vacuum tubes

Abstract

To provide an electron tube that can appropriately make electromagnetic waves having a predetermined electric field oscillation direction incident on an electron emission section and can appropriately multiply electrons emitted from the electron emission section in response to the incidence of the electromagnetic waves having the predetermined electric field oscillation direction. [Solution] The electron tube (1) comprises an electron emitter (3) including a metasurface (32) that emits electrons in response to incidence of an electromagnetic wave (W) having a predetermined electric field oscillation direction (V), an electron multiplier (4) that multiplies the electrons emitted from the electron emitter (3), and a first mesh electrode (5) arranged between the electron emitter (3) and the electron multiplier (4). The first mesh electrode (5) includes a plurality of wires (52) that define a plurality of openings aligned in a first direction (D1) parallel to the electric field oscillation direction (V). When viewed from the propagation direction (T) of the electromagnetic wave (W), each of the plurality of openings has an elongated shape whose longitudinal direction is a second direction (D2) that intersects with the first direction (D1) at an angle of 45 degrees or more.

Description

[Technical Field]

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

[0002] An electron tube is known that includes an electron emitter including a metasurface that emits electrons in response to incident electromagnetic waves, and an electron multiplier that multiplies the electrons emitted from the electron emitter (see, for example, Patent Document 1). [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, the metasurface may be configured to emit electrons in response to the incidence of electromagnetic waves (i.e., polarized light) having a predetermined electric field oscillation direction. In such cases, it is important to properly cause the electromagnetic waves having the predetermined electric field oscillation direction to be incident on the electron emitter and to properly multiply the electrons emitted from the electron emitter in response to the incidence of the electromagnetic waves having the predetermined electric field oscillation direction.

[0005] The present invention aims to provide an electron tube that can appropriately input electromagnetic waves having a predetermined electric field oscillation direction to an electron emission section and appropriately multiply electrons emitted from the electron emission section in response to the input of electromagnetic waves having a predetermined electric field oscillation direction. [Means for solving the problem]

[0006] The electron tube of the present invention is [1] "an electron tube comprising: an electron emitter including a metasurface that emits electrons in response to incidence of an electromagnetic wave having a predetermined electric field oscillation direction; an electron multiplier that multiplies the electrons emitted from the electron emitter; and a mesh electrode arranged between the electron emitter and the electron multiplier, wherein the mesh electrode includes a plurality of thin wires that define a plurality of openings aligned in a first direction parallel to the electric field oscillation direction, and when viewed from the propagation direction of the electromagnetic wave, each of the plurality of openings has an elongated shape whose longitudinal direction is a second direction that intersects the first direction at an angle of 45 degrees or more."

[0007] In the electron tube, a mesh electrode is disposed between the electron emitter and the electron multiplier. By applying a desired potential to the mesh electrode, electrons emitted from the electron emitter in response to the incidence of electromagnetic waves having a predetermined electric field oscillation direction can be appropriately multiplied. Furthermore, in the electron tube, the mesh electrode defines a plurality of openings arranged in a first direction parallel to the electric field oscillation direction of the electromagnetic waves, and each of the openings has an elongated shape with a second direction intersecting the first direction at an angle of 45 degrees or more as its longitudinal direction when viewed from the direction of propagation of the electromagnetic waves. This reduces the likelihood of electromagnetic waves having a predetermined electric field oscillation direction being reflected by the mesh electrode, thereby suppressing interference between the electromagnetic waves incident on the electron emitter and those reflected by the mesh electrode. Therefore, the electron tube allows electromagnetic waves having a predetermined electric field oscillation direction to be appropriately incident on the electron emitter and appropriately multiplying electrons emitted from the electron emitter in response to the incidence of electromagnetic waves having a predetermined electric field oscillation direction.

[0008] The electron tube of the present invention may be [2] "the electron tube according to the above [1], wherein the second direction is a direction perpendicular to the first direction." According to this electron tube, an electromagnetic wave having a predetermined electric field oscillation direction can be more appropriately incident on the electron emission section, and electrons emitted from the electron emission section in response to the incidence of the electromagnetic wave having the predetermined electric field oscillation direction can be more appropriately multiplied.

[0009] The electron tube of the present invention may be [3] "the electron tube according to the above [1] or [2], wherein the metasurface includes a plurality of antenna structures, each of the plurality of antenna structures including a pair of ends facing each other in the first direction." According to this electron tube, electrons are reliably emitted from the metasurface in response to incidence of an electromagnetic wave having a predetermined electric field oscillation direction.

[0010] The electron tube of the present invention may be [4] "the electron tube according to any one of the above [1] to [3], in which the width of each of the plurality of openings in the first direction is equal to or greater than the wavelength of the electromagnetic wave." With this electron tube, electrons emitted from the electron emitter in response to incidence of an electromagnetic wave having a predetermined electric field oscillation direction can be passed to the electron multiplier section side, and the electromagnetic wave having the predetermined electric field oscillation direction can be prevented from being reflected by the mesh electrode.

