Photomultiplier and sensor module

A photomultiplier comprising:

• a sealed container the interior of which is maintained in a vacuum state, the sealed container including a first ceramic side tube and a second ceramic side tube arranged in order along a first tube axis of the sealed container;
• a photocathode housed in the sealed container and configured to emit photoelectrons into the sealed container in response to light of a predetermined wavelength;
• an electron multiplier unit housed in the sealed container, the electron multiplier unit comprising:
• a dynode unit including multi-stage dynodes to emit secondary electrons in response to the photoelectrons arriving from the photocathode and successively cascade-multiply the secondary electrons;
• an anode for extracting as a signal, secondary electrons resulting from cascade multiplication by the dynode unit;
• a pair of insulating support members for integrally holding the dynode unit and the anode, while grasping the dynode unit and the anode;
• and a focusing electrode arranged between the photocathode and the dynode unit while being fixed to the pair of insulating support members, the focusing electrode having a through hole for letting the photoelectrons from the photocathode pass through;
• and
• a fixing member separated from the focusing electrode and having an aperture for defining an installation position of the focusing electrode, an inside end defining the aperture, and an outside end surrounding the inside end, the fixing member being fixed to the sealed container so that the outside end is grasped by the first ceramic side tube and the second ceramic side tube, while the inside end located in the sealed container is fixed to the focusing electrode,
• wherein the inside end has a shape that extends toward the photocathode, and an outer periphery of the focusing electrode is fixed to the inside end while the focusing electrode is housed in the inside end.