Dynamics and its modulation of laser-induced plasma and shockwave in femtosecond double-pulse ablation of silicon

The dynamics of laser-induced plasma and shockwave was studied using time-resolved shadowgraphy in femtosecond double-pulse ablation of silicon. The morphology and expansion distances of laser-induced plasma and shockwave can be controlled by adjusting the pulse delay. The underlying mechanism was interpreted in terms of suppressed laser-induced air breakdown and enhanced laser energy deposition. The former is proposed to reduce the expansion distance in the longitudinal direction for small pulse delay, while the latter is the dominant mechanism for increasing the expansion distance in the longitudinal and radial directions for pulse delay exceeding a few picoseconds.