Development of a spin-polarized helium(+) ion source for surface studies

[摘要] Development of a low-energy electron-spin-polarized He$sp+$ ion source is described. The ion source uses an optically pumped rf discharge. Metastable He(2$sp3$S) atoms are produced by electron impact in the discharge and then are optically pumped into the M$sb{m j}$(M$sb{m s}$) = +1 or $-$1 magnetic sublevels by circularly polarized radiation from a Ti:sapphire laser operating at 1.083 $mu$m. He$sp+$ ions are produced by Penning ionization in metastable-metastable collisions and should be spin-polarized because of spin conservation in such processes. A method for accurately determining the net polarization of He(2$sp3$S) atoms in the discharge by measuring the absorption of light from a tunable diode laser is described. This method can be used to optimize source performance. Optically pumping the discharge on the D0, D1, or D2 transitions gave polarizations of 31.2%, 47.1%, and 18.2%, respectively. It is expected that optically pumping the discharge on the D1 transition will produce $sim$80+% polarization of the metastable atoms after suitable optimization of operating parameters.

[发布机构] Rice University

[效力级别] matter