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

: Roling, Sebastian; Appel, Karen; Braun, Stefan; Buzmakov, Alexey; Chubar, Oleg; Gawlitza, Peter; Samoylova, Liubov; Siemer, Björn; Schneidmiller, Evgeni; Sinn, Harald; Siewert, Frank; Tschentscher, Thomas; Wahlert, Frank; Wöstmann, Michael; Yurkov, Mikhail; Zacharias, Helmut


Hau-Riege, S.P. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
X-ray free-electron lasers: beam diagnostics, beamline instrumentation, and applications II : 18 - 19 August 2014, San Diego, California, United States
Bellingham, WA: SPIE, 2014 (Proceedings of SPIE 9210)
ISBN: 978-1-62841-237-6
Paper 92100B
Conference "X-Ray Free-Electron Lasers - Beam Diagnostics, Beamline Instrumentation, and Applications" <2, 2014, San Diego/Calif.>
Bundesministerium für Bildung und Forschung BMBF
Conference Paper
Fraunhofer IWS ()
coatings; free electron lasers; photonics; diffractive optics; high energy densities; multilayers; x-ray optics

For the High Energy Density (HED) experiment at the European XFEL an x-ray split- and delay-unit (SDU) is built covering photon energies from 5 keV up to 20 keV. This SDU will enable time-resolved x-ray pump/x-ray probe experiments as well as sequential diffractive imaging on a femtosecond to picosecond time scale. Further, direct measurements of the temporal coherence properties will be possible by making use of a linear autocorrelation. The set-up is based on geometric wavefront beam splitting, which has successfully been implemented at an autocorrelator at FLASH. The x-ray FEL pulses are split by a sharp edge of a silicon mirror coated with multilayers. Both partial beams will then pass variable delay lines. For different photon energies the angle of incidence onto the multilayer mirrors will be adjusted in orderto match the Bragg condition. For a photon energy of hv = 20 keV a grazing angle of θ = 0.57° has to be set, which results in a footprint of the beam (6σ) on the mirror of l =98 mm. At this photon energy the reflectance of a Mo/B4C multi layer coating with a multilayer periodof d = 3.2 nm and N = 200 layers amounts to R = 0.92. In order to enhance the maximum transmission for photon energies of hv = 8 keV and below, a Ni/B4C multilayer coating can be applied beside the Mo/B4C coating for this spectral region. Because of the different incidence angles, the path lengths of the beams will differ as a function of wavelength. Hence, maximum delays between +/- 2.5 ps at hv = 20 keV and up to +/- 23 ps at hv = 5 keV will be possible.