Photocathode, electron tube, field assist type photocathode, field assist type photocathode array, and field assist type electron tube
When light is incident to an antenna layer AA 6 of a photocathode AA 1 , light of a specific wavelength included in the incident light couples with surface plasmons in the antenna layer AA 6 whereupon near-field light is outputted from a through hole AA 14 . The intensity of the output near-field light is proportional to and greater than the intensity of the light of the specific wavelength. The output near-field light has a wavelength that can be absorbed in a photoelectric conversion layer AA 4 . The photoelectric conversion layer AA 4 receives the near-field light outputted from the through hole AA 14 . A region of the photoelectric conversion layer AA 4 around the through hole AA 14 absorbs the near-field light and generates photoelectrons (e − ) in an amount according to the intensity of the near-field light. The photoelectrons (e − ) generated in the photoelectric conversion layer AA 4 are outputted to the outside.
1. A photocathode comprising:
an antenna layer which has a through hole penetrating in a thickness direction and in a surface of which a pattern according to a predetermined rule is formed for inducing surface plasmon resonance; and
a photoelectric conversion layer which is joined to the antenna layer and which absorbs light outputted from the through hole, to generate photoelectrons.
2. The photocathode according to claim 1 , wherein the photoelectrons generated in the photoelectric conversion layer are outputted through the through hole of the antenna layer to the outside.
3. The photocathode according to claim 1 , wherein the antenna layer has a plurality of projections and a recess located between the projections, the projections and the recess form said pattern, and the through hole is provided in the recess.
4. The photocathode according to claim 3 , wherein the predetermined rule in the pattern is determined so that an amount of photoelectrons generated in said photoelectric conversion layer is larger than an amount of photoelectrons generated in a photoelectric conversion layer in a configuration in which an antenna layer having a through hole and having neither of the projections and the recess formed in a surface thereof is joined to the photoelectric conversion layer.
5. The photocathode according to claim 1 , wherein the antenna layer has a plurality of said through holes and the plurality of through holes form said pattern.
6. The photocathode according to claim 1 , wherein a minimum width of the through hole is shorter than a wavelength of light incident to the antenna layer.
7. The photocathode according to claim 1 , wherein a portion exposed through the through hole of the antenna layer in the surface of the photoelectric conversion layer is provided with an active layer for lowering a work function of said portion.
8. The photocathode according to claim 7 , wherein the active layer is comprised of an alkali metal, an oxide of an alkali metal, or a fluoride of an alkali metal.
9. An electron tube comprising a photocathode,
wherein said photocathode comprising:
an antenna layer which has a through hole penetrating in a thickness direction and in a surface of which a pattern according to a predetermined rule is formed for inducing surface plasmon resonance;
a photoelectric conversion layer which is joined to the antenna layer and which absorbs light outputted from the through hole, to generate photoelectrons.
10. A photocathode according to claim 1 , wherein the antenna layer is composed of Ag or Al.
11. An electron tube comprising a photocathode according to claim 9 , wherein the antenna layer is composed of Ag or Al.