共轴双脉冲激光诱导击穿光谱等离子体辐射信号的增强机制

Enhancement mechanism of coaxial dual-pulse laser-induced breakdown spectroscopy plasma radiation signal

双脉冲激光诱导击穿光谱(DP-LIBS)在痕量元素的高灵敏探测中发挥着重要作用,有关其信号增强机制已存在有诸多解释,但有必要进一步从等离子体辐射荧光特性、等离子体温度和数密度的空间分布等方面开展深入探讨。构建了基于激光热烧蚀和二维轴对称流体动力学的理论模型,并用它模拟了单脉冲LIBS和共轴双脉冲DP-LIBS激发条件下激光烧蚀铝镁合金产生等离子体及其辐照度的时空演化过程,对比了不同脉冲间隔下谱线强度的增强效果,分析了等离子体温度、各类粒子数密度的空间分布结构以及等离子体的屏蔽效应,并由此阐释了DP-LIBS的光谱信号增强机制。结果表明,共轴DP-LIBS诱导等离子体辐射信号的增强主要源于第二束激光增加了粒子数密度和等离子体温度,而等离子体的屏蔽效应主要出现在靶材表面的羽流层。这一研究为DP-LIBS实验研究和信号增强溯源提供了重要的理论基础,也能够帮助科研人员快速准确地优化DP-LIBS实验装置参数。

Dual-pulse laser-induced breakdown spectroscopy(DP-LIBS)is essential for highly sensitive trace element detection.Although various mechanisms have been proposed for its signal enhancement,fur⁃ther investigation is needed regarding plasma radiation fluorescence characteristics,spatial distribution of plasma temperature,and particle number density.This study developed a theoretical model based on laser ablation and two-dimensional axisymmetric fluid dynamics to simulate the spatiotemporal evolution of plas⁃ma generation and irradiance in aluminum-magnesium alloy under single-pulse LIBS and coaxial dual-pulse DP-LIBS conditions.We compared spectral line intensity enhancements at different pulse intervals and an⁃alyzed the spatial distribution of plasma temperature,particle number densities,and plasma shielding ef⁃fects to clarify the signal enhancement mechanism of DP-LIBS.Results indicate that the increased particle number density and plasma temperature from the second laser beam primarily drive the enhanced plasma ra⁃diation signals,while plasma shielding occurs mainly at the target surface boundary layer.This study offers a vital theoretical foundation for experimental research and signal enhancement in DP-LIBS,aiding re⁃searchers in optimizing experimental device parameters efficiently.