Photocathode, photomultiplier and electron tube

摘要

The present invention relates to a photocathode (1A) having a structure to dramatically improve the effective quantum efficiency in comparison with that of a conventional art, an photomultiplier and an electron tube. The photocathode comprises a supporting substrate (100A) transmitting or blocking an incident light, a photoelectron emitting layer (300) containing an alkali metal provided on the supporting substrate, and an underlayer (200) provided between the supporting substrate and the photoelectron emitting layer. Particularly, the underlayer contains a beryllium oxide, and is adjusted in its thickness such that a thickness ratio of the underlayer to the photoelectron emitting layer falls within a specific range. This structure allows to obtain a photocathode having a dramatically improved quantum efficiency.