Optical Quenching of Metastable Helium Atoms using Excitation to the $4P$ State

Abstract

Discharge and electron-impact excitation lead to the production of metastable helium atoms in two metastable states, 2${}^1$S${}_0$ and 2${}^3$S${}_1$. However, many applications require pure beams of one of these species or at least a detailed knowledge of the relative state populations. In this paper, we present the characterization of an original experimental scheme for the optical depletion of He(2${}^1$S${}_0$) in a supersonic beam which is based on the optical excitation of the 4${}^1$P${}_1\leftarrow 2^1$S${}_0$ transition at 397 nm using a diode laser. From our experimental results and from a comparison with numerical calculations, we infer a near unit depletion efficiency at all beam velocities under study (1070 m/s $\le v\le$ 1750 m/s). Since the technique provides a direct means to determine the singlet-to-triplet ratio in a pulsed supersonic helium beam, our results show that the intrabeam singlet-to-triplet ratio is different at the trailing edges of the gas pulse.