Transient 210-nm absorption in fused silica induced by high-power UV laser irradiation

Synthetic fused silica, exposed to high-power KrF excimer laser irradiation, shows the well-known induced absorption at 210 nm owing to E′ center generation. Time-resolved absorption spectroscopy reveals that this induced absorption is transient in nature. The generation rate of E′ centers depends strongly on the irradiation history, the OH content, and previous high-temperature processes. In order to explain the experimental observations, a nonabsorbing state of the E′ center is postulated. The recovery of the induced optical absorption in high-OH fused silica is explained as a conversion from E′ centers to these nonabsorbing centers.