Electron tubes and electron tube devices

Abstract

The object is to provide an electron tube and an electron tube device that can appropriately multiply electrons emitted from a metasurface in response to the incidence of electromagnetic waves. The electron tube 1 includes an electron emitter 3 including a metasurface that emits electrons in response to incidence of electromagnetic waves W, an electron multiplier 4 that multiplies the electrons emitted from the electron emitter 3, and a second mesh electrode 6 disposed between the electron emitter 3 and the electron multiplier 4. The potential of the second mesh electrode 6 is set to a negative value when the potential of the metasurface of the electron emitter 3 is used as a reference.

Description

[Technical Field]

[0001] The present invention relates to an electron tube and an electron tube device. [Background technology]

[0002] There is known an electron tube that includes an electron emitter including a metasurface that emits electrons in response to incidence of electromagnetic waves, and an electron multiplier that multiplies the electrons emitted from the electron emitter (see, for example, Patent Document 1). In such an electron tube, field emission occurs in the metasurface in response to incidence of electromagnetic waves, causing electrons to be emitted from the metasurface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2023-512566 Summary of the Invention [Problem to be solved by the invention]

[0004] In the electron tube described above, there are cases where it is desired to multiply only the electrons emitted from the metasurface in response to the incidence of electromagnetic waves. In such cases, noise electrons, which are electrons that can become noise other than the electrons emitted from the antenna structure of the metasurface, may be emitted from the electron emitting section. For example, photoelectrons may be emitted from the electron emitting section due to the incidence of visible light, or thermoelectrons may be emitted from the electron emitting section due to an increase in temperature. In such cases, in the electron multiplier section, noise electrons may be multiplied along with the electrons emitted from the metasurface in response to the incidence of electromagnetic waves.

[0005] The present invention aims to provide an electron tube and an electron tube device that can appropriately multiply electrons emitted from a metasurface in response to the incidence of electromagnetic waves. [Means for solving the problem]

[0006] The electron tube of the present invention is [1] "an electron tube comprising: an electron emitting section including a metasurface that emits electrons in response to incidence of electromagnetic waves; an electron multiplier section that multiplies the electrons emitted from the electron emitting section; and a mesh electrode arranged between the electron emitting section and the electron multiplier section, wherein the potential of the mesh electrode is set to a negative value when the potential of the metasurface is used as a reference."

[0007] In the electron tube, the potential of the mesh electrode is set to a negative value relative to the potential of the metasurface. This allows electrons emitted from the metasurface in response to incident electromagnetic waves to pass through the mesh electrode and reach the electron multiplier. An electric field can be formed between the electron emitter and the electron multiplier, preventing noise electrons (e.g., photoelectrons and thermoelectrons emitted from the electron emitter), which are electrons that may become noise other than electrons emitted from the antenna structure of the metasurface, from passing through the mesh electrode. This utilizes the fact that the energy of electrons emitted from the metasurface in response to incident electromagnetic waves (e.g., several keV or more) is greater than the energy of noise electrons (e.g., 10 eV or less). Therefore, the electron tube can appropriately multiply electrons emitted from the metasurface in response to incident electromagnetic waves.

[0008] The electron tube of the present invention may be [2] "the electron tube according to [1], further comprising at least one first conductive member electrically connected to the mesh electrode, for applying a voltage to the mesh electrode so that the potential of the mesh electrode becomes negative relative to the potential of the metasurface." With this electron tube, electrons emitted from the metasurface in response to the incidence of electromagnetic waves can be reliably and appropriately multiplied.

[0009] The electron tube of the present invention may be [3] "the electron tube according to [2], further comprising at least one second conductive member electrically connected to the electron emitting section for applying a voltage to the electron emitting section, and at least one third conductive member electrically connected to the electron multiplier section for applying a voltage to the electron multiplier section." With this electron tube, it is possible to reliably apply a predetermined potential to each of the electron emitting section, the electron multiplier section, and the mesh electrode.

[0010] The electron tube of the present invention may be [4] "an electron tube according to any one of [1] to [3], wherein the electron emitter further includes a metal layer covering the metasurface, the metasurface being formed of a first metal, the metal layer being formed of a second metal, and the work function of the second metal being lower than the work function of the first metal." According to this electron tube, the sensitivity (electron emission ability) of the metasurface is improved, so that even when the intensity of the electromagnetic wave is low, field emission can be generated in the metasurface, causing electrons to be emitted from the metasurface. Furthermore, although the improved sensitivity of the metasurface makes it easier for noise electrons to be emitted from the electron emitter, even in such cases, for the reasons described above, the electrons emitted from the metasurface in response to the incidence of the electromagnetic wave can be appropriately multiplied.

[0011] The electron tube of the present invention may be [5] "the electron tube according to [4], in which the second metal is an alkali metal." With this electron tube, the sensitivity of the metasurface can be reliably improved.

[0012] The electron tube of the present invention may be [6] "the electron tube according to [4] or [5], wherein the mesh electrode includes a frame and a plurality of thin wires suspended across the frame, the metal layer includes a first portion located on the metasurface and a second portion located outside the metasurface, and when viewed from a direction in which the electron emitter and the mesh electrode face each other, at least a portion of the second portion overlaps at least a portion of the frame." With this electron tube, the metasurface is reliably covered by the metal layer, thereby reliably improving the sensitivity of the metasurface. Meanwhile, noise electrons are also likely to be emitted from the second portion of the metal layer. However, since at least a portion of the second portion of the metal layer overlaps at least a portion of the mesh electrode frame, it is possible to prevent the noise electrons emitted from the second portion of the metal layer from passing through to the electron multiplier section.

[0013] The electron tube of the present invention may be [7] "the electron tube according to any one of the above [1] to [6], wherein the mesh electrode includes a plurality of thin wires, and the distance between the metasurface and the mesh electrode is equal to or less than the distance between adjacent thin wires among the plurality of thin wires." According to this electron tube, an electric field can be reliably and easily formed between the electron emitter and the electron multiplier, which allows electrons emitted from the metasurface in response to incidence of electromagnetic waves to pass through the mesh electrode and reach the electron multiplier, and prevents noise electrons emitted from the electron emitter from passing through the mesh electrode.

[0014] The electron tube of the present invention may be [8] "the electron tube according to any one of the above [1] to [7], wherein the electron multiplier section includes a plurality of dynodes." With this electron tube, electrons emitted from the electron emitting section in response to incidence of electromagnetic waves can be reliably multiplied.

[0015] The electron tube of the present invention may be [9] "the electron tube according to any one of the above [1] to [8], wherein the electron multiplier section includes a microchannel plate." With this electron tube, electrons emitted from the electron emitting section in response to incidence of electromagnetic waves can be reliably multiplied.

