Electron tube

Abstract

Provided is an electron tube comprising: an electron emitting part including a metasurface that emits electrons in response to incidence of electromagnetic waves; an electron multiplying part that multiplies the electrons emitted from the electron emitting part; and a first mesh electrode disposed between the electron emitting part and the electron multiplying part. The electron multiplying part has an electron incident region on which the electrons emitted from the electron emitting part are incident. The distance between the metasurface and the electron incident region is inferior to the width of the electron incident region.

Description

electron tube

[0001] The present disclosure relates to electron tubes.

[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).

[0003] Special Publication No. 2023-512566

[0004] In the above-described electron tube, it is important that the electrons emitted from the electron emitting section reach the electron multiplier section reliably and that the electrons are reliably multiplied in the electron multiplier section.

[0005] An object of the present disclosure is to provide an electron tube that can reliably cause electrons emitted from an electron emitting section to reach an electron multiplier section and reliably multiply the electrons in the electron multiplier section.

[0006] An electron tube according to one aspect of the present disclosure is [1] "an electron tube comprising: an electron emitter including a metasurface that emits electrons in response to incidence of electromagnetic waves; an electron multiplier that multiplies the electrons emitted from the electron emitter; and a first mesh electrode arranged between the electron emitter and the electron multiplier, wherein the electron multiplier has an electron incidence region onto which the electrons emitted from the electron emitter are incident, and the distance between the metasurface and the electron incidence region is smaller than the width of the electron incidence region."

[0007] In the above electron tube, the distance between the metasurface of the electron emitter and the electron incidence region of the electron multiplier is smaller than the width of the electron incidence region. This allows electrons emitted from the electron emitter in response to incident electromagnetic waves to reliably reach the electron multiplier. Furthermore, in the above electron tube, a first mesh electrode is disposed between the electron emitter and the electron multiplier. This allows electrons emitted from the electron emitter in response to incident electromagnetic waves to reliably reach the electron multiplier and reliably multiply the electrons in the electron multiplier by applying a potential appropriate for the purpose to the first mesh electrode. Therefore, with the above electron tube, electrons emitted from the electron emitter can reliably reach the electron multiplier and be reliably multiplied in the electron multiplier.

[0008] An electron tube according to one aspect of the present disclosure may be [2] "the electron tube according to the above [1], further comprising: a first support portion supporting the electron emitter; a second support portion supporting the first mesh electrode; and a spacer formed in a frame shape from an electrically insulating material and disposed between the electron emitter and the first mesh electrode." With this electron tube, in a configuration in which the distance between the metasurface of the electron emitter and the electron incident region of the electron multiplier portion is smaller than the width of the electron incident region, it is possible to reliably support the electron emitter and the first mesh electrode and ensure electrical insulation between the metasurface of the electron emitter and the first mesh electrode.

[0009] An electron tube according to one aspect of the present disclosure may be [3] "the electron tube described in [2] above, wherein the first support portion includes a plurality of first claw portions, the second support portion includes a plurality of second claw portions, the spacer has a plurality of first penetration portions with which the plurality of first claw portions engage and a plurality of second penetration portions with which the plurality of second claw portions engage, the first support portion exposing the plurality of second penetration portions on a first surface of the spacer facing the electron emitter, and the second support portion exposing the plurality of first penetration portions on a second surface of the spacer facing the electron multiplier." This electron tube can prevent physical interference between the first support portion and each second claw portion engaging with each second penetration portion, and between the second support portion and each first claw portion engaging with each first penetration portion, thereby reducing the distance between the metasurface of the electron emitter and the electron incidence region of the electron multiplier.

[0010] An electron tube according to one aspect of the present disclosure may be [4] "the electron tube according to the above [1], further comprising a second mesh electrode disposed between the electron emitter and the first mesh electrode." With this electron tube, by applying a potential according to a purpose to each of the first mesh electrode and the second mesh electrode, electrons emitted from the electron emitter in response to incidence of electromagnetic waves can be more reliably made to reach the electron multiplier section, and the electrons can be more reliably multiplied in the electron multiplier section.

