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Mott and helium polarimetry of a spin polarized electron source

An absolute determination of the electron spin polarization of a GaAs photoemission source was made using the method of helium polarimetry. Measurements of the source polarization were also made using a Mott spin polarization analyzer. The authors report an electron beam polarization of (25.5+or-1)% and an effective Sherman function of 0.26+or-0.01 for the Mott detector at 31.8+or-0.6 keV incident electron energy. The Sherman function is also presented for a number of incident energies between 10 keV and 37 keV. A complete set of Stoke's parameters is reported for the 33P-23S (3889 AA) helium line. The characteristics of the source, Mott detector and helium polarimeter are discussed in detail.