[0011] The electron tube of the present invention may be [5] "the electron tube according to any one of the above [1] to [4], wherein the width of each of the plurality of openings in the second direction is at least 10 times the wavelength of the electromagnetic wave." With this electron tube, even if an electromagnetic wave having a predetermined electric field oscillation direction is reflected by the mesh electrode, interference between the electromagnetic wave incident on the electron-emitting section and the electromagnetic wave reflected by the mesh electrode can be suppressed.

[0012] The electron tube of the present invention may be [6] "the electron tube according to any one of the above [1] to [5], wherein the line width of each of the plurality of thin wires when viewed from the propagation direction is equal to or less than the wavelength of the electromagnetic wave." With this electron tube, it is possible to suppress interference between the electromagnetic wave incident on the electron emission section and the electromagnetic wave reflected by each thin wire.

[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 each of the plurality of thin wires has a cross-sectional shape tapering toward the electron emission section." According to this electron tube, electrons emitted from the electron emission section in response to incidence of an electromagnetic wave having a predetermined electric field oscillation direction are more likely to pass toward the electron multiplier section.

[0014] The electron tube of the present invention may be [8] "the electron tube according to the above [7], in which a secondary electron emission layer is provided on each of the inclined surfaces of the plurality of fine wires." With this electron tube, the electrons emitted from the electron emission section can also be multiplied by the mesh electrode, thereby improving the detection efficiency of electromagnetic waves having a predetermined electric field oscillation direction.

[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 plurality of thin wires include a plurality of first thin wires and a plurality of second thin wires, each of the plurality of first thin wires extending in the second direction, and each of the plurality of second thin wires extending in the first direction." With this electron tube, it is possible to prevent each of the first thin wires from bending due to its own weight.

[0016] The electron tube of the present invention may be

[10] "the electron tube according to the above [9], wherein each of the plurality of second thin wires extends in the first direction for each of the plurality of openings, and each of the plurality of second thin wires is not continuous in the first direction." With this electron tube, it is possible to suppress interference caused by each second thin wire with electromagnetic waves having a predetermined electric field oscillation direction.

[0017] The electron tube of the present invention may be

[11] "the electron tube according to any one of the above [1] to

[10] , wherein the electron multiplier section includes a plurality of dynodes." With this electron tube, it is possible to reliably multiply electrons emitted from the electron emitter in response to incidence of an electromagnetic wave having a predetermined electric field oscillation direction. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an electron tube that can appropriately input electromagnetic waves having a predetermined electric field oscillation direction to an electron emission section and appropriately multiply electrons emitted from the electron emission section in response to the input of electromagnetic waves having a predetermined electric field oscillation direction. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view of an example electron tube. [Figure 2] 2 is a bottom view of the electron-emitting portion shown in FIG. 1. FIG. [Figure 3] FIG. 3 is a schematic diagram of the antenna structure shown in FIG. 2. [Figure 4] 2 is a cross-sectional view of a portion of the electron tube shown in FIG. 1. [Figure 5] FIG. 5 is an exploded perspective view of a portion of the electron tube shown in FIG. 4. [Figure 6] FIG. 2 is a schematic diagram of a first mesh electrode and a second mesh electrode shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII shown in FIG. 6. [Figure 8] 7A and 7B are diagrams for explaining the functions of the first mesh electrode and the second mesh electrode shown in FIG. 6. [Figure 9] FIG. 10 is a cross-sectional view of a portion of a modified electron tube. [Figure 10] FIG. 10 is an exploded perspective view of a portion of the electron tube shown in FIG. 9. [Figure 11] FIG. 10 is a schematic diagram of a modified antenna structure. [Figure 12] 10A and 10B are schematic diagrams of a first mesh electrode and a second mesh electrode of a modified example. [Figure 13] FIG. 10 is a cross-sectional view of a modified wire. 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 includes a housing 2, an electron emitter 3, an electron multiplier 4, a first mesh electrode (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 within 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 wire 70 is a linear member made of metal, and has a strength that enables "support of the electron multiplier section 4 by the plurality of lead pins 7 and the plurality of wires 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. As shown in FIG. 3, each antenna structure 35 includes a pair of end portions 35a facing each other in a first direction D1. In the electron tube 1, each antenna structure 35 is configured as a bowtie antenna. Each such antenna structure 35 emits electrons in response to incidence of an electromagnetic wave W having an electric field oscillation direction V that is the first direction D1. That is, the metasurface 32 emits electrons in response to incidence of the electromagnetic wave W having an electric field oscillation direction V. In other words, the metasurface 32 emits electrons when the direction in which the line connecting the pair of end portions 35a of each antenna structure 35 extends coincides with the electric field oscillation direction V of the electromagnetic wave W.

