Interference of Fine-Structure Levels of He ii

Abstract

Passage of a beam of foil-excited ${\mathrm{He}}^{+}$ ions through a small electric field induced quasiperiodic fluctuations in the intensity of the light emitted from levels $n=7, 8, 9, \mathrm{and} 10$. Both ${\mathrm{He}}^3$ and ${\mathrm{He}}^4$ beams were used. Only one foil was needed, in contrast to the double-foil arrangement reported necessary for hydrogen. The observations are discussed in terms of Stark-induced interference of the fine-structure levels of He ii, but discrepancies between the data and the calculations are large.