Femtosecond laser ablation is becoming more and more important in micro- and nanomachining fields, as it can remove materials from their surface with significantly less damages at the surrounding area. However, since the laser ablation is strongly non-linear and multi-physics phenomenon, it is not easy to fully understand it only by theoretical and experimental approaches. Molecular dynamics (MD) simulation is one of promising approaches for studying the materials response to the strong laser injection and thus a lot of MD techniques have been developed for the study of laser ablation. Recent theoretical studies suggested that the penetration depth of laser energy into materials surface can be much different from the traditional theory [1] and entropy stemming from the electron excitation can induce softening of irradiated material causing stronger stress confinement near the surface [2]. In order to study these effects on laser ablation phenomena, we apply energy penetration depth obtained from a time-dependent DFT result and electron-temperature dependent force-field [3] to laser ablation MD simulation. The force-field reproduces the softening according to the rise of electron temperature. We will discuss in detail how these affect the laser ablation of materials surface from the point of atomic scale.

[1] Sato, S. A., Yabana, K., Shinohara, Y., Otobe, T., & Bertsch, G. F. (2014). Physical Review B, 92, 205413.

[2] Tanaka, Y., & Tsuneyuki, S. (2018). Applied Physics Express, 11(4), 46701–46704.

[3] Shokeen, L., & Schelling, P. K. (1995). IEEE Transactions on Microwave Theory and Techniques, 43(8), 1826–1833.