Comparison of plume expansion in femtosecond laser ablation on oxidized and non-oxidized Sm surfaces

Time development of Sm+ and Sm ablation plume produced by the femtosecond laser irradiation has been investigated. The two-dimensional spatial profiles of Sm and Sm+ emitted from oxidized and non-oxidized Sm surface were visualized using a planar laser-induced fluorescence method. It was observed that the flow velocity of Sm+ is much faster than that of Sm plume in both surfaces. The plumes from the oxidized Sm surface show higher velocity than that from non-oxidized surface, which is originated by the small electric conductivity at the surface. Expansion property observed for Sm+ and Sm plume in the oxidized Sm surface ablation implies the formation of the Knundsen layer nearby the surface. Meanwhile, continuous emission of Sm indicates the large contribution of heating effect to emission process at the non-oxidized surface. We conclude that the fsLA process strongly depends on the electric property of the ablated surface and the heating effect contributes to the particle emission process on the conductive material surface.