Effects of KrF laser radiation on fused-silica glass: a comparison of samples exposed in air vs vacuum

High-purity synthetic fused silica glass is known to undergo changes in optical properties during high repetition rate KrF laser exposures. (Results of studies on six glass types irradiated in air are summarized elsewhere at this symposium.) We have also irradiated several samples in vacuum (248 nm, 300 Hz, (Phi) equals 400 mJ/cm²). Transmission at 248 nm, transmission at 210 nm, fluorescence at 650 nm, and vacuum cell pressure were monitored in real time. Although bulk outgassing is expected to be very slow at room temperature, our results indicate that the vacuum environment does affect the interior of the sample. Furthermore, a curious irradiation effect on the transmission of the CaF₂ windows used on the vacuum cell is discussed.