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
Defining the Scope of Pump-Probe Endstation
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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?
Core Capability for Pump-Probe Experiments
Contained 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
Beam Splitting Monochromator
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Asymmetric Bragg geometry will lead to temporal pulse broadening
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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
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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
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
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
Vacuum up to
the x-ray slits
x-ray slits
x-ray BPM
Laser table: 4’X12’
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
X-ray table: 5’X15’
experiments. Motion
needs to be high
1.5 m Mono+CCD Monochromator and CCD array for simultaneous
precision.
UV to near IR light probing of system dynamics
Room 9.5 X 10 m2
Side view of emission spectrometer set-up
1.5 m
displaced, monochromatic beam
direct beam
array of cylindrically bent analyzer
crystals
‘1-D detector’, though the x-ray detector I would work
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
Ultrafast Charge Transfer in Photovoltaic Cell
Schematic of cell
time scale for carrier generation
Hagfeldt and Grätzel Acc. Chem. Res. 33, 269 (2000).
Asbury et al. J. Phys. Chem. B 104, 4545 (2001).
Phonon vs. Electron Driven Catalysis – Oxidation of CO on Ru(0001)
Bonn et al. Science 285, 1042 (1999).
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).