Silver-oxygen-caesium photocathodes with enhanced infrared sensitivity

The technique of developing Ag-O-Cs photocathodes which are sensitive to visible and near infrared spectrum and have enhanced infrared sensitivity is described. Cathodes exhibiting a threshold wavelength of 1250 nm and an average luminous sensitivity of about 30 mu A 1m -1 , have been obtained using a source of colour temperature 2870 K, and in infrared transmitting and visible absorption filter of type Corning Cs-7-56. These cathodes have an infrared response of 12-15% of the integral sensitivity. The effect of different rates of evaporation of parent silver film on the sensitivity of the finished cathode has been studied. The effect of additional silver on the finished cathode is also described briefly. The dark currents of such cathodes are found to be of the order of 10 -12 A cm -2 .