The influence of residual heat on the fictive temperature modification zone of fused silica for different CO₂ laser scanning time intervals was investigated to precisely control the profiles of hydrofluoric (HF) acid-etched fused silica surface, which were formed by the increasing HF acid-etching rate for fused silica with increasing fictive temperature induced by CO₂ laser scanning. The surface profiles of HF acid-etched fused silica treated by different scanning time intervals of CO₂ laser were measured by a stylus profilometry, and experimental results indicate that the CO₂ laser scanning time intervals intensively influence the HF acid-etched surface profiles of fused silica. The increasing depth of surface profiles treated by shorter scanning time intervals shows that the fictive temperature modification zone significantly expands. Numerical simulations of the fictive temperature modification zone induced by different scanning time intervals indicate that the residual heat of CO₂ laser scanning with shorter time intervals leads to a dramatical increase in the fictive temperature modification zone. By adjusting the residual heat of CO₂ laser scanning intervals, various surface profiles of fused silica can be obtained by HF acid-etching of fused silica.

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.

SiO₂ sol-gel antireflection film coated on fused silica can reduce the reflection loss and improve the transmittance of the optical component, although it is still prone to laser induced damage. Laser conditioning is an effective way to improve the laser induced damage threshold (LIDT) of SiO₂ sol-gel antireflection film. In this paper, single-layer SiO₂ sol-gel antireflection films pretreated by triple-frequency laser with different parameters are characterized by the macroscopical parameters, such as transmittance, refractive index, and thickness. The law of surface modification and the defect removal mechanism of the SiO₂ sol-gel antireflection film by laser conditioning are obtained. It is found that laser conditioning can reduce the thickness of the film and introduce densification. In addition, laser conditioning can eliminate micro-defects, such as vacancies and voids in the preparation of SiO₂ sol-gel antireflection films, which is the main reason to improve the laser damage resistance of films. Finally, the laser conditioning process with three step laser energy combinations of (0.2–0.6–1.0) F_th0 (zero damage threshold) is the best one to obtain high transmittance, and excellent effects on structure modification and defect removal of films. The research in this paper provides data support for the engineering application and mechanism research of laser conditioning.