Conventionally, there is known an electron tube such as a photomultiplier tube which detects weak light such as fluorescence generated from a sample. The electron tube includes a vacuum container with a light transmitting substrate and a photocathode provided on a vacuum side inner surface of the light transmitting substrate. Non Patent Literature 1 (W. D. Gunter, Jr., G. R. Grant, and S. A. Shaw. Optical devices to increase photocathode quantum efficiency. APPLIED OPTICS Vol. 9, No. 2 251-257 (1970)) discloses a configuration in which a prism is provided in an outer surface of a light transmitting substrate provided with such a photocathode. In this configuration, light incident to an incident surface of the prism is totally reflected at an interface between the photocathode and a vacuum space and then is further reflected at a surface on the side opposite to the incident surface of the prism so as to return to the photocathode. Accordingly, the quantum efficiency (QE) of the photocathode is improved.
USPTO Backgrounds
USPTO Backgrounds