Coated photocathodes for visible photon imaging with gaseous photomultipliers

We report on our latest results of K–Cs–Sb visible photocathodes, coated with thin CsI and CsBr protective films, for applications within gas avalanche photomultipliers. Data on the sensitivity to exposure to oxygen and moisture is presented, as well as on the stability under gas multiplication and aging under gas avalanche. There are good indications that the protected photocathodes can withstand long-term multiplication mode, with low-level impurity gases. Possible applications are discussed.