Study on the radiation and self-absorption characteristics of plasma under various background gases

Abstract

The self-absorption effect is a primary factor responsible for the decline in the precision of quantitative analysis techniques using plasma emission spectroscopy, such as laser-induced breakdown spectroscopy (LIBS). In this study, based on the thermal ablation and hydrodynamics models, the radiation characteristics and self-absorption of laser-induced plasmas under different background gases were theoretically simulated and experimentally verified to investigate ways of weakening the self-absorption effect in plasma. The results reveal that the plasma temperature and density increase with higher molecular weight and pressure of the background gas, leading to stronger species emission line intensity. To reduce the self-absorption effect in the later stages of plasma evolution, we can decrease the gas pressure or substitute the background gas with a lower molecular weight. As the excitation energy of the species increases, the impact of the background gas type on the spectral line intensity becomes more pronounced. Moreover, we accurately calculated the optically thin moments under various conditions using theoretical models, which are consistent with the experimental results. From the temporal evolution of the doublet intensity ratio of species, it is deduced that the optically thin moment appears later with higher molecular weight and pressure of the background gas and lower upper energy of the species. This theoretical research is essential in selecting the appropriate background gas type and pressure and doublets in self-absorption-free LIBS (SAF-LIBS) experiments to weaken the self-absorption effect.

A Review Of Development In The Research Of Self-Absorption On Laser-Induced Breakdown Spectroscopy

“…Their findings suggest that the attenuation of self-absorption manifests as apparent when helium is used as the ambient gas. Wang et al 102 simulated and verified the radiation characteristics and selfabsorption effect of laser-induced plasmas under different background gases. They found that the self-absorption effect can be alleviated by utilizing a gas with a low ionization potential.…”

Effect of laser energy on temporal evolution of self-absorption at different air pressures

“…Rezaei et al used calibration curves and growth curves to discuss the influence of He gas on the self-absorption of spectral lines (Cu I 324.75 nm and Cu I 327.40 nm) at different air pressures; the results of both methods showed that the self-absorption increased with the air pressure [14]. Wang et al found that the self-absorption of atomic spectral lines (Mg and Al) increased with decreasing ambient pressure [15]. Rezaei et al studied the self-absorption of spectral lines (Al) by comparing the spectral intensities with and without self-absorption in Ar and He gas environments at atmospheric pressure [16].…”