Patent ID: 8421354

Claim:
A photocathode having a light incident surface into which light with a predetermined wavelength is made incident and a photoelectron emitting surface which emits photoelectrons in response to incidence of the light, comprising: a supporting substrate having a first main surface and a second main surface opposing the first main surface; a photoelectron emitting layer, in which the photoelectrons are generated in response to incidence of the light, having a first main surface and a second main surface opposing said first main surface, and comprised of a compound of antimony and an alkali metal, said photoelectron emitting layer being provided on the second main surface of said supporting substrate such that the first main surface of said photoelectron emitting layer faces the second main surface of said supporting substrate; and an underlayer provided between said supporting substrate and said photoelectron emitting layer while being in direct contact with the second main surface of said supporting substrate and the first main surface of said photoelectron emitting layer, said underlayer being comprised of an oxide of a beryllium alloy or a beryllium oxide, wherein said supporting substrate is comprised of a material that transmits light with the predetermined wavelength made incident thereinto, and wherein said photocathode includes a transmissive photocathode where the first main surface of said supporting substrate functions as the light incident surface, while the second main surface of said photoelectron emitting layer functions as the photoelectron emitting surface.