INTENSE SOURCE OF SPIN-POLARIZED ELECTRONS

Spin angular momentum conservation in chemiionization reactions involving optically oriented He(23S) atoms in a flowing helium afterglow has been exploited to yield a source of spin-polarized electrons. Either transversely or longitudinally polarized electrons can be extracted. Polarized electron beam currents of ∼2 μA have been realized at 40% polarization. The beam has an effective emittance of ∼2 mrad/cm over the energy range 100-400 eV, an energy spread of ≲0.15 eV, and the polarization is readily reversible. The source is relatively inexpensive and appears suitable for the majority of low-energy spin-dependent scattering experiments proposed to date.