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CHESS & LEPP
Sceince III.ppt
Science IIIScience III
Coherent Imaging and DiffractionCoherent Imaging and Diffraction
Qun Shen (CHESS)
CHESS & LEPP
Sceince III.ppt
ERL Spatial CoherenceERL Spatial Coherence
Diffraction limited @ 8keVESRF emittance(4nm x 0.01nm) 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
PhasePhase--II ERLII ERL: diffraction: diffraction--limited source limited source E < 6.6 E < 6.6 keVkeValmostalmost diffractiondiffraction--limited tolimited to 13 13 keVkeV
CHESS & LEPP
Sceince III.ppt
ERL Coherent FluxERL Coherent Flux
3 4 5 6 7 8 910 20 30 40 50
109
1010
1011
1012
1013
1014
1015LCLS SASE
APS 2.4m
ESRF U35
APS 4.8m
Sp8 5m
Sp8 25m
0.15nm 100mA
ERL 25m0.015nm 10mA
Coh
eren
t Flu
x (p
hoto
ns/s
/0.1
%)
Photon Energy (keV)
• 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
CHESS & LEPP
Sceince III.ppt
Coherence ExperimentsCoherence Experiments
⇒ X-ray Photon Correlation Spectroscopy (Speckle)
⇒ X-ray Imaging Microscopy:
• Flash imaging
• Transmission x-ray microscopy
• Far-field diffraction microscopy• Holographic techniques
• Scanning x-ray microscopy (zone-plate)• Phase imaging & microscopy
⇒ Phase Tomography & 3D Structures
⇒ Coherent Crystallography, etc.
CHESS & LEPP
Sceince III.ppt
Background on Background on XX--ray Imaging Microscopyray Imaging Microscopy
ESRF ID21: 3-6 keV
• All types of materials are studied, from biological to magnetic
• Increasing number of SR imaging microscopes worldwide due to availability of => high-resolution lens-like optics: zone plates=> high-brilliance synchrotron sources
• Most are based on soft x-rays, only 3-4 go beyond 3 keV
CHESS & LEPP
Sceince III.ppt
Why only a few Why only a few hard xhard x--ray microscopes ?ray microscopes ?
• Focusing opticsFocusing optics
Refraction index: n = 1 − δ − iβ
absorption contrast: µz = 4πβz/λphase contrast: φ(z) = 2πδz/λ z
C94H139N24O31S
1010
108
106
104
103102 104
Kirz (1995): 0.05µm protein in 10µm thick ice
X-ray Energy (eV)
Dos
e (G
ray)
absorption contrast
phase contrast
• In general, phase contrast requires:=> coherent hard x-ray beams !
Only recently has Fresnel zone-plate (FZP) achieved <100nm resolution at 8keV (Yun, 1999)
• High coherence sources:
Coherence fraction ~ λ2/(εxεy). => Requires 100x smaller emittance product for
1keV => 10 keV
ERL would offer 102-103x better emittanceproduct than present-day hard x-ray sources
=> Better coherence @10 keV than @1 keV at ALS
High coherence sources
• Absorption vs. phase contrastAbsorption vs. phase contrast
CHESS & LEPP
Sceince III.ppt
Advantages ofAdvantages ofHard XHard X--ray Microscopyray Microscopy
• Much larger penetration depth, good for natural thick living specimens and materials science samples
• Larger depth of focus, which is necessary for 3D tomography
Advantages of hard xAdvantages of hard x--rays: rays:
• Possibility of imaging in diffractionconditions for nanocrystals or thin specimens in materials science
• Access to higher-energy absorption edges for fluorescence imaging and element mapping
CHESS & LEPP
Sceince III.ppt
Phase Imaging & TomographyPhase Imaging & Tomography
λ
• A form of Gabor in-line holography• Coherence over 1st Fresnel zone (λR)1/2
• Image reconstruction (phase retrieval)
Cloetens et al. (1999): ESRF, ID19, 18 keVPolystyrene foam 0.7x0.5x1mm3
1.4T wiggler, B~7x1014 ph/s/mr2/mm2/0.1% @100mA4x700 images at 25 sec/image ~ 1 day
• With ERL: it would be possible to reduce the exposure times by a factor ~10, at bend-magnet beam lines!
• It offers great potential for flash imaging studies of biological specimens, at ID beam lines.
• Spatial resolution limited by pixel size
CHESS & LEPP
Sceince III.ppt
Phase Contrast MicroscopyPhase Contrast Microscopy
Allman et al. JOSA (2000). APS, 2-ID-B, 1.8 keV
holographic geometry
spider silk fiber: φ1.7µm
imaging geometry
retrieved phase: 2.5 rad
ERL: extends these techniques to higher energies, with higher coherent flux
CHESS & LEPP
Sceince III.ppt
Diffraction MicroscopyDiffraction Microscopy
• Spatial resolution: essentially no limit.(only limited by ∆λ/λ and weak signals at large angles)
• Coherence requirement: coherent illumination of sample
• Key development: oversampling phasing methodcoherent flux!!
• Coherent diffraction from noncrystalline specimen:=> continuous Fourier transform
• Diffraction microscopy is analogous to crystallography, but for noncrystalline materials
Coherent X-rays
Miao et al. (1999) >>>soft x-rays, reconstruction to 75 nm
CHESS & LEPP
Sceince III.ppt
Diffraction MicroscopyDiffraction Microscopymost recent resultsmost recent results
reconstructed image: to d~7nm resolution
Miao et al. (2002) λ = 2 Å
Gold: 2.5µm x 2µm x 0.1µm
=> could achieve higher resolution,limited only by radiation damage
ERL high-coherence option:B=5x1022 ph/s/mr2/mm2/0.1% @10mAExposure time for Si & d~7nm: 0.6 min.
for C & d~7nm: 3.5 min.
SPring-8 BL29XU:standard undulator 140 periods λu=3.2 cmB=2x1019 ph/s/mr2/mm2/0.1% @100mAFor Au, exposure time 50 min, d~7nmbut: for Si, (ZSi/ZAu)2~1/32 => 26 hrs !
for C, (Zc/ZAu)2~1/173 => 6 days !!
CHESS & LEPP
Sceince III.ppt
More Ideas on More Ideas on Coherence Experiments ...Coherence Experiments ...
• Coherent diffraction in crystallography• X-ray holography
Robinson et al. (2001): 1µm Au nanocrystalLeitenberger & Snigirev (2001).
Au (111)
Fourier transform holography using spherical wave by FZP
Wilhein et al. (2001).Two coherent spherical waves produced by double zone-plates
Howells et al. (2001); Szoke (2001). • Imaging of shape and strain innanocrystalsIllumination of two objects, one
as reference, e.g. pin-hole arrays
• Phase-contrast x-ray topography ?• X-ray holography is exciting but not ready for applications • TEM-like microscopy for hard x-rays ?• ERL is an ideal source for further research in this area
• Hard x-ray holographic lithography ?
CHESS & LEPP
Sceince III.ppt
ConclusionsConclusions
PhasePhase--II ERLII ERL: : • It would be the first high-intensity, continuous, diffraction-limited ~1Å x-ray source
• It would open up structural science from largely crystal-based to noncrystalline and nanocrystal materials
• With advances in optics and phasing algorithms, it would make phase-contrastmicroscopy routine for hard x-rays
• It would offer state-of-the-art research opportunities for developing advanced imaging methods such as holographyand high-resolution x-ray microscopy