260 likes | 422 Views
X-ray Pump-Probe Instrument D. M. Fritz. Pump-probe Experiments System Description X-ray optics Laser System Detector Sample environments Laser/X-ray Timing Technical Choice. Science Team. Specifications and instrument concept developed with the science team. The XRPP team
E N D
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
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
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
X-ray Pump-Probe Instrument Laser System (Fundamental) Small Angle Scattering X-ray Diffractometer Wavelength Conversion Offset Monochromator
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)
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
X-ray Optics • Double Crystal Offset Monochromator (cont.) • motion • 0.02 arcsecond resolution and repeatability (100 nrad) Flexure Stages Piezoelectric Stages
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
Ultrafast Laser System Ti:Sapphire Oscillator & Power Amplifiers Compressor, OPA, Harmonic Generation, Delay Stage
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
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
Ultrafast Laser System • Temporal Pulse Shaper • Create complex excitation pulse envelopes • Multi-pulses • Compression optimization
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
XPP Diffractometer System Rotary Stages vs. Robot Arm
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
Small Angle Scattering Capability • 10 µrad angular resolution with XAMPS detector • Detector translation • Operate in both direct and monochromatic beam
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
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
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 !
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
SPPS Laser/X-ray Timing Single shot, Lorentzian fit 100 consecutive shots
Data Sorting at SPPS • 10 Hz • Point Detector
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?
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