Deep-ultraviolet damage to fused silica

Abstract

Several experiments using 213-nm radiation have been performed with the goals of characterizing and understanding better the mechanisms behind UV damage to fused silica. A novel method of monitoring compaction in real time was discovered which measures the amount which the damaged fused silica depolarizes the incident beam. Refractive index changes of less than one part in ten million were resolved. Compaction induced stress was observed to extend well beyond the irradiation site with a maximum at the edge of the irradiation site. Detection of compaction occurred much earlier than the detection of color center absorption when fused silica was irradiated. The rates of both compaction and of color center formation depend superlinearly on pulse energy density and can be fitted by a quadratic function, suggesting a two-photon damage process. In the same energy density range, the absorption coefficient depends linearly on energy density, from which we extract a 213-nm two-photon absorption coefficient of 5×10−4 (cm/MW). This value is a factor of 4 smaller than the value published for 193 nm [R. S. Taylor et al., Appl. Opt. 27, 3124 (1988)].