Theoretical study on signal enhancement mechanism of coaxial DP-LIBS

Abstract

In the field of dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) research, the pursuit for determining pulse interval and other parameters quickly and conveniently in order to achieve optimal spectral signal enhancement is paramount. To aid researchers in identifying the optimal signal enhancement conditions and more accurately interpreting the underlying signal enhancement mechanisms, theoretical simulations of the spatiotemporal processes of coaxial DP-LIBS plasma inducing have been established in this work. By means of a model based on laser ablation and two-dimensional axisymmetric fluid dynamics, plasma evolution during aluminum-magnesium alloy laser ablation under single pulse and coaxial dual pulse excitations have been simulated. The influence of factors such as delay time, laser fluence, plasma temperature, particle number density, etc., on the DP-LIBS spectral signals are investigated. Under pulse intervals ranging from 50 to 1500 ns, the time evolution of spectral line intensity, dual-pulse emission enhancement relative to the single-pulse results, laser irradiance, spatial distribution of plasma temperature and species number density, as well as laser irradiance shielded by plasma have been obtained. The study indicates that the main reason behind the radiation signal enhancement in coaxial DP-LIBS induced plasma is attributed to increased species number density and plasma temperature caused by the second laser, and it is inferred that the shielding effect of the plasma mainly occurs in the boundary layer of the stagnation point flow over the target surface. This research provides a theoretical basis for experimental research, parameter optimization, and signal enhancement tracing in DP-LIBS.