ABSTRACT
The optogalvanic effect (OGE) is due to a change (increase or decrease) in the electrical properties (conductivity) within a self-sustained gaseous discharge when illuminated by radiation that is resonant with an atomic or molecular transition of the element within the discharge. The main principle of this effect is that the absorption of radiation causes a redistribution of populations in the atomic or molecular energy levels. Under steady-state discharge conditions, there exists a dynamic equilibrium (as a result of various radiative and/or collisional and/or collective processes) between the various plasma species causing a well-defined impedance to the flow of current. At dynamic equilibrium, changes in the electron/ion densities and/or mobilities, with a concomitant change in the electrical impedance of the plasma, are caused by optical perturbations. Such a change in impedance alters the current in the plasma and can be either real for direct current (DC) discharges or complex for alternating current (AC) discharges.
