Wavelength Dispersive Optics for Ultrafast X-ray Spectroscopy at LCLS

Ultrafast X-ray absorption spectroscopy (XAS) performed at an x-ray free electron laser (XFEL) is a potentially very powerful tool to study numerous phenomena including dissociation in the gas phase , phase transitions in material science 2 and metal ligand charge transfer reactions 3 in coordination chemistry (for a recent review see ). At energies of 5-8 keV the LCLS is expected to provide pulses of order 10 photons within an energy band pass of < 8 eV. Such a band pass is not sufficient to perform single shot XAS, which requires > 30 eV for XANES and several hundred eV for EXAFS. In pump-probe experiments, using many pulses, it will in principle be possible to quickly vary the LINAC energy to provide a larger spectral range. But this approach is very challenging with regards to systematical errors inherent to XFEL radiation, most notably variations in pulse intensity, pulse energy distribution and time jitter.