Repair of Fused Silica Damage Using Selective Femtosecond Laser-Induced Etching

Abstract

Timely repair of fused silica damage ensures the stable operation of high-power laser systems. In the traditional repair process, the material nearby the damaged area is gradually ablated with CO2 or femtosecond laser. Subsequently, homogenization and residual stress removal are required because of the microcracks and thermal accumulation generated with the ablation. As a result, the repair efficiency is greatly restricted. In this paper, a new method using in-volume, selective femtosecond laser-induced etching to repair the damage of fused silica is proposed. The region irradiated by femtosecond laser becomes more susceptible to the etching solution due to its constitutive characteristics having undergone chemical restructuring. In this way, material nearby the damaged area transparent to the laser radiation is modified locally inside the volume. A femtosecond laser is used to scan the damaged area with a 3D hollow trajectory. The applicable modification of fused silica occurs when the single pulse energy is approximately 2 μJ to 5 μJ, the repetition frequency is approximately 200 kHz to 500 kHz, and the scanning speed is approximately 10 mm/s. Then, the etching solution reacts quickly along the 3D profile of the modified path, and the damaged area is removed as a whole piece. This method can greatly reduce the workload of repair, and the etching process of fused silica is carried out synchronously. So, the etching efficiency is not affected by the number of damage points. In addition, the weak reaction between the etching solution and the substrate could homogenize the interface. It provides an efficient way to repair the surface damage of fused silica.