Micro-Shaping, Polishing, and Damage Repair of Fused Silica Surfaces Using Focused Infrared Laser Beams

Localized infrared (IR) laser heating of fused silica optics has proven highly effective in reducing or removing surface flaws, which tend to limit performance in high power laser systems. Here, we present both simulation and experimental results to examine the use of IR laser light to polish, anneal, and micro-shape fused silica surfaces used in high power laser systems. We show how the resulting material response can be tuned by considering the temperature-dependent optical constants of the material and choosing the appropriate laser parameter set. For example, non-evaporative laser polishing of glass surfaces to heal crack networks is shown most effective when using mid-IR lasers, which lead to laser energy coupling up to approximate to 1mm in depth. In contrast, long-wave IR light tuned to the Restrahlen frequency of the material is shown to evaporate material most efficiently with penetration depths of <1m. Through calibrated, time-resolved thermal imaging we are able to monitor the laser polishing process, to control material response. The results of our studies can be applied beyond the practical application of damage mitigation in high energy pulsed laser systems to any which require laser-smoothing and shaping of silica surfaces.