Electron tubes, tube modules and optical devices

Abstract

An electron tube includes a vacuum container having a translucent substrate; a photoelectric element disposed on the inner surface of the translucent substrate; an anode disposed within the vacuum container; and a prism. The prism has a bottom surface bonded to the outer surface of the translucent substrate; a light incident surface; and a light reflecting surface that further reflects light that enters the photoelectric element via the prism and the translucent substrate and is reflected at the interface between the photoelectric element and the vacuum space, causing the light to enter the photoelectric element again. The light reflecting surface has an outwardly convex curved surface. The light incident surface is located inward of an imaginary spherical surface extending along the light reflecting surface.

Description

Technical Field

[0001] The present invention relates to an electron tube, an electron tube module and an optical device. Background Art

[0002] In the prior art, electron tubes such as photomultiplier tubes are known that detect weak light such as fluorescence generated from a sample. The electron tube includes: a vacuum container having a translucent substrate; and a photocathode disposed on the inner surface of the translucent substrate on the vacuum side. Non-patent document 1 discloses a structure in which a hemispherical prism is disposed on the outer surface of the translucent substrate. In this structure, light incident on the light incident surface of the prism is reflected at the interface between the photocathode and the vacuum space, and then further reflected at the light reflecting surface on the side of the prism opposite to the light incident surface and returned to the photocathode. As a result, the quantum efficiency (QE) of the photocathode is improved.

[0003] Prior art literature

[0004] [Non-patent literature]

[0005] [Non-patent document 1] JBOke and Rudolph E.Schild.A Practical MultipleReflection Technique for Improving the Quantum Efficiency of PhotomultiplierTubes.APPLIED OPTICS Vol.7.No.4 617-622(1968) Summary of the Invention

[0006] Problems to be solved by the invention

[0007] However, in the structure disclosed in non-patent document 1, the light incident surface of the prism is along a hemispherical surface, and the distance between the light incident surface of the prism and the photoelectric surface is relatively large. Therefore, it is sometimes impossible to make the light source of the detected light sufficiently close to the photoelectric surface. For example, when the prism is hemispherical, the distance from the light incident surface of the prism to the photoelectric surface becomes larger. Therefore, when the detected light is divergent light, it is assumed that the detected light (primary light) does not completely enter the photoelectric surface. In addition, when the prism is hemispherical, it is difficult for the light reflected from the center of the photoelectric surface (the center of the sphere corresponding to the prism shape) to return to the photoelectric surface again via the light reflecting surface. Therefore, when the detected light is convergent light, from the perspective of obtaining good quantum efficiency, it is preferred to align the focus of the detected light with the photoelectric surface. However, since the light source cannot be made sufficiently close to the photoelectric surface, it is sometimes difficult to adjust the focus position as described above. Therefore, in the structure disclosed in non-patent document 1, there is room for improvement in terms of improving the quantum efficiency of the photoelectric surface.

[0008] Therefore, an object of the present invention is to provide an electron tube, an electron tube module and an optical device that can effectively improve the quantum efficiency of a photoelectric element.

[0009] Methods for solving problems

[0010] An electron tube according to one aspect of the present invention includes: a vacuum container having a light-transmitting substrate defining a vacuum space; a photoelectric element provided on a surface of the light-transmitting substrate facing the vacuum space, i.e., an inner surface, for emitting photoelectrons into the vacuum space in response to light incident through the light-transmitting substrate; an electron detecting portion provided within the vacuum container for detecting electrons originating from the photoelectrons; and a prism bonded to an outer surface of the light-transmitting substrate opposite to the inner surface, the prism having a bottom surface bonded to the outer surface of the light-transmitting substrate; a light incident surface having a light incident portion for incident light; and a light reflecting surface for further reflecting light incident on the light incident portion and reflected at an interface between the photoelectric element and the vacuum space, thereby causing the light to re-enter the photoelectric element, the light reflecting surface having a curved surface shape convex outwardly, the light incident portion being located inward of an imaginary spherical surface extending along the light reflecting surface.

[0011] According to the above-described electron tube, light incident from the light incident portion of the prism and reflected at the interface between the photoelectric surface and the vacuum space can be further reflected by the light reflecting surface of the prism and re-incident upon the photoelectric surface. As a result, the amount of light to be detected absorbed by the photoelectric surface can be increased. The light reflecting surface has a curved surface that is convex outward, so that light traveling from the photoelectric surface toward the light reflecting surface can be appropriately returned to the photoelectric surface. Furthermore, the light incident portion of the prism is located further inboard of an imaginary spherical surface along the light reflecting surface. This allows the light source to be closer to the photoelectric surface than, for example, when the prism is hemispherical (i.e., when the light incident portion (light incident surface) is formed by the surface of a hemispherical prism). As a result, when the light to be detected is divergent, excessive diffusion of the light to be detected can be suppressed during its journey from the light incident portion to the photoelectric surface, allowing the light to be detected (including light reflected by the light reflecting surface) to be appropriately incident upon the photoelectric surface. Furthermore, when the light to be detected is converging, it is easier to adjust the focus of the light to be detected near the photoelectric surface. As described above, according to the electron tube, the quantum efficiency of the photoelectric element can be effectively improved.

[0012] The photoelectric element may be formed in a flat plate shape along the inner surface of the light-transmitting substrate. In this case, the photoelectric element can be easily formed by forming a film on the inner surface of the light-transmitting substrate.

[0013] The photoelectric element may be formed on a portion of the inner surface of the light-transmitting substrate. In this case, the material cost of the photoelectric element can be reduced compared to the case where the photoelectric element is formed on the entire inner surface of the light-transmitting substrate.

[0014] The light incident portion can also be formed into a flat surface. Thus, for example, by linearly cutting a hemispherical prism component, a prism can be manufactured relatively simply. Furthermore, the light incident portion can also have a curved surface that convexly projects outward. Alternatively, the light incident portion can also have a curved surface that convexly projects inward.

[0015] The light incident portion may be formed entirely of the light incident surface. In this case, the light incident surface can be formed as a uniform surface, so the structure of the light incident surface can be simplified.

[0016] The light incident portion may be formed of a recessed portion opened in a portion of the light incident surface. In this case, for example, by inserting the tip (light source) of a light guide such as an optical fiber into the recessed portion, the light source can be brought closer to the photoelectric surface.

[0017] Alternatively, an antireflection coating may be provided on at least the light incident portion of the light incident surface. In this case, the antireflection coating effectively reduces reflection losses of the detection light in the light incident portion (light incident surface). As a result, the absorption of the detection light by the photoelectric element can be increased, further effectively improving the quantum efficiency of the photoelectric element.

[0018] A reflective film can also be provided on the light-reflecting surface. In this case, the reflective film can reduce light transmission loss (the component that transmits through the light-reflecting surface) on the light-reflecting surface. This can suppress the reduction in the amount of light that is reflected from the light-reflecting surface and re-enters the photoelectric surface, thereby more effectively improving the quantum efficiency of the photoelectric surface.

[0019] The prism may also have a pair of side surfaces, which are arranged between the light incident surface, the light reflecting surface, and the bottom surface, and are opposite to each other across the light incident surface and the light reflecting surface when viewed from a direction opposite to the bottom surface. Such a pair of side surfaces functions as a surface for supporting (holding) the prism. For example, an operator can hold the prism by clamping the pair of side surfaces. This improves the operability of, for example, when the prism is mounted on a translucent substrate.

[0020] The electron tube may further include an electron multiplying unit disposed within the vacuum chamber to multiply photoelectrons. Alternatively, the electron detection unit may be a semiconductor element that multiplies photoelectrons. With this configuration, even when the light being detected is weak (e.g., fluorescence or Raman scattered light secondary to the excitation light irradiated on the sample being measured), the electron detection unit can appropriately detect electrons corresponding to the light being detected.

