Effect of Varying Discharge Current on Optogalvanic Waveforms Associated with the Neon Transition at 640.2 nm

Laser optogalvanic spectroscopy is useful in calibrating the frequency of tunable dye lasers and in determining parameters that characterize the state of the plasma within a hollow cathode discharge. Optogalvanic spectral transitions of neon have been investigated in a discharge lamp when illuminated with a Nd: YAG-pumped pulsed dye laser. For the present study, our focus is on the neon transition at 640.2 nm. Optogalvanic waveforms were recorded for this transition at various currents in the range 0.30 mA -1.3 mA. A theoretical model has been developed to fit these waveforms in order to determine several important parameters that characterize the plasma inside the hollow cathode discharge. Monte Carlo least-squares fitting of these waveforms has helped to specifically determine the exponential rates and time constant parameters associated with the evolution of the 640.2 nm optogalvanic waveforms. A detailed analysis of the time evolution of the optogalvanic signal waveforms associated with the 640.2 nm neon transition is presented here, together with a summary of the fitted decay rates and collisional parameters for the range of currents used.