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Kelly GaffneyStanford Synchrotron Radiation Laboratory

[email protected] 27, 2006

Ultrafast X-ray Measurements of Structural Dynamics: Key Technical Challenges to the Optimal Use of the LCLS

Unprecedented X-ray Peak Brightness

courtesy T. Shintake

~109 increase

peak brightness defines the science opportunities and technical challenges at the LCLS

Science Enabled by the LCLS

• Femtosecond Structural dynamics of laser excited materials- requires measuring the time delay between the optical and

x-ray pulses for every shot. - requires reading a large area detector on every shot.

• Femtosecond Dynamic light scattering measurements of equilibrium dynamics- requires x-ray beam splitters and translation stages.- requires reading a large area detector with excellent spatial

resolution on every shot

• Coherent imaging with Ångström resolution- projects to need 100 nm focus with ~1012 x-rays in ~10 fs.- requires reading a large area detector on every shot.

• High field, nonlinear x-ray optics- requires the LCLS peak brightness

• Single shot studies of extreme states of matter, plasma physics- requires the LCLS single shot flux.

Schematic View of Single Molecule Imaging

• Provides two dimensional projection. even if all objects are indentical, they will have random orientation. Successive images cannot be averaged.

• High resolution data will be sparse, requiring single photon sensitivity.

x-ray pulse

time

laser pulse

Schematic View of Laser Pump XFEL Probe

laser induced change in scattering pattern

• Ability to measure determines time resolution. • Fast dynamics occur at high Q, requiring a large Q-range.• Sparse signal at high Q requires single photon sensitivity.

Schematic View of X-ray Photon Correlation Spectroscopy

x-ray pulse

x-ray split and delay

dual pulses with variable delay

sample2-D scattering pattern

• Coherent scattering probes equilibrium deviations from the mean electron density via fluctuations in the speckle pattern

• Fast dynamics occur on short length scale – high Q. • Signal sparse at high Q, requiring single photon sensitivity.

LCLS Supported Pixel Array Detector (PAD) Development ProgramDirected by Saul Gruner at Cornell University

Strengths• Independent signal shaping electronics

for each pixel provides maximum flexibility

• Individualized electronics provideoptimal readout rate (~1 MHz frame rate)

• Ability to use Ge, GaAs, and CdTe asx-ray absorbing material

Disadvantages• Large mimimum pixel size (~100-150 m)• Direct exposure of electronics to radiation.

from Hugh Philipp Cornell U.

Schematic of Pixel Array Detector

Large Area Needs will Require Tiling

from Hugh Philipp Cornell U.

PAD Design Specifications and Performance-to-Date

A. Ercan et al., J. Synchro. Rad. 13, 110 (2006)

Parameter Requirement

energy range 4-8 keV

well depth 103

readout frame rate 120 Hz

S:N (single 8keV x-ray) >3

pixel size 100-200 m2

DQE 0.9 at 8 keV

detector area >500X500 pixels

LCLS PRD 1.6-002-r0

LUSI Supported X-ray Active Matrix Pixel Sensor (XAMPS)for Pump-Probe Measurements

Directed by Brookhaven Instrumentation Division and NSLS

Strengths• Radiation hardness• Simultaneous Row Readout

optimal readout rate (~1 kHz frame rate)• Moderate spatial resolution (~50m)

Disadvantages• Moderate DQE at high energy (LCLS 3rd harmonic)

QE ~ 0.25 at 24 keV• Direct exposure of electronics to radiation.

W. Chen et al., IEEE Trans. Nucl. Sci. 49, 1006 (2002)

XAMPS Schematic and Pump-Probe Specifications



well depth 103-104


Noise <500 e-

pixel size 85 m2

DQE 0.9 at 8 keV

detector area 10242 pixels

LUSI Supported Small Pixel Development for XPCS Directed by Brookhaven Instrumentation Division and NSLS

• XPCS high spatial resolution (~20 mm2) cannot be achieved with transistor switches in XAMPS design.

• An alternative pixel design based on charge storage and release, like a drift detector, will be used.

• Design achieves high energy resolution spatial resolution.• Design will also be tuned to a lower count rate and noise.

from D. Peter Siddons NSLS and BNL



well depth 102


Noise < 100 e-

pixel size < 35 m2

DQE 0.9 at 8 keV

detector area 10242 pixels

• Charge-pump pixel has two front-side implants, p+ and n+

• p+ in n-type wafer forms rectifying junction

• n+ forms ohmic contact for charge extraction.

• Back-side has uniform p+ rectifying contact.

Charge Pump Schematic

from D. Peter Siddons NSLS and BNL

confined charge transfer charge

Charge Pumping Signal Storage and Readout

from Jochen Schneider of DESY

Detector Development Also Part of theEuropean XFEL Project

DESY MPI Detector Based on pnCCD Design

Laser X-ray Time Synchronizationsy

stem

res

pons

e

0S2S3S4S 6S7S 5S8S9S1S time

impu

lse

No Intrinsic Synchronization

Laser phase locked to accelerator RF…BUT How good is the phase lock?

