engleski

Spectroscopic investigations of aluminum plasma produced by a nitrogen laser

Aluminum plasma produced by radiation of a nitrogen laser focused onto an aluminum target in air at atmospheric pressure was studied spectroscopically. Time integrated spectroscopy provided general information about plasma emission spectrum in the UV-VIS spectral region. Individual plasma emission lines were then studied with more elaborate time-resolved spectroscopic method in which line profiles were sinthesysed from individual measurements at many closely separated wavelengths. Overall time resolution of the order of 2-3 ns was readily achieved. This alowed studies of the temporal evolution of electron density and temperature in the plasma with spatial resolution of about 0.1 mm. Initial plasma temperatures of a few eV and electron densities of about 1019 cm-3 were observed, together with indication of plasma expansion velocity of a few km/s. Dependence of plasma parameters on various buffer gases was also studied. Some plasma emission enhancement was observed in air and was atributed to oxidation of the target surface. The generation and evolution of the plasma was also studied with the help of one-dimensional numerical models of target heating and plasma evolution. A comparison with published experiments and theoretical models is made, and qualitative agreement between this experiment and published data is found. This experiment allowed making a discrimination between two competing models of plasma expansion, clearly supporting the so called effusion model and outruling the outflow model of plasma expansion. Quantitative comparison was not possible as there exist no adequate models for plasma expansion in air.

laser produced plasma; plasma spectroscopy

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