Generation and annealing of defects in virgin fused silica (type III) upon ArF laser irradiation: Transmission measurements and kinetic model

Abstract

The transmission of ArF laser pulses in virgin fused silica (type III) samples changes during N = 10 6 pulses at an incoming fluence H in = 5 mJ cm −2 pulse −1. The related absorption is determined by the pulse energy absorption coefficient α( N, H in) using a modified Beer’s law, yielding initial values α ini around 0.005 cm −1, a maximum α max ⩽ 0.02 cm −1 at N = 10 3–10 4 and stationary values 0.0045 cm −1 ⩽ α end ⩽ 0.0094 cm −1 after N ≈ 6 × 10 5 pulses. The development α( N, H in = const.) is simulated by a rate equation model assuming a pulse number dependent E′ center density E′( N). E′( N) is determined by a dynamic equilibrium between E′ center generation and annealing. Generation occurs photolytically from the precursors ODC II and unstable SiH structures upon single photon absorption and from strained SiO bonds via two-photon excitation. Annealing in the dark periods between the laser pulses is dominated by the reaction of E′ with H 2 present in the SiO 2 network. The development α( N, H in = const.) is observed for the very first sample irradiation only (virgin state). The values α end are not accessible by simple spectrophotometer measurements.