US Patent 7102284 Photomultiplier

In a photomultiplier, focusing pieces of a focusing electrode are formed with sufficient height that the photocathode in the adjacent channels cannot be viewed from the first and second stage dynodes of each channel in order to prevent light reflected from the first and second stage dynodes from returning to the adjacent channels. This construction prevents the photocathode from emitting undesired electrons, thereby suppressing crosstalk. Further, by arranging condensing lenses on the outer surface of a light-receiving faceplate in correspondence with each channel, light is reliably condensed in each channel. Further, an oxide film formed over the surface of the focusing pieces prevents the reflection of light off the focusing pieces.