Plasma and ablation dynamics in ultrafast laser processing of crystalline silicon

Mechanisms of ultrafast (femtosecond) laser-induced ablation on crystalline silicon are investigated by time-resolved pump-and-probe microscopy in normal imaging and shadowgraph arrangements. A one-dimensional model of the energy transport is utilized to predict the carrier temperature and lattice temperature as well as the electron and vapor flux emitted from the surface. The temporal delay between the pump and probe pulses is set by a precision translation stage up to about 500 ps and then extended to the nanosecond regime by an optical fiber assembly. The ejection of material is observed at several picoseconds to tens of nanoseconds after the main (pump) pulse by high-resolution, ultrafast shadowgraphs.