激光诱导氩气等离子体时间分辨特性研究

Study on Time-Resolved Characteristics of Laser-Induced Argon Plasma

激光诱导击穿光谱(LIBS)以激光诱导微等离子体的原子发射为技术特征,在科研与工业领域正得到重视与蓬勃发展。作为环境气体的氩气对等离子体演化过程中粒子的碰撞过程有重要影响,决定着LIBS技术分析性能的发挥。利用光谱诊断技术深入研究LIBS技术条件下氩气的光谱特征,对于提升LIBS技术及其应用水平具有重要的意义。利用中阶梯光栅光谱仪记录时间序列光谱信息研究了瞬态Ar等离子体碰撞和衰减过程,包括等离子体演化过程中的辐射机制和等离子体电子数密度及温度的时间演化特征。结果表明,在激光与氩气相互作用的初始阶段,光谱主要由连续辐射组成,在0.6μs后,光谱开始主要由氩原子、离子的离散跃迁辐射谱线组成。氩原子线和离子线的演化周期不同,在0~1.0μs延迟时间内离子线占主导,在1.0~30μs原子线占主导。利用Stark展宽,Saha-Boltzmann曲线方程对60,80和100 mJ脉冲激光能量激发下的等离子体的电子数密度和温度进行了计算,等离子体电子数密度在0.2~2.0μs延迟时间内快速衰减,之后在较长的延迟时间内缓慢下降,大约在4.0μs达到同一个数量级;等离子体温度(80 mJ)从初始0.2μs时的18000 K迅速下降到13000 K(2.0μs),在5.0μs后缓慢下降到12000 K。为进一步检验和优化激光脉冲用于氩气的分析性能,对氩的不同特征谱线信噪比随时间演化的特征进行了研究,结果表明,氩原子线在2.0~6.0μs的延迟窗口具有较高的信噪比,氩离子线则在0.1~1.0μs延迟窗口具有较高的信噪比。

Laser-induced breakdown spectrometry(LIBS) is technically characterized by the atomic emission of laser-induced microplasma,and it is receiving attention and vigorous development in scientific research and industrial fields.As the ambient gas,argon has an important influence on the collision process of particles in the plasma evolution process,which determines the performance of LIBS technology analysis.It is of great significance to improve the LIBS technology and its application level to study the spectral characteristics of argon in depth with the spectroscopic diagnosis technology.This paper uses an echelle spectrometer to record time series spectral information to study the transient Ar plasma collision and decay process,including the radiation mechanism during plasma evolution and the time evolution characteristics of plasma electron number density and temperature.The results show that the spectrum is mainly composed of continuous at the initial stage of the interaction between laser and argon.After 0.6 μs,the spectrum is mainly composed of discrete transition radiation lines of argon atoms and ions.The evolution period of the argon atomic line is different from that of the ion line.The ion line is dominant in the delay time of 0~1.0 μs,and the atomic line is dominant in the 1.0~30 μs.Using Stark broadening and Saha-Boltzmann curve equation,the electron number density and temperature of plasma excited by 60,80 and 100 mJ pulsed laser energy are calculated.The plasma electron number density decays rapidly within 0.2~2.0 μs delay time,and then decreases slowly during a longer delay time,reaching the same order of magnitude at about 4.0 μs.The plasma temperature(with 80 mJ laser energy) dropped rapidly from 18 000 K at the initial 0.2 μs to 13 000 K(2.0 μs),and slowly dropped to 12 000 K after 5.0 μs.In order to further verify and optimize the analytical performance of laser pulses for argon,the evolution of the signal-to-noise ratio of different characteristic spectral lines of argon with time was studied.The research results show that the argon atom line has a higher signal-to-noise ratio in the delay window of 2.0~6.0 μs,and the argon-ion line has a higher signal-to-noise ratio in the delay window of 0.1~1.0 μs.