Table-top kHz hard X-ray source with ultrashort pulse duration for time-resolved X-ray diffraction

摘要

The interaction of ultrashort laser pulses with solid state targets is studied concerning the production of short X-ray pulses with photon energies up to about 10 keV. The influence of various parameters such as pulse energy, repetition rate of the laser system, focusing conditions, the application of prepulses, and the chirp of the laser pulses on the efficiency of this highly nonlinear process is examined. In order to increase the X-ray flux, the laser pulse energy is increased by a 2nd multipass amplifier from 750 μJ to 5 mJ. By applying up to 4 mJ of the pulse energy a X-ray flux of 4 × 10~(10) Fe Kα photons/s or 2.75 × 10~(10) Cu Kα. Photons/s are generated. The energy conversion efficiency is therefore calculated to η_(Fe)≈ 1.4 × 10~(-5) and η_(Cu) 1.0 × 10~(-5). The X-ray source size is determined to 15 × 25 μm~2. By focusing the produced X-rays using a toroidally bent crystal a quasi-monochromatic X-ray point source with a diameter of 56 μm × 70μm is produced containing ≈10~4 Fe K_(α1) photons/s which permits the investigation of lattice dynamics on a picosecond or even sub-picosecond time scale. The lattice movement of a GaAs( 111) crystal is shown as a typical application.