Arrival timing diagnostics at a soft X-ray free-electron laser beamline of SACLA BL1.

Shigeki Owada,Hirokatsu Yumoto,Tadashi Togashi,Tetsuo Katayama,Makina Yabashi,Haruhiko Ohashi,Kyo Nakajima

doi:10.1107/s1600577519002315

Abstract

An arrival timing monitor for the soft X-ray free-electron laser (XFEL) beamline of SACLA BL1 has been developed. A small portion of the soft XFEL pulse is branched using the wavefront-splitting method. The branched FEL pulse is one-dimensionally focused onto a GaAs wafer to induce a transient reflectivity change. The beam branching method enables the simultaneous operation of the arrival timing diagnostics and experiments. The temporal resolution evaluated from the imaging system is ∼22 fs in full width at half-maximum, which is sufficient considering the temporal durations of the soft XFEL and the optical laser pulses.

Highlights

The soft X-ray free-electron laser (XFEL) beamline BL1 of SACLA (Ishikawa et al, 2012), which employs a dedicated 800 MeV LINAC, started user operation in July 2016
In hard XFEL beamlines, transient optical reflectivity or transmissivity changes of semiconductors induced with XFEL irradiation have been probed using a spatial or spectral encoding scheme
In the extreme ultraviolet (EUV) and soft XFELs, the THz field streaking method with gas targets has been applied (Grguras et al, 2012; Juranic et al, 2014; Ivanov et al, 2018) because it is non-destructive in this photon energy region

Summary

Introduction

The soft X-ray free-electron laser (XFEL) beamline BL1 of SACLA (Ishikawa et al, 2012), which employs a dedicated 800 MeV LINAC, started user operation in July 2016. In this beamline, SASE–FEL in the photon energy range 40–150 eV is available with an average pulse energy of $80 mJ at 100 eV (Owada et al, 2018a,b). At SACLA BL3, a beam branching method using transmissive grating combined with one-dimensional focusing enabled the performance of pump– probe experiments simultaneously with the arrival timing diagnostics (Sato et al, 2015; Katayama et al, 2016). We report the design of the timing diagnostics system and the commissioning results including the arrival-timing correlation between the branched beam and the main beam

Design

Single-shot arrival timing diagnostics

Temporal resolution

Correlation measurement

Summary