectral features have reference locations, excitation and detection can be done reliably without any specialized equipment. With this device, a LED light source can be used instead of a laser and a photocell or camera image can be used instead of a high-end spectrometer. "Because of our multi-layer high-performing plasmonic structure, we were able to very efficiently scatter out the light to the far field," Hackett said. "When you increase the refractive index of the sensing region, it causes the stored energy to couple out. Usually when you have these types of refractometric plasmonic sensors, you have a shift in the angle or a change in your wavelength when the resonance condition is met. In our case, because we have incorporated a nanocavity, we have a fixed resonance wavelength." Electromagnetic simulation of a single nanocup on ML-nanoLCA showing the field intensity in the cross section. The device combines two sensing methods, which hadn't until this time been able to be used together. First, it uses a 3D multi-layer nanocavity in a nanocup array, which allows for the light to be stored in the cavity comprised of two metal layers (in this case gold) surrounding one insulator layer. Secondly, it uses plasmonic sensing, which detects sensitive nanoscale light-matter interactions with biomolecules on the device surface. It produces an enhanced field confinement and an enhanced localized field. Because of the plasmonic structure, the light is out-coupled more efficiently as the surrounding refractive index changes. "By combining plasmonic properties and the optical cavity properties together in one device we are able to detect lower concentration of biomarker by light confinement and transmission in the cavity layer and from the top of the device respectively, based on the thickness of the multilayers and the refractive index of the cavity layer," Ameen explained. "The nanocup array provides extraordinary optical transmission," Hackett added. "If you take a thin metal film and try to shine light through it, there will be almost Schematic illustration of the multilayer nanolca (ML-nanoLCA) shows the multilayer structure and direction of illumination. As the concentration of biomolecules (in this case CEA) increases, so does the refractive index, which produces an increase of the transmission intensity at a fixed wavelength that can be easily detected. "What that means in the future is we can take this sensor, which we've optimized and incorporated with an LED and have the most compact instrumentation, in fact no sophisticated instrumentation at all," Ameen said. "This allows high performance plasmonic sensing the ability to go toward portable sensing systems and large scale portable sensors." For now, detection methods for cancer biomarkers are being implemented in high-risk patients, especially cancer patients in remission. They take time, specialized equipment, and are labor-intensive. In the future, however, because of the portability and inexpensive nature of this method, it can be more easily administered to any patient at routine check-ups. This would allow those with an elevated concentration of CEA to be treated even before cancer cells spread in the body. "Right now cancer is detected closer to end stage," Ameen noted. "We want to detect it as early as possible. Our device is providing us with that opportunity." 5

14 光学与工程 While this study demonstrated detection in a small human serum sample, the method could be used for the detection of other diseases down the road. "In the future, if they are made very cost-effective and portable," Hackett said, "it would be great to see people be able to take more control over their health and monitor something like this on their own." 5. Seeing through materials with visible light A patterned spot of laser light appears on the slide filled with yogurt. Moussa N'Gom and his team measured the brightness of the light getting through for hundreds of patterns, which their algorithm built into a mathematical representation of the yogurt's scattering pattern. With yogurt and crushed glass, University of Michigan researchers have taken a step toward using visible light to image inside the body. Their method for focusing light through these materials is much faster and simpler than today's dominant approach. Dense structures like bone show up clearly in x-rays, but softer tissues like organs and tumors are difficult to make out. That's because x-rays are strongly deflected by bones, while they cut straight through soft tissue. Visible light, on the other hand, is deflected by soft tissue. Until recently, this has made seeing through skin with visible light a nonstarter while light can get through, it's scattered every which way. At the same time, visible light would be safer for diagnostic imaging than higher-energy x-rays. "Light comes in, it hits a molecule, hits another, hits another, does something really crazy, and exits this way," said Moussa N'Gom, assistant research scientist in electrical engineering and computer science and first author on a study in Scientific Reports that explains the challenge of predicting the paths of individual light rays. By understanding exactly how a patch of skin scatters the light, researchers hope to carefully pattern light beams so that they focus inside the body a first step toward seeing into it. In their experiments, the researchers spelled "MICHIGAN" with a beam of light shone through yogurt and crushed glass. They chose those materials because they scatter light strongly and serve as good models for skin. Their demonstration, reminiscent of writing a name with a flashlight, shows that they can take a single, quick scan of the material and focus through it at many points as they would need to do if imaging tissue inside the body. An improvement on today's approach Michigan, spelled out in 157 points. The images of each point of focus were layered on top of each other to produce the video. The field of imaging objects through materials, from layers of paint to eggshells and even mouse skulls, has made great strides in the last decade. The typical "holographic" method untangles the scattering pattern by looking at how the light waves interfere with each other this gives information about how different rays were delayed on their way through the material. This method is very precise, said N'Gom, but it is slow. To speed things up, researchers typically figure out just enough of the scattering pattern to focus on a particular point. To focus on a different point, the material has to be scanned again. This would slow the process of measuring the size or texture of a tumor, for example. "Our method is significantly faster and more convenient because we use a single set of measurements to generate all these points, and we don't have to rescan," N'Gom said. As is typical for focusing-through-materials experiments, the researchers used a spatial light modulator to produce patterns of light. If you shone a laser through frosted glass, it would enter at a point on one side, at a particular angle, and then leave the other side through many points, in different directions. By combining a screen with an array of mirrors, a spatial light modulator can do the reverse, sending light to a surface at many points, at many angles, so that these rays converge on a point on the other side of the material. They set up the spatial light modulator to shine in hundreds of different patterns (461 in all). But rather than analyzing the paths of individual light rays emerging from the other side, N'Gom's team measured the brightness how much light made it out. They developed an algorithm to trawl through the incoming light patterns and outgoing brightness measurements, using the information to build up a mathematical representation of the material's scattering pattern, called the transmission matrix. "Previous techniques, instead, used complex so-called holographic setups to extract the necessary information," said Raj Rao Nadakuditi, associate professor of electrical engineering and computer science and senior author on the study. "We were able to achieve the same 6

15 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) through simple brightness measurements and as a result operate much faster." Moussa N'Gom points to a display showing how the yogurt scatters light. He hopes that the speedy algorithm developed by his team is another step toward medical imaging that can see through skin with visible light. Using the transmission matrix, N'Gom's team could figure out exactly how to set the spatial light modulator to get a bright spot at any point on the other side of the ground glass or yogurt. In the yogurt, there was a time limit on how long the map was good just a few minutes. It was enough time for N'Gom and his colleagues to spell "MICHIGAN" in 157 shots. First images possible within five years In skin, the time constraints are much tighter they would need a new map about every millisecond. Even so, with state-of-the-art electronics, N'Gom thinks their algorithm could run that fast. Another challenge in seeing through skin is that they wouldn't be able to position a detector beneath it to measure the brightness of the light. For this, N'Gom said that researchers are using ultrasound to detect heating in the target tissue a measure of how much light is getting through. Finally, with the light focused inside, an imaging device would still need to focus the light coming back out of the skin. For this, they could essentially run the pattern of light back through the transmission matrix to deduce where the reflection was coming from. Considering recent progress and ongoing studies in focusing light through translucent materials, N'Gom anticipates that we may see the first visible light images taken through skin within the next five years 'Scrambled light' wavemeter breakthrough A breakthrough innovation in the measurement of lasers can measure changes one millionth of the size of an atom and could revolutionize their use in quantum technologies and healthcare thanks to new, lower-cost technology. A team from the University of St Andrews and UK company M Squared Lasers has used the principle of random scattering of light to create a new class of laser wavemeter that breaks through a glass ceiling in the way wavelength is measured. Wavemeters are used in many areas of science to identify the wavelength (i.e. colour) of light. All atoms and molecules absorb light at very precise wavelengths, therefore the ability to identify and manipulate them at high resolution is important in diverse fields ranging from the identification of biological and chemical samples to the cooling of individual atoms to temperatures colder than the depths of outer space Waves, whether they are water waves or light waves, interact via interference: sometimes two waves reach a peak at the same time and place and the result is a higher wave, but it is also possible that a peak of one wave meets the trough of another, resulting in a smaller wave. The combination of these effects produces an interference pattern. Conventional wavemeters analyse changes in the interference pattern produced by delicate assemblies of high-precision optical components. The cheapest instruments cost hundreds or thousands of pounds, and most in everyday research use cost tens of thousands. In contrast, the team realised a robust and low-cost device which surpasses the resolution of all commercially-available wavemeters. They did this by shining laser light inside a 5 cm diameter sphere which had been painted white, and recording images of the light which escapes through a small hole. The pattern formed by the light is incredibly sensitive to the wavelength of the laser. Dr Graham Bruce from the School of Physical and Astronomy explains: "If you take a laser pointer, and shine it through Sellotape or on a rough surface like a painted wall, on closer inspection of the illuminated surface you'll see that the spot itself looks grainy or speckled, with bright and dark patches. This so-called 'speckle pattern' is a result of interference between the various parts of the beam which are reflected differently by the rough surface. "This speckle pattern might seem of little use but in fact the pattern is rich in information about the illuminating laser. "The pattern produced by the laser through any such scattering medium is in fact very sensitive to a change in the laser's parameters and this is what we've made use of." The breakthrough, which has been published in the prestigious journal Nature Communications, opens a new route for ultra-high precision measurement of laser wavelength, realizing a precision of close to one part in 7

16 光学与工程 three billion, which is around 10 to 100 times better than current commercial devices. This precision allowed the team to measure tiny changes in wavelength below 1 femtometre: equivalent to just one millionth of the diameter of a single atom. They also showed that this sensitive measurement could be used to actively stabilize the wavelength of the laser. In future, the team hope to demonstrate the use of such approaches for quantum technology applications in space and on Earth, as well as to measure light scattering for biomedical studies in a new, inexpensive way. Professor Kishan Dholakia from the School of Physical and Astronomy said: "This is an exciting team effort for what we believe is a major breakthrough in the field. It is a testament to strong UK industry university co-operation and links to future commercial opportunities with quantum technologies and those in healthcare." eakthrough.html 7. Manufacturing hybrid silicon lasers for mass-produced photonic devices Oblique angle scanning electron microscopy image of a 500 nanometer diameter microdisk. Producing semiconductor lasers on a silicon wafer is a long-held goal for the electronics industry, but their fabrication has proved challenging. Now, researchers at A*STAR have developed an innovative way to manufacture them that is cheap, simple and scalable. Hybrid silicon lasers combine the light-emitting properties of group III V semiconductors, like gallium arsenide and indium phosphide, with the maturity of silicon manufacturing techniques. These lasers are attracting considerable attention as they promise inexpensive, mass-producible optical devices that can integrate with photonic and microelectronic elements on a single silicon chip. They have potential in a wide range of applications, from short-distance data communication to high-speed, long-distance optical transmission. In the current production process, however, lasers are fabricated on separate III V semiconductor wafers before being individually aligned to each silicon device a time-consuming, costly process that limits the number of lasers that can be placed on a chip. To overcome these limitations, Doris Keh-Ting Ng and her colleagues from the A*STAR Data Storage Institute have developed an innovative method for producing a hybrid III V semiconductor and silicon-on-insulator (SOI) optical microcavity. This greatly reduces the complexity of the fabrication process and results in a more compact device. "It's very challenging to etch the entire cavity," says Ng. "Currently, there is no single etch recipe and mask that allows the whole microcavity to be etched, and so we decided to develop a new approach." By first attaching a thin film of III V semiconductor to a silicon oxide (SiO2) wafer using a SOI interlayer thermal bonding process, they produced a strong bond that also removes the need for strong oxidizing agents, such as Piranha solution or hydrofluoric acid. And by using a dual hard-mask technique to etch the microcavity that confined etching to the intended layer, they eliminated the requirement to use multiple overlay lithography and etching cycles a challenging procedure. "Our approach cuts down the number of fabrication steps, reduces the use of hazardous chemicals, and requires only one lithography step to complete the process," explains Ng. The work presents, for the first time, a new heterocore configuration and integrated fabrication process that combines low-temperature SiO2 interlayer bonding with dual hard-mask, single lithography patterning. "The process not only makes it possible to produce heterocore devices, it also greatly reduces the challenges of fabricating them, and could serve as an alternative hybrid microcavity for use by the research community," says Ng. ss-produced-photonic.html 8. New laser technique identifies the makeup of space debris, from painted shards to Teflon Aerospace engineers from MIT have developed a laser sensing technique that can decipher not only where but what kind of space junk may be passing overhead. Hundreds of millions of pieces of space junk orbit the Earth daily, from chips of old rocket paint, to shards of solar panels, and entire dead satellites. This cloud of high-tech detritus whirls around the planet at about 17,500 miles per hour. At these speeds, even trash as 8

17 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) small as a pebble can torpedo a passing spacecraft. NASA and the U.S. Department of Defense are using ground-based telescopes and laser radars (ladars) to track more than 17,000 orbital debris objects to help prevent collisions with operating missions. Such ladars shine high-powered lasers at target objects, measuring the time it takes for the laser pulse to return to Earth, to pinpoint debris in the sky. Now aerospace engineers from MIT have developed a laser sensing technique that can decipher not only where but what kind of space junk may be passing overhead. For example, the technique, called laser polarimetry, may be used to discern whether a piece of debris is bare metal or covered with paint. The difference, the engineers say, could help determine an object's mass, momentum, and potential for destruction. "In space, things just tend to break up over time, and there have been two major collisions over the last 10 years that have caused pretty significant spikes in debris," says Michael Pasqual, a former graduate student in MIT's Department of Aeronautics and Astronautics. "If you can figure out what a piece of debris is made of, you can know how heavy it is and how quickly it could deorbit over time or hit something else." Kerri Cahoy, the Rockwell International Career Development Associate Professor of aeronautics and astronautics at MIT, says the technique can easily be implemented on existing groundbased systems that currently monitor orbital debris. "[Government agencies] want to know where these chunks of debris are, so they can call the International Space Station and say, 'Big chunk of debris coming your way, fire your thrusters and move yourself up so you're clear,'" Cahoy says. "Mike came up with a way where, with a few modifications to the optics, they could use the same tools to get more information about what these materials are made of." Pasqual and Cahoy have published their results in the journal IEEE Transactions on Aerospace and Electronic Systems. The team's technique uses a laser to measure a material's effect on the polarization state of light, which refers to the orientation of light's oscillating electric field that reflects off the material. For instance, when the sun's rays reflect off a rubber ball, the incoming light's electric field may oscillate vertically. But certain properties of the ball's surface, such as its roughness, may cause it to reflect with a horizontal oscillation instead, or in a completely different orientation. The same material can have multiple polarization effects, depending on the angle at which light hits it. Pasqual reasoned that a material such as paint could have a different polarization "signature," reflecting laser light in patterns that are distinct from the patterns of, say, bare aluminum. Polarization signatures therefore could be a reliable way for scientists to identify the composition of orbital debris in space. To test this theory, he set up a benchtop polarimeter an apparatus that measures, at many different angles, the polarization of laser light as it reflects off a material. The team used a high-powered laser beam with a wavelength of 1,064 nanometers, similar to the lasers used in existing ground-based ladars to track orbital debris. The laser was horizontally polarized, meaning that its light oscillated along a horizontal plane. Pasqual then used polarization filtering optics and silicon detectors to measure the polarization states of the reflected light. Sifting through space trash In choosing materials to analyze, Pasqual picked six that are commonly used in satellites: white and black paint, aluminum, titanium, and Kapton and Teflon two filmlike materials used to shield satellites. "We thought they were very representative of what you might find in space debris," Pasqual says. He placed each sample in the experimental apparatus, which was motorized so measurements could be made at different angles and geometries, and measured its polarization effects. In addition to reflecting light with same polarization as the incident light, materials can also display other, stranger polarization behaviors, such as rotating the light's oscillation slightly a phenomenon called retardance. Pasqual identified 16 main polarization states, then took note of which efffects a given material exhibited as it reflected laser light. "Teflon had a very unique property where when you shine laser light with a vertical oscillation, it spits back some in-between angle of light," Pasqual says. "And some of the paints had depolarization, where the material will spit out equal combinations of vertical and horizontal states." Each material had a suffiiciently unique polarization signature to distinguish it from the other five samples. Pasqual believes other aerospace materials, such as various shielding films, or composite materials for antennas, solar cells, and circuit boards, may also exhibit unique polarization effects. His hope is that scientists can use laser polarimetry to establish a library of materials with unique polarization signatures. By adding certain filters to lasers on existing groundbased ladars, scientists can measure the polarization states of passing debris and match them to a library of signatures to determine the object's composition. "There are already a lot of facilities on the ground for tracking debris as it is," Pasqual says. "The point of this technique is, while you're doing that, you might as well put some filters on your detectors that detect polarization changes, and it's those polarization features that can help you infer what the material is made of. And you can get more information, basically for free." -space-debris.html 9

