Characterization of ultrafast hard x-ray pulses for LCLS using gas phase techniques

The availability of ultrafast (sub-100 fs) hard x-ray pulses (E $>$ 1000 eV) promises new experimental opportunities, but also requires new techniques for their use. The Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Center (SLAC) is such a source that is expected to provide a high flux of 230 fs monochromatic x-ray photons with energy between 0.8 and 8 keV. Characterization methods for beams with such characteristics still need to be developed. We are presenting several techniques that show promise for the spatial and temporal characterization of ultrafast hard x-rays. They were developed and used at the Advanced Light Source (ALS), and will undergo further testing at the Sub-Picosecond Photon Source (SPPS) at SLAC. Our methods exploit effects such as ultrafast core-hole binding energy changes in atoms after laser excitation, and creation of energy sidebands on Auger electrons that are emitted in a laser field. We have demonstrated the usefulness of these effects on a picosecond time scale, but their use can be extended well into the femtosecond domain. We will also discuss time-of-flight techniques which offer the possibility of nondestructive x-ray spatial mode characterization. Our focus is on gas phase experiments, since they offer the possibility of nondestructive, transparent monitoring of the x-rays, leaving the main beam nearly undisturbed and available for experiments.