Preparation of individual magnetic sub-levels of 4He(23S1) in a supersonic beam using laser optical pumping and magnetic hexapole focusing

Abstract

We compare two different experimental techniques for the magnetic-sub-level preparation of metastable 4He in the 23S1 level in a supersonic beam, namely, magnetic hexapole focusing and optical pumping by laser radiation. At a beam velocity of v = 830 m/s, we deduce from a comparison with a particle trajectory simulation that up to 99% of the metastable atoms are in the MJ″ = +1 sub-level after magnetic hexapole focusing. Using laser optical pumping via the 23P2–23S1 transition, we achieve a maximum efficiency of 94% ± 3% for the population of the MJ″ = +1 sub-level. For the first time, we show that laser optical pumping via the 23P1–23S1 transition can be used to selectively populate each of the three MJ″ sub-levels (MJ″ = −1, 0, +1). We also find that laser optical pumping leads to higher absolute atom numbers in specific MJ″ sub-levels than magnetic hexapole focusing.

Spin-state-controlled chemi-ionization reactions between metastable helium atoms and ground-state lithium atoms

“…The determination of relative magnetic-sublevel populations in He * is described in detail in Ref. 34 . By analyzing the polarization of the fluorescence light emitted by the He atoms during laser-optical pumping, we infer a relative population η + ≈ 0.92 in the M J ′′ = +1 magnetic sublevel for excitation using σ + -polarized light and η − ≈ 0.90 in the M J ′′ = −1 magnetic sublevel for excitation using σ − -polarized light, respectively, which is the same for all valve temperatures in this study.…”

“…Most parts of the experimental setup have already been described elsewhere [31][32][33][34] . In the following, we thus briefly provide details about the most important parts of the setup and about those features which have specifically been implemented for this study.…”

“…More details about the optical pumping scheme for He * and about the fluorescence detection system are discussed in Ref. 34 .…”

“…The relative magnetic-sublevel populations in He * are determined following the procedure described in Ref. 34 . In short, this involves an analysis of the polarization state of the fluorescence light emitted by the He atoms while they are being optically pumped.…”

“…To achieve the maximum transfer efficiency to the M J ′′ = +1 (M J ′′ = −1) sublevel of He * , the laser polarization for optical pumping is set to σ + (σ − ) and a laser power of P = 200 mW is used 34 .…”