Patent Description:
Electron guns equipped with a photocathode and electron beam applicators such as an electron microscope, a free electron laser accelerator, an inspection device, or the like including such an electron gun are known. For example, Patent Literatures <NUM> and <NUM> disclose an electron gun using a photocathode irradiated with excitation light from a light source and emits an electron beam.

Patent Literature <NUM> discloses an electron gun using a so-called transmission type photocathode. The photocathode disclosed in Patent Literature <NUM> has a transparent substrate and a photocathode film formed on the surface of the transparent substrate. A light source is arranged so that light enters the transparent substrate side of the photocathode, the photocathode film is irradiated with excitation light from the light source, and electrons are emitted into vacuum from the photocathode film side. At this time, a lens is arranged between the light source and the photocathode so that the excitation light is focused on the photocathode film.

Further, Patent Literature <NUM> discloses an electron gun having a housing container that can accommodate a photocathode. The housing container is a container that can have a surface treatment material arranged inside to vaporize the surface treatment material and can perform EA surface treatment on the photocathode with the vaporized surface treatment material. Patent Literature <NUM> discloses that, with the housing container being provided, it is possible to perform EA surface treatment inside a chamber without taking the photocathode to the outside.

Patent Literature <NUM> relates to a method for manufacturing an image intensifier and discloses a corresponding tube, comprising a light entrance window having a photocathode on an inner surface thereof, a light output window having a fluorescent film on an inner surface thereof, a photoelectron emitted from the photocathode, and an electron lens for accelerating and forming an image on the image side of the evaporation source container.

Patent Literature <NUM> discloses an electron microscope suitable for observing and measuring a fine pattern of a semiconductor device.

Patent Literature <NUM> discloses a polarized electron generating device which employs a strained superlattice layer for improving crystallinity of the strained superlattice layer in order to enhance spin polarization and external quantum efficiency.

Patent Literature <NUM> discloses an electron beam generating apparatus and an electron beam applying apparatus capable of relatively moving a photocathode holder with respect to an activation container.

When the light irradiation is being continued, this deteriorates electron emission characteristics of the photocathode and reduces the electron emission amount. Thus, it is known that the intensity of the electron beam of an electron beam source using a photocathode decreases with operating time. EA surface treatment is then applied to the deteriorated photocathode to recover the photocathode.

In Patent Literature <NUM>, EA surface treatment is performed outside a vacuum chamber, and the photocathode is required to be taken out of the vacuum chamber. Since the photocathode is then arranged inside the vacuum chamber after the EA surface treatment, it is required to adjust the lens position with respect to the photocathode so that excitation light is suitably emitted to the photocathode film. Thus, there is a problem of complex operation in moving the photocathode and adjusting the lens position. Further, it is required to provide a motion mechanism used for taking the photocathode to the outside and a lens position adjustment mechanism, and this causes a problem of an increase in size and complexity of the device.

Further, when the housing container as disclosed in Patent Literature <NUM> is provided, the EA surface treatment of the photocathode is not required to be performed outside a vacuum chamber. However, the EA surface treatment inside a vacuum chamber causes a surface treatment material arranged inside the housing container to be vaporized, and this causes a problem of contamination of the lens when a transmission type photocathode is used.

Accordingly, in a transmission type photocathode, when the photocathode and the lens are installed inside the electron gun, the disclosure in the present application is to provide a photocathode kit, an electron gun, and an electron beam applicator equipped with the electron gun, which no adjustment of the distance between a photocathode film and a lens that focuses on the photocathode film is required. Other optional, additional advantageous effects of the disclosure in the present application will be apparent from embodiments of the invention.

According to the disclosure in the present application, in a transmission type photocathode, no adjustment of the distance between a photocathode film and a lens that focuses on the photocathode film is required when the photocathode and the lens are installed inside the electron gun.

A photocathode kit, an electron gun, and an electron beam applicator will be described below in detail with reference to the drawings. Note that, in this specification, members having the same type of functions are labeled with the same or similar references. Further, for members labeled with the same or similar references, the duplicated description thereof may be omitted.

Further, the position, size, range, or the like of each feature illustrated in the drawings do not always represent the actual position, size, range, or the like for easier understanding. Thus, the disclosure in the present application is not necessarily limited to the position, size, range, or the like disclosed in the drawings.

A photocathode kit 1A in the first embodiment will be described with reference to <FIG> is a general sectional view schematically illustrating the photocathode kit 1A in the first embodiment. <FIG> is a general perspective view schematically illustrating a spacer <NUM> that is a retaining member.

The photocathode kit 1A in the first embodiment has a photocathode <NUM>, a lens <NUM>, and a holder <NUM>.

In <FIG>, the photocathode <NUM> is formed of a transparent substrate <NUM> and a photocathode film <NUM> adhered to a first surface <NUM> of the transparent substrate <NUM>. The photocathode <NUM> emits an electron beam from the photocathode film <NUM> in response to receiving excitation light incident from a second surface <NUM> side, which is opposite side to the first surface <NUM> on which the photocathode film <NUM> is formed, of the transparent substrate <NUM>.

The transparent substrate <NUM> is not particularly limited as long as it can transmit excitation light received from a light source. For example, quartz glass or sapphire glass may be used.

