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Two localized CO2 laser treatment methods for mitigation of UV damage growth in fused silica

Two methods: high-power, short-time, single-shot irradiation (Method A) and low-power, long-time, multi-shot irradiation (Method B) are investigated to mitigate the UV damage growth in fused silica by using a 10.6-μm CO2 laser. To verify the mitigation effect of the two methods, the laser induced damage thresholds (LIDTs) of the mitigated sites are tested with a 355-nm, 6.4-ns Nd:YAG laser, and the light modulation of the mitigation sites are tested with a 351-nm continuous Nd:YLF laser. The mitigated damaged sites treated with the two methods have almost the same LIDTs, which can recover to the level of pristine material. Compared with Method A, Method B produces mitigated sites with low crater depth and weak light modulation. In addition, there is no raised rim or re-deposited debris formed around the crater edge for Method B. Theoretical calculation is utilized to evaluate the central temperature of the CO2 laser beam irradiated zone and the radius of the crater. It is indicated that the calculated results are consistent with the experimental results.