LASER OPTOGALVANIC EFFECT FROM AR POSITIVE-IONS IN A HOLLOW-CATHODE DISCHARGE

The optogalvanic effect from Ar positive-ion transitions, correspondin g to the spectral lines emitted by an Ar laser, has been investigated in this work by using a hollow-cathode glow discharge. The Ar+ optogal vanic signal amplitude and sign have been registered as a function of Ar pressure, discharge current, radial position of the illuminating la ser beam and laser power. The change of intensity of the different spe ctral lines of ArI, ArII and ArIII has been simultaneously measured. T he experimental results showed that the optogalvanic signal has an amp litude one order of magnitude higher in cathode dark space than in neg ative glow. The correlation between the dependences of optogalvanic si gnal and estimated number of charge-exchange collisions vs. discharge current proved our assumption that these high-amplitude Ar+ optogalvan ic signals were caused by increased Ar+ mobility as a result of decrea sed cross-section of charge exchange collisions with participation of excited ions. The additional secondary electron emission from cathode walls due to Ar+ can also cause a significant part of the measured opt ogalvanic signal. The contribution of other elementary processes relat ed to the Arf optogalvanic-effect appearance has been discussed.