Photomultiplier tube with focusing electrode plate

An electron multiplier, comprising:

• a dynode unit constructed from a plurality of dynodes laminated one on another, the plurality of dynodes including a first dynode and subsequent dynodes, each dynode having a plurality of channels each for multiplying electrons, the plurality of channels being separated from one another by a channel-separating portion;
• a focusing electrode plate located confronting the first dynode and having a plurality of channels each for guiding electrons to a corresponding channel of the first dynode, the plurality of channels being separated from one another by a channel-separating electrode which is located in correspondence with the channel-separating portion of the first dynode, the channel-separating electrode having an opening, at a position confronting the channel-separating portion of the first dynode, for transmitting electrons therethrough and for guiding the electrons to the channel-separating portion of the first dynode;
• and
• an anode unit for receiving electrons multiplied at the plurality of channels in the dynode unit.