A split- and delay-unit for the European XFEL

Abstract

For the European XFEL [1] an x-ray split-and delay-unit (SDU) is built covering photon energies from 5 keV up to 20 keV [2]. This SDU will enable time-resolved x-ray pump / x-ray probe experiments as well as sequential diffractive imaging [3] 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 [4]. The x-ray FEL pulses will be split by a sharp edge of a silicon mirror coated with Mo/B 4 C multi layers. Both partial beams will then pass variable delay lines. For different wavelengths the angle of incidence onto the multilayer mirrors will be adjusted in order to match the Bragg condition. For a photon energy of h = 20 keV a grazing angle of  = 0.57° has to be set, which results in a footprint of the beam () on the mirror of l = 120 mm. At this photon energy the reflectance of a Mo/B 4 C multi layer coating with a multi layer period of d = 3.2 nm and N = 200 layers amounts to R = 0.92. In order to enhance the maximum transmission for photon energies of h = 8 keV and below, a Ni/B 4 C multilayer coating can be applied beside the Mo/B 4 C 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 h20 keV and up to +/-23 ps at h5 keV will be possible.

MaRIE: Opportunities for new x-ray sources to shed light on mesoscale functional materials

“…Similarly, XFELs, like the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory, have increased peak coherent X-ray brilliance by nearly 10 orders of magnitude ( Figure 1). The world's first hard X-ray FEL, the LCLS, began operations in 2009, and a recent summary of the first five years of operation highlights the numerous discoveries enabled by such sources that have fundamentally changed our understanding of materials behavior at the femtosecond and nanometer scale [9]. The success of the LCLS has spawned numerous other XFELs that are operation, or are soon to achieve first light in the near future, including SACLA at Spring-8 in Japan (operational in 2011), PAL-XFEL in South Korea (first light in 2016), the European XFEL in Germany (first light due in 2017), the Swiss FEL, and many other planned facilities.…”

“…XPCS is used to study dynamics by comparing changes in coherent scattering from samples as a function of time [7], [8]. This method will be pushed to the limit of single X-ray pulse lengths by advances in X-ray split and delay technology [9]. In the following, we discuss two specific areas of opportunity for MaRIE studies of nanomaterials that were identified during this breakout session: nanomaterial growth and assembly.…”

Spatial and temporal pre-alignment of an X-ray split-and-delay unit by laser light interferometry

“…22 The first optical split-and-delay systems have been operated at visible to soft X-ray wavelengths. [23][24][25][26] Equivalent devices for hard X-rays have been discussed over many years. The first hard X-ray split-and-delay system, based on the perfect crystal optics and fixed scattering geometry, has been developed at DESY.…”

Mo/Si multilayer-coated amplitude-division beam splitters for XUV radiation sources

“…Fresnel's double mirror and Lloyd's mirror (Rus et al, 2001;Rocca et al, 1999), edge mirror splitting (Mitzner et al, 2008(Mitzner et al, , 2009Schlotter et al, 2010;Roling et al, 2011Roling et al, , 2012, half-splitted mirror (Moshammer et al, 2011)] and amplitude splitting [e.g. diffraction gratings (Goulielmakis et al, 2002) or semitransparent membranes].…”