Thermal ablation of metal films by femtosecond laser bursts

Thermal ablations of metal films by a single femtosecond laser pulse and by a laser burst were investigated using a comprehensive computational model, including a two-temperature model with dynamic optical properties, two phase change models for melting and evaporation under superheating, and a phase explosion criterion for ejection of the mixture of metastable liquid droplets and vapor. Numerical simulations were performed for copper films. The simulation of material ablation by the single pulse showed a good agreement with existing experimental data for a broad range of laser fluence 0.6-30 J/cm². In the study of material ablation by femtosecond laser bursts, it was found that under the same total fluence a laser burst with a pulse separation time of 50 ps or longer can significantly boost the ablation rate, compared to the single pulse. It was also demonstrated that for a given total fluence the ablation rate can be optimized by selecting a proper combination of pulse number and separation time in a laser burst.