The photocathode film <NUM> is not particularly limited as long as it can emit an electron beam when irradiated with excitation light and may be made of a material requiring EA surface treatment, a material not requiring EA surface treatment, or the like. The material requiring EA surface treatment may be, for example, a group III-V semiconductor material or a group II-VI semiconductor material. Specifically, AlN, Ce<NUM>Te, GaN, a compound of one or more types of alkali metals and Sb, AlAs, GaP, GaAs, GaSb, InAs, or the like, and a mixed crystal thereof, or the like may be used. Another example may be a metal, specifically, Mg, Cu, Nb, LaB<NUM>, SeB<NUM>, Ag, or the like. With EA surface treatment being performed, the photocathode film <NUM> can be fabricated, and for the photocathode film <NUM>, not only can excitation light be selected in the near-ultraviolet-infrared wavelength region in accordance with gap energy of a semiconductor but also desired electron beam source performance (quantum yield, durability, monochromaticity, time response, spin polarization) in accordance with a use of the electron beam can be achieved through selection of the material or the structure of the semiconductor.

Further, the material not requiring EA surface treatment may be, for example, a single metal, an alloy, or a metal compound of Cu, Mg, Sm, Tb, Y, or the like or diamond, WBaO, Cs<NUM>Te, or the like. The photocathode film not requiring EA surface treatment can be fabricated by a known method (for example, see <CIT> or the like).

The lens <NUM> converges excitation light received from a light source to the photocathode film <NUM>. The converged excitation light is focused on the photocathode film <NUM>, and an electron beam is emitted from the photocathode film <NUM>. The lens <NUM> is not particularly limited as long as it can collect light, and a commonly used lens can be used.

The holder <NUM> holds the photocathode <NUM> and the lens <NUM>. The holder <NUM> has a hollow structure so that externally incident excitation light is emitted to the photocathode <NUM> via the lens <NUM>. Further, the holder <NUM> has, inside the hollow structure, a substrate holding part <NUM> that holds the transparent substrate <NUM> of the photocathode <NUM> and a retaining member <NUM> by which the photocathode film <NUM> and the lens <NUM> are spaced apart by a predetermined distance. <FIG> illustrates an example using a spacer <NUM> as the retaining member <NUM>.

Note that, although the lens <NUM> is interposed between and held by the holder <NUM> and the spacer <NUM> in the example illustrated in <FIG>, the lens <NUM> and the spacer <NUM> can be fixed by a screw. When the lens <NUM> and the spacer <NUM> are fixed by a screw, there may be a space between the convex surface of the lens <NUM> and the holder <NUM>.

While details will be described later, the holder <NUM> can have a heater and thus be preferably formed of a material with good heat transfer. The material may be, for example, a metal such as titanium, molybdenum, an alloy thereof, Inconel, stainless steel (SUS), or the like.

The substrate holding part <NUM> is not particularly limited as long as it can hold (fix) the transparent substrate <NUM> to the holder <NUM>. <FIG> illustrates the example in which a recess that accepts the end of the transparent substrate <NUM> is formed in the holder <NUM>. Alternatively, a protrusion may be formed on the holder <NUM>, and the protrusion and a recess formed in the transparent substrate <NUM> may be engaged with each other.

The spacer <NUM> is arranged between the photocathode <NUM> and the lens <NUM> and defines the distance between the photocathode <NUM> and the lens <NUM>, in other words, the positional relationship between the photocathode <NUM> and the lens <NUM> so that the focal point of the lens <NUM> is located on the photocathode film <NUM>. The spacer <NUM> illustrated in <FIG> as an example has an internally hollowed cylindrical shape. Further, one end <NUM> of the spacer <NUM> is in contact with the lens <NUM>, and the other end <NUM> is in contact with a second surface <NUM> (the surface opposite side to the first surface <NUM> formed with the photocathode film <NUM>) of the transparent substrate <NUM> forming the photocathode <NUM>. Note that, although the spacer <NUM> illustrated in <FIG> as an example has flanges formed to the hollow cylinder ends (<NUM>, <NUM>) so that the contact areas with the lens <NUM> and the transparent substrate <NUM> are increased, the formation of the flanges is not essential, and no flange may be formed.

The material forming the spacer <NUM> is not particularly limited as long as it can retain the photocathode film <NUM> and the lens <NUM> to be spaced apart by a predetermined distance. For example, the spacer <NUM> may be formed of a metal or the like similarly to the holder <NUM>. Alternatively, the spacer <NUM> may be formed of a non-metal material such as synthetic quartz or ceramics. The non-metal material such as synthetic quartz or ceramics is less deformed by heating than a metal or the like. Therefore, if the non-metal material such as synthetic quartz or ceramics is used as the material forming the spacer, this achieves an advantageous effect that the distance between the photocathode film <NUM> and the lens <NUM> is less likely to be changed.