[0021] The curved surface shape of the light reflecting surface may also be a curved surface shape approximately constituted by a plurality of planes. In this case, the light reflecting surface can be formed simply by processing the prism member in a straight line, so processing becomes easy.

[0022] A electron tube module according to another aspect of the present invention includes the electron tube and a housing for housing the electron tube. The housing has a wall portion with an opening formed therein. The electron tube is arranged in the housing such that light introduced through the opening is incident on a light incident surface.

[0023] The electron tube module includes the electron tube, thereby achieving the same effects as the electron tube. Furthermore, the electron tube can be appropriately protected by housing the electron tube in the housing.

[0024] The light incident surface may be formed into a flat surface and arranged parallel to the wall portion, thereby facilitating the positioning of the electron tube within the housing.

[0025] According to another embodiment of the present invention, an optical device is provided, comprising: the above-mentioned electron tube; and a light source configured to output light irradiated onto a measurement object, wherein the electron tube is configured so that detected light generated by irradiating the light onto the measurement object is incident on a light incident surface.

[0026] The optical device includes the electron tube as a detection unit for detecting the light to be detected, thereby achieving the same effect as the electron tube.

[0027] The electron tube can also be configured so that part or all of the detection light entering the photoelectric element via the prism and the translucent substrate is totally reflected at the interface between the photoelectric element and the vacuum space. This configuration increases the amount of detection light absorbed by the photoelectric element by returning to the photoelectric element after total reflection, effectively improving the quantum efficiency of the photoelectric element.

[0028] Effects of the Invention

[0029] According to the present invention, an electron tube, an electron tube module, and an optical device capable of effectively improving the quantum efficiency of a photoelectric element can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a cross-sectional view of the electron tube according to the first embodiment.

[0031] Figure 2 yes Figure 1 A top view of the electron tube.

[0032] Figure 3 yes Figure 1 A three-dimensional diagram of the prism included in the electron tube.

[0033] Figure 4 Yes Figure 1 Schematic diagram of the optical path of the detected light in the electron tube.

[0034] Figure 5 This is a schematic diagram for explaining the conditions under which the light to be detected is totally reflected at the interface between the photoelectric surface and the vacuum space.

[0035] Figure 6 This is a cross-sectional view of an electron tube according to a second embodiment.

[0036] Figure 7 This is a perspective view of a electron tube module according to the embodiment.

[0037] Figure 8 This is a partial cross-sectional view of the electron tube module.

[0038] Figure 9 This is a schematic structural diagram of a first example of an optical device.

[0039] Figure 10 This is a schematic structural diagram of a second example of an optical device.

[0040] Figure 11 This is a schematic structural diagram of the third example of the optical device.

[0041] Figure 12 It is a perspective view showing a first modified example of the prism.

[0042] Figure 13It is a cross-sectional view showing a second modified example of the prism.

[0043] Figure 14 It is a cross-sectional view showing a third modified example of the prism.

[0044] Figure 15 It is a cross-sectional view showing a fourth modified example of the prism.

[0045] Figure 16 It is a cross-sectional view showing a fifth modified example of the prism. DETAILED DESCRIPTION

[0046] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0047] [First embodiment]

[0048] like Figure 1 and Figure 2 As shown in FIG. 1 , the electron tube 1A of the first embodiment is a photomultiplier tube having an electron multiplying function (an electron multiplying section 9 described later). Figure 1 and Figure 2 In the diagram, the Z-axis direction is the direction in which the electron tube 1A extends (i.e., the direction in which the side tube 2, described later, extends). The Y-axis direction is the direction in which a pair of side surfaces 16d of the prism 16, described later, face each other. The X-axis direction is a direction perpendicular to the Y-axis and Z-axis directions. When viewed from the Z-axis direction, the X-axis direction is also a direction along the optical axis (central axis) of the detection light L, described later.

[0049] The electron tube 1A includes a metal side tube 2 having a generally cylindrical shape. A translucent substrate 3, which has good translucency for incident light (light to be detected), is airtightly secured to the upper end of the side tube 2. In this embodiment, the translucent substrate 3 is formed in a circular plate shape, with its peripheral edge secured to the upper end of the side tube 2. A circular stem 4 is disposed at the lower open end of the side tube 2. A plurality of conductive stem pins 5, spaced apart from one another along the circumference, are airtightly secured to the stem 4. Each stem pin 5 is inserted through an opening 4a formed at a corresponding position on the upper and lower surfaces of the stem 4. Furthermore, a metal annular side tube 6 is airtightly secured to the stem 4 from the side. A flange 2a formed at the lower end of the side tube 2 and a flange 6a formed at the upper end of the annular side tube 6 are welded together, thereby airtightly securing the side tube 2 and the annular side tube 6 to one another. In this manner, the vacuum container 7 , the interior of which is maintained in a vacuum state, is formed by the side tubes 2 , the light-transmitting substrate 3 , and the stem 4 .

[0050] A photoelectric element 8, an electron multiplying section 9 and an anode 10 (electron detection section) are provided in the vacuum container 7. The photoelectric element 8 is provided on the inner surface 3a of the translucent substrate 3 on the vacuum space S side. The photoelectric element 8 can be provided directly on the inner surface 3a of the translucent substrate 3, or it can be provided on the inner surface 3a of the translucent substrate 3 via a base layer (such as oxides such as manganese oxide, magnesium oxide, titanium oxide, etc.). The photoelectric element 8 emits photoelectrons into the vacuum space S according to the light incident through the translucent substrate 3. The photoelectric element 8 is a so-called transmission-type photoelectric element, which receives light on the upper surface on the translucent substrate 3 side and emits photoelectrons from the lower surface on the vacuum space S side. The photoelectric element 8 can be formed of materials such as GaAsP, GaAs, InGaAs, etc. Alternatively, the photoelectric element 8 can also be an alkali antimonide photoelectric element or an alkali telluride photoelectric element.

[0051] Here, from the perspective of increasing the amount of light to be detected absorbed by the photoelectric element 8, the thickness of the photoelectric element 8 is preferably large. On the other hand, from the perspective of improving the efficiency of electron emission from the photoelectric element 8 to the vacuum space S, the thickness of the photoelectric element 8 is preferably small. The electron tube 1A includes a prism 16 (described later), which effectively increases the amount of light to be detected absorbed by the photoelectric element 8. Therefore, the thickness of the photoelectric element 8 can be reduced accordingly. Based on the above, when the photoelectric element 8 is formed of GaAsP, GaAs, or InGaAs, the film thickness of the photoelectric element 8 can also be 3 μm or less. Furthermore, when the photoelectric element 8 is an alkali antimonide photoelectric element or an alkali telluride photoelectric element, the film thickness of the photoelectric element 8 can be set to 0.5 μm or less.

[0052] The photoelectric surface 8 is formed in a flat plate shape along the inner surface 3a of the translucent substrate 3. In this case, the photoelectric surface 8 can be easily formed by forming a film on the inner surface 3a of the translucent substrate 3. In addition, the photoelectric surface 8 is formed on a portion of the inner surface 3a of the translucent substrate 3. As an example, when observed from the thickness direction (Z-axis direction) of the translucent substrate 3, the photoelectric surface 8 is formed in a circular shape centered on the approximate center position of the translucent substrate 3 and having a radius smaller than that of the translucent substrate 3. That is, the photoelectric surface 8 is not provided on the outer edge portion of the inner surface 3a of the translucent substrate 3. In this case, compared with the case where the photoelectric surface 8 is formed on the entire inner surface 3a of the translucent substrate 3, the material cost of the photoelectric surface 8 can be reduced.

