Composite photocathodes for visible photon imaging with gaseous photomultipliers

We report on the results of coating K–Cs–Sb visible photocathodes, with thin CsBr and CsI protective films, in view of their possible combination with gas electron multipliers. Absolute quantum efficiency, photoelectron transport through the coating film, the effect of exposure to oxygen and to air and the photocathode behavior under intense photon flux are presented. The coated K–Cs–Sb photocathodes have typically maximum quantum efficiency values of 5–6% at 312 nm. They can withstand exposure to 150 Torr of oxygen for more than half an hour. Appropriate electron multipliers and possible applications are briefly discussed.