Determination of the absolute concentration of B,Al, Ga,and Si atoms in a nonequilibrium plasma by the reabsorption-distorted intensity ratios in resonance multiplets

The recently developed method of spectroscopic determination of the concentration of boron atoms in a nonequilibrium plasma is extended to B, Al, Ga, and Si atoms and generalized by taking into account the gas temperature and the non-Boltzmann distribution of the sublevel populations of the ground state multiplet structure of the atoms. The approach suggested is based on the measurement of the reabsorption-distorted intensity ratios of pairs of spectral lines having the same upper level and belonging to the resonance multiplet. It is shown that, at a sufficiently large optical thickness of the plasma along the line of observation, the measured values of the intensity ratios depend on the plasma gas temperature T and the product NL of the total concentration N of normal atoms and the length L of the plasma column along the line of observation. Hence, to determine the concentration N using the resonance doublets of B, Al, and Ga atoms, it is necessary to have data about the temperature T. The structure of the resonance multiplet of Si allows measurement of three independent intensity ratios. This circumstance not only makes possible the simultaneous and purely spectroscopic determination of N and T but also enables one to perform internal testing of the applicability of the suggested method under real experimental conditions. The intensity ratios are calculated for the resonance multiplets of B, Al, Ga, and Si in the regions T = 300–6500 K and NL = 10⁷–10¹⁵ cm^?3 m. The calculation results and the range of applicability of the method are discussed.