Laser irradiation-induced regulation of molten lead surface tension

Despite ultrafast control already achieved for solid-state properties via femtosecond lasers, manipulation of liquid surfaces has long remained confined to macroscopic spatiotemporal scales. This study employs molecular dynamics simulations combined with a two-temperature model (TTM-MD) to investigate the dynamic response of a molten Pb surface under irradiation by a single 200 fs laser pulse at a low absorbed fluence of 16 mJ/cm 2 . The results show that the surface tension drops sharply to about 77% of its equilibrium value within 2 ps after irradiation, and then recovers to approximately 90% within 10 ps. This modulation arises from non-uniform energy deposition that induces a non-equilibrium stress state and interfacial field reconstruction, with the subsurface liquid layer dominating the relaxation process. The observed changes do not follow the equilibrium thermodynamic temperature dependence, indicating a distinct mechanism. This work offers new physical insights into ultrafast control of liquid surfaces and opens avenues for atomic-scale directed transport.