[0016] The electron tube device of the present invention is

[10] "an electron tube having an electron emitting section including a metasurface that emits electrons in response to incidence of electromagnetic waves, an electron multiplier section that multiplies the electrons emitted from the electron emitting section, and a mesh electrode arranged between the electron emitting section and the electron multiplier section, and a voltage application section that applies a voltage to at least the mesh electrode, wherein the voltage application section applies a voltage to the mesh electrode so that the potential of the mesh electrode becomes a negative value when the potential of the metasurface is taken as a reference."

[0017] As described above, this electron tube device can appropriately multiply electrons emitted from the metasurface in response to the incidence of electromagnetic waves. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an electron tube device and an electron tube that can appropriately multiply electrons emitted from a metasurface in response to the incidence of electromagnetic waves. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a cross-sectional view of an electron tube included in an example of an electron tube device. [Figure 2] FIG. 2 is a bottom view of the electron emission portion shown in FIG. [Figure 3] 2 is a cross-sectional view of a portion of the electron tube shown in FIG. 1. [Figure 4] FIG. 4 is an exploded perspective view of a portion of the electron tube shown in FIG. 3. [Figure 5] 4 is a bottom view of the mesh electrode and the electron-emitting portion shown in FIG. 3. FIG. [Figure 6] FIG. 10 is a cross-sectional view of an electron tube included in an electron tube device according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] An example of the present invention will now be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be omitted. [Example of electron tube configuration]

[0021] As shown in FIG. 1, the electron tube 1 and a voltage application unit 10 constitute an electron tube device 100. That is, the electron tube device 100 includes the electron tube 1 and the voltage application unit 10. The electron tube 1 includes a housing 2, an electron emitter 3, an electron multiplier 4, a first mesh electrode 5, a second mesh electrode (mesh electrode) 6, and a plurality of lead pins 7. The electron emitter 3, the electron multiplier 4, the first mesh electrode 5, and the second mesh electrode 6 are disposed within the housing 2. The electron emitter 3 emits electrons in response to incidence of electromagnetic waves W. The electron multiplier 4 multiplies the electrons emitted from the electron emitter 3. Each lead pin 7 penetrates the housing 2. Each lead pin 7 is used to apply a potential to each of the electron emitter 3, the electron multiplier 4, the first mesh electrode 5, and the second mesh electrode 6, and to output a signal current from the electron multiplier 4. In the electron tube 1, the end of each lead pin 7 inside the housing 2 is electrically connected to each of the electron emitter 3, the electron multiplier 4, the first mesh electrode 5, and the second mesh electrode 6 via wiring 70. Each wiring 70 is a linear member made of metal, and has strength that enables "support of the electron multiplier 4 by the plurality of lead pins 7 and the plurality of wiring 70" to be described later.

[0022] The electromagnetic wave W is an electromagnetic wave having a predetermined electric field oscillation direction V perpendicular to the propagation direction T of the electromagnetic wave W (i.e., an electromagnetic wave having a predetermined polarization (polarization) component). The electromagnetic wave W is, for example, an electromagnetic wave in a predetermined band included in the frequency band from millimeter waves to infrared light, and in this example, is a terahertz wave. Hereinafter, a direction parallel to the electric field oscillation direction V of the electromagnetic wave W is referred to as a first direction D1, and a direction perpendicular to the propagation direction T of the electromagnetic wave W and the electric field oscillation direction V is referred to as a second direction D2. In this example, the second direction D2 is a direction perpendicular to the first direction D1.

[0023] The housing 2 has a bulb 21 and a stem 22. The bulb 21 is formed into a cylindrical shape with a bottom and made of a material (e.g., quartz) that is transparent to the electromagnetic wave W. As an example, the bulb 21 is formed into a cylindrical shape with a bottom and a center line that is an axis A parallel to the traveling direction T. In this case, the height of the bulb 21 is several tens of millimeters, and the outer diameter of the bulb 21 is several millimeters to a dozen or so millimeters. The bottom of the bulb 21 functions as a window 21a that allows the electromagnetic wave W to enter the bulb 21. The stem 22 is airtightly fixed to the opening 21b of the bulb 21 and faces the window 21a on the axis A. The stem 22 is made of, for example, glass. The space inside the housing 2 is a vacuum space. It is sufficient that at least the window 21a of the housing 2 is transparent to the electromagnetic wave W.

[0024] The electron emitter 3, the second mesh electrode 6, the first mesh electrode 5, and the electron multiplier 4 are arranged in this order from the window 21a side along the axis A. That is, the first mesh electrode 5 is disposed between the electron emitter 3 and the electron multiplier 4, and the second mesh electrode 6 is disposed between the electron emitter 3 and the first mesh electrode 5. The first mesh electrode 5, the second mesh electrode 6, and the electron emitter 3 are supported by the electron multiplier 4. The electron multiplier 4 is supported by a plurality of lead pins 7. In the electron tube 1, the electron multiplier 4 is supported by a plurality of lead pins 7 and a plurality of wirings 70. Each lead pin 7 extends in a direction parallel to the axis A and airtightly penetrates the stem 22.

[0025] As shown in FIG. 2, the electron emitter 3 includes a substrate 31, a metasurface 32, a pair of electrodes 33, and a metal layer 34. The substrate 31 is formed in a plate shape (e.g., a rectangular plate shape) from a material that is transparent to electromagnetic waves W. The substrate 31 is made of an electrically insulating material (e.g., silicon, quartz, sapphire, zinc selenide, etc.). The metasurface 32 and the pair of electrodes 33 are formed on a surface 31a of the substrate 31. The metal layer 34 is formed on the surface 31a of the substrate 31, covering the metasurface 32 and the pair of electrodes 33. The surface 31a is the surface of the substrate 31 on the electron multiplier section 4 side. Note that in FIG. 2, the metal layer 34 is indicated by a two-dot chain line.

[0026] The metasurface 32 includes a plurality of antenna structures 35 arranged two-dimensionally along the surface 31a. Each antenna structure 35 emits electrons in response to incidence of an electromagnetic wave W whose electric field oscillation direction V is the first direction D1. That is, the metasurface 32 emits electrons in response to incidence of the electromagnetic wave W having the electric field oscillation direction V. As an example, each antenna structure 35 is configured as a bowtie antenna, a dipole antenna, a split ring antenna, or a double split ring antenna, and includes a pair of ends facing each other in the first direction D1. In this case, the metasurface 32 emits electrons when the direction in which the straight line connecting the pair of ends of each antenna structure 35 extends coincides with the electric field oscillation direction V of the electromagnetic wave W.