18 光学与工程 9. Scientists turbocharge high-resolution, 3-D imaging Mouse ear pinna, OCT vs SM-OCT. You may not have heard of optical coherence tomography, or OCT. But if you've visited an ophthalmologist recently, chances are your eye came within an inch or two of a scanning device employing the technology. Tens of thousands of these devices are in place in doctors' offices, where they're widely used to check for eye diseases. Now, Stanford University scientists have figured out how to retrofit these high-performance machines with off-the-shelf components, increasing OCT's resolution by several-fold and promising earlier detection of retinal and corneal damage, incipient tumors and more. The relatively simple, low-cost fix entailing a pair of lenses, a piece of ground glass and some software tweaks erases blemishes that have bedeviled images obtained via OCT since its invention in This improvement, combined with the technology's ability to optically penetrate up to 2 millimeters into tissue, could enable physicians to perform "virtual biopsies," visualizing tissue in three dimensions at microscope-quality resolution without excising any tissue from patients. In a study to be published online June 20 in Nature Communications, the researchers tested the enhancement in two different commercially available OCT devices. They were able to view cell-scale features in intact tissues, including in a living mouse's ear and a human fingertip, said the study's senior author, Adam de la Zerda, PhD, assistant professor of structural biology. The study's lead author is electrical-engineering graduate student Orly Liba. Boosting resolution with minimal tinkering "We showed that you can take effectively any OCT system out there and, with minimal changes, boost its resolution to the point where it can detect anatomical features smaller than the size of a typical cell," de la Zerda said. OCT is a billion-dollar business. Every year, more than 10 million OCT scans are performed to diagnose or monitor conditions from age-related macular degeneration to melanoma. The technology has been adapted for endoscopic use in pulmonary, gastrointestinal and cardiovascular medicine. Somewhat analogous to ultrasound, OCT penetrates tissues optically instead of with sound waves. The device aims beams of laser light at an object say, a tissue sample, or a patient's eye and records what comes back when light bounces off reflective elements within the sample or eyeball. Adjusting the depth of penetration, a user can scan layer upon layer of a tissue and, piling virtual slices of tissue atop one another, assemble them to generate a volumetric image. But to this day, OCT continues to be plagued by a form of noise that, unlike the random noise generated by any sensing system, can't be "washed away" simply by repeatedly imaging the object of interest and averaging the results with a computer program. The noise generated by OCT, called "speckle," is an inherent feature of the architecture of the object being viewed and the unique properties of laser light. A photon isn't a mere particle. It's also a wave whose power waxes and wanes as it travels, similar to an ocean wave heading toward the shore. When two waves collide, their combined height at the moment of their collision depends on whether each was at its peak, its trough or somewhere in between. Mouse ear pinna, close up, OCT vs SM-OCT. When photons get out of phase The photons comprising a beam of laser light are in phase: They share the same wavelength, with their peaks and troughs occurring in sync. But when these photons bounce off of two separate surfaces say, two closely situated components of a cell the length of their return routes differs slightly, so they're no longer in phase. Now, they can interfere with one another just like intersecting ocean waves. They may cancel each other out, creating a false-black speckle on the resulting image. Or they may reinforce one another, creating a false-white speckle. If the speckle-generating components' positions are fixed, as is the case in most tissues (circulating blood being one exception), those same speckles will pop up in the same places on every successive OCT scan. "Other researchers have tried various fixes, such as scanning repeatedly at different angles or from consecutive adjacent positions or with shifting wavelengths, or 'removing' the speckles using computer post-processing," de la Zerda said. "But the result is always the same: a blurred image." It's like covering up freckles with a coat of makeup: a smoother appearance, at the cost of lost detail. In principle, if you could reach in with a molecular tweezers and move one of those two interfering components just a tiny bit, you would change the speckle pattern. But you can't. However, the Stanford scientists found a way to do essentially the same thing, 10

19 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) optically speaking. "We wanted to make the speckles dance, so they'd be in a slightly different pattern each time we scanned the tissue," Liba said. "And we found a way to do it." Mouse cornea, OCT vs SM-OCT. Creating a virtual image By positioning a couple of additional lenses in the OCT device's line of sight, the investigators were able to create a second image a holograph-like exact lookalike of the viewed sample that appeared elsewhere along the line of sight, between the added lenses and the sample. By inserting what they call a "diffuser" a plate of glass they'd had roughened by randomly etching tiny grooves into it at just the right point in the line of sight and methodically moving it between each round of repeated scans, they achieved the optical equivalent of shifting the geographical relationship of the sample's components just a tiny bit each time they scanned it. Now, averaging the successive images removed the speckles. The Stanford team used the resulting enhanced capability to acquire detailed, essentially noise-free images of a living, anesthetized mouse's ear. "We saw sebaceous glands, hair follicles, blood vessels, lymph vessels and more," Liba said. They also obtained high-resolution images of a mouse retina and cornea. And an incision-free look at the fingertip of one of the study's co-authors let them see an anatomical feature never before glimpsed with OCT: Meissner's corpuscle, a nerve bundle responsible for tactile sensations. The technological advance gets around a 25-year-old problem that has persistently limited OCT's diagnostic capabilities, de la Zerda said. The work is an example of Stanford Medicine's focus on precision health, the goal of which is to anticipate and prevent disease in the healthy and precisely diagnose and treat disease in the ill. igh-resolution-d-imaging.html D virus cam catches germs red-handed The Duke team used their 3D virus cam to spy on this small lentivirus as it danced through a salt water solution. Before germs like viruses can make you sick, they first have to make a landing on one of your cells Mars Rover style and then punch their way inside. A team of physical chemists at Duke is building a microscope so powerful that it can spot these minuscule germs in the act of infection. The team has created a new 3D "virus cam" that can spy on tiny viral germs as they wriggle around in real time. In a video caught by the microscope, you can watch as a lentivirus bounces and jitters through an area a little wider that a human hair. Next, they hope to develop this technique into a multi-functional "magic camera" that will let them see not only the dancing viruses, but also the much larger cell membranes they are trying breech. "Really what we are trying to investigate is the very first contacts of the virus with the cell surface how it calls receptors, and how it sheds its envelope," said group leader Kevin Welsher, assistant professor of chemistry at Duke. "We want to watch that process in real time, and to do that, we need to be able to lock on to the virus right from the first moment." This isn't the first microscope that can track real-time, 3D motions of individual particles. In fact, as a postdoctoral researcher at Princeton, Welsher built an earlier model and used it to track a bright fluorescent bead as it gets stuck in the membrane of a cell. To test out the microscope, the team attached a fluorescent bead to a motion controller and tracked its movements as it spelled out a familiar name. But the new virus cam, built by Duke postdoc Shangguo Hou, can track particles that are faster-moving and dimmer compared to earlier microscopes. "We were trying to overcome a speed limit, and we were trying to do so with the fewest number of photons collected possible," Welsher said. The ability to spot dimmer particles is particularly important when tracking viruses, Welsher said. These small bundles of proteins and DNA don't naturally give off any light, so to see them under a microscope, researchers first have to stick something fluorescent on them. But many bright fluorescent particles, such as quantum dots, are pretty big compared to the size of most viruses. Attaching one is kind of like sticking a baseball onto a basketball there is a good chance it 11

20 光学与工程 might affect how the virus moves and interacts with cells. The new microscope can detect the fainter light given off by much smaller fluorescent proteins which, if the virus is a basketball, are approximately the size of a pea. Fluorescent proteins can also be inserted to the viral genome, which allows them to be incorporated into the virus as it is being assembled. "That was the big move for us," Welsher said, "We didn't need to use a quantum dot, we didn't need to use an artificial fluorescent bead. As long as the fluorescent protein was somewhere in the virus, we could spot it." To create their viral video, Welsher's team enlisted Duke's Viral Vector Core to insert a yellow fluorescent protein into their lentivirus. Now that the virus-tracking microscope is up-and-running, the team is busy building a laser scanning microscope that will also be able to map cell surfaces nearby. "So if we know where the particle is, we can also image around it and reconstruct where the particle is going," Welsher said. "We hope to adapt this to capturing viral infection in real time." New screen coating makes reading in sunlight a lot easier the secret? Moth eyes Researchers created a film of moth-eye-like nanostructures that can improve the sunlight visibility of screens on mobile phones and tablets. The images show the nanostructures from above (left) and from the side (right). Screens on even the newest phones and tablets can be hard to read outside in bright sunlight. Inspired by the nanostructures found on moth eyes, researchers have developed a new antireflection film that could keep people from having to run to the shade to look at their mobile devices. The antireflection film exhibits a surface reflection of just.23 percent, much lower than the iphone's surface reflection of 4.4 percent, for example. Reflection is the major reason it's difficult to read a phone screen in bright sunlight, as the strong light reflecting off the screen's surface washes out the display. Researchers led by Shin-Tson Wu of the College of Optics and Photonics, University of Central Florida (CREOL), report on their new antireflection coating in Optica, The Optical Society's journal for high impact research. "Using our flexible anti-reflection film on smartphones and tablets will make the screen bright and sharp, even when viewed outside," said Wu. "In addition to exhibiting low reflection, our nature-inspired film is also scratch resistant and self-cleaning, which would protect touch screens from dust and fingerprints." The new film contains tiny uniform dimples, each about 100 nanometers in diameter (about one one-thousandth of the width of a human hair). The coating can also be used with flexible display applications such as phones with screens that fold like a book, which are expected to hit the market as soon as next year. Inspired by nature Many of today's smartphones use a sensor to detect bright ambient light and then boost the screen's brightness level enough to overcome the strong surface reflection. Although this type of adaptive brightness control can help improve readability, it also drains battery power. Other methods for solving the sunlight visibility problem have proved difficult to implement. Looking for a simpler approach to improve screen readability outside, the researchers turned to nature. The eyes of moths are covered with a pattern of antireflective nanostructures that allow moths to see in the dark and prevent eye reflections that might be seen by predators. Because other research groups have experimented with using moth-eye-like nanostructures to reduce the sunlight reflected off the surface of solar cells, Wu and his team thought the same technique might also work on mobile screens. "Although it is known that moth-eye structures can reduce surface reflection, it is relatively difficult to fabricate an antireflection film with this nanostructure that is large enough to use on a mobile phone or tablet," said Guanjan Tan, first author of the paper. "Because the structures are so small, a high-resolution and high-precision fabrication technique is necessary." The researchers developed a fabrication technique that uses self-assembled nanospheres to form a precise template that can be used to create the moth-eye-like structure on a coating. The simplicity and precision of this process allowed fabrication of the intricate structure in a film large enough to apply to a mobile screen. The researchers also created a computational model to simulate the optical behavior of the coatings. After showing that the model accurately represented experimental results, the researchers used it to optimize the size of the moth-eye nanostructures to achieve the best performance. Seeing in the sunlight Tests of the film after optimization showed that when viewed in sunlight, glass covered with the new film exhibited a more than four-fold improvement in contrast ratio the difference between the brightest white and darkest black. When viewed in the shade, glass with the new film showed about a ten-fold improvement in 12

21 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) contrast ratio. The researchers also used standard industrial procedures to test its flexibility as well as its anti-scratch and self-cleaning capabilities. "Our measured results indicate the moth-eye-like antireflection film shows excellent optical behavior and mechanical strength," said Jun-Haw Lee of National Taiwan University, a key member of the research team. "Our film provides an efficient and low-cost method to reduce the surface reflection and improve the sunlight readability of mobile devices." The researchers are now working to further improve the anti-reflection film's mechanical properties, including finding the best balance of surface hardness and flexibility, to make the film surface rugged enough for long-term use on touch screens. They are also using the simulation model to further optimize the moth-eye structure's shape and size to obtain even better optical performance than ever thought possible One billion suns: World's brightest laser sparks new behavior in light A scientist at work in the Extreme Light Laboratory at the University of Nebraska-Lincoln, where physicists using the brightest light ever produced were able to change the way photons scatter from electrons. Physicists from the University of Nebraska-Lincoln are seeing an everyday phenomenon in a new light. By focusing laser light to a brightness one billion times greater than the surface of the sun - the brightest light ever produced on Earth - the physicists have observed changes in a vision-enabling interaction between light and matter. Those changes yielded unique X-ray pulses with the potential to generate extremely high-resolution imagery useful for medical, engineering, scientific and security purposes. The team's findings, detailed June 26 in the journal Nature Photonics, should also help inform future experiments involving high-intensity lasers. Donald Umstadter and colleagues at the university's Extreme Light Laboratory fired their Diocles Laser at helium-suspended electrons to measure how the laser's photons - considered both particles and waves of light - scattered from a single electron after striking it. Under typical conditions, as when light from a bulb or the sun strikes a surface, that scattering phenomenon makes vision possible. But an electron - the negatively charged particle present in matter-forming atoms - normally scatters just one photon of light at a time. And the average electron rarely enjoys even that privilege, Umstadter said, getting struck only once every four months or so. Using the brightest light ever produced, University of Nebraska-Lincoln physicists obtained this high-resolution X-ray of a USB drive. The image reveals details not visible with ordinary X-ray imaging Though previous laser-based experiments had scattered a few photons from the same electron, Umstadter's team managed to scatter nearly 1,000 photons at a time. At the ultra-high intensities produced by the laser, both the photons and electron behaved much differently than usual. "When we have this unimaginably bright light, it turns out that the scattering - this fundamental thing that makes everything visible - fundamentally changes in nature," said Umstadter, the Leland and Dorothy Olson Professor of physics and astronomy. A photon from standard light will typically scatter at the same angle and energy it featured before striking the electron, regardless of how bright its light might be. Yet Umstadter's team found that, above a certain threshold, the laser's brightness altered the angle, shape and wavelength of that scattered light. "So it's as if things appear differently as you turn up the brightness of the light, which is not something you normally would experience," Umstadter said. "(An object) normally becomes brighter, but otherwise, it looks just like it did with a lo wer light level. But here, the light is changing (the object's) appearance. The light's coming off at different angles, with different colors, depending on how bright it is." That phenomenon stemmed partly from a change in the electron, which abandoned its usual up-and-down motion in favor of a figure-8 flight pattern. As it would under normal conditions, the electron also ejected its own photon, which was jarred loose by the energy of the incoming photons. But the researchers found that the ejected photon absorbed the collective energy of all the scattered photons, granting it the energy and wavelength of an X-ray. 13

