1. Fujian Provincial Collaborative Innovation Center for Advanced High-Field Superconducting Materials and Engineering, Fuzhou 350117, China
2. School of Physics and Energy, Fujian Normal University, Fuzhou 350117, China
3. Center for Superconducting and New Energy Research and Development, Southwest Jiaotong University, Chengdu 610031, China
Abstract：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.
Key words：Laser-induced breakdown spectroscopy; Argon; Plasma; Timing characteristics; Time resolved
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