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 ← 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 ≤ v ≤ 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.

Preparation of individual magnetic sub-levels of $^4$He($2^3$S$_1$) in a supersonic beam using laser optical pumping and magnetic hexapole focusing

“…This is also consistent with previous observations [34]. At time t 0 = 0, we assume a He(2 1 S 0 )/He(2 3 S 1 ) ratio of 66 % which is in line with the results of previous measurements in our laboratory [42]. At the focal point, the signal contribution by He atoms in the 2 3 S 1 , M J = −1 sub-level is decreased by more than a factor of 7 compared to the signal intensity by atoms in the 2 3 S 1 , M J = 0 sub-level.…”

“…Major parts of the experimental setup have already been described elsewhere [41,42]. Briefly, a pulsed 4 He beam is produced by a supersonic expansion of 4 He gas from a high-pressure reservoir (30 − 40 bar) into the vacuum using a home-built CRUCS valve [43] (30 µs pulse duration).…”

Suppression of Penning ionization by orbital angular momentum conservation

“…All individual parts of the setup have already been described elsewhere [20,21]. Therefore, only the most relevant details are given here.…”

“…The He * beam intensity and its mean velocity (v He * = 1850 ± 20 m/s) are measured on two gold-coated Faraday cup detectors located downstream from the Li-MOT. In order to determine the role of He(2 1 S 0 ) and He(2 3 S 1 ) on the reaction rate, we optically deplete the population in the 2 1 S 0 state using 46 mW of diode laser radiation resonant with the 2 1 S 0 -4 1 P 1 transition at 397 nm [21]. To minimize influences by the Doppler effect, the laser beam is incident perpendicular to the supersonic beam.…”

Single-Source, Collinear Merged-Beam Experiment for the Study of Reactive Neutral-Neutral Collisions

“…36 and. 43 Here, two supersonic beams are produced by expanding room-temperature He gas from a 30 bar reservoir into the vacuum using a pulsed CRUCS valve. The first gas pulse is triggered at 200 ms intervals, while ∆t gp is varied in between measurements.…”