Localized CO₂ laser damage repair of fused silica optics

A technique has been developed for the localized treatment of laser damage sites in fused silica optics by CO₂ laser melt-flow smoothing, by using a 50 to 125 µm diameter beam in a regime that avoids mass removal by ablation. A detailed calibration of the laser irradiance for the threshold ablation of craters was carried out for a range of beam diameters and pulses in the 20 µs to 200 ms range. The results agree with a thermal model that also provides estimates of the melt depth for the different irradiation conditions. Smoothing trials for glass melting at irradiance values just below the ablation threshold irradiance were conducted to determine the optimum conditions and limits for the smoothing process. The technique has been found to remove damage pits up to a depth of 0.5 µm, while the small melt depth associated with localized treatment limits the smoothing to a <5 µm lateral size. © 2006 Optical Society of America.