This article reports the progress in the beamlines at the SPring-8 Angstrom Compact free electron LAser (SACLA). The beamline optical and diagnostics systems have been upgraded to further accelerate the scientific applications of X-ray free-electron lasers (XFELs). End-station instruments have also been developed to provide user-friendly experimental platforms which allow efficient data collection. Along with the upgrades of beamlines and experimental stations, we have established reliable and efficient procedures of the beamline operation.
We proposed a split and delay optics setup with Si(220) crystals combined with Kirkpatric-Baez mirror optics for x-ray
pump-x-ray probe experiments at x-ray free-electron laser facilities. A prototype of the split-delay optics and its
alignment procedure were tested at BL29XUL of SPring-8. The horizontal focal profile, measured via double-beam
operation, showed good spatial overlap between the split beams with an FWHM of 100 nm, near the diffraction limit at
10 keV. High throughputs of the split-delay optics of 12% (upper) and 7.4% (lower) were obtained. The throughputs can
be improved to 30% and 20% by optimizing the upper and lower central energy, respectively.
We have developed a new method to fabricate ultrathin silicon single crystals, which can be used as spectral beam
splitters for the hard x-ray regime, based on a reactive dry etching process using plasma at atmospheric pressure. The
high crystalline perfection of the crystals was verified by both topographic and high-resolution rocking curve
measurements using coherent x-rays at the 1-km-long beamline, BL29XUL of SPring-8. The development of thin
crystals enables the construction of a split-delay unit and the provision of a dedicated branch for photon diagnostics. By
using a 20-μm-thick Si(111) crystal in the symmetric Bragg geometry as a component of a Si(111) double-crystal
monochromator, an arrival-time monitor using a destructive manner has been upgraded to a non-destructive method at
SPring-8 Angstrom Compact free-electron LAser. Using the splitting crystals in a helium atmosphere can prevent
oxidation, which can introduce a lattice distortion.