A micro channel-cut crystal X-ray monochromator for a self-seeded hard X-ray free-electron laser

A channel-cut Si(111) crystal with a channel width of 90   µ m was developed for achieving reflection self-seeding in hard X-ray free-electron lasers (XFELs). With the crystal a monochromatic seed pulse is produced from a broadband XFEL pulse generated in the first undulator section with an optical delay of 119   fs at 10   keV. The small optical delay allows a temporal overlap between the seed optical pulse and the electron bunch by using a small magnetic chicane for the electron beam placed between two undulator sections. Peak reflectivity reached 67%, which is reasonable compared with the theoretical value of 81%. By using this monochromator, a monochromatic seed pulse without broadband background in the spectrum was obtained at SACLA with a conversion efficiency from a broadband XFEL pulse of 2 × 10 − 2, which is ∼ 10 times higher than the theoretical efficiency of transmission self-seeding using a thin diamond (400) monochromator.

Source: Journal of Synchrotron Radiation - August 26, 2019 Category: Physics Authors: Osaka, T. Inoue, I. Kinjo, R. Hirano, T. Morioka, Y. Sano, Y. Yamauchi, K. Yabashi, M. Tags: XFELs self-seeding channel-cut crystals research papers Source Type: research