Picosecond Laser Ablation of Glass Surface by Dual-pulse Temporal Shaping

Based on the dual-pulse with sub-nanosecond interval, we investigated the regulation of dual-pulse temporal shaping on picosecond ablation characteristics of K9 glass surface, including ablation morphology, size, and threshold. With sub-pulse interval of 667 ps, the dependence of the ablation morphology on the laser fluence are significantly different for various shapes of dual-pulse, and the pump pulse plays the critical role. When the pump fluence is below the threshold, the dual-pulse ablation characteristics are basically similar to those of a single pulse. When the pump fluence is near the threshold, the ablation of the pump pulse on the surface at the submicron scale significantly enhances the ablation effect of the probe pulse. When the pump fluence is above the threshold of 1.3 times, the pump pulse generates a shock wave near the surface, and the probe pulse is reflected and interfered by the high-density shock front, which produces concentric rings around the central ablation region. The distribution of the concentric rings is closely related to the probe fluence. The core size of the dual-pulse ablation is related to the pump fluence, while the outer diameter size is related to both the dual-pulse shape and fluence. In addition, we compared the ablation morphology of flat-shaped dual-pulse with sub-pulse intervals of 333 ps and 667 ps. The smaller interval enhances the ablation effect at a low fluence, while the ablation outcome of a pump pulse above the threshold prevents the energy deposition of the probe pulse. The difference in the concentric ring morphology between the two intervals reflects the transmission of the shock front caused by the pump pulse. Finally, the physical mechanism of surface ablation regulation by the dual-pulse temporal shaping is discussed based on the experimental results.