Low-energy, electron-spin-polarized 4 He + ion source

A source of low-energy, electron-spin-polarized 4 He + ions based on an optically pumped, rf-excited helium discharge is described. Ion polarizations P + of ∼0.13 are achieved at beam currents of ∼0.1 nA , decreasing to ∼0.09 at currents of ∼0.5 nA . Ion beam energies as low as 10 eV have been realized, with an energy spread of ≲3 eV full width half maximum. The ion polarization can be reversed (P + →−P + ) simply by changing the sense of circular polarization of the optical pumping radiation. The source is suitable for use in a wide variety of applications including surface physics studies.