Laser-plasma interaction and plasma enhancement by ultrashort double-pulse ablation

In this study, the laser-plasma interaction and the resultant plasma enhancement by ultrashort double-pulse ablation of silicon are investigated. It is found that by carefully selecting inter-pulse delay, the plasma temperature and electron number density can be effectively increased, compared to the case of single-pulse ablation. The strong plasma enhancement is observed at long-pulse delay (above 20 ps), companied by the ablation rate suppression. At short-pulse delay (below 20 ps), strong ablation rate enhancement is observed, with no plasma enhancement. The spatial analysis of plasma temperature shows that the second pulse energy is mainly absorbed by the front portion of the plasma, where the temperature is increased the most. The plasma reheating leads to a faster expansion of the plasma.