Kinetics of UV laser radiation defects in high performance glasses

High purity fluoride phosphate glasses are attractive candidates as UV tran smitting materials. The calculated values for the ultraviolet resonance wav elength are comparable with those of pure silica glass or fluoride single c rystal CaF2. The formation of radiation-induced defect centers leads to add itional absorption bands in the VUV-UV-vis range. The damage and the healin g behavior by lamps and lasers are investigated in dependence on phosphate content and the content of impurities, mainly transition metals. Experiment s were carried out using pulsed lasers with a duration of femto- and nanose conds at a wavelength of 248 nm. The initial slope of the induced absorptio n shows a nonlinear dependence on the pulse energy density. Resonant and no n-resonant two-photon mechanisms were observed. Two-photon-absorption coeff icients at 248 nm for samples with different phosphate contents were measur ed. Models of the kinetics of the radiation-induced defects were developed. The inclusion of energy transfer was necessary to explain the difference i ll the damage behavior for nanosecond (248 nm, 193 nm) and femtosecond (248 nm) laser pulses. (C) 2000 Elsevier Science B.V. All rights reserved.