Transient absorption in excimer-exposed silica

The transient absorption produced in high-purity fused silica by exposure t o a 193-nm excimer laser is investigated as a function of exposure, dissolv ed molecular hydrogen content, and hydrogen-related processing. Long-term r ecovery of transmittance was found to correlate with the dissolved molecula r hydrogen concentration, whereas short-term fade was due to geminate recom bination of an E' center with an Il radical. The redarkening process was sh own to be the result of photolysis of SiH, which regenerates color centers. When the silica was processed in a hydrogen atmosphere at high temperature and subsequently exposed at 193 nn, the glass was found to produce an abso rption spike, a fast, recoverable decrease in transmittance. The origin of the spike was linked to the creation of a precursor produced in the thermal reaction of silica with hydrogen. The precursor can be identified by its s ignal in the Raman spectrum. It is suggested that the precursor has absorpt ion at 193 nm. (C) 2000 Optical Society of America. OCIS codes: 160.750, 16 0.4760, 160.6030, 220.3740.