[0027] As shown in FIG. 2 , the metasurface 32 is disposed on an axis A. A pair of electrodes 33 are disposed on both sides of the metasurface 32. Each electrode 33 is electrically connected to each antenna structure 35 via wiring (not shown). A predetermined potential difference is applied between a pair of opposing ends 35a 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 electrically conductive inorganic carbon material 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) with 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 35a. 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 end 35a. 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] 4 and 5, 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 (thin 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 an area inside 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 area inside 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 the corresponding lead pin 7 is 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. Note that noise electrons include photoelectrons emitted by 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 the first mesh electrode and the second mesh electrode]

[0047] The configurations of the first mesh electrode 5 and the second mesh electrode 6 will be described with reference to Fig. 6 and Fig. 7. Since the second mesh electrode 6 has the same configuration as the first mesh electrode 5, the reference numerals for the second mesh electrode 6 are written in parentheses in Fig. 6 and Fig. 7.

[0048] As shown in FIG. 6 , in the first mesh electrode 5, a plurality of openings 53 are defined by a plurality of wires 52. The plurality of openings 53 are aligned in a first direction D1 parallel to the electric field oscillation direction V. When viewed from the propagation direction T of the electromagnetic wave W (i.e., a direction parallel to the axis A), each opening 53 has an elongated shape with its longitudinal direction aligned in a second direction D2, which is a direction perpendicular to the first direction D1. In this example, each opening 53 has a rectangular shape with its longitudinal direction aligned in the second direction D2. The plurality of wires 52 include a plurality of first wires (first thin wires) 52a and a plurality of second wires (second thin wires) 52b. Each of the first wires 52a extends in the second direction D2, and both ends of each of the first wires 52a are connected to the frame 51. Each of the second wires 52b extends in the first direction D1, and both ends of each of the second wires 52b are connected to the frame 51. In this example, the plurality of second wires 52b are pairs of second wires 52b.

[0049] The width of each opening 53 in the first direction D1 is equal to or greater than the wavelength of the electromagnetic wave W. The width of each opening 53 in the second direction D2 is equal to or greater than 10 times the wavelength of the electromagnetic wave W. In other words, the spacing between the multiple first wires 52a is equal to or greater than the wavelength of the electromagnetic wave W, and the spacing between the multiple second wires 52b is equal to or greater than 10 times the wavelength of the electromagnetic wave W. The line width of each wire 52 when viewed from a direction parallel to the axis A (the width of the wire 52 in a direction perpendicular to the extension direction of the wire 52) is equal to or less than the wavelength of the electromagnetic wave W. The wavelength of the electromagnetic wave W means the maximum wavelength in the wavelength range to which the metasurface 32 is sensitive. As an example, the wavelength of the electromagnetic wave W is approximately 300 μm, the width of each opening 53 in the first direction D1 (the spacing between the multiple first wires 52a) is approximately 0.5 mm, the width of each opening 53 in the second direction D2 (the spacing between the multiple second wires 52b) is approximately 5 mm, and the line width of each wire 52 when viewed from a direction parallel to the axis A is approximately 50 μm.

[0050] 7, each wire 52 has a cross-sectional shape (cross-sectional shape of wire 52 in a direction perpendicular to the extending direction of wire 52) that tapers toward the electron emitting portion 3. As an example, each wire 52 has a trapezoidal cross-sectional shape that tapers toward the electron emitting portion 3. Such a cross-sectional shape is formed by etching the multiple wires 52 from the side that should be tapered.

[0051] As shown in FIG. 6 , in the second mesh electrode 6, a plurality of openings 63 are defined by a plurality of wires 62. The plurality of openings 63 are aligned in a first direction D1 parallel to the electric field oscillation direction V. When viewed from the propagation direction T of the electromagnetic wave W (i.e., a direction parallel to the axis A), each opening 63 has an elongated shape with its longitudinal direction aligned in a second direction D2, which is a direction perpendicular to the first direction D1. In this example, each opening 63 has a rectangular shape with its longitudinal direction aligned in the second direction D2. The plurality of wires 62 include a plurality of first wires (first thin wires) 62a and a plurality of second wires (second thin wires) 62b. Each of the first wires 62a extends in the second direction D2, and both ends of each first wire 62a are connected to the frame 51. Each of the second wires 62b extends in the first direction D1, and both ends of each second wire 62b are connected to the frame 51. In this example, the plurality of second wires 62b are pairs of second wires 62b.

