Fig. 4: Illustration of split-and-delay XPCS technique. A single X-ray pulse is split into two equal intensity pulses using the hard X-ray delay line. The pulses propagate collinearly in the sample direction. (Inset): Concept of the hard X-ray delay line. BR-1, BR-2, BR-3, BR-4, BR-5, BR-6, Bragg reflectors; BS: beam splitter, BM: beam mixer. Paths of the upper and lower branch of the delay line are denoted by red and blue lines, respectively.
In the frame of this research project we study ultrafast phenomena using modern free electron x-ray sources. Our research portfolio includes development of novel and science enabling split-and-delay X-ray optics [1,2,3]. Our experiments are performed at various free-electron laser (FEL) facilities including LCLS, SACLA, and European XFEL. Static characterization of our sample systems via small angle X-ray scattering and Fourier transform holography is performed at 3rd generation storage rings.
Split-and-delay unit - A tool for studying ultrafast dynamics
X-ray free electron laser (XFEL) sources produce ultrashort, coherent and very intense pulses creating excellent conditions for investigation of ultrafast phenomena. However, the time structure of an XFEL source can compromise the applicability of experimental techniques such as X-ray pump/X-ray probe or X-ray photon correlation spectroscopy (XPCS). XFEL facilities provide ultra short (< 100 fs) single pulses at relatively low frequencies (120 Hz at LCLS in USA, 60 Hz at SACLA in Japan).
To fully exploit the potential of XFEL light with the aforementioned techniques we have successfully developed the first hard X-ray split-and-delay line [3,4,5,6,7] and employed it to perform first split-pulse XPCS at hard X-ray FEL [8]. Figure 4 illustrates this approach with the XPCS method. The experimental technique is based on splitting each X-ray pulse into two equal pulses, separating them in time and bringing them back on the primary beam path. The speckle pattern obtained from the sample, which is illuminated by both pulses, is summed on the area detector. The dynamics of the sample are studied by analyzing the contrast in the summed speckle patterns as a function of the applied delay times (i.e. time intervals between the two pulses).
References
[1] W. Roseker et al. Opt. Lett. 34, 1768 (2009).
[2] W. Roseker et al. J. Synchr. Rad. 18, 481 (2011).
[3] W. Roseker et al. Proc. SPIE 8504, 850401 (2012).
[4] W.Roseker et al., Sci Rep. 10, 5054 (2020)
[5] W.Roseker et al., Rev Sci Instr. 90(4), 045106 (2019)
[6] W.Roseker et al., Nat. Comm. 9 1704 (2018)