22 光学与工程 A rendering of how changes in an electron's motion (bottom view) alter the scattering of light (top view), as measured in a new experiment that scattered more than 500 photons of light from a single electron. Previous experiments had managed to scatter no more than a few photons at a time. The unique properties of that X-ray might be applied in multiple ways, Umstadter said. Its extreme but narrow range of energy, combined with its extraordinarily short duration, could help generate three-dimensional images on the nanoscopic scale while reducing the dose necessary to produce them. Those qualities might qualify it to hunt for tumors or microfractures that elude conventional X-rays, map the molecular landscapes of nanoscopic materials now finding their way into semiconductor technology, or detect increasingly sophisticated threats at security checkpoints. Atomic and molecular physicists could also employ the X-ray as a form of ultrafast camera to capture snapshots of electron motion or chemical reactions. As physicists themselves, Umstadter and his colleagues also expressed excitement for the scientific implications of their experiment. By establishing a relationship between the laser's brightness and the properties of its scattered light, the team confirmed a recently proposed method for measuring a laser's peak intensity. The study also supported several longstanding hypotheses that technological limitations had kept physicists from directly testing. "There were many theories, for many years, that had never been tested in the lab, because we never had a bright-enough light source to actually do the experiment," Umstadter said. "There were various predictions for what would happen, and we have confirmed some of those predictions. "It's all part of what we call electrodynamics. There are textbooks on classical electrodynamics that all physicists learn. So this, in a sense, was really a textbook experiment." test-laser.html 13. The sharpest laser in the world: Physicists develop a laser with a linewidth of only 10 mhz One of the two silicon resonators. No one had ever come so close to the ideal laser before: theoretically, laser light has only one single color (also frequency or wavelength). In reality, however, there is always a certain linewidth. With a linewidth of only 10 mhz, the laser that the researchers from the Physikalisch-Technische Bundesanstalt (PTB) have now developed together with US researchers from JILA, has established a new world record. This precision is useful for various applications such as optical atomic clocks, precision spectroscopy, radioastronomy and for testing the theory of relativity. The results have been published in the current issue of Physical Review Letters. Lasers were once deemed a solution without problems - but that is now history. More than 50 years have passed since the first technical realization of the laser, and we cannot imagine how we could live without them today. Laser light is used in numerous applications in industry, medicine and information technologies. Lasers have brought about a real revolution in many fields of research and in metrology - or have even made some new fields possible in the first place. One of a laser's outstanding properties is the excellent coherence of the emitted light. For researchers, this is a measure for the light wave's regular frequency and linewidth. Ideally, laser light has only one fixed wavelength (or frequency). In practice, the spectrum of most types of lasers can, however, reach from a few khz to a few MHz in width, which is not good enough for numerous experiments requiring high precision. Research has therefore focused on developing ever better lasers with greater frequency stability and a narrower linewidth. Within the scope of a nearly 10-year-long joint project with the US colleagues from JILA in Boulder, Colorado, a laser has now been developed at PTB whose linewidth is only 10 mhz (0.01 Hz), hereby establishing a new world record. "The smaller the linewidth of the laser, the more accurate the measurement of the atom's frequency in an optical clock. This new laser will enable us to decisively improve the quality of our clocks", PTB physicist Thomas Legero explains. In addition to the new laser's extremely small linewidth, Legero and his colleagues found out by means of measurements that the emitted laser light's frequency was more precise than what had ever been achieved before. Although the light wave oscillates approx. 200 trillion times per second, it only gets out of 14

23 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) sync after 11 seconds. By then, the perfect wave train emitted has already attained a length of approx. 3.3 million kilometers. This length corresponds to nearly ten times the distance between the Earth and the moon. Since there was no other comparably precise laser in the world, the scientists working on this collaboration had to set up two such laser systems straight off. Only by comparing these two lasers was it possible to prove the outstanding properties of the emitted light. The core piece of each of the lasers is a 21-cm long Fabry-Pérot silicon resonator. The resonator consists of two highly reflecting mirrors which are located opposite each other and are kept at a fixed distance by means of a double cone. Similar to an organ pipe, the resonator length determines the frequency of the wave which begins to oscillate, i.e., the light wave inside the resonator. Special stabilization electronics ensure that the light frequency of the laser constantly follows the natural frequency of the resonator. The laser's frequency stability - and thus its linewidth - then depends only on the length stability of the Fabry-Pérot resonator. The scientists at PTB had to isolate the resonator nearly perfectly from all environmental influences which might change its length. Among these influences are temperature and pressure variations, but also external mechanical perturbations due to seismic waves or sound. They have attained such perfection in doing so that the only influence left was the thermal motion of the atoms in the resonator. This "thermal noise" corresponds to the Brownian motion in all materials at a finite temperature, and it represents a fundamental limit to the length stability of a solid. Its extent depends on the materials used to build the resonator as well as on the resonator's temperature. For this reason, the scientists of this collaboration manufactured the resonator from single-crystal silicon which was cooled down to a temperature of -150 C. The thermal noise of the silicon body is so low that the length fluctuations observed only originate from the thermal noise of the dielectric SiO2/Ta2O5 mirror layers. Although the mirror layers are only a few micrometers thick, they dominate the resonator's length stability. In total, the resonator length, however, only fluctuates in the range of 10 attometers. This length corresponds to no more than a ten-millionth of the diameter of a hydrogen atom. The resulting frequency variations of the laser therefore amount to less than of the laser frequency. The new lasers are now being used both at PTB and at JILA in Boulder to further improve the quality of optical atomic clocks and to carry out new precision measurements on ultracold atoms. At PTB, the ultrastable light from these lasers is already being distributed via optical waveguides and is then used by the optical clocks in Braunschweig. "In the future, it is planned to disseminate this light also within a European network. This plan would allow even more precise comparisons between the optical clocks in Braunschweig and the clocks of our European colleagues in Paris and London", Legero says. In Boulder, a similar plan is in place to distribute the laser across a fiber network that connects between JILA and various NIST labs. The scientists from this collaboration see further optimization possibilities. With novel crystalline mirror layers and lower temperatures, the disturbing thermal noise can be further reduced. The linewidth could then even become smaller than 1 mhz. ysicists-linewidth.html 14. A material that can switch between multiple phases that have distinct electronic, optical and magnetic properties Reversible phase transformation of SrCoO2.5 through an electric-field-controlled, dual-ion (O 2 and H + ) switch. The structures shown were obtained from first-principles calculations. Red and blue arrows represent negative and positive voltages, respectively. A large team of researchers with members from China, the U.K., the U.S. and Japan has developed a material that can switch between multiple phases with distinct electronic, optical and magnetic properties. In their paper published in the journal Nature, the team describes how they made their material, how it can be caused to switch properties and possible uses for it. Shriram Ramanathan, with Purdue University offers a News & Views piece on the work done by the team in the same journal issue and adds some additional background on the search for functional materials. As Ramanathan points out, humans have been searching for functional materials for centuries we want more out of our materials than simply bearing loads. As he further notes, many such materials have been developed due to clearly directed efforts, but some have also come about by changing a material that has already been discovered. In this new effort, the researchers have taken the latter approach they have modified an existing material to make it more useful by causing it to have different properties depending on how it is used. To create the new material, the researchers created a thin layer of ceramic material in the traditional way, on top of a substrate. But instead of cooking it, as has been done historically, they covered the surface of the material with an ionic gel-like liquid. To provide for additional functionality, the liquid was an electrical insulator and able to conduct ions. It also held dissolved 15

24 光子学 oxide ions and hydrogen ions. When electricity was applied to the material, the result depended on the polarity of the voltage ions from either the hydrogen or oxide ions were driven into the ceramic material below. Reversing the voltage induced the reverse, which quite obviously meant that the system was reversible, as well. The researchers report that the system works at room temperature and that analysis with magnetic probing and X-ray diffraction showed the phases of the material to be distinct. They also demonstrated one application of the material as a means for altering the transmissivity of light through a sheet of glass. Ramanathan suggests such a material could have a wide range of uses, particularly as a base for research work being done by other groups. s-distinct-electronic.html 二. 光子学 15. Researchers create ultrafast tunable semiconductor metamaterial A semiconductor-based metamaterial tuned by ultrashort laser pulses. An international team of researchers from Moscow State University (Russia), Sandia National Laboratories (U.S.), and Friedrich-Schiller University (Germany) have devised an ultrafast tunable metamaterial based on gallium arsenide nanoparticles. Their study was published in Nature Communications. The new optical metamaterial paves the way to ultrafast information transfer on the nanoscale. Optical metamaterials are man-made media that acquire unusual optical properties due to nanostructuring. For almost 20 years, researchers have designed many metamaterial-based devices, including those hiding objects to those sensitive to minute concentrations of substances. However, upon fabrication, metamaterial properties remain fixed. The team came up with a way to turn metamaterials "on" and "off," and do it very quickly more than 100 billion times per second. Researchers fabricated the metamaterial from a thin gallium arsenide film by electron-beam lithography with subsequent plasma etching. The material consists of an array of semiconductor nanoparticles, which can resonantly concentrate and "hold" light at the nanoscale. In other words, when the light illuminates the metamaterial, it is "trapped" inside the nanoparticles and interacts more efficiently with them. The working principle of the ultrafast tunable metamaterial lies in the generation of electron-hole pairs. In the steady state, the metamaterial is reflective. Then, researchers illuminate the metamaterial with an ultrashort laser pulse. Its energy is used to generate electrons and electron vacancies "holes" in the material. The presence of electrons and holes changes the properties of the metamaterial such that it is no longer reflective. In a split second, electrons and holes disappear by meeting each other, and the metamaterial is reflective again. In this way, it is possible to construct optical logic elements, which also opens the possibility of creating ultrafast optical computers. In 2015, a part of the same collaboration reported a similar device based on silicon nanostructures. In their new study, gallium arsenide was used instead of silicon, which increased by an order of magnitude the efficiency of controlling light via light in metamaterials. In the future, the research could allow for creating information transfer devices with processing speeds of tens and hundreds of terabits per second. The demonstration of highly efficient tunable semiconductor metamaterials is a significant step towards such information processing speeds. nductor-metamaterial.html 16. Group develops technique to shape pulses of intense infrared light To capture fast-moving action in a dimly lit environment, a photographer will use the combination of a fast shutter speed and a quick burst of light. Laser physicists employ the same principle capturing a microscopic event of short duration by hitting it with a quick pulse of infrared light. Of course, while the action a photographer is trying to capture might last a hundredth of a second or two, the physicist's window of opportunity might last a few femtoseconds (quadrillionths of a second). But in order to make a pulse of light short enough to capture what a physicist might want to see say, the effect of light-induced vibration on a molecule in the retina you need a light source that produces a broad range of frequencies. And a group led by Jeffrey Moses, assistant professor of applied and engineering physics, has developed a process for generating and shaping intense mid-infrared (mid-ir) pulses of light. "We have the ability to create this very broadband source of mid-ir light that's intense, and we have the ability to precisely shape it," said Moses, whose group published a paper in Nature Photonics, "Generation and multi-octave shaping of mid-infrared intense single-cycle pulses," March 20. Peter Krogen, Ph.D. '16, now a research associate at the Massachusetts Institute of Technology, is lead author. 16

25 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) Other contributors included doctoral student Noah Flemens, a member of the Moses Group. Mid-IR wavelengths are of particular importance to materials scientists, chemists, biologists and condensed-matter physicists. Recently, the advent of high-pulse-energy and ultrashort-duration mid-ir sources has ushered in a new range of nonlinear light matter interactions, and establishing mid-ir sources that feature not only an extreme bandwidth, but also an arbitrary control of the pulse shape, is of great interest. One method for analyzing short-duration phenomena is pump-probe spectroscopy. The first beam of laser light acts as the "pump," to generate a wanted reaction in a material, and the second is the "probe," used to analyze the reaction. In order to create pulses of light short enough to capture these events, the light must contain a wide range of frequencies within the IR spectrum. "The more frequencies I have, the shorter a pulse I can make," Moses said. The problem, however, is that in shaping the light for a specific purpose, you lose bandwidth. To overcome that problem, Moses and his group developed a way to create and shape a broadband, near-ir light pulse and change its "color" (wave frequency) to mid-ir while retaining its bandwidth and shape. In fact, the relative bandwidth of the near-ir wave a measure of how short a pulse can be made compared to the smallest achievable duration at that color is effectively increased when converted to a mid-ir wave. The result: pulses lasting only a single cycle of the wave period, which is very close to the minimum allowed by nature. "When we go through this process, we have bandwidth in the near-ir that's less than an octave," Moses said, "and we end up with bandwidth in the mid-ir that's more than an octave." In wavelengths, an octave is the spread between a frequency and twice that frequency. One particular application of interest to the group is tracking the way electron energy flows in a system, such as human vision. Rhodopsin molecules in the retina absorb light and then change shape from bent to straight and it's this straightening that serves to send a signal through the optic nerve to the brain. "The change in the electronic configuration of these molecules happens over tens of femtoseconds," Moses said. "We think we have the right source of light here to gain a lot more information about what's going on during that ultrashort time period." And what can that information tell a scientist? For one thing, that process is very efficient in humans, but there are other similar biological processes which theorists believe are regulated by a similar type of structure that are highly inefficient. "Using this tool, we're trying to develop a method for studying this sort of class of structures that is responsible for the way molecules respond to light," Moses said. "This could help us understand something that we're fabricating and help us make it do whatever it does more efficiently." Photonic 'hypercrystals' shed stronger light This drawing depicts a photonic hypercrystal, which is promising for future Li-Fi technologies that offer major advantages over Wi-Fi and other radiofrequency communications systems. Sources that integrate two artificial optical material concepts may drive ultrafast "Li-Fi" communications. In many applications, Li-Fi through-the-air optical networks potentially offer major advantages over Wi-Fi and other radiofrequency systems. Li-Fi nets can operate at extremely high speeds. They can exploit an extremely broad spectrum of frequencies. They avoid the interference problems that plague radiofrequency systems, which are especially problematic in high-security environments such as airplane cockpits and nuclear power stations. They are less open to hackers. And while their range is relatively limited, they don't need line-of-sight connections to operate, said Evgenii Narimanov, a Purdue University professor of electrical and computer engineering. Today's Li-Fi nets can't fully achieve all these potential benefits because they lack suitable light sources, he said. But designs that integrate two optical material concepts into "photonic hypercrystals" may fill this gap. Narimanov first proposed this concept in This month, he and colleagues at the City College of New York reported demonstrations of photonic hypercrystals with greatly increased light emission rates and intensities in the Proceedings of the National Academy of Sciences (PNAS). Photonic hypercrystals combine the properties of metamaterials and photonic crystals, both "artificial" optical materials with properties that are not usually found in nature, Narimanov said. Metamaterials are created from artificial building blocks that are much smaller than the wavelength of 17

