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

Abstract

The self-absorption effect is one of the key factors influencing the accuracy of quantitative analysis. Laser energy is the key influencing factor of laser-induced breakdown spectroscopy (LIBS), and the mechanism of its influence on temporal evolution of self-absorption under different air pressures is still not fully understood due to complex physical processes. In this study, the temporally resolved spectra of Cu I 521.82 nm were acquired from the direction of laser incidence and the influence of laser energy on the temporal evolution of self-absorption in a low-vacuum (at pressures of 105, 104 and 103Pa) and high-vacuum (at pressures of 10, 10−1 and 10−3Pa) environment was studied. The experimental results indicate that the self-absorption effect of spectral line Cu I 521.82 nm is enhanced with an increase in delay time and laser energy in both high-vacuum and low-vacuum environments in this study. This is because increasing the delay time and laser energy leads to an increase in plasma column density. An intriguing phenomenon observed in this experiment is that at a pressure of 105Pa, the self-absorption of Cu I 521.82 nm initially increases but eventually weakens with laser energy, while at air pressures of 104Pa and 103Pa the self-absorption monotonically weakens with increasing laser energy during the measurement. This is because temporal evolution of plasma at 104Pa and 103Pa is significantly faster than that at 105Pa, and an increase in laser energy can delay the enhancement of self-absorption, the self-absorption has rapidly evolved to decrease with laser energy during spectral measurement at air pressure of 104 Pa and 103 Pa. This work is helpful in understanding the influence of air pressure and laser energy on the self-absorption effect of spectral lines and optimizing experimental parameters, and provides a reference for LIBS application.