[0027] The metasurface 32 is disposed on the axis A. A pair of electrodes 33 are disposed on both sides of the metasurface 32. Each electrode 33 is electrically connected to a corresponding antenna structure 35 via wiring (not shown). A predetermined potential difference is applied between a pair of ends of each antenna structure 35 via the pair of electrodes 33. The metasurface 32 is formed of a conductive material (e.g., a metal material such as gold, platinum, aluminum, silver, or copper, or an inorganic carbon material having electrical conductivity such as graphene or graphite). The metasurface 32 is formed by patterning a conductive material. Each electrode 33 is formed, for example, of the same material as the metasurface 32. The metal layer 34 entirely covers the metasurface 32 and the pair of electrodes 33 and is in contact with the metasurface 32 and the pair of electrodes 33. The metal layer 34 is deposited to a thickness of approximately one to several atomic layers using a metal (e.g., an alkali metal such as cesium) having a lower work function than the material of the metasurface 32. The metal layer 34, when attached to the surface of each antenna structure 35, has the effect of lowering the work function of the surface of the material constituting each antenna structure 35, thereby promoting field electron emission from each end of each antenna structure 35. In other words, the metal layer 34 functions to improve the sensitivity (electron emission ability) of the metasurface 32. In this example, different potentials are applied to each of the pair of electrodes 33 so that a predetermined potential difference is applied between the pair of ends of each antenna structure 35. However, instead of the pair of electrodes 33, a frame-shaped electrode 33 may be formed on the surface 31a. In this case, a uniform potential is applied to the entire metasurface 32.

[0028] As shown in FIG. 1 , the electron multiplier unit 4 has a pair of support walls 41, a plurality of dynodes 42, and an anode 43. The pair of support walls 41 face each other in the first direction D1. Each support wall 41 is formed into a plate shape from an electrically insulating material. The plurality of dynodes 42 and the anode 43 are disposed between the pair of support walls 41 and are sandwiched between the pair of support walls 41. Each dynode 42 is electrically connected to a wiring 70 connected to a corresponding lead pin 7 on the outer side of the pair of support walls 41. Similarly, the anode 43 is electrically connected to a wiring 70 connected to a corresponding lead pin 7 on the outer side of the pair of support walls 41. In this way, in the electron tube 1, the pair of support walls 41, the plurality of dynodes 42, and the anode 43 are unitized as the electron multiplier unit 4, and the unitized electron multiplier unit 4 is supported within the housing 2 by a plurality of lead pins 7.

[0029] The multiple dynodes 42 include a first dynode 421 and a second dynode 422. The first dynode 421 is the first-stage dynode 42, and the second dynode 422 is the second-stage dynode 42. The electron emission surface 42a of the first dynode 421 faces the electron emitter 3 and the electron emission surface 42a of the second dynode 422, respectively. The electron emission surface 42a of each dynode 42 from the second stage onwards, except for the final-stage dynode 42, faces the electron emission surface 42a of the preceding-stage dynode 42 and the electron emission surface 42a of the succeeding-stage dynode 42, respectively. The electron emission surface 42a of the final-stage dynode 42 faces the electron emission surface 42a of the preceding-stage dynode 42 and the anode 43, respectively.

[0030] With a predetermined potential applied to each dynode 42 via the corresponding lead pin 7 and wiring 70, electrons emitted from the electron emitter 3 pass through the second mesh electrode 6 and the first mesh electrode 5 and are incident on the electron emission surface 42a of the first dynode 421, causing secondary electrons to be emitted from the electron emission surface 42a of the first dynode 421, and these secondary electrons are then incident on the electron emission surface 42a of the second dynode 422. Electrons sequentially multiplied at each dynode 42 by such incidence and emission of secondary electrons finally enter the anode 43, and a signal current is output from the anode 43 via the corresponding wiring 70 and lead pin 7.

[0031] 3 and 4, the electron tube 1 includes a base 8, a first support portion 11, a second support portion 12, a third support portion 13, and a spacer 14. The first support portion 11 supports the electron emitter portion 3. The second support portion 12 supports the first mesh electrode 5. The third support portion 13 supports the second mesh electrode 6. The base 8, the second support portion 12, the spacer 14, the third support portion 13, and the first support portion 11 are arranged in this order from the electron multiplier portion 4 side along the axis A. In other words, the spacer 14 is disposed between the first mesh electrode 5 and the second mesh electrode 6.

[0032] The base 8 is formed into a frame shape using, for example, a metal plate. The base 8 includes a frame portion 81 having an opening 81a and a plurality of spring portions 82. The frame portion 81 is disposed on a pair of support walls 41 of the electron multiplier section 4. When viewed from a direction parallel to the axis A, the opening 81a overlaps the electron emission surface 42a of the first dynode 421. Each spring portion 82 extends outward from the frame portion 81 (i.e., on the opposite side from the opening 81a). Each spring portion 82 contacts the inner surface of the bulb 21. A pair of notches 81b are formed in the frame portion 81. Each notch 81b engages with a protrusion 41a that protrudes from the corresponding support wall 41 toward the window portion 21a.

[0033] The second support portion 12 is formed in a frame shape using, for example, a metal plate. The second support portion 12 includes a frame portion 121 having an opening 121a and a plurality of second claw portions 122. The frame portion 121 is disposed on the frame portion 81 of the base 8. When viewed from a direction parallel to the axis A, the opening 121a overlaps the opening 81a of the frame portion 81. Each second claw portion 122 extends from the frame portion 121 toward the window portion 21a. More specifically, each second claw portion 122 extends from the frame portion 121 toward the spacer 14. A pair of through holes 121b is formed in the frame portion 121. A protrusion 41a of each support wall 41 engages with each through hole 121b.

[0034] The first mesh electrode 5 includes a frame 51 and a plurality of wires 52. The first mesh electrode 5 is formed by etching a plate-like member, and the frame 51 and the plurality of wires 52 are integrally formed. The first mesh electrode 5 is made of a conductive metal material such as copper, nickel, titanium, or stainless steel. The plurality of wires 52 are hung across the frame 51, defining a plurality of openings in the inner region of the frame 51. The frame 51 is fixed to the surface of the frame portion 121 facing the electron emitter 3. When viewed from a direction parallel to the axis A, the inner region of the frame 51 overlaps with the openings 121a of the frame portion 121. Wiring 70 connected to the corresponding lead pins 7 is connected to the second support portion 12, and a predetermined potential is applied to the first mesh electrode 5 via the second support portion 12. The first mesh electrode 5 may be formed by forming the frame 51 and the plurality of wires 52 separately, and then suspending the plurality of wires 52 around the frame 51.

