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

Abstract

We compare two different experimental techniques for the magnetic-sub-level preparation of metastable 4 He in the 2 3 S 1 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 M J = +1 sub-level after magnetic hexapole focusing. Using laser optical pumping via the 2 3 P 2 − 2 3 S 1 transition, we achieve a maximum efficiency of 94 ± 3 % for the population of the M J = +1 sub-level.For the first time, we show that laser optical pumping via the 2 3 P 1 − 2 3 S 1 transition can be used to selectively populate each of the three M J sub-levels (M J = -1, 0, +1). We also find that laser optical pumping leads to higher absolute atom numbers in specific M J sub-levels than magnetic hexapole focusing.