Laser optogalvanic effect from Ar positive ions in a hollow-cathode discharge

The optogalvanic effect from Ar positive-ion transitions, corresponding to the spectral lines emitted by an Ar laser, has been investigated in this work by using a hollow-cathode glow discharge. The $\rm Ar^+$ optogalvanic signal amplitude and sign have been registered as a function of Ar pressure, discharge current, radial position of the illuminating laser beam and laser power. The change of intensity of the different spectral lines of ArI, ArII and ArIII has been simultaneously measured. The experimental results showed that the optogalvanic signal has an amplitude one order of magnitude higher in cathode dark space than in negative glow. The correlation between the dependences of optogalvanic signal and estimated number of charge-exchange collisions vs. discharge current proved our assumption that these high-amplitude $\rm Ar^+$ optogalvanic signals were caused by increased $\rm Ar^+$ mobility as a result of decreased cross-section of charge exchange collisions with participation of excited ions. The additional secondary electron emission from cathode walls due to $\rm Ar^+$ can also cause a significant part of the measured optogalvanic signal. The contribution of other elementary processes related to the $\rm Ar^+$ optogalvanic-effect appearance has been discussed