The photocathode kit 1A illustrated in <FIG> as an example is arranged inside a vacuum chamber of an electron gun, and the inside of the holder <NUM> has a hollow structure. When the photocathode <NUM> and the lens <NUM> are held and thereby the inside of the holder <NUM> is in an airtight state, a gas inside the hollow structure expands in vacuum, and this may affect the distance between the photocathode film <NUM> and the lens <NUM>. Thus, to prevent expansion of the gas inside the holder <NUM> in vacuum, the holder <NUM> has a gas vent <NUM> (first communication path) communicating between the inside and the outside of the holder <NUM>. The first communication path <NUM> may be, for example, a through hole communicating between the inside and the outside of the holder <NUM>. In the example illustrated in <FIG>, the holder <NUM> is formed of a holder first member 4a and a holder second member 4b and formed such that, when the holder first member 4a and the holder second member 4b are in engagement, a gap (first communication path <NUM>) occurs in the engaged portion. Alternatively, although not illustrated, a through hole (first communication path <NUM>) may be formed in advance in a portion other than the engaged portion of the holder first member 4a and/or the holder second member 4b, the engaged portions of the holder first member 4a and the holder second member 4b may be formed of an external thread and an internal thread, for example, and thereby a gap may not be positively generated in the engaged portion.

Further, in the example illustrated in <FIG>, the transparent substrate <NUM> is held in a recess (the substrate holding part <NUM>) formed in the holder second member 4b. Therefore, to insert the end of the transparent substrate <NUM> in the substrate holding part <NUM>, the holder second member 4b may be formed so as to be dividable into a plurality of members. Further, <FIG> illustrates an example in which the holder first member 4a and the holder second member 4b are divided in the vertical direction of <FIG>. Alternatively, the holder first member 4a and the holder second member 4b may be able to be divided in the horizontal direction of <FIG>.

Further, since the spacer <NUM> illustrated in <FIG> as an example has an internally hollowed cylindrical shape, when the ends (<NUM>, <NUM>) of the spacer <NUM> come into contact with the lens <NUM> and the transparent substrate <NUM>, respectively, the inside of the spacer <NUM> becomes airtight. Therefore, similarly to the holder <NUM>, the spacer <NUM> has a second communication path <NUM> communicating between the inside and the outside (inside the holder <NUM>) of the spacer <NUM>.

The second communication path <NUM> of the spacer <NUM> illustrated in <FIG> as an example is a hole 46a formed in a cylindrical portion of the spacer <NUM> and communicating between the inside and the outside of the cylindrical portion. <FIG> is a perspective view illustrating the overview of the spacer <NUM> illustrated as an example in <FIG>. Note that the second communication path <NUM> is not limited to the example illustrated in <FIG> as long as the inside of the spacer <NUM> does not become airtight. <FIG> is a perspective view illustrating another embodiment of the second communication path <NUM> and illustrates an example provided with a recess 46b, which is a cutout, in the one end <NUM> of the spacer <NUM>. Further, the second communication path <NUM> may be any path that can cause the inside of the spacer <NUM> and the inside of the holder <NUM> to communicate with each other, and a recess may be provided in the other end <NUM>. Alternatively, the hole 46a and the recess 46b may be combined. Further, although <FIG>and <FIG>illustrate the example in which the shape of the spacer <NUM> is cylindrical, the shape of the spacer <NUM> is not particularly limited as long as it can retain the lens <NUM> and the photocathode film <NUM> to be spaced apart by a predetermined distance. For example, as illustrated in <FIG>, the spacer <NUM> may be formed of a plurality of divided members. In the example illustrated in <FIG>, each gap 46c between adjacent spacers <NUM> forms the second communication path <NUM>.

The photocathode kit 1A in the first embodiment holds the transparent substrate <NUM> and the lens <NUM> so that the focal point of the lens <NUM> is located on the photocathode film <NUM> of the photocathode <NUM>. Therefore, with the photocathode kit 1A being installed on a light path from a light source, the focal point of excitation light that has passed through the lens <NUM> can be located on the photocathode film <NUM>. In the conventional art, adjustment for matching the focal point of the lens <NUM> to the photocathode film <NUM> is required every time the photocathode <NUM> is installed inside an electron gun. On the other hand, the use of the photocathode kit 1A illustrated in the first embodiment eliminates the need for position adjustment of the lens <NUM>, and this achieves an advantageous effect that an operation of installing the photocathode <NUM> and the lens <NUM> inside the electron gun is simplified.

Further, in the conventional art, two drive units of a drive unit that moves the photocathode and a drive unit that moves the lens are required when the photocathode is installed inside an electron gun. On the other hand, the use of the photocathode kit 1A illustrated in the first embodiment eliminates the need for position adjustment of the lens <NUM>. Thus, the position of the photocathode <NUM> installed in the electron gun can be adjusted by using only the drive unit which moves the photocathode kit 1A, and this achieves an advantageous effect that the device can be reduced in size and simplified.

A photocathode kit 1B in the second embodiment will be described with reference to <FIG> is a general sectional view schematically illustrating an example of the photocathode kit 1B in the second embodiment.

In the first embodiment, the spacer <NUM> is used as a retaining member for maintaining the distance between the photocathode film <NUM> and the lens <NUM> to be a predetermined distance. On the other hand, the second embodiment differs from the first embodiment in that, instead of the spacer <NUM>, a lens holding part is used as the retaining member. Therefore, in the second embodiment, features different from those of the first embodiment will be mainly described, and duplicated description for the features already described in the first embodiment will be omitted. Thus, needless to say, the feature already described in the first embodiment can be employed in the second embodiment even when not explicitly described in the second embodiment.

