Investigation on emission spectra of reheating and pre-ablation dual-pulse laser-induced breakdown spectroscopy

Two configurations of orthogonal double-pulse laser-induced breakdown spectroscopy (DP-LIBS) and their corresponding signal enhancement mechanisms were investigated in this paper. For pre-ablation DP-LIBS configuration, the first laser was input in parallel to the sample surface while the second laser was perpendicularly input onto the sample surface. For reheating DP-LIBS configuration, the first laser was perpendicularly input onto the sample surface and the second laser was input in parallel to the sample surface. The signal intensities were enhanced using both orthogonal DP-LIBS configurations compared to single laser pulse LIBS. The differences of physical mechanisms involved for both schemes were analyzed using time-resolved spectroscopic technique. Continuous spectrum intensity was reduced using pre-ablation DP-LIBS excitation while it was increased with reheating DP-LIBS excitation. Nine consecutive intensity measurements were performed. Fifteen spectral lines were investigated. The average relative standard deviation of fifteen lines for pre-ablation, reheating DP-LIBS and single pulse LIBS was 5.83%, 1.69% and 4.82%, respectively. It was demonstrated that signal repeatability of reheating configuration was better than that of pre-ablation configuration. A correlation between the enhancements of emission line intensities and their excitation energy levels was established for reheating and pre-ablation double-pulse approach. It was found that reheating configuration showed better improvement in sensitivity at high excitation energy levels compared with pre-ablation configuration.