High Bragg reflectivity of diamond crystals exposed to multi‐kW mm−2 X‐ray beams. (19th June 2018) - Kolodziej, Tomasz
Abstract : Ultrahigh‐precision Bragg reflectivity studies of diamond single crystals exposed to X‐ray beams of power densities corresponding to the X‐ray Free Electron Laser Oscillator are presented. Abstract : 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.