XDL2011 Workshop 3
Ultra-fast Science with "Tickle and Probe"
Monday, June 20th - Tuesday, June 21st, 2011
Organizers: Robert Schoenlein (Lawrence Berkeley National Laboratory), Brian Stephenson (Argonne National Laboratory), Eric Dufresne (APS), & Joel Brock (Cornell University) Workshop Agenda (html)
Workshop Poster (pdf)
Purpose: The purpose of the workshop is to assess the potential use of ultra-fast (50 fs) x-ray pulses at high repetition rates (MHz to GHz) for time-resolved studies of weakly pumped (tickled) condensed matter systems. We are especially interested in exploring what might be feasible with the (nearly) diffraction-limited hard x-ray beams produced by Energy Recovery Linac (ERL) and Ultimate Storage Ring (USR) sources. Description: The characteristic time for the structural rearrangement of atoms in condensed matter is set by the characteristic vibrational frequency of an atom, Tvib=2π(k/m)½≈1ps (k~eV/a2, a=3A, and m = 10-25kg). Thus, the ultra-short (ps to < 50 fs) x-ray pulses produced by an ERL, or the ps pulses produced by a USR with crab cavities, will enable the opportunity to study the rearrangement of atoms (structural phase transitions, chemical reactions) on their natural time- and length-scales. Similarly, the natural time-scale for electronic structural dynamics (bond dynamics, valence charge flow, electronic phase transitions, correlated electron systems) mediated by the electron-phonon interaction is on the order of 1 ps. The nature of the x-ray pulse train from an ERL or USR is complimentary to that of an X-FEL. An X-FEL produces very intense pulses at low repetition rates (100Hz @ LCLS); the ERL or USR with a crab cavity arrangement produces small pulses at very high repetition rates (MHz to GHz) but the time-average flux of these two sources is comparable. High repetition rate pump-probe experiments on atomic length- and time-scales take place in a largely unexplored regime of experimental phase space. Clearly, due to the low signal/x-ray pulse, ERL/USR experiments will require signal averaging over many pulses. On the other hand, ERL/USR pulses will not damage many samples. Similarly, to take advantage of the high repetition rate, the sample must be able to relax between driving pulses. Hence the driving pulse must only "tickle" rather than "pump" the sample. Weak optical pumps (e.g., Ti:Al2O3 laser running at >800MHz), nanofabricated (e.g. stripline) excitation/sample cells, and ultrafast THz pulses are possible pumps. Micro-focusing minimizes pump power required and speeds up relaxation via (thermal) diffusion. Time-resolved microscopy is also possible. Examples of Potential Science:
- AMO (EXAFS, SAXS, XRD)
- Molecular rotational dynamics
- Cluster dynamic
- Spin dynamics
- Dipole-dipole interactions
- Chemistry (Laser-Induced Time-Resolved: XAS, SAXS, and XRD)
- Photo-electrochemistry
- Photo-induced solvation
- Charge transfer in ionic liquids
- Coherent control
- Pump-dump vs pump-pump
- Shaping of single or multi-photon spectrum
- Control of excited state wave packets directing reactivity
- Photo-electrochemistry
- Condensed Matter (XMCD, XRD, XAS, XANES, ARPES)
- Beyond Born-Oppenheimer approximation
- Complex correlated materials
- Strongly correlated systems (high-Tc cuprates, CMR manganites)
- Magnetic materials (ferromagnetics, heterostructures)
- Multiferroics (ferromagnetism/ferroelectricity, interfaces)
- Organics - molecular crystals
- Optical quenching of CDWs and SDWs
- Molecular Dynamics
- Solute dynamics
- Solvent dynamics
- Surface chemistry/catalysis
- Magnetism
- TR Microscopy