  For short, high-intensity electron bunches, alkali-tellurides have proved to
be a reliable photo-cathode material. Measurements of lifetimes in an RF gun of
the CLIC Test Facility II at field strengths greater than 100 MV/m are
presented. Before and after using them in this gun, the spectral response of
the Cs-Te and Rb-Te cathodes were determined with the help of an optical
parametric oscillator. The behaviour of both materials can be described by
Spicer's 3-step model. Whereas during the use the threshold for photo-emission
in Cs-Te was shifted to higher photon energies, that of Rb-Te did not change.
Our latest investigations on the stoichiometric ratio of the components are
shown. The preparation of the photo-cathodes was monitored with 320 nm
wavelength light, with the aim of improving the measurement sensitivity. The
latest results on the protection of Cs-Te cathode surfaces with CsBr against
pollution are summarized. New investigations on high mean current production
are presented.
