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

摘要

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 alpha(N, H-in) using a modified Beer's law, yielding initial values alpha(ini) around 0.005cm(-1), a maximum alpha(max) <= 0.02 cm(-1) at N= 10(3)-10(4) and stationary values 0.0045 cm(-1) <= alpha(end) <= 0.0094 cm(-1) after N approximate to 6 x 10(5) pulses. The development alpha(N, H-in = const.) is simulated by a rate equation model assuming a pulse number dependent P 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 SiO2 network. The development alpha(N, H-in = const.) is observed for the very first sample irradiation only (virgin state). The values alpha(end) are not accessible by simple spectrophotometer measurements. (c) 2007 Elsevier B.V. All rights reserved.