Molecular dynamics simulation study on the ablative copper forming process at the atomic level by femtosecond laser

Investigating the intrinsic physical mechanisms governing the interaction between femtosecond lasers and copper is pivotal for developing efficient copper material processing techniques. This study integrated a two-temperature model with atomic-scale molecular dynamics simulations to elucidate the interaction mechanisms between femtosecond lasers and copper. The laser ablation process of copper was simulated across a range of distinct laser energy densities and varied laser pulse widths. We disclosed the femtosecond laser sintering process's intricate spatiotemporal dynamics and energy characteristics through a meticulous quantitative analysis of the temporal fluctuations in atomic displacement, temperature, phase content, and pressure. The results show that laser energy density and pulse width are pivotal parameters influencing the laser ablation mechanism. At an energy density of 0.2 J/cm², the interaction between the laser and the copper surface predominantly results in surface stripping. However, at an energy density of 0.6 J/cm², the interaction is more likely to induce explosive stripping. Furthermore, the extension of pulse duration facilitates the formation of explosive stripping. At 1 ps, gaseous atoms swiftly experience a phase transition, producing a significant quantity of liquid atoms. Concurrently, this transition is accompanied by a thermal diffusion effect that facilitates the transition of solid atoms to the liquid phase. The accuracy of the simulation outcomes is validated by correlating the simulated lattice and electron temperatures with corresponding experimental data. Besides, calculating the atomic velocity reveals the nature of the explosive mechanism during laser interaction with the material. These findings establish a theoretical foundation and offer practical guidance for utilizing femtosecond lasers in material processing, particularly within atomic and near-atomic scale manufacturing.