[0011] An electron tube according to one aspect of the present disclosure may be [5] "the electron tube according to the above [4], further comprising: a first support portion supporting the electron emitter; a second support portion supporting the first mesh electrode; a third support portion supporting the second mesh electrode; and a spacer formed in a frame shape from an electrically insulating material and disposed between the first mesh electrode and the second mesh electrode." With this electron tube, in a configuration in which the distance between the metasurface of the electron emitter and the electron incident region of the electron multiplier is smaller than the width of the electron incident region, the electron emitter, the first mesh electrode, and the second mesh electrode can be reliably supported, and electrical insulation can be ensured between the metasurface of the electron emitter, and the first mesh electrode and the second mesh electrode.

[0012] An electron tube according to one aspect of the present disclosure may be [6] "the electron tube described in [5] above, wherein the first support portion includes a plurality of first claw portions, the second support portion includes a plurality of second claw portions, the third support portion includes a plurality of third claw portions, the spacer has a plurality of first through-portions with which the plurality of first claw portions are engaged, a plurality of second through-portions with which the plurality of second claw portions are engaged, and a plurality of third through-portions with which the plurality of third claw portions are engaged, the first support portion exposes the plurality of second through-portions on a first surface of the spacer that faces the electron emitter, the second support portion exposes the plurality of first through-portions and the plurality of third through-portions on a second surface of the spacer that faces the electron multiplier, and the third support portion exposes the plurality of second through-portions on the first surface." According to this electron tube, physical interference between each second claw portion engaged with each second penetration portion and the first support portion, physical interference between each second claw portion engaged with each second penetration portion and the third support portion, physical interference between each first claw portion engaged with each first penetration portion and the second support portion, and physical interference between each third claw portion engaged with each third penetration portion and the second support portion can be prevented, thereby reducing the distance between the metasurface of the electron emission portion and the electron incidence region of the electron multiplier portion.

[0013] An electron tube according to one aspect of the present disclosure may be [7] "the electron tube according to any one of the above [1] to [6], in which the electron multiplier section includes a plurality of dynodes." With this electron tube, electrons emitted from the electron emitter in response to incidence of electromagnetic waves can be reliably multiplied.

[0014] According to the present disclosure, it is possible to provide an electron tube that can reliably cause electrons emitted from an electron emitting section to reach an electron multiplier section and reliably multiply the electrons in the electron multiplier section.

[0015] Fig. 1 is a cross-sectional view of an example electron tube. Fig. 2 is a bottom view of the electron emission section shown in Fig. 1. Fig. 3 is a cross-sectional view of a portion of the electron tube shown in Fig. 1. Fig. 4 is an exploded perspective view of a portion of the electron tube shown in Fig. 3. Fig. 5 is a cross-sectional view of a portion of a modified electron tube. Fig. 6 is an exploded perspective view of a portion of the electron tube shown in Fig. 5.

[0016] Hereinafter, an example of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted. [Configuration of an Example Electron Tube]

[0017] 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 5, a second 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 allows "support of the electron multiplier section 4 by the plurality of lead pins 7 and the plurality of wires 70" to be described later.

[0018] 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 will be 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 will be referred to as a second direction D2. In this example, the second direction D2 is a direction perpendicular to the first direction D1.

[0019] The housing 2 includes 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 waves 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 waves 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 within 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 waves W.

[0020] 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.

[0021] 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 31 a of the substrate 31. The metal layer 34 is formed on the surface 31 a of the substrate 31, covering the metasurface 32 and the pair of electrodes 33. The surface 31 a 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.

[0022] 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 having an electric field oscillation direction V in 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. 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 a 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.

[0023] 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 each 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 the 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 of each antenna structure 35. In other words, the metal layer 34 has the function of improving 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 31 a. In this case, a uniform potential is applied to the entire metasurface 32.

[0024] 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 by a plurality of lead pins 7 within the housing 2.

[0025] 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. 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 subsequent-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.

[0026] 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.

[0027] 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 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.

[0028] 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.

[0029] 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.

[0030] 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 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 in 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 separately forming a frame 51 and a plurality of wires 52 and then suspending the plurality of wires 52 around the frame 51 .

[0031] 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 to the electron emitter 3 side and the electron multiplier 4 side.

[0032] 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, multiple connection portions 132, and multiple 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 connection portion 132 extends outward from the frame portion 131 (i.e., opposite the opening 131a). The multiple connection portions 132 are disposed on the spacer 14. Each third claw portion 133 extends from each connection portion 132 in a direction opposite the window portion 21a. More specifically, each third claw portion 133 extends from each connection portion 132 toward the spacer 14.

