Time-resolved spectroscopy of collinear femtosecond and nanosecond dual-pulse laser-induced Cu plasmas

In this paper, we investigate the time-resolved spectroscopy of collinear femtosecond (fs) and nanosecond (ns) dual-pulse (DP) laser-induced plasmas. A copper target was used as an experimental sample, and the fs laser was considered as the time zero reference point. The interpulse delay between fs and ns laser beams was 3 μs. First, we compared the time-resolved peak intensities of Cu (I) lines from Cu plasmas induced by fs+ns and ns+fs DP lasers with collinear configuration. The results showed that compared with the ns+fs DP, the fs+ns DP laser-induced Cu plasmas had stronger peak intensities and longer lifetimes. Second, we calculated time-resolved plasma temperatures using the Boltzmann plot with three spectral lines at Cu (I) 510.55, 515.32 and 521.82 nm. In addition, time-resolved electron densities were calculated based on Stark broadening with Cu (I) line at 521.82 nm. It was found that compared with ns+fs DP, the plasma temperatures and electron densities of the Cu plasmas induced by fs+ns DP laser were higher. Finally, we observed images of ablation craters under the two experimental conditions and found that the fs+ns DP laser-produced stronger ablation, which corresponded to stronger plasma emission.