Experimental and Numerical Approaches to Controlling CO₂ Laser Micro-Ablation of Fused Silica Glass: Surface Profile and Heat-Affected Zone

Fused silica is a cornerstone material in photonics thanks to its outstanding optical, thermal and mechanical robustness. Its surface can be selectively functionalized with CO₂ lasers, whose strong infrared absorption confines energy to a thin layer and enables precise thermal effects—from annealing to ablation and laser polishing. Here we quantify how CO₂ laser parameters govern crater morphology and the surrounding heat-affected zone (HAZ). Pits were machined with a 180 µm-diameter focused beam using single pulses from 10 µs to 2 s across the evaporative regime. Optical profilom-etry coupled with quantitative phase microscopy maps both topography and subsurface refractive-index changes, providing a rapid, non-destructive assessment of the HAZ. We show that, for a fixed removal depth, crater aspect ratio and HAZ width can be tuned independently by modulating pulse width and power: short, high-fluence pulses minimize collateral damage and favor smooth profiles. A two-dimensional finite-element model reproduces the transient temperature field and corroborates the experimental trends. The resulting guidelines enable high-precision CO₂ laser processing of fused silica while mitigating HAZ and associated thermo-mechanical stress, microcracking and debris— crucial for generation of advanced optical components.