[0033] 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 an 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 in 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 a frame 61 and a plurality of wires 62 separately, and then suspending the plurality of wires 62 around the frame 61 .

[0034] 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.

[0035] 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. When viewed from a direction parallel to the axis A, the opening 114a overlaps with the metasurface 32 of the electron emitter 3. Each claw portion 115 extends from the frame portion 114 to the side opposite the window portion 21a. More specifically, each claw portion 115 extends from the frame portion 114 toward the spacer 14.

[0036] 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 21 a. 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.

[0037] 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 to engage 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 to engage 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 to engage 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 plurality of first through portions 141 and the plurality of 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.

[0038] 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. As a result, 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 are unitized 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 that is formed from an electrically insulating material, so electrical insulation between the second support plate 112 and the metasurface 32 is ensured.

[0039] 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, 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. 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 is applied to the second mesh electrode 6 that suppresses the progression of electrons from the metasurface 32 side to the first mesh electrode 5 side. 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 relative 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 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.

[0040] 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 are incident on the metasurface 32, electrons are emitted from each antenna structure 35 of the metasurface 32 in response to the incident electromagnetic waves W. The electrons emitted from each antenna structure 35 are accelerated by the electric field of the incident electromagnetic waves W, thereby being given high energy and escaping in random directions. The electrons emitted from the metasurface 32 in response to the incident electromagnetic waves W 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. At this time, even if electrons that could become noise (noise electrons) other than the electrons emitted from each antenna structure 35 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 (e.g., 10 eV or less) is significantly smaller than the energy (e.g., 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.

[0041] When electrons that have passed 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 serves to guide the secondary electrons, from being distorted by the potential of the metasurface 32. This prevents the path of 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 electrically connected to the anode 43 and the lead pin 7 .

[0042] 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, the first mesh electrode 5 may be applied with a potential that 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. This configuration allows for optimal secondary electron multiplication while suppressing the propagation of noise electrons. [Relationship between the metasurface and the electron incidence area]

[0043] 3, the electron multiplier section 4 has an electron incidence region 4a. The electron incidence region 4a is a region onto which electrons emitted from the electron emitter 3 are incident. The electron incidence region 4a is a region that corresponds to at least a portion of the electron emission surface 42a of the first dynode 421 when viewed from the direction in which the metasurface 32 and the first dynode 421 face each other (in the electron tube 1, a direction parallel to the axis A), and is a region of the electron emission surface 42a of the first dynode 421 that is exposed from the electron multiplier section 4 to the metasurface 32 side.

[0044] The distance α between the metasurface 32 and the electron incidence region 4a is smaller than the width β of the electron incidence region 4a. The distance α is, for example, a value equal to or less than half the width β. In the electron tube 1, the distance α is the distance between the metasurface 32 and the electron incidence region 4a in a direction parallel to the axis A, and the width β is the width of the electron incidence region 4a in a direction perpendicular to the axis A. Note that if the distance α varies with position, the distance α is the minimum value of the distance between the metasurface 32 and the electron incidence region 4a in a direction parallel to the axis A. Also, if the width β varies with position, the width β is the minimum value of the width of the electron incidence region 4a in a direction perpendicular to the axis A. [Actions and Effects]

[0045] In the electron tube 1, the distance α between the metasurface 32 of the electron emitter 3 and the electron incidence region 4a of the electron multiplier section 4 is smaller than the width β of the electron incidence region 4a. This allows electrons emitted from the electron emitter 3 in response to the incidence of electromagnetic waves W to reliably reach the electron multiplier section 4. Furthermore, in the electron tube 1, a first mesh electrode 5 is disposed between the electron emitter 3 and the electron multiplier section 4. This allows electrons emitted from the electron emitter 3 in response to the incidence of electromagnetic waves W to reliably reach the electron multiplier section 4 and be reliably multiplied in the electron multiplier section 4 by applying a potential according to the purpose to the first mesh electrode 5. Therefore, the electron tube 1 allows electrons emitted from the electron emitter 3 to reliably reach the electron multiplier section 4 and be reliably multiplied in the electron multiplier section 4.

