PHOTOEMISSION OF SPINPOLARIZED ELECTRONS FROM STRAINED GAASP

Strained layer GaAs.95P.05 photo cathodes are presented, which emit el ectron beams spinpolarized to a degree of P = 75% typically. Quantum y ields around QE = 0.4% are observed routinely. The figure of merit P-2 x QE = 2.3 x 10(-3) is comparable to that of the best strained layer cathodes reported in literature. The optimum wavelength of irradiating light around 830 nm is in convenient reach of Ti:sapphire lasers or d iode lasers respectively. The cathodes are produced using MOCVD-techni ques. A GaAs.55P.45-GaAs.85P.15 superlattice structure prevents the mi gration of dislocations from the substrate and bottom layers to the st rained overlayer. The surface is protected by an arsenic layer so that no chemical cleaning is necessary before installation into vacuum. Th e source of polarized electrons attached to the Mainz race track micro tron MAMI works with such cathodes now. More than 1000 hours beamtime have been performed successfully.