Single-crystal silicon ablation with temporally delayed femtosecond laser double-pulse trains

A double-pulse femtosecond laser is used to process single-crystal silicon. Modulating the delay time was discovered to increase the ablation depth and improve the morphology of the ablated surface. The hole fabricated by a dual-pulse with a 200 ps interval is 24.4% deeper than that created by a single pulse of the same energy. Moreover, utilizing a dual pulse with an interval ranging from 100 to 1000 ps produces a considerably smoother ablation area as compared to the single pulse. The effect of the sub-pulse energy ratio of the double-pulse femtosecond laser on the size and morphology of the ablated area was also investigated. As the sub-pulse energy ratio decreases from 3:1 to 1:3, the size of the ablation area initially decreases and then increases, while the size of the ablation area is minimized when the sub-pulse ratio is 1:1, enabling precise control over the machining size. As the energy of the second sub-pulse increases, the ablation area becomes smoother due to the plasma heating of the double-pulse femtosecond laser.