The holder <NUM> in the second embodiment illustrated in <FIG> as an example has a substrate holding part <NUM>, which holds the transparent substrate <NUM> of the photocathode <NUM>, and a lens holding part <NUM>. Further, the distance between the photocathode film <NUM> and the lens <NUM> is maintained to be a predetermined distance by the substrate holding part <NUM> and the lens holding part <NUM>.

The lens holding part <NUM> is not particularly limited as long as it can fix and hold the lens <NUM> inside the holder <NUM> without contacting with the transparent substrate <NUM>. The lens holding part <NUM> illustrated in <FIG> as an example is substantially an annular member formed of a separate component from the holder <NUM>. In the example illustrated in <FIG>, the outer edge portion of the lens holding part <NUM> engages with a recess formed in the holder first member 4a, and the inner edge portion of the lens holding part <NUM> protrudes inside the holder <NUM>. Therefore, the lens <NUM> can be held by the portion protruding inside the holder <NUM>. Note that the lens holding part <NUM> may be formed of a plurality of members instead of substantially an annular member. When the lens holding part <NUM> is formed of a plurality of members, the number of members is not limited as long as one end of each of the members engages with the recess formed in the holder first member 4a, the other end of each of the members protrudes inside the holder <NUM>, and thereby the lens <NUM> can be held.

Further, although depiction is omitted, the lens holding part <NUM> may be formed integrally with the holder <NUM>. More specifically, similarly to the substrate holding part <NUM>, the lens holding part <NUM> may be formed as a recess provided in the holder <NUM>, and the lens <NUM> may be engaged with the recess. Alternatively, the lens holding part <NUM> may be formed as a protrusion provided integrally with the holder <NUM>. The holder <NUM>, as described in the first embodiment, may be divided if necessary.

When the lens holding part <NUM> and the holder <NUM> are formed as separate components, the lens holding part <NUM> may be formed of a metal or a non-metal material such as ceramics similar to the holder <NUM>, for example.

In the second embodiment, the photocathode film <NUM> and the lens <NUM> can be retained to be spaced apart by a predetermined distance by the substrate holding part <NUM> and the lens holding part <NUM>. Therefore, also in the second embodiment, the same advantageous effects as achieved by the photocathode kit 1A of the first embodiment can be achieved.

A photocathode kit 1C in the third embodiment will be described with reference to <FIG> are general sectional views schematically illustrating an example of the photocathode kit 1C in the third embodiment.

The photocathode kit 1C in the third embodiment differs from the photocathode kit 1A illustrated in the first embodiment in that a heater <NUM> is further provided, and other features are the same as those of the first embodiment. Therefore, in the third embodiment, features different from those of the first embodiment will be mainly described, and duplicated description for the features already described in the first embodiment will be omitted. Thus, needless to say, the feature already described in the first embodiment can be employed in the third embodiment even when not explicitly described in the third embodiment. Further, although the examples illustrated in <FIG> will be described with reference to the first embodiment, needless to say, the feature already described in the second embodiment can be employed in the third embodiment.

Before the photocathode <NUM> is installed in the electron gun, the photocathode <NUM> is exposed to impurities in the atmospheric air. It is thus necessary to clean up the surface of the photocathode <NUM> by heating at <NUM> to <NUM> degrees Celsius in vacuum for <NUM> minutes to <NUM> hour and removing surface impurities such as an oxide or a carbide.

In the third embodiment, the photocathode kit 1C has the heater <NUM>. It is thus possible to heat the photocathode <NUM> by using the configuration provided to the photocathode kit 1C. In the example illustrated in <FIG>, the heater <NUM> is provided so as to be inserted in a heater insertion space <NUM> facing the hollow space of the holder <NUM>. In the example illustrated in <FIG>, since the heater <NUM> is arranged so as to be in contact with the transparent substrate <NUM>, the transparent substrate <NUM> can be directly heated. Alternatively, the heater <NUM> may be arranged not in contact with the transparent substrate <NUM>, and the transparent substrate <NUM> may be heated via the holder <NUM>. <FIG> are general sectional views illustrating other embodiments of the arrangement of the heater <NUM>. As illustrated in <FIG>, the heater <NUM> may be arranged in the heater insertion space <NUM> provided outside the holder <NUM>. In the example illustrated in <FIG>, even when the heater <NUM> fails, easy replacement is possible. Further, as illustrated in <FIG>, the heater <NUM> can be attached afterward.

In the example illustrated in <FIG>, the heater <NUM> is arranged in the heater insertion space <NUM> provided inside the holder <NUM>. When the heater <NUM> is heated, a gas may occur from the material forming the heater <NUM>. Then, if the generated gas flows into the holder <NUM>, this may contaminate the second surface <NUM> of the photocathode <NUM> and the lens <NUM>. In the example illustrated in <FIG>, a second gas vent <NUM> communicating between the heater insertion space <NUM> and the outside of the holder <NUM> is provided in the holder <NUM>. It is thus possible to prevent a gas generated from the heater <NUM> from flowing into the holder <NUM>. The second gas vent <NUM> may be, for example, a through hole communicating between the inside and the outside of the holder <NUM>.

