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Many books including the book (Hamamatsu, "Photomultiplier Tubes", link to PDF) says that a photocathode of a photomultiplier tube is damaged by intense light.

Do not expose to strong light. The photocathode of photomultiplier tubes may be damaged if exposed to direct sunlight or intense illumination. Never allow strong light to strike the photocathode.

Buy why is it damaged by intense light? Surely, intense light causes excessive photocurrent and many electrons will be emitted from the photocathode of photomultiplier. Why does a large current damage the photocathode?

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Photomultiplier tubes are made up of multiple photocathodes. Wikipedia states:

A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound.

These compounds are usually degrade if the photocurrent is very high. Basically if a macroscopic amount of electrons bombard the electrode, the compound will undergo irreversible chemical changes that alter (reduce) the emission capabilities.

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  • $\begingroup$ Almost every photomultplier I've ever seen (I spent five years of my career years ago designing them; things may have changed) has one cathode, and one anode, and at least one dynode, usually several dynodes. There are specialty tubes that have more than one cathode, but they are not common. When you say "electrode" which of those do you mean? The cathode is negatively charged. That, plus geometry that guides electrons to the first dynode, means that practically zero electrons (not a bomardment) hit the cathode. $\endgroup$
    – garyp
    Commented Jun 6, 2020 at 18:27
  • $\begingroup$ I assumed cathodes anodes and dynodes were all electrodes, perhaps I am wrong. So when I meant electrode I meant the dynode for which the electrons reaching are macroscopically large. Perhaps my understanding is rudimentary. $\endgroup$
    – Superfast Jellyfish
    Commented Jun 6, 2020 at 18:47

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