[0035] The spacer 14 is formed in a frame shape from an electrically insulating material. As an example, the spacer 14 is formed in a circular frame shape from ceramic. The spacer 14 is disposed on the frame portion 121 of the second support portion 12. When viewed in a direction parallel to the axis A, the spacer 14 surrounds the first mesh electrode 5. The spacer 14 has a first surface 14a on the electron emitter 3 side and a second surface 14b on the electron multiplier 4 side. The spacer 14 is formed with a plurality of first through-holes 141, a plurality of second through-holes 142, and a plurality of third through-holes 143. Each of the through-holes 141, 142, and 143 defines a space penetrating the spacer 14 between the first surface 14a and the second surface 14b. In the electron tube 1, each of the through-holes 141, 142, and 143 is a through-hole that opens toward the electron emitter 3 side and the electron multiplier 4 side.

[0036] The third support portion 13 is formed into a frame shape using, for example, a metal plate. The third support portion 13 includes a frame portion 131 having an opening 131a, a plurality of connecting portions 132, and a plurality of third claw portions 133. The frame portion 131 is surrounded by the spacer 14 when viewed in a direction parallel to the axis A. The opening 131a overlaps the opening 121a of the frame portion 121 when viewed in a direction parallel to the axis A. Each connecting portion 132 extends outward from the frame portion 131 (i.e., opposite the opening 131a). The plurality of connecting portions 132 are disposed on the spacer 14. Each third claw portion 133 extends from each connecting portion 132 to the opposite side of the window portion 21a. More specifically, each third claw portion 133 extends from each connecting portion 132 toward the spacer 14.

[0037] The second mesh electrode 6 includes a frame 61 and a plurality of wires (thin wires) 62. The second mesh electrode 6 is formed by etching a plate-like member, and the frame 61 and the plurality of wires 62 are integrally formed. The second mesh electrode 6 is made of a conductive metal material such as copper, nickel, titanium, or stainless steel. The plurality of wires 62 are hung across the frame 61, defining a plurality of openings in the inner region of the frame 61. The frame 61 is fixed to the surface of the frame portion 131 facing the electron emitter 3. When viewed from a direction parallel to the axis A, the inner region of the frame 61 overlaps with the openings 131a of the frame portion 131. Wiring 70 connected to the corresponding lead pins 7 is connected to the third support portion 13, and a predetermined potential is applied to the second mesh electrode 6 via the third support portion 13. The second mesh electrode 6 may be formed by forming the frame 61 and the plurality of wires 62 separately, and then suspending the plurality of wires 62 over the frame 61.

[0038] The first support section 11 has a first support plate 111, a second support plate 112, and a plurality of support pieces 113. The first support plate 111 is formed in a frame shape from an electrically insulating material such as ceramic. The first support plate 111 is disposed on a plurality of connection portions 132 of the third support section 13. The electron emitter 3 is disposed in an opening 111a of the first support plate 111. This restricts movement of the electron emitter 3 in a direction perpendicular to the axis A.

[0039] The second support plate 112 is formed into a frame shape using, for example, a metal plate. The second support plate 112 includes a frame portion 114 having an opening 114a and a plurality of claw portions 115. The frame portion 114 is disposed on the first support plate 111. The opening 114a overlaps with the metasurface 32 of the electron emitter 3 when viewed from a direction parallel to the axis A. Each of the claw portions 115 extends from the frame portion 114 to the side opposite the window portion 21a. More specifically, each of the claw portions 115 extends from the frame portion 114 toward the spacer 14.

[0040] Each support piece 113 includes a spring portion 116 and a first claw portion 117. Each support piece 113 is formed, for example, into an L-shape using a metal plate. The spring portion 116 of each support piece 113 presses the electron emitter 3 against the second support plate 112 between the spacer 14 and the first support plate 111 so that the electron emitter 3 is spaced from the second mesh electrode 6 and the substrate 31 of the electron emitter 3 contacts the second support plate 112. In each support piece 113, the first claw portion 117 extends from the spring portion 116 to the side opposite the window portion 21a. More specifically, the first claw portion 117 extends from the spring portion 116 toward the spacer 14. A wiring 70 connected to a corresponding lead pin 7 is electrically connected to each pair of support pieces 113 among the plurality of support pieces 113. Each electrode 33 of the electron emitter 3 is in physical and electrical contact with the respective spring portions 116 of the pair of support pieces 113, and a predetermined potential is applied to the metasurface 32 of the electron emitter 3 via the pair of support pieces 113.

[0041] The first claw portions 117 of each support piece 113 of the first support portion 11 are inserted into the respective first through-portions 141 of the spacer 14, and then the tips of the first claw portions 117 are crimped, thereby engaging with the spacer 14. The second claw portions 122 of each second support portion 12 are inserted into the respective second through-portions 142 of the spacer 14, and then the tips of the second claw portions 122 are crimped, thereby engaging with the spacer 14. The third claw portions 133 of the third support portion 13 are inserted into the respective third through-portions 143 of the spacer 14, and then the tips of the third claw portions 133 are crimped, thereby engaging with the spacer 14. Each of the first support portion 11 and the third support portion 13 exposes a plurality of second through-portions 142 on the first surface 14a of the spacer 14. This prevents the second claw portions 122 engaged with the second through portions 142 from physically interfering with the first support portion 11 and the third support portion 13. The second support portion 12 exposes the multiple first through portions 141 and the multiple third through portions 143 on the second surface 14b of the spacer 14. This prevents the first claw portions 117 engaged with the first through portions 141 and the third claw portions 133 engaged with the third through portions 143 from physically interfering with the second support portion 12.

[0042] Each claw portion 115 of the second support plate 112 in the first support portion 11 is inserted into a through-hole 121c formed in the frame portion 121 of the second support portion 12 via a notch 144 formed in the spacer 14, and then the tip of the claw portion 115 is crimped to engage with the frame portion 121. This unitizes the electron emitter 3, the first mesh electrode 5, the second mesh electrode 6, the first support portion 11, the second support portion 12, and the third support portion 13 via the spacer 14, and in this unitized state, electrical insulation is ensured between the metasurface 32 of the electron emitter 3, the first mesh electrode 5, and the second mesh electrode 6. In the electron tube 1, the metasurface 32 of the electron emitter 3 and the multiple support pieces 113 of the first support unit 11 are at the same potential, the first mesh electrode 5, the second support unit 12, and the second support plate 112 of the first support unit 11 are at another same potential, and the second mesh electrode 6 and the third support unit 13 are at yet another same potential. Note that the second support plate 112 of the first support unit 11 is in contact with the substrate 31 of the electron emitter 3, which is made of an electrically insulating material, so electrical insulation between the second support plate 112 and the metasurface 32 is ensured.

