Quasi-periodic grating for a monochromator at the Photon Factory BL19B

A quasi-periodic grating, ruled to eliminate second order diffraction, is installed in the monochromator at the Photon Factory BL19B. Higher order diffraction in the spectra of undulator radiation is observed at the non-integer multiples of a fundamental wavelength with the use of the quasi-periodic grating. The quantity of second order diffraction, estimated by photoelectron spectra of gold, is almost zero except at some photon energies.