Measurement of plasma temperature by absorption of resonant laser radiation

Abstract

Proposes a method of evaluation of plasma temperature by measurement of its transmission coefficient with respect to radiation that has a resonance with one of the plasma emission lines. The optical thickness of this line can be calculated if the Saha-Boltzmann relation is valid and this is very sensitive to temperature and very insensitive to electron density. The laser used as radiation source must be powerful enough to prevent the self emission of the plasma interfering with the measurement, but not so powerful that it disturbs the population densities in the plasma. Limits on the laser power are calculated and there is a margin of 107 for most experimental plasmas. Calculations show that this method may be used to measure the temperature of an argon plasma if it lies between 15000 degrees K and 20000 degrees K to an accuracy of 1 per cent using an AII laser operated at lambda 4880 AA wave length. No knowledge of the electron density is required except that it should lie between 4*1016cm-3 and 2*1020cm-3.