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

Abstract

A source of low-energy, electron-spin-polarized 4 He ϩ ions based on an optically pumped, rf-excited helium discharge is described. Ion polarizations P ϩ of ϳ0.13 are achieved at beam currents of ϳ0.1 nA, decreasing to ϳ0.09 at currents of ϳ0.5 nA. Ion beam energies as low as 10 eV have been realized, with an energy spread of Շ3 eV full width half maximum. The ion polarization can be reversed ( P ϩ →Ϫ P ϩ ) 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.

Spin-polarized ion scattering spectroscopy of CCl4 adsorption on Fe(001) surfaces

“…The spin-polarized He + ions were generated from Penning ionization of spin-polarized He 2 3 S 1 atoms (He * ), which were generated in an RF discharge [15,16]. The spin polarization of He * was performed by optical pumping (OP) [17].…”

Current enhancement of a He+ion beam by optical pumping

“…Assuming equivalent populations among the magnetic sublevels of the 2 3 S and 2 1 S levels, i.e., N + + N 0 + N − = 3N S [23],…”

“…The key point in polarized He + ion source is PI of polarized He (2 3 S) atoms. The polarization of the He (2 3 S) atoms has been conventionally achieved by OP using 1083 nm radiation (2 3 S → 2 3 P ) [23]. The selection of a shorter wavelength for the OP radiation, such as 389 nm (2 3 S → 3 3 P ) or 295 nm (2 3 S → 4 3 P ), may enhance the polarized He + ion current because of the larger cross-section of PI with He (2 3 S).…”