Design of an 18 m spherical-grating monochromator at UVSOR

An 18 m spherical-grating monochromator with high resolution and high photon flux has been developed at the bending-magnet beamline BL2B2 of the UVSOR facility in the Institute for Molecular Science. The monochromator is designed to cover the energy range 20-200 eV by using three gratings: G1 (2400 lines mm(-1), R = 18 m) at 80-200 eV; G2 (1200 lines mm(-1), R = 18 m) at 40-100 eV; G3 (2400 lines mm(-1), R = 9.25 m) at 20-50 eV. A resolving power of 5000 and a photon flux of more than 10(10) photons s(-1) are expected at a 100 mA ring current. A small including angle of 140 degrees is adopted for G3 and two plane mirrors coated with aluminium are located between G3 and the exit slit as optical filters. These geometrical devices may contribute significantly to the reduction of the high-order lights.