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time (ps). pulse number. Ultrafast X-ray Measurements of Structural Dynamics: Key Technical Challenges to the Optimal Use of the LCLS. Kelly Gaffney Stanford Synchrotron Radiation Laboratory kgaffney@slac.stanford.edu June 27, 2006. Unprecedented X-ray Peak Brightness. ~10 9 increase.

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  1. time (ps) pulse number Ultrafast X-ray Measurements of Structural Dynamics: Key Technical Challenges to the Optimal Use of the LCLS Kelly Gaffney Stanford Synchrotron Radiation Laboratory kgaffney@slac.stanford.edu June 27, 2006

  2. Unprecedented X-ray Peak Brightness ~109 increase peak brightness defines the science opportunities and technical challenges at the LCLS courtesy T. Shintake

  3. 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.

  4. 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.

  5. Schematic View of Laser Pump XFEL Probe Dt laser pulse x-ray pulse time laser induced change in scattering pattern • Ability to measureDtdetermines time resolution. • Fast dynamics occur at high Q, requiring a large Q-range. • Sparse signal at high Q requires single photon sensitivity.

  6. dual pulses with variable delay x-ray pulse sample 2-D scattering pattern x-ray split and delay Schematic View of X-ray Photon Correlation Spectroscopy • 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.

  7. LCLS Supported Pixel Array Detector (PAD) Development Program Directed by Saul Gruner at Cornell University • Strengths • Independent signal shaping electronics • for each pixel provides maximum • flexibility • Individualized electronics provide • optimal readout rate (~1 MHz frame rate) • Ability to use Ge, GaAs, and CdTe as • x-ray absorbing material • Disadvantages • Large mimimum pixel size (~100-150 mm) • Direct exposure of electronics to radiation.

  8. Schematic of Pixel Array Detector from Hugh Philipp Cornell U.

  9. Large Area Needs will Require Tiling from Hugh Philipp Cornell U.

  10. PAD Design Specifications and Performance-to-Date LCLS PRD 1.6-002-r0 A. Ercan et al., J. Synchro. Rad. 13, 110 (2006)

  11. 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 (~50mm) • Disadvantages • Moderate DQE at high energy (LCLS 3rd harmonic) • QE ~ 0.25 at 24 keV • Direct exposure of electronics to radiation.

  12. XAMPS Schematic and Pump-Probe Specifications W. Chen et al., IEEE Trans. Nucl. Sci. 49, 1006 (2002)

  13. 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

  14. Charge Pump Schematic • 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.

  15. Charge Pumping Signal Storage and Readout transfer charge confined charge from D. Peter Siddons NSLS and BNL

  16. Detector Development Also Part of the European XFEL Project from Jochen Schneider of DESY

  17. DESY MPI Detector Based on pnCCD Design

  18. Laser X-ray Time Synchronization No Intrinsic Synchronization How good is the phase lock? Laser phase locked to accelerator RF…BUT system response impulse time Measure relative delay for each pulse pair Electro-Optic Sampling

  19. Electro-Optic Sampling of Time Synchronization EOS undulator EOS timing applicable IF optical path lengths remain constant X osc amp Holger Schlarb: DESY Patrick Krejcik, Jerome Hastings: SLAC/SSRL Adrian Cavalieri, David Fritz, SooHeyong Lee, Philip Bucksbaum, David Reis FOCUS Center, University of Michigan

  20. Electro-Optic Sampling • 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

  21. Spatially Resolved Electro-Optic Sampling (EOS) Laser probe later relative to electron bunch Laser probe earlier relative to electron bunch EO Crystal

  22. Spatially Resolved EOS time polarizing beamsplitter integrated intensity time; space time integrated intensity Arrival time and duration of bunch is encoded on profile of laser beam

  23. Single-Shot Data acquired with 200 mmZnTe Single-Shot w/ high frequency filtering Timing Jitter Data (20 Successive Shots) CCD counts shot time (ps) color representation time (ps)

  24. Synchronization Using RF Reference typically 0.5 – 1.0 ps rms

  25. EOS measure of e- beam bunch compressionresolution limited by crystal

  26. Coherent Phonon Excitation in Bismuth S222 initial equilibrium position displaced quasi- equilibrium position S111 distance between 2 basis atoms • Bismuth has a carrier density dependent Peierls Distortion • Optical excitation coherently excites the LO phonon along body diagonal

  27. EOS Studies of Coherent Phonons in Bismuth

  28. Carrier Density Dependence of Lattice Dynamics

  29. 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.

  30. Electro-Optic Sampling and Bismuth Experiment at TheSub-Picosecond Pulse Source Collaboration Jena and Essen Lund SSRL and SLAC DESY Jerry Hastings Aaron Lindenberg John Arthur Sean Brennan Katerina Lüning Paul Emma Ron Akre Patrick Krejcik Eric Bong Pat Hillyard Drew Meyer Jen Kaspar Klaus Sokolowski-Tinten Dietrich von der Linde Jorgen Larsson Ola Synnergren Tue Hansen Christian Blome Stephan Duesterer Rasmus Ischebeck Holgar Schlarb Horst Schulte-Schrepping Thomas Tschentscher Jochen Schneider California - Berkeley Michigan David Fritz Adrian Cavalieri David Reis Phil Bucksbaum Soo-Hong Lee Roger Falcone Andrew MacPhee Dana Weinstein Donacha Lowney Tom Allison Tristan Matthews Oxford Jon Sheppard Justin Wark NSLS Brookhaven BIOCARS APS Argonne Pete Siddons Chi-Chang Kao Reinhard Paul Keith Moffat Juana Rudati Paul Fuoss Dennis Mills Brian Stephenson Albert Macrander Uppsala Carl Caleman Magnus Bergh Gösta Huldt David van der Spoel Nicusor Timeanu Janos Hajdu ESRF Lawrence Livermore Olivier Hignette Francesco Sette Dick Lee Henry Chapman MPI Göttingen Copenhagen Jens Als-Nielsen Simone Techert Department of Energy Swedish Research Council Deutsche Forschungsgemeinschaft Keck Foundation European Commission: FEMTO, XPOSE, and X-ray FEL pump-probe

  31. Projected Requirements for Single Molecule Imaging Required Pulse Duration for a Given Resolution Required coherent flux in 100 nm2 for a Given Resolution Study suggests short pulse requirement results from plasma formation not molecular explosion S. Hau-Riege et al.Phys. Rev. E71 061919 (2005).

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