LCLS Studies of Laser Initiated Dynamics

1
LCLS Studies of Laser Initiated Dynamics

• Jorgen Larsson, David Reis, Thomas
  Tschentscher, and Kelly Gaffney provided
• LUSI management with preliminary Specifications
  on February 2, 2006
• I have provided you with a print out of the
  specifications

2
Defining the Scope of Pump-Probe Endstation

• Is this where multi-shot imaging will be
  performed?
• Where will intense x-ray pump x-ray probe
  experiments be performed?
• Will pulsed magnetic field experiments be
  performed here?
• Will all general scattering experiments be
  performed in this endstation?
• - Where will x-ray pump x-ray probe
  experiments be conducted?
• - Will imaging experiments be conducted in this
  endstation?
• - Will pulsed magnetic field experiments be done
  here?
• - Will gas phase, cluster, and UHV/surface
  experiments be performed here?
• - Where will the soft x-ray pump probe
  experiments be conducted?

3
Core Capability for Pump-Probe Experiments Contain
ed in the LOI

• X-ray scattering probes of sturctural dynamics
  in condensed phases
• This will include diffuse scattering
  measurements of structure factors
• in the liquid phase
• Diffuse scattering in crystals
• Bragg and Laue scattering in crystals
• Hard x-ray emission spectroscopy
• - Initially focused on non-resonant XES
• - Extended to XANES and RIXS
• X-ray pump studies to be probed by x-rays or
  laser pulses

4
Beam Splitting Monochromator

• Asymmetric Bragg geometry will lead to temporal
  pulse broadening
• Cannot preserve full LCLS intensity need to
  maintain direct beam capability
• - This presents the potential problem of
  needing to reproducibly move the
• table with a beam diameter precision
• Needs to cover a large energy range, including
  3rd harmonic
• - Ideally 4 keV to 20 keV, low range for XANES
  and high range for
• liquid scattering

5
LCLS Diagnostics

• LCLS Pulse synchronization diagnostics
• - Implementing electro-optic sampling from the
  beginning is essential
• Developing x-ray laser pulse cross correlation
  methods needs to be
• integrated into the LCLS commissioning
• LCLS Pulse energy diagnostics
• - With beam splitting monochromator set-up,
  metal foil calibration should be sufficient
• - With direct beam studies the e- beam energy
  diagnostic has been
• proposed as a measure of the relative energy
  shot-to-shot
• LCLS Pulse energy diagnostics
• - This is essential for diffuse scattering
  experiments, either in solids or liquids,
• where the pump induced change will often be a
  small fraction of the total scatter
• - For liquids, normalizing to the solvent
  molecular structure factor at high-Q
• provides an alternative way of observing
  relative changes. This makes the
• 3rd harmonic essential to these studies
• Optical Laser diagnostics
• - Online measures of pulse position, spectrum,
  energy, and duration will be important

6
Overhead view of laser pump x-ray probe hutch

• Dual crystal x-ray monochromator with large
  horizontal
• displacement for running in parallel with far
  hall.
• 10-3 and 10-4 resolving power from 4 to 16 keV
• Ability to work with either the fundamental or
  the 3rd harmonic

x-ray slits
Vacuum up to the x-ray slits
x-ray BPM
Laser table 4X12
x-ray emission spectrometer
Five-circle goniometer with 1 m diameter capable
of accommodating liquid, crystal, and powder
samples, and potentially a small vacuum chamber.
Needs to be compatible with sample heating and
cooling.
Table rails for doing direct beam and displaced
beam experiments. Motion needs to be high
precision.
X-ray table 5X15
Monochromator and CCD array for simultaneous UV
to near IR light probing of system dynamics
1.5 m
MonoCCD
Room 9.5 X 10 m2
7
Side view of emission spectrometer set-up
1.5 m
displaced, monochromatic beam
array of cylindrically bent analyzer crystals
direct beam
1-D detector, though the x-ray detector I would
work
8
Significance of Soft X-ray Probing of Laser
Induced Dynamics

• Photoinduced charge transfer at interfaces
  critical to key DOE programs
• - Photovoltaics
• Photoelectrochemical production of hydrogen
• Presents the opportunity to develop non-linear
  spectroscopy
• - surface selective probes of electronic
  structure and potentially surface chemistry
• - potential for x-ray laser cross correlation
• Photo-doped studies of carrier dynamics in
  correlated electron systems
• - Use L-edge spectroscopy for studying transient
  electronic structure in metal oxides

9
Ultrafast Charge Transfer in Photovoltaic Cell
Schematic of cell
time scale for carrier generation
Asbury et al. J. Phys. Chem. B 104, 4545 (2001).
Hagfeldt and Grätzel Acc. Chem. Res. 33, 269
(2000).
10
Phonon vs. Electron Driven Catalysis Oxidation
of CO on Ru(0001)
Bonn et al. Science 285, 1042 (1999).
11
Photo-doping Studies of Metal Insulator
Transition in VO2
Cavalleri et al. Phys. Rev. Lett. 95, 67405
(2005) and Cavalleri et al. Phys. Rev. B 70,
R161102 (2004).