Further, the photocathode kit <NUM> is arranged inside the electron gun and can perform EA surface treatment on the photocathode <NUM> inside the electron gun. The EA surface treatment is performed by vaporizing and depositing a surface treatment material on the photocathode <NUM>. In this process, if the heater <NUM> is exposed to the outside of the holder <NUM>, the surface treatment material of the photocathode <NUM> may deposit to the heater <NUM>. In the example illustrated in <FIG>, by arranging the heater <NUM> inside the holder <NUM>, it is possible to suppress the surface treatment material from depositing to the heater <NUM>. Needless to say, the heater insertion space <NUM> may be formed in the holder <NUM> illustrated in the first and second embodiment.

The heater <NUM> is not particularly limited as long as it can heat the photocathode film <NUM> to around <NUM> to <NUM> degrees Celsius in vacuum. The heater <NUM> may be, for example, a heating wire of tantalum or the like or a laser heating device.

The photocathode kit 1C in the third embodiment synergistically achieves the following advantageous effects in addition to the advantageous effects achieved by the photocathode kit <NUM> of the first and second embodiments.

It is possible to perform heat treatment on the photocathode <NUM> inside an electron gun after the photocathode kit 1C is installed in the electron gun. Further, even when the photocathode <NUM> is deteriorated by attachment of impurities due to usage, it is possible to perform heat treatment on the photocathode <NUM> without taking the electron gun to the outside.

A photocathode kit 1D in the fourth embodiment will be described with reference to <FIG> is a general sectional view schematically illustrating an example of the photocathode kit 1D in the fourth embodiment.

In the first embodiment, the substrate holding part <NUM> is provided to the holder <NUM> to hold the transparent substrate <NUM>. On the other hand, the fourth embodiment differs from the first embodiment in that the transparent substrate <NUM> is held by a substrate holding member <NUM> instead of being held by the substrate holding part <NUM>, and other features are the same as those of the first embodiment. Therefore, in the fourth embodiment, features different from those of the first embodiment will be mainly described, and duplicated description for the features already described in the first embodiment will be omitted. Thus, needless to say, the feature already described in the first embodiment can be employed in the fourth embodiment even when not explicitly described in the fourth embodiment. Further, although the example illustrated in <FIG> will be described with reference to the first embodiment, needless to say, the feature already described in the second and third embodiments can be employed in the fourth embodiment.

In the example illustrated in <FIG>, the transparent substrate <NUM> is held by the holder <NUM> by using the substrate holding member <NUM> at the lower end of the holder <NUM>. Further, the transparent substrate <NUM> is held by the holder <NUM>, and the distance between the photocathode film <NUM> and the lens <NUM> is maintained to be a predetermined distance via the spacer <NUM>.

The substrate holding member <NUM> is not particularly limited as long as it can hold the transparent substrate <NUM> at the lower end of the holder <NUM>. The substrate holding member <NUM> illustrated in <FIG> is substantially an annular member having substantially an L-shaped cross section formed of a separate component from the holder <NUM>. In the example illustrated in <FIG>, the transparent substrate <NUM> is interposed between and held by the lower end of the holder <NUM> and the substrate holding member <NUM>, the holder <NUM> and the substrate holding member <NUM> are engaged with each other, and thereby, the transparent substrate <NUM> is held in the holder <NUM>. The engagement scheme between the holder <NUM> and the substrate holding member <NUM> is not particularly limited, and a known scheme such as fixing by using a screw, fixing by using an engagement groove, or the like can be used.

The substrate holding member <NUM> can be formed of a metal or a non-metal material such as ceramics similar to the holder <NUM>, for example.

The photocathode kit 1D in the fourth embodiment synergistically achieves the following advantageous effects in addition to the advantageous effects achieved by the photocathode kit <NUM> of the first to third embodiments.

When the transparent substrate <NUM> is held inside the holder <NUM> as with the first embodiment, the holder <NUM> is required to be formed of a plurality of members. On the other hand, in the fourth embodiment, since the transparent substrate <NUM> can be held from the outside of the holder <NUM>, the holder <NUM> can be formed of a single cylindrical component.

Further, when the transparent substrate <NUM> is held inside the holder <NUM>, handling of the transparent substrate <NUM> will be difficult unless the transparent substrate <NUM> has a certain thickness. On the other hand, in the fourth embodiment, since the transparent substrate <NUM> can be arranged between the lower end of the holder <NUM> and the substrate holding member <NUM> and held by the holder <NUM>, the transparent substrate <NUM> can be thinner. With the thinner transparent substrate <NUM>, a loss of light with which the photocathode film <NUM> is irradiated is suppressed, and this enables efficient emission of an electron beam. Further, since the thermal capacity of the transparent substrate <NUM> is reduced, the surface of the photocathode <NUM> can be efficiently cleaned up.

A photocathode kit 1E in the fifth embodiment will be described with reference to <FIG> and <FIG>. <FIG> is a general sectional view schematically illustrating an example of the photocathode kit 1E in the fifth embodiment, and <FIG> is a general perspective view schematically illustrating a lens fixing method using a lens pressing member <NUM>.

In the first embodiment, the lens <NUM> is interposed between and held by the holder <NUM> and the spacer <NUM> to hold the lens <NUM> in the holder <NUM>. On the other hand, the fifth embodiment differs from the first embodiment in that the lens <NUM> is held by the lens pressing member <NUM> and the spacer <NUM> instead of being held by the holder <NUM> and the spacer <NUM>, and other features are the same as those of the first embodiment. Therefore, in the fifth embodiment, features different from those of the first embodiment will be mainly described, and duplicated description for the features already described in the first embodiment will be omitted. Thus, needless to say, the feature already described in the first embodiment can be employed in the fifth embodiment even when not explicitly described in the fifth embodiment. Further, although the example illustrated in <FIG> will be described with reference to the first embodiment, needless to say, the feature already described in the second to fourth embodiments can be employed in the fifth embodiment.

