Numerical study of titanium film ablation under different ultrafast laser parameters: a molecular dynamics simulation combined with a two-temperature model

To study the ablation mechanism of titanium (Ti) film under ultrafast laser, the irradiation process of Ti film under various pulse widths, energy densities, and wavelengths is analyzed by molecular dynamics combined with a two-temperature model (MD-TTM). The temperature distribution of Ti film under ultrafast laser irradiation is solved based on TTM and the ablation phenomenon is explored through MD simulation. It is found that the energy density and wavelength have a more significant impact on the ablation than pulse width. The shorter the laser wavelength, the smaller the penetration depth, and the more obvious the ablation phenomenon. The higher laser energy density and shorter wavelength result in higher irradiation temperature of the Ti film, wherein the ablation phenomenon becomes more pronounced. Moreover, the stress distribution of Ti film after ultrafast laser irradiation is investigated, and it can be found that the instantaneous laser irradiation induces compressive stress on the entire Ti film. The stress within the non-penetration layer is significantly higher than that within the penetration layer of the Ti film, and stress mutations are mainly concentrated at the interface between the penetration and non-penetration layers of the Ti film. Furthermore, the pulse width has little effect on the stress of the Ti film in the penetration layer while larger energy density and shorter wavelength lead to faster stress release.