低压环境下激光入射角对激光诱导等离子体影响研究

doi:10.3964/j.issn.1000-0593(2023)09-2740-07

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摘要：激光诱导击穿光谱（LIBS）因其无需制样、样品损伤小、可在线检测以及检测速度快等优点被广泛应用。激光诱导等离子体是一个十分复杂的物理过程，受多种因素的影响，激光入射角是其关键影响因素之一。脉冲激光入射角的改变会直接改变脉冲激光在样品表面的聚焦光斑形状，导致脉冲激光照射在靶材表面的功率密度发生改变，直接影响到脉冲激光诱导等离子体过程，脉冲激光与靶材法线所成角度的改变还会直接影响等离子体扩散过程。尽管脉冲激光入射角是激光诱导等离子体过程的关键影响因素之一，但是在低压环境下，脉冲激光入射角对激光诱导等离子体过程的影响研究较少，对激光等离子体的影响仍不明确，对激光等离子体影响的内在机制还需更加深入的研究。首先研究了激光入射角对脉冲激光在靶材表面形成的聚焦光斑的影响，实验和仿真的结果都表明脉冲激光在靶材表面的聚焦光斑尺寸随着入射角的增大而增大，导致相同激光能量下脉冲激光的功率密度下降；其次，采用同轴成像的方式研究了不同气压下激光入射角对激光等离子体的影响，实验结果显示激光等离子体中心辐射强度会随着入射角的增大而减弱。当激光入射方向与靶材表面法线成0~15°时；脉冲激光入射角对激光等离子体中心辐射强度影响较小，辐射强度降低仅为3.05%，当激光入射方向与靶材表面法线成60°时，辐射强度降低可达25.415%，对激光等离子体中心辐射强度有着较为明显的影响。最后，对处于气压10^-4 Pa下激光从不同角度入射所产生的激光烧蚀坑进行了微观结构分析，分析结果表明靶材烧蚀量会随着入射角的增大而增加，但靶材烧蚀效率，即单位光斑面积靶材烧蚀量，则会随着入射角度的增大而下降，这解释了激光等离子体中心辐射强度随入射角增大而减弱的现象。该工作有助于理解激光入射角对激光等离子体的影响，为优化LIBS实验参数提供参考。

关键词：环境气压；激光入射角；激光诱导等离子体；烧蚀坑

Abstract：Laser-induced breakdown spectroscopy (LIBS) is widely used because of its advantages, such as no sample preparation, small sample damage, online detection, and fast detection. The process of laser-induced plasma is very complex and is affected by many factors.The incidence angle of a pulsed laser is one of the key factors. The change of pulsed laser incident angle will change the laser focal spot shape on the sample surface, affecting the laser-induced plasma process. The change of angle between the pulsed laser and the normal direction of the target will directly affect the plasma expansion. Although the laser incident angle is one of the key factors affecting the laser-plasma, however, there are few studies on the incident angle of pulsed laser at low pressure, the effect of pulsed laser incident angle on laser-plasma is still unclear, and the internal mechanism of the influence of pulsed laser incident angle on laser-plasma needs further study. The present study studies the influence of pulsed laser incident angle on the focal spot formed by pulse laser on the target surface. The results of the experiment and simulation show that the focal spot size increases with the pulsedlaser incident angle, resulting in the power density of the pulsed laser decreasing. Secondly, the influence of pulsed laser incident angle on laser-plasma at different ambient pressure is studied by coaxial imaging. The experimental results show that the radiation intensity of the laser-plasma core decreases against the laser incident angle. When the incident laser direction deviates from the target surface normal directionof 0°~15°; the reduction of radiation intensity is only 3.05%. When the direction of the incident laser deviates 60° from the normal direction of the target surface, the reduction of radiation intensity can reach 25.415%, which means that the pulsed laser incident angle has an obvious influence on the plasma core radiation intensity. Finally, the microstructure of pulsed laser ablation pits generated by laser from different angles at 10^-4 is analyzed. The results show that the ablation volume of the target increases with the laser incident angle, but the ablation efficiency of the target, i.e. the ablation amount of target per unit spot area, is against with the pulsed laser incident angle. It explains that the radiation intensity of the laser-plasmacore decreases against the laser incident.

Key words：Ambient pressure; Laser incidence angle; Laser-induced plasma; Ablation crater

收稿日期: 2022-04-11 修订日期: 2022-10-09

中图分类号:

O531

基金资助: 国家自然科学基金项目(51777145)，中国博士后科学基金项目(2020M683481)资助

通讯作者: 袁欢 E-mail: huanyuan@xjtu.edu.cn

作者简介: 杨帆，1986年生，平高集团有限公司技术中心工程师 e-mail: 785601094@qq.com

引用本文:

杨帆，郝留成，柯伟，刘庆，王俊，陈敏源，袁欢，杨爱军，王小华，荣命哲. 低压环境下激光入射角对激光诱导等离子体影响研究[J]. 光谱学与光谱分析, 2023, 43(09): 2740-2746.
YANG Fan, HAO Liu-cheng, KE Wei, LIU Qing, WANG Jun, CHEN Min-yuan, YUAN Huan, YANG Ai-jun, WANG Xiao-hua, RONG Ming-zhe. Research on Effect of Laser Incident Angle on Laser-Induced Plasma at Low Pressure. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2023, 43(09): 2740-2746.

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https://www.gpxygpfx.com/CN/10.3964/j.issn.1000-0593(2023)09-2740-07 或 https://www.gpxygpfx.com/CN/Y2023/V43/I09/2740

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