The lens <NUM> in the fifth embodiment is interposed between and held by the lens pressing member <NUM> and the spacer <NUM> as illustrated in <FIG>. Further, the lens <NUM> is held inside the holder <NUM> by the spacer <NUM> and the lens pressing member <NUM> (<FIG>). As a result, the distance between the photocathode film <NUM> and the lens <NUM> is maintained to be a predetermined distance.

The lens pressing member <NUM> is not particularly limited as long as it can press the lens against the spacer <NUM> without interfering the light path of excitation light emitted to the photocathode film <NUM>. The lens pressing member <NUM> illustrated in <FIG> is an elastic plate-like member (plate spring) formed of a separate component from the holder <NUM>. Further, the lens pressing member <NUM> has a fixing part <NUM> fixed to the holder <NUM>. The way to fix the lens pressing member <NUM> is not particularly limited as long as the lens pressing member <NUM> can be fixed to the holder <NUM>. For example, a recess may be formed in the holder <NUM>, and the fixing part <NUM> may be engaged with and fixed to the recess, or the holder <NUM> may be divided, and the fixing part <NUM> is interposed therebetween and fixed by a screw. The lens pressing member <NUM> illustrated in <FIG> as an example does not block the light path of excitation light because the portion in contact with the lens <NUM> is annular. Since the lens pressing member <NUM> is elastic, the lens <NUM> can be pressed against the spacer <NUM> when the lens <NUM> is held in the holder <NUM>. Note that the lens pressing member <NUM> may be formed of a plurality of members. When the lens pressing member <NUM> is formed of a plurality of members, one end of each of the members is engaged with the holder <NUM>, the other end of each of the members is protruded into the holder <NUM>, and the other end can be held in contact with the lens <NUM>. When the lens pressing member <NUM> is formed of a plurality of members, the number of members is not limited as long as the lens <NUM> can be pressed against the spacer <NUM>.

The material forming the lens pressing member <NUM> is not particularly limited as long as it is elastic. The material may be, for example, a metal or the like similar to the holder <NUM>. Note that, as described above, when heat treatment of the photocathode <NUM> is performed, since the temperature thereof is elevated to around <NUM> to <NUM> degrees Celsius in vacuum, the temperature of the lens pressing member <NUM> is also elevated. Since the lens pressing member <NUM> is used for maintaining the distance between the lens <NUM> and the photocathode film <NUM> to be a predetermined distance, it is more preferable that the material forming the lens pressing member <NUM> be sufficiently heat-resistant, have small thermal expansion, and less emitting a gas when heated. In terms of the above, as the material forming the lens pressing member <NUM>, titanium is most preferred, and molybdenum or Inconel is next most preferred. The material forming the lens pressing member <NUM> and the material forming the holder <NUM> may be the same or may be different from each other.

The photocathode kit 1E in the fifth embodiment synergistically achieves the following advantageous effects in addition to the advantageous effects achieved by the photocathode kit <NUM> of the first to fourth embodiments.

When heat treatment on the photocathode <NUM> or EA surface treatment on the photocathode <NUM> is performed, the photocathode kit <NUM> is heated. In this process, the holder <NUM> is distorted due to influence of heat, and the distortion may affect the distance between the photocathode film <NUM> and the lens <NUM>. In the fifth embodiment illustrated in <FIG> as an example, even when the holder <NUM> is distorted due to heat, since the lens pressing member <NUM> presses the lens <NUM> against the spacer <NUM>, this enables a state where the distance between the photocathode film <NUM> and the lens <NUM> is always maintained by the spacer <NUM>.

A photocathode kit 1F in the sixth embodiment will be described with reference to <FIG> is a general sectional view schematically illustrating an example of the photocathode kit 1F in the sixth embodiment.

The sixth embodiment differs from the first embodiment in that a vapor-inflow prevention part <NUM> is provided on the upper end side of the holder <NUM>, and other features are the same as those of the first embodiment. Therefore, in the sixth embodiment, features different from those of the first embodiment will be mainly described, and duplicated description for the features already described in the first embodiment will be omitted. Thus, needless to say, the feature already described in the first embodiment can be employed in the sixth embodiment even when not explicitly described in the sixth embodiment. Further, although the example illustrated in <FIG> will be described with reference to the first embodiment, needless to say, the feature already described in the second to fifth embodiments can be employed in the sixth embodiment.

Although details will be described later, the photocathode kit <NUM> is arranged inside an electron gun and can perform EA surface treatment on the photocathode <NUM> inside the electron gun. The EA surface treatment is performed by vaporizing and depositing a surface treatment material on the photocathode <NUM>.

While most of the vaporized surface treatment material reaches the lower end side of the photocathode kit <NUM>, a part of the vaporized surface treatment material may reach the upper end side of the photocathode kit <NUM>. The sixth embodiment illustrated in <FIG> as an example is such that the vapor-inflow prevention part <NUM> that prevents the lens <NUM> from being contaminated by a surface treatment material reaching the upper end side of the photocathode kit <NUM> when EA surface treatment on the photocathode <NUM> is performed inside the electron gun is provided on the upper end of the holder <NUM>.

