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

Area of Science:

• Plasma Physics
• Spectroscopy
• Analytical Chemistry

Background:

• Accurate elemental analysis using laser-induced breakdown spectroscopy (LIBS) relies on ideal plasma conditions.
• Real-world plasma often deviates, particularly regarding optical thinness, leading to self-absorption.
• Self-absorption, the reabsorption of emitted radiation, hinders quantitative analysis.

Purpose of the Study:

• To investigate the effect of self-absorption in laser-produced plasma.
• To analyze the factors influencing the self-absorption coefficient.
• To evaluate the impact of self-absorption on quantitative analysis using calibration-free LIBS.

Main Methods:

• Simulated optically thick emission spectra under typical laser-produced plasma conditions.
• Employed Saha-Boltzmann, Boltzmann, and Stark broadening equations for spectral simulation.
• Applied self-absorption to simulated spectra and analyzed its dependence on plasma temperature, path length, and concentration.
• Assessed calibration-free LIBS accuracy with and without resonance lines.

Main Results:

• Self-absorption decreases with increasing plasma temperature.
• Self-absorption increases with optical path length and analyte concentration.
• Excluding resonance lines in calibration-free LIBS for a Mg-Ca alloy reduced composition estimation error from 27% to 2%.

Conclusions:

• Self-absorption is a critical factor affecting quantitative elemental analysis in LIBS.
• Understanding and mitigating self-absorption, particularly by managing resonance lines, is crucial for accurate LIBS results.
• The study provides insights into optimizing LIBS analysis by addressing plasma self-absorption.