Heat treatment of fused silica optics repaired by CO2 laser

In the context of high power laser applications, we study the effect of a heat treatment on CO2 laser mitigation of laser damage sites on fused silica samples. The isothermal annealing in a furnace is investigated and then compared to the local annealing by CO2 laser irradiation that is applied to enhance laser damage resistance on mitigated sites. Before and after isothermal annealing, we study the sites morphology, the evolution of residual stress and the laser-induced damage threshold measured at 355nm, 3ns. The results show that the initial laser damage probabilities were significantly improved after annealing at 1050 degrees C for 12 hours. These results are compared to simulations with a thermo-mechanical model based on finite-element method.