The vapor-inflow prevention part <NUM> is not particularly limited as long as the vaporized surface treatment material is less likely to deposit to the upper surface of the lens <NUM>. In the example illustrated in <FIG>, the vapor-inflow prevention part <NUM> is formed of a hollow cylindrical member through which excitation light L can pass. The vapor-inflow prevention part <NUM> may be formed integrally with the holder <NUM>. Alternatively, the vapor-inflow prevention part <NUM> may be formed as a separate component from the holder <NUM> and attached to the holder <NUM>.

The photocathode kit 1F in the sixth embodiment synergistically achieves the following advantageous effects in addition to the advantageous effects achieved by the photocathode kit <NUM> of the first to fifth embodiments.

With the vapor-inflow prevention part <NUM> being provided, the lens <NUM> can be kept cleaner.

A first embodiment of an electron gun <NUM> having the photocathode kit <NUM> will be described with reference to <FIG> is a general sectional view schematically illustrating the electron gun <NUM> in the first embodiment and a counterpart device E equipped with the electron gun <NUM>. <FIG> is a general sectional view schematically illustrating an example of EA surface treatment on the photocathode <NUM> inside the electron gun.

The electron gun <NUM> in the first embodiment has the photocathode kit <NUM>, a light source <NUM>, an anode <NUM>, a vacuum chamber <NUM>, and a housing container <NUM> that can accommodate the photocathode kit <NUM>.

Further, the photocathode kit <NUM> illustrated in <FIG> as an example is arranged inside the housing container <NUM> having an electron beam passage hole <NUM>. A surface treatment material <NUM> for performing EA surface treatment (in other words, treatment to reduce electron affinity) on the photocathode <NUM> is arranged inside the housing container <NUM>.

The light source <NUM> is not particularly limited as long as it can irradiate the photocathode <NUM> with the excitation light L to emit an electron beam B. The light source <NUM> may be, for example, a high power (watt order) and high frequency (several hundred MHz) ultrashort pulse laser light source, a relatively inexpensive laser diode, an LED, or the like. The irradiating excitation light L may be any of pulse light or continuous light and may be adjusted as appropriate in accordance with the purpose. The light source <NUM> can be any light source that emits the excitation light L from the second surface <NUM> side of the transparent substrate <NUM> via the lens <NUM> of the photocathode kit <NUM>. In the example illustrated in <FIG>, although the light source <NUM> is arranged outside the vacuum chamber <NUM>, the light source <NUM> may be arranged inside the vacuum chamber <NUM>.

In the example illustrated in <FIG>, the photocathode kit <NUM> and the anode <NUM> are arranged inside the vacuum chamber <NUM>. The photocathode <NUM> emits the electron beam B in response to receiving the excitation light L emitted from the light source <NUM>. More specifically, electrons in the photocathode <NUM> are excited by the excitation light L, and the excited electrons are emitted from the photocathode <NUM>. The emitted electrons form the electron beam B by an electric field formed by the anode <NUM> and the cathode <NUM>. Note that, with respect to usage of the terms "photocathode" and "cathode" in this specification, the term "photocathode" may be used when emission of an electron beam is meant, and the term "cathode" may be used when a counter electrode of "anode" is meant, however, the reference "<NUM>" is used for both the cases of "photocathode" and "cathode".

The anode <NUM> is not particularly limited as long as it can form an electric field with the cathode <NUM>, and an anode commonly used in the field of electron guns can be used.

There is no particular restriction on the arrangement of a power supply as long as the electron beam B can be emitted from the cathode <NUM> to the anode <NUM>. In the example illustrated in <FIG>, the power supply is arranged so that a potential difference is generated between the cathode <NUM> and the anode <NUM>, and thereby, an electric field can be formed.

In the first embodiment of the electron gun <NUM>, EA surface treatment on the deteriorated photocathode <NUM> can be performed inside the vacuum chamber <NUM>. The housing container <NUM> in which the photocathode kit <NUM> is accommodated is a container that can vaporize the surface treatment material <NUM> arranged therein and is used for performing EA surface treatment on the photocathode <NUM> with the vaporized surface treatment material. The housing container <NUM> at least includes the electron beam passage hole <NUM> through which electrons emitted from the photocathode <NUM> passes. The electron beam passage hole <NUM> needs to have a size that enables passage of at least an electron and may be a size of <NUM> to <NUM> or may be a size of <NUM> to <NUM> in order to facilitate fabrication and adjustment of the angle or the positional relationship between the electron emitted from the photocathode <NUM> and the electron beam passage hole <NUM>.

There is no particular restriction on the material of the housing container <NUM>, and the housing container <NUM> can be formed of a heat resistant material that can withstand heat of <NUM> degrees Celsius or higher, more preferably <NUM> degrees Celsius or higher, such as glass, molybdenum, ceramic, sapphire, titanium, tungsten, tantalum, or the like, for example.

