Characterization of laser-generated microplasmas for use in quantitative analysis of liquids

Abstract

We report on the application of the technique of Laser Induced Breakdown Spectroscopy (LIBS) for the analysis of liquids. The technique of LIBS offers a fast, simple, real- time method of elemental analysis. With our simple LIBS set- up numerous elements, including the alkali and alkaline earth metals, and a range of toxic heavy metals, have been measured over a wide range of concentrations. In order to provide quantitative data in the evaluation of laser generated plasmas, parameters such as electron densities, plasma temperature, line shape functions, and others need to be measured. The method of measurement utilized in this study is primarily based on the analysis of the hydrogen Balmer lines which exhibit linear Stark broadening. Ca and Al lines, which exhibit quadratic Stark broadening, were also used. During the measurements it also must be established that the plasma is optically thin, and that the assumption of the existence of Local Thermodynamic Equilibrium is valid. Calibration curves for elements such as Na, Ca, Li, Mn, K, Cr, Al, Pb and Cu using H<SUB>(alpha</SUB> ), H<SUB>(beta</SUB> ) and H<SUB>(gamma</SUB> ) lines as a reference and calibration curves for Ca, Cu, Mn, Li and Na using carefully chosen elements as a reference elements added at `reference concentration' were obtained. Emphasis is placed establishing plasma diagnostics for use in non-laboratory environments, for example for the analysis of pollutants in water in harsh environments. Consequently, all spectroscopic measurements were made under standard atmospheric pressure conditions.