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We compare two different experimental techniques for the magnetic-sub-levelpreparation 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 abeam velocity of $v = 830\,$m/s, we deduce from a comparison with a particletrajectory simulation that up to $99\,$\% of the metastable atoms are in the$M_{J^{''}} = +1$ sub-level after magnetic hexapole focusing. Using laseroptical pumping via the $2^3$P$_2-2^3$S$_1$ transition, we achieve a maximumefficiency of $94\pm3\,$\% 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 thethree $M_{J^{''}}$ sub-levels ($M_{J^{''}} = $ -1, 0, +1). We also find thatlaser optical pumping leads to higher absolute atom numbers in specific$M_{J^{''}}$ sub-levels than magnetic hexapole focusing.

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