Plasma diagnostics from self-absorbed doublet lines in laser-induced breakdown spectroscopy

- LIBS is presented as a complementary technique for quantifying components.
- A model of a homogeneous plasma was employed with a computational calculus.
- Line profiles of Mg II doublet transition were analyzed for plasma characterization.
- Characterization by ratios of certain plasma parameters.
- Estimation of plasma parameters from the use of resonant lines of moderate to high self-absorption.

In this paper, a generalized approach is developed and applied for plasma characterization and quantitative purposes in laser-induced breakdown spectroscopy (LIBS) experiences by employing a selected pair of spectral lines belonging to the same multiplet. It is based on the comparison between experimental ratios of line parameters and the theoretical calculus obtained under the framework of a homogeneous plasma in local thermodynamic equilibrium. The applicability of the method was illustrated by using the atomic resonance transitions 279.55-280.27 nm of Mg II, which are usually detected in laser-induced plasma (LIP) during laser ablation of many kinds of targets. The laser induced plasmas were produced using a Nd:YAG laser from a pressed pellet of powdered calcium hydroxide with a concentration of 300 ppm of Mg. The experimental ratios for peak intensities, total intensities and Stark widths were obtained for different time windows and matched to the theoretical calculus. The temperature and the electron density of the plasma, as well as the Mg columnar density (the atom/ion concentration times the length of the plasma along the line-of-sight), were determined. The results were interpreted under the employed approach.