[0052] The width of each opening 63 in the first direction D1 is equal to or greater than the wavelength of the electromagnetic wave W. The width of each opening 63 in the second direction D2 is equal to or greater than 10 times the wavelength of the electromagnetic wave W. In other words, the spacing between the multiple first wires 62a is equal to or greater than the wavelength of the electromagnetic wave W, and the spacing between the multiple second wires 62b is equal to or greater than 10 times the wavelength of the electromagnetic wave W. The line width of each wire 62 when viewed from a direction parallel to the axis A is equal to or less than the wavelength of the electromagnetic wave W. As shown in FIG. 7, each wire 62 has a cross-sectional shape that tapers toward the electron emitter 3. As an example, each wire 62 has a trapezoidal cross-sectional shape that tapers toward the electron emitter 3.

[0053] In the first mesh electrode 5 configured as described above, each first wire 52a extends in the second direction D2 (i.e., a direction perpendicular to the direction in which a straight line connecting a pair of ends 35a in each antenna structure 35 of the metasurface 32 extends), and the multiple first wires 52a are configured to have selective polarization transparency for the electromagnetic wave W. That is, the multiple first wires 52a are arranged so that each opening 53 has an elongated shape whose longitudinal direction is the second direction D2 perpendicular to the electric field oscillation direction V. As a result, as shown in FIG. 8(a), when the electromagnetic wave W having a predetermined electric field oscillation direction V is incident on the first mesh electrode 5, the multiple first wires 52a act as transparent bodies for the electromagnetic wave W having the electric field oscillation direction V, and the electromagnetic wave W passes through the first mesh electrode 5.

[0054] Similarly, in the second mesh electrode 6, each first wire 62a extends in the second direction D2, and the multiple first wires 62a are configured to have selective polarization transparency for the electromagnetic wave W. That is, the multiple first wires 62a are arranged so that each opening 63 has an elongated shape with its longitudinal direction aligned with the second direction D2 perpendicular to the electric field oscillation direction V. As a result, when the electromagnetic wave W having the predetermined electric field oscillation direction V is incident on the second mesh electrode 6, the multiple first wires 62a act as transparent bodies for the electromagnetic wave W having the electric field oscillation direction V, and the electromagnetic wave W passes through the second mesh electrode 6.

[0055] In contrast, as shown in (b) of Figure 8, when an electromagnetic wave W having a predetermined electric field oscillation direction V is incident on the mesh electrode 100, if the multiple wires 101 are arranged so that each opening 102 has an elongated shape with a first direction D1 parallel to the electric field oscillation direction V as its longitudinal direction, the multiple wires 101 act as metal with respect to the electromagnetic wave W having the electric field oscillation direction V, and the electromagnetic wave W is reflected by the mesh electrode 100.

[0056] In the first mesh electrode 5, each second wire 52b extends in a first direction D1 parallel to the electric field oscillation direction V of the electromagnetic wave W. Therefore, the electromagnetic wave W may be reflected by the plurality of second wires 52b. However, the arrangement interval of the plurality of second wires 52b is equal to or greater than 10 times the wavelength of the electromagnetic wave W, and the line width of each second wire 52b is equal to or less than the wavelength of the electromagnetic wave W. Therefore, interference between the incident electromagnetic wave W and the reflected electromagnetic wave W is suppressed. Similarly, in the second mesh electrode 6, each second wire 62b extends in the first direction D1 parallel to the electric field oscillation direction V of the electromagnetic wave W. Therefore, the arrangement interval of the plurality of second wires 62b is equal to or greater than 10 times the wavelength of the electromagnetic wave W, and the line width of each second wire 62b is equal to or less than the wavelength of the electromagnetic wave W. Therefore, interference between the incident electromagnetic wave W and the reflected electromagnetic wave W is suppressed. [Action and effect]

[0057] In the electron tube 1, a first mesh electrode 5 and a second mesh electrode 6 are disposed between the electron emitter 3 and the electron multiplier 4. This allows for the appropriate multiplication of electrons emitted from the electron emitter 3 in response to the incidence of an electromagnetic wave W having a predetermined electric field oscillation direction V by applying a desired potential to each of the first mesh electrode 5 and the second mesh electrode 6. In the electron tube 1, a plurality of openings 53 are defined in the first mesh electrode 5 by a plurality of wires 52 and arranged in a first direction D1 parallel to the electric field oscillation direction V of the electromagnetic wave W. When viewed from the propagation direction T of the electromagnetic wave W, each opening 53 has an elongated shape with its longitudinal direction aligned in a second direction D2 perpendicular to the first direction D1. Similarly, in the second mesh electrode 6, a plurality of openings 63 arranged in a first direction D1 parallel to the electric field oscillation direction V of the electromagnetic wave W are defined by a plurality of wires 62, and each opening 63 has an elongated shape with its longitudinal direction in a second direction D2 perpendicular to the first direction D1 when viewed from the traveling direction T of the electromagnetic wave W. This makes it difficult for the electromagnetic wave W having the predetermined electric field oscillation direction V to be reflected by each of the first mesh electrode 5 and the second mesh electrode 6, and suppresses interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by each of the first mesh electrode 5 and the second mesh electrode 6. Therefore, the electromagnetic wave W having the predetermined electric field oscillation direction V can be appropriately incident on the electron emitter 3 while suppressing attenuation of the intensity of the electromagnetic wave W. Therefore, according to the electron tube 1, the electromagnetic wave W having the predetermined electric field oscillation direction V can be appropriately incident on the electron emitter 3, and the electrons emitted from the electron emitter 3 in response to the incidence of the electromagnetic wave W having the predetermined electric field oscillation direction V can be appropriately multiplied, thereby preventing a decrease in the detection efficiency of the electromagnetic wave W having the predetermined electric field oscillation direction V.

