Photo-electrode for electron photomultiplier tube - has thin conductive layer forming cylindrical portion between photocathode and accelerating electrode to correct focussing

摘要

Electrons emitted at the edges of the photo-emissive surface (12) are prevented from being focussed in front of the collector (17). A conducting film (14) of aluminium (or other metal) constituting the cathode is evaporated in a ring at the end of a glass envelope (13). The photo emission layer (12) is deposited on the metal surface. A second electrode (20), also fabricated by evaporation deposition is located between the cathode and the anode ring (18) and has the effect of producing equi-potential surfaces which converge the electron beam. The potential of the second, focussing electrode (Vf) is made positive with respect to the cathode by a potential divider chain between the anode and cathode. The electrical voltage supply leads are deposited on the inner face of the glass tube and travel in a direction parallel to the electron beam to minimise the perturbation of the beam.