Effects of excimer laser irradiation on the transmission, index of refraction, and density of ultraviolet grade fused silica

TLDR

The study investigates radiation‑induced changes in high‑purity fused silica under prolonged 193‑nm pulsed laser irradiation, analyzing formation mechanisms as radiolytic atomic rearrangement of a‑SiO₂ initiated by two‑photon absorption. The irradiation produces UV absorption bands, increases the index of refraction, and induces stress birefringence, with a quantum efficiency of ~7.5×10⁻⁴ for E′ defect formation and matrix compaction of a few parts in 10⁻⁵ as the source of these changes, and E′ centers can be photobleached.

Abstract

Radiation-induced changes in high-purity fused silica during prolonged irradiation with a pulsed laser at 193 nm have been studied. Radiolytically induced UV absorption bands, an increase in index of refraction, and stress birefringence are observed. The formation mechanisms are analyzed in terms of radiolytic atomic rearrangement of a-SiO2 initiated by two-photon absorption. The quantum efficiency for the formation of E′ point defects per pair of absorbed 193 nm photons has been determined to be ∼7.5×10−4; matrix compaction, as high as a few parts in 10−5, is identified as the source of the birefringence and index change. It has been further observed that E′ centers can be photobleached.