Diamond optomagnetic sensor

Abstract

A diamond optical magnetic sensor includes a diamond having a color center with an electron spin, and a reflection surface that reflects excitation light that propagates through an optical system and is incident to an inside of the diamond, the reflection surface reflecting emission light emitted from the color center excited by the excitation light so as to converge in a direction of the optical system.

Description

Technical Field

[0001] This disclosure relates to diamond optical-magnetic sensors. This application claims priority based on Japanese Application No. 2021-059798, filed on March 31, 2021, and invokes all the contents described in the aforementioned Japanese application. Background Technology

[0002] A known optical-magnetic sensor utilizes a diamond NV center (hereinafter referred to as the NV center). When the NV center, composed of nitrogen at a carbon substitution site in diamond and a hole adjacent to that nitrogen, becomes negatively charged, its ground state is a triplet state (i.e., spin S = S = 1). When the NV center is excited by light at a wavelength of 532 nm (i.e., green light), it emits fluorescence at a wavelength of 637 nm (i.e., red light). The fluorescence intensity varies depending on the spin state, which is influenced by the magnetic field applied to the NV center and magnetic resonance based on microwaves or radio waves, thus enabling its use as a diamond optical-magnetic sensor.

[0003] The diamond photomagnetic sensor comprises: a diamond substrate containing an NV center; an optical system that transmits excitation light from a light source to the NV center; an optical system that focuses fluorescence from the NV center to a photodetector; and a waveguide that transmits microwaves from a power source to the NV center.

[0004] For example, Non-Patent Document 1 discloses a structure in which a diamond sensor is mounted on a coplanar waveguide and microwaves are irradiated. The diamond substrate is rectangular in shape, and excitation light is irradiated from the side of the diamond substrate, while fluorescence is focused from the diamond substrate.

[0005] Existing technical documents

[0006] Non-patent literature

[0007] Non-Patent Document 1: Yuta Masuyama, Yuji Hatano, Takayuki Iwasaki, Mutsuko Hatano, “High-Sensitivity Macroscopic Diamond Magnetometer Using Coplanar Waveguide,” Proceedings of the 79th Autumn Academic Conference of the Chinese Society of Applied Physics (Published: September 5, 2018) Summary of the Invention

[0008] One aspect of this disclosure relates to a diamond photomagnetic sensor comprising: a diamond having a color center with electron spin; and a reflective surface that reflects excitation light propagating through an optical system and incident into the interior of the diamond, the reflective surface reflecting emitted light emitted from the color center excited by the excitation light, causing it to focus towards the optical system.

[0009] Another aspect of this disclosure relates to a diamond photomagnetic sensor comprising: a diamond having a color center with electron spin; a minute portion capable of allowing excitation light propagating via an optical system to penetrate into the interior of the diamond; and a reflective surface that reflects emitted light from the color center excited by the excitation light penetrating from the minute portion, concentrating it in a direction toward a light-receiving optical system guiding the light to a light-receiving element. The reflective surface has an area larger than the minute portion, and the reflective surface guides emitted light from the same position in different directions to the light-receiving optical system via multiple optical paths. Attached Figure Description

[0010] Figure 1 This is a graph showing the light transmittance associated with type Ib diamond.

[0011] Figure 2 This is a graph showing the relationship between spin detection contrast ratio and excitation light power density.

[0012] Figure 3 This is a perspective view showing the diamond optical-magnetic sensor according to an embodiment of the present disclosure.

[0013] Figure 4 It means Figure 3 Three-view diagram showing the configuration of the diamond optical-magnetic sensor and optical fiber.

[0014] Figure 5 This is a side view showing the structure in which a focusing element is placed between a diamond photomagnetic sensor and an optical fiber.

[0015] Figure 6 This is a schematic diagram showing the optical path of the excitation light incident on the NV center of the diamond photomagnetic sensor.

[0016] Figure 7 This is a schematic diagram showing the optical path of fluorescence emitted from the NV center of the diamond photomagnetic sensor.

[0017] Figure 8 This is a schematic diagram showing the optical path of fluorescence emitted from diamond without considering the refractive index.

