Morphology and free-electron density evolution in ablation of fused silica with mJ-level femtosecond pulsed laser

This investigation aims to elucidate the morphology and mechanism of laser-induced damage on fused silica surfaces, and the temporal evolution of electron density within the irradiated areas under a 35 fs mJ-level laser system. Several ablation features, including budge and ablated structures, splash, microdroplets, and debris, were observed and subjected to detailed analysis. By distinguishing budge and ablated structures, the ablation occurred when the free-electron density exceeded the critical electron density. Additionally, to achieve a satisfactory cutting situation, a rational scan speed for the mJ-level laser system was considered within the range of 1-5 mm·s^-1, and an ablation threshold was identified around 6 J·cm^-2. The mathematical model proposed in this study provides insights into the launch conditions of ablation on fused silica and analyzes the ablation of fused silica in high energy pulse. The mathematical model could also be used in optimizing technological parameters for processing.