26 光子学 light, while in photonic crystals the size of the "unit cell" is comparable to this wavelength. While these two types of composite materials generally show very different properties, the photonic hypercrystals combine them all within the same structure. Photonic hypercrystals are based on one type called hyperbolic metamaterials, which can be built with alternating layers of metal and dielectric materials where the electrical current can only travel along the metallic layers. "Generally, for light, metals and dielectrics are fundamentally different: light can travel in dielectrics, but is reflected back from metals," Narimanov said. "But a hyperbolic metamaterial behaves as metal along the layers and as a dielectric in the direction perpendicular to the layers, at the same time. For light, hyperbolic media is, therefore, the third estate of matter, entirely different from the usual metals and dielectrics." Among the interesting properties that this structure produces, the metamaterial accommodates a large number of photonic states, allowing spontaneous light emission at extremely high rates. "For a light source, the problem is that this light in the hyperbolic metamaterial can't get out," said Narimanov. Enter photonic crystals periodic nanostructures that can manipulate optical interference to optimize light transmission. In the integrated photonic hypercrystals presented in the PNAS paper, the hyperbolic metamaterial consists of alternating layers of silver (the metal) and aluminum oxide (the dielectric). Hexagonal arrays of holes milled into the layers create the photonic crystal. In the design, the visible light is emitted by quantum dots (semiconductor nanoparticles that can emit light) embedded in one of the layers that form the hyperbolic metamaterial. The result: extremely high levels of control and enhancement of the emitted light. "These photonic hypercrystals were fabricated at the City University of New York's Advanced Science Research Center using standard nano- and micro-fabrication techniques such as thin film evaporation and focused ion beam milling," said Tal Galfsky, a CCNY graduate student who is lead author on the PNAS paper. "These techniques are scalable with modern industry capabilities. " Vinod Menon, CCNY professor of physics, is senior author on the paper, and CCNY graduate student Jie Gu also contributed to the work. The work reported in PNAS demonstrates that "on a fundamental level, the problem of designing photonic hypercrystals has been solved," said Narimanov. He cautions, however, that significant engineering challenges must be overcome before these devices can be commercialized. Among these barriers, the demonstration devices are pumped optically by a laser, but commercial versions will need to be driven electrically and incorporate either semiconductor or organic LEDs, he said. As they mature, photonic hypercrystals also may fill many other demanding roles in ultrafast optoelectronics. One of the most promising avenues of research, Narimanov suggested, is to create more efficient versions of the single-photon guns employed in quantum information processing. tronger.html 18. Optical communication at record-high speed via soliton frequency combs generated in optical microresonators Soliton frequency combs, generated in silicon nitride microresonators, are used for massively parallel data transmission via various frequency channels. Optical solitons are special wave packages that propagate without changing their shape. In optical communications, solitons can be used for generating frequency combs with various spectral lines, which allow to realize particularly efficient and compact high-capacity optical communication systems. This was demonstrated recently by researchers from KIT's Institute of Photonics and Quantum Electronics (IPQ) and Institute of Microstructure Technology (IMT) together with researchers from EPFL's Laboratory of Photonics and Quantum Measurements (LPQM). As reported in Nature, the researchers used silicon nitride microresonators that can easily be integrated into compact communication systems. Within these resonators, solitons circulate continuously, thus generating broadband optical frequency combs. Such frequency combs, for which John Hall and Theodor W. Hãnsch were awarded the Nobel Prize in Physics in 2005, consist of a multitude of spectral lines, which are aligned on a regular equidistant grid. Traditionally, frequency combs serve as high-precision optical references for measurement of frequencies. So-called Kerr frequency combs feature large optical bandwidths along with rather large line spacings, and are particularly well suited for data transmission. Each individual spectral line can be used for transmitting a separate data channel. In their experiments, the researchers from Karlsruhe and Lausanne used two interleaved frequency combs to transmit data on 179 individual optical carriers, which 18

27 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) completely cover the optical telecommunication C and L bands and allow a transmission of data in a rate of 55 terabits per second over a distance of 75 kilometers. "This is equivalent to more than five billion phone calls or more than two million HD TV channels. It is the highest data rate ever reached using a frequency comb source in chip format," explains Christian Koos, professor at KIT's IPQ and IMT and recipient of a Starting Independent Researcher Grant of the European Research Council (ERC) for his research on optical frequency combs. According to Christian Koos, this is an important step towards highly efficient chip-scale transceivers for future petabit networks. on-frequency-microresonators.html 19. Learning with light: New system allows optical 'deep learning' Optical chip carrying a multitude of silicon nitride microresonators. The components have the potential to reduce the energy consumption of the light source in communication systems drastically. The basis of the researchers' work are low-loss optical silicon nitride microresonators. In these, the soliton state described was for the first time generated by the working group around Professor Tobias Kippenberg at EPFL in Explaining the advantages of the approach, Professor Kippenberg says, "Our soliton comb sources are ideally suited for data transmission and can be produced in large quantities at low costs on compact microchips." The soliton forms through so-called nonlinear optical processes occurring due to the high intensity of the light field in the microresonator. The microresonator is only pumped through a continuous-wave laser from which, by means of the soliton, hundreds of new equidistant laser lines are generated. The comb sources are currently being brought to application by a spin-off of EPFL. The work published in Nature shows that microresonator soliton frequency comb sources can considerably increase the performance of wavelength division multiplexing (WDM) techniques in optical communications. WDM allows to transmit ultra-high data rates by using a multitude of independent data channels on a single optical waveguide. To this end, the information is encoded on laser light of different wavelengths. For coherent communications, microresonator soliton frequency comb sources can be used not only at the transmitter, but also at the receiver side of WDM systems. The comb sources dramatically increase scalability of the respective systems and enable highly parallel coherent data transmission with light. "Deep Learning" computer systems, based on artificial neural networks that mimic the way the brain learns from an accumulation of examples, have become a hot topic in computer science. In addition to enabling technologies such as face- and voice-recognition software, these systems could scour vast amounts of medical data to find patterns that could be useful diagnostically, or scan chemical formulas for possible new pharmaceuticals. But the computations these systems must carry out are highly complex and demanding, even for the most powerful computers. Now, a team of researchers at MIT and elsewhere has developed a new approach to such computations, using light instead of electricity, which they say could vastly improve the speed and efficiency of certain deep learning computations. Their results appear today in the journal Nature Photonics in a paper by MIT postdoc Yichen Shen, graduate student Nicholas Harris, professors Marin Soljacic and Dirk Englund, and eight others. Soljacic says that many researchers over the years have made claims about optics-based computers, but that "people dramatically over-promised, and it backfired." While many proposed uses of such photonic computers turned out not to be practical, a light-based neural-network system developed by this team "may be applicable for deep-learning for some applications," he says. Traditional computer architectures are not very efficient when it comes to the kinds of calculations needed for certain important neural-network tasks. Such tasks typically involve repeated multiplications of matrices, which can be very computationally intensive in conventional CPU or GPU chips. After years of research, the MIT team has come up with a way of performing these operations optically instead. "This chip, once you tune it, can carry out matrix multiplication with, in principle, zero energy, almost instantly," Soljacic says. "We've demonstrated 19

28 光子学 the crucial building blocks but not yet the full system." By way of analogy, Soljacic points out that even an ordinary eyeglass lens carries out a complex calculation (the so-called Fourier transform) on the light waves that pass through it. The way light beams carry out computations in the new photonic chips is far more general but has a similar underlying principle. The new approach uses multiple light beams directed in such a way that their waves interact with each other, producing interference patterns that convey the result of the intended operation. The resulting device is something the researchers call a programmable nanophotonic processor. The result, Shen says, is that the optical chips using this architecture could, in principle, carry out calculations performed in typical artificial intelligence algorithms much faster and using less than one-thousandth as much energy per operation as conventional electronic chips. "The natural advantage of using light to do matrix multiplication plays a big part in the speed up and power savings, because dense matrix multiplications are the most power hungry and time consuming part in AI algorithms" he says. The new programmable nanophotonic processor, which was developed in the Englund lab by Harris and collaborators, uses an array of waveguides that are interconnected in a way that can be modified as needed, programming that set of beams for a specific computation. "You can program in any matrix operation," Harris says. The processor guides light through a series of coupled photonic waveguides. The team's full proposal calls for interleaved layers of devices that apply an operation called a nonlinear activation function, in analogy with the operation of neurons in the brain. To demonstrate the concept, the team set the programmable nanophotonic processor to implement a neural network that recognizes four basic vowel sounds. Even with this rudimentary system, they were able to achieve a 77 percent accuracy level, compared to about 90 percent for conventional systems. There are "no substantial obstacles" to scaling up the system for greater accuracy, Soljacic says. Englund adds that the programmable nanophotonic processor could have other applications as well, including signal processing for data transmission. "High-speed analog signal processing is something this could manage" faster than other approaches that first convert the signal to digital form, since light is an inherently analog medium. "This approach could do processing directly in the analog domain," he says. The team says it will still take a lot more effort and time to make this system useful; however, once the system is scaled up and fully functioning, it can find many user cases, such as data centers or security systems. The system could also be a boon for self-driving cars or drones, says Harris, or "whenever you need to do a lot of computation but you don't have a lot of power or time." Using thermal light sources to take accurate distance measurements Simplified scheme of the sensing technique published in Optics Express. New research has made it possible for the first time to compare the spatial structures and positions of two distant objects, which may be very far away from each other, just by using a simple thermal light source, much like a star in the sky. This sensing technique, introduced by Dr Vincenzo Tamma at the University of Portsmouth in collaboration with the University of Bari in Italy and the University of Maryland, Baltimore County in the US in the recent publication in Optics Express, enables the comparison of the spatial structure of a remote object with a reference object, paving the way for important remote sensing applications. The technique builds on the famous Hanbury Brown and Twiss effect, originally employed to measure the angular size of a distant star, which gave birth to the novel field of quantum optics. The reported new research has now taken the physics behind this effect an important step further. Dr Tamma said: "These results not only deepen our understanding of the interesting physics behind multiphoton interference but are also of interest in the development of quantum technologies for remote sensing, biomedical imaging and information processing." The multiphoton interference phenomenon at the heart of this novel sensing technique was first predicted by Dr Tamma and his student Johannes Seiler in 2014 and reported as a Fast Track Communication in the journal New Journal of Physics. The counterintuitive nature of this phenomenon made it difficult to accept by part of the scientific community. Nonetheless, it has already led to three independent verifications (here,here and here) in three different experimental scenarios in US, Italy and South Korea. In the recent publication in Scientific Reports in collaboration with the University of Bari, this technique has been experimentally employed for the spatial 20

29 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) characterization of two remote objects, namely two double-pinhole masks, at distances that, in principle, could be arbitrarily large. In the experimental setup, thermal light impinges on a balanced beam splitter and then reaches the two remote double-pinhole masks through the two beam splitter output channels. Dr Tamma said: "In the experiment reported here, the distance between the two pinholes is large enough that there is no coherence between the light passing through them. The classic Young's double-slit experiment teaches us that in this case no single-photon interference can be measured behind each mask separately. Nonetheless, multiphoton interference is observed by performing correlation measurements with two detectors, one placed behind each of the two masks. Even more interesting, the measured interference pattern allows us to retrieve information about the position and spatial structure of both masks. "Remarkably, this sensing technique allows the measurement, via multiphoton interference, of the relative shrinking/stretching of one object with respect to the other. Furthermore, if both detectors are moved, symmetrically, farther away from the optical axis it is even possible to increase the measurement sensitivity to the changes in the object spatial structures. Similar analysis can be performed to determine the relative position of the two different objects." The application of this technique to sensing of arbitrary remote objects could pave the way to a broad spectrum of applications in remote sensing. Furthermore, the extension of this scheme to the use of entangled photons may lead to applications in high-precision metrology beyond any classical capability. The physics of multipath correlations at the heart of this effect has been already demonstrated to be crucial in the simulation of quantum logic gates with a thermal source. This has potentially important applications in information processing and the development of novel optical algorithms. e-distance.html 21. Camera captures microscopic holograms at femtosecond speeds for recording holograms of tiny objects like living cells at femtosecond speeds. The new method reconstructs the phase topography of a sample according to deformations that emerge in a laser pulse when it passes through the specimen. In comparison to electron microscopes, the device can visualize transparent biological structures without introducing contrast agents. The paper was published in Applied Physics Letters. The vital activity of living cells is a complex sequence of biochemical reactions and physical processes; many of them take place with high temporal resolution. To register such rapid transformations, scientists need more accurate and faster equipment. Biological tissue can be studied with an electron microscope, but this method requires introducing a special dye in the sample. The dye makes cells contrast, although it may affect their metabolism. Digital holographic microscopes can cope with this drawback, but have low spatial resolution. The new camera created by ITMO scientists can register fast processes in transparent specimens and provides increased resolution of images in a wide range. The device records phase deformations of ultrashort femtosecond laser pulses that emerge when light passes through the sample. The phase images, or holograms, will contribute to better understanding mechanisms of autoimmune, oncological and neurodegenerative diseases, as well as monitoring cells during surgical interventions such as cancer therapy. "Our device will help biologists and genetic engineers track what is happening inside a living cell with a resolution of about 50 femtoseconds this is enough to resolve many biochemical reactions. Theoretically, the camera can even capture an electron jumping to another orbit. We can now study the viability of cells when initiating certain processes, for example, heating or transferring viruses and cells in three-dimensional space using femtosecond laser radiation. The device also supports tracking cell states during changing ph, adding and editing of genetic material," says Arseny Chipegin, lead author of the paper and researcher at the Laboratory of Digital and Display Holography at ITMO University. The filament was formed by the reflection of radiation from the parabolic lens. The iridescent picture indicates the occurrence of a spark known as a filament. Researchers from ITMO University have built a setup For the analysis, a femtosecond laser beam is split in three. The first beam has 95 percent energy and starts the process; two other beams are used for diagnostics. The second, known as the object beam, passes through 21

30 光子学 the specimen. The third, a reference beam, is deflected by mirrors and goes around. The rays meet behind the sample, where they form an interference pattern of bright bands. The strips emerge when crests of light waves overlap and amplify each other. By adjusting the position of the mirrors, the scientists delay the reference beam, forcing it to meet the first one at different times. In other words, the second beam scans the one that passes through the sample. Every collision of the beams is recorded on a subhologram. A fast computer algorithm compiles all the subholograms in a series. The device removes one of the most important issues of digital holographic microscopy associated with increasing resolution capability of a system at the stage of recording holograms. "Technically, we can scale the images dozens of times, setting the magnifying system between the object and the camera. Not only does this enhance resolution, the measurement accuracy grows, too, since the number of interference bands does not change. Thus, it is possible to calculate the phase difference between the object and reference beams more precisely," says Nikolai Petrov, head of the Laboratory of Digital and Display Holography. According to the scientists, the research will continue. The developed system is designed to be simpler than many modern microscopes, but has several advantages in speed of recording and processing holograms. copic-holograms-femtosecond.html 22. The world's most powerful X-ray laser beam creates 'molecular black hole' The extremely intense X-ray flash knocks so many electrons out of the iodine atom (right) such that it pulls in the electrons of the methyl group (left) like an elecetromagnetic version of a black hole, before finally spitting them out. When scientists at the Department of Energy's SLAC National Accelerator Laboratory focused the full intensity of the world's most powerful X-ray laser on a small molecule, they got a surprise: A single laser pulse stripped all but a few electrons out of the molecule's biggest atom from the inside out, leaving a void that started pulling in electrons from the rest of the molecule, like a black hole gobbling a spiraling disk of matter. Within 30 femtoseconds - millionths of a billionth of a second - the molecule lost more than 50 electrons, far more than scientists anticipated based on earlier experiments using less intense beams, or isolated atoms. Then it blew up. The results, published today in Nature, give scientists fundamental insights they need to better plan and interpret experiments using the most intense and energetic X-ray pulses from SLAC's Linac Coherent Light Source (LCLS) X-ray free-electron laser. Experiments that require these ultrahigh intensities include attempts to image individual biological objects, such as viruses and bacteria, at high resolution. They are also used to study the behavior of matter under extreme conditions, and to better understand charge dynamics in complex molecules for advanced technological applications. "For any type of experiment you do that focuses intense X-rays on a sample, you want to understand how it reacts to the X-rays," said Daniel Rolles of Kansas State University. "This paper shows that we can understand and model the radiation damage in small molecules, so now we can predict what damage we will get in other systems." Like Focusing the Sun Onto a Thumbnail The experiment, led by Rolles and Artem Rudenko of Kansas State, took place at LCLS's Coherent X-ray Imaging instrument. CXI delivers X-rays with the highest possible energies achievable at LCLS, known as hard X-rays, and records data from samples in the instant before the laser pulse destroys them. How intense are those X-ray pulses? "They are about a hundred times more intense than what you would get if you focused all the sunlight that hits the Earth's surface onto a thumbnail," said LCLS staff scientist and co-author Sebastien Boutet. X-rays Trigger Electron Cascades For this study, researchers used special mirrors to focus the X-ray beam into a spot just over 100 nanometers in diameter - about a hundredth the size of the one used in most CXI experiments, and a thousand times smaller than the width of a human hair. They looked at three types of samples: individual xenon atoms, which have 54 electrons each, and two types of molecules that each contain a single iodine atom, which has 53 electrons. Heavy atoms around this size are important in biochemical reactions, and researchers sometimes add them to biological samples to enhance contrast for imaging and crystallography applications. But until now, no one had investigated how the ultra-intense CXI beam affects molecules with atoms this heavy. The team tuned the energy of the CXI pulses so they would selectively strip the innermost electrons from the xenon or iodine atoms, creating "hollow atoms." Based on earlier studies with less energetic X-rays, they thought cascades of electrons from the outer parts of the atom would drop down to fill the vacancies, only to be 22