[0018] Figure 9 This is a schematic diagram showing the optical path of fluorescence emitted from diamond, taking refractive index into account.

[0019] Figure 10 This is a schematic diagram showing the optical path of fluorescence emitted from diamond when a reflector is provided.

[0020] Figure 11 This is a schematic diagram showing the light path of fluorescence emitted from a diamond prism-shaped object.

[0021] Figure 12This is a cross-sectional view showing the structure of the diamond optical-magnetic sensor involved in the first modified example.

[0022] Figure 13 These are two views showing the structure of the diamond optical-magnetic sensor involved in the second variation.

[0023] Figure 14 It means and Figure 13 Three-dimensional views of the structures of diamond optical-magnetic sensors involved in different second variations.

[0024] Figure 15 This is a side view showing the structure of the diamond optical-magnetic sensor involved in the third variation.

[0025] Figure 16 This is a perspective view showing the structure of the diamond optical-magnetic sensor involved in the fourth variation.

[0026] Figure 17 This is a perspective view showing the structure of the diamond optical-magnetic sensor involved in the fifth variation.

[0027] Figure 18 It means Figure 17 Three-view diagram showing the configuration of the diamond optical-magnetic sensor and optical fiber.

[0028] Figure 19 It indicates the shape of the front end and Figure 17 The diagram shows cross-sectional views of different diamond optical-magnetic sensors.

[0029] Figure 20 This is a perspective view showing the structure of the diamond optical-magnetic sensor involved in the sixth variation.

[0030] Figure 21 It indicates the shape of the front end and Figure 20 The diagram shows cross-sectional views of different diamond optical-magnetic sensors.

[0031] Figure 22 This is a perspective view showing the structure of the diamond optical-magnetic sensor involved in the seventh variation.

[0032] Figure 23 It indicates the shape of the front end and Figure 22 The diagram shows cross-sectional views of different diamond optical-magnetic sensors.

[0033] Figure 24 This is a perspective view showing the structure of the diamond optical-magnetic sensor involved in the eighth variation.

[0034] Figure 25 It indicates the shape of the front end and Figure 24The diagram shows cross-sectional views of different diamond optical-magnetic sensors.

[0035] Figure 26 This is a schematic diagram illustrating an example of a structure that enables spatial transport of excitation light and fluorescence.

[0036] Figure 27 This is a schematic diagram showing the structure of Embodiment 1.

[0037] Figure 28 It means Figure 27 A three-dimensional view of the structure of the microwave irradiation section is shown.

[0038] Figure 29 It is a graph representing the experimental results.

[0039] Figure 30 It is a chart that shows the comparison results.

[0040] Figure 31 This is a schematic diagram showing the structure of Embodiment 2. Detailed Implementation

[0041] [The problem this disclosure aims to solve]

[0042] An optical system that transmits excitation light from a light source and illuminates the NV center initializes the spin state of the NV center, and then illuminates the NV center with excitation light to read subsequent changes. To obtain high responsivity and high sensitivity as a photomagnetic sensor, the NV center needs to be illuminated with excitation light as uniformly, strongly, and over a wide range as possible.

[0043] An optical system that focuses fluorescence from the NV center and transmits it to a photodetector focuses fluorescence that varies according to the spin state of the NV center. To obtain high responsivity and high sensitivity as a photomagnetic sensor, it is necessary to efficiently focus fluorescence from the NV center over the widest possible range.

[0044] Specifically, the preferred method is to further improve the focusing efficiency of fluorescence emitted from the NV center of diamond, the absorption efficiency of excitation light that excites the NV center, and the irradiation power density of the excitation light. The following provides a detailed explanation of each issue.

[0045] (Fluorescence focusing efficiency)

[0046] The diameter of the fiber core of the optical fiber transmitting fluorescence is set to The numerical aperture is set to Nc, the refractive index of diamond is set to n, and the diameter of the region capable of focusing fluorescence from the NV center inside the diamond is set to... Let the depth at which light can be focused be dd, and the numerical aperture at which light can be focused be Nd. Here, regarding... The product with Nd, due to the Lagrange invariant law and the refraction of the diamond surface, is subject to the following restrictions:

[0047]

[0048] Additionally, regarding dd,

[0049]

[0050] For example, at the end of an optical fiber, where the diamond is positioned close to the fiber core, it can be considered that... Derived from Equation 1

[0051] Nd < Nc / n (Equation 3)

[0052] Commercially available optical fibers have numerical apertures (Nc) ranging from approximately 0.07 to approximately 0.5. Even when using fibers with a large numerical aperture (e.g., Nc = 0.5), since the refractive index of diamond (n) is approximately 2.5, according to Equation 3, the numerical aperture Nd capable of focusing light is Nd < 0.2. Therefore, considering that fluorescence from the NV center is emitted roughly randomly across the entire celestial sphere, the focusing efficiency η of the fluorescence reaching the fiber core end face and propagating in the fiber, relative to the solid angle 4πsr (steradians) across the entire celestial sphere, is...

[0053] η≈(0.2×0.2×π) / (4×π)=0.01 (Equation 4)

[0054] The maximum efficiency is limited to 1%.

[0055] For example, a focusing objective could be placed between the diamond and the fiber core at the end face of the optical fiber. In this case, if the numerical aperture of the objective is set to Nt, the efficiency is maximized when the magnification of the optical system is set to Nt / Nc. However, in this case, According to Equation 1 above, the following limitations apply to the numerical aperture Nd:

[0056] Nd < Nt / n (Equation 5)

[0057] Even with a large numerical aperture (Nt) of the objective lens, it stops at approximately greater than 1. Therefore, even when combined with an optical fiber with a large numerical aperture (Nc) (e.g., Nc = 0.5), the refractive index (n) of diamond is approximately 2.5. Thus, according to Equation 5, Nd < 0.4. Consequently, the focusing efficiency (η) of the fluorescence reaching the end face of the fiber core and propagating in the fiber is...

[0058] η≈(0.4×0.4×π) / (4×π)=0.04 (Equation 6)

[0059] The maximum efficiency is capped at 4%.

[0060] Thus, if optical fiber is used in the transmission of fluorescence from the NV center to the photodetector to facilitate measurements in high-voltage power equipment, the concentration efficiency of the fluorescence from the NV center stops at a low level of only a few percent.

[0061] The theoretical formula for the sensitivity δB (i.e., the resolution of the detected magnetic field B) of a diamond optical-magnetic sensor is known as Equation 7 below.

[0062]

[0063] In Equation 7, γ is the gyrometry ratio (i.e., a constant), which is close to the gyrometry ratio of the electron (1.76 × 10⁻⁶). 11 The value of η (rad / s / T). η is the fluorescence detection efficiency, i.e., the focusing efficiency, which, as mentioned above, stops at a few percent. C is the spin detection contrast ratio (i.e., the rate of decrease in red light brightness), described later. N is the number of negatively charged NV centers present in the region where the excitation light is irradiated and the fluorescence is focused. T2 is the transverse relaxation time of the electron spin. According to the theoretical formula for the above sensitivity (Equation 7), and in a photomagnetic sensor, photon noise determines the limit of the measurement sensitivity, therefore a higher fluorescence focusing efficiency η is preferable, but as mentioned above, a fluorescence focusing efficiency of a few percent is insufficient.

[0064] (Absorption efficiency of excitation light)

[0065] To initialize the spin state of the NV center and read its subsequent changes, excitation light with a wavelength of 532 nm is applied. A green semiconductor laser or a YAG second-harmonic solid-state laser is readily available as the excitation light source. Diamonds are classified according to the presence and type of impurities. Type Ib diamonds, containing nitrogen atoms as impurities (i.e., possessing NV centers), appear yellowish and have low transmittance. Figure 1 This represents the transmittance of light associated with type Ib diamond. The vertical axis represents transmittance (%), and the horizontal axis represents wavelength (μm). Figure 1 In this model, the scale of the horizontal axis differs at wavelengths of 1.0 μm. From Figure 1 It is known that even with type Ib diamond, green light with a wavelength of 532 nm (i.e., 0.532 μm) is transmitted to a certain extent, thus requiring an absorption length exceeding several millimeters for the diamond to absorb the light. When the optical path length of the diamond substrate is short (e.g., thin), almost all the excitation light is transmitted, resulting in poor absorption efficiency of the excitation light.

