Coherent X-ray Imaging & Microscopy

Shen / CHESS July 29, 2002

Coherent XCoherent X--ray Imaging & Microscopyray Imaging & Microscopy

=> => Opportunities Using a DiffractionOpportunities Using a Diffraction--LimitedLimitedEnergy RecoveryEnergy Recovery LinacLinac (ERL) Synchrotron Source(ERL) Synchrotron Source

Q. ShenD. Bilderback, K.D. Finkelstein, E. Fontes, & S. Gruner

Cornell High Energy Synchrotron Source (CHESS)Cornell University, Ithaca, New York 14853, USA

Talk OutlineTalk Outline

•• Introduction of ERLIntroduction of ERL•• Benefits to XRMBenefits to XRM•• Coherent microscopy examples Coherent microscopy examples •• Conclusions Conclusions


Growth in Growth in Synchrotron Radiation ScienceSynchrotron Radiation Science


StorageStorage--Ring Based vs. Ring Based vs. Energy Recovery Energy Recovery Linac Linac SourcesSources

M. Tigner, Nuovo Cimento 37, 1228 (1965)

400 m

Accelerating

Returning

StorageStorage--RingRing

ERLERL

• Mature and well-understood

• Equilibrium of stored beam in entire ring

• ~ 10,000 turns to reach equilibrium • Single-pass non-equilibrium device• Emission of synchrotron radiation• Low emittance and short pulses from injector • Perturbations on electron trajectories• Ultra-small round beam

• Limits on ∆E, emittance, bunch length• Ultra-high brilliance and coherence


PreliminaryPreliminaryDesign Parameters of ERLDesign Parameters of ERL

ERLhigh-flux

ERLhigh-coherence

Energy EG (GeV) 5.3 5.3

Current I (mA) 100 10

Charge q (nC/bunch) 0.077 0.008

εx (nm-rad) 0.15 0.015

εy (nm-rad) 0.15 0.015

Bunch fwhm τ (ps) 0.3 − 5 0.3 − 5

Mac

hine

des

ign

# of bunches f (Hz) 1.3·109 1.3·109

Undulator L (m) 25 25

Period λu (cm) 1.7 1.7

# of period Nu 1470 1470

Horizontal βx (m) 12.5 4.0

Vertical βy (m) 12.5 4.0

Undulator K @ E1 1.38 1.38

Inse

rtion

dev

ice

1st harmonic E1 (keV) 8.0 8.0


ERL: Expected PerformanceERL: Expected Performance

10 1001015

1016

1017

1018

1019

1020

1021

1022

1023

1024

1025

1026

1027

0.15nm100mA 0.3ps

CHESS 49-pole G/A-wigglerτ=153ps, f=17.6MHz (9x5)

CHESS 24-pole F-wiggler

Sp8 25m

Sp8 5m

ESRF U35APS 2.4m

0.15nm 100mA 4.7ps

ERL 25m 0.015nm 10mA 0.3ps

Peak

Bril

lianc

e (p

h/s/

0.1%

/mm

2 /mr2 )

Photon Energy (keV)10 100

1013

1014

1015

1016

1017

1018

1019

1020

1021

1022

1023

ESRF U35Sp8 5m

Sp8 25m

APS 4.8m

APS 2.4m

0.15nm 100mA

ERL 25m 0.015nm 10mA

LCLS SASE

LCLS spont.

CHESS 24p wiggler

CHESS 49p wiggler

Aver

age

Brilli

ance

(ph/

s/0.

1%/m

m2 /m

r2 )

Photon Energy (keV)


Cornell ERL Coherent FluxCornell ERL 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


ERL Spatial CoherenceERL Spatial Coherence

ERL emittance (0.015nm)ESRF emittance(4nm x 0.01nm)

Cornell ERLCornell ERL: diffraction: diffraction--limited source limited source E < 6.6 E < 6.6 keVkeValmostalmost diffractiondiffraction--limited tolimited to 13 13 keVkeV

Diffraction limited @ 8keV

Diffraction limited source: 2πσ'σ = λ/2 or ε = λ/4π

Almost diffraction limited: 2πσ'σ ~ λ or ε ~ λ/2π


Benefits of ERL to XRMBenefits 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.


Issues in Hard XIssues in Hard X--ray Microscopyray Microscopy

• 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)D

ose

(Gra

y)

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


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


Phase Imaging & TomographyPhase Imaging & Tomography

λ

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

• 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.


Phase Contrast Phase Contrast MicroscopyMicroscopy

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: would extend these techniques to higher energies, with higher coherent flux


Diffraction MicroscopyDiffraction Microscopy

• Spatial resolution: essentially no limit.(only limited by ∆λ/λ and weak signals at large angles)

• Key development: oversampling phasing methodcoherent flux!!

• Coherent diffraction from noncrystalline specimen:=> continuous Fourier transform

• Diffraction microscopy is analogous to crystallography, but for noncrystalline materials

• Coherence requirement: coherent illumination of sample

Coherent X-rays

Miao et al. (1999) >>>soft x-rays, reconstruction to 75 nm


Other Coherence ExperimentsOther Coherence Experiments

• Coherent crystallography: overlapping Bragg reflections => phases?

• Coherent Bragg imaging of shape and strain in nanocrystals

Sinha (2001).

Robinson et al. (2001): 1µm Au nanocrystal

• Coherent x-ray topography: phase-contrast imaging of defects?

Hu et al. (2001).

Au (111)


XX--ray Holography with Reference Waveray Holography with Reference Wave

Wilhein et al. (2001).Leitenberger & Snigirev (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


ConclusionsConclusions

Cornell ERLCornell 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-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

! ERL Workshop on Coherent Imaging and Diffraction (Aug. 2003)


AcknowledgmentsAcknowledgments

• Cornell Physics: M. Tigner I.V. Bazarov H.S. Padamsee C.K. Sinclair R. Talman

• Jefferson Lab: G.A. KrafftL. Merminga

• National Science Foundation

• Thanks to Ian McNulty (APS) andChris Jacobsen (SUNY-SB)

! ERL website: http://erl.chess.cornell.edu/

Coherent X-ray Imaging & Microscopy

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