Optimization of a laser mitigation process in damaged fused silica

One of the major concerns encountered in high power laser is the laser-induced damage of optical components. This is a main issue of the development of the Europe's biggest laser, known as Laser Méga Joule (LMJ) especially in the section where the beam wavelength is 351 nm. This study deals with the development of a laser treatment process to improve the laser damage resistance of silica optical components. First, by irradiating the component at 355 nm in the nanosecond regime, defects of the silica optic are revealed and evolve as damage. Next, the damaged sites are irradiated with a CO₂ laser at a 10.6 μm wavelength in order to melt and evaporate the silica in the damage neighborhood. In this study, we performed a variation of the CO₂ laser parameters to obtain the most efficient stabilization. To check this stabilization, damage resistance tests were performed with an UV laser representative of the LMJ (at 355 nm/2.5 ns). The results show that we can stabilize weak points and thereby make the component resistant to subsequent UV laser irradiation.