  New spin-dependent photoemission properties of alkali antimonide
semiconductor cathodes are predicted based on the detected optical spin
orientation effect and DFT band structure calculations. Using these results,
the Na$_2$KSb/Cs$_3$Sb heterostructure is designed as a spin-polarized electron
source in combination with the Al$_{0.11}$Ga$_{0.89}$As target as a
spin-detector with spatial resolution. In the Na$_2$KSb/Cs$_3$Sb photocathode,
spin-dependent photoemission properties were established through detection of
high degree of photoluminescence polarization and high polarization of the
photoemitted electrons. It was found that the multi-alkali photocathode can
provide electron beams with emittance very close to the limits imposed by the
electron thermal energy. The vacuum tablet-type sources of spin-polarized
electrons have been proposed for accelerators, that can exclude the
construction of the photocathode growth chambers for photoinjectors.