[0043] In the electron tube 1 configured as described above, a predetermined potential is applied to the metasurface 32 of the electron emitter 3, the second mesh electrode 6, the first mesh electrode 5, the dynodes 42 of the electron multiplier unit 4, and the anode 43 of the electron multiplier unit 4. The potential applied to the first dynode 421 is a potential that is positive relative to the potential of the metasurface 32. The potential applied to the second dynode 422 is a potential that is positive relative to the potential of the first dynode 421. The potential applied to the first mesh electrode 5 is a potential that is positive relative to the potential of the metasurface 32. In this example, the first mesh electrode 5 is electrically connected to the first dynode 421, and the same potential as that of the first dynode 421 is applied to the first mesh electrode 5. The potential applied to the second mesh electrode 6 is a potential that is negative relative to the potential of the metasurface 32. That is, a potential that suppresses the movement of electrons from the metasurface 32 side to the first mesh electrode 5 side is applied to the second mesh electrode 6. That is, a reverse bias voltage is applied between the metasurface 32 and the second mesh electrode 6. As an example, the potential applied to the metasurface 32 is approximately −1500 V, the potential applied to the second mesh electrode 6 is approximately −several volts with respect to the potential of the metasurface 32, the potential applied to the first mesh electrode 5 and the first dynode 421 is approximately +100 to 200 V with respect to the potential of the metasurface 32, and the potential applied to the second dynode 422 is approximately +several hundred volts with respect to the potential of the first dynode 421.

[0044] With a predetermined potential applied to each component of the electron tube 1, when electromagnetic waves W having a predetermined electric field oscillation direction V pass through the window 21a of the bulb 21 and the substrate 31 of the electron emitter 3 and strike the metasurface 32, electrons are emitted from each antenna structure 35 of the metasurface 32 in response to the electromagnetic waves W. The electrons emitted from each antenna structure 35 are accelerated by the electric field of the incident electromagnetic waves W, giving them high energy and causing them to fly in random directions. The electrons emitted from the metasurface 32 in response to the electromagnetic waves W pass through the second mesh electrode 6 and the first mesh electrode 5 and strike the electron emission surface 42a of the first dynode 421. Even if electrons other than those emitted from the antenna structures 35 (noise electrons) are emitted from the electron emitter 3, the noise electrons are prevented from passing through the second mesh electrode 6 because a potential (reverse bias voltage) that is negative relative to the potential of the metasurface 32 is applied to the second mesh electrode 6. This is because the energy of noise electrons (for example, 10 eV or less) is significantly smaller than the energy (for example, several keV or more) of electrons emitted from the metasurface 32 in response to the incidence of electromagnetic waves W. Examples of noise electrons include photoelectrons emitted due to the photoelectric effect and thermoelectrons emitted depending on the temperature.

[0045] When electrons passing through the second mesh electrode 6 and the first mesh electrode 5 are incident on the electron emission surface 42a of the first dynode 421, secondary electrons are emitted from the electron emission surface 42a of the first dynode 421, and these secondary electrons are incident on the electron emission surface 42a of the second dynode 422. At this time, because the first mesh electrode 5 is disposed between the metasurface 32 and the first dynode 421, the potential of the metasurface 32 is prevented from penetrating into the first dynode 421. This prevents the electric field formed between the first dynode 421 and the second dynode 422, which guides the secondary electrons, from being distorted by the potential of the metasurface 32. This prevents the path of the secondary electrons from being affected by the electron emitter 3. The electrons sequentially multiplied at each dynode 42 by the incidence and emission of secondary electrons ultimately enter the anode 43. The total number of electrons incident on the anode 43 is output as a signal as a current value via the wiring 70 and the lead pin 7 electrically connected to the anode 43 .

[0046] In the above example, the first mesh electrode 5 and the first dynode 421 are at the same potential, but this is not limited to this. A potential different from that of the first dynode 421 may be applied to the first mesh electrode 5. More specifically, a potential that is positive with respect to the potential of the metasurface 32 and negative with respect to the potential of the first dynode 421 may be applied to the first mesh electrode 5. This configuration enables favorable secondary electron multiplication while suppressing the propagation of noise electrons. [Configuration of electron emission section and mesh electrode]

[0047] As shown in FIG. 2, in the electron emitter 3, the metasurface 32 is covered with a metal layer 34. The metasurface 32 is made of a first metal. The metal layer 34 is made of a second metal. The work function of the second metal is lower than the work function of the first metal. In the electron tube 1, the second metal is an alkali metal. As an example, the first metal is gold and the second metal is cesium.

[0048] The metal layer 34 includes a first portion 34a and a second portion 34b. The first portion 34a is located on the metasurface 32. The first portion 34a covers the metasurface 32. The second portion 34b is located outside the metasurface 32. In the electron tube 1, the second portion 34b extends in a frame shape along the outer edge of the first portion 34a. The second portion 34b covers the pair of electrodes 33 and areas of the surface 31a of the substrate 31 where the metasurface 32 and the pair of electrodes 33 are not formed. The first portion 34a and the second portion 34b are formed as a single piece.

[0049] 5, when viewed in a direction parallel to the axis A (the direction in which the electron emitter 3 and the second mesh electrode 6 face each other), the second portion 34b of the metal layer 34 overlaps with the frame 61 of the second mesh electrode 6. In the electron tube 1, when viewed in a direction parallel to the axis A, the inner portions of the first portion 34a and the second portion 34b are located inside the frame 61 (i.e., do not overlap with the frame 61), and the outer portion of the second portion 34b overlaps with the frame 61 and the frame portion 131 of the third support portion 13.

[0050] As shown in FIG. 3, the distance α between the metasurface 32 of the electron emitter 3 and the second mesh electrode 6 is smaller than the distance β between the second mesh electrode 6 and the electron emission surface 42a of the first dynode 421 (the electron input surface of the electron multiplier 4). The distance α is the distance between the metasurface 32 of the electron emitter 3 and the multiple wires 62 of the second mesh electrode 6 along a direction parallel to the axis A, and if this distance varies with position, it is the shortest distance. The distance β is the distance between the multiple wires 62 of the second mesh electrode 6 and the electron emission surface 42a of the first dynode 421 along a direction parallel to the axis A, and if this distance varies with position, it is the shortest distance.

[0051] In the electron tube 1, the distance α between the metasurface 32 and the second mesh electrode 6 is smaller than the distance γ between adjacent wires 62 among the multiple wires 62. The distance γ is the distance in the first direction D1 between adjacent wires 62 among the multiple wires 62, and if the distance varies depending on the position in the second direction, it is the shortest distance. For example, the distance γ is the arrangement interval (pitch) of the multiple wires 62. [Configuration of voltage application section]

[0052] The voltage application unit 10 shown in FIG. 1 applies a voltage to each of the electron emitter 3, electron multiplier 4, first mesh electrode 5, and second mesh electrode 6. The voltage application unit 10 is electrically connected to each of the electron emitter 3, electron multiplier 4, first mesh electrode 5, and second mesh electrode 6 via each of the lead pins 7. The voltage application unit 10 applies a predetermined potential to the metasurface 32 of the electron emitter 3, the second mesh electrode 6, the first mesh electrode 5, each dynode 42 of the electron multiplier 4, and the anode 43 of the electron multiplier 4.

