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Using beams of polarised electrons and polarised hydrogen atoms we measured the spin antiparallel-parallel ionisation asymmetry from threshold to 500 eV. Our measurements are generally more precise than those of earlier studies and, more significantly, are characterised by an energy spread that is at least an order of magnitude smaller than that of the earlier work. We compare our results with several theoretical models as well as with the results from similar experiments using polarised alkali atoms.

We report on the development of several operating procedures that promise to make GaAs photoemission electron sources easier to construct, more reliable to operate, and more amenable to use in dynamic vacuum systems. We describe in particular a method for ‘‘ohmically’’ heating a 〈100〉 crystal of GaAs under vacuum to approximately 600 °C. We also discuss our observations of the role of oxygen in the activation of the crystal surface, the use of continuous cesiation, and of the performance of the crystal under varying vacuum conditions.

The spin polarization of photoelectrons emitted by an activated gallium arsenide photocathode excited with circularly polarized light has been measured by an optical method:, A crossed-beam experiment has been performed in which polarized electrons transfer spin angular momentum to zinc atoms in inelastic exchange collisions. The polarized atoms emit circularly polarized light in the direction of the spin transfer. The degree of circular polarization is directly related to the electron polarization. PACS numbers: 34.80. Dp, 34.90.+q, 79.60. Eq, 32.80.FbWe have performed the first experiment where spin polarization of free electrons is detected by an optical method. The method used was discussed theoretically a few years ago. ' ' Polarized electrons can transfer spin angular momentum to atoms by inelastic exchange collisions. In such a collision, the electrons polarize the atoms and the information about the polarization of the electron beam is contained in the emitted light.