Optogalvanic effects in a hollow cathode glow discharge plasma

The hollow cathode glow discharge is a very suitable source to measure the optogalvanic effect (OGE). A detailed study of this effect in neon has been made using a tunable, single-frequency dye laser. It was found that the lower level of the irradiated transition together with the plasma conditions determine the sign of the effect. Three situations occur: the lower level can either be metastable, resonant, or highly excited. With a five-level model taking into account electronic collisions and radiative decay a qualitative description of all the cases found in the experiment can be given. Further, it is shown that from a frequency scan of the OGE, line profiles can be obtained which, under certain conditions, contain the gas temperature in their Doppler part. Temperatures ranging from 700 to 1300 K determined this way are consistent with other results. This method makes it possible to measure the temperature as a function of the position, showing that inside the glow the gas temperature is constant. Finally, the time-dependent OGE is measured and analyzed in terms of ambipolar diffusion. This way an average transport temperature for the plasma electrons in the hollow cathode discharge in neon between 0.2 and 1.2 eV is found