Effects of Non-Uniformity of Laser Induced Plasma on Plasma Temperature and Concentrations Determined by the Boltzmann Plot Method: Implications from Plasma Modeling

The validity of the popular Boltzmann plot method was theoretically tested for the case of a non-homogenious non-isothermal laser-induced plasma. A collisional-dominated plasma model was employed to generate synthetic spectra by solving the radiative transfer equation. The spectra were processed with home-made software that calculated values for the plasma temperature and concentrations using the Boltzmann plot approach. Both static and dynamic plasmas were investigated at various temperature and density gradients. The plasma parameters obtained from the Boltzmann plots were subsequently compared with the exact parameters of the model. The results are shown to have a direct implication for calibration-free laser-induced breakdown spectroscopy (CF LIBS). For nearly all tested situations, the Boltzmann plot method was capable of semi-quantitative analysis providing the accurate determination of concentrations for main plasma components and failing to accurately predict the concentrations of minor components and trace elements.