Evolution of a copper vapour plasma obtained by laser ablation in a gas at atmospheric pressure

Abstract

Summary form only given, as follows. Laser Induced Breakdown Spectroscopy (LIBS) is a powerful method for direct measurement of element concentration in all material analysis and metallurgical applications. This technique consists on the measurement of the emission line intensity of the different species in the plasma produced near the surface by interaction between the laser beam and the sample. The present study is devoted to a numerical simulation of the expansion of the metallic plasma (copper) in the ambient gas (nitrogen or argon) at atmospheric pressure, and to a comparison with experimental results.The hydrodynamic model, established in a 1D configuration uses the continuity equations. The code is based on the control volume method of Patankar. The calculation starts after thermalisation of the copper vapour plasma. The initial conditions assume the knowledge of temperature and mass fraction profiles. A parametric study allowed us to know the influence of this initial conditions on the plasma decay. After calculation of the mass density and of the transport coefficients as a function of the plasma composition and of the temperature, the model allows us to calculate the plasma parameters (temperature evolution, expansion speed, mass fraction evolution, cooling velocity, radiation, thermal diffusion and convection). We used a Nd:YAG laser (1064 nm, 120 mJ), a fiber cable and a spectrometer in conjunction with a gated optical multi-channel analyzer for the analysis of the emission lines. This system allowed both spatially and temporally resolved spectra to be recorded. The metallic plasma parameters are obtained by recording spectral lines of iron contained in the copper.