31 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) kicked out themselves by subsequent X-rays. That would leave just a few of the most tightly bound electrons. And, in fact, that's what happened in both the freestanding xenon atoms and the iodine atoms in the molecules. But in the molecules, the process didn't stop there. The iodine atom, which had a strong positive charge after losing most of its electrons, continued to suck in electrons from neighboring carbon and hydrogen atoms, and those electrons were also ejected, one by one. Rather than losing 47 electrons, as would be the case for an isolated iodine atom, the iodine in the smaller molecule lost 54, including the ones it grabbed from its neighbors - a level of damage and disruption that's not only higher than would normally be expected, but significantly different in nature. Results Feed Into Theory to Improve Experiments "We think the effect was even more important in the larger molecule than in the smaller one, but we don't know how to quantify it yet," Rudenko said. "We estimate that more than 60 electrons were kicked out, but we don't actually know where it stopped because we could not detect all the fragments that flew off as the molecule fell apart to see how many electrons were missing. This is one of the open questions we need to study." For the data analyzed to date, the theoretical model provided excellent agreement with the observed behavior, providing confidence that more complex systems can now be studied, said LCLS director Mike Dunne. "This has important benefits for scientists wishing to achieve the highest resolution images of biological molecules (for example, to inform the development of better pharmaceuticals). These experiments also guide the development of a next-generation instrument for the LCLS-II upgrade project, which will provide a major leap in capability due to the increase in repetition rate from 120 pulses per second to 1 million." ser-molecular.html 三. 电子工程 23. Researchers discover way to make solar cells more efficient Yuri Dahnovsky and TeYu Chien, both UW faculty members in the Department of Physics and Astronomy, co-wrote a research paper that studied improving the efficiency of solar cells that could prolong the life of solar panels (pictured) or solar car batteries. The paper was published in Applied Physics Letters. When it comes to improving the efficiency of solar cells, a group of University of Wyoming professors has discovered a way to do so by adding manganese atoms an alternate metal to the mix. Doing so, they found, dramatically increases solar cell energy conversion by an average 300 percent and, in some cases, up to 700 percent. This research finding could be used in the future to help Wyoming farmers and ranchers access electric power in remote areas important to the state to aid crops and livestock, to boosting the use of electric cars in big cities, such as Los Angeles, in an effort to reduce smog there. Jinke Tang and Yuri Dahnovsky, both UW professors in the Department of Physics and Astronomy; TeYu Chien, an assistant professor of physics and astronomy; and Wenyong Wang, an associate professor of physics and astronomy, co-wrote a research paper, which was published in Applied Physics Letters last fall. The paper, titled "Giant Photocurrent Enhancement by Transition Metal Doping in Quantum Dot Sensitized Solar Cells," was recently spotlighted again, in April, by the Department of Energy's (DOE) Office of Basic Energy Sciences. The research was funded by the DOE, Office of Basic Energy Sciences, as part of the Established Program to Stimulate Competitive Research (EPSCoR) Program. "They usually highlight the research funded by them," Chien says. "They pick key achievements and highlight them." The Office of Basic Energy Sciences supports fundamental research to understand, predict and, ultimately, control matter and energy at the electronic, atomic and molecular levels to provide the foundations for new energy technologies and to support DOE missions in energy, environment and national security. "We added into the PbS quantum dot with 4 percent manganese atoms. Our expectations were a 4 percent increase in solar efficiency," Dahnovsky says. "We had a 700 percent increase. That's very unusual." Dahnovsky says it's unusual because electrons "tunneling" between manganese and zinc atoms do so much easier than between lead and zinc atoms located at the interface between a quantum dot and a semiconductor. The quest for high efficiency solar cells has led to the search for new materials, such as manganese, to replace traditional silicon used for sensitizers and photoconductor oxide electrodes. This might lead to a technical revolution for some industrial applications, Dahnovsky and Chien both say. Practical uses for increased solar cells include more efficient solar panels at a lower cost for houses and other structures; if combined with portable devices, such as iphones, ipads and computers, solar cells could keep 23

32 电子工程 them powered much longer before needing to be recharged; and allow electric cars to travel farther before needing to stop at a recharge station, which might make buying an electric car a more viable alternative, Chien says. Dahnovsky adds that the science also could assist Wyoming, which is spread out, remote and has areas that lack electricity. For example, he says a herd of cattle that moves from one place to another to graze may be located far from electricity. "A farmer may need a water pump in a remote area to water his livestock," he says. "If there's no electricity, he may use solar cells to power the water pump." Chien says farmers also could use solar-powered sensors that could measure light, humidity, oxygen and temperature in their crop soil Magnetoelectric memory cell increases energy efficiency for data storage MELRAM cell and the electric scheme for the magnetic state identification. Today's computers provide storage of tremendous quantities of information with extremely large data densities, but writing and retrieving this information expends a lot of energy. More than 99 percent of the consumed power of information storage and processing is wasted in the form of heat, a big headache that still has not abated. A team of researchers from France and Russia has now developed a magnetoelectric random access memory (MELRAM) cell that has the potential to increase power efficiency, and thereby decrease heat waste, by orders of magnitude for read operations at room temperature. The research could aid production of devices such as instant-on laptops, close-to-zero-consumption flash drives, and data storage centers that require much less air conditioning. The research team reported their findings this week in Applied Physics Letters. Billions of transistors can now be etched onto single chips in a space the size of a dime, but at some point, increasing this number for even better performance using the same space will not be possible. The sheer density of these nanoscopic transistors translates into more unwanted heat along with quantum-level interactions that must now be addressed. Over the last several years, research has ramped up to explore the magnetic properties of electrons in a phenomenon called the magnetoelectric effect. This effect, often of interest in the field of research known as spintronics, takes advantage of an electron's spin, instead of its charge. Spins can potentially be manipulated at smaller size scales using far less energy. Most efforts have focused on reducing the energy of the write operations in magnetic memories, since these operations typically use more energy than read operations. In 2010, the same French and Russian team showed that a combination of magnetoelastic and piezoelectric materials in a magnetoelectric memory cell could allow a 100-fold reduction of the energy needed for the writing process. In the researchers' latest paper, they show that the same magnetoelectric principle also can be used for read operations with extra-low energy consumption. "We focused on read operations in this paper because the potential for the writing energy to be very low in magnetoelectric systems means that the energy output will now be higher for read operations," said Nicolas Tiercelin, co-author of the paper and a research scientist from the Centre national de la recherche scientifique (CNRS) who is conducting research at the Institute of Electronics, Microelectronics and Nanotechnology in Lille, France. The core of the researchers' MELRAM memory cell is based on combining the properties of two types of materials by coupling them mechanically. Magnetic alloys one based on a combination of terbium-cobalt and the other based on iron and cobalt with thicknesses of a few nanometers are stacked on top of one another. The alloys form a magnetoelastic nanocomposite material whose magnetic spins react to mechanical stress. These alloys are then placed on a piezoelectric substrate, which consists of relaxor ferroelectrics, exotic materials that change their shape or dimensions when they are exposed to an electric field. "Together, these materials constitute multiferroic heterostructures in which the control of the magnetic properties is made possible by the application of an electric voltage," Tiercelin said. "The nanocomposite multilayer provides strong magnetoelectric interaction at room temperature," said Vladimir Preobrazhensky, another co-author of the paper and research director at the Wave Research Center, Prokhorov General Physics Institute of the Russian Academy of Sciences in Moscow. "This interaction is the basic mechanism for control of magnetic states by the electric field. This feature of the magnetoelectric memory is the origin of its extra-low power consumption." 24

33 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) y-cell-energy-efficiency.html 四. 纳米物理与材料 25. Three-dimensional graphene: Experiment at BESSY II shows that optical properties are tuneable SEM-images of 3-D graphene with different pore size (a,b,c, scale = 1μm). Optical properties (d,e,f) change with pore size. An international research team has for the first time investigated the optical properties of three-dimensional nanoporous graphene at the IRIS infrared beamline of the BESSY II electron storage ring. The experiments show that the plasmonic excitations (oscillations of the charge density) in this new material can be precisely controlled by the pore size and by introducing atomic impurities. This could facilitate the manufacture of highly sensitive chemical sensors. Carbon is a very versatile element. It not only forms diamonds, graphite, and coal, but can also take a planar form as a hexagonal matrix - graphene. This material, consisting of only a single atomic layer, possesses many extreme properties. It is highly conductive, optically transparent, and is mechanically flexible as well as able to withstand loads. André Geim and Konstantin Novoselov received the 2010 Nobel Prize in Physics for the discovery of this exotic form of carbon. And just recently, a Japanese team has been successful in stacking two-dimensional graphene layers in a three-dimensional architecture with nanometre-sized pores. Tuneable plasmons A research team operated by a group at Sapienza University in Rome has now for the first time made a detailed investigation of the optical properties of 3D graphene at BESSY II. The team was able to ascertain from the data how charge density oscillations, known as plasmons, propagate in three-dimensional graphene. In doing so, they determined that these plasmons follow the same physical laws as 2D graphene. However, the frequency of the plasmons in 3D graphene can be very precisely controlled, either by introducing atomic impurities (doping), by the size of the nanopores, or by attaching specific molecules in certain ways to the graphene. In this way, the novel material might also lend itself to manufacturing specific chemical sensors, as the authors write in Nature Communications. In addition, the new material is interesting as an electrode material for employment in solar cells. Advantages provided by the IRIS beamline The researchers used the IRIS beamline at the BESSY II synchrotron source in Berlin to their advantage for their investigations. Broad-band infrared is available there, which especially facilitates spectroscopic analysis of novel materials using terahertz radiation. "A special operating mode of the BESSY II storage ring called low-alpha allowed us to measure the optical conductivity of three-dimensional graphene with a particularly high signal-to-noise ratio. This is hardly possible with standard methods, especially in the terahertz region. However, it is exactly this region that is important for observing critical physical properties", says Dr. Ulrich Schade, head of the group at the infrared beamline. hene-bessy-ii-optical.html 26. Making flexible electronics with nanowire networks Your smartphone can t do this yet. A smartphone touchscreen is an impressive piece of technology. It displays information and responds to a user's touch. But as many people know, it's easy to break key elements of the transparent, electrically conductive layers that make up even the sturdiest rigid touchscreen. If flexible smartphones, e-paper and a new generation of smart watches are to succeed, they can't use existing touchscreen technology. We'll need to invent something new something flexible and durable, in addition to being clear, lightweight, electrically responsive and inexpensive. Many researchers are pursuing potential options. As a graduate researcher at the University of California, Riverside, I'm part of a research group working to solve this challenge by weaving mesh layers out of microscopic strands of metal building what we call metal nanowire networks. These could form key components of new display systems; they could also make existing smartphones' touchscreens even faster and easier to use. The problem with indium tin oxide A standard smartphone touchscreen has glass on the 25

34 纳米物理与材料 outside, on top of two layers of conductive material called indium tin oxide. These layers are very thin, transparent to light and conduct small amounts of electrical current. The display lies underneath. When a person touches the screen, the pressure of their finger bends the glass very slightly, pushing the two layers of indium tin oxide closer together. In resistive touchscreens, that changes the electrical resistance of the layers; in capacitive touchscreens, the pressure creates an electrical circuit. Indium tin oxide is very conductive, making touchscreens respond to a user's touch with lightning fast speeds. But it's also very brittle, making it unsuitable for more flexible displays. In addition, there isn't enough indium, largely produced by refining zinc and lead ore, to meet ever-increasing demand. Potential replacements Any replacement for indium tin oxide must be transparent otherwise, there would be no point to using it for a screen. It must also conduct electricity well. Some potential replacements for this indium tin oxide layer include carbon nanotubes, graphene and conductive polymers But each of them has its problems. Carbon nanotubes usually have high electrical resistance when contacted to one another so they do not function well as meshes. Someday soon, metal nanowire networks will be sprayed directly onto rollable plastic sheets. Graphene would be excellent it is highly conductive, flexible and transparent. However, there is not yet an industrial-scale process for producing enough graphene to meet the demand. Conductive polymers are easily molded into different shapes and conductive enough to be used in some photovoltaics and LED-based devices, but their tendency to absorb light means they're not yet good enough to be used as a fully competitive replacement for indium tin oxide. Exploring metal nanowire networks A promising replacement for indium tin oxide could be metal nanowire networks. They are made up of individual silver or copper wires, tens to hundreds of nanometers in diameter, woven together in an interconnected mesh. It's transparent in the same way that a screen door is the individual strands of the mesh are so small they don't obscure the overall view. Silver nanowires can be prepared in solution by a chemical reaction between silver nitrate and ethylene glycol at high temperature. When the solution is spread across the back of a touchscreen (made of an insulating material like glass or flexible plastic), the liquid dries and the nanowires form junctions with each other, creating the mesh. Producing devices with silver nanowires has several advantages over the current standard, indium tin oxide. Silver is 50 times more conductive and can be used in a wider variety of devices. Making silver nanowire devices is also projected to be cheaper. Other benefits are obvious when comparing fabrication methods. Indium tin oxide is applied to a touchscreen surface in an industrial process called "sputtering," which involves effectively vaporizing the indium tin oxide, some of which lands on the touchscreen. But up to 70 percent of the material ends up on the walls of the sputtering chamber and must be removed before it can be reused. And indium tin oxide can't be applied directly to flexible plastic surfaces, because sputtering involves lots of heat, which will warp the plastic. By contrast, metal nanowires are made in a solution in the open air and can then be sprayed onto sheets of flexible material with a process called roll to roll coating. This process has been used since the 1980s to make components for solar panels. Remaining challenges No one is quite ready to bring metal nanowire networks into the smartphone market. Silver and copper corrode when they're exposed to air; researchers including my lab group and many others are trying to find ways to coat them with conductive polymers or even other metals, to protect them from the air without sacrificing transparency or conductivity. And another challenge that remains is how to embed metal nanowires in between flexible plastic sheets. But one day, perhaps not long from now, we will be able to marshal all this research into creating fully working devices using metal nanowire networks. owire-networks.html 27. Breakthrough in thin electrically conducting sheets paves way for smaller electronic devices Queen's University Belfast researchers have discovered a new way to create extremely thin electrically conducting sheets, which could revolutionise the tiny electronic devices that control everything from smart phones to banking and medical technology. Through nanotechnology, physicists Dr Raymond 26

