<title>Degradation of fused silica at 193 nm and 213 nm</title>

Abstract

Accelerated damage experiments were conducted to better predict the lifetime of fused silica optics under Deep-UV lithographic conditions. Real-time monitoring of UV-induced absorption showed that 193-nm radiation produced color centers four to five times faster that 213-nm radiation. Since the two-photon absorption coefficient at 193-nm is also about five times larger than the 213-nm value, a two-photon initiated damage process was supported. Refractive index changes in irradiated samples extrapolated from stress-induced birefringence distributions and a compaction model correlated with the refractive index changes calculated from interferometry measurements. The rates of UV-induced refractive index changes varied by over a factor of two among five different fused silica types, indicating that fused silica chemistry and processing history effect compaction susceptibility. The compaction rates, when extrapolated down to lithographic intensities, predict that the lifetimes of fused silica optical systems may be limited by UV- damage.