Molecular dynamics of the mechanism of ultrashort laser ablation of metals
By means of combining a heat conduction equation for electron with molecular dynamics method, the dynamics of melting and ablation processes at Ni surfaces under femtosecond laser irradiation is studied. The temperature distribution of lattice and the components of ablation products are analyzed, single atoms and clusters constitute the ablation products. The location where ablation occurs and the time when ablation sets in are marked by a strong increase in temperature as well as a sharp decrease in density. Simulation results show that intense evaporation and tensile stresses generated in the target are responsible for the ejection of single atoms and big clusters. The propagation of laser-induced stress wave is also further investigated, and the velocity of stress wave is predicted to be nearly 4.97 km/s simultaneously. The rates of ablation predicted are close to experimental data. A trend of increase with time for the depth of molten zone is predicted. Superheating phenomenon is also discovered.