Optically Thick Laser-Induced Plasmas in Spectroscopic Analysis

Abstract

Studies on the plasma physics has been grown over the past few decades as a major research field. The plasma can be produced by different sources such as acr, spark, electric discharge, laser and so on. The spectral radiation of the plasma which acts as its fingerprint, contains valuable information about plasma features. Characterization of plasmas by spectroscopic measurement is a powerful tool for increasing the knowledge and applications of these kinds of radiation sources. Therefore, the spectral diagnostics methods are proposed which are based on measurement of spectral lines intensity, estimation of continuous and absorption radiation, and as well as determination of shifts and halfwiths of the spectrum [1]. The fundamental characteristic parameters of the plasma, i.e., the number densities of plasma species, electron temperature, and as well as particle transport property at each plasma space can be determined by optical emission spectroscopy and utilizing appropriate methods [2]. For accurate evaluation of plasma parameters, its thickness must be thoroughly considered. Generally, the plasmas can be separated into two categories of thin and thick groups. In thin plasmas, the re-absorption of radiation is negligible. Consequently, in spectroscopic analysis, the non-self-absorbed spectral radiation is evaluated by considering the summation of all spectral emissions along the line of sight. In optically thick plasmas, the radiation trapping happens which leads to the selfabsorption phenomenon in spectroscopic analysis that is explained with details in below section.

A numerical procedure for understanding the self-absorption effects in laser induced breakdown spectroscopy

“…Numerous articles discussed the physical mechanism of selfabsorption in LIBS and their corrective methods from theoretical and experimental perspectives. [3][4][5][6] Novel approaches and methods for self-absorption correction or reduction have garnered signicant attention in numerous studies in an effort to reduce this undesirable effect. [7][8][9][10][11][12][13][14] Different works have been reported in the literature exclusively discussing self-absorption correction.…”

“…The eqn (6) expresses an inverse relationship between the SA coefficient and q. The self-absorption effect is high when q is large and weak when q is small.…”

“…Self-absorption also has an impact on the line width's value. 11,29 The precise correlation between the observed width (Dl 1/2 ) and the width of the corresponding non-self-absorbed state (l 1/20 ) can be mathematically expressed through the utilization of the eqn (6), and the relation given by, 30 Dl 1=2…”