Varied line-spacing plane grating monochromator for undulator beamline

Abstract
A varied line‐spacing plane grating monochromator is installed at an undulator beamline BL‐19B of the Photon Factory. Small contribution of aberrations to image sizes at a focal plane of the varied line‐spacing plane grating is calculated with use of an optical path function. The largest resolving power obtained from a ray tracing is estimated to be 4600 at a photon energy of 1239.85 eV and 10 000 at 91.2 eV. Gas absorption spectra show the similar extent of resolution obtained by the ray tracing. A high brightness with a high resolution may be realized in this monochromator.