[0053] The electron multiplier section 9 multiplies the photoelectrons emitted from the photoelectrode 8. In this embodiment, the electron multiplier section 9 is formed into a block by stacking multiple stages of thin, plate-like dynode plates 11 having multiple electron multiplying holes. The block is then mounted on the upper surface of the stem 4. Each dynode plate 11 has an outwardly protruding dynode plate connection piece 11a formed at its edge. The tip of a designated stem pin 5, inserted into the stem 4, is welded to the lower surface of each dynode plate connection piece 11a. This electrically connects each dynode plate 11 to each stem pin 5.

[0054] The anode 10 detects electrons originating from photoelectrons emitted from the photoelectric element 8. Here, the electrons originating from the photoelectrons emitted from the photoelectric element 8 may be the photoelectrons themselves or electrons secondary generated based on the photoelectrons. In this embodiment, the anode 10 detects secondary electrons multiplied by the electron multiplier 9 (i.e., electrons secondary generated based on the photoelectrons emitted from the photoelectric element 8). In this embodiment, the anode 10 is disposed one stage higher than the final dynode plate 11b and is configured as a flat anode component for extracting the secondary electrons emitted from the final dynode plate 11b as an output signal.

[0055] Between the photoelectric surface 8 and the electron multiplying section 9, a flat-plate-shaped converging electrode 12 is provided for converging the photoelectrons emitted from the photoelectric surface 8 and guiding them to the electron multiplying section 9. A tube base pin 5 (not shown) is welded and fixed to the converging electrode 12. Thus, the converging electrode 12 is electrically connected to the tube base pin 5. In addition, an anode pin 5A, which is one of the tube base pins 5, is welded and fixed to the anode 10. Thus, the anode 10 is electrically connected to the anode pin 5A. Moreover, by connecting to a power supply circuit (for example, Figure 8 A voltage is applied to the base pin 5 connected to the circuit board 41 shown in FIG. 1 , so that the photoconductor 8 and the focusing electrode 12 are at the same potential and the potential of each dynode plate 11 increases from the upper stage to the lower stage. Furthermore, a voltage is applied so that the anode 10 has a higher potential than the last-stage dynode plate 11b.

[0056] The shaft tube seat 4 is formed into a three-layer structure consisting of a base material 13, an upper pressing material 14 bonded to the upper side (inner side) of the base material 13, and a lower pressing material 15 bonded to the lower side (outer side) of the base material 13. The aforementioned annular side tube 6 is fixed to the side of the tube seat 4. In this embodiment, the tube seat 4 is fixed to the annular side tube 6 by bonding the side surface of the base material 13 to the inner wall surface of the annular side tube 6.

[0057] The electron tube 1A includes a prism 16 as a transparent structure outside the vacuum container 7. The prism 16 is bonded to the outer surface 3b on the opposite side of the inner surface 3a of the light-transmitting substrate 3. Figures 1 to 3 As shown, the prism 16 has a bottom surface 16a, a light incident surface 16b, a light reflecting surface 16c, and a pair of side surfaces 16d. The material of the prism 16 is, for example, acrylic resin, glass, or the like.

[0058] The bottom surface 16a is a surface that is bonded to the outer surface 3b of the translucent substrate 3. The bottom surface 16a and the outer surface 3b of the translucent substrate 3 can be bonded to each other by an optical adhesive. Alternatively, the bottom surface 16a and the outer surface 3b of the translucent substrate 3 can be bonded to each other by optical contact. The bottom surface 16a is formed into a plane (flat surface). The bottom surface 16a is formed into a roughly rectangular shape. The light incident surface 16b is connected to one end in the longitudinal direction (X-axis direction) of the bottom surface 16a. The light reflecting surface 16c is connected to the other end in the longitudinal direction of the bottom surface 16a. The side surfaces 16d are respectively connected to the two ends in the short side direction (Y-axis direction) of the bottom surface 16a.

[0059] The length of the bottom surface 16a in the longitudinal direction is substantially the same as the diameter of the light-transmitting substrate 3. Figure 2 As shown, when viewed from a direction perpendicular to the bottom surface 16a (the Z-axis direction), the positions of both ends of the bottom surface 16a in the longitudinal direction coincide with the positions of the edge of the light-transmitting substrate 3. One end of the bottom surface 16a in the longitudinal direction (i.e., the end connected to the light incident surface 16b) is not located further inward than the edge of the light-transmitting substrate 3. As a result, when the electron tube 1A is arranged in the housing 31 of the electron tube module 30 described later, the light incident surface 16b can abut against the inner side surface 32c of the top wall 32 of the housing 31 (see FIG. 1 ). Figure 8 However, if it is not necessary to position the electron tube 1A within the housing 31, the end of the bottom surface 16a connected to the light incident surface 16b may be located further inward from the edge of the translucent substrate 3. Furthermore, in this embodiment, as an example, one longitudinal end of the bottom surface 16a has a rectangular corner. Meanwhile, the other longitudinal end of the bottom surface 16a has an arc shape that follows the edge of the translucent substrate 3 because the light reflecting surface 16c connected thereto has a curved surface.

[0060] The light incident surface 16b is the detection light L (refer to Figure 4 ) incident surface. Light incident surface 16b is formed into a planar shape (flat surface). When viewed in the direction of the short side of bottom surface 16a (the Y-axis direction), light incident surface 16b is inclined relative to bottom surface 16a. The angle between bottom surface 16a and light incident surface 16b is an acute angle. In this embodiment, the entire light incident surface 16b constitutes the light incident portion into which detection light L is incident.

[0061] An anti-reflection film 17 is provided on the light incident surface 16b. By providing the anti-reflection film 17 so as to cover the light incident surface 16b, the reflection loss of the detected light on the light incident surface 16b can be effectively reduced. The anti-reflection film 17 can be a single-layer film or a multi-layer film. When the anti-reflection film 17 is formed as a single-layer film, the anti-reflection film 17 can be formed of, for example, MgF2. When the anti-reflection film 17 is formed as a multi-layer film, the anti-reflection film 17 can be formed of, for example, TiO2, Ta2O5, SiO2, Al2O3, MgF2, etc. As a film forming method of the anti-reflection film 17, for example, vacuum evaporation, sputtering, etc. can be used.

[0062] The light reflecting surface 16c further reflects light that has entered the photoelectric surface 8 via the prism 16 and the translucent substrate 3 and reflected at the interface between the photoelectric surface 8 and the vacuum space S, thereby functioning as a reflecting portion that causes the light to enter the photoelectric surface 8 again. The light reflecting surface 16c is formed into a curved surface shape that is convex outward. For example, the light reflecting surface 16c is formed into a dome shape (a curved surface shape such as a spherical or parabolic shape).

[0063] Here, Figure 1 The imaginary line in represents an imaginary spherical surface P along the light-reflecting surface 16c. Furthermore, in the case where the light-reflecting surface 16c is a curved surface other than a spherical surface, the imaginary spherical surface P is a spherical surface that is approximately the same as the light-reflecting surface 16c and does not need to completely overlap with the light-reflecting surface 16c. The light-incident surface 16b is located closer to the inside of the imaginary spherical surface P. In other words, in this embodiment, the light-incident surface 16b is not smoothly continuous with the light-reflecting surface 16c. That is, the light-incident surface 16b is located on the inside compared to the case where the light-incident surface is assumed to be a surface that is smoothly continuous with the light-reflecting surface 16c. According to the above structure, the distance between the light-incident surface 16b and the photoelectric surface 8 is shorter than when the prism is simply formed into a hemispherical shape.

[0064] The light reflecting surface 16c is provided with a reflective film 18 for increasing the reflectivity of light. The reflective film 18 can be formed of, for example, aluminum, an aluminum alloy, silver, a silver alloy, gold, a dielectric multilayer film, or the like.

[0065] A pair of side surfaces 16d are provided between the light incident surface 16b, the light reflecting surface 16c and the bottom surface 16a. When viewed from the direction opposite to the bottom surface 16a (Z-axis direction), the pair of side surfaces 16d are opposite to each other across the light incident surface 16b and the light reflecting surface 16c. More specifically, one side surface 16d is provided so as to connect one end of the light incident surface 16b and the light reflecting surface 16c in the Y-axis direction and one end of the bottom surface 16a in the Y-axis direction. The other side surface 16d is provided so as to connect the other end of the light incident surface 16b and the light reflecting surface 16c in the Y-axis direction and the other end of the bottom surface 16a in the Y-axis direction. Each side surface 16d is a surface intersecting the Y-axis direction. In this embodiment, each side surface 16d is orthogonal to the Y-axis direction and is along the XZ plane. Such a pair of side surfaces 16d functions as a surface for supporting (holding) the prism 16. In addition, positioning the center of the prism 16 is also facilitated by the pair of side surfaces 16d. Furthermore, when the electron tube 1A is modularized, the pair of side surfaces 16d can also be used to secure the electron tube 1A (prism 16) to the housing. For example, an operator can hold the prism 16 by sandwiching the pair of side surfaces 16d. This improves workability, for example, when attaching the prism 16 to the translucent substrate 3.

[0066] Reference Figure 4 , the principle of improving the quantum efficiency of the photoelectric element 8 by the prism 16 is explained. Figure 4 , a portion of the side tube 2, the light-transmitting substrate 3, the photoelectric element 8, and the prism 16 are schematically shown among the components of the electron tube 1A. Figure 4 As shown in FIG, the light to be detected L is the light directed toward the light incident surface 16b of the prism 16. The light to be detected L can be parallel light or non-parallel light. Figure 4 In the example of FIG. 5 , the light to be detected L is light (non-parallel light) focused by a lens (not shown) or the like so as to have a focal point substantially at the center of the photoelectric surface 8 .

[0067] like Figure 4As shown, the detection light L passes through the prism 16 and the translucent substrate 3 and enters the photoelectric element 8. In this embodiment, the electron tube 1A is configured so that part or all of the detection light L is totally reflected relative to the optical axis of the detection light L at the interface between the inner surface 8a of the photoelectric element 8 on the vacuum space S side and the vacuum space S (i.e., so as to satisfy Equation (3) described later). In this case, the detection light L is totally reflected at the interface between the inner surface 8a of the photoelectric element 8 and the vacuum space S and travels toward the light reflecting surface 16c of the prism 16. This detection light L is reflected by the light reflecting surface 16c of the prism 16, which is provided with the reflective film 18, and then travels back toward the photoelectric element 8. Furthermore, when the light reflecting surface 16c is formed into a perfect hemispherical shape, it is possible that most of the light reflected by the light reflecting surface 16c does not return to the photoelectric element 8. Therefore, the curvature of the light reflecting surface 16c can also be set according to the angle of the expected incident light (light incident on the light incident surface 16b). That is, the curvature of the light-reflecting surface 16c can also be optimized so as to maximize the efficiency (incident amount) of light reflected from the light-reflecting surface 16c incident on the photoelectric surface 8. More specifically, in order to ensure that most of the light totally reflected at the interface between the photoelectric surface 8 and the vacuum space S is appropriately incident on the photoelectric surface 8 again, the curvature, position, size, etc. of the light-reflecting surface 16c can be designed based on the convergence angle or divergence angle of the light incident on the light-incident surface 16b, or the diameter of the incident light on the photoelectric surface 8.

[0068] Reference Figure 5, the conditions for causing a portion or all of the detection light L to be totally reflected at the interface between the inner surface 8a of the photoelectric surface 8 and the vacuum space S are described. Here, the refractive index of the prism 16 is set to n1 (>1), the refractive index of the transparent substrate 3 is set to n2 (>1), and the refractive index of the photoelectric surface 8 is set to n3 (>1). The refractive index of the vacuum space S is 1. In addition, the incident angle of the detection light L incident from the prism 16 to the transparent substrate 3 is set to θ1, the incident angle of the detection light L incident from the transparent substrate 3 to the photoelectric surface 8 is set to θ2, and the incident angle of the detection light L incident from the photoelectric surface 8 to the vacuum space S is set to θ3. In addition, the critical angle of the detection light L incident from the photoelectric surface 8 to the vacuum space S (the minimum incident angle at which total reflection occurs at the interface between the photoelectric surface 8 and the vacuum space S) is set to θ0. In this case, the following equations (1) and (2) hold. Furthermore, the condition for causing the detected light L to be totally reflected at the interface between the inner surface 8a of the photoelectric surface 8 and the vacuum space S is expressed by the following equation (3). Therefore, in order to cause the detected light L to be totally reflected at the interface between the inner surface 8a of the photoelectric surface 8 and the vacuum space S, the electron tube 1A only needs to be arranged relative to the optical axis of the detected light L in such a manner that θ3, which is determined based on the incident angle θ1 of the detected light L relative to the translucent substrate 3, satisfies the following equation (3). However, all components of the detected light L do not necessarily need to satisfy the following equation (3). Even in the case where the configuration of the electron tube 1A is adjusted so that a portion of the detected light L satisfies the following equation (3), the efficiency of light incident on the photoelectric surface 8 can be improved.

[0069] n1sinθ1=n2sinθ2=n3sinθ3…(1)

[0070] n3sinθ0=1…(2)

[0071] θ3≧θ0…(3)

[0072] According to the electron tube 1A described above, light incident from the light incident portion of prism 16 (light incident surface 16b in this embodiment) and reflected at the interface between photoelectric element 8 and vacuum space S can be further reflected by light reflecting surface 16c of prism 16 and re-incident upon photoelectric element 8. As a result, the amount of detection light L absorbed by photoelectric element 8 can be increased. The outwardly convex curved shape of light reflecting surface 16c allows light traveling from photoelectric element 8 toward light reflecting surface 16c to be appropriately returned to photoelectric element 8. Furthermore, the light incident portion of prism 16 (light incident surface 16b) is located further inward than the imaginary spherical surface P extending along light reflecting surface 16c. This allows the light source to be brought closer to photoelectric element 8 than, for example, when prism 16 is hemispherical (i.e., when the light incident portion is formed by the surface of a hemispherical prism). As a result, when the detection light L is divergent light, excessive diffusion of the detection light L during its journey from the light incident surface 16 b to the photoelectric surface 8 can be suppressed, and the detection light L (including light reflected by the light reflecting surface 16 c) can be appropriately incident on the photoelectric surface 8. Furthermore, when the detection light L is convergent light, the focus of the detection light L can be easily adjusted near the photoelectric surface 8. As described above, according to the electron tube 1A, the quantum efficiency of the photoelectric surface 8 can be effectively improved.

[0073] Furthermore, the light incident portion (light incident surface 16b) is formed into a planar shape (flat surface). This allows for relatively simple production of the prism 16, for example, by linearly cutting a hemispherical prism member. Furthermore, positioning of the electron tube 1A in the electron tube module 30 described later can be facilitated.

[0074] Furthermore, the entire light incident surface 16b constitutes the light incident portion. In this case, the light incident surface 16b can be formed as a uniform surface (a flat surface in this embodiment), thereby simplifying the structure of the light incident surface 16b. In other words, there is no need to machine a special area for light incidence on a portion of the light incident surface 16b, making it easier to machine the light incident surface 16b.

[0075] Furthermore, an antireflection film 17 is provided on the light incident surface 16b. In this case, the antireflection film 17 effectively reduces reflection losses of the detection light L on the light incident surface 16b. Specifically, the proportion of the detection light L that does not pass through the prism 16 and is reflected by the light incident surface 16b can be reduced. This increases the amount of detection light L absorbed by the photoelectric element 8, effectively improving the quantum efficiency of the photoelectric element 8.

[0076] Furthermore, a reflective film 18 is provided on the light-reflecting surface 16c. The reflective film 18 reduces light transmission loss (the component that transmits through the light-reflecting surface 16c) in the light-reflecting surface 16c. This reduces the amount of light that is reflected by the light-reflecting surface 16c and re-enters the photoelectric element 8, thereby effectively improving the quantum efficiency of the photoelectric element 8.

[0077] Furthermore, the electron tube 1A is disposed within a vacuum container 7 and includes an electron multiplying section 9 for multiplying photoelectrons emitted from the photoelectric element 8. Thus, even when the light to be detected L is weak light (e.g., fluorescence or Raman scattered light secondary to the light emitted by irradiating the sample to be measured with excitation light), electrons corresponding to the light to be detected L can be appropriately detected at the anode 10.

[0078] [Second embodiment]

[0079] like Figure 6 As shown, the electron tube 1B of the second embodiment differs from the electron tube 1A in its structure for multiplying the photoelectrons emitted from the photoelectrode 8 (i.e., the structure within the vacuum chamber). The components of the electron tube 1B, including the light-transmitting substrate 3, photoelectrode 8, prism 16, antireflection film 17, and reflective film 18, are identical to those of the electron tube 1A. The electron tube 1B is a so-called electron injection multiplication photosensor (HPD) that accelerates photoelectrons emitted from the photoelectrode 8 in response to incident light, achieving high gain in the semiconductor element and thus enabling detection of weak light.

[0080] like Figure 6 As shown, the electron tube 1B includes a vacuum vessel 20 whose interior is maintained at a vacuum. In this embodiment, as an example, the vacuum vessel 20 includes: a translucent substrate 3; a cylindrical cathode electrode 21; a cylindrical side plate 22 made of an insulating material such as ceramic; an annular intermediate electrode 23a fixed between a first side plate 22a and a second side plate 22b formed by dividing the side plate 22 into four parts; an annular intermediate electrode 23b fixed between a second side plate 22b and a third side plate 22c; an annular intermediate electrode 23c fixed between a third side plate 22c and a fourth side plate 22d; a metal flange 24; and a disc-shaped stem 25 airtightly connected to the metal flange 24. The translucent substrate 3, cathode electrode 21, side plate 22, intermediate electrode 23, metal flange 24, and stem 25 are stacked concentrically with one another.

[0081] The side plate 22 is disposed between the cathode electrode 21 and the metal flange 24. One end of the side plate 22 is airtightly bonded to the end surface of the cathode electrode 21 using solder or the like. The other end of the side plate 22 is airtightly bonded to the metal flange 24 provided on the outer periphery of the stem 25 using solder or the like. Furthermore, the intermediate electrodes 23a, 23b, and 23c are annular in shape with an opening centered on the central axis AX of the vacuum vessel 20. They are arranged at predetermined intervals along the inner wall of the side plate 22, electrically independent of the photocathode 8. The outer diameters of the cathode electrode 21, the side plate 22, and the cylindrical portion of the metal flange 24 are substantially the same, while the inner diameter of the cathode electrode 21 is smaller than that of the side plate 22. Therefore, along the central axis AX, the inner wall surface of the cathode electrode 21 is located inward of the inner wall surface of the side plate 22 from one end to the other. In contrast, the inner diameter of the openings of the intermediate electrodes 23a, 23b, and 23c is minimized to prevent interference with electron orbits, that is, to prevent the diameter of the photocathode 8 from becoming significantly smaller. The intermediate electrodes 23a, 23b, and 23c protrude further inward from the inner wall of the cylindrical side plate 22 than the cathode electrode 21. This eliminates the effects of stray electrons on the electron orbits during electron orbit control, thereby eliminating the effects of this electrification on the electron orbits. The intermediate electrodes 23a, 23b, and 23c are fixed to the side plates 22 using solder or other means while being sandwiched between them, thereby achieving integration with the side plates 22.

[0082] Furthermore, a ring-shaped standing electrode 26 is fixed to the central axis AX side of the metal flange 24 of the vacuum container 20. This standing electrode 26 is concentrically arranged with the metal flange 24 and has an opening with a smaller diameter than the intermediate electrodes 23a, 23b, and 23c. This opening forms a generally cylindrical front end 26a extending along the inner wall of the side plate 22 toward the light-transmitting substrate 3.

[0083] A semiconductor element 27 (electron detection unit) comprising an APD (avalanche photodiode) is fixed to the surface of the stem 25 facing the vacuum space S, facing the photoelectric element 8. The APD is a semiconductor element that combines a high-concentration P region with an N region, creating a sufficiently high electric field required for avalanche amplification. When photoelectrons emitted from the photoelectric element 8 strike the surface of the semiconductor element 27, i.e., the electron incident surface, the semiconductor element 27 multiplies the photoelectrons and converts them into an electrical signal, which is then output to the outside via a pin 28 extending through the stem 25.

[0084] As described above, in the electron tube 1B, the semiconductor element 27, which has the function of multiplying photoelectrons, functions as an electron detection unit. This configuration allows the semiconductor element 27 to appropriately detect electrons corresponding to the light being detected, even when the light being detected is weak. Furthermore, in the electron tube 1B, since the semiconductor element 27, which functions as the electron detection unit, also has an electron multiplication function, the electron multiplication unit 9 of the electron tube 1A of the first embodiment is unnecessary. The specific structure of the electron tube 1B is not limited to the example described above. For example, a portion of the intermediate electrode 23 may be omitted, or the rising electrode 26 may be omitted.

[0085] [Electron tube module]

[0086] Reference Figure 7 and Figure 8 , an electron tube module 30 including the above-mentioned electron tube (here, as an example, the electron tube 1A) is described. The electron tube module 30 includes the electron tube 1A and a housing 31 that houses the electron tube 1A. The housing 31 is formed into a roughly rectangular parallelepiped shape. The housing 31 is formed, for example, of metal or resin. The housing 31 has a top wall 32 (wall portion), a bottom wall 33, and side walls 34. The top wall 32 and the bottom wall 33 are opposite to each other in the direction along the central axis AX1 of the housing 31. When viewed from the direction along the central axis AX1, the top wall 32 and the bottom wall 33 are formed into rectangular plates of the same size. The side wall 34 is formed into a square cylinder extending along the central axis AX1, connecting the edge of the top wall 32 and the edge of the bottom wall 33.

[0087] like Figure 8 As shown in this embodiment, a circuit board 41 for supplying voltage to the electron tube 1A via the tube base pin 5 and a booster circuit 42 connected to the circuit board 41 and generating a high voltage to be supplied to the electron tube 1A are housed together with the electron tube 1A in the housing 31. The electron tube 1A is centered about the central axis AX2 of the electron tube 1A (which is aligned with the center axis AX2 of the electron tube 1A). Figure 1 The axis (an axis parallel to the Z axis in the shell) is configured and fixed in the shell 31 in a manner inclined relative to the central axis AX1 of the shell 31.

[0088] An opening 32a for guiding detection light into the electron tube 1A in the housing 31 is formed in the top wall 32. The opening 32a extends from the outer side surface 32b to the inner side surface 32c of the top wall 32. In this embodiment, the opening 32a is formed in a circular shape when viewed from the direction along the central axis AX1.

[0089] The electron tube 1A is arranged within the housing 31 such that light introduced through the opening 32a is incident on the light incident surface 16b. As an example, the electron tube 1A is arranged within the housing 31 such that the light incident surface 16b of the prism 16 is parallel to the top wall 32, and at least a portion of the light incident surface 16b of the prism 16 is exposed to the outside through the opening 32a. The light incident surface 16b of the prism 16 abuts against the inner surface 32c of the top wall 32. This allows the electron tube 1A to be easily and accurately positioned within the housing 31 so that the light incident surface 16b is parallel to the top wall 32 (inner surface 32c).

[0090] Furthermore, assuming that, when viewed from the direction along the central axis AX2, the end of the bottom surface 16a (the end connected to the light incident surface 16b) is located further inboard than the edge of the translucent substrate 3, the edge of the translucent substrate 3 interferes with the top wall 32, thereby creating a gap between the light incident surface 16b and the inner side surface 32c of the top wall 32. In such a case, a spacer may be disposed between the inner side surface 32c of the top wall 32 and the light incident surface 16b to fill this gap. Alternatively, the inner side surface 32c of the top wall 32 may be brought into contact with the light incident surface 16b by making the thickness of the top wall 32 greater at the portion corresponding to the gap than at other portions.

[0091] In this embodiment, the light incident surface 16b of the prism 16 is bonded to the inner side surface 32c of the top wall 32. The light incident surface 16b and the inner side surface 32c can be bonded, for example, using an adhesive. For example, a glass bonding adhesive, such as a silicone adhesive, can be used as the adhesive. To ensure good compatibility between the inner side surface 32c and the glass bonding adhesive, a primer suitable for the material of the inner side surface 32c can be pre-coated on the inner side surface 32c. In this case, after the primer applied to the inner side surface 32c dries, the inner side surface 32c coated with the primer is bonded to the light incident surface 16b using the glass bonding adhesive. Alternatively, an adhesive that blends well with the material of the inner side surface 32c can be used. In this case, to ensure good compatibility between the light incident surface 16b and the adhesive, a glass primer can be pre-coated on the light incident surface 16b. However, the use of such a primer is not essential. By fixing the prism 16 of the electron tube 1A to the top wall 32 in this manner, it is possible to appropriately prevent the position of the electron tube 1A from shifting relative to the top wall 32. Furthermore, the entire portion of the light incident surface 16b that contacts the inner side surface 32c may be joined to the inner side surface 32c, or only a portion of the portion of the light incident surface 16b that contacts the inner side surface 32c may be joined to the inner side surface 32c. Furthermore, the light incident surface 16b does not necessarily need to be joined to the inner side surface 32c of the top wall 32; the electron tube 1A may be fixed to the housing 31 at a portion other than the light incident surface 16b.

[0092] The electron tube module 30 described above, by including the electron tube 1A, achieves the same effects as the aforementioned electron tube 1A. Furthermore, by housing the electron tube 1A within the housing 31, the electron tube 1A can be appropriately protected. Furthermore, the planar light incident surface 16b is arranged parallel to the top wall 32, making it easier to position the electron tube 1A within the housing 31. For example, as described above, by abutting the light incident surface 16b against the inner side surface 32c of the top wall 32, the electron tube 1A can be easily positioned. Furthermore, by adjusting the position of the electron tube module 30 so that the top wall 32 is orthogonal to the optical axis of the light to be detected, the electron tube module 30 can be easily and appropriately positioned. Furthermore, since the central axis AX1 of the housing 31 is parallel to the optical axis of the light to be detected, the electron tube module 30 can be housed and positioned in a natural orientation within an optical system (such as the optical devices 50A to 50C described below) that includes the electron tube module 30.

[0093] [Optical device]

[0094] Next, refer to Figures 9 to 11 Optical devices 50A to 50C including the above-mentioned electron tubes (here, as an example, the electron tube module 30 including the electron tube 1A) will be described.

[0095] [First example of an optical device]

[0096] like Figure 9 As shown, the optical device 50A of the first example is a two-photon laser microscope (two-photon excitation microscope, two-photon microscope) that irradiates the sample 100 placed on the sample stage 51 with excitation light Le and detects the weak fluorescence Lf generated from the sample 100 at the focal position P0 of the objective lens 56.

[0097] The optical device 50A includes a sample stage 51, a laser irradiation unit 52A (light source), a condenser lens 53, a collimator lens 54, a dichroic mirror 55, an objective lens 56, a condenser lens 57, a collimator lens 58, and a tube module 30 for detecting fluorescence Lf. However, the collimator lens 58 may be omitted.

[0098] The sample table 51 is a portion on which the sample 100 to be measured is placed. The sample table 51 is, for example, a movable workbench. The sample 100 is, for example, a biological sample, and emits fluorescence Lf by being irradiated with excitation light Le. The laser irradiation unit 52A is a light source that outputs the excitation light Le (light) to be irradiated onto the sample 100 to be measured. The excitation light Le output by the laser irradiation unit 52A is a near-infrared ultrashort pulse laser. In this embodiment, as an example, the excitation light Le output by the laser irradiation unit 52A is parallel light. The focusing lens 53 is arranged on the optical path of the excitation light Le output from the laser irradiation unit 52A, and by focusing the excitation light Le, the excitation light Le is converted into a point light source. The collimating lens 54 is arranged at a position later than the focusing lens 53 to parallelize (collimate) the excitation light Le. The dichroic mirror 55 is a mirror component configured to reflect the excitation light Le and transmit the fluorescence Lf, and is arranged later than the collimating lens 54. The excitation light Le converted into parallel light by the collimator lens 54 is reflected by the dichroic mirror 55, passes through the objective lens 56, and reaches the sample 100. Thus, two-photon excitation occurs only at the focal position P0 of the objective lens 56, and fluorescence Lf is generated from the sample 100 at the focal position P0.

[0099] The fluorescence Lf generated in the sample 100 passes through the objective lens 56 along the opposite path to the excitation light Le and is transmitted through the dichroic mirror 55. Thereafter, the fluorescence Lf is focused by the condenser lens 57. The fluorescence Lf focused by the condenser lens 57 is collimated by the collimator lens 58 arranged behind the focal point of the condenser lens 57. Figure 9 As shown, the electron tube module 30 is arranged after the collimator lens 58 so that the optical axis OA of the fluorescence Lf generated in the sample 100 is perpendicular to the light incident surface 16b of the prism 16. Furthermore, the fluorescence Lf is collimated by the collimator lens 58 so as to be received by the opening 32a of the top wall 32. The collimated fluorescence Lf is incident on the light incident surface 16b of the prism 16 through the opening 32a and is detected by the electron tube module 30.

[0100] The optical device 50A described above includes the electron tube module 30 as a detection unit for detecting the light to be detected (here, the fluorescence Lf), and thus achieves the same effect as the electron tube module 30 described above. Specifically, by utilizing the prism 16, the quantum efficiency of the photocathode 8 in the electron tube 1A can be effectively improved. As a result, the electrons corresponding to the fluorescence Lf can be appropriately detected at the anode 10 of the electron tube 1A. In addition, as Figure 9 As shown, by housing the electron tube 1A in the housing 31, the optical device 50A can be arranged with the central axis AX1 (refer to FIG. Figure 8 ) The electron tube module 30 is well accommodated and arranged in a manner parallel to the optical axis OA of the light to be detected (fluorescent light Lf).

[0101] In the optical device 50A, the electron tube 1A may be configured so that part or all of the fluorescence Lf (detected light) incident on the photoelectric surface 8 via the prism 16 and the light-transmitting substrate 3 is totally reflected at the interface between the photoelectric surface 8 and the vacuum space S. Specifically, the electron tube 1A may be configured and arranged in the optical device 50A so that Figure 5 The above formula (3) holds true for the fluorescence Lf as the detected light L in the photoelectric surface 8. In this case, the fluorescence Lf is returned to the photoelectric surface 8 after total reflection at the interface between the photoelectric surface 8 and the vacuum space S. This increases the amount of fluorescence Lf absorbed by the photoelectric surface 8, effectively improving the quantum efficiency of the photoelectric surface 8.

[0102] [Second example of optical device]

[0103] like Figure 10 As shown, optical device 50B of the second example is a confocal laser microscope that irradiates excitation light Le onto sample 100 (measurement target) placed on sample stage 51 and detects weak fluorescence Lf1 generated from sample 100 at focal position P0 of objective lens 56. Optical device 50B differs from optical device 50A in that it includes a laser irradiation unit 52B in place of laser irradiation unit 52A and a pinhole 59. The remaining configuration is the same as that of optical device 50A.

[0104] Specifically, the excitation light Le output by the laser irradiation unit 52B is a visible ultraviolet laser. In this case, by irradiating the sample 100 with the excitation light Le, fluorescence is generated from the irradiated area including the area other than the focal position P0 of the objective lens 56. Figure 10 In the figure, fluorescence Lf1 represents fluorescence generated at focal position P0, and fluorescence LF2 represents fluorescence generated at locations other than focal position P0 (here, as an example, near the contact point between sample 100 and sample stage 51). Thus, in optical device 50B, fluorescence LF2 is also generated in areas other than focal position P0. Therefore, a pinhole 59 is provided after condenser lens 57 to allow only fluorescence Lf1 from focal position P0 to pass through. Consequently, only fluorescence Lf1 passes through pinhole 59 and is guided to the incident surface of electron tube module 30 (light incident surface 16b of prism 16) via collimator lens 58. In other words, pinhole 59 blocks fluorescence LF2 generated in areas other than focal position P0. The aforementioned optical device 50B also achieves the same effects as the aforementioned optical device 50A.

[0105] [Third example of optical device]

[0106] like Figure 11As shown, an optical device 50C according to the third example is a device (flow cytometer) for performing flow cytometry. The optical device 50C includes a laser irradiation unit 52C, a flow cell FC, a collimating lens 60, a plurality of (three in this example) dichroic mirrors 61A, 61B, and 61C, a plurality of condenser lenses 62A, 62B, and 62C, a plurality of collimating lenses 63A, 63B, and 63C, and a plurality of electron tube modules 30A, 30B, and 30C. However, the collimating lenses 63A, 63B, and 63C may be omitted.

[0107] The flow cell FC is a device that circulates a sample solution containing multiple samples 100, such as cells, to be measured. The flow cell FC has the function of arranging the samples 100 in the sample solution so that each sample 100 flows sequentially. The laser irradiation unit 52C is configured to irradiate excitation light Le (here, as an example, a 488nm argon laser) at a predetermined irradiation position within the flow cell FC. Thus, each sample 100 that circulates within the flow cell FC and passes through the irradiation position is sequentially irradiated with the excitation light Le. This irradiation of the sample 100 with the excitation light Le generates fluorescence Lf in the sample 100.

[0108] The collimating lens 60 collimates the fluorescence Lf generated in the sample 100. Dichroic mirrors 61A, 61B, and 61C are sequentially arranged after the collimating lens 60. Here, as an example, the first-stage dichroic mirror 61A is configured to reflect red light Lr and transmit light with a wavelength shorter than that of the red light Lr. The second-stage dichroic mirror 61B, arranged after the dichroic mirror 61A, is configured to reflect yellow light Ly in the light that passes through the dichroic mirror 61A and transmit light with a wavelength shorter than that of the yellow light Ly. The third-stage dichroic mirror 61C, arranged after the dichroic mirror 61B, is configured to reflect green light Lg in the light that passes through the dichroic mirror 61B and transmit light with a wavelength shorter than that of the green light Lg.

[0109] A condenser lens 62A, a collimator lens 63A, and a tube module 30A are arranged on the optical path of the red light Lr reflected by the dichroic mirror 61A. Specifically, the dichroic mirror 61A, the condenser lens 62A, the collimator lens 63A, and the tube module 30A constitute an optical system for detecting the red light Lr contained in the fluorescence Lf. The tube module 30A is positioned downstream of the collimator lens 63A such that the optical axis OA1 of the red light Lr reflected by the dichroic mirror 61A is orthogonal to the light incident surface 16b of the prism 16. The red light Lr passes through the condenser lens 62A and the collimator lens 63A, where it is collimated so as to converge toward the opening 32a of the top wall 32. The collimated red light Lr is incident on the light incident surface 16b of the prism 16 through the opening 32a and is detected by the tube module 30A.

[0110] A condenser lens 62B, a collimator lens 63B, and a tube module 30B are positioned along the optical path of the yellow light Ly reflected by the dichroic mirror 61B. Specifically, the dichroic mirror 61B, condenser lens 62B, collimator lens 63B, and tube module 30B constitute an optical system for detecting the yellow light Ly contained in the fluorescence Lf. The tube module 30B is positioned downstream of the collimator lens 63B such that the optical axis OA2 of the yellow light Ly reflected by the dichroic mirror 61B is orthogonal to the light incident surface 16b of the prism 16. The yellow light Ly is collimated by the condenser lens 62B and collimator lens 63B so as to converge toward the opening 32a of the top wall 32. The collimated yellow light Ly then enters the light incident surface 16b of the prism 16 through the opening 32a and is detected by the tube module 30B.

[0111] A condenser lens 62C, a collimator lens 63C, and a tube module 30C are arranged on the optical path of the green light Lg reflected by the dichroic mirror 61C. In other words, the dichroic mirror 61C, condenser lens 62C, collimator lens 63C, and tube module 30C constitute an optical system for detecting the green light Lg contained in the fluorescence Lf. The tube module 30C is positioned downstream of the collimator lens 63C such that the optical axis OA3 of the green light Lg reflected by the dichroic mirror 61C is orthogonal to the light incident surface 16b of the prism 16. The green light Lg is collimated by the condenser lens 62C and collimator lens 63C, converging toward the opening 32a of the top wall 32. The collimated green light Lg is incident on the light incident surface 16b of the prism 16 through the opening 32a and is detected by the tube module 30C.

[0112] In the above, three optical devices 50A, 50B, and 50C are described as examples of optical devices including electron tubes (here, electron tube modules), but the structure of the optical device is not limited to the above structure. For example, in the above-mentioned optical devices 50A, 50B, and 50C, as a part for detecting the light to be detected, the electron tube module 30 may not be provided, and the electron tube 1A in a state not housed in the housing 31 may be provided. In addition, the electron tube 1A, 1B or the electron tube module 30 may also be assembled into an optical device other than the optical devices 50A, 50B, and 50C illustrated in the present invention. That is, the electron tube 1A, 1B or the electron tube module 30 may also be used for purposes other than two-photon laser microscopes, confocal laser microscopes, and flow cytometers. In addition, the light to be detected may also be used without using the electron tube module 30. Figures 9 to 11 The light is guided to the light incident portion (light incident surface 16b) of the prism 16 via a light guide such as an optical fiber, in an optical system as in the example of FIG.

[0113] [Modification]

[0114] While one embodiment of the present invention has been described above, the present invention is not limited to the aforementioned embodiment. For example, the materials and shapes of the various components are not limited to those described above; various materials and shapes can be employed. For example, the shape of the prism is not limited to prism 16 in the aforementioned embodiment. Several variations of the prism are described below.

[0115] (First Modification of Prism)

[0116] Figure 12 1 is a perspective view of a prism 16A according to a first modified example. In the prism 16A, the curved surface shape of the light reflecting surface 16c is approximately formed by a plurality of planar portions 19. More specifically, the light reflecting surface 16c is formed by a plurality of planar portions 19. That is, the light reflecting surface 16c is formed by connecting a plurality of planar portions (planar portions 19) to each other. In this case, the light reflecting surface 16c can be formed simply by cutting the prism components in a straight line, so processing becomes easy. In addition, the number of planar portions 19 constituting the light reflecting surface 16c, as well as the shape and size of each planar portion 19, are not limited to a specific method. In addition, by reducing the size of each planar portion 19 and increasing the number of planar portions 19 constituting the light reflecting surface 16c, a highly similar curved surface shape can be obtained.

