Electron energy spectra in neon, xenon, and helium-neon laser discharges

Absolute measurements of the electron energy spectrum in a helium-neon mixture and in pure neon and xenon have been obtained by an energy analysis of a sample of electrons extracted through a small hole in the anode. The spectrum appears to be nearly Maxwellian for the lower pressures but deviates markedly from a Maxwellian at higher pressures. At higher pressures, the energetic part of the spectrum drops off faster, and one can describe this part by a Maxwellian of lower temperature than that for the bulk of the distribution. The average energies agree with those obtained from microwave measurements of the radiation temperature of the electrons if corrections are made for nonthermal distribution. Several production rates are computed with the help of the measured spectra, and they are related to the wall current, the power dissipation, and the possible electron depopulation of helium metastables. The production and destruction rates for the different parts of the energy spectrum have been formulated mathematically. A theoretical formula, which describes the actual spectra, has been derived for the faster part of the spectrum. For the helium-neon laser discharge we can say definitely that the de-excitation of helium metastables by electrons is negligible.