Optogalvanic effect as a probe of plasma processes

One of these components is attributable to optically induced ionization rate changes, the other to a photoacoustic effect. These components carry information about many dynamic plasma processes, and the ability to separate the two of them suggests that the OG effect can be used as a weakly perturbative but highly sensitive probe of plasma processes. In this work, we use this sensitivity to accomplish the following: (i) preparation of an OG signal that consists solely of the ionization component; (ii) preparation of an OG signal that consists solely of a photoacoustic component; (iii) demonstration of how to distinguish a true photoacoustic effect from one which leads to electron mobility changes; (iv) demonstration of the role of radiation trapping; (v) demonstration of the effects of the decay branching ratios of optically excited plasma species; (vi) detection of collisional transfer of excitation energy; and (vii) discrimination of the roles played by particular states in the maintenance of the discharge. The effects will be exemplified using low power radiofrequency discharges in neon and iodine. 24 refs., 7 figs., 1 tab.