Electron energy distributions in the negative glow and their relevance to hollow cathode lasers

Electron energy distributions have been measured in and near the negative glow of an abnormal glow discharge in helium at pressures in the range 3-25 Torr. The experimental technique involved the use of a differentially pumped retarding-field analyser. The measured distributions are distinctly non-Maxwellian. In particular, the distribution in the negative glow close to the cathode dark space shows a prominent 'tail' of high-energy electrons and a 'beam' component at the cathode fall potential ( approximately 300 V). The significance of these results for hollow cathode helium/metal-vapour lasers is discussed.