A hard x-ray split-and-delay unit for the HED instrument at the European XFEL

Abstract

For the High Energy Density Instrument (HED) at the European XFEL a hard x-ray split-and-delay unit (SDU) is built covering photon energies in the range between 5 keV and 24 keV. This SDU enables time-resolved x-ray pump / x-ray probe experiments as well as sequential diffractive imaging on a femtosecond to picosecond time scale. The set-up is based on wavefront splitting that has successfully been implemented at an autocorrelator at FLASH. The x-ray FEL pulses will be split by a sharp edge of a silicon mirror coated with Mo/B 4 C and W/B 4 C multilayers. Both partial beams then pass variable delay lines. For different photon energies the angle of incidence onto the multilayer mirrors is adjusted in order to match the Bragg condition. Hence, maximum delays between +/-1 ps at 24 keV and up to +/-23 ps at 5 keV will be possible. Time-dependent wave-optics simulations are performed with Synchrotron Radiation Workshop (SRW) software. The XFEL radiation is simulated using the output of the time-dependent SASE code FAST. For the simulations diffraction on the edge of the beam-splitter as well as height and slope errors of all eight mirror surfaces are taken into account. The impact of these effects on the ability to focus the beam by means of compound refractive lenses (CRL) is analyzed.

Hard X-ray USAXS Fourier Transform Holography

“…Further attempts of hard X-ray FTH have been very limited. Combining FTH with the split-and-delay technique [13,14,15,16,17] at FEL sources opened the possibility to measure dynamics with femtoseconds resolution [18]. In this way FTH was employed to measure X-ray holograms using a soft X-ray autocorrelator, where FEL pulses were geometrically separated and split into two with femtoseconds delay to overlap on the sample position.…”