An electron tube includes a housing having a window having an electromagnetic wave transmitting property, an electron emission plate disposed inside the housing, the electron emission plate emitting electrons, and a holding member disposed inside the housing and configured to hold the electron emission plate and to apply a voltage to the electron emission plate. The electron emission plate has a first main surface and a second main surface facing each other. The holding member has a base portion being in contact with the first main surface, and a plurality of electron emission plate biasing portions which are in contact with an edge of the second main surface and are configured to elastically bias the electron emission plate to the base portion. The holding member is electrically connected to the second main surface through the plurality of electron emission plate biasing portions.

An electron tube includes a housing that is internally held in a vacuum and has a window transmitting an electromagnetic wave, an electron emitting unit that is disposed in the housing and has a meta-surface emitting electrons in response to incidence of the electromagnetic wave, an electron multiplying unit that is disposed in the housing and multiplies the electrons emitted from the electron emitting unit, and an electron collecting unit that is disposed in the housing and collects the electrons multiplied by the electron multiplying unit. The window contains at least one selected from quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate.

An electron tube includes a housing that is internally held in a vacuum and has a window transmitting an electromagnetic wave, an electron emitting unit that is disposed in the housing and has a meta-surface emitting electrons in response to incidence of the electromagnetic wave, an electron multiplying unit that is disposed in the housing and multiplies the electrons emitted from the electron emitting unit, and an electron collecting unit that is disposed in the housing and collects the electrons multiplied by the electron multiplying unit. The window contains at least one selected from quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate.

A photocathode including a substrate, a photoelectric conversion layer provided on the substrate and generating photoelectrons in response to incidence of light, and an underlayer provided between the substrate and the photoelectric conversion layer and containing beryllium, in which the underlayer has a first underlayer containing a nitride of beryllium.

A photocathode including a substrate, a photoelectric conversion layer provided on the substrate and generating photoelectrons in response to incidence of light, and an underlayer provided between the substrate and the photoelectric conversion layer and containing beryllium, in which the underlayer has a first underlayer containing a nitride of beryllium.

An electron tube includes a housing having a window having an electromagnetic wave transmitting property, an electron emission plate disposed inside the housing, the electron emission plate emitting electrons, and a holding member disposed inside the housing and configured to hold the electron emission plate and to apply a voltage to the electron emission plate. The electron emission plate has a first main surface and a second main surface facing each other. The holding member has a base portion being in contact with the first main surface, and a plurality of electron emission plate biasing portions which are in contact with an edge of the second main surface and are configured to elastically bias the electron emission plate to the base portion. The holding member is electrically connected to the second main surface through the plurality of electron emission plate biasing portions.

A method of patterning lithographic substrates, the method including using a free electron laser to generate EUV radiation and delivering the EUV radiation to a lithographic apparatus which projects the EUV radiation onto lithographic substrates, wherein the method further includes reducing fluctuations in the power of EUV radiation delivered to the lithographic substrates by using a feedback-based control loop to monitor the free electron laser and adjust operation of the free electron laser accordingly.

An electron tube module includes an electron tube and a casing. The electron tube includes a vacuum container with a light transmitting substrate, a photocathode provided in an inner surface of the light transmitting substrate, an anode, and a prism. The prism includes a first surface bonded to an outer surface of the light transmitting substrate, a second surface inclined with respect to the first surface, and a third surface which further reflects light incident to the photocathode through the prism and the light transmitting substrate and reflected at an interface between the photocathode and a vacuum space so that the light is incident to the photocathode again. The casing includes a ceiling wall provided with an opening. The second surface is parallel to the ceiling wall. At least a part of the second surface is exposed to outside through the opening.

An electron tube module includes an electron tube and a casing. The electron tube includes a vacuum container with a light transmitting substrate, a photocathode provided in an inner surface of the light transmitting substrate, an anode, and a prism. The prism includes a first surface bonded to an outer surface of the light transmitting substrate, a second surface inclined with respect to the first surface, and a third surface which further reflects light incident to the photocathode through the prism and the light transmitting substrate and reflected at an interface between the photocathode and a vacuum space so that the light is incident to the photocathode again. The casing includes a ceiling wall provided with an opening. The second surface is parallel to the ceiling wall. At least a part of the second surface is exposed to outside through the opening.

An electron tube module includes an electron tube and a casing. The electron tube includes a vacuum container with a light transmitting substrate, a photocathode provided in an inner surface of the light transmitting substrate, an anode, and a prism. The prism includes a first surface bonded to an outer surface of the light transmitting substrate, a second surface inclined with respect to the first surface, and a third surface which further reflects light incident to the photocathode through the prism and the light transmitting substrate and reflected at an interface between the photocathode and a vacuum space so that the light is incident to the photocathode again. The casing includes a ceiling wall provided with an opening. The second surface is parallel to the ceiling wall. At least a part of the second surface is exposed to outside through the opening.