The Structure Evolution of Fused Silica Induced by CO₂ Laser Irradiation

The structure evolution of fused silica induced by CO₂ laser irradiation (with a wavelength of 10.6 µm ) is studied in detail. In the non-evaporation mitigation process, the irradiation time should be long enough to completely eliminate damage. However, there is a raised rim around the mitigated site. The rim height is enhanced when the irradiation time increases, and the mitigated site can lead to off-axis and on-axis downstream light intensification. Volume shrinkage occurs during the irradiation and rapid cooling processes, and this may be due to a decrease in the Si–O–Si bond angle. The distribution of debris overlaps with the maximum phase retardance induced by stress. The debris arouses an enhanced light absorption in the region from 220 nm to 800 nm.