The surface treatment material <NUM> arranged inside the housing container <NUM> is not particularly limited as long as it is a material that enables EA surface treatment. The element forming the surface treatment material <NUM> may be, for example, Li, Na, K, Rb, Cs, Te, Sb, or the like. Note that Li, Na, K, Rb, and Cs out of the above elements will spontaneously ignite by itself and are unable to be stored and utilized. Thus, Li, Na, K, Rb, and Cs are required to be used in a form of a composite element of the above element or a compound containing the above element. On the other hand, when the element is used in a form of a compound, it is required to prevent an impurity gas from emitting during deposition of the element. Therefore, when the element selected from Li, Na, K, Rb, and Cs is used as the surface treatment material <NUM>, it is preferable to combine and use a compound such as Cs<NUM>CrO<NUM>, Rb<NUM>CrO<NUM>, Na<NUM>CrO<NUM>, or K<NUM>CrO<NUM> and a reducing agent that suppresses emission of an impurity gas. The surface treatment material <NUM> is vaporized inside the photocathode housing container <NUM> by using a heating device and deposited on the photocathode <NUM>.

In the first embodiment of the electron gun <NUM>, EA surface treatment is performed by moving the photocathode kit <NUM> to a deposition position inside the housing container <NUM> through a drive device <NUM> as illustrated in <FIG> as an example and vaporizing and depositing the surface treatment material <NUM> on the photocathode <NUM>. The drive device <NUM> is not particularly limited as long as it can move the photocathode kit <NUM>, and the drive device disclosed by International Publication No. <CIT> and International Publication No. <CIT> can be used, for example. The features disclosed in International Publication No. <CIT> and International Publication No. <CIT> are included in this specification.

The electron gun <NUM> in the first embodiment synergistically achieves the following advantageous effects in addition to the advantageous effects achieved by the photocathode kit <NUM> according to the first to sixth embodiments.

If EA surface treatment is performed in a state where a photocathode and a lens are exposed in a vacuum chamber (in a housing container), respectively, the surface treatment material <NUM> that has drifted around the end of the transparent substrate <NUM> may deposit on the lens <NUM>. In such a case, the surface treatment material <NUM> attached to the lens <NUM> intervenes in the optical system, and the position at which the excitation light is focused may change. On the other hand, in the example illustrated in <FIG>, the lens <NUM> is held in the holder <NUM> of the photocathode kit <NUM>, the electron gun <NUM> is in a state of being sucked by a vacuum pump (not illustrated), and thus, the vaporized surface treatment material <NUM> does not enter the inside of the holder <NUM> during EA surface treatment on the photocathode <NUM>. That is, this achieves an advantageous effect that the lens <NUM> is prevented from being contaminated with the surface treatment material <NUM> to keep the lens <NUM> clean.

In <FIG>, the example using the photocathode kit 1F of the sixth embodiment is illustrated as the photocathode kit <NUM>. In the example illustrated in <FIG>, since the photocathode kit 1F has the vapor-inflow prevention part <NUM>, the vaporized surface treatment material <NUM> is less likely to deposit on the upper surface of the lens <NUM>. Note that, in the example illustrated in <FIG>, a gap is present between the upper end of the vapor-inflow prevention part <NUM> and the light source <NUM> when the photocathode kit 1F has been moved to the deposition position. If necessary, the vapor-inflow prevention part <NUM> may be designed such that the height thereof is adjusted and the gap is eliminated between the upper end of the vapor-inflow prevention part <NUM> and the light source <NUM> when the photocathode kit 1F has been moved to the deposition position. In such a case, a risk of deposition of the vaporized surface treatment material <NUM> on the top surface of the lens <NUM> is further reduced. Further, although the drive device <NUM> is attached to the side face of the photocathode kit 1F in the example illustrated in <FIG>, alternatively, the drive device <NUM> may be attached to the vapor-inflow prevention part <NUM> to drive the photocathode kit 1F.

The electron beam applicator E equipped with the electron gun may be a known device equipped with an electron gun. For example, the electron beam applicator E may be a free electron laser accelerator, an electron microscope, an electron holography device, an electron beam drawing device, an electron diffractometer, an electron beam inspection device, an electron beam metal additive manufacturing device, an electron beam lithography device, an electron beam processing device, an electron beam curing device, an electron beam sterilization device, an electron beam disinfection device, a plasma generation device, an atomic element generation device, a spin-polarized electron beam generation device, a cathodoluminescence device, an inverse photoemission spectroscopy device, or the like.

The present invention is not limited to the respective embodiments described above, and it is clear that each embodiment may be modified or changed as appropriate within the scope defined by the appended claims. Further, any component used in each embodiment can be combined to another embodiment, within the scope of the appended claims.

Claim 1:
A photocathode kit (<NUM>) comprising:
a photocathode (<NUM>) including a substrate (<NUM>) on which a photocathode film (<NUM>) is formed on a first surface (<NUM>);
a lens (<NUM>) which converges excitation light (L) to the photocathode film (<NUM>); and
a holder (<NUM>) that holds the substrate (<NUM>) and the lens (<NUM>),
wherein the holder (<NUM>) has
a hollow structure, with the lens (<NUM>) being held in the hollow structure, and
a retaining member that retains the photocathode film (<NUM>) and the lens (<NUM>) to be spaced apart by a predetermined distance,
characterised in that the holder further has a gas vent (<NUM>) which is a through hole communicating between the inside and the outside of the holder (<NUM>) to prevent expansion of the gas inside the holder (<NUM>) in vacuum.