Collision-Induced Transitions within Excited Levels of Neon

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-{μ} 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 2s₂ and 2s₃ levels. In pure neon this has been found to be σ₂₃=(2.3±0.3)×10^-16 cm². For a helium-neon mixture the measured cross section is σ₂₃=(1.8±0.3)×10^-16 cm². 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 2s₂→2p₁₀ and 2s₃→2p₁₀. The measured ratio is A₂A₃=3.0±0.4.