Multi-element signal enhancement mechanism investigation for laser ablation-assisted ultraviolet laser excited atomic fluorescence

Abstract

Multi-element detectable laser excited atomic fluorescence (LEAF) technique has been regarded as impressive progress in the analytical field because it possesses high sensitivity and overcomes the specific resonant wavelength constraint. However, a limited understanding of the universal signal enhancement mechanism restricts its further development and follow-up studies. In this study, experiments of LEAF are conducted to investigate the details of the ablation process, excitation process, and coupling behavior. Multi-element signals were dramatically enhanced with 1.49 mJ ablation laser energy at t_ip = 200 ns, and quantitative analysis with minimal destruction was obtained. Compared with the literature, the following new understandings are firstly proposed: (1) the ablated mass from the ablation process was plasma instead of just a plume, which was stimulated by an excitation laser; (2) photoexcitation contributes to the enhanced signal other than the electron thermal excitation supported by the fact that the signal gains its higher intensity when the re-excited plasma was less bright. That is, the multi-element excitation may relate to the atom energy-level distortion by the electric field. With the elucidation of key processes and mechanisms, there would be a much broader application for laser ablation-assisted ultraviolet LEAF due to its distinctive advantages.