Collision-Induced Transitions within Excited Levels of Neon

Abstract

The interaction of an intense optical-maser field with excited atoms in a gas discharge leads to a considerable change in the population of those levels which are resonant at the maser frequency. This will cause a change in the population of other levels that are connected to the maser levels through collision-induced nonradiative as well as radiative transitions. Using the 1.15-\ensuremath{\mu} optical maser, these effects have been studied in detail for the $2s$ levels of neon where the changes are completely due to collisions. By analyzing the intensity changes in spontaneous emission originating from a gas-discharge cell placed within the maser resonator, we have observed the approach to a partial thermalization of two closely spaced levels. In this way we have been able to obtain the atomic-collision cross section for excitation transfer between the $2{s}_{2}$ and $2{s}_{3}$ levels. In pure neon this has been found to be ${\ensuremath{\sigma}}_{23}=(2.3\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$. For a helium-neon mixture the measured cross section is ${\ensuremath{\sigma}}_{23}=(1.8\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$. The experimental method used to determine these cross sections eliminates the uncertainties caused by the effects of electron-atom collisions and radiative cascade. These techniques also yield the ratio of the Einstein coefficients for the transitions $2{s}_{2}\ensuremath{\rightarrow}2{p}_{10}$ and $2{s}_{3}\ensuremath{\rightarrow}2{p}_{10}$. The measured ratio is $\frac{{A}_{2}}{{A}_{3}}=3.0\ifmmode\pm\else\textpm\fi{}0.4$.