[0053] The plurality of lead pins 7 include a first lead pin (first conductive member) 71, a second lead pin (second conductive member) 72, a plurality of third lead pins (third conductive members) 73, and a fourth lead pin 74. The first lead pin 71 is electrically connected to the second mesh electrode 6, for example, via a wiring 70 connected to the first lead pin 71. The second lead pin 72 is electrically connected to the electron emitter 3, for example, via a wiring 70 connected to the second lead pin 72. Each third lead pin 73 is electrically connected to each part of the electron multiplier section 4 (each dynode 42, anode 43), for example, via a wiring 70 connected to the third lead pin 73. The fourth lead pin 74 is electrically connected to the first mesh electrode 5, for example, via a wiring 70 connected to the fourth lead pin 74.

[0054] The voltage application unit 10 applies a voltage to the second mesh electrode 6 via the first lead pin 71 so that the potential of the second mesh electrode 6 becomes a negative value when the potential of the metasurface 32 is taken as a reference. In other words, the first lead pin 71 is electrically connected to the second mesh electrode 6 to apply a voltage to the second mesh electrode 6 so that the potential of the second mesh electrode 6 becomes a negative value when the potential of the metasurface 32 is taken as a reference.

[0055] The voltage application unit 10 applies a voltage to the electron emitting unit 3 via the second lead pin 72 so that field emission occurs in the metasurface 32 in response to the incidence of the electromagnetic wave W (i.e., so that electrons are emitted from the metasurface 32 in response to the incidence of the electromagnetic wave W). In other words, the second lead pin 72 is electrically connected to the electron emitting unit 3 in order to apply a voltage to the electron emitting unit 3 so that field emission occurs in the metasurface 32 in response to the incidence of the electromagnetic wave W.

[0056] The voltage application unit 10 applies a voltage to each part of the electron multiplier unit 4 via each third lead pin 73 so that electrons are multiplied in each dynode 42 and the multiplied electrons are collected by the anode 43. In other words, each third lead pin 73 is electrically connected to each part of the electron multiplier unit 4 in order to apply a voltage to each part of the electron multiplier unit 4 so that electrons are multiplied in each dynode 42 and the multiplied electrons are collected by the anode 43.

[0057] The voltage application unit 10 applies a voltage to the first mesh electrode 5 so that the voltage is positive when the potential of the metasurface 32 is used as a reference and negative when the potential of the first dynode 421 is used as a reference. In other words, the fourth lead pin 74 is electrically connected to the first mesh electrode 5 in order to apply a voltage to the first mesh electrode 5 so that the voltage is positive when the potential of the metasurface 32 is used as a reference and negative when the potential of the first dynode 421 is used as a reference. [Action and effect]

[0058] In the electron tube device 100 and the electron tube 1, the potential of the second mesh electrode 6 is set to a negative value relative to the potential of the metasurface 32. For example, the voltage application unit 10 applies a voltage to the second mesh electrode 6 so that the potential of the second mesh electrode 6 is a negative value relative to the potential of the metasurface 32. This allows electrons emitted from the metasurface 32 in response to the incidence of electromagnetic waves W to pass through the second mesh electrode 6 and reach the electron multiplier unit 4, while forming an electric field between the electron emitter 3 and the electron multiplier unit 4 that prevents noise electrons (e.g., photoelectrons and thermoelectrons emitted from the electron emitter 3), which are electrons that may become noise other than electrons emitted from each antenna structure 35 of the metasurface 32, from passing through the second mesh electrode 6. This utilizes the fact that the energy (e.g., several keV or more) of the electrons emitted from the metasurface 32 in response to the incidence of electromagnetic waves W is greater than the energy (e.g., 10 eV or less) of the noise electrons. Therefore, according to the electron tube device 100 and the electron tube 1, the electrons emitted from the metasurface 32 in response to the incidence of the electromagnetic wave W can be appropriately multiplied.

[0059] The electron tube device 100 and the electron tube 1 can form an electric field that suppresses ion feedback between the metasurface 32 and the first dynode 421 (i.e., ions generated by electrons colliding with gas between the metasurface 32 and the first dynode 421 reaching the metasurface 32). More specifically, when electrons emitted from the metasurface 32 are incident on the first dynode 421, a large number of secondary electrons are emitted toward the second dynode 422. Then, when the secondary electrons collide with residual gas molecules, positively charged ions are generated. The generated ions are bombarded into the metasurface 32 by the electric field formed between the metasurface 32 and the first dynode 421, following a path opposite to that of the electrons incident on the first dynode 421 from the metasurface 32. Ion feedback generated in this manner may shorten the life of the metasurface 32. In addition, electrons emitted from the metasurface 32 are amplified when they enter the first dynode 421 and emit a large number of secondary electrons, increasing the electron density near the electron emission surface 42a of the first dynode 421 and the probability of collisions between the electrons and residual gas molecules in the housing 2. This increases the probability of ion feedback occurring, which could further shorten the life of the metasurface 32. In contrast, the electron tube device 100 and the electron tube 1 can suppress ion feedback caused by ions generated between the metasurface 32 and the first dynode 421, thereby extending the life of the metasurface 32.

[0060] In the electron tube device 100 and the electron tube 1, the first lead pin 71 is electrically connected to the second mesh electrode 6. This allows the electrons emitted from the metasurface 32 in response to the incidence of the electromagnetic wave W to be reliably and appropriately multiplied.

[0061] In the electron tube device 100 and the electron tube 1, the second lead pin 72 is electrically connected to the electron emitting section 3, each of the third lead pins 73 is electrically connected to each section of the electron multiplier section 4, and the fourth lead pin 74 is electrically connected to the first mesh electrode 5. This ensures that a predetermined potential is applied to each section of the electron tube 1.

[0062] In the electron tube device 100 and the electron tube 1, a metal layer 34 formed of a second metal covers a metasurface 32 formed of a first metal, and the work function of the second metal is lower than that of the first metal. This improves the sensitivity of the metasurface 32, so that even when the intensity of the electromagnetic wave W is low, field emission can occur in the metasurface 32, causing electrons to be emitted from the metasurface 32. Furthermore, although the improved sensitivity of the metasurface 32 makes it easier for noise electrons to be emitted from the electron emitter 3, even in such cases, for the reasons described above, it is possible to appropriately multiply the electrons emitted from the metasurface 32 in response to the incidence of the electromagnetic wave W.

