Numerical simulation and experimental validation of light modulation by laser-ablated ripples on fused silica surfaces

Laser ablation is a commonly employed technique to enhance the damage resistance of fused silica optics due to its non-contact nature and the absence of polishing aids. However, during the ablation process, laser-induced ripples are inevitably formed, posing significant risks by potentially lowering the laser-induced damage threshold (LIDT). This study investigates the impact of these laser-ablated ripples on damage resistance using numerical models that account for electromagnetic fields, heat transfer, and solid mechanics. The simulations reveal that the laser-induced ripples on the fused silica surface locally increase light field, temperature, and thermal stress, which in turn reduce both the damage threshold and the optical transmittance. The period and height of these ripples play a critical role in modulating the intensity of light, temperature, and thermal stress within the silica material. Ripples with a period from 0.5 µm to 1 µm and a height of over 500 nm typically significantly intensify light and should be carefully avoided. The accuracy of simulated models is supported by their agreement with damage threshold and optical transmittance results. This research provides insights into how surface topography affects the performance of optical components and offers a theoretical basis for producing fused silica optics with high damage resistance.