Design of Ultrahigh Energy Resolution RIXS Beamline at NanoTerasu
Jun Miyawaki, Kentaro Fujii, Takashi Imazono, Koji Horiba, Yoshiyuki Ohtsubo, Nobuhito Inami, Takeshi Nakatani, Kento Inaba, Akane Agui, Hiroaki Kimura, Masamitu Takahasi
Abstract
Abstract The optical design of the ultrahigh-resolution RIXS beamline, which is currently developed at NanoTerasu in Japan, is described. The main goal of this beamline is to perform ultrahigh-resolution RIXS measurements with a total energy resolution of <10 meV at 250–1000 eV with E /Δ E >150,000 for both beamline and RIXS spectrometer. To achieve the ultra-high resolution, a 2D-RIXS spectrometer using energy-dispersive X-ray is employed to compensate for lower throughput at higher energy resolution, and the optics of the beamline is optimized for the 2D-RIXS spectrometer. A vertically dispersing in-focus variable-included-angle varied-line-spacing plane grating monochromator is employed for the beamline, with an entrance slit to ensure the ultrahigh resolution. First and second mirrors focus X-ray on entrance slits vertically and horizontally, respectively, and the divergent X-ray is irradiated onto the grating. For the 2D-RIXS spectrometer, there is no exit slit, and the vertically energy-dispersed X-ray is irradiated directly onto a sample. In front of the sample, X-ray is horizontally refocused by a Wolter type-I mirror. The expected horizontal focus size at the sample is ~0.7 μm. The expected photon flux is ~1×10 11 photons/s at 500–1000 eV with a virtual slit width of 2 μm required for E /Δ E >150,000. The height of the dispersed X-ray available in the 2D-RIXS spectrometer is ~120 μm, which allows the use of a remarkably high flux of ~6×10 12 photons/s, and the beamline will serve as an ultrahigh-resolution and high-efficiency RIXS facility.