[0063] In the electron tube device 100 and the electron tube 1, the metal layer 34 is made of an alkali metal, which can reliably improve the sensitivity of the metasurface 32.

[0064] In the electron tube device 100 and the electron tube 1, the first portion 34a of the metal layer 34 is located on the metasurface 32, and the second portion 34b is located outside the metasurface 32. This ensures that the metasurface 32 is completely covered by the metal layer 34, thereby reliably improving the sensitivity of the metasurface 32. On the other hand, noise electrons are also likely to be emitted from the second portion 34b of the metal layer 34, but because the second portion 34b of the metal layer 34 overlaps with the frame 61 of the second mesh electrode 6, it is possible to prevent the noise electrons emitted from the second portion 34b of the metal layer 34 from passing through to the electron multiplier section 4 side.

[0065] In the electron tube device 100 and the electron tube 1, the distance α between the metasurface 32 and the second mesh electrode 6 is equal to or less than the distance γ between adjacent wires 62 among the plurality of wires 62. This allows electrons emitted from the metasurface 32 in response to the incidence of electromagnetic waves W to pass through the second mesh electrode 6 and reach the electron multiplier section 4, and an electric field that prevents noise electrons emitted from the electron emitter 3 from passing through the second mesh electrode 6 can be reliably and easily formed between the electron emitter 3 and the electron multiplier section 4.

[0066] In the electron tube device 100 and the electron tube 1, the electron multiplier section 4 includes a plurality of dynodes 42. This ensures that the electrons emitted from the electron emitter 3 in response to the incidence of the electromagnetic wave W can be reliably multiplied. [Configuration of Modified Electron Tube Device]

[0067] 6, the electron tube device 100A includes an electron tube 1A and a voltage application unit 10. The electron tube 1A is an image intensifier. Note that, among the configurations of the electron tube device 100A and the electron tube 1A, descriptions of configurations similar to those of the electron tube device 100 and the electron tube 1 described above will be omitted.

[0068] The electron tube 1A includes a tube 15, a window member 16, and an FOP (fiber optic plate) 17. As an example, the tube 15 is made of an electrically insulating material and is formed into a cylindrical shape with an axis A as its center line. The window member 16 is airtightly fixed to one opening 15a of the tube 15. The FOP 17 is airtightly fixed to the other opening 15b of the tube 15. The space airtightly sealed by the tube 15, the window member 16, and the FOP 17 is a vacuum space.

[0069] The window member 16 is made of a material that is transparent to the electromagnetic wave W. The FOP 17 is composed of a bundle of multiple optical fibers. The FOP 17 has a light input surface 17a and a light output surface 17b. The light input surface 17a is the surface of the FOP 17 facing the window member 16 and is located inside the tubular body 15. The light output surface 17b is the surface of the FOP 17 opposite to the window member 16 and is located outside the tubular body 15.

[0070] The electron tube 1A further includes an electron emitting section 3, an electron multiplier section 4, a mesh electrode 9, and a fluorescent film 18. The electron emitting section 3, the electron multiplier section 4, the mesh electrode 9, and the fluorescent film 18 are disposed inside the tube body 15 between the window member 16 and the FOP 17.

[0071] The electron emitter 3 is disposed on the surface of the window member 16 facing the FOP 17, with the metasurface 32 facing the FOP 17. The electron emitter 3 is electrically connected to a second conductive member 192 attached to the tubular body 15. The mesh electrode 9 is disposed between the electron emitter 3 and the FOP 17. The mesh electrode 9 includes a frame 91 and a plurality of wires 92. The plurality of wires 92 are hung across the frame 91 and define a plurality of openings in the region inside the frame 91. The mesh electrode 9 is supported by a pair of first conductive members 191 attached to the tubular body 15. The mesh electrode 9 is electrically connected to the pair of first conductive members 191. The electron multiplier 4 is disposed between the mesh electrode 9 and the FOP 17. The electron multiplier 4 includes an MCP (microchannel plate) 44. The MCP 44 has an electron input surface 44a on the mesh electrode 9 side and an electron output surface 44b on the FOP 17 side. The MCP 44 is supported by a pair of third conductive members 193a, 193b attached to the tubular body 15. The electron input surface 44a of the MCP 44 is electrically connected to the third conductive member 193a, and the electron output surface 44b of the MCP 44 is electrically connected to the third conductive member 193b. The fluorescent screen 18 is disposed on the light input surface 17a of the FOP 17. The fluorescent screen 18 is a so-called fluorescent screen formed on the light input surface 17a of the FOP 17. The fluorescent screen 18 is electrically connected to a fourth conductive member 194 attached to the tubular body 15.

[0072] The distance α between the metasurface 32 of the electron emitter 3 and the mesh electrode 9 is smaller than the distance β between the mesh electrode 9 and the electron input surface 44a of the MCP 44 (the electron input surface of the electron multiplier 4). The distance α is the "distance between the metasurface 32 of the electron emitter 3 and the multiple wires 92 of the mesh electrode 9" along a direction parallel to the axis A, and if this distance varies depending on the position, it is the shortest distance. The distance β is the "distance between the multiple wires 92 of the mesh electrode 9 and the electron input surface 44a of the MCP 44" along a direction parallel to the axis A, and if this distance varies depending on the position, it is the shortest distance.

[0073] In the electron tube 1A, the distance α between the metasurface 32 and the mesh electrode 9 is smaller than the distance between adjacent wires 92 among the plurality of wires 92. This distance is the distance between adjacent wires 92 among the plurality of wires 92 in the arrangement direction of each wire 92, and if this distance varies depending on the position in the extension direction of each wire 92, it is the shortest distance. For example, this distance is the arrangement interval (pitch) of the plurality of wires 92.

[0074] The voltage application unit 10 is electrically connected to each of the electron emitting unit 3, the electron multiplier unit 4, the mesh electrode 9, and the fluorescent film 18 via each of the conductive members 191, 192, 193a, 193b, and 194. The voltage application unit 10 applies a predetermined potential to each of the electron emitting unit 3, the electron multiplier unit 4, the mesh electrode 9, and the fluorescent film 18.

[0075] The potential applied to the mesh electrode 9 is a potential that is negative relative to the potential of the metasurface 32. The potential applied to the electron input surface 44a of the MCP 44 is a potential that is positive relative to the potential of the metasurface 32. The potential applied to the electron output surface 44b of the MCP 44 is a potential that is positive relative to the potential of the electron input surface 44a. The potential applied to the fluorescent film 18 is a potential that is positive relative to the potential of the electron output surface 44b of the MCP 44.

