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

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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

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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

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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
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Time Resolved Scattering
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Laser System (Fundamental)
Small Angle Scattering
X-ray Diffractometer
Wavelength Conversion
Offset Monochromator
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X-ray Optics
Scattering Angles (2 theta) Scattering Angles (2 theta) Scattering Angles (2 theta)
1.5 Å 0.5 Å
Silicon 111 27.6 9.1
Silicon 220 45.8 14.9
Diamond 111 42.5 13.9
Diamond 220 - 22.8

• Double Crystal Offset Monochromator
• Narrows x-ray spectrum for resonant scattering
  experiments
• Multiplexes LCLS beam (mono. beam, diagnostic
  beam)

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X-ray Optics

• Double Crystal Offset Monochromator
• for 2 µm Si (111) _at_ 1.5 Å
• 85 transmission ,2.5 - Mono beam, 1.3 -
  Diagnostics beam

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X-ray Optics
Flexure Stages
Piezoelectric Stages

• Double Crystal Offset Monochromator (cont.)
• motion
• 0.02 arcsecond resolution and repeatability (100
  nrad)

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X-ray Optics
Lens
Mono
190 m
4 m

• Beryllium lens focusing optic
• Variable spot size from 2-10 µm and 40-60 µm _at_
  8.3 keV
• Variable spot size from 2-10 µm _at_ 24.9 keV
• gt 40 throughput
• Positioning resolution and repeatability to 1 µm

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Laser System Overview
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Ultrafast Laser System
TiSapphire Oscillator Power Amplifiers
Compressor, OPA, Harmonic Generation, Delay Stage
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Ultrafast Laser System
Cavity Length Stabilization Mirror

• TiSapphire Oscillator
• 119 MHz rep. rate, lt30 fs 2.5 nJ/pulse
• Frequency stabilized to LCLS RF lt 300 fs rms
  phase jitter
• Demonstrated at SPPS

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Ultrafast Laser System

• Power Amplifiers
• Regenerative amplifier
• 2.5 mJ (lt 1 rms stability), 120 Hz, lt35 fs
• Multipass amplifier
• 20 mJ (lt1.5 rms stability), 120 Hz, lt35 fs
• Second Compressor
• External Pockels Cell
• Arbitrary laser pulse train structure

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Ultrafast Laser System

• Temporal Pulse Shaper
• Create complex excitation pulse envelopes
• Multi-pulses
• Compression optimization

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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

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XPP Diffractometer System

Rotary Stages vs. Robot Arm
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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

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Small Angle Scattering Capability

• 10 µrad angular resolution with XAMPS detector
• Detector translation
• Operate in both direct and monochromatic beam

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Sample Environments
Det. Array
Collinear Geometry
Det. Array
Non-collinear Geometry

• Cryostat System
• Vacuum shroud
• Optical and x-ray windows (collinear
  non-collinear geometry)
• Decoupled sample motion

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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

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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 !
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Electro-optic Sampling
Stabilized Fiber Optic RF Distribution (10
fs) LBNL
Electro-optic Sampling Laser
Pump-probe Laser
Gun Laser
LTU
NEH
Sector 20

• Temporal resolution is now limited by
• Our ability to phase lock the lasers to the RF
• Intra-bunch SASE jitter

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SPPS Laser/X-ray Timing
100 consecutive shots
Single shot, Lorentzian fit
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Data Sorting at SPPS

• 10 Hz
• Point Detector

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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?

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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
• TiSapphire Oscillator vs. Fiber Oscillator
• - Bandwidth vs. Synchronization