The Spatiotemporal Dynamics of Electron Plasma in Femtosecond Laser Double Pulses Induced Damage in Fused Silica

In this study, we employed the fs time-resolved shadowgraphy method to investigate the impact of the first pump pulse (DP1) on the transient temporal and spatial evolution of electron plasma induced by femtosecond (fs) laser double pulses (DPs) in fused silica. It was observed that the DP1-induced phase transition acted as a waveguide, confining the propagation of the second pump pulse (DP2) light inside the material and resulting in a decrease in the diameter of the DP2-induced electron plasma region. Moreover, the DP2-induced maximum peak electron density was higher than that induced by a single pulse (SP) at the same pulse energy, which may be explained by the DP1-induced highly absorbing semi-metallic state of warm dense glass in fused silica. Importantly, as the energy of DP1 increased, the mean diameter of the DP2-induced electron plasma region further decreased, and the maximum peak electron density increased. Compared with SPs, DPs more easily produced damage in fused silica. In addition, the mean diameter of the DP2-induced electron plasma region and the maximum peak electron density remained almost unchanged when the pulses’ time separation (t_s) was changed from 1 to 50 ps, mainly due to the long relaxation time of the phase transition caused by DP1.