[0046] In the electron tube 1, the second mesh electrode 6 is disposed between the electron emitter 3 and the first mesh electrode 5. By applying a potential according to the purpose to each of the first mesh electrode 5 and the second mesh electrode 6, the electrons emitted from the electron emitter 3 in response to the incidence of the electromagnetic wave W can be more reliably made to reach the electron multiplier section 4, and the electrons can be more reliably multiplied in the electron multiplier section 4.

[0047] In the electron tube 1, the electron emitter 3, the first mesh electrode 5, and the second mesh electrode 6 are supported by a first support 11, a second support 12, and a third support 13, respectively, and a frame-shaped spacer 14 made of an electrically insulating material is disposed between the first mesh electrode 5 and the second mesh electrode 6. This ensures that the electron emitter 3, the first mesh electrode 5, and the second mesh electrode 6 are reliably supported and that 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 a configuration in which the distance α between the metasurface 32 of the electron emitter 3 and the electron incident region 4a of the electron multiplier 4 is smaller than the width β of the electron incident region 4a.

[0048] In the electron tube 1, the first support 11 and the third support 13 expose a plurality of second through portions 142 on the first surface 14a of the spacer 14, and the second support 12 exposes a plurality of first through portions 141 and a plurality of third through portions 143 on the second surface 14b of the spacer 14. This prevents physical interference between the first support 11 and each second claw portion 122 engaged with each second through portion 142, between the third support 13 and each second claw portion 122 engaged with each second through portion 142, between the second support 12 and each first claw portion 117 engaged with each first through portion 141, and between the second support 12 and each third claw portion 133 engaged with each third through portion 143, and the second support 12, thereby making it possible to reduce the distance α between the metasurface 32 of the electron emitter 3 and the electron incidence region 4a of the electron multiplier 4.

[0049] 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 the electromagnetic wave W can be reliably multiplied. [Configuration of the electron tube according to the modified example]

[0050] 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 5 and 6. 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.

[0051] As shown in FIGS. 5 and 6 , 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. 4 ). 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.

[0052] The first support portion 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 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.

[0053] 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 the window portion 21a.

[0054] 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.

[0055] 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 multiple 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 multiple first through portions 141 from physically interfering with the second support portion 12.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] As described above, in the electron tube 1A, the distance α between the metasurface 32 of the electron emitter 3 and the electron incidence region 4a of the electron multiplier section 4 is smaller than the width β of the electron incidence region 4a. This allows electrons emitted from the electron emitter 3 in response to the incidence of electromagnetic waves W to reliably reach the electron multiplier section 4. Furthermore, in the electron tube 1A, the first mesh electrode 5 is disposed between the electron emitter 3 and the electron multiplier section 4. This allows electrons emitted from the electron emitter 3 in response to the incidence of electromagnetic waves W to reliably reach the electron multiplier section 4 and be reliably multiplied in the electron multiplier section 4 by applying a potential according to the purpose to the first mesh electrode 5. Therefore, according to the electron tube 1A, it is possible to reliably allow electrons emitted from the electron emitter 3 to reach the electron multiplier section 4 and to reliably multiply the electrons in the electron multiplier section 4.

[0061] In the electron tube 1A, the electron emitter 3 and the first mesh electrode 5 are supported by a first support 11 and a second support 12, respectively, and a frame-shaped spacer 14 made of an electrically insulating material is disposed between the electron emitter 3 and the first mesh electrode 5. This ensures that the electron emitter 3 and the first mesh electrode 5 are reliably supported and that electrical insulation between the metasurface 32 of the electron emitter 3 and the first mesh electrode 5 is ensured in a configuration in which the distance α between the metasurface 32 of the electron emitter 3 and the electron incidence region 4a of the electron multiplier 4 is smaller than the width β of the electron incidence region 4a.

[0062] In the electron tube 1A, the first support 11 exposes a plurality of second penetration portions 142 on the first surface 14a of the spacer 14, and the second support 12 exposes a plurality of first penetration portions 141 on the second surface 14b of the spacer 14. This prevents physical interference between the first support 11 and each second claw portion 122 engaged with each second penetration portion 142, and between the second support 12 and each first claw portion 117 engaged with each first penetration portion 141, and makes it possible to reduce the distance α between the metasurface 32 of the electron emitter 3 and the electron incidence region 4a of the electron multiplier 4. [Modification]

[0063] The present disclosure is not limited to the above-described examples. For example, the metasurface 32 described above emits electrons in response to incidence of electromagnetic waves W having a predetermined electric field oscillation direction V. However, the metasurface 32 may emit electrons in response to incidence of electromagnetic waves W, regardless of whether the electromagnetic waves W have the predetermined electric field oscillation direction V.

