光纤传能便携式激光诱导等离子体自吸收行为研究

Laser-induced breakdown spectroscopy (LIBS) is an appealing technique for elemental analyses. However, traditional LIBS does not meet the requirements of modern industrial on in-situ detection due to their large size and high requirements of the environment. In addition, the precision and accuracy of quantitative analysis in LIBS are seriously affected by the self-absorption effect, which cause distortion of lines. Therefore, there is an urgency to develop a portable, robust, and high-precision LIBS system. In this work, a portable, fiber-optic, laser-induced breakdown spectroscopy (FO-LIBS) system was developed for high-precision element analyses. The plasmas generated in FO-LIBS are thinner, weaker, and more uniform, with lower electron density than those in conventional LIBS, which probably lead to less self-absorption or self-reversal of emission lines. Hence, the precision and accuracy of quantitative analysis were improved. Furthermore, the influence mechanism of the behavior and self-absorption effect of the plasma excited by the laser pulse transmitted through optical fiber will be investigated. The correlation between the self-absorption of spectral line and the behaviors of the laser-induced plasma will be established finally. The study will solve the long-standing scientific and technical problem of self-absorption in laser-induced plasma and provide a new method for rapid high precision analyses of elements for portable LIBS, forming a solid theoretical and technical foundation for LIBS applications, improving the accuracy, precision and reliability of quantitative analysis.

激光诱导击穿光谱(LIBS)是一种快速的物质成分分析技术。由于传统的桌面级LIBS存在着体积庞大，环境要求高等缺点，不能满足现代工业现场快速检测的需要；同时，由于等离子体波动性和自吸收效应的影响，导致LIBS信号的波动和失真，严重影响了定量分析的精度和准确度。因此，本项目提出采用特种光纤传导激光能量的便携式LIBS设计方案，利用多模光纤的模间耦合等因素使激光能量分布得更均匀化，在样品表面烧蚀产生薄而均匀的、较低电子密度的、稳定的等离子体，有效地降低自吸收效应，提高定量分析的精确度。同时，深入研究光纤传能对等离子体行为和自吸收效应的影响机制，在此基础上建立定量分析精确度与等离子体行为及光谱自吸收效应之间对应的函数关系。项目成果有望解决激光等离子体光谱自吸收效应的科学难题，大幅提高LIBS定量分析的精确度和稳定性，为便携式LIBS高精度快速分析提供一条新的途径。

为了满足工业现场实时快速检测的需要，解决传统的激光诱导击穿光谱（LIBS）技术由于自吸收效应导致的光谱信号失真和分析精度下降问题，本项目提出采用特种光纤传输激光的方案，得到薄而均匀的、较低电子密度的稳定的等离子体，有效地降低自吸收效应，提高定量分析的精准度。. 项目首先设计并搭建了光纤传能便携式LIBS系统方案，并进行参数优化和整机性能测试。然后分别从烧蚀坑形貌、等离子体形貌及演化规律、等离子体温度和电子数密度等几个方面展开研究，深入研究光纤传能对等离子体行为和自吸收效应的影响机制，得出光谱自吸收效应与等离子体特征之间变化规律。. 开展了对LIBS自吸收效应时空演化规律的探究。设计并搭建了分辨率100μm的空间分辨光谱采集装置，采用金属单质、合金样品和土壤粉末压片等标准样品探究了激光诱导击穿光谱自吸收效应的空间分辨规律，得到自吸收系数SA、等离子体温度和电子数密度的空间分布。. 开展了光纤传能激光等离子体行为调控对探测灵敏度及稳定性增强研究。通过一系列不同口径和形状的约束腔装置对等离子体行为进行机械约束和调控，来压缩改变等离子体的膨胀形状。同时，通过改变离焦量的方法来改变烧蚀坑光斑大小和激光能量密度，从而改变等离子体的大小形状和稀薄程度，经过调控优化，得到一种较为理想的光学薄等离子体，从而有效地降低激光诱导击穿光谱中的自吸收效应。. 项目研究共发表SCI论文16篇，授权专利7项，在国际、国内学术会议上做口头报告1次、Poster报告5次，5名硕士研究生受本项目支持。. 本项目提出的基于光纤传能的便携式LIBS方案及对等离子体自吸收行为的研究成果，能够克服传统LIBS存在的缺陷，提高定量分析的精度，具有较大的科学意义，其技术成果可在冶金、采矿、地质勘探和农业生产等方面获得广泛应用。