CHESS & LEPP

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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

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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

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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.

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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

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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

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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

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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

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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

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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

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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 !!

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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 ?

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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