Patent ID: 7323674

Claim:
A photodetector comprising: a photomultiplier functioning as a photo-sensing device, said photomultiplier comprising: a sealed container having an entrance face plate partitioned into a plurality of light incidence regions, and a stem opposing said entrance face plate; a photocathode emitting photoelectrons into said sealed container in response to light having passed through said entrance face plate; a plurality of anodes respectively prepared for electron multiplier channels which are assigned to said light incidence regions partitioned on said entrance face plate, said plurality of anodes being respectively positioned inside said sealed container so as to oppose said associated light incidence regions; and a dynode unit housed in said sealed container, disposed between said anodes and said photocathode and constituted by N (an integer of no less than 3) dynode plates, each of said dynode plates being provided with an electron multiplier hole for the associated channel, concerning all channels, arranged at a position corresponding to the associated one of said plurality of light incidence regions, wherein a n-th (an integer of no less than 2) dynode plate in said dynode unit is constituted by a plurality of control plates each having an electron multiplier hole for the associated channel and being electrically and physically separated from the others; and a bleeder circuit unit for setting at least each of said dynode plates constituting said dynode unit in said photomultiplier to predetermined potentials, said bleeder circuit unit comprising: a primary section setting potentials of a first to (n−1)-th and (n+1)-th to N-th dynode plates respectively; and a secondary section setting potentials of said control plates constituting said n-th dynode plate respectively, said secondary section having a structure, for adjusting gains of the electron multiplier channels respectively, capable of individually changing a potential of the selected one of said control plates over the potential range that is wider than a potential difference between said (n−1)-th dynode plate and said (n+1)-th dynode plate.