Damage study of optical substrates using 1-μm-focusing beam of hard X-ray free-electron laser

Abstract

We evaluated the ablation threshold of silicon and synthetic fused silica, which are widely used as optical substrates such as those in X-ray mirrors. A focusing XFEL beam with a beam size of approximately 1 μm at a photon energy of 10 keV was used. We confirmed that the ablation thresholds of these materials, which were 0.8 μJ/μm2 for the silicon and 4 μJ/μm2 for the synthetic fused silica, approximately agreed with the melting dose.