Imaging & Microscopy

Transcription

1 Coherent X-ray X Imaging & Microscopy => Opportunities Using a Diffraction-Limited Energy Recovery Linac (ERL) Synchrotron Source Q. Shen D. Bilderback, K.D. Finkelstein, E. Fontes, & S. Gruner Cornell High Energy Synchrotron Source (CHESS) Cornell University, Ithaca, New York 14853, USA Talk Outline Introduction of ERL Benefits to XRM Coherent microscopy examples Conclusions

2 Growth in Synchrotron Radiation Science

3 Storage-Ring Based vs. Energy Recovery Linac Sources M. Tigner, Nuovo Cimento 37, 1228 (1965) Accelerating Returning Storage-Ring 400 m Mature and well-understood Equilibrium of stored beam in entire ring ~ 10,000 turns to reach equilibrium Emission of synchrotron radiation Perturbations on electron trajectories Limits on E, emittance, bunch length ERL Single-pass non-equilibrium device Low emittance and short pulses from injector Ultra-small round beam Ultra-high brilliance and coherence

4 Preliminary Design Parameters of ERL ERL high-flux ERL high-coherence Machine design Insertion device Energy E G (GeV) Current I (ma) Charge q (nc/bunch) ε x (nm-rad) ε y (nm-rad) Bunch fwhm τ (ps) # of bunches f (Hz) Undulator L (m) Period λ u (cm) # of period N u Horizontal β x (m) Vertical β y (m) Undulator E st harmonic E 1 (kev)

5 ERL: Expected Performance Average Brilliance (ph/s/0.1%/mm 2 /mr 2 ) LCLS SASE Sp8 25m APS 4.8m APS 2.4m LCLS spont. Sp8 5m ESRF U35 CHESS 24p wiggler ERL 25m 0.015nm 10mA 0.15nm 100mA CHESS 49p wiggler Peak Brilliance (ph/s/0.1%/mm 2 /mr 2 ) nm 100mA 4.7ps Sp8 25m ESRF U35 Sp8 5m APS 2.4m CHESS 49-pole G/A-wiggler τ=153ps, f=17.6mhz (9x5) CHESS 24-pole F-wiggler ERL 25m 0.015nm 10mA 0.3ps 0.15nm 100mA 0.3ps Photon Energy (kev) Photon Energy (kev)

6 Cornell ERL Coherent Flux Coherent Flux (photons/s/0.1%) LCLS SASE APS 4.8m ESRF U35 APS 2.4m ERL 25m 0.015nm 10mA Sp8 25m 0.15nm 100mA Sp8 5m Time-averaged coherent flux comparable to LCLS XFEL Coherent fraction ~100x greater than 3rd SR sources Peak coherent flux (coherent flux per pulse) ~1000x greater than 3rd SR sources Photon Energy (kev)

7 ERL Spatial Coherence ESRF emittance (4nm x 0.01nm) Diffraction 8keV ERL emittance (0.015nm) Diffraction limited source: 2πσ'σ = λ/2 or ε = λ/4π Almost diffraction limited: 2πσ'σ ~ λ or ε ~ λ/2π Cornell ERL: : diffraction-limited source E < 6.6 kev almost diffraction-limited to 13 kev

8 Benefits of ERL to XRM Brings high coherence to hard x-ray regime Better optical performance for STXM & µ-probe Phase imaging & microscopy Far-field diffraction microscopy Holographic techniques Time-resolved and flash microscopy Larger depth of focus for tomography & 3D structures Coherent Crystallography, etc.

9 Issues in Hard X-ray X Microscopy Focusing optics Only recently has Fresnel zone-plate (FZP) achieved <100nm resolution at 8keV (Yun, 1999) Kirz (1995): 0.05µm protein in 10µm thick ice C 94 H 139 N 24 O 31 S High coherence sources: Coherence fraction ~ λ 2 /(ε x ε y ). => Requires 100x smaller emittance product for 1keV => 10 kev Dose (Gray) absorption contrast ERL would offer x better emittance product than present-day hard x-ray sources => Better kev kev at ALS 10 6 phase contrast Absorption vs. phase contrast Refraction index: n = 1 δ iβ absorption contrast: µz = 4πβz/λ phase contrast: φ(z) = 2πδz/λ z X-ray Energy (ev) In general, phase contrast requires: => coherent hard x-ray beams

10 Advantages of Hard X-ray X Microscopy Advantages of hard x-rays: x Much larger penetration depth, good for natural thick living specimens and materials science samples Larger depth of focus, which is necessary for 3D tomography Possibility of imaging in diffraction conditions for nanocrystals or thin specimens in materials science Access to higher-energy absorption edges for fluorescence imaging and element mapping

11 Phase Imaging & Tomography λ Cloetens et al. (1999): ESRF, ID19, 18 kev Polystyrene foam 0.7x0.5x1mm 3 1.4T wiggler, B~7x10 14 ph/s/mr 2 /mm 2 4x700 images at 25 sec/image A form of Gabor in-line holography Coherence over 1st Fresnel zone (λr) 1/2 Image reconstruction (phase retrieval) Spatial resolution limited by pixel size With ERL: it would be possible to reduce the exposure times by orders of magnitude. It offers great potential for flash imaging studies of biological specimens, at ID beam lines.

12 Phase Contrast Microscopy Allman et al. JOSA (2000). APS, 2-ID-B, 1.8 kev spider silk fiber: φ1.7µm holographic geometry retrieved phase: 2.5 rad imaging geometry ERL: would extend these techniques to higher energies, with higher coherent flux

13 Diffraction Microscopy Diffraction microscopy is analogous to crystallography, but for noncrystalline materials Coherent diffraction from noncrystalline specimen: => continuous Fourier transform Spatial resolution: essentially no limit. (only limited by λ/λ and weak signals at large angles) Coherence requirement: coherent illumination of sample Coherent X-rays Key development: oversampling phasing method coherent flux!! Miao et al. (1999) >>> soft x-rays, reconstruction to 75 nm

14 Other Coherence Experiments Coherent crystallography: overlapping Bragg reflections => phases? Sinha (2001). Coherent Bragg imaging of shape and strain in nanocrystals Robinson et al. (2001): 1µm Au nanocrystal Coherent x-ray topography: phasecontrast imaging of defects? Hu et al. (2001). Au (111)

15 X-ray Holography with Reference Wave Leitenberger & Snigirev (2001) Wilhein et al. (2001). Howells et al. (2001); Szoke (2001). Illumination of two objects, one as reference, e.g. pin-hole arrays X-ray holography is exciting but not ready for applications ERL is an ideal source for further research in this area

16 Conclusions Cornell ERL: It would be a high-intensity, continuous, diffraction-limited ~1Å x-ray source It would offer an almost coherent hard x- ray source so one does not have to trade resolution with flux & E/E With advances in optics and phasing algorithms, it would make phase-contrast microscopy routine for hard x-rays It would offer state-of-the-art research opportunities for developing advanced imaging methods such as holography and high-resolution x-ray microscopy! ERL Workshop on Coherent Imaging and Diffraction (Aug. 2003)

17 Acknowledgments Cornell Physics: M. Tigner I.V. Bazarov H.S. Padamsee C.K. Sinclair R. Talman Jefferson Lab: G.A. Krafft L. Merminga National Science Foundation Thanks to Ian McNulty (APS) and Chris Jacobsen (SUNY-SB)! ERL website: