Electron tubes and imaging devices

Abstract

[Solution] The electron tube includes a housing whose interior is maintained at a vacuum and which has a window that transmits electromagnetic waves, an electron emitter disposed within the housing and having a metasurface that emits electrons in response to incident electromagnetic waves, an electron multiplier disposed within the housing and which multiplies the electrons emitted from the electron emitter, and an electron collector disposed within the housing and which collects the electrons multiplied by the electron multiplier. The window contains at least one material selected from quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate.

Description

[Technical field]

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

[0002] A detector for detecting terahertz waves is known (see, for example, Patent Document 1). This detector includes a substrate having a metamaterial structure and an optical sensor. Terahertz waves are incident on the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2016 / 0216201 Summary of the Invention [Problem to be solved by the invention]

[0004] In the detector described in Patent Document 1, when terahertz waves are incident on a substrate having a metamaterial structure, the substrate emits electrons. The electrons emitted from the substrate excite molecules that make up the atmosphere. When excited, the molecules generate light. An optical sensor detects the generated light. With such a detector, it is difficult to detect terahertz waves, which have a weak intensity.

[0005] It is an object of one aspect of the present invention to provide an electron tube in which the detection accuracy of electromagnetic waves is ensured. It is an object of another aspect of the present invention to provide an imaging device in which the detection accuracy of electromagnetic waves is ensured. [Means for solving the problem]

[0006] An electron tube according to one embodiment of the present invention includes a housing, an electron emitter, an electron multiplier, and an electron collector. The housing has a window that is maintained in a vacuum and transmits electromagnetic waves. The electron emitter is disposed within the housing. The electron emitter has a metasurface that emits electrons in response to incidence of electromagnetic waves. The electron multiplier is disposed within the housing. The electron multiplier multiplies electrons emitted from the electron emitter. The electron collector is disposed within the housing. The electron collector collects electrons multiplied by the electron multiplier. The window includes at least one selected from quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate.

[0007] In the above-mentioned one aspect, the window of the housing includes at least one selected from quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate. Therefore, the intensity of the electromagnetic wave guided into the housing, for example, the electromagnetic wave in the frequency band related to terahertz waves to infrared light, can be ensured. When the electromagnetic wave transmitted through the window is incident on the metasurface of the electron emitter, electrons are emitted from the electron emitter. The emitted electrons are multiplied by the electron multiplier in the housing. The multiplied electrons are collected by the electron collector. Therefore, the detection accuracy is ensured even for the above-mentioned electromagnetic waves.

[0008] In one of the above aspects, the electron emitter may have a substrate including a first main surface on which the metasurface is provided and a second main surface opposite to the first main surface. The electron multiplier may have an incident surface on which the electrons emitted from the electron emitter are incident. The substrate may be transparent to electromagnetic waves passing through the window. The substrate may be arranged such that the first main surface faces the incident surface of the electron multiplier and the second main surface faces the window. In this case, in a configuration in which the electromagnetic waves passing through the window and the substrate are incident on the metasurface, the electrons emitted from the metasurface in response to the incidence of the electromagnetic waves are guided to the electron multiplier with a simple configuration.

[0009] In one aspect, the electron multiplier may have an incident surface on which the electrons emitted from the electron emitter are incident. The metasurface may be provided on the window so as to face the incident surface of the electron multiplier. In this case, it is not necessary to separately dispose a substrate on which the metasurface is provided within the housing. This can reduce the size and weight of the electron tube.

[0010] In one of the above aspects, the electron emitter may have a substrate having a first main surface on which the metasurface is provided and a second main surface opposite the first main surface. The electron multiplier may have an incident surface on which electrons emitted from the electron emitter are incident. The substrate may be disposed such that the first main surface faces the window and the incident surface of the electron multiplier. In this case, in a configuration in which an electromagnetic wave that has passed through the window is incident on the metasurface without passing through the substrate, electrons emitted from the metasurface in response to the incidence of the electromagnetic wave are guided to the electron multiplier with a simple configuration.

[0011] In one aspect, the metasurface may be included in a patterned oxide layer or a patterned metal layer, which increases electron emission from the metasurface in response to the incidence of the electromagnetic wave as described above.

[0012] In one embodiment, the electron multiplier and the electron collector may be diodes and integrally configured, which can further reduce the size of the electron tube.

[0013] In one of the above aspects, the electron multiplier may have a plurality of dynodes spaced apart from each other. The electron collector may have an anode or a diode that collects the electrons multiplied by the electron multiplier. In this case, the electrons emitted from the metasurface are multiplied by the plurality of dynodes. This improves the multiplication factor of the electrons collected by the anode or dynode.

[0014] In the above aspect, the electron multiplier section may include a microchannel plate. The electron collector section may include an anode or a diode that collects the electrons multiplied by the electron multiplier section. In this case, the size, weight, and power consumption are reduced and the response speed and gain are improved, compared to the case where a plurality of dynodes are used in the electron multiplier section.

[0015] In one embodiment, the electron multiplier may have a microchannel plate. The electron collector may have a phosphor that receives the electrons multiplied by the electron multiplier and emits light. In this case, the two-dimensional position of the electrons emitted from the metasurface can be detected by the light emitted by the phosphor.

[0016] According to another aspect of the present invention, there is provided an imaging device including the above-mentioned electron tube and an imaging section for capturing an image based on light from a phosphor. In the above-mentioned another aspect, the above-mentioned detection accuracy of the electromagnetic wave is ensured. Effect of the Invention

[0017] According to one aspect of the present invention, there is provided an electron tube that ensures high accuracy in detecting electromagnetic waves, and according to another aspect of the present invention, there is provided an imaging device that ensures high accuracy in detecting electromagnetic waves. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view showing an electron tube according to an embodiment of the present invention. [Diagram 2] FIG. [Diagram 3] A partially enlarged view of the metasurface. [Figure 4] FIG. [Diagram 5] FIG. 13 is a partially enlarged view of an electron tube according to a modified example of the present embodiment. [Figure 6] FIG. 13 is a partially enlarged view of an electron tube according to a modified example of the present embodiment. [Figure 7] FIG. 13 is a partially enlarged view of an electron tube according to a modified example of the present embodiment. [Figure 8] FIG. 11 is a cross-sectional view of an electron tube according to a modified example of the present embodiment. [Figure 9] FIG. 11 is a cross-sectional view of an electron tube according to a modified example of the present embodiment. [Figure 10] FIG. 2 is a perspective cutaway view of a microchannel plate. [Figure 11] FIG. 11 is a partial cross-sectional view of an electron tube according to a modified example of the present embodiment. [Figure 12] FIG. 11 is a cross-sectional view of an electron tube according to a modified example of the present embodiment. [Figure 13] FIG. 13 is a side view of an imaging device according to a modified example of the present embodiment. [Figure 14] FIG. 11 is a cross-sectional view of an electron tube according to a modified example of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same elements or elements having the same functions will be denoted by the same reference numerals, and duplicated descriptions will be omitted.

[0020] First, the configuration of an electron tube according to the present embodiment will be described with reference to Figures 1 to 4. Figure 1 is a cross-sectional view showing an example of an electron tube. Figure 2 is a partially enlarged view showing the example of the electron tube.

[0021] The electron tube 1 is a photomultiplier tube that outputs an electric signal in response to the incidence of electromagnetic waves. When electromagnetic waves are incident on the electron tube 1, the electron tube 1 emits electrons internally and multiplies the emitted electrons. In this specification, the "electromagnetic waves" incident on the electron tube are electromagnetic waves having a frequency band ranging from so-called millimeter waves to infrared light. As shown in FIG. 1, the electron tube 1 includes a housing 10, an electron emission section 20, an electron multiplier section 30, and an electron collection section 40.

[0022] The housing 10 has a valve 11 and a stem 12. The inside of the housing 10 is hermetically sealed by the valve 11 and the stem 12, so that a vacuum is maintained. The vacuum includes not only an absolute vacuum, but also a state in which the housing 10 is filled with a gas at a pressure lower than atmospheric pressure. For example, the inside of the housing 10 is 1×10 -4 ~1×10 -7 The housing 10 is held at a pressure of 1000 MPa (Pa). The bulb 11 has a window 11a that transmits electromagnetic waves. In this embodiment, the housing 10 has a cylindrical shape. The stem 12 forms the bottom surface of the housing 10. The bulb 11 forms the side surface of the housing 10 and the bottom surface facing the stem 12.

[0023] The window 11a constitutes a bottom surface facing the stem 12. The window 11a is, for example, circular in plan view. The window 11a includes at least one selected from quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate. In this embodiment, the window 11a is made of quartz. Note that the frequency characteristics of the transmittance of electromagnetic waves differ depending on the material. Therefore, the optimal material for the window 11a differs depending on the frequency band of the electromagnetic waves passing through the window 11a. For example, quartz is suitable as a material for a member that transmits electromagnetic waves having a frequency band of 0.1 to 5 THz, silicon is suitable as a material for a member that transmits electromagnetic waves having a frequency band of 0.04 to 11 THz and 46 THz or more, magnesium fluoride is suitable as a material for a member that transmits electromagnetic waves having a frequency band of 40 THz or more, germanium is suitable as a material for a member that transmits electromagnetic waves having a frequency band of 13 THz or more, and zinc selenide is suitable as a material for a member that transmits electromagnetic waves having a frequency band of 14 THz or more.

[0024] The electron tube 1 further has a plurality of wires 13 that enable electrical connection between the outside and the inside of the housing 10. The plurality of wires 13 are, for example, lead wires or pins. In this embodiment, the plurality of wires 13 are pins that penetrate the stem 12 and extend from the inside to the outside of the housing 10. At least one of the plurality of wires 13 is connected to various members provided inside the housing 10.

[0025] The electron emitter 20 is disposed in the housing 10 and emits electrons in response to the incidence of electromagnetic waves within the housing 10. The electron emitter 20 has a metasurface 50 and a substrate 21 on which the metasurface 50 is provided. The substrate 21 is transparent to electromagnetic waves passing through the window 11a. In this specification, "transparency" refers to a property of transmitting at least a part of the frequency band of the incident electromagnetic waves. That is, the substrate 21 transmits at least a part of the frequency band of the electromagnetic waves passing through the window 11a. The substrate 21 is made of, for example, silicon. The substrate 21 is rectangular in plan view. The substrate 21 is spaced apart from the window 11a and the electron multiplier 30.

[0026] 2, the substrate 21 includes a pair of principal surfaces 21a and 21b facing each other. The metasurface 50 is provided on the principal surface 21a. For example, when the principal surface 21a constitutes a first principal surface, the principal surface 21b constitutes a second principal surface. The principal surfaces 21a and 21b are disposed parallel to the window 11a.

[0027] The metasurface 50 is included in an oxide layer or a metal layer patterned on the main surface 21a of the substrate 21. The oxide layer is, for example, titanium oxide. The metal layer is, for example, gold. The metasurface 50 is rectangular in plan view. FIG. 3 is a partially enlarged view showing an example of a metasurface. In this embodiment, as shown in FIG. 3, the metal layer constituting the passive type metasurface 50 forms a plurality of antennas 51 on the main surface 21a.

[0028] The smaller the size of the antenna 51, the more sensitive it is to electromagnetic waves with shorter wavelengths, that is, electromagnetic waves with higher frequencies. The metasurface 50 can accommodate a frequency band of about 0.01 to 50 THz, that is, a frequency band from so-called millimeter waves to mid-infrared light, by changing the structure of the antenna 51. The metasurface 50 may be configured to accommodate a frequency band of 0.01 to 10 THz, which corresponds to a frequency band from so-called millimeter waves to terahertz waves. The metasurface 50 may be configured to accommodate a frequency band of 10 to 50 THz, which corresponds to a frequency band from terahertz waves to mid-infrared light. In this embodiment, the size of the metasurface 50 in a plan view is 10×10 mm. The pitch of each antenna 51 is about 20 μm to 30 μm. The metasurface 50 is compatible with electromagnetic waves with a frequency of 0.5 THz.

[0029] In this embodiment, the metasurface 50 is a transmissive metasurface. When an electromagnetic wave is incident on a transmissive metasurface, electrons are emitted from the side opposite to the surface on which the electromagnetic wave is incident. In the electron tube 1, the electromagnetic wave transmitted through the window 11a is incident on the main surface 21b of the substrate 21. The electromagnetic wave transmitted through the substrate 21 is incident on the metasurface 50 provided on the main surface 21a. The metasurface 50 emits electrons in response to the electromagnetic wave transmitted through the window 11a and the substrate 21 and incident thereon.

[0030] The electron multiplier section 30 is disposed in the housing 10 and has an incident surface 35 on which the electrons emitted from the electron emitter 20 are incident. The electron multiplier section 30 multiplies the electrons incident on the incident surface 35. In this embodiment, the main surface 21a of the substrate 21 faces the incident surface 35 of the electron multiplier section 30. That is, the metasurface 50 faces the incident surface 35 of the electron multiplier section 30, and the electrons emitted from the metasurface 50 are incident on the incident surface 35. The main surface 21b of the substrate 21 faces the window 11a of the housing 10.

[0031] In this specification, "α faces β" means that β is located in the normal direction of α rather than the plane tangent to α. In other words, "α faces β" means that when the space is divided into two by the plane tangent to α, β is located on the α side, not the back side of α. For example, in the electron tube 1, as described above, the metasurface 50 faces the incident surface 35 of the electron multiplier section 30. This means that the incident surface 35 of the electron multiplier section 30 is located in the normal direction of the metasurface 50 rather than the plane tangent to the metasurface 50.

[0032] In this embodiment, the electron multiplier section 30 has a multi-stage dynode of a so-called line focus type, as shown in Figures 1 and 4. Figure 4 is a partial exploded view of the electron multiplier section 30, the electron collector section 40, and the periphery thereof.

[0033] In this embodiment, the electron multiplier section 30 has a focusing electrode 31 that focuses electrons, and multiple stages of dynodes 32a, 32b, 32c, 32d, 32e, 32f, 32g, 32h, 32i, and 32j that are spaced apart from each other. The dynode 32a includes the above-mentioned incident surface 35. In this embodiment, the electron multiplier section 30 has ten stages of dynodes 32a to 32j. A circular incident aperture 31a is provided in the center of the focusing electrode 31. The dynodes 32a to 32j are arranged behind the incident aperture 31a. One of the multiple wirings 13 is connected to each of the dynodes 32a to 32j. A predetermined potential is applied to each of the dynodes 32a to 32j through the wiring 13. The dynodes 32a to 32j multiply the electrons that have passed through the incident aperture 31a in accordance with the applied potential.

[0034] The electron collecting unit 40 is disposed within the housing 10, and collects electrons multiplied by the electron multiplier unit 30. In this embodiment, the electron collecting unit 40 has a mesh-shaped anode 41. The anode 41 faces the main surface 21b of the substrate 21. One of the multiple wirings 13 is connected to the anode 41. A predetermined potential is applied to the anode 41 through the wiring 13. The anode 41 captures the electrons multiplied by the dynodes 32a to 32j. The electron collecting unit 40 may have a diode instead of the anode 41.

[0035] In this embodiment, the electron tube 1 has insulating substrates 52, 53 that fix the dynodes 32a-32j and the anode 41 inside the housing 10. The insulating substrates 52, 53 are made of alumina. The insulating substrates 52, 53 face each other. The dynodes 32a-32j have a pair of ends 32k extending in the opposing direction of the insulating substrates 52, 53. The anode 41 has a pair of ends 41k extending in the opposing direction of the insulating substrates 52, 53. The ends 32k, 41k of the dynodes 32a-32j and the anode 41 are inserted into slit-shaped through holes 52a, 53a provided in advance in the insulating substrates 52, 53.

[0036] The electron tube 1 has a shielding plate 36 that surrounds part of the dynodes 32a-32j and the anode 41. The shielding plate 36 prevents light and ions generated by collision of electrons multiplied by the dynodes 32a-32j from scattering within the housing 10. The shielding plate 36 is connected to one of the multiple wirings 13. A predetermined potential is applied to the shielding plate 36 through the wiring 13.

[0037] Next, the operation of the electron tube 1 when an electromagnetic wave is incident thereon will be described. After passing through the window 11a of the housing 10, the electromagnetic wave is incident on the main surface 21b of the substrate 21. The electromagnetic wave incident on the main surface 21b passes through the substrate 21 and is incident on the metasurface 50 provided on the main surface 21a of the substrate 21. The metasurface 50 emits electrons in response to the incidence of the electromagnetic wave. The electrons are emitted toward the incident surface 35 of the electron multiplier section 30.

[0038] Electrons emitted from the metasurface 50 are converged by the focusing electrode 31 and sent to the first-stage dynode 32a (incident surface 35). When electrons are incident on the first-stage dynode 32a (incident surface 35), secondary electrons are emitted from the dynode 32a toward the second-stage dynode 32b. When electrons are incident on the second-stage dynode 32b, secondary electrons are emitted from the dynode 32b toward the third-stage dynode 32c. In this way, electrons are multiplied and sequentially sent from the first-stage dynode 32a to the tenth-stage dynode 32j. That is, cascade multiplication is performed on the electrons emitted from the metasurface 50 in the electron multiplier unit 30. The electrons multiplied by the electron multiplier unit 30 are collected by the anode 41, which is the electron collector 40, and output as an output signal from the anode 41 through the wiring 13.

[0039] Next, an electron tube according to a modification of this embodiment will be described with reference to Fig. 5 and Fig. 6. Fig. 5 and Fig. 6 each show a partially enlarged view of an electron tube according to a modification.

[0040] 5 is generally similar to or the same as the embodiment described above, but differs from the embodiment described above in that the substrate 21 is provided in the window 11a. The following mainly describes the differences between the embodiment described above and the modification.

[0041] In the electron tube 1A shown in FIG. 5, the metasurface 50 is indirectly provided on the window 11a in the housing 10 with the substrate 21 sandwiched therebetween. The substrate 21 is provided on the window 11a in the housing 10. The substrate 21 is transparent to electromagnetic waves passing through the window 11a. That is, the substrate 21 transmits at least a part of the frequency band of the electromagnetic waves passing through the window 11a. The substrate 21 is made of, for example, silicon. The substrate 21 is rectangular in plan view. The substrate 21 is spaced apart from the window 11a and the electron multiplier section 30.

[0042] The substrate 21 includes a principal surface 21a on which the metasurface 50 is provided and a principal surface 21b opposite to the principal surface 21a. The principal surface 21a faces the incident surface 35 of the electron multiplier section 30. That is, the metasurface 50 faces the electron multiplier section 30. The principal surface 21b faces the window 11a of the housing 10. The principal surfaces 21a and 21b are arranged parallel to the window 11a. The principal surface 21b of the substrate 21 and the window 11a are bonded together by a vacuum adhesive L that is transparent to electromagnetic waves passing through the window 11a. The vacuum adhesive L is, for example, a polyethylene resin or epoxy resin adhesive.

[0043] In the electron tube 1A shown in Fig. 5, an electromagnetic wave transmitted through the window 11a is incident on the principal surface 21b of the substrate 21. The electromagnetic wave incident on the principal surface 21b of the substrate 21 is transmitted through the substrate 21 and is incident on the metasurface 50 provided on the principal surface 21a. When the terahertz wave is incident on the metasurface 50, the metasurface 50 emits electrons. The electrons are emitted from the metasurface 50 toward the incident surface 35 of the electron multiplier section 30.

[0044] 6 is generally similar or the same as the embodiment described above, but differs from the embodiment described above in that the metasurface 50 is provided directly on the window 11a without sandwiching a substrate within the housing 10. The following mainly describes the differences between the embodiment described above and the modification.

[0045] In the electron tube 1B shown in Fig. 6, the metasurface 50 faces the incident surface 35 of the electron multiplier section 30. In the electron tube 1B shown in Fig. 6, an electromagnetic wave transmitted through the window 11a is incident on the metasurface 50 provided on the window 11a, and electrons are emitted from the metasurface 50. The electrons are emitted from the metasurface 50 toward the incident surface 35 of the electron multiplier section 30.

[0046] Next, an electron tube according to a modified example of this embodiment will be described with reference to FIG. 7. FIG. 7 is a cross-sectional view of an example of an electron tube. The modified example shown in FIG. 7 is generally similar or the same as the above-described embodiment, but the modified example differs from the above-described embodiment in that the window 11a is provided on the side surface of the housing 10, the incident direction of the electromagnetic wave on the metasurface 50 is different, and the electron multiplier section 30 has a so-called circular gauge type multi-stage dynode. Below, the differences between the above-described embodiment and the modified example will be mainly described.

[0047] 7, the window 11a is provided on a side surface of a cylindrical housing 10. In the electron tube 1C, the main surface 21a of the substrate 21 faces the window 11a and the incident surface 35 of the electron multiplier section 30. In other words, the metasurface 50 provided on the main surface 21a faces the window 11a and the incident surface 35 of the electron multiplier section 30.

[0048] In the electron tube 1C, the metasurface 50 of the electron emitter 20 is a reflective metasurface. When an electromagnetic wave is incident on a reflective metasurface, electrons are emitted from the surface on which the electromagnetic wave is incident. In the electron tube 1C, the electromagnetic wave that has passed through the window 11a is incident on the metasurface 50 provided on the main surface 21a of the substrate 21 without passing through the substrate 21. The metasurface 50 emits electrons in response to the electromagnetic wave that has passed through the window 11a and is incident thereon.

[0049] The electron tube 1C includes a grid 55 between the metasurface 50 and the window 11a. The electromagnetic waves transmitted through the window 11a are transmitted through the grid 55 and enter the metasurface 50. A voltage is applied to the grid 55 through the wiring 13. Due to the influence of the electric field caused by the grid 55, the electrons emitted from the metasurface 50 are guided to the entrance surface 35 of the electron multiplier section 30.

[0050] The electron multiplier section 30 of the electron tube 1C has multiple stages of so-called circular cage type dynodes 32a, 32b, 32c, 32d, 32e, 32f, 32g, 32h, and 32i. The dynode 32a includes an incident surface 35. In this modification, the electron multiplier section 30 has nine stages of dynodes 32a to 32i. The dynodes 32a to 32i are provided along the side surface of the housing 10 so as to wrap around the electron emitter 20. A predetermined potential is applied to each of the dynodes 32a to 32i through the wiring 13. The dynodes 32a to 32i multiply the incident electrons in accordance with the applied potential.

[0051] The electron collecting section 40 of the electron tube 1C is surrounded by curved dynodes 32i. In this modification, the electron collecting section 40 is an anode 41. One of the multiple wirings 13 is connected to the anode 41. A predetermined potential is applied to the anode 41 through the wiring 13. The anode 41 captures the electrons multiplied by the dynodes 32a to 32i.

[0052] In the electron tube 1C shown in Fig. 7, an electromagnetic wave passes through the window 11a of the housing 10, passes through the grid 55, and is incident on the metasurface 50 provided on the main surface 21a of the substrate 21. The metasurface 50 emits electrons in response to the incidence of the electromagnetic wave. The electrons emitted from the metasurface 50 are emitted toward the incident surface 35 of the electron multiplier section 30 due to the influence of the electric field caused by the grid 55.

[0053] Electrons emitted from the metasurface 50 are sent to the first-stage dynode 32a. When electrons are incident on the first-stage dynode 32a (incident surface 35), secondary electrons are emitted from the dynode 32a toward the second-stage dynode 32b. When electrons are incident on the second-stage dynode 32b, secondary electrons are emitted from the dynode 32b toward the third-stage dynode 32c. In this way, the electrons are multiplied from the first-stage dynode 32a to the ninth-stage dynode 32i and sequentially sent around the substrate 21. The electrons multiplied by the electron multiplier 30 are collected by the anode 41, which is the electron collector 40, and output from the anode 41 through the wiring 13 as an output signal.

[0054] Next, an electron tube according to a modified example of this embodiment will be described with reference to Fig. 8. Fig. 8 is a cross-sectional view of an example of an electron tube. The modified example shown in Fig. 8 is generally similar to or the same as the embodiment described above, but differs from the embodiment described above in that the electron multiplier section 30 and the electron collector section 40 are integrally configured by a diode 60. Below, the differences between the embodiment described above and the modified example will be mainly described.

[0055] 8, the electron multiplier section 30 and the electron collector section 40 are diodes 60. In the electron tube 1D, the electron multiplier section 30 and the electron collector section 40 are integrally configured. In the electron tube 1D, the metasurface 50 faces the window 11a.

[0056] In this modification, the diode 60 is an avalanche diode. The diode 60 has a rectangular shape in a plan view, and has a pair of principal surfaces 61 and 62 facing each other. The principal surface 61 is provided with an electron incident surface 61a. The principal surface 61 faces the window 11a of the housing 10. The principal surface 62 faces the stem 12 of the housing 10. The principal surfaces 61 and 62 are arranged parallel to the window 11a, the substrate 21, and the metasurface 50.

[0057] An insulating layer 65 is provided on a main surface 62 of the diode 60. The diode 60 is connected to the stem 12 with the insulating layer 65 sandwiched therebetween. One of the multiple wirings 13 is connected to each of the main surface 61 and the main surface 62.

[0058] A reverse bias voltage is applied to the diode 60 through the wiring 13. In this modification, a reverse bias voltage larger than the breakdown voltage is applied between the main surface 61 side (electron incident surface 61a) and the main surface 62 side of the diode 60. In the electron tube 1D, when electrons emitted from the metasurface 50 of the substrate 21 are incident on the electron incident surface 61a of the diode 60, the incident electrons are multiplied by avalanche multiplication inside the diode 60. The multiplied electrons are output as an output signal through the wiring 13.

[0059] Next, an electron tube according to a modified example of this embodiment will be described with reference to Figs. 9 and 10. Fig. 9 is a cross-sectional view showing an example of an electron tube. The modified example shown in Fig. 9 is generally similar to or the same as the above-mentioned embodiment, but differs from the above-mentioned embodiment in that the electron multiplier section 30 has a microchannel plate 70 instead of the focusing electrode 31 and the dynodes 32a to 32j. Below, differences between the above-mentioned embodiment and the modified example will be mainly described.

[0060] In the electron tube 1E shown in FIG. 9, the microchannel plate 70 is supported by the inner edges of mounting members 71, 72 fixed to the inner wall of the bulb 11. The microchannel plate 70 is disposed between the electron emitting section 20 and the electron collecting section 40. Specifically, the microchannel plate 70 is disposed between the substrate 21 on which the metasurface 50 is provided and the anode 41. The microchannel plate 70 is spaced apart from the substrate 21 and the anode 41. In the electron tube 1E as well, the electron collecting section 40 may have a diode instead of the anode 41.

[0061] FIG. 10 is a perspective cutaway view of an example of a microchannel plate. In this modification, as shown in FIG. 10, the microchannel plate 70 has a base 73, a plurality of channels 74, a partition wall portion 75, and a frame member 76. The base 73 has an input surface 73a and an output surface 73b facing the input surface 73a. The base 73 is formed in a disk shape. The input surface 73a faces the substrate 21. The output surface 73b faces the anode 41, which is the electron collector 40. The input surface 73a and the output surface 73b are arranged parallel to the window 11a, the substrate 21, and the metasurface 50. The anode 41 has a flat plate shape and is arranged parallel to the output surface 73b of the microchannel plate 70.

[0062] The plurality of channels 74 are formed on the base 73 from the input surface 73a to the output surface 73b. Specifically, each channel 74 extends from the input surface 73a to the output surface 73b in a direction perpendicular to the input surface 73a and the output surface 73b. The plurality of channels 74 are arranged in a matrix in a plan view. Each channel 74 has a circular cross section. A partition wall 75 is provided between the plurality of channels 74. In addition, the microchannel plate 70 has a resistive layer and an electron emission layer (not shown) on the surface of the partition wall 75 in the channel 74 in order to function as an electron multiplier. The frame member 76 is provided on the periphery of the input surface 73a and the output surface 73b of the base 73.

[0063] In the electron tube 1E, one of the multiple wirings 13 is connected to each of the mounting members 71 and 72. A voltage is applied to the input surface 73a and the output surface 73b of the microchannel plate 70 through the wiring 13 and the mounting members 71 and 72. Specifically, a potential is applied to the input surface 73a and the output surface 73b so that the output surface 73b has a higher potential than the input surface 73a. When electrons emitted from the metasurface 50 enter the input surface 73a, they are multiplied in the channel 74 and emitted from the output surface 73b. The electrons multiplied by the microchannel plate 70 are collected by the anode 41, which is the electron collector 40, and are output from the anode 41 through the wiring 13 as an output signal.

[0064] Next, an electron tube according to a modified example of this embodiment will be described with reference to Figs. 11 and 12. Fig. 11 is a partial cross-sectional view showing an example of an electron tube. Fig. 12 is a cross-sectional view showing a part of the electron tube shown in Fig. 11. The modified example shown in Figs. 11 and 12 is generally similar or the same as the above-mentioned embodiment, but differs from the above-mentioned embodiment in that the electron tube is a so-called image intensifier. Below, the differences between the above-mentioned embodiment and the modified example will be mainly described.

[0065] In an electron tube 1F shown in Fig. 11, an electron emitter 20, an electron multiplier 30, and an electron collector 40 are disposed within a housing 80. In the electron tube 1F, similarly to the electron tube 1E shown in Fig. 9, the electron multiplier 30 has a microchannel plate 70 instead of the focusing electrode 31 and the dynodes 32a to 32j. In the electron tube 1F, the electron collector 40 has a phosphor 81 instead of the anode 41. In the electron tube 1F, inside the housing 80, the metasurface 50, the microchannel plate 70, and the phosphor 81 are adjacent to each other.

[0066] The housing 80 has a sidewall 82, an entrance window 83 (window 11a), and an exit window 84. The sidewall 82 has a hollow cylindrical shape. The entrance window 83 and the exit window 84 each have a disk shape. The inside of the housing 80 is maintained at a vacuum by hermetically sealing both ends of the sidewall 82 with the entrance window 83 and the exit window 84. For example, the inside of the housing 80 has a volume of 1×10 -5 ~1×10 -7 Held in Pa.

[0067] The side wall 82 is composed of, for example, a side tube 85, a molded member 86 that covers the side of the side tube 85, and a case member 87 that covers the side and bottom of the molded member 86. The side tube 85, the molded member 86, and the case member 87 are hollow cylindrical. The side tube 85 is composed of, for example, ceramic. The molded member 86 is composed of, for example, silicone rubber. The case member 87 is composed of, for example, ceramic.

[0068] A through hole is formed at each of both ends of the molded member 86. One end of the case member 87 is open. A through hole is formed at the other end of the case member 87, the periphery of which is aligned with one of the through holes of the molded member 86. An entrance window 83 is joined to the surface of the molded member 86 around the through hole at one end side of the molded member 86. The entrance window 83 transmits electromagnetic waves, similar to the window 11a of the electron tube 1. The entrance window 83, similar to the window 11a of the electron tube 1, contains at least one material selected from quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate.

[0069] In the electron tube 1F, the metasurface 50 is provided directly on the entrance window 83 in the housing 80. The metasurface 50 faces the microchannel plate 70, which is the electron multiplier section 30. The microchannel plate 70 is disposed between the metasurface 50 and the phosphor 81. The microchannel plate 70 is spaced apart from the metasurface 50 and the phosphor 81.

[0070] At the other end side of the molded member 86, an emission window 84 is fitted into the other through hole of the molded member 86. The emission window 84 is, for example, a fiber plate configured by bundling a large number of optical fibers into a plate shape. The end faces 84a of the optical fibers of the fiber plate on the inner side of the housing 80 are configured to be flush with each other. The end faces 84a are arranged parallel to the metasurface 50.

[0071] The phosphor 81 is disposed on the end face 84a. The phosphor 81 is formed, for example, by applying a fluorescent material to the end face 84a. The fluorescent material is, for example, (ZnCd)S:Ag (zinc cadmium sulfide doped with silver). A metal back layer and a low electron reflectance layer are sequentially laminated on the surface of the phosphor 81. The metal back layer is formed, for example, by vapor deposition of Al, and has a relatively high reflectance for light that has passed through the microchannel plate 70, and a relatively high transmittance for electrons from the microchannel plate 70. The low electron reflectance layer is formed, for example, by vapor deposition of C (carbon), Be (beryllium), or the like, and has a relatively low reflectance for electrons from the microchannel plate 70.

[0072] In the electron tube 1F, similarly to the electron tube 1E, one of the multiple wirings 13 extending outside the housing 80 is connected to each of the mounting members 71, 72 that hold the microchannel plate 70. A voltage is applied to the input surface 73a and the output surface 73b of the microchannel plate 70 through the mounting members 71, 72.

[0073] When electrons emitted from the metasurface 50 enter the input surface 73a, they are multiplied in the channel 74 and emitted from the output surface 73b. In the electron tube 1F, the electrons multiplied in the microchannel plate 70 are collected by the phosphor 81. The phosphor 81 receives the electrons multiplied in the microchannel plate 70 and emits light. The light emitted by the phosphor 81 passes through the fiber plate and is emitted to the outside of the housing 80 from the exit window 84.

[0074] Next, an imaging device including an electron tube according to a modified example of this embodiment will be described with reference to Fig. 13. Fig. 13 is a side view of the imaging device. The imaging device 90 shown in Fig. 13 acquires an image based on electromagnetic waves emitted by an observation target or electromagnetic waves reflected or scattered by the observation target. The imaging device 90 includes, as components, an electron tube 1F which is an image intensifier, an objective lens 91, a relay lens 92, and an imaging unit 93. In the imaging device 90, the above components are joined in the order of the objective lens 91, the electron tube 1F, the relay lens 92, and the imaging unit 93.

[0075] The objective lens 91 is composed of a lens having a refractive index for the electromagnetic waves incident on the electron tube 1. The objective lens 91 guides the electromagnetic waves T from the observation target to the entrance window 83 of the electron tube 1F. The relay lens 92 guides the light emitted from the exit window 84 of the electron tube 1F to the imaging unit 93. The imaging unit 93 captures an image based on the light guided from the relay lens 92, i.e., the light from the phosphor 81. The imaging unit 93 is, for example, a CCD camera.

[0076] Next, an electron tube according to a modified example of this embodiment will be described with reference to Fig. 14. Fig. 14 is a partial cross-sectional view showing an example of an electron tube. The modified example shown in Fig. 14 is generally similar or the same as the above-mentioned embodiment, but differs from the above-mentioned embodiment in that the electron multiplier section 30 has an electron multiplier 95 instead of the focusing electrode 31 and the dynodes 32a to 32j. The following mainly describes the differences between the above-mentioned embodiment and the modified example. The electron multiplier 95 is a so-called channel electron multiplier (CEM).

[0077] In the electron tube 1G shown in FIG. 14, the electron multiplier 95 is supported by a holding member 96 fixed to the inner wall of the bulb 11. The electron multiplier 95 is disposed between the electron emitting section 20 and the electron collecting section 40. Specifically, the microchannel plate 70 is disposed between the window 11a on which the metasurface 50 is provided and the anode 41. The electron multiplier 95 is spaced apart from the window 11a and the anode 41. In the electron tube 1G as well, the electron collecting section 40 may have a diode instead of the anode 41.

[0078] In this modification, the electron multiplier 95 has an input surface 95a and an output surface 95b facing the input surface 95a. The input surface 95a faces the window 11a. The output surface 95b faces the anode 41, which is the electron collector 40. The input surface 95a and the output surface 95b are arranged parallel to the window 11a and the metasurface 50. The anode 41 has a flat plate shape and is arranged parallel to the output surface 95b of the electron multiplier 95. In this embodiment, the distance S between the input surface 95a and the metasurface 50 in a direction perpendicular to the input surface 95a is, for example, 0.615 mm.

[0079] The electron multiplier 95 has a main body 97 and a plurality of channels 98. The main body 97 has a rectangular parallelepiped shape. The plurality of channels 98 are defined by the main body 97. Each channel 98 is formed from the input surface 95a to the output surface 95b. Specifically, each channel 98 extends from the input surface 95a to the output surface 95b in a direction perpendicular to the input surface 95a and the output surface 95b. In the configuration shown in FIG. 14, three channels 98 are arranged in one direction parallel to the input surface 95a.

[0080] Each channel 98 includes an electron incident portion 98a and a multiplication portion 98b. The electron incident portion 98a of each channel 98 has an opening provided on the input surface 95a. The opening of the electron incident portion 98a has a rectangular shape when viewed from a direction perpendicular to the input surface 95a. The electron incident portion 98a gradually narrows in the arrangement direction of the multiple channels 98 from the input surface 95a to the output surface 95b. That is, the electron incident portion 98a has a tapered shape that narrows along a direction perpendicular to the input surface 95a.

[0081] The multiplier section 98b of each channel 98 is formed in a zigzag or wave shape when viewed in a direction parallel to the input surface 95a and perpendicular to the arrangement direction of the multiple channels 98. In other words, the multiplier section 98b has a shape that repeatedly bends in the arrangement direction of the multiple channels 98.

[0082] In the electron tube 1G, two of the multiple wirings 13 are connected to a holding member 96. A voltage is applied to the electron multiplier 95 through the wirings 13 and the holding member 96. Specifically, a potential is applied to the input surface 95a and the output surface 95b such that the output surface 95b has a higher potential than the input surface 95a. A wiring 13 different from the wiring 13 connected to the holding member 96 is connected to the anode 41. The holding member 96 and the anode 41 are electrically insulated from each other by an insulating member 99.

[0083] Electrons emitted from the metasurface 50 enter the opening of the input surface 95a of one of the channels 98, and then enter the multiplier section 98b through the electron entrance section 98a. As a result, the electrons emitted from the metasurface 50 are multiplied in each channel 98 and emitted from the output surface 95b. The electrons multiplied by the electron multiplier 95 are collected by the anode 41, which is the electron collector 40, and are output from the anode 41 through the wiring 13 as an output signal.

[0084] As described above, the electron tubes 1, 1A, 1B, 1C, 1D, 1E, and 1F have a window 11a in the housing 10 that transmits electromagnetic waves. The window 11a includes at least one selected from quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate. Therefore, the intensity of the electromagnetic waves guided into the housing 10 and 80, for example, electromagnetic waves in a frequency band related to terahertz waves to infrared light, can be ensured. When the electromagnetic waves transmitted through the window 11a are incident on the metasurface 50 of the electron emitter 20, electrons are emitted. The emitted electrons are multiplied by the electron multiplier 30 in the housing 10 and 80 and then collected by the electron collector 40. Therefore, detection accuracy is ensured even for the above-mentioned electromagnetic waves having a weak intensity.

[0085] In the electron tubes 1, 1A, 1B, 1D, 1E, and 1F, the electron emitter 20 has a substrate 21 including a main surface 21a on which the metasurface 50 is provided and a main surface 21b facing the main surface 21a. The electron multiplier 30 has an incident surface 35 on which the electrons emitted from the electron emitter 20 are incident. The substrate 21 is transparent to the electromagnetic wave passing through the window 11a. The substrate 21 is arranged so that the main surface 21a faces the incident surface 35 of the electron multiplier 30 and the main surface 21b faces the window 11a. In this case, in a configuration in which the electromagnetic wave passing through the window 11a and the substrate 21 is incident on the metasurface 50, the electrons emitted from the metasurface 50 in response to the incidence of the electromagnetic wave are guided to the electron multiplier 30 in a simple configuration.

[0086] In the electron tubes 1B and 1F, the metasurface 50 is provided on the window 11a so as to face the incident surface 35 of the electron multiplier section 30. With this configuration, it is not necessary to separately dispose a substrate on which the metasurface 50 is provided within the housing 10 or 80. This makes it possible to reduce the size and weight of the electron tube.

[0087] In the electron tube 1C, the substrate 21 is disposed so that the main surface 21a faces the window 11a and the incident surface 35 of the electron multiplier section 30. In this case, in a configuration in which an electromagnetic wave transmitted through the window 11a is incident on the metasurface 50 without transmitting through the substrate 21, electrons emitted from the metasurface 50 in response to the incidence of the electromagnetic wave are guided to the electron multiplier section 30 with a simple configuration.

[0088] The metasurface 50 is included in a patterned oxide layer or a patterned metal layer, which increases the number of electrons emitted from the metasurface 50 in response to the incidence of the electromagnetic wave described above.

[0089] In the electron tube 1D, the electron multiplier section 30 and the electron collector section 40 are integrally formed as a diode 60. With this configuration, the size of the electron tube can be further reduced.

[0090] In the electron tubes 1, 1A, and 1B, the electron multiplier section 30 has a plurality of dynodes 32a to 32j spaced apart from one another. The electron collector section 40 has an anode 41 or a diode that collects electrons multiplied by the electron multiplier section 30. With this configuration, electrons emitted from the metasurface 50 are multiplied by the plurality of dynodes 32a to 32j. This improves the multiplication factor of electrons collected by the anode 41 or the dynodes.

[0091] In the electron tube 1E, the electron multiplier section 30 has a microchannel plate 70. The electron collector section 40 has an anode 41 or a diode that collects the electrons multiplied by the electron multiplier section 30. With this configuration, the size, weight, and power consumption are reduced and the response speed and gain are improved, compared to when multiple dynodes are used in the electron multiplier section 30.

[0092] In the electron tube 1F, the electron multiplier section 30 has a microchannel plate 70. The electron collector section 40 has a phosphor 81 that receives electrons multiplied by the electron multiplier section 30 and emits light. With this configuration, the two-dimensional position of the electrons emitted from the metasurface 50 can be detected by the light emitted by the phosphor 81.

[0093] The imaging device 90 includes an electron tube 1F and an imaging section 93 that captures an image based on the light from the phosphor 81. This configuration ensures the detection accuracy of the electromagnetic waves described above. An image showing the two-dimensional positions of the electrons emitted from the metasurface 50 can be obtained.

[0094] The above describes the embodiments and modifications of the present invention, but the present invention is not necessarily limited to the above-described embodiments and modifications, and various modifications are possible without departing from the spirit of the present invention.

[0095] In the electron tubes 1, 1A, 1B, 1C, 1E, 1F, and 1G, the metasurface 50 may be of a passive type or an active type. FIG. 3 shows a passive type metasurface 50. The electron emitter 20 having a passive type metasurface 50 operates without applying a bias voltage to each antenna 51 of the metasurface 50. That is, the passive type metasurface 50 is a metasurface that assumes that each antenna 51 emits electrons in response to the incidence of an electromagnetic wave when they are at the same potential.

[0096] The electron emitter 20 having an active type metasurface 50 operates in a state where a bias voltage is applied to each antenna 51 of the metasurface 50. In other words, the active type metasurface 50 is a metasurface that is premised on emitting electrons in response to incidence of electromagnetic waves in a state where a bias voltage is applied to each antenna. In this case, a voltage is applied to the metasurface 50 from one of the multiple wirings 13.

[0097] In the electron tubes 1, 1A, 1B, 1C, 1E, and 1G, the electron collecting section 40 may have a diode instead of the anode 41. In this case, the electrons multiplied by the electron multiplier section 30 are collected by the diode.

[0098] In the electron tubes 1, 1A, and 1B, the window 11a may be provided on the side surface of the housing 10 or 80, as in the electron tube 1C. In this case, for example, by changing the arrangement of the dynodes of the electron multiplier section 30, the electrons based on the electromagnetic waves incident from the window 11a can be collected by the electron collector 40.

[0099] In the electron tubes 1, 1A, 1B, 1D, 1E, 1F, and 1G, the metasurface 50 of the electron emitting section 20 may be a so-called reflective metasurface, as in the electron tube 1C. When a reflective metasurface is used, the electron tube is configured such that the metasurface 50 faces the window 11a and also faces the entrance surface 35 of the electron multiplier section 30.

[0100] The housings 10 and 80 are not limited to a cylindrical shape, and may be, for example, a tubular shape having a polygonal cross section.

[0101] The electron tube 1F may be provided with a sweep electrode between the metasurface 50 and the microchannel plate 70. This may constitute a so-called streak tube. In this case, a slit for irradiating the light to be measured and a lens system for forming a slit image may be provided outside the window 11a of the electron tube 1F as a streak tube. This may constitute a so-called streak camera.

[0102] In the imaging device 90, electrons multiplied by the microchannel plate 70 in the electron tube 1F are collected by the phosphor 81, and light emitted by the phosphor 81 is imaged by an imaging section 93 provided outside the electron tube 1F. In this regard, an electron bombardment type solid-state image sensor may be provided inside the electron tube as the electron collecting section 40 instead of the phosphor 81, so that the electron tube functions as an imaging device. In this case, the electrons multiplied by the microchannel plate 70 can be imaged by the electron bombardment type solid-state image sensor without providing an imaging section 93 outside the electron tube. The electron bombardment type solid-state image sensor is, for example, an EBCCD (Electron-Bombarded Charge-Coupled Device). [Explanation of symbols]

[0103] 1,1A,1B,1C,1D,1E,1F,1G...electron tube 10,80…Housing 11a…Window 20...Electron emission part 21...Substrate 21a, 21b...main surface 30...Electron multiplier 35...Incidence plane 40...Electronic collection section 41...Anode 50…Metasurface 60…Diode 70...Microchannel plate 81...Phosphor 90...Imaging device 93...Imaging unit.

Claims

1. a housing whose interior is maintained at a vacuum and which has a window that transmits electromagnetic waves; an electron emitter disposed within the housing and having a metasurface that emits electrons in response to the electromagnetic wave; an electron multiplier section disposed within the housing and configured to multiply electrons emitted from the electron emitting section; an electron collector disposed within the housing and configured to collect the electrons multiplied by the electron multiplier; The metasurface is composed of only a metal layer and faces the electron multiplier section, forming a plurality of antennas each having a size corresponding to the wavelength of the electromagnetic wave and emitting electrons in response to the incidence of the electromagnetic wave in a state of the same potential without the application of a bias voltage; An electron tube, wherein the window comprises at least one material selected from the group consisting of quartz, silicon, germanium, sapphire, zinc selenide, zinc sulfide, magnesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, magnesium oxide, and calcium carbonate.

2. The electron emission portion has a substrate including a first main surface on which the metasurface is provided and a second main surface opposite to the first main surface; the electron multiplier section has an incident surface onto which the electrons emitted from the electron emission section are incident, 2. The electron tube according to claim 1, wherein the substrate is transparent to electromagnetic waves passing through the window, and is arranged such that the first principal surface faces the incident surface of the electron multiplier section and the second principal surface faces the window.

3. the electron multiplier section has an incident surface onto which the electrons emitted from the electron emission section are incident, The electron tube according to claim 1 , wherein the metasurface is provided on the window so as to face the incident surface of the electron multiplier section.

4. The electron emission portion has a substrate having a first main surface on which the metasurface is provided and a second main surface opposite to the first main surface; the electron multiplier section has an incident surface onto which the electrons emitted from the electron emission section are incident, The electron tube according to claim 1 , wherein the substrate is disposed so that the first main surface faces the window and the entrance surface of the electron multiplier section.

5. The electron tube of any one of claims 1 to 4, wherein the metasurface is included in a patterned metal layer.

6. 6. The electron tube according to claim 1, wherein the electron multiplier section and the electron collector section are diodes and are integrally formed.

7. The electron multiplier section has a plurality of dynodes spaced apart from one another, 6. The electron tube according to claim 1, wherein the electron collecting section has an anode or a diode that collects the electrons multiplied by the electron multiplier section.

8. the electron multiplier unit has a microchannel plate, 6. The electron tube according to claim 1, wherein the electron collecting section has an anode or a diode that collects the electrons multiplied by the electron multiplier section.

9. the electron multiplier unit has a microchannel plate, 6. The electron tube according to claim 1, wherein the electron collector section has a phosphor that receives the electrons multiplied by the electron multiplier section and emits light.

10. The electron tube according to claim 9 ; an imaging section configured to capture an image based on the light from the phosphor.

11. 11. The electron tube according to claim 1, wherein the pitch of the antenna is 20 μm to 30 μm.

Images