[0058] In the electron tube 1, the metasurface 32 includes a plurality of antenna structures 35, each of which includes a pair of ends 35a facing each other in the first direction D1. This ensures that electrons are emitted from the metasurface 32 in response to the incidence of an electromagnetic wave W having a predetermined electric field oscillation direction V.

[0059] In the electron tube 1, the width of each opening 53 in the first direction D1 in the first mesh electrode 5 is equal to or greater than the wavelength of the electromagnetic wave W. This allows electrons emitted from the electron emitter 3 in response to the incidence of the electromagnetic wave W having a predetermined electric field oscillation direction V to pass toward the electron multiplier section 4, and also makes it possible to prevent the electromagnetic wave W having the predetermined electric field oscillation direction V from being reflected by the first mesh electrode 5.

[0060] Similarly, in the second mesh electrode 6, the width of each opening 63 in the first direction D1 is equal to or greater than the wavelength of the electromagnetic wave W. This allows electrons emitted from the electron emitter 3 in response to the incidence of the electromagnetic wave W having a predetermined electric field oscillation direction V to pass toward the electron multiplier 4, and also makes it possible to prevent the electromagnetic wave W having the predetermined electric field oscillation direction V from being reflected by the second mesh electrode 6.

[0061] In the electron tube 1, the width of each opening 53 in the first mesh electrode 5 in the second direction D2 is at least 10 times the wavelength of the electromagnetic wave W. This makes it possible to suppress interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by the first mesh electrode 5, even if the electromagnetic wave W having a predetermined electric field oscillation direction V is reflected by the first mesh electrode 5.

[0062] Similarly, in the second mesh electrode 6, the width of each opening 63 in the second direction D2 is at least 10 times the wavelength of the electromagnetic wave W. This makes it possible to suppress interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by the second mesh electrode 6, even if the electromagnetic wave W having a predetermined electric field oscillation direction V is reflected by the second mesh electrode 6.

[0063] In the electron tube 1, the line width of each wire 52 in the first mesh electrode 5 when viewed from the traveling direction T of the electromagnetic wave W is equal to or less than the wavelength of the electromagnetic wave W. This makes it possible to suppress interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by each wire 52.

[0064] Similarly, in the second mesh electrode 6, the line width of each wire 62 when viewed from the traveling direction T of the electromagnetic wave W is equal to or less than the wavelength of the electromagnetic wave W. This makes it possible to suppress interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by each wire 62.

[0065] In the electron tube 1, in the first mesh electrode 5, each wire 52 has a cross-sectional shape that tapers toward the electron emitter 3. This makes it easier for electrons emitted from the electron emitter 3 in response to incidence of an electromagnetic wave W having a predetermined electric field oscillation direction V to pass toward the electron multiplier 4.

[0066] Similarly, in the second mesh electrode 6, each wire 62 has a cross-sectional shape that tapers toward the electron emitter 3. This makes it easier for electrons emitted from the electron emitter 3 in response to incidence of an electromagnetic wave W having a predetermined electric field oscillation direction V to pass toward the electron multiplier 4.

[0067] In the electron tube 1, the wires 52 in the first mesh electrode 5 include a plurality of first wires 52a and a plurality of second wires 52b, with each of the first wires 52a extending in the second direction D2 and each of the second wires 52b extending in the first direction D1. This prevents each of the first wires 52a from bending due to its own weight. It also prevents deformation of the wires 52 due to assembly work.

[0068] Similarly, in the second mesh electrode 6, the multiple wires 62 include multiple first wires 62a and multiple second wires 62b, where each of the first wires 62a extends in the second direction D2 and each of the second wires 62b extends in the first direction D1. This prevents each of the first wires 62a from bending due to its own weight. It also prevents the multiple wires 62 from being deformed during assembly.

