Time resolved x-ray diffraction with subpicosecond x-ray pulses

The emission from plasmas created with fs-lasers provides sub-picosecond x-ray pulses in the keV-range. Intense emission of Kα lines as well as quasi continuum x-rays can be used for time-resolved diffraction and spectroscopy, i.e. to study lattice or atomic dynamics with sub-picosecond resolution by using a laser pump - x-ray probe technique. The x-ray yield and x-ray pulse duration of the laser plasma source depend on the laser parameters and the target design, such as intensity, laser wavelength, pulse duration and prepulse level. To accumulate as many photons as possible of the isotropic source an efficient large aperture optic has to be used to select an x-ray line or a wavelength range and focus the radiation onto the sample. It is shown that the use of toroidally bent crystals provides the possibility to refocus 10^-4 of the photons emitted in the whole solid angle to a spot size of around 80 μm with a temporal broadening below 100 fs. Combinations of bent focusing crystals with a flat sample crystal for fast x-ray diffraction application are discussed. Experiments showing the temporal response of laser heated crystals are presented and compared with theoretical simulations based on Takagi-Taupin theory.