Laser induced plasma spectroscopy (LIPS) is nowadays recognized as a fast and accurate technique for elemental analysis of unknown samples. Analytical implications of the non-thermal equilibrium plasma generated at high pressure and electron temperature in 8000-15000K range, after the interaction of a sharply focused laser beam with a metals surface are investigated. On the basis of recent laboratory experiments, an attempt is made to defme the effects of non-equilibrium on the species population densities and on their spectroscopic emissions, which affect the achieved analytical accuracy. Experimental data on a steel sample are presented and discussed in combination with some theoretical modelling. The laser induced plasma is formed at the sample surface in air at atmospheric pressure, so that it is mainly constituted of light elements from air and evaporated atoms and ions from the sample surface. Species considered for modelling are metals such as iron and chromium with well known spectroscopic parameters, which are of special interest for analytical applications such as their characterization of ancient metal alloys, soil analysis and marine sediments analysis.
|