[0076] With a predetermined potential applied to each component of the electron tube 1A in this manner, when electromagnetic wave W passes through the window member 16 and is incident on the metasurface 32, electrons are emitted from the metasurface 32 in response to the incidence of the electromagnetic wave W. The electrons emitted from the metasurface 32 in response to the incidence of the electromagnetic wave W pass through the mesh electrode 9 and are incident on the electron input surface 44a of the MCP 44. The electrons multiplied by the MCP 44 are emitted from the electron output surface 44b of the MCP 44 and are incident on the fluorescent film 18. When the electrons are incident on the fluorescent film 18, fluorescence is emitted from the fluorescent film 18 in response to the incidence of the electrons. The fluorescence emitted from the fluorescent film 18 is incident on the light input surface 17a of the FOP 17, guided by the FOP 17, and emitted from the light output surface 17b of the FOP 17.

[0077] As described above, in the electron tube device 100A and the electron tube 1A, the potential of the mesh electrode 9 is set to a negative value relative to the potential of the metasurface 32. For example, the voltage application unit 10 applies a voltage to the mesh electrode 9 so that the potential of the mesh electrode 9 is a negative value relative to the potential of the metasurface 32. This allows electrons emitted from the metasurface 32 in response to the incidence of electromagnetic waves W to pass through the mesh electrode 9 and reach the electron multiplier unit 4, while forming an electric field between the electron emitter 3 and the electron multiplier unit 4 that prevents noise electrons (e.g., photoelectrons and thermoelectrons emitted from the electron emitter 3), which are electrons that could become noise other than electrons emitted from each antenna structure 35 of the metasurface 32, from passing through the mesh electrode 9. This utilizes the fact that the energy (e.g., several keV or more) of the electrons emitted from the metasurface 32 in response to the incidence of electromagnetic waves W is greater than the energy (e.g., 10 eV or less) of the noise electrons. Therefore, according to the electron tube device 100A and the electron tube 1A, the electrons emitted from the metasurface 32 in response to the incidence of the electromagnetic wave W can be appropriately multiplied.

[0078] According to the electron tube device 100A and the electron tube 1A, an electric field that suppresses the occurrence of ion feedback between the metasurface 32 and the mesh electrode 9 can be formed.

[0079] In the electron tube device 100A and the electron tube 1A, the electron multiplier section 4 includes an MCP 44. This makes it possible to reliably multiply electrons emitted from the electron emitter 3 in response to the incidence of the electromagnetic wave W. [Variations]

[0080] The present invention is not limited to the above examples. For example, in the electron emitting portion 3, the second metal forming the metal layer 34 may be any metal having a work function lower than the work function of the first metal forming the metasurface 32, and may be an alkali metal other than cesium or a metal other than an alkali metal.

[0081] In the above-described electron tube 1, when viewed from a direction parallel to the axis A (the direction in which the electron emitter 3 and the second mesh electrode 6 face each other), it is sufficient that at least a part of the second portion 34b of the metal layer 34 overlaps with at least a part of the frame 61 of the second mesh electrode 6. In the above-described electron tube 1A, when viewed from a direction parallel to the axis A (the direction in which the electron emitter 3 and the mesh electrode 9 face each other), it is sufficient that at least a part of the second portion 34b of the metal layer 34 overlaps with at least a part of the frame 91 of the mesh electrode 9.

[0082] In the above-described electron tube 1, the plurality of wires 62 of the second mesh electrode 6 are hung across the frame 61. However, the plurality of wires 62 may be hung across the frame portion 131 of the third support portion 13 without going through the frame 61. In this case, the frame portion 131 corresponds to the frame of the second mesh electrode 6.

[0083] In the electron emitting portion 3, the sensitivity of the metasurface 32 can be improved as long as the metal layer 34 includes at least the first portion 34a. In other words, the metal layer 34 does not need to include the second portion 34b in order to improve the sensitivity of the metasurface 32. Furthermore, as long as the sensitivity of the metasurface 32 is sufficient, the electron emitting portion 3 does not need to include the metal layer 34. [Explanation of symbols]

[0084] 100,100A...electron tube device, 1,1A...electron tube, 3...electron emission section, 4...electron multiplier section, 6...second mesh electrode, 9...mesh electrode, 10...voltage application section, 32...metasurface, 34...metal layer, 34a...first part, 34b...second part, 42...dynode, 44...MCP (microchannel plate), 61...frame, 62...wire (thin wire), 71...first lead pin (first conductive member), 72...second lead pin (second conductive member), 73...third lead pin (third conductive member), 191...first conductive member, 192...second conductive member, 193a,193b...third conductive member, α...distance, γ...distance, W...electromagnetic wave.

Claims

1. An electron emitter including a metasurface that emits electrons in response to incidence of an electromagnetic wave, an electron multiplier that multiplies the electrons emitted from the electron emitter, and a mesh electrode disposed between the electron emitter and the electron multiplier, An electron tube in which the potential of the mesh electrode is set to be a negative value when the potential of the metasurface is used as a reference.

2. The electron tube of claim 1, further comprising at least one first conductive member electrically connected to the mesh electrode for applying a voltage to the mesh electrode so that the potential of the mesh electrode becomes a negative value when the potential of the metasurface is taken as a reference.

3. at least one second conductive member electrically connected to the electron emission portion for applying a voltage to the electron emission portion; 3. The electron tube according to claim 2, further comprising at least one third conductive member electrically connected to the electron multiplier section for applying a voltage to the electron multiplier section.

4. The electron emission portion further includes a metal layer covering the metasurface, the metasurface is formed of a first metal; the metal layer is formed of a second metal, 2. The electron tube of claim 1, wherein the work function of the second metal is lower than the work function of the first metal.

5. 5. The electron tube according to claim 4, wherein the second metal is an alkali metal.

6. the mesh electrode includes a frame and a plurality of thin wires stretched across the frame; the metal layer includes a first portion located on the metasurface and a second portion located outside the metasurface; 5. The electron tube according to claim 4, wherein at least a part of the second portion overlaps with at least a part of the frame when viewed from a direction in which the electron-emitting portion and the mesh electrode face each other.

7. the mesh electrode includes a plurality of fine wires; The electron tube according to claim 1 , wherein the distance between the metasurface and the mesh electrode is equal to or less than the distance between adjacent ones of the plurality of thin wires.

8. 8. The electron tube according to claim 1, wherein the electron multiplier section includes a plurality of dynodes.

9. 8. The electron tube according to claim 1, wherein the electron multiplier section includes a microchannel plate.

10. an electron tube having an electron emitter including a metasurface that emits electrons in response to incidence of an electromagnetic wave, an electron multiplier that multiplies the electrons emitted from the electron emitter, and a mesh electrode disposed between the electron emitter and the electron multiplier; a voltage application unit that applies a voltage to at least the mesh electrode, The voltage application unit applies a voltage to the mesh electrode so that the potential of the mesh electrode becomes a negative value when the potential of the metasurface is used as a reference.

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