[0069] In 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 an electromagnetic wave W having a predetermined electric field oscillation direction V can be reliably multiplied. [Configuration of the electron tube of the modified example]

[0070] The electron tube 1 may not have either the first mesh electrode 5 or the second mesh electrode 6. The configuration around the electron emitter 3 in an electron tube 1A that does not have the second mesh electrode 6 will be described with reference to Figures 9 and 10. Note that, among the configuration around the electron emitter 3 in the electron tube 1A, the description of the same configuration as that of the electron tube 1 described above will be omitted.

[0071] As shown in FIGS. 9 and 10 , the electron tube 1A includes an electron emitter 3, a first mesh electrode 5, a base 8, a first support 11, a second support 12, and a spacer 14. The electron emitter 3 has a configuration similar to that of the electron emitter 3 of the electron tube 1 described above. The first mesh electrode 5 has a configuration similar to that of the first mesh electrode 5 of the electron tube 1 described above. The base 8 differs from the base 8 of the electron tube 1 described above in that it does not include multiple spring portions 82 (see FIG. 5 ). Except for this, the base 8 has a configuration similar to that of the base 8 of the electron tube 1 described above. The second support 12 has a configuration similar to that of the second support 12 of the electron tube 1 described above. The spacer 14 has a configuration similar to that of the spacer 14 of the electron tube 1 described above. In the electron tube 1A, the spacer 14 is disposed between the electron emitter 3 and the first mesh electrode 5.

[0072] The first support section 11 has a first support plate 91 and a second support plate 92. The first support plate 91 is formed into a frame shape using, for example, a metal plate. The first support plate 91 includes a frame portion 93 having an opening 93a and a plurality of spring portions 94. The frame portion 93 is disposed on the electron emitter 3. When viewed from a direction parallel to the axis A, the opening 93a overlaps with the metasurface 32 of the electron emitter 3. Each spring portion 94 extends outward from the frame portion 93 (i.e., on the opposite side from the opening 93a). Each spring portion 94 contacts the inner surface of the bulb 21.

[0073] The second support plate 92 is formed into a frame shape using, for example, a metal plate. The second support plate 92 includes a frame portion 95 having an opening 95a, multiple spring portions 96, and multiple first claw portions 97. The frame portion 95 is joined to the frame portion 93 of the first support plate 91. The frame portion 95 is disposed on the spacer 14. When viewed from a direction parallel to the axis A, the frame portion 95 surrounds the electron emitter 3. That is, when viewed from a direction parallel to the axis A, the electron emitter 3 is located within the opening 95a. Each spring portion 96 extends inward (i.e., toward the axis A) from the frame portion 95. Each spring portion 96 presses the electron emitter 3 against the first support plate 91 so that the substrate 31 of the electron emitter 3 contacts the first support plate 91. Each first claw portion 97 extends from the frame portion 95 on the side opposite to the window portion 21a.

[0074] In the second support plate 92, each spring portion 96 is in contact with each electrode 33 of the electron emitter 3. The second support plate 92 is connected to a wiring 70 that is connected to a corresponding lead pin 7, and a predetermined potential is applied to the metasurface 32 of the electron emitter 3 via the second support plate 92.

[0075] Each first claw portion 97 of the second support plate 92 of the first support portion 11 engages with each first through portion 141 of the spacer 14. Each second claw portion 122 of the second support portion 12 engages with each second through portion 142 of the spacer 14. The first support portion 11 exposes the multiple second through portions 142 on the first surface 14a of the spacer 14. This prevents the second claw portions 122 engaged with the respective second through portions 142 from physically interfering with the first support portion 11. The second support portion 12 exposes the multiple first through portions 141 on the second surface 14b of the spacer 14. This prevents the first claw portions 97 engaged with the respective first through portions 141 from physically interfering with the second support portion 12.

[0076] In the electron tube 1A, the electron emitter 3, first mesh electrode 5, first support 11, and second support 12 are unitized via a spacer 14, ensuring electrical insulation between the metasurface 32 of the electron emitter 3 and the first mesh electrode 5. In the electron tube 1A, the metasurface 32 of the electron emitter 3 and the first support 11 are at the same potential. In addition, the first mesh electrode 5, the first dynode 421, the base 8, and the second support 12 are at another same potential.

[0077] In the electron tube 1A configured as described above, a predetermined potential is applied to the metasurface 32 of the electron emitter 3, the first mesh electrode 5, each dynode 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 and negative relative to the potential of the first dynode 421. As an example, the potential applied to the metasurface 32 is approximately −1500 V, the potential applied to the first mesh electrode 5 and the first dynode 421 is approximately +100 to +200 V relative to the potential of the metasurface 32, and the potential applied to the second dynode 422 is approximately +several hundred volts relative to the potential of the first dynode 421.

