Use of the Optogalvanic Effect to Examine the Laser Power Dependency of Several Excitation/Ionization Mechanisms in a Hollow Cathode Discharge

Abstract

Several examples of the relationship between resonant and nonresonant collisional ionization and photoionization, laser intensity, and the ability to saturate both resonant and nonresonant transitions are illustrated. The effects of energy deficit and effective energy overshoot in determining the dominant ionization pathway are also discussed. An approximation of the lifetime of the virtual level is made, and its relationship to the probability of two-photon nonresonant absorption is discussed. Finally, the theoretical model described above is fitted to the optogalvanic data for two single-step resonance transitions of Ne to determine the applicability of the model developed for flame LEI to the hollow cathode discharge environment (under our experimental conditions) and to obtain estimates of the collisional ionization rate constant, k2i, and photoionization cross section, σ2i.