Wavelength dependence of the damage threshold of inorganic materials under extreme-ultraviolet free-electron-laser irradiation

We exposed bulk SiC and films of SiC and B4C to single 25 fs long free-electron-laserpulses with wavelengthsbetween 13.5 and 32 nm. The materials are candidates for x-ray free-electron laseroptics. We found that the thresholdfor surface-damage of the bulk SiC samples exceedsthe fluence required for thermal melting at all wavelengths. The damage thresholdof the film sample shows a strong wavelengthdependence. For wavelengthsof 13.5 and 21.7 nm, the damage thresholdis equal to or exceedsthe melting threshold, whereas at 32 nm the damage thresholdfalls below the melting threshold.