An intense source of spin-polarized electrons based on an optically-pumped flowing helium afterglow
Rutherford, George Henry
Dunning, F. B.
Master of Science
The optimization of an optically-pumped, flowing helium afterglow for use as a high-current dc polarized electron source with high electron spin polarization is described. The atomic electron spins of He (2$\sp3\rm S\sb1$) metastable atoms created by a microwave discharge are aligned in the presence of a weak magnetic field by circularly polarized radiation from a recently developed LNA laser. The polarized outer 2s electrons are liberated in spin-conserving Penning ionization reactions with CO$\sb2$ and are extracted from the flow tube for polarization analysis. Polarizations approaching 90% were obtained at currents below.1 $\mu$A, falling gradually to 70% at 20 $\mu$A. Comparisons with other sources, chiefly photoemission from GaAs, suggest that for most applications requiring dc currents less than 50 $\mu$A, the flowing afterglow source is superior. Possible future improvements to the present source are also discussed.