A beam branching method for timing and spectral characterization of hard X-ray free-electron lasers

Abstract

We report a method for achieving advanced photon diagnostics of x-ray free-electron lasers (XFELs) under a quasi-noninvasive condition by using a beam-splitting scheme. Here, we used a transmission grating to generate multiple branches of x-ray beams. One of the two primary diffracted branches (+1st-order) is utilized for spectral measurement in a dispersive scheme, while the other (−1st-order) is dedicated for arrival timing diagnostics between the XFEL and the optical laser pulses. The transmitted x-ray beam (0th-order) is guided to an experimental station. To confirm the validity of this timing-monitoring scheme, we measured the correlation between the arrival timings of the −1st and 0th branches. The observed error was as small as 7.0 fs in root-mean-square. Our result showed the applicability of the beam branching scheme to advanced photon diagnostics, which will further enhance experimental capabilities of XFEL.

A soft X-ray free-electron laser beamline at SACLA: the light source, photon beamline and experimental station

“…In parallel to the operation, upgrades and developments of the beamline continue. For example, we plan to install an arrival-timing monitor between soft X-ray FEL and optical laser pulses (Maltezopoulos et al, 2008;Harmand et al, 2013;Katayama et al, 2016), and a nondestructive spectrometer (Frassetto et al, 2008;Brenner et al, 2011) at the experimental station. We will also expand the diameter of the orifices to 10 mm in the transport channel in order to improve the beam profile with increased transmission in long-wavelength regions.…”

“…The SPring-8 Å ngstrom Compact free-electron LAser (SACLA), constructed in Harima, Japan, achieved first lasing at 10 keV in June 2011 and started operation for users in March 2012 with two beamlines: BL3 for a hard X-ray FEL, which is capable of generating the shortest wavelength FEL below 0.8 Å , and BL1 for wide range spontaneous emission (Ishikawa et al, 2012;Yabashi et al, 2015). Based on unique capabilities and continuous upgrades (Hara et al, 2013;Mimura et al, 2014;Katayama et al, 2016) and users' demands for higher availability led us to construct the second XFEL beamline (BL2), which has been operating since April 2015. At the same time, a much smaller number of research proposals applied for BL1, mainly because only spontaneous radiation was available with one undulator unit of 4.5 m length.…”

Status of the SACLA Facility

“…To improve the time resolution, we developed an arrival timing monitor by probing the ultrafast change in optical transmittance induced by intense XFEL light with a spatial decoding technique [36,37]. A unique feature of our optical design is the utilization of an X-ray elliptical mirror for increasing X-ray intensity to form a line-focused profile, which suppresses the X-ray pulse energy that is required to be as small as several microjoules at~10 keV.…”

“…One of the most critical demands from users is to increase beam time, which recently led us to construct new beamlines and to develop an innovative scheme to switch XFEL over multiple beamlines in a pulse-by-pulse manner [28]. We have also developed various new beamline/end-station instruments and data acquisition/analysis systems to advance experimental capabilities [29][30][31][32][33][34][35][36][37].…”

“…The gratings are used for simultaneous diagnostics of timing [36] and/or spectrum [29] at the first experimental hutch EH1 with user experiments performed at another experimental hutch [37].…”