[0078] With a predetermined potential applied to each part of the electron tube 1A in this manner, when electromagnetic waves W having a predetermined electric field oscillation direction V pass through the window portion 21a of the bulb 21 and the substrate 31 of the electron emitter 3 and are incident on the metasurface 32, electrons are emitted from each antenna structure 35 of the metasurface 32 in response to the incidence of the electromagnetic waves W. The electrons emitted from the metasurface 32 in response to the incidence of the electromagnetic waves W pass through the first mesh electrode 5 and are incident on the electron emission surface 42a of the first dynode 421.

[0079] When electrons that have passed through 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 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 is applied to the first mesh electrode 5, the movement of secondary electrons from the first dynode 421 to the second dynode 422 is prevented from being affected by the electric field on the electron emitter 3 side. Then, the electrons that have been sequentially multiplied in each dynode 42 by the incidence and emission of secondary electrons finally enter the anode 43.

[0080] As described above, in the electron tube 1A, the first mesh electrode 5 is disposed between the electron emitter 3 and the electron multiplier 4. By applying a desired potential to the first mesh electrode 5, electrons emitted from the electron emitter 3 in response to the incidence of electromagnetic waves W having a predetermined electric field oscillation direction V can be appropriately multiplied. Furthermore, in the electron tube 1A, the first mesh electrode 5 has a plurality of openings 53 defined by a plurality of wires 52 and arranged in a first direction D1 parallel to the electric field oscillation direction V of the electromagnetic waves W. When viewed from the propagation direction T of the electromagnetic waves W, each opening 53 has an elongated shape with its longitudinal direction being a second direction D2 perpendicular to the first direction D1. This reduces the reflection of the electromagnetic waves W having the predetermined electric field oscillation direction V by the first mesh electrode 5, suppressing interference between the electromagnetic waves W incident on the electron emitter 3 and the electromagnetic waves W reflected by the first mesh electrode 5. This allows the electromagnetic waves W having the predetermined electric field oscillation direction V to be appropriately incident on the electron emitter 3. Therefore, according to the electron tube 1A, an electromagnetic wave W having a predetermined electric field oscillation direction V can be appropriately incident on the electron emitting section 3, and the electrons emitted from the electron emitting section 3 in response to the incidence of the electromagnetic wave W having the predetermined electric field oscillation direction V can be appropriately multiplied. [Variations]

[0081] The present invention is not limited to the above-described examples. For example, in the above-described electron emitter 3, each antenna structure 35 is configured as a bowtie antenna, but each antenna structure 35 may be configured as another antenna. As an example, each antenna structure 35 may be configured as a dipole antenna as shown in FIG. 11(a), as a split ring antenna as shown in FIG. 11(b), or as a double split ring antenna as shown in FIG. 11(c). In any case, each antenna structure 35 includes a pair of ends 35a facing each other in the first direction D1.

[0082] In the above-described first mesh electrode 5, both ends of each second wire 52b are fixed to the frame 51, but at least one of both ends of each second wire 52b may be fixed to the first wire 52a. Similarly, in the above-described second mesh electrode 6, both ends of each second wire 62b are fixed to the frame 51, but at least one of both ends of each second wire 62b may be fixed to the first wire 62a.

[0083] 12(a), (b), and (c), in the first mesh electrode 5, each second wire 52b extends in the first direction D1 for each opening 53 (i.e., for each of the multiple openings 53), and may not be continuous in the first direction D1. In this case, it is possible to suppress interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by each second wire 52b. In particular, as shown in FIG. 12(b) and (c), when all the second wires 52b are misaligned in the second direction D2, it is possible to reliably suppress interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by each second wire 52b.

[0084] 12(a), (b), and (c), in the second mesh electrode 6, each second wire 62b extends in the first direction D1 for each opening 63 (i.e., for each of the multiple openings 63), and may not be continuous in the first direction D1. In this case, it is possible to suppress interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by each second wire 62b. In particular, as shown in FIG. 12(b) and (c), when all the second wires 62b are misaligned in the second direction D2, it is possible to reliably suppress interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by each second wire 62b.

[0085] The electron multiplier section 4 does not have to include multiple dynodes 42. As an example, the electron multiplier section 4 may include a microchannel plate. In this case, too, it is possible to reliably multiply the electrons emitted from the electron emitter 3 in response to the incidence of the electromagnetic wave W having a predetermined electric field oscillation direction V.