[0064] The electron multiplier unit 4 does not have to include multiple dynodes 42. As an example, the electron multiplier unit 4 may include a microchannel plate. In this case, it is still possible to reliably multiply 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. When the electron multiplier unit 4 includes a microchannel plate, the electron incidence region 4a is a region that corresponds to at least a portion of the electron incidence surface when viewed from the direction in which the metasurface 32 and the electron incidence surface of the microchannel plate face each other, and is a region of the electron incidence surface that is exposed from the electron multiplier unit 4 to the metasurface 32 side.

[0065] In the above-described electron tube 1, the through portions 141, 142, 143 of the spacer 14 are through holes, but the through portions 141, 142, 143 may be notches that open at least toward the electron emitter 3 and the electron multiplier 4. Similarly, in the above-described electron tube 1A, the through portions 141, 142 of the spacer 14 are through holes, but the through portions 141, 142 may be notches that open at least toward the electron emitter 3 and the electron multiplier 4.

[0066] 1, 1A...electron tube, 3...electron emission section, 4...electron multiplier section, 4a...electron incidence area, 5...first mesh electrode, 6...second mesh electrode, 11...first support section, 12...second support section, 13...third support section, 14...spacer, 14a...first surface, 14b...second surface, 32...metasurface, 42...dynode, 117...first claw portion, 122...second claw portion, 133...third claw portion, 141...first penetration section, 142...second penetration section, 143...third penetration section, W...electromagnetic wave, α...distance, β...width.

Claims

1. An electron tube comprising: an electron emitter including a metasurface that emits electrons in response to incidence of electromagnetic waves; an electron multiplier that multiplies the electrons emitted from the electron emitter; and a first mesh electrode arranged between the electron emitter and the electron multiplier, wherein the electron multiplier has an electron incidence region onto which the electrons emitted from the electron emitter are incident, and the distance between the metasurface and the electron incidence region is smaller than the width of the electron incidence region.

2. The electron tube according to claim 1, further comprising: a first support portion supporting the electron-emitting portion; a second support portion supporting the first mesh electrode; and a spacer formed in a frame shape from an electrically insulating material, disposed between the electron-emitting portion and the first mesh electrode.

3. An electron tube as described in claim 2, wherein the first support portion includes a plurality of first claw portions, the second support portion includes a plurality of second claw portions, the spacer has a plurality of first penetration portions with which the plurality of first claw portions engage and a plurality of second penetration portions with which the plurality of second claw portions engage, the first support portion exposes the plurality of second penetration portions on a first surface of the spacer on the electron emission portion side, and the second support portion exposes the plurality of first penetration portions on a second surface of the spacer on the electron multiplier portion side.

4. The electron tube according to claim 1, further comprising a second mesh electrode disposed between said electron-emitting portion and said first mesh electrode.

5. The electron tube according to claim 4, further comprising: a first support portion supporting the electron-emitting portion; a second support portion supporting the first mesh electrode; a third support portion supporting the second mesh electrode; and a spacer formed in a frame shape from an electrically insulating material and disposed between the first mesh electrode and the second mesh electrode.

6. An electron tube as described in claim 5, wherein the first support portion includes a plurality of first claw portions, the second support portion includes a plurality of second claw portions, the third support portion includes a plurality of third claw portions, the spacer has a plurality of first penetration portions with which the plurality of first claw portions engage, a plurality of second penetration portions with which the plurality of second claw portions engage, and a plurality of third penetration portions with which the plurality of third claw portions engage, the first support portion exposes the plurality of second penetration portions on a first surface of the spacer on the electron emission portion side, the second support portion exposes the plurality of first penetration portions and the plurality of third penetration portions on a second surface of the spacer on the electron multiplier portion side, and the third support portion exposes the plurality of second penetration portions on the first surface.

7. The electron tube according to any one of claims 1 to 6, wherein the electron multiplier section includes a plurality of dynodes.

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