Effect of dual-pulse temporal shaping on ultraviolet nanosecond laser damage of fused silica surface in high fluence regime

We present the effect of dual-pulse temporal shaping on ultraviolet nanosecond laser damage characteristics of fused silica exit surface in the high fluence regime. The pre-pulse and post-pulse have the opposite effects on the damage behaviors at pulse delay of 20 ns. The pre-pulse irradiation significantly increases the main-pulse threshold to be much higher than the single-pulse threshold, but the post-pulse has little effect on the main-pulse threshold. For near-threshold damage sites, the pre-pulse reduces the average damage size and depth to be smaller than those of single-pulse, while the post-pulse drastically increases the average size and depth to be much larger than single-pulse. The average size of the damage site is monotonously increased from 43.6 µm to 127.9 µm with raising the post-pulse energy. For the pre-pulse case with the shape factor of 0.61, the damage threshold of main-pulse increases with the delay and nearly stabilizes after 10 ns. The underlying mechanism of the temporal-shaping effect on laser damage is discussed based on the switch of the precursor modification to absorption enhancement, which could provide insights for studying ultraviolet laser damage of fused silica optics.