Influence of plasma discharge operating regime and laser beam intensity on optogalvanic spectra

The optogalvanic (OG) spectrum — over the tuning range of R 6G dye (568 nm to 605 nm) — of a Pr/Ne discharge tube is studied. The positive OG signals are approximately two orders of magnitude larger than the negative OG signals. The magnitude of the signals depend mainly on the operating regime of the discharge. Specifically, operation of the discharge in the abnormal glow regime leads to an enhancement in the negative OG signals. The operating point on theV-I characteristic of the discharge should be stipulated. To study the variation of the OG signal with the intensity of the laser beam two OG signals, of different polarities, were examined. We observed that with respect to positive OG signals, there is a trend towards pumping saturation. A minimum threshold of 0.3 kW laser power is required to generate negative OG signals. For the same attenuation in the laser beam there is a ten times more efficient reduction in the negative OG signals than in the case of positive OG signals. This confirms the important role of metastable atoms in the conduction in gas discharges.The hypothesis that negative OG signals can be obtained only abnormal glow regime needs more experimental data. The required study of the temporal variation in the OG signal with increase in the discharge current is being carried out and the results are to be published.