X-ray Pump-Probe Instrument D. M. Fritz

1. X-ray Pump-Probe InstrumentD. M. Fritz • Pump-probe Experiments • System Description • X-ray optics • Laser System • Detector • Sample environments • Laser/X-ray Timing • Technical Choice

2. Science Team • Specifications and instrument concept developed with the science team. The XRPP team • Kelly Gaffney (leader), SSRL/SLAC • Jorgen Larsson, Lund Institute of Technology, Sweden • David Reis, University of Michigan • Thomas Tschentscher, DESY, Germany

3. X-ray Pump-Probe Science • Phase Transitions • Order / Disorder • Metal/Insulator • Phonon Dynamics • Charge Transfer Reactions • Photosynthesis • Photovoltaics • Vision • Photoactive Proteins photo- excitation Stampfli and Bennemann Phys. Rev. B 49, 7299 (1994) photo- excitation

4. Time Resolved Scattering

5. X-ray Pump-Probe Instrument Laser System (Fundamental) Small Angle Scattering X-ray Diffractometer Wavelength Conversion Offset Monochromator

6. Parameter Value Energy Range 6 – 24 keV Horizontal Offset 600 mm Scattering Angle 90 - 500 • Accuracy 0.02 arcsec χ Accuracy 4 arcsec X-ray Optics • Double Crystal Offset Monochromator • Narrows x-ray spectrum for resonant scattering experiments • Multiplexes LCLS beam (mono. beam, diagnostic beam)

7. X-ray Optics • Double Crystal Offset Monochromator • for 2 µm Si (111) @ 1.5 Å • 85% transmission ,2.5% - Mono beam, 1.3% - Diagnostics beam

8. X-ray Optics • Double Crystal Offset Monochromator (cont.) • motion • 0.02 arcsecond resolution and repeatability (100 nrad) Flexure Stages Piezoelectric Stages

9. X-ray Optics • Beryllium lens focusing optic • Variable spot size from 2-10 µm and 40-60 µm @ 8.3 keV • Variable spot size from 2-10 µm @ 24.9 keV • > 40% throughput • Positioning resolution and repeatability to 1 µm Lens Mono 190 m 4 m

10. Laser System Overview

11. Ultrafast Laser System Ti:Sapphire Oscillator & Power Amplifiers Compressor, OPA, Harmonic Generation, Delay Stage

12. Ultrafast Laser System • Ti:Sapphire Oscillator • 119 MHz rep. rate, <30 fs ~ 2.5 nJ/pulse • Frequency stabilized to LCLS RF < 300 fs rms phase jitter • Demonstrated at SPPS Cavity Length Stabilization Mirror

13. Ultrafast Laser System • Power Amplifiers • Regenerative amplifier • ~ 2.5 mJ (< 1% rms stability), 120 Hz, <35 fs • Multipass amplifier • ~ 20 mJ (<1.5% rms stability), 120 Hz, <35 fs • Second Compressor • External Pockels Cell • Arbitrary laser pulse train structure

14. Ultrafast Laser System • Temporal Pulse Shaper • Create complex excitation pulse envelopes • Multi-pulses • Compression optimization

15. XPP Detector - BNL • Pixel array detector • 1000 x 1000 pixels • 80 micron pixel size • High Detector Quantum Efficiency (DQE) • 10 4 dynamic range at 8 keV • 120 Hz Readout Rate

16. XPP Diffractometer System Rotary Stages vs. Robot Arm

17. XPP Diffractometer System • X-ray Diffractometer • Operate in both direct and monochromatic beam • Sample orientation & translation • Detector motion about a spherical surface centered at sample (variable radius from 0.1 m to 1.5 m) • Accommodate various sample environments

18. Small Angle Scattering Capability • 10 µrad angular resolution with XAMPS detector • Detector translation • Operate in both direct and monochromatic beam

19. Sample Environments • Cryostat System • Vacuum shroud • Optical and x-ray windows (collinear & non-collinear geometry) • Decoupled sample motion Det. Array Collinear Geometry Det. Array Non-collinear Geometry

20. Expected Fluctuations of the LCLS • Intensity fluctuations exceeding 30% • Expected spatial jitter ~25% of beam diameter • Wavelength fluctuations expected to be ~ 0.2% of center wavelength (≈ LCLS intrinsic bandwidth) • Pulse duration expected to vary ~15% • X-ray Pulse/LCLS RF timing will fluctuate by ~ 1 ps - Diagnostics are required to measure these parameters since they cannot be controlled - This information must be available to accelerator operations and experiments

21. Temporal Jitter Master Clock Coax RF Distribution Network Accelerating Elements Experimental Pump Laser Electron Gun Sources of Short Term Jitter • Coax RF distribution Network • e-beam phase to RF phase • End Station Laser phase to RF phase Limited to ~ 1 ps !

22. Electro-optic Sampling Stabilized Fiber Optic RF Distribution (10 fs) LBNL Electro-optic Sampling Laser Pump-probe Laser Gun Laser Sector 20 LTU NEH • Temporal resolution is now limited by: • Our ability to phase lock the lasers to the RF • Intra-bunch SASE jitter

23. SPPS Laser/X-ray Timing Single shot, Lorentzian fit 100 consecutive shots

24. Data Sorting at SPPS • 10 Hz • Point Detector

25. XPP Data Sorting at LCLS X-ray Detector LCLS Beam Parameters Intensity Time of Arrival Wavelength 180 MB/s ~ 1 MB/s Real Time Processing Unit t1 t2 t3 t4 …………………………………………………….………………tN • 120 Hz • 1 Megapixel Area Detector • 2-dimensional binning or data filtering?

26. Key Technological Choices • Diamond vs. Silicon Monochromator Crystal - Absorption, Damage vs. Quality • Flexure vs. Piezo Monochromator Rotation Stage - Stability vs. Range • Robot Arm vs. Rotary Stage Detector Mover - Reciprocal Space Access vs. Control, Safety • Hexapod vs. Stages Sample Manipulator - Range of Motion vs. Stability, Control • Ti:Sapphire Oscillator vs. Fiber Oscillator - Bandwidth vs. Synchronization