Photoabsorption of synthetic silica glass under ArF excimer laser irradiation

In-situ measurement of the transmittance change at 220 nm in synthetic sili ca glass under the ArF excimer laser irradiation showed three phenomenologi cal stages: 1) initial coloring stage, 2) saturation stage where the colori ng reaction equilibrates to the discoloring reaction and 3) heavy dosing st age where a rapid increase in photoabsorption occurs after an increase in t he number of laser shots. The coloring rate at the initial stage depends on ly on the sum of the exposed laser power regardless of laser energy density , frequency and OH concentration. The concentration of OH in the glass redu ces the photoabsorption at the saturation stage by increasing the extent of discoloring reaction while it scarcely influences on the number of shots a t which the rapid photoabsorption occurs in the heavy-dose region.