[0066] (Power density of excitation light)

[0067] Regarding the NV centers formed in a type Ib diamond substrate, the relationship between the spin detection contrast ratio (i.e., the rate of decrease in red light brightness) and the power density of the excitation light was evaluated experimentally. The results are presented below. Figure 2 .exist Figure 2 In the diagram, the vertical axis represents the spin detection contrast ratio, and the horizontal axis represents the power density of the excitation light. From... Figure 2 It is known that in order to increase the spin detection contrast ratio to above 0.06, a speed of 20 mW / mm is required. 2 The excitation light is irradiated with the above power density to obtain high sensitivity as a photomagnetic sensor.

[0068] Furthermore, regarding the NV centers formed in the Ib-type diamond substrate, the relationship between the response speed (specifically, the time constant) to microwave frequency changes and the power density of the excitation light was evaluated experimentally. The results show that, in order to obtain a high response speed as a photomagnetic sensor, it is necessary to increase the power density of the irradiated excitation light.

[0069] Therefore, the purpose of this disclosure is to provide a diamond optical-magnetic sensor with high fluorescence focusing efficiency, high excitation light absorption efficiency, and high power density.

[0070] [The Effects of This Disclosure]

[0071] According to this disclosure, a diamond optical-magnetic sensor with high fluorescence focusing efficiency, high excitation light absorption efficiency, and high power density can be provided.

[0072] [Description of embodiments of this disclosure]

[0073] The embodiments described herein are presented in an explanatory manner. At least some of the embodiments described below may be combined arbitrarily.

[0074] (1) The diamond photomagnetic sensor according to the first aspect of this disclosure comprises: a diamond having a color center with electron spin; and a reflective surface that reflects excitation light propagating through an optical system and incident into the interior of the diamond, the reflective surface reflecting emitted light emitted from the color center excited by the excitation light, thus focusing the light towards the optical system. This improves the focusing efficiency of the fluorescence, the absorption efficiency of the excitation light, and the power density. Consequently, it improves the responsiveness and sensitivity of the diamond photomagnetic sensor.

[0075] (2) Alternatively, the excitation light can be incident on the diamond from the output of the optical fiber, and the reflecting surface can focus the emitted light onto the output of the optical fiber. This can further improve the focusing efficiency of the fluorescence, the absorption efficiency of the excitation light, and the power density. Consequently, the responsiveness and sensitivity of the diamond photomagnetic sensor can be further improved.

[0076] (3) The diamond photomagnetic sensor according to the second aspect of this disclosure comprises: a diamond having a color center with electron spin; a minute portion capable of allowing excitation light propagating via an optical system to enter the interior of the diamond; and a reflective surface that reflects emitted light from the color center excited by the excitation light entering from the minute portion, concentrating it in a direction guided to a light-receiving optical system of a light-receiving element. The reflective surface has an area larger than the minute portion, and the reflective surface guides emitted light from the same position in different directions to the light-receiving optical system through multiple optical paths. This improves the focusing efficiency of fluorescence, the absorption efficiency of excitation light, and the power density. Consequently, it enhances the responsivity and sensitivity of the diamond photomagnetic sensor.

[0077] (4) Alternatively, the excitation light is incident on the diamond from the output of the optical fiber through a small portion, and the emitted light is focused at the output of the optical fiber through a reflective surface. This can further improve the focusing efficiency of the fluorescence, the absorption efficiency of the excitation light, and the power density. Therefore, it can further improve the responsiveness and sensitivity of the diamond photomagnetic sensor.

[0078] (5) Alternatively, the diamond optical-magnetic sensor may also include a component containing diamond that allows excitation light and emitted light to pass through, with a reflective surface formed on the component. This reduces the amount of expensive diamond and lowers the cost of the diamond optical-magnetic sensor.

