Experimental and theoretical study of the expansion of a metallic vapour plasma produced by laser

Abstract

The interaction between a metallic plasma produced by laser ablation and an ambient gas (argon, air and nitrogen) at atmospheric pressure is studied. The experimental results are compared with theoretical ones given by numerical simulation. Aluminium and copper targets are used. The uniform repartition of iron impurities included in the target (1.6% for Al and 2% for Cu) is warranted by the manufacturer. The Nd : YAG laser delivers pulses of 8 ns FWHM duration with an energy ranging from 70 to 100 mJ at a rate of 10 Hz. The temperature measurements have been performed by the Boltzmann diagram method using iron lines. The influence of ambient gas and target material is studied. After an Abel transform, we observe a maximum of the line intensities off the plasma axis. This shows the formation of gas plasma around the metallic one before complete diffusion of the ambient gas in the metallic plasma. The hydrodynamic model built in one dimension uses the continuity equations. This code is based on the control volume method of Patankar. A temperature and mass fraction profiles are needed as initial conditions. This model is able to describe the temporal evolution of the temperature and of the diffusion in the plasma. It allows us to study the mixture of the metallic plasma and the ambient gas as soon as the plasma is thermalized and local thermodynamic equilibrium is established. There is good agreement between the results of the simulation and the experimental results.

Temporal Variations in the Excitation Temperature of a Laser-induced Argon Plasma Estimated with Copper Emission Lines

“…Gomes et al reported that the gas temperature of an LIP, which was evaluated from a Boltzmann plot of iron atomic lines having small excitation energies, was monotonically declined with increasing the delay time, and that this result could be well explained by a model for the gas expansion. 13 Their result disagrees with the behaviors shown in Fig. 3; therefore, our experimental results cannot be explained simply from the gas temperature of the LIP, but the excitation processes of each emission line should be taken into account.…”

Effect of laser parameters on laser ablation and laser-induced plasma formation: A numerical modeling investigation

“…Our calculated temperature values appear to be slightly higher than some experimental values reported in the literature, which are typically in the order of 10,000 -40,000 K for the early stage (e.g., first 100 ns), in the laser irradiance range of 10 9 -10 10 W/cm 2 [22,23,49,58]. It is possible that our model overestimates the plume temperature to some extent, because some energy loss mechanisms are not yet included in the model, such as excitation (i.e., energy transfer into excited levels) and radial plume expansion (resulting in heat loss in the radial direction).…”

“…Calculations are always carried out until 100 ns. The reason is that the model is one-dimensional, hence it assumes forward expansion of the vapor plume, which is only a reasonable assumption for the early stage, e.g., until an expansion distance of about 1 mm (depending on the laser beam spot size) [18,37,48,49]. At later stages, expansion in the radial direction will become important, so that our model will have to be extended to two dimensions (radial symmetry), in order to describe the expansion process.…”

Spectroscopic studies of Ca plasma generated by the fundamental, second, and third harmonics of a Nd:YAG laser

“…In literature, a variety of models for laser ablation are available operating in different regimes of wavelengths (1064 nm, 532 nm, 355 nm, and 308 nm), laser irradiance and pulse duration (fs, ps, ns) target materials and gas environment (Bulgakov & Bulgakov, 1998;Colonna et al, 2001;Laville et al, 2004;Gomes et al, 2004;Capitelli et al, 2004;Chen & Bogaerts, 2005;Bogaerts et al, 2006;Wang et al, 2007;Bussoli et al, 2007;Bashir et al 2007). Moreover, different kinds of mechanisms can play a role depending on the type of the material, the laser irradiance, the laser pulse duration, etc.…”