Estimation of self-absorption effect on aluminum emission in the presence of different noble gases: comparison between thin and thick plasma emission.

Aluminum spectra in the noble gases of helium and argon at initial delay times after plasma formation are numerically calculated. Temporal behavior of plasma emissions up to 200 ns after laser irradiation is investigated. Plasma parameters are computed by coupling the thermal model of laser ablation, hydrodynamic of plasma expansion, and Saha-Eggert equations. A spectrum is constructed from the superposition of 13 strong lines of aluminum and several strong lines of ambient gases. Spectral radiations are superimposed on a continuous emission composed of bremsstrahlung and recombination radiation. The self-absorption effect on plasma radiation at 1 atm gas pressure is studied. In this paper, a comparison between thin and thick aluminum radiation is done. Furthermore, the self-absorption coefficient of each strong line at laser energies of 0.5, 0.7, 0.9, and 1.1 GW/cm(2) is estimated. Results show that at specific laser energy, the self-absorption effect in argon is more significant than in helium. For most of the spectral lines in both noble gases, the self-absorption coefficient will diminish with the delay time. As indicated with passing time, the line widths of the self-absorbed lines will rise. More intense continuous emissions are observed at higher wavelengths, and these radiations will be increased with laser energy.