Hydrodynamic expansion and plume splitting of the ultrafast laser-induced plasma during ablation of multi-element metallic materials under atmospheric condition

Abstract

In this study, the hydrodynamic expansion and splitting effect of ultrafast laser-induced plasma plume for multi-element alloys were studied. A fully coupled hydrodynamic model for femtosecond laser ablation of multi-element alloys was presented to study the ambipolar electric field during the plume expansion process. The model utilized a level-set equation to capture the interface between the condensed phase and the gaseous phase and accounted for the reaction between different species. A time-gate direct fluorescence measurement was conducted for the target material of brass, a Cu–Zn alloy, to validate the simulation results. The simulation results showed good agreement with the experimental results and were able to predict the plume-splitting effect. The ambipolar electric field induced by charged particle distribution difference was studied in detail. It was found that the ambipolar electric field was the dominant cause for the acceleration of ions, which yielded plume splitting during the expansion process. The fully coupled HD model was further used to explore the effect of the beam spot size, laser fluence, and the pulse width on plasma plume splitting.