35 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) McQuaid, Dr Amit Kumar and Professor Marty Gregg from Queen's University's School of Mathematics and Physics, have created unique 2-D sheets, called domain walls, which exist within crystalline materials. The sheets are almost as thin as the wonder-material graphene, at just a few atomic layers. However, they can do something that graphene can't they can appear, disappear or move around within the crystal, without permanently altering the crystal itself. This means that in future, even smaller electronic devices could be created, as electronic circuits could constantly reconfigure themselves to perform a number of tasks, rather than just having a sole function. Professor Marty Gregg explains: "Almost all aspects of modern life such as communication, healthcare, finance and entertainment rely on microelectronic devices. The demand for more powerful, smaller technology keeps growing, meaning that the tiniest devices are now composed of just a few atoms a tiny fraction of the width of human hair." "As things currently stand, it will become impossible to make these devices any smaller we will simply run out of space. This is a huge problem for the computing industry and new, radical, disruptive technologies are needed. One solution is to make electronic circuits more 'flexible' so that they can exist at one moment for one purpose, but can be completely reconfigured the next moment for another purpose." The team's findings, which have been published in Nature Communications, pave the way for a completely new way of data processing. Professor Gregg says: "Our research suggests the possibility to "etch-a-sketch" nanoscale electrical connections, where patterns of electrically conducting wires can be drawn and then wiped away again as often as required. "In this way, complete electronic circuits could be created and then dynamically reconfigured when needed to carry out a different role, overturning the paradigm that electronic circuits need be fixed components of hardware, typically designed with a dedicated purpose in mind." There are two key hurdles to overcome when creating these 2-D sheets, long straight walls need to be created. These need to effectively conduct electricity and mimic the behavior of real metallic wires. It is also essential to be able to choose exactly where and when the domain walls appear and to reposition or delete them. Through the research, the Queen's researchers have discovered some solutions to the hurdles. Their research proves that long conducting sheets can be created by squeezing the crystal at precisely the location they are required, using a targeted acupuncture-like approach with a sharp needle. The sheets can then be moved around within the crystal using applied electric fields to position them. Dr Raymond McQuaid, a recently appointed lecturer in the School of Mathematics and Physics at Queen's University, added: "Our team has demonstrated for the first time that copper-chlorine boracite crystals can have straight conducting walls that are hundreds of microns in length and yet only nanometres thick. The key is that, when a needle is pressed into the crystal surface, a jigsaw puzzle-like pattern of structural variants, called "domains", develops around the contact point. The different pieces of the pattern fit together in a unique way with the result that the conducting walls are found along certain boundaries where they meet. "We have also shown that these walls can then be moved using applied electric fields, therefore suggesting compatibility with more conventional voltage operated devices. Taken together, these two results are a promising sign for the potential use of conducting walls in reconfigurable nano-electronics." rically-sheets-paves.html 28. Chemists create 3-D printed graphene foam Laser sintering was used to 3-D print objects made of graphene foam, a 3-D version of atomically thin graphene. At left is a photo of a fingertip-sized cube of graphene foam; at right is a close-up of the material as seen with a scanning electron microscope. Nanotechnologists from Rice University and China's Tianjin University have used 3-D laser printing to fabricate centimeter-sized objects of atomically thin graphene. The research could yield industrially useful quantities of bulk graphene and is described online in a new study in the American Chemical Society journal ACS Nano. "This study is a first of its kind," said Rice chemist James Tour, co-corresponding author of the paper. "We 27

36 纳米物理与材料 have shown how to make 3-D graphene foams from nongraphene starting materials, and the method lends itself to being scaled to graphene foams for additive manufacturing applications with pore-size control." Graphene, one of the most intensely studied nanomaterials of the decade, is a two-dimensional sheet of pure carbon that is both ultrastrong and conductive. Scientists hope to use graphene for everything from nanoelectronics and aircraft de-icers to batteries and bone implants. But most industrial applications would require bulk quantities of graphene in a three-dimensional form, and scientists have struggled to find simple ways of creating bulk 3-D graphene. For example, researchers in Tour's lab began using lasers, powdered sugar and nickel to make 3-D graphene foam in late Earlier this year they showed that they could reinforce the foam with carbon nanotubes, which produced a material they dubbed "rebar graphene" that could retain its shape while supporting 3,000 times its own weight. But making rebar graphene was no simple task. It required a pre-fabricated 3-D mold, a 1,000-degree Celsius chemical vapor deposition (CVD) process and nearly three hours of heating and cooling. they trace out two-dimensional patterns. In 3-D laser sintering, a laser shines down onto a flat bed of powder. Wherever the laser touches powder, it melts or sinters the powder into a solid form. The laser is rastered, or moved back and forth, line by line to create a single two-dimensional slice of a larger object. Then a new layer of powder is laid over the top of that layer and the process is repeated to build up three-dimensional objects from successive two-dimensional layers. The new Rice process used a commercially available CO2 laser. When this laser was shone onto the sugar and nickel powder, the sugar was melted and the nickel acted as a catalyst. Graphene formed as the mixture cooled after the laser had moved on to melt sugar in the next spot, and Sha and colleagues conducted an exhaustive study to find the optimal amount of time and laser power to maximize graphene production. The foam created by the process is a low-density, 3-D form of graphene with large pores that account for more than 99 percent of its volume. "The 3-D graphene foams prepared by our method show promise for applications that require rapid prototyping and manufacturing of 3-D carbon materials, including energy storage, damping and sound absorption," said co-lead author Yilun Li, a graduate student at Rice. am.html 29. Researchers create very small sensor using 'white graphene' 3-D graphene foam objects are produced by shining a laser on a mixture of powdered sugar and nickel powder. The laser is moved back and forth to melt sugar in a 2-D pattern, and nickel acts as a catalyst to spur the growth of graphene foam. The process is repeated with successive layers of powder to build up 3-D objects. In the latest study, a team from Tour's lab and the labs of Rice's Jun Luo and Tianjin's Naiqin Zhao adapted a common 3-D printing technique to make fingertip-size blocks of graphene foam. The process is conducted at room temperature. No molds are required and the starting materials are powdered sugar and nickel powder. "This simple and efficient method does away with the need for both cold-press molds and high-temperature CVD treatment," said co-lead author Junwei Sha, a former student in Tour's lab who is now a postdoctoral researcher at Tianjin. "We should also be able to use this process to produce specific types of graphene foam like 3-D printed rebar graphene as well as both nitrogen- and sulfur-doped graphene foam by changing the precursor powders." Three-D laser printers work differently than the more familiar extrusion-based 3-D printers, which create objects by squeezing melted plastic through a needle as Researchers from TU Delft in The Netherlands, in collaboration with a team at the University of Cambridge (U.K.), have found a way to create and clean tiny mechanical sensors in a scalable manner. They created these sensors by suspending a two-dimensional sheet of hexagonal boron nitride (h-bn), or 'white graphene' over small holes in a silicon substrate. This innovation could lead to extremely small gas and pressure sensors for future electronics. Hexagonal boron nitride (h-bn) is an interesting material with a honeycomb lattice structure similar to that of graphite. But while graphite conducts electricity, while h-bn acts as an insulator. This property makes h-bn popular as a high-end lubricant, especially in industrial applications where electrical conductivity is undesirable. Since h-bn has the added benefit of being chemically and thermally more stable than graphite, it is also used in harsh environments such as space, for 28

37 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) example, in deep ultraviolet applications. Sticky stuff While layers of the two-dimensional material graphene can be exfoliated from graphite with sticky tape, creating single layers of h-bn is much more difficult. The reason for this is that the layers that make up h-bn 'stick' to one another and other materials much more strongly than layers of graphene do. Thus, not many researchers have been able to study the properties of h-bn as a 2-D material until now. "There are only two or three institutions in the world that can produce single, two-dimensional layers of white graphite, and the University of Cambridge is one of them," said lead author Santiago J. Cartamil-Bueno. "This project is a success thanks to our effective collaboration with them." Using a technique called chemical vapour deposition, researchers at the University of Cambridge grew a one-atom-thick sheet of h-bn, or 'white graphene," onto a piece of iron foil. They then mailed it to TU Delft in The Netherlands. There, through a series of steps, the Delft researchers transferred the sheet of transparent white graphene onto a silicon substrate containing tiny circular cavities. By doing so, they created microscopic 'drums". These drums function as mechanical resonators and could be used as infinitesimal gas or pressure sensors, for instance in mobile phones. Cleaning the drums While creating the h-bn drums was a significant challenge in itself, this project posed another, even bigger challenge. As a result of the steps needed to transfer the monoatomic sheet onto the silicon substrate, the drums were contaminated with a number of polymers. Common contaminations such as this are undesirable since they change the properties of the sensors. The result is that all of the sensors may behave slightly differently. "In order to outperform the normal sensors in the market, however, it is important that all 2-D sensors behave in exactly the same way," Cartamil-Bueno explains. The Delft researchers found a solution: Using ozone gas, they managed to clean the drums. The aggressive gas removed all of the organic polymers. However, traces of PMMA, a polymer with inorganic components, were left behind on the resonators. "Fortunately, this problem can be solved by only using organic substrates while transferring the sheet of white graphite onto the cavities," says Cartamil-Bueno. Thus, the Delft researchers have provided proof of principle for the fabrication of incredibly small sensors for future electronics. hene.html 30. A way to engineer photoactive junctions in iron-chloride-intercalated graphene using a laser Short-circuit configuration (top) for scanning photocurrent measurements of a p-p -p junction (p-p region in green). Schematic band structure (bottom) of each region shows photogenerated carriers drifting under a chemical potential gradient. A combined team of researchers from the University of Exeter in the U.K and the Institut de Ciències Fotòniques in Spain has found a way to create a material that takes pictures inside hostile environments such as nuclear reactors. In their paper published on the open access site Science Advances, the group explains how they made the new material, how well it works, and future applications. As some scientists invent new ways to produce power, such as nuclear reactors, other scientists refashion old technology or develop something new to keep such systems under control this includes developing cameras that could operate inside of a reactor to allow administrators to actually see what is going on inside. As the researchers note, one promising area of study is using graphene as a flexible photodetector, but as they also note, the limited power of such devices and their low resolution leave much to be desired recent research has led to doping of graphene to improve its limitations. In this new effort, the researchers started where other teams left off, with iron-chloride molecules added between graphene layers resulting in FeCl3-intercalated few-layer graphene (FLG). To use the FLG as a photodetection device, the researchers applied a laser to extract some of the FeCl3 molecules, resulting in junctions left between sections of the material. Shining a light on the junctions, the researchers report, showed current moving across the material, just like a pixel in a traditional camera one that is not dominated, they point out, by the photothermoelectric effect. This means that the material could conceivably be used inside of a nuclear reactor or in other environments where high-energy lasers are used, such as one utilizing fusion as an energy source. The team reports also that the size of junctions created in the material are dependent on the laser that is used to make them they were able to create junctions just 250nm wide. They plan to continue their research with the material, looking first to determine if it would be 29

38 纳米物理与材料 feasible to produce large enough sheets of the material to create an actual camera. Abstract Graphene-based photodetectors have demonstrated mechanical flexibility, large operating bandwidth, and broadband spectral response. However, their linear dynamic range (LDR) is limited by graphene's intrinsic hot-carrier dynamics, which causes deviation from a linear photoresponse at low incident powers. At the same time, multiplication of hot carriers causes the photoactive region to be smeared over distances of a few micrometers, limiting the use of graphene in high-resolution applications. We present a novel method for engineering photoactive junctions in FeCl3-intercalated graphene using laser irradiation. Photocurrent measured at these planar junctions shows an extraordinary linear response with an LDR value at least 4500 times larger than that of other graphene devices (44 db) while maintaining high stability against environmental contamination without the need for encapsulation. The observed photoresponse is purely photovoltaic, demonstrating complete quenching of hot-carrier effects. These results pave the way toward the design of ultrathin photodetectors with unprecedented LDR for high-definition imaging and sensing. on-chloride-intercalated-graphene-laser.html 31. Scientists detect light-matter interaction in single layer of atoms University of Central Florida Professor Aristide Dogariu led a research team that conducted the first demonstration of an elastic scattering, near-field experiment performed on a single layer of atoms. University of Central Florida researchers have developed a new and better way of detecting interactions between light and matter at the atomic level, a discovery that could lead to advances in the emerging field of two-dimensional materials and new ways of controlling light. Scientists typically use spectrometry tools to study the way light interacts with a gas, liquid or solid. That method is described as "inelastic," meaning the light's energy is altered by its contact with matter. A team led by Professor Aristide Dogariu of UCF's CREOL, The College of Optics & Photonics, has pioneered a way to detecting such interaction on a single layer of atoms - an exceedingly hard task because of the atom's minute size - using a method that's "elastic." That means the light's energy remains unchanged. "Our experiment establishes that, even at atomic levels, a statistical optics-based measurement has practical capabilities unrivaled by conventional approaches," Dogariu said. As reported this month in Optica, the academic journal of The Optical Society, it's the first demonstration of an elastic scattering, near-field experiment performed on a single layer of atoms. The researchers demonstrate this novel and fundamental phenomenon using graphene, a two-dimensional, crystalline material. Their technique involved random illumination of the atomic monolayer from all possible directions and then analyzing how the statistical properties of the input light are influenced by miniscule defects in the atomic layer. The method provided scientists not only with a simple and robust way to assess structural properties of 2D materials but also with new means for controlling the complex properties of optical radiation at subwavelength scales. The team's finding that its method is superior to conventional ones is of broad interest to the physics community. Beyond that, it could lead to other advances. Graphene and other two-dimensional materials have properties that researchers are trying to leverage for use in display screens, batteries, capacitors, solar cells and more. But their effectiveness can be limited by impurities and finding those defects requires sophisticated microscopy techniques that are sometimes impractical. Dogariu's research has yielded a more effective way of discovering those defects a potentially valuable technique for industry. The finding that a single layer of atoms modifies properties of light and other electromagnetic radiation has implications for controlling light at subwavelength scales in photonic devices such as LEDs and photovoltaic cells. teraction-layer-atoms.html 32. Researchers measure light fields in 3-D 3D image of plasmon fields on nanparticles. 30