[0086] The second direction D2 does not have to be perpendicular to the first direction D1. The second direction D2 may be any direction that intersects with the first direction D1 at an angle of 45 degrees or more. That is, in the first mesh electrode 5, each opening 53 may have an elongated shape whose longitudinal direction is the second direction D2 that intersects with the first direction D1 at an angle of 45 degrees or more when viewed from the propagation direction T of the electromagnetic wave W. Even in this case, the electromagnetic wave W having a predetermined electric field oscillation direction V is less likely to be reflected by the first mesh electrode 5, thereby suppressing interference between the electromagnetic wave W incident on the electron emitter 3 and the electromagnetic wave W reflected by the first mesh electrode 5. Similarly, in the second mesh electrode 6, each opening 63 may have an elongated shape whose longitudinal direction is the second direction D2 that intersects with the first direction D1 at an angle of 45 degrees or more when viewed from the propagation direction T of the electromagnetic wave W. Even in this case, the electromagnetic waves W having the predetermined electric field vibration direction V are less likely to be reflected by the second mesh electrode 6, thereby suppressing interference between the electromagnetic waves W incident on the electron emitter 3 and the electromagnetic waves W reflected by the second mesh electrode 6. Note that in the first mesh electrode 5, some of the openings 53 do not have to have an elongated shape with the second direction D2 as the longitudinal direction. The ratio of the number of openings 53 that do not have an elongated shape to the total number of openings 53 may be 10% or less. Similarly, in the second mesh electrode 6, some of the openings 63 do not have to have an elongated shape with the second direction D2 as the longitudinal direction. The ratio of the number of openings 63 that do not have an elongated shape to the total number of openings 63 may be 10% or less.

[0087] As shown in FIG. 13 , a pair of inclined surfaces 52c of each wire 52 may be provided with a secondary electron emission layer 54. The pair of inclined surfaces 52c are a pair of side surfaces inclined to approach each other toward the electron emitter 3. With this configuration, electrons emitted from the electron emitter 3 can also be multiplied by the first mesh electrode 5, thereby improving the detection efficiency of the electromagnetic wave W having the predetermined electric field oscillation direction V. Similarly, a pair of inclined surfaces 62c of each wire 62 may be provided with a secondary electron emission layer 64. The pair of inclined surfaces 62c are a pair of side surfaces inclined to approach each other toward the electron emitter 3. With this configuration, electrons emitted from the electron emitter 3 can also be multiplied by the second mesh electrode 6, thereby improving the detection efficiency of the electromagnetic wave W having the predetermined electric field oscillation direction V. As an example, the material of each secondary electron emission layer 54, 64 may be MgO, MgF2, Al2O3, or the like. [Explanation of symbols]

[0088] 1,1A...electron tube, 3...electron emitter, 4...electron multiplier, 5...first mesh electrode (mesh electrode), 6...second mesh electrode (mesh electrode), 32...metasurface, 35...antenna structure, 35a...end, 42...dynode, 52,62...wire (thin wire), 52a,62a...first wire (first thin wire), 52b,62b...second wire (second thin wire), 52c,62c...inclined surface, 53,63...aperture, 54,64...secondary electron emitter layer, D1...first direction, D2...second direction, T...propagation direction, V...electric field oscillation direction, W...electromagnetic wave.

Claims

1. an electron emitter including a metasurface that emits electrons in response to incidence of an electromagnetic wave having a predetermined electric field oscillation direction; an electron multiplier section that multiplies the electrons emitted from the electron emitting section; a mesh electrode disposed between the electron emitting section and the electron multiplier section, the mesh electrode includes a plurality of thin wires defining a plurality of openings aligned in a first direction parallel to the electric field oscillation direction; When viewed from the direction of propagation of the electromagnetic wave, each of the plurality of openings has an elongated shape with its longitudinal direction being a second direction that intersects with the first direction at an angle of 45 degrees or more.

2. The electron tube according to claim 1 , wherein the second direction is a direction perpendicular to the first direction.

3. the metasurface includes a plurality of antenna structures; The electron tube according to claim 1 , wherein each of the plurality of antenna structures includes a pair of ends facing each other in the first direction.

4. The electron tube according to claim 1 , wherein the width of each of the plurality of openings in the first direction is equal to or greater than the wavelength of the electromagnetic wave.

5. 2. The electron tube according to claim 1, wherein the width of each of the plurality of openings in the second direction is at least 10 times the wavelength of the electromagnetic wave.

6. 2. The electron tube according to claim 1, wherein the line width of each of the plurality of thin lines when viewed from the propagation direction is equal to or less than the wavelength of the electromagnetic wave.

7. 2. The electron tube according to claim 1, wherein each of said plurality of thin wires has a cross-sectional shape tapering toward said electron emission portion.

8. 8. The electron tube according to claim 7, wherein a secondary electron emitting layer is provided on each of the inclined surfaces of said plurality of fine wires.

9. the plurality of thin wires include a plurality of first thin wires and a plurality of second thin wires; each of the plurality of first thin wires extends in the second direction; The electron tube according to claim 1 , wherein each of the plurality of second thin wires extends in the first direction.

10. each of the second thin wires extends in the first direction for each of the openings; The electron tube according to claim 9 , wherein each of the plurality of second thin wires is discontinuous in the first direction.

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

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