溶液中Ba元素的水下单脉冲与正交双脉冲LIBS的比较研究  

Comparative Study of Underwater Single Pulse and Orthogonal Double Pulse Laser-Induced Breakdown Spectroscopy of Barium Element in Solution

作　　者：李文平 周卫东[1,2] Li Wenping;Zhou Weidong(College of Physics and Electronic Information Engineering , Zhejiang Normal University ,Jinhua , Zhejiang 321004, China;Key Laboratory of Optical Information Detecting and Display Technology Re sea rch of Zhejiang Province ,Jinhua , Zhejiang 321004, China)

机构地区：[1]浙江师范大学物理与电子信息工程学院,浙江金华321004 [2]浙江省光信息检测与显示技术研究重点实验室,浙江金华321004

出　　处：《中国激光》2019年第9期298-307,共10页Chinese Journal of Lasers

基　　金：国家自然科学基金(61178034)

摘　　要：使用两台波长为1064 nm的Nd∶YAG调Q激光器,对BaCl2溶液样品开展水下单脉冲与正交双脉冲激光诱导击穿光谱(LIBS)实验,系统地探究了各关键实验参数对水下单脉冲LIBS(SP-LIBS)及双脉冲LIBS(DP-LIBS)光谱特性和信号增强的影响。当采集延时为500~900 ns时,谱线的信噪比很高,有利于进行光谱的采集与分析,可称之为水下DP-LIBS探测的时间窗口。对两束激光焦点的相对位置以及激光能量进行优化,在优化的实验条件下观察到DP-LIBS的谱线强度(BaⅡ455.4 nm)是SP-LIBS的最大谱线强度的20倍,同时谱线展宽变窄,光谱信号持续时间更长。在双脉冲实验中,谱线强度随着第二束激光能量的增加呈指数增长,这与在液体表面进行的共线DP-LIBS实验中所观察到的线性增长不同,这种增长趋势上的不同可能与等离子体所处的气体环境条件有关。最后,对水下SP-LIBS及DP-LIBS的检测能力进行了比较,结果表明,DP-LIBS的检测灵敏度比SP-LIBS提高了37倍,检测限从单脉冲的31.35×10^-6下降到1.78×10^-6。Two Q-switched Nd∶YAG lasers operating at 1064 nm are used and combined in orthogonal beam geometry to perform underwater single and double pulse laser-induced breakdown spectroscopy(SP-LIBS and DP-LIBS) experiments in barium chloride(BaCl2) solution. The influences of key experimental parameters on the spectral characteristics and signal enhancement of underwater SP-LIBS and DP-LIBS are investigated systematically. There is a time window from approximately 500 ns to 900 ns in underwater DP-LIBS, where signal-to-noise ratios are very high. The time window favors the selection of delay time for spectral acquisition and analysis. By properly setting the relative position of two laser foci and using optimized laser energy, a 20-time enhancement of the Ba II 455.4 nm line intensity of DP-LIBS over the maximal intensity of SP-LIBS is obtained. The spectral line of DP-LIBS is narrower and last longer than that of SP-LIBS. In addition, dependence of spectral line intensity of DP-LIBS on the second laser energy is observed, which demonstrates an exponential increase. This is quite different to the linear growth observed in collinear DP-LIBS experiment on the liquid surface, and the difference in growth trend may be related to the gaseous environment in which the second laser induced plasma is produced and confined. Finally, the detection capability of underwater SP-LIBS and DP-LIBS is compared. The results show that the detection sensitivity of DP-LIBS is improved by a factor of 37, and the limit of detection of Ba in bulk water is reduced from 31.35×10-6 in SP-LIBS to 1.78×10-6 in DP-LIBS.

关 键 词：光谱学 单脉冲激光诱导击穿光谱 双脉冲激光诱导击穿光谱 水下 激光能量 检测灵敏度 

分 类 号：O433.4[机械工程—光学工程]