Impact of real mirror profiles inside a split-and-delay unit on the spatial intensity profile in pump/probe experiments at the European XFEL
-
Published:2021-01-01
Issue:1
Volume:28
Page:350-361
-
ISSN:1600-5775
-
Container-title:Journal of Synchrotron Radiation
-
language:
-
Short-container-title:J Synchrotron Radiat
Author:
Kärcher V., Roling S., Samoylova L., Buzmakov A.ORCID, Zastrau U.ORCID, Appel K.ORCID, Yurkov M., Schneidmiller E., Siewert F., Zacharias H.
Abstract
For the High-Energy-Density (HED) beamline at the SASE2 undulator of the European XFEL, a hard X-ray split-and-delay unit (SDU) has been built enabling time-resolved pump/probe experiments with photon energies between 5 keV and 24 keV. The optical layout of the SDU is based on geometrical wavefront splitting and multilayer Bragg mirrors. Maximum delays between Δτ = ±1 ps at 24 keV and Δτ = ±23 ps at 5 keV will be possible. Time-dependent wavefront propagation simulations were performed by means of the Synchrotron Radiation Workshop (SRW) software in order to investigate the impact of the optical layout, including diffraction on the beam splitter and recombiner edges and the three-dimensional topography of all eight mirrors, on the spatio-temporal properties of the XFEL pulses. The radiation is generated from noise by the code FAST which simulates the self-amplified spontaneous emission (SASE) process. A fast Fourier transformation evaluation of the disturbed interference pattern yields for ideal mirror surfaces a coherence time of τc = 0.23 fs and deduces one of τc = 0.21 fs for the real mirrors, thus with an error of Δτ = 0.02 fs which is smaller than the deviation resulting from shot-to-shot fluctuations of SASE2 pulses. The wavefronts are focused by means of compound refractive lenses in order to achieve fluences of a few hundred mJ mm−2 within a spot width of 20 µm (FWHM) diameter. Coherence effects and optics imperfections increase the peak intensity between 200 and 400% for pulse delays within the coherence time. Additionally, the influence of two off-set mirrors in the HED beamline are discussed. Further, we show the fluence distribution for Δz = ±3 mm around the focal spot along the optical axis. The simulations show that the topographies of the mirrors of the SDU are good enough to support X-ray pump/X-ray probe experiments.
Funder
Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie European Metrology Programme for Innovation and Research
Publisher
International Union of Crystallography (IUCr)
Subject
Instrumentation,Nuclear and High Energy Physics,Radiation
Reference50 articles.
1. Perspective: Opportunities for ultrafast science at SwissFEL 2. Altarelli, M., Brinkmann, R., Chergui, M., Decking, W., Dobson, B., Dsterer, S., Grbel, G., Graeff, W., Graafsma, H., Hajdu, J., Marangos, J., Pflger, J., Redlin, H., Riley, D., Robinson, I., Rossbach, J., Schwarz, A., Tiedtke, K., Tschentscher, T., Vartaniants, I. A., Wabnitz, H., Weise, H., Wichmann, R., Witte, K., Wolf, A., Wulff, M., Yurkov, M. &. (2006). ) The European XFEL Technical Design Report. DESY, Hamburg, Germany. 3. Femtosecond time-delay X-ray holography 4. Time-dependent FEL wavefront propagation calculations: Fourier optics approach 5. Nonlinear Coherence Effects in Transient-Absorption Ion Spectroscopy with Stochastic Extreme-Ultraviolet Free-Electron Laser Pulses
Cited by
2 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|