DEGRADATION OF TRANSMISSION OF SILICA GLASS ON EXCIMER LASER IRRADIATION

The effects of prolonged irradiation of KrF (248 nm) and ArF (193 nm) lasers on the optical properties of silica glass were studied, with a glass made from a high purity silicon tetrachloride by the oxy-hydrogen flame hydrolysis method for sample. Experiments were conducted as an acceleration test for services in excimer laser apparatuses, and the results were examined in terms of solarization, i.e., degradation in transmission, T, or increase in the absorption coefficient at 5.8 eV, k2, as a function of the per pulse laser energy density, epsilon. It was found that k2 was related to epsilon as in: for KrF excimer laser: k2 = 2.38 x 10(-7).epsilon3.15 (epsilon.p)1.31, and for ArF excimer laser: k2 = 8.71 x 10(-8).epsilon1.42 (epsilon.p)1.45, where p is the number of shots. It was demonstrated that these formulas were precise enough to make reasonable estimates of the service lifetime for silica glass in industrial excimer laser apparatus, where the intensity of the laser would be much smaller.