[0117] (Second Modification of Prism)

[0118] Figure 13 1 is a cross-sectional view of a prism 16B according to a second modified example. Prism 16B differs from prism 16 in that a recess 16e is formed that opens onto a portion of light incident surface 16b. Recess 16e is, for example, a non-through hole having a cylindrical cross-section. In prism 16B, for example, when the light to be detected is output from the front end of a light guide such as an optical fiber (i.e., when the front end of the optical fiber serves as the light source), the distance between the light source and photoelectric surface 8 can be further shortened by allowing the front end of the optical fiber to enter recess 16e. In such a prism 16B, the light incident portion is formed by recess 16e. More specifically, the bottom surface 16f of recess 16e functions as a light incident portion into which light is incident. In prism 16B, an anti-reflection film 17 is provided on the entire light incident surface 16b. However, as described above, when light is incident only on bottom surface 16f (light incident portion) of recess 16e, the anti-reflection film 17 may be provided only on bottom surface 16f. In addition, in prism 16B, bottom surface 16f is formed into a flat surface (flat surface), but bottom surface 16f can be formed into a curved surface shape that is convex inward or outward. According to prism 16B, by making the light source (here, the front end of the optical fiber) enter the recess 16e, the light source can be brought closer to the photoelectric surface 8.

[0119] (Third Modification of Prism)

[0120] Figure 14 This is a cross-sectional view of a prism 16C according to a third modified example. Prism 16C differs from prism 16B in that its light incident surface 16b has a curved surface continuous with its light reflecting surface 16c. Specifically, prism 16C has a concave portion 16e formed in a portion of its hemispherical light incident surface 16b. This structure achieves the same effects as prism 16B.

[0121] (Fourth Modification of Prism)

[0122] Figure 15 This is a cross-sectional view of a prism 16D according to a fourth modified example. Prism 16D differs from prism 16 in that light incident surface 16b is not a flat surface but rather has an inwardly convex curved surface. With this prism 16D, by bringing the light source closer to light incident surface 16b, the distance between the light source and photoelectric element 8 can be shortened compared to the case of prism 16.

[0123] (Fifth Modification of Prism)

[0124] Figure 16 This is a cross-sectional view of a prism 16E according to a fifth modified example. Prism 16E differs from prism 16 in that light incident surface 16b is not a flat surface but rather has a convex, curved shape. Furthermore, the curvature of light incident surface 16b is set within a range inward of the imaginary spherical surface P. With this prism 16E, for example, when the light to be detected incident on light incident surface 16b is parallel light, the parallel light can be focused toward the approximate center of photoelectric surface 8.

[0125] As an example of an electron tube, electron tubes 1A and 1B (i.e., photomultiplier tubes or HPDs) are described as including an electron multiplying function (electron multiplying section 9 in the first embodiment or semiconductor element 27 in the second embodiment). However, such an electron multiplying function is not essential for electron tubes. In other words, electron tubes 1A and 1B may be configured as phototubes (photoelectric converters) having a photoelectric element 8 and an anode that directly detects photoelectrons emitted from the photoelectric element 8 within a vacuum container.

[0126] Description of Reference Numerals

[0127] 1A, 1B…Electron tube, 3…Translucent substrate, 3a…Inner surface, 3b…Outer surface, 7, 20…Vacuum container, 8…Photoelectric element, 9…Electron multiplying unit, 10…Anode (electron detection unit), 16…Prism, 16a…Bottom surface, 16b…Light incident surface (light incident unit), 16c…Light reflecting surface, 16d…Side surface, 16e…Concave portion (light incident unit), 17…Antireflection film, 18…Reflection film, 27…Semiconductor element (electron detection unit), 30, 30A, 30B, 30C…Electron tube module, 31…Casing Body, 32…top wall (wall portion), 32a…opening, 32b…outer side surface, 32c…inner side surface, 50A, 50B, 50C…optical device, 52A, 52B, 52C…laser irradiation portion (light source), 57, 62A, 62B, 62C…condensing lens, 100…sample (measurement object), L…detected light, Le…excitation light (light), Lf…fluorescence (detected light), Lr…red light (detected light), Ly…yellow light (detected light), Lg…green light (detected light), S…vacuum space.

Claims

1. An electron tube, characterized in that: include: A vacuum container having a light-transmitting substrate and forming a vacuum space; a photoelectric element provided on an inner surface of the light-transmitting substrate facing the vacuum space and emitting photoelectrons into the vacuum space in response to light incident through the light-transmitting substrate; an electron detection unit disposed in the vacuum container and configured to detect electrons originating from the photoelectrons; and a prism bonded to the outer surface of the light-transmitting substrate on the side opposite to the inner surface; The prism has: a bottom surface bonded to the outer surface of the light-transmitting substrate; a light incident surface having a light incident portion for incident light; and a light reflecting surface that further reflects the light that has entered the light incident portion and reflected at the interface between the photoelectric surface and the vacuum space, thereby causing the light to enter the photoelectric surface again; The light reflecting surface has a curved shape convex outward, The light incident portion is located inside a virtual spherical surface along the light reflecting surface.

2. The electron tube according to claim 1, wherein: The photoelectric element is formed in a flat plate shape along the inner surface of the light-transmitting substrate.

3. The electron tube according to claim 1 or 2, characterized in that: The photoelectric element is formed on a portion of the inner surface of the light-transmitting substrate.

4. The electron tube according to any one of claims 1 to 3, characterized in that: The light incident portion is formed in a planar shape.

5. The electron tube according to any one of claims 1 to 3, characterized in that: The light incident portion has a curved surface shape that is convex outward.

6. The electron tube according to any one of claims 1 to 3, characterized in that: The light incident portion has a curved surface shape that is convex toward the inside.

7. The electron tube according to any one of claims 1 to 6, characterized in that: The light incident portion is constituted by the entire light incident surface.

8. The electron tube according to any one of claims 1 to 6, characterized in that: The light incident portion is formed of a recessed portion opened in a portion of the light incident surface.

9. The electron tube according to any one of claims 1 to 8, characterized in that: An antireflection film is provided on at least the light incident portion of the light incident surface.

10. The electron tube according to any one of claims 1 to 9, characterized in that: A reflective film is provided on the light reflecting surface.

11. The electron tube according to any one of claims 1 to 10, characterized in that: The prism further includes a pair of side surfaces provided between the light incident surface, the light reflecting surface, and the bottom surface, and facing each other across the light incident surface and the light reflecting surface when viewed from a direction opposite to the bottom surface.

12. The electron tube according to any one of claims 1 to 11, characterized in that: The electron tube further includes an electron multiplying portion, which is disposed in the vacuum container and multiplies the photoelectrons.

13. The electron tube according to any one of claims 1 to 11, characterized in that: The electron detection unit is a semiconductor element that multiplies the photoelectrons.

14. The electron tube according to any one of claims 1 to 13, characterized in that: The curved surface shape of the light reflecting surface is a curved surface shape approximately constituted by a plurality of planar portions.

15. An electron tube module, characterized in that: include: The electron tube according to any one of claims 1 to 14; and a housing for housing the electron tube; The housing has a wall portion formed with an opening, The electron tube is arranged in the housing so that light introduced from the opening is incident on the light incident surface.

16. The electron tube module according to claim 15, wherein: The light incident surface is formed in a planar shape and is arranged parallel to the wall portion.

17. An optical device, characterized in that: include: The electron tube according to any one of claims 1 to 14; and a light source that outputs light to illuminate the measurement object, The electron tube is configured so that the light to be detected, which is generated by irradiating the measurement object with the light, is incident on the light incident surface.

18. The optical device according to claim 17, wherein: The electron tube is configured such that a part or all of the light to be detected that enters the photoelectric surface via the prism and the light-transmitting substrate is totally reflected at the interface between the photoelectric surface and the vacuum space.

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