Damage threshold of inorganic solids under free-electron-laser irradiation at $32.5nm$ wavelength

Samples of $B4C$⁠, amorphous C, chemical-vapor-deposition-diamond C, Si, and SiC were exposed to single $25fs$ long pulses of $32.5nm$ free-electron-laser radiation at fluences of up to $2.2J∕cm2$⁠. The samples were chosen as candidate materials for x-ray free-electron-laser optics. It was found that the threshold for surface damage is on the order of the fluence required for thermal melting. For larger fluences, the crater depths correspond to temperatures on the order of the critical temperature, suggesting that the craters are formed by two-phase vaporization.