39 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) Researchers from TU Graz and the University of Graz present the new method of 3-D-plasmon tomography in Nature Communications. Light as a carrier of information is indispensable to modern communication technology. The controlled manipulation of light quanta, so-called photons, form the basis for wireless transmission or data transfer in optical glass fibres. Due to the wave-like nature of light and its diffraction limit, however, optical components can only focus light down to the micron scale (10-6 m). Ulrich Hohenester from the Institute of Physics at the University of Graz explains: "To enable photons and nanostructures to interact more efficiently, in the research field of plasmonics, we couple light onto a metallic nanoparticle, typically made out of gold or silver." Depending on size, shape, environment and material, resonating clouds of electrons are formed so-called surface plasmons. Hohenester continues: "This collective electron vibration enables us to focus light at the nano scale and so use a variety of applications in sensor technology and photovoltaics." Imaging plasmon fields The direct observation of plasmon fields is only possible thanks to Austria's most powerful electron microscope the ASTEM, Austrian Scanning Transmission Electron Microscope, at the Graz Centre for Electron Microscopy. In the last few years, electron microscopy has developed into an ideal method for measuring plasmon fields. Gerald Kothleitner, head of the Working Group for Analytic Transmission Electron Microscopy at TU Graz's Institute of Electron Microscopy and Nanoanalysis, elaborates: "A high-energy electron beam moves near the sample or penetrates it. Electrons in the vicinity of the sample experience a loss of energy, something we can measure spectroscopically. This results in two- dimensional images of plasmon fields at sub-nanometre resolution. Information about the third dimension along which the electrons move is lost in this method." Breakthrough in 3-D In the present work which has been published in the open access journal Nature Communications, the NAWI Graz researchers could show for the first time how the third dimension can be reconstructed completely in the framework of a tomographic imaging process by rotating the sample and processing a series of tilted two-dimensional projections. This method works similarly to the computer tomography used in medicine and appropriately bears the name 3-D-plasmon tomography. Kothleitner and Hohenester on the effects of their successful research: "By using this novel method it is now possible to measure plasmon fields in a way that will help better understand applications in the fields of sensor technology, solar cell technology and computer storage or even lead to new ones." A levitated nanosphere as an ultra-sensitive sensor A microscope objective (right) focuses laser light to create the optical tweezers in which a nanosphere (tiny red dot in the centre of the image) is levitated. Sensitive sensors must be isolated from their environment as much as possible to avoid disturbances. Scientists at ETH Zurich have now demonstrated how to remove from and add elementary charges to a nanosphere that can be used for measuring extremely weak forces. A tiny sphere and a laser beam inside of which it hovers as if by magic with these simple ingredients Martin Frimmer and co-workers at the Photonics Laboratory of ETH Zurich have developed a highly sensitive sensor. In the future this device is expected to measure, amongst other things, extremely weak forces or electric fields very precisely. Now the researchers have taken a major step in that direction, as they write in a recently published scientific paper. Nanosphere in a laser beam Martin Frimmer, a post-doctoral researcher in the group of ETH professor Lukas Novotny, explains the working principle of a sensor very plausibly: "First I need to know how the object acting as a sensor is influenced by its environment. Anything that happens beyond that influence tells me: there is a force at work." In practice this usually means that interactions with the environment should be kept at a minimum in order to maximize the sensitivity of the sensor to the forces one wants to measure. The scientists achieved precisely that by trapping a silica nanoparticle, whose diameter is about a hundred times smaller than a human hair, using a focused laser beam. The beam creates "optical tweezers" in which the nanosphere is held in the focus of the beam by light forces. If an additional force acts on the sphere, it is shifted from is rest position, which in turn can be measured with the help of a laser beam. Discharging by high voltage Since the optical tweezers keep the nanosphere hovering in midair without any mechanical contact, the influence of the environment can easily be reduced to a minimum. To do so, Frimmer and his team place the optical tweezers inside a vacuum chamber so that there are virtually no more collisions with air molecules. The only thing left now that could create a disturbance is a possible electric charge on the nanoparticle. Owing to 31

40 纳米物理与材料 such a charge, insufficiently screened electric fields could influence the sphere and, therefore, a possible measurement. For this reason the ETH researchers have now developed a simple but highly efficient method by which the charge on the sphere can be neutralised. To this end they mounted a wire inside the vacuum chamber that was connected to a 7000 volt high-voltage generator. The high voltage caused the air molecules to be ionized, i.e., to be split into negatively charged electrons and positively charged ions. Either of those could now jump onto the nanosphere and make its charge more positive or more negative. To measure the charge carried by the sphere at any given moment, the physicists exposed it to an oscillating electric field and observed how strongly the sphere reacted to that. In this way they were able to confirm that the charge of the sphere changed in steps of exactly one elementary charge (i.e., the charge of an electron) to the negative or to the positive. When the high voltage is switched off, the sphere's instantaneous charge remains constant for days. Gravity and quantum mechanics This perfect control allows the scientists to completely neutralize the electric charge on the nanoparticle. As a result, electric fields no longer have any effect on the sphere, which makes it possible to precisely measure other very weak forces. One such force is gravity. Martin Frimmer speculates, albeit cautiously, that in future the nano-sensor he developed should enable studies of the interplay between gravity and quantum mechanics. By clever manipulation of the optical tweezers the researchers can already cool the sphere down to below a ten thousandth of a degree above absolute zero. For even lower temperatures the nanoparticle is expected to start behaving quantum mechanically, so that phenomena such as quantum superpositions and their dependence on gravity can be observed. Interesting applications of the sensor also present themselves in everyday contexts, such as the measurement of accelerations. Since the charge of the nanosphere cannot only be neutralized, but also set to a well-defined value at will, the sensor is equally suitable for precision measurements of electric fields. ra-sensitive-sensor.html 34. Optical nanomotors: Tiny 'motors' are driven by light Researchers have created in simulations the first system in which can be manipulated by a beam of ordinary light rather than the expensive specialized light sources required by other systems. Science fiction is full of fanciful devices that allow light to interact forcefully with matter, from light sabers to photon-drive rockets. In recent years, science has begun to catch up; some results hint at interesting real-world interactions between light and matter at atomic scales, and researchers have produced devices such as optical tractor beams, tweezers, and vortex beams. Now, a team at MIT and elsewhere has pushed through another boundary in the quest for such exotic contraptions, by creating in simulations the first system in which particles ranging from roughly molecule- to bacteria-sized can be manipulated by a beam of ordinary light rather than the expensive specialized light sources required by other systems. The findings are reported today in the journal Science Advances, by MIT postdocs Ognjen Ilic PhD '15, Ido Kaminer, and Bo Zhen; professor of physics Marin Soljacic; and two others. Most research that attempts to manipulate matter with light, whether by pushing away individual atoms or small particles, attracting them, or spinning them around, involves the use of sophisticated laser beams or other specialized equipment that severely limits the kinds of uses of such systems can be applied to. "Our approach is to look at whether we can get all these interesting mechanical effects, but with very simple light," Ilic says. The team decided to work on engineering the particles themselves, rather than the light beams, to get them to respond to ordinary light in particular ways. As their initial test, the researchers created simulated asymmetrical particles, called Janus (two-faced) particles, just a micrometer in diameter one-hundredth the width of a human hair. These tiny spheres were composed of a silica core coated on side with a thin layer of gold. When exposed to a beam of light, the two-sided configuration of these particles causes an interaction that shifts their axes of symmetry relative to the orientation of the beam, the researchers found. At the same time, this interaction creates forces that set the particles spinning uniformly. Multiple particles can all be affected at once by the same beam. And the rate of spin can be changed by just changing the color of the light. The same kind of system, the researchers, say, could be applied to producing different kinds of manipulations, such as moving the positions of the particles. Ultimately, this new principle might be applied to moving particles around inside a body, using light to control their position and activity, for new medical treatments. It might also find uses in optically based nanomachinery. About the growing number of approaches to controlling interactions between light and material objects, Kaminer says, "I think about this as a new tool 32

41 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) in the arsenal, and a very significant one." Ilic says the study "enables dynamics that may not be achieved by the conventional approach of shaping the beam of light," and could make possible a wide range of applications that are hard to foresee at this point. For example, in many potential applications, such as biological uses, nanoparticles may be moving in an incredibly complex, changing environment that would distort and scatter the beams needed for other kinds of particle manipulation. But these conditions would not matter to the simple light beams needed to activate the team's asymmetric particles. "Because our approach does not require shaping of the light field, a single beam of light can simultaneously actuate a large number of particles," Ilic says. "Achieving this type of behavior would be of considerable interest to the community of scientists studying optical manipulation of nanoparticles and molecular machines." Kaminer adds, "There's an advantage in controlling large numbers of particles at once. It's a unique opportunity we have here." Soljacic says this work fits into the area of topological physics, a burgeoning area of research that also led to last year's Nobel Prize in physics. Most such work, though, has been focused on fairly specialized conditions that can exist in certain exotic materials called periodic media. "In contrast, our work investigates topological phenomena in particles," he says. And this is just the start, the team suggests. This initial set of simulations only addressed the effects with a very simple two-sided particle. "I think the most exciting thing for us," Kaminer says, "is there's an enormous field of opportunities here. With such a simple particle showing such complex dynamics," he says, it's hard to imagine what will be possible "with an enormous range of particles and shapes and structures we can explore." -motors-driven.html 五. 量子物理 35. Testing quantum field theory in a quantum simulator experiments. Now, there is a new way of putting them to the test. Scientists have created a quantum system consisting of thousands of ultra cold atoms. By keeping them in a magnetic trap on an atom chip, this atom cloud can be used as a 'quantum simulator', which yields new insights into some of the most fundamental questions of physics. What happened right after the beginning of the universe? How can we understand the structure of quantum materials? How does the Higgs-Mechanism work? Such fundamental questions can only be answered using quantum field theories. These theories do not describe particles independently from each other; all particles are seen as a collective field, permeating the whole universe. But these theories are often hard to test in an experiment. At the Vienna Center for Quantum Science and Technology (VCQ) at TU Wien, researchers have now demonstrated how quantum field theories can be put to the test in new kinds of experiments. They have created a quantum system consisting of thousands of ultra cold atoms. By keeping them in a magnetic trap on an atom chip, this atom cloud can be used as a "quantum simulator", which yields information about a variety of different physical systems and new insights into some of the most fundamental questions of physics. Complex Quantum Systems More than the Sum of their Parts "Ultra cold atoms open up a door to recreate and study fundamental quantum processes in the lab", says Professor Jörg Schmiedmayer (VCQ, TU Wien). A characteristic feature of such a system is that its parts cannot be studied independently. The classical systems we know from daily experience are quite different: The trajectories of the balls on a billiard table can be studied separately the balls only interact when they collide. "In a highly correlated quantum system such as ours, made of thousands of particles, the complexity is so high that a description in terms of its fundamental constituents is mathematically impossible", says Thomas Schweigler, the first author of the paper. "Instead, we describe the system in terms of collective processes in which many particles take part similar to waves in a liquid, which are also made up of countless molecules." These collective processes can now be studied in unprecedented detail using the new methods. Experiments at TU Wien (Vienna) -- with a quantum chip, controlling a cloud of atoms. Quantum field theories are often hard to verify in The atom chip at TU Wien (Vienna). 33

42 量子物理 In high-precision measurements, it turns out that the probability of finding an individual atom is not the same at each point in space and there are intriguing relationships between the different probabilities. "When we have a classical gas and we measure two particles at two separate locations, this result does not influence the probability of finding a third particle at a third point in space", says Jörg Schmiedmayer. "But in quantum physics, there are subtle connections between measurements at different points in space. These correlations tell us about the fundamental laws of nature which determine the behaviour of the atom cloud on a quantum level." "The so-called correlation functions, which are used to mathematically describe these relationships, are an extremely important tool in theoretical physics to characterize quantum systems", says Professor Jürgen Berges (Institute for Theoretical Physics, Heidelberg University). But even though they have played an important part in theoretical physics for a long time, these correlations could hardly be measured in experiments. With the help of the new methods developed at TU Wien, this is now changing: "We can study correlations of different orders - up to the tenth order. This means that we can investigate the relation between simultaneous measurements at ten different points in space", Schmiedmayer explains. "For describing the quantum system, it is very important whether these higher correlations can be represented by correlations of lower order in this case, they can be neglected at some point or whether they contain new information." Quantum Simulators Using such highly correlated systems like the atom cloud in the magnetic trap, various theories can now be tested in a well-controlled environment. This allows us to gain a deep understanding of the nature of quantum correlations. This is especially important because quantum correlations play a crucial role in many, seemingly unrelated physics questions: Examples are the peculiar behaviour of the young universe right after the big bang, but also for special new materials, such as the so-called topological insulators. Important information on such physical systems can be gained by recreating similar conditions in a model system, like the atom clouds. This is the basic idea of quantum simulators: Much like computer simulations, which yield data from which we can learn something about the physical world, a quantum simulation can yield results about a different quantum system that cannot be directly accessed in the lab. The study is published in the journal Nature. mulator.html 36. A stream of superfluid light The flow of polaritons encounters an obstacle in the supersonic (top) and superfluid (bottom) regime. Scientists have known for centuries that light is composed of waves. The fact that light can also behave as a liquid, rippling and spiraling around obstacles like the current of a river, is a much more recent finding that is still a subject of active research. The "liquid" properties of light emerge under special circumstances, when the photons that form the light wave are able to interact with each other Researchers from CNR NANOTEC of Lecce in Italy, in collaboration with Polytechnique Montreal in Canada have shown that for light "dressed" with electrons, an even more dramatic effect occurs. Light become superfluid, showing frictionless flow when flowing across an obstacle and reconnecting behind it without any ripples. Daniele Sanvitto, leading the experimental research group that observed this phenomenon, states that "Superfluidity is an impressive effect, normally observed only at temperatures close to absolute zero (-273 degrees Celsius), such as in liquid Helium and ultracold atomic gasses. The extraordinary observation in our work is that we have demonstrated that superfluidity can also occur at room-temperature, under ambient conditions, using light-matter particles called polaritons." "Superfluidity, which allows a fluid in the absence of viscosity to literally leak out of its container", adds Sanvitto, "is linked to the ability of all the particles to condense in a state called a Bose-Einstein condensate, also known as the fifth state of matter, in which particles behave like a single macroscopic wave, oscillating all at the same frequency. Scientists have known for centuries that light is composed of waves. The fact that light can also behave as a liquid, rippling and spiraling around obstacles like the current of a river, is a much more recent finding that is still a subject of active research. The 'liquid' properties of light emerge under special 34

43 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) circumstances, when the photons that form the light wave are able to interact with each other. Something similar happens, for example, in superconductors: electrons, in pairs, condense, giving rise to superfluids or super-currents able to conduct electricity without losses." These experiments have shown that it is possible to obtain superfluidity at room-temperature, whereas until now this property was achievable only at temperatures close to absolute zero. This could allow for its use in future photonic devices. Stéphane Kéna-Cohen, the coordinator of the Montreal team, states: "To achieve superfluidity at room temperature, we sandwiched an ultrathin film of organic molecules between two highly reflective mirrors. Light interacts very strongly with the molecules as it bounces back and forth between the mirrors and this allowed us to form the hybrid light-matter fluid. In this way, we can combine the properties of photons such as their light effective mass and fast velocity, with strong interactions due to the electrons within the molecules. Under normal conditions, a fluid ripples and whirls around anything that interferes with its flow. In a superfluid, this turbulence is suppressed around obstacles, causing the flow to continue on its way unaltered". "The fact that such an effect is observed under ambient conditions", says the research team, "can spark an enormous amount of future work, not only to study fundamental phenomena related to Bose-Einstein condensates with table-top experiments, but also to conceive and design future photonic superfluid-based devices where losses are completely suppressed and new unexpected phenomena can be exploited". The study is published in Nature Physics Prototype device enables photon-photon interactions at room temperature for quantum computing A micrograph of the MIT researchers new device, with a visualization of electrical-energy measurements and a schematic of the device layout superimposed on it. Ordinarily, light particles photons don't interact. If two photons collide in a vacuum, they simply pass through each other. An efficient way to make photons interact could open new prospects for both classical optics and quantum computing, an experimental technology that promises large speedups on some types of calculations. In recent years, physicists have enabled photon-photon interactions using atoms of rare elements cooled to very low temperatures. But in the latest issue of Physical Review Letters, MIT researchers describe a new technique for enabling photon-photon interactions at room temperature, using a silicon crystal with distinctive patterns etched into it. In physics jargon, the crystal introduces "nonlinearities" into the transmission of an optical signal. "All of these approaches that had atoms or atom-like particles require low temperatures and work over a narrow frequency band," says Dirk Englund, an associate professor of electrical engineering and computer science at MIT and senior author on the new paper. "It's been a holy grail to come up with methods to realize single-photon-level nonlinearities at room temperature under ambient conditions." Joining Englund on the paper are Hyeongrak Choi, a graduate student in electrical engineering and computer science, and Mikkel Heuck, who was a postdoc in Englund's lab when the work was done and is now at the Technical University of Denmark. Photonic independence Quantum computers harness a strange physical property called "superposition," in which a quantum particle can be said to inhabit two contradictory states at the same time. The spin, or magnetic orientation, of an electron, for instance, could be both up and down at the same time; the polarization of a photon could be both vertical and horizontal. If a string of quantum bits or qubits, the quantum analog of the bits in a classical computer is in superposition, it can, in some sense, canvass multiple solutions to the same problem simultaneously, which is why quantum computers promise speedups. Most experimental qubits use ions trapped in oscillating magnetic fields, superconducting circuits, or like Englund's own research defects in the crystal structure of diamonds. With all these technologies, however, superpositions are difficult to maintain. Because photons aren't very susceptible to interactions with the environment, they're great at maintaining superposition; but for the same reason, they're difficult to control. And quantum computing depends on the ability to send control signals to the qubits. That's where the MIT researchers' new work comes in. If a single photon enters their device, it will pass through unimpeded. But if two photons in the right quantum states try to enter the device, they'll be reflected back. The quantum state of one of the photons can thus be thought of as controlling the quantum state of the other. And quantum information theory has established that simple quantum "gates" of this type are all that is necessary to build a universal quantum computer. 35

