Excitation mechanisms of the CW He-As laser

The collisional processes responsible for populating and depopulating excited As⁺ levels in the He-As system have been studied using flowing afterglow techniques. Excitation of several As⁺ levels lying above the energetic limit for charge transfer from the neutral atom ground state has also been observed. The process responsible for this excitation has been identified as He⁺ charge transfer on arsenic metastables. The experiments further indicate strong effects due to rapid transfer of population among the excited As⁺ levels due to second-kind collisions of electrons. The very noticeable preference for abnormally high helium pressure for optimum operation of tbe He-As laser system can he understood in the light of these results.