Simulation of Plasma Emission Spectra for Quantitative Elemental Analysis via Laser-Induced Breakdown Spectroscopy
Résumé
The calculation of the plasma emission spectrum with the aid of an appropriate model presents a promising approach for material analysis via laser-induced breakdown spectroscopy (LIBS) as it may lead to an increase of the versatility of the method. Indeed, the properties of laser-produced plasmas strongly depend on the material's elemental compositionelemental composition of the material, and the calibration of LIBS measurements is often difficult. Therefore, the analyses remain qualitative or semi-quantitative in many cases. This is in particular the case for organic materials as the mechanisms of laser energy deposition and plasma formation critically depend on the content of minor elements with low ionization potential. The development of the appropriate plasma model is a particularly difficult task, as laser-produced plasmas are characterized by a complex expansion process into the surrounding atmosphere. Several experimental investigations show that the plasma's temperature and density profiles are spatially non-uniform. The gradients remain up to time delays typically applied in LIBS experiments. The nonuniformity may be ignored when the analysis only concerns plasma species of similar excitation and ionization energies. Contrarily, the gradients have to be considered if species of significantly different excitation energies are involved as these species are located in zones of different temperature [1]. In the present paper, we discuss the possibilities of performing LIBS analysis via plasma modelling by considering the nonuniform character of the laser-produced plasma. In particular, we present an approach based on the calculation of the plasma's spectral radiance that takes advantage of the analysis of the spectral line shapes as a feedback in the LIBS measurement procedure [2]. [1] E. Tognoni, G. Cristoforetti, S. Legnaioli, V. Palleschi, Spectrochim. Acta. Part B (2010) 65, 1-14. [2] L. Mercadier, J. Hermann, C. Grisolia, A. Semerok, J. Anal. At. Spectrom. (2013) to be published