A source of spin-polarized electrons based on a laser-pumped flowing helium afterglow is described. He(23S) atoms contained in the afterglow are optically pumped using circularly polarized 1.08-μm (23S→23P) radiation provided by a NaF (F2+)* color-center laser. Spin angular momentum conservation in subsequent chemi-ionization reactions with CO2 produces polarized electrons that are extracted from the afterglow. At low currents, ≲1 μA, polarizations of ∼70%–80% are achieved. At higher currents the polarization decreases, falling to ∼40% at 50 μA. The spin polarization can be simply reversed (P→−P) and the source is suitable for use in the majority of low-energy spin-dependent scattering experiments proposed to date.

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A color-center laser operating at 1.08 μm has been used to optically pump a thermal He(23S) atom beam via 23S→23P transitions. Even modest laser powers (∼10 mW) result in more efficient optical pumping than is obtained using a 400-W rf-excited helium resonance lamp. The laser also permits optical pumping via transitions to selected 23P fine structure levels.

Efficient, stable optical pumping of a collimated beam of Ar((3)P(2)) metastable atoms is obtained using a low-power, frequency-modulated multimode dye laser. The advantages provided by frequency modulation are discussed. The technique is suitable for use in optically pumping a wide variety of atomic species.

A technique is described that enables simple, direct determination of the spin polarization of an optically pumped ensemble of He (23S) atoms. The polarization is obtained from measurements of the attenuation of the circularly polarized output of a color-center laser tuned to the 1.08 μm He (23S1→23P0) transition.