Molecular dynamics simulation of femtosecond ablation and spallation with different interatomic potentials

Fast heating of target material by femtosecond laser pulse (fsLP) with duration τL∼40-100 fs results in the formation of thermomechanically stressed state. Its unloading may cause frontal cavitation of subsurface layer at a depth of 50 nm for Al and 100 nm for Au. The compression wave propagating deep into material hits the rear-side of the target with the formation of rarefaction wave. The last may produce cracks and rear-side spallation. Results of MD simulations of ablation and spallation of Al and Au metals under action fsLP are presented. It is shown that the used EAM potentials (Mishin et al. and our new one) predict the different ablation and spallation thresholds on absorbed fluence in Al: ablation Fa=60{65} mJ/cm2and spallation Fs=120{190} mJ/cm2, where numbers in brackets { } show the corresponding values for Mishin potential. The strain rate in spallation zone was 4.3×109 1/s at spallation threshold. Simulated spall strength of Al is 7.4{8.7} GPa, that is noticeably less than 10.3{14} GPa obtained from acoustic approximation with the use of velocity pullback on velocity profile of free rear surface. The ablation threshold Fa≈120 mJ/cm2 and crater depth of 110 nm are obtained in MD simulations of gold with the new EAM potential. They agree well with experiment.