Short-pulse laser ablation of solids: from phase explosion to fragmentation

The mechanisms of laser ablation in silicon are investigated close to the threshold energy for pulse durations of 500 fs and 50 ps. This is achieved using a unique model coupling carrier and atom dynamics within a unified Monte Carlo and molecular-dynamics scheme. Under femtosecond laser irradiation, isochoric heating and rapid adiabatic expansion of the material provide a natural pathway to phase explosion. This is not observed under slower, nonadiabatic cooling with picosecond pulses where fragmentation of the hot metallic fluid is the only relevant ablation mechanism.