High Bragg reflectivity of diamond crystals exposed to multi-kW   mm − 2 X-ray beams

X-ray free-electron lasers in the oscillator configuration (XFELO) are future fully coherent hard X-rays sources with ultrahigh spectral purity. X-ray beams circulate in an XFELO optical cavity comprising diamond single crystals. They function as high-reflectance (close to 100%), narrowband ( ∼ 10   meV) Bragg backscattering mirrors. The average power density of the X-ray beams in the XFELO cavity is predicted to be as high as ∼ 10   kW   mm − 2. Therefore, XFELO feasibility relies on the ability of diamond crystals to withstand such a high radiation load and preserve their high reflectivity. Here the endurance of diamond crystals to irradiation with multi-kW   mm − 2 power density X-ray beams is studied. It is shown that the high Bragg reflectivity of the diamond crystals is preserved after the irradiation, provided it is performed at ∼ 1 × 10 − 8   Torr high-vacuum conditions. Irradiation under 4 × 10 − 6   Torr results in a ∼ 1   meV shift of the Bragg peak, which corresponds to a relative lattice distortion of 4 × 10 − 8, while the high Bragg reflectivity stays intact.

Source: Journal of Synchrotron Radiation - June 17, 2018 Category: Physics Authors: Kolodziej, T. Shvyd'ko, Y. Shu, D. Kearney, S. Stoupin, S. Liu, W. Gog, T. Walko, D.A. Wang, J. Said, A. Roberts, T. Goetze, K. Baldini, M. Yang, W. Fister, T. Blank, V. Terentyev, S. Kim, K.-J. Tags: diamond X-ray optics radiation damage X-ray free-electron laser oscillators Bragg reflectivity research papers Source Type: research