Electro-Optic Sampling Measure relative delay for each pulse pair

Electro-Optic Sampling of Time Synchronization

Adrian Cavalieri, David Fritz, SooHeyong Lee,Philip Bucksbaum, David Reis

FOCUS Center, University of Michigan

EOS timing applicable IF

optical path lengths

remain constant

osc amp

EOS

X

undulatort

t

Holger Schlarb: DESY

Patrick Krejcik, Jerome Hastings: SLAC/SSRL

Electro-Optic Sampling

x

• Crystal is affected by applied DC electric field– Principal axes of crystal system

are modified

– Index of refraction along these axes changes

• Probe laser field is decomposed in primed coordinate system

• Phase shift between components can be detected

•

y

DCE

x

y

x

ylaserE

DCE

k

k

k

k

k

28.5GeV 28.5GeV 28.5GeV 28.5GeV 28.5GeV

EO Crystal

Spatially Resolved Electro-Optic Sampling (EOS)

k

k

k

k

k

k

k

k

k

k

Laser probe later relative to electron bunchLaser probe earlier relative to electron bunch

polarizing beamsplitter

laserk

s polarizedk

p polarizedk

time;

space

Arrival time and duration of bunch is encoded on profile of laser beam

Spatially Resolved EOS

tim

eti

me

integrated intensity

integrated intensity

Single-Shot Data acquired with 200 mZnTe

160fs

Single-Shotw/ high frequency filtering

CC

D c

ount

s

time (ps)

color representation

Timing Jitter Data(20 Successive Shots)

time (ps)

shot

Synchronization Using RF Reference

typically 0.5 – 1.0 ps rms

EOS measure of e- beam bunch compressionresolution limited by crystal

Coherent Phonon Excitation in Bismuth

• Bismuth has a carrier density dependent Peierls Distortion• Optical excitation coherently excites the LO phonon along body diagonal

distance between2 basis atoms

initialequilibrium

position displaced quasi-equilibriumposition

S222

S111

EOS Studies of Coherent Phonons in Bismuth

Carrier Density Dependence of Lattice Dynamics

Measuring X-ray Timing Jitter

• Electro-optic sampling has shown merit, but does not directly correlate laser with x-ray pulse.- amplified x-ray intensity does not need to match electron density profile.- temporal resolution unlikely to be better than many tens of femtoseconds.

• Laser induced energy shifts of x-ray pulse generated Auger electron another option. • Non-linear optics provides opportunities for timing diagnostics as well as novel science.

- weak non-resonant x-ray matter interaction makes this difficult.- x-ray absorption techniques will not be tunable.- photoelectric techniques have space charge limitations.- non-resonant x-ray emission based techniques need to be considered.

• Any timing diagnostic requires the data to be read at the repetition rate of the source.

Electro-Optic Sampling and Bismuth Experiment at The Sub-Picosecond Pulse Source Collaboration

SSRL and SLACJerry HastingsAaron Lindenberg John ArthurSean BrennanKaterina LüningPaul EmmaRon AkrePatrick KrejcikEric BongPat HillyardDrew MeyerJen Kaspar

LundJorgen LarssonOla SynnergrenTue Hansen

Jena and EssenKlaus Sokolowski-TintenDietrich von der Linde

DESYChristian BlomeStephan DuestererRasmus IschebeckHolgar SchlarbHorst Schulte-SchreppingThomas TschentscherJochen Schneider

MichiganDavid FritzAdrian Cavalieri David ReisPhil BucksbaumSoo-Hong Lee

California - BerkeleyRoger FalconeAndrew MacPheeDana WeinsteinDonacha LowneyTom AllisonTristan Matthews

OxfordJon SheppardJustin Wark

UppsalaCarl CalemanMagnus BerghGösta HuldtDavid van der SpoelNicusor TimeanuJanos Hajdu

APS ArgonneJuana RudatiPaul FuossDennis MillsBrian StephensonAlbert Macrander

NSLS BrookhavenPete SiddonsChi-Chang Kao

BIOCARSReinhard PaulKeith Moffat

Lawrence LivermoreDick LeeHenry Chapman

ESRFOlivier HignetteFrancesco Sette

CopenhagenJens Als-Nielsen

MPI GöttingenSimone Techert

Department of Energy Swedish Research Council Deutsche ForschungsgemeinschaftKeck Foundation European Commission: FEMTO, XPOSE, and X-ray FEL pump-probe

Required coherent flux in 100 nm2

for a Given Resolution

S. Hau-Riege et al. Phys. Rev. E 71 061919 (2005).

Projected Requirements for Single Molecule Imaging

Required Pulse Duration for a Given Resolution

Study suggests short pulse requirement results from plasma formation not molecular explosion

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