Determination of Temperature, Velocity Distribution, and Population Densities of Neutral Helium by Means of Laser Light Tuned on Atomic Resonances

Temperature, velocity distribution, and population density of neutral Helium in the 23P level in a discharge of different current and pressure values are measured by absorption, dispersion, and resonant scattering experiments. The light source for these investigations is a tunable dye laser with linewidth of 2 MHz. The measurements show that there is a good mutual agreement among each of these methods and that these diagnostic methods are very easily adapted to investigate discharges with low densities of population, where Doppler-broadening mechanisms predominate. In addition, the experimental values of the index of refraction are compared with the linear dispersion theory confirming the predicted theoretical profiles.