Ultrafast Modulation Of The Molten Metal Surface Tension Under Femtosecond Laser Irradiation

The atomic liquid surface tension is due to its crucial role in advanced manufacturing,microfluidics,different chemical/biological engineering scenarios.Compared with modern ultrafast modulation solid-state(ferro-)electronic properties,the manipulation of the liquid surface has long been limited on the macroscopic space and time scales.Meanwhile,the widely used fs-laser processing in the beyond-extreme manufacturings has shown significant advantages in precisely manipulating the thermodynamic properties of atomic material systems.In this dissertation,based on the computer simulation technology combining the electron-atom dual temperature model and molecular dynamics,a set of precise calculation methods for the spatiotemporal evolution of thermodynamic quantities on the surface of metal liquids under the action of ultrafast laser irradiation are developed.It is used in metal liquid surface systems(Al,Ti and Ni)under low-dose single-pulse femtosecond laser and picosecond laser irradiation.The theoretical possibility of precisely manipulating the atomic structure of the material interface by means of ultrashort-time energy packet injection is demonstrated.This work predicts the formation of a non-hydrostatic pressure region below the surface induced by femtosecond laser action and an ultrafast change in surface tension value.The physical mechanism of ultrafast regulation of surface tension is elucidated by means of the high-precision pressure tensor and the spatiotemporal evolution of stress,and new insights into the relaxation anisotropy of particle packing induced by femtosecond laser irradiation are presented.At the same time,it was found that under the same radiation absorbed dose,the single-pulse picosecond laser could not adjust the mechanical properties of the metal surface because the pulse width was much longer than the characteristic time scale of the density relaxation of the liquid itself.The research found in this paper raises the standard of statistical accuracy for exploring ultrafast physical processes in extreme non-equilibrium states and the dynamic evolution of related properties,and is expected to elevate metal surface control engineering to a new level,inspiring new application potentials,such as : Ultrafast surface directional mass transport and control of liquid surface topography/texture,etc.