44 技术与应用 Unsympathetic resonance The researchers' device consists of a long, narrow, rectangular silicon crystal with regularly spaced holes etched into it. The holes are widest at the ends of the rectangle, and they narrow toward its center. Connecting the two middle holes is an even narrower channel, and at its center, on opposite sides, are two sharp concentric tips. The pattern of holes temporarily traps light in the device, and the concentric tips concentrate the electric field of the trapped light. The researchers prototyped the device and showed that it both confined light and concentrated the light's electric field to the degree predicted by their theoretical models. But turning the device into a quantum gate would require another component, a dielectric sandwiched between the tips. (A dielectric is a material that is ordinarily electrically insulating but will become polarized all its positive and negative charges will align in the same direction when exposed to an electric field.) When a light wave passes close to a dielectric, its electric field will slightly displace the electrons of the dielectric's atoms. When the electrons spring back, they wobble, like a child's swing when it's pushed too hard. This is the nonlinearity that the researchers' system exploits. The size and spacing of the holes in the device are tailored to a specific light frequency the device's "resonance frequency." But the nonlinear wobbling of the dielectric's electrons should shift that frequency. Ordinarily, that shift is mild enough to be negligible. But because the sharp tips in the researchers' device concentrate the electric fields of entering photons, they also exaggerate the shift. A single photon could still get through the device. But if two photons attempted to enter it, the shift would be so dramatic that they'd be repulsed. Practical potential The device can be configured so that the dramatic shift in resonance frequency occurs only if the photons attempting to enter it have particular quantum properties specific combinations of polarization or phase, for instance. The quantum state of one photon could thus determine the way in which the other photon is handled, the basic requirement for a quantum gate. Englund emphasizes that the new research will not yield a working quantum computer in the immediate future. Too often, light entering the prototype is still either scattered or absorbed, and the quantum states of the photons can become slightly distorted. But other applications may be more feasible in the near term. For instance, a version of the device could provide a reliable source of single photons, which would greatly abet a range of research in quantum information science and communications. "This work is quite remarkable and unique because it shows strong light-matter interaction, localization of light, and relatively long-time storage of photons at such a tiny scale in a semiconductor," says Mohammad Soltani, a nanophotonics researcher in Raytheon BBN Technologies' Quantum Information Processing Group. "It can enable things that were questionable before, like nonlinear single-photon gates for quantum information. It works at room temperature, it's solid-state, and it's compatible with semiconductor manufacturing. This work is among the most promising to date for practical devices, such as quantum information devices." s-photon-photon-interactions.html 六. 技术与应用 38. New design improves performance of flexible wearable electronics NC State's thermoelectric harvester has the material quality of rigid devices inside a flexible package. In a proof-of-concept study, North Carolina State University engineers have designed a flexible thermoelectric energy harvester that has the potential to rival the effectiveness of existing power wearable electronic devices using body heat as the only source of energy. Wearable devices used to monitor a variety of health and environmental measures are becoming increasingly popular. The performance and efficiency of flexible devices, however, pale in comparison to rigid devices, which have been superior in their ability to convert body heat into usable energy. "We wanted to design a flexible thermoelectric harvester that does not compromise on the material quality of rigid devices yet provides similar or better efficiency," said Mehmet Ozturk, a professor of electrical and computer engineering at NC State and corresponding author of a paper describing the work. "Using rigid devices is not the best option when you consider a number of different factors." Ozturk mentioned superior contact resistance - or skin contact - with flexible devices, as well as the ergonomic and comfort considerations to the device wearer. Ozturk said that he and colleagues Michael Dickey and Daryoosh Vashaee wanted to utilize the best thermoelectric materials used in rigid devices in a flexible package, so that manufacturers wouldn't need to develop new materials when creating flexible devices. 36

45 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) Liquid metal in the flexible thermoelectric device allows for self-healing. Rigid devices do not have the ability to heal themselves. Ozturk said one of the key challenges of a flexible harvester is to connect thermoelectric elements in series using reliable, low-resistivity interconnects. "We use a liquid metal of gallium and indium - a common, non-toxic alloy called EGaIn - to connect the thermoelectric 'legs,'" Ozturk said. "The electric resistance of these connections is very low, which is critical since the generated power is inversely proportional to the resistance: Low resistance means more power. "Using liquid metal also adds a self-healing function: If a connection is broken, the liquid metal will reconnect to make the device work efficiently again. Rigid devices are not able to heal themselves," Ozturk added. Ozturk said future work will focus on improving the efficiencies of these flexible devices, by using materials and techniques to further eliminate parasitic resistances. Dickey, Vashaee, Francisco Suarez, Dishit P. Parekh and Collin Ladd co-authored the paper, which appears in Applied Energy. The group also has a pending patent application on the technology. onics.html 39. World's smallest and most accurate 3-D-printed biopsy robot of tissue) during a breast cancer scan in an MRI significantly increases accuracy. The robot won a prestigious award during the Surgical Robotic Challenge at the international Hamlyn Symposium in London: one of the world's most important events in the field of robotic surgery. The Stormram 4 is a stimulus for the entire diagnostic phase of breast cancer; the accurate needle control, effectively real-time MRI scanning and a single, thin-needle biopsy enable quicker and more accurate diagnoses to be made. Medical robotics is sure to become standard procedure in hospitals in the near future. Stormram 4 The Stormram 4 is driven by rectilinear and curved air-pressure motors. The robot is controlled from outside the MRI scanner by means of 5-metre-long air pipes. The design is smaller than the previous version, enabling it to fit inside the MRI scanner's narrow tunnel. Biopsy Breast cancer is the most common form of cancer among women. By inserting a needle in the patient's breast and navigating to the abnormal tissue (lesion), it is possible to take a tissue sample. A good diagnosis is made possible through subsequent clinical analysis; a process known as a biopsy. S 4 controller. No invasive surgery Accurate navigation of the biopsy needle is of crucial importance in combating breast cancer and other forms of cancer. Through the use of special needles, the tip of which can be very hot (thermal ablation) or very cold (cryoablation), it is possible to destroy tumour cells close to the tip of the needle. This enables the treatment of cancer without the need for invasive surgical procedures. S 4 side wide annotated. The world's smallest and most accurate 3-D-printed biopsy robot was revealed last week. The Stormram 4, as the robot is named, is made from 3-D-printed plastic and is driven by air pressure. The advantage of plastic is that the robot can be used in an MRI scanner. Carrying out a biopsy (removing a piece S 4 side wide. Robotics is the solution MRI scanners are the answer when it comes to the extremely accurate detection and visualisation of the 37

46 技术与应用 location of abnormal tissue. Unfortunately, it is not possible to make full use of this accuracy as long as needles are controlled by hand. Robotics offers the solution. Not all robots can be used in combination with MRI scanners. Robots are often made of metal, a material that cannot be used in the strong magnetic fields of MRI scanners. For this reason, the UT, in collaboration with Ziekenhuis Groep Twente (ZGT), has made the robot entirely of plastic. -d-printed-biopsy.html 40. First atomic structure of an intact virus deciphered with an X-ray laser Schematic of the experimental set-up: The chip loaded with nanocrystals is scanned by the fine X-ray beam (green) pore by pore. Ideally, each crystal produces a distinctive diffraction pattern. An international team of scientists has for the first time used an X-ray free-electron laser to unravel the structure of an intact virus particle on the atomic level. The method used dramatically reduces the amount of virus material required, while also allowing the investigations to be carried out several times faster than before. This opens up entirely new research opportunities, as the research team lead by DESY scientist Alke Meents reports in the journal Nature Methods. In the field known as structural biology, scientists examine the three-dimensional structure of biological molecules in order to work out how they function. This knowledge enhances our understanding of the fundamental biological processes taking place inside organisms, such as the way in which substances are transported in and out of a cell, and can also be used to develop new drugs. "Knowing the three-dimensional structure of a molecule like a protein gives great insight into its biological behaviour," explains co-author David Stuart, Director of Life Sciences at the synchrotron facility Diamond Light Source in the UK and a professor at the University of Oxford. "One example is how understanding the structure of a protein that a virus uses to 'hook' onto a cell could mean that we're able to design a defence for the cell to make the virus incapable of attacking it." X-ray crystallography is by far the most prolific tool used by structural biologists and has already revealed the structures of thousands of biological molecules. Tiny crystals of the protein of interest are grown, and then illuminated using high-energy X-rays. The crystals diffract the X-rays in characteristic ways so that the resulting diffraction patterns can be used to deduce the spatial structure of the crystal - and hence of its components - on the atomic scale. However, protein crystals are nowhere near as stable and sturdy as salt crystals, for example. They are difficult to grow, often remaining tiny, and are easily damaged by the X-rays. "X-ray lasers have opened up a new path to protein crystallography, because their extremely intense pulses can be used to analyse even extremely tiny crystals that would not produce a sufficiently bright diffraction image using other X-ray sources," adds co-author Armin Wagner from Diamond Light Source. However, each of these microcrystals can only produce a single diffraction image before it evaporates as a result of the X-ray pulse. To perform the structural analysis, though, hundreds or even thousands of diffraction images are needed. In such experiments, scientists therefore inject a fine liquid jet of protein crystals through a pulsed X-ray laser, which releases a rapid sequence of extremely short bursts. Each time an X-ray pulse happens to strike a microcrystal, a diffraction image is produced and recorded. This method is very successful and has already been used to determine the structure of more than 80 biomolecules. However, most of the sample material is wasted. "The hit rate is typically less than two per cent of pulses, so most of the precious microcrystals end up unused in the collection container," says Meents, who is based at the Center for Free-Electron Laser Science (CFEL) in Hamburg, a cooperation of DESY, the University of Hamburg and the German Max Planck Society. The standard method therefore typically requires several hours of beamtime and significant amounts of sample material. In order to use the limited beamtime and the precious sample material more efficiently, the team developed a new method. The scientists use a micro-patterned chip containing thousands of tiny pores to hold the protein crystals. The X-ray laser then scans the chip line by line, and ideally this allows a diffraction image to be recorded for each pulse of the laser. The research team tested its method on two different virus samples using the LCLS X-ray laser at the SLAC National Accelerator Laboratory in the US, which produces 120 pulses per second. They loaded their sample holder with a small amount of microcrystals of the bovine enterovirus 2 (BEV2), a virus that can cause miscarriages, stillbirths, and infertility in cattle, and which is very difficult to crystallise. In this experiment, the scientists achieved a hit rate - where the X-ray laser successfully targeted the crystal - of up to nine per cent. Within just 14 minutes they had collected enough data to determine the correct structure 38

47 光电技术情报 2017 年第 7 期 ( 总第 32 期 ) of the virus - which was already known from experiments at other X-ray light sources - down to a scale of 0.23 nanometres (millionths of a millimetre). "To the best of our knowledge, this is the first time the atomic structure of an intact virus particle has been determined using an X-ray laser," Meents points out. "Whereas earlier methods at other X-ray light sources required crystals with a total volume of 3.5 nanolitres, we managed using crystals that were more than ten times smaller, having a total volume of just 0.23 nanolitres." This experiment was conducted at room temperature. While cooling the protein crystals would protect them to some extent from radiation damage, this is not generally feasible when working with extremely sensitive virus crystals. Crystals of isolated virus proteins can, however, be frozen, and in a second test, the researchers studied the viral protein polyhedrin that makes up a viral occlusion body for up to several thousands of virus particles of certain species. The virus particles use these containers to protect themselves against environmental influences and are therefore able to remain intact for much longer times. For the second test, the scientist loaded their chip with polyhedrin crystals and examined them using the X-ray laser while keeping the chip at temperatures below minus 180 degrees Celsius. Here, the scientists achieved a hit rate of up to 90 per cent. In just ten minutes they had recorded more than enough diffraction images to determine the protein structure to within 0.24 nanometres. "For the structure of polyhedrin, we only had to scan a single chip which was loaded with four micrograms of protein crystals; that is orders of magnitude less than the amount that would normally be needed," explains Meents. "Our approach not only reduces the data collection time and the quantity of the sample needed, it also opens up the opportunity of analysing entire viruses using X-ray lasers," Meents sums up. The scientists now want to increase the capacity of their chip by a factor of ten, from 22,500 to some 200,000 micropores, and further increase the scanning speed to up to one thousand samples per second. This would better exploit the potential of the new X-ray free-electron laser European XFEL, which is just going into operation in the Hamburg region and which will be able to produce up to 27,000 pulses per second. Furthermore, the next generation of chips will only expose those micropores that are currently being analysed, to prevent the remaining crystals from being damaged by scattered radiation from the X-ray laser. Researchers from the University of Oxford, the University of Eastern Finland, the Swiss Paul Scherrer Institute, the Lawrence Berkeley National Laboratory in the US and SLAC were also involved in the research. Diamond scientists have collaborated with the team at DESY, with much of the development and testing of the micro-patterned chip being done on Diamond's I02 and I24 beamlines. phered-x-ray.html 41. New prototypes for superconducting undulators show promise for more powerful, versatile X-ray beams Argonne and Berkeley national laboratories have collaborated to design, build and test two superconducting undulator devices that could make X-ray lasers more powerful, versatile, compact and durable. Above: Argonne Accelerator Systems Division engineer Matt Kasa checks the instrumentation of the undulator. Researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and Argonne National Laboratory have collaborated to design, build and test two devices that utilize different superconducting materials and could make X-ray lasers more powerful, versatile, compact and durable These prototype devices, called superconducting undulators (SCUs), successfully produced stronger magnetic fields than conventional permanent magnetic undulators of the same size. These fields, in turn, can produce higher-energy laser light to open up a broader range of experiments. Several large-scale X-ray lasers are in the works around the globe to allow scientists to probe the properties of matter at ever smaller and faster scales, and superconducting undulators are considered among the most enabling technologies for the next generation of these and other types of light sources. Such light sources are powerful tools for studying the microscopic structure and other properties of samples, such as proteins that are key to drug design, exotic materials relevant to electronics and energy applications, and chemistry that is central to industrial processes like fuel production. The recent development effort was motivated by SLAC National Accelerator Laboratory's upgrade of its Linac Coherent Light Source (LCLS), which is the nation's only X-ray free-electron laser (FEL). The new project, now underway, is known as LCLS-II. X-ray FELs now use permanent magnetic undulators to produce X-ray light by wiggling high-energy bunches of electrons in alternating magnetic fields produced by a sequence of permanent magnets. But for the first time, Argonne scientists have demonstrated that a superconducting undulator could be 39