Patent ID: 7687992

Claim:
A photomultiplier tube, comprising: an envelope, the envelope having a first opening and a second opening; a photocathode for emitting electrons in correspondence with incident light entering the envelope, the photocathode disposed at the first opening; a collecting anode having a semiconductor device, the semiconductor device having an electron incident surface for receiving photoelectrons emitted from the photocathode, the collecting anode disposed at the second opening of the envelope, the photocathode and the collecting anode creating a vacuum in the envelope, the electron incident surface facing the photocathode; a gating grid for gating the photoelectrons emitted from the photocathode, the gating grid disposed within the envelope; an electron optical system for focusing and directing the photoelectrons generated by the photocathode toward the electron incident surface, the electron optical system disposed between the photocathode and the semiconductor device, the electron optical system comprising focusing electrodes formed as cylindrical rings mounted between isolation rings; and an ion target for collecting positive ions from the photoelectrons, the ion target disposed at or about the center of the gating grid.