Effects of pulse energy ratios on plasma characteristics of dual-pulse fiber-optic laser-induced breakdown spectroscopy  

作　　者：Yu-Hua Hang Yan Qiu Ying Zhou Tao Liu Bin Zhu Kaixing Liao Ming-Xin Shi Fei Xue 杭玉桦;邱岩;周颖;刘韬;朱斌;廖开星;时铭鑫;薛飞(Suzhou Nuclear Power Research Institute,Suzhou 215004,China;Key Laboratory for Physical Electronics and Devices of the Ministry of Education,Faculty of Electronic and Information Engineering,Xi’an Jiaotong University,Xi’an 710049,China;State Key Laboratory of Electrical Insulation and Power Equipment,Xi’an Jiaotong University,Xi’an 710049,China)

机构地区：[1]Suzhou Nuclear Power Research Institute,Suzhou 215004,China [2]Key Laboratory for Physical Electronics and Devices of the Ministry of Education,Faculty of Electronic and Information Engineering,Xi’an Jiaotong University,Xi’an 710049,China [3]State Key Laboratory of Electrical Insulation and Power Equipment,Xi’an Jiaotong University,Xi’an 710049,China

出　　处：《Chinese Physics B》2022年第2期387-397,共11页中国物理B（英文版）

基　　金：the Foundation Research Project of Jiangsu Province,China(the Natural Science Fund No.BK20190187)。

摘　　要：Laser-induced plasmas of dual-pulse fiber-optic laser-induced breakdown spectroscopy with different pulse energy ratios are studied by using the optical emission spectroscopy(OES)and fast imaging.The energy of the two laser pulses is independently adjusted within 0–30 m J with the total energy fixed at 30 m J.The inter-pulse delay remains 450 ns constantly.As the energy share of the first pulse increases,a similar bimodal variation trend of line intensities is observed.The two peaks are obtained at the point where the first pulse is half or twice of the second one,and the maximum spectral enhancement is at the first peak.The bimodal variation trend is induced by the change in the dominated mechanism of dual-pulse excitation with the trough between the two peaks caused by the weak coupling between the two mechanisms.By increasing the first pulse energy,there is a transition from the ablation enhancement dominance near the first peak to the plasma reheating dominance near the second peak.The calculations of plasma temperature and electron number density are consistent with the bimodal trend,which have the values of 17024.47 K,2.75×10^(17)cm;and 12215.93 K,1.17×10^(17)cm;at a time delay of 550 ns.In addition,the difference between the two peaks decreases with time delay.With the increase in the first pulse energy share,the plasma morphology undergoes a transformation from hemispherical to shiny-dot and to oblate-cylinder structure during the second laser irradiation from the recorded images by using an intensified charge-coupled device(ICCD)camera.Correspondingly,the peak expansion distance of the plasma front first decreases significantly from 1.99 mm in the single-pulse case to 1.34 mm at 12/18(dominated by ablation enhancement)and then increases slightly with increasing the plasma reheating effect.The variations in plasma dynamics verify that the change of pulse energy ratios leads to a transformation in the dual-pulse excitation mechanism.

关 键 词：fiber-optic laser-induced breakdown spectroscopy(FO-LIBS) dual-pulse excitation pulse energy ratio spectral enhancement 

分 类 号：O53[理学—等离子体物理] O657.38[理学—物理]