The onset of optical breakdown in KrF-laser-irradiated silica glass surfaces

We have investigated the onset of surface optical breakdown on a polished, synthetic silica glass under KrF excimer laser irradiation. With increasing laser fluence, a transient, localized luminescence is often observed. If the fluence is increased further, the luminescence reappears and grows gradually more intense with continued exposure. Subsequent examination of damaged surfaces show small craters, about 1 mm in diameter, in the damaged region. Surfaces damaged by single laser pulses at still higher fluences show similar morphologies, suggesting that the same defects or flaws are responsible for damage under multiple pulse and single pulse conditions