[0079] (6) Alternatively, the reflective surface can be formed in diamond. Thus, it is not necessary to separate the component that serves as the reflective surface from the diamond. Furthermore, it is possible to compactly form a sensor that can reduce the critical angle at the reflective surface and achieve high reflection efficiency due to the large difference in refractive index between diamond and the atmosphere.

[0080] (7) Alternatively, the reflective surface can be formed on a component containing diamond. This allows for the easy processing of the reflective surface only on components that are easier to process than diamond, making it easier to focus the excitation light onto the diamond. Furthermore, by selecting a material with a refractive index closer to that of diamond as the component, a larger difference in refractive index with the atmosphere can be maintained, making it easier for the excitation light to penetrate the diamond. This also reduces the critical angle at the reflective surface, enabling the compact formation of a sensor with high reflection efficiency.

[0081] (8) Alternatively, the reflecting surface may include a curved surface or multiple planes connecting the focal point. This can further improve the focusing efficiency of the fluorescence. Here, the focal point is simply the point where two or more different optical paths are concentrated at a position closer than the distance between them when they enter the diamond; it does not have to be a strictly optical focal point. Geometrically, the more concentrated at one point, the better, and even more preferably, multiple optical paths are concentrated at one point.

[0082] (9) Alternatively, the diamond may have a flat surface and a spherical cap, or the reflective surface may be formed by a spherical cap. This makes it easier to design the shape of diamonds with high fluorescence focusing efficiency.

[0083] (10) Alternatively, the diamond may have two spherical caps, or the reflective surface may be formed by the first of the two spherical caps. This makes it easier to design the shape of diamonds with high fluorescence focusing efficiency.

[0084] (11) Alternatively, the diamond can be formed as a polyhedron, or the reflective surface can be formed by multiple faces of the polyhedron. This makes it easier to manufacture diamonds with high fluorescence focusing efficiency.

[0085] (12) Alternatively, the reflecting surface may be a plane, or the angle between the plane perpendicular to the incident axis of the excitation light and the plane on the incident side of the excitation light may be 20° or more and 70° or less. Thus, diamond with high fluorescence focusing efficiency can be achieved.

[0086] (13) Alternatively, the angle between the perpendicular plane and the plane can be greater than 30° and less than 50°. This allows for the realization of diamonds with higher fluorescence focusing efficiency.

[0087] (14) Alternatively, the diamond may have a pyramidal prism. This allows for the realization of diamonds with higher fluorescence focusing efficiency.

[0088] (15) Alternatively, the diamond-containing component may have a pyramidal prism. This allows for the use of diamond with higher fluorescence focusing efficiency.

[0089] (16) Alternatively, the optical system may include an optical fiber, and the size of the diamond may be more than 1 / 3 and less than 3 times the core diameter of the optical fiber. Thus, the excitation light transmitted in the optical fiber can be efficiently irradiated onto the diamond, and the fluorescence emitted from the diamond can be efficiently injected into the optical fiber.

[0090] (17) Alternatively, the optical system may include an optical fiber, and the diamond may be larger than or equal to the size of a circle inscribed in the circle with the core diameter of the optical fiber and smaller than or equal to the size of the circle circumscribed in the circle. Thus, excitation light transmitted in the optical fiber can be efficiently irradiated onto the diamond, and fluorescence emitted from the diamond can be efficiently injected into the optical fiber.

[0091] (18) Alternatively, the optical system may include an optical fiber and a lens, with excitation light propagating through the optical fiber exiting from the lens and entering the diamond photomagnetic sensor; alternatively, a reflective surface may focus the emitted light from the color center onto the lens; alternatively, the magnification of the lens may be the reciprocal of the numerical aperture of the optical fiber; alternatively, the size of the diamond may be in the range of 80% to 120% of the product of the core diameter and the numerical aperture of the optical fiber. Thus, excitation light propagating in the optical fiber can be efficiently irradiated onto the diamond via the lens, and fluorescence emitted from the diamond can be efficiently input into the optical fiber via the lens.

[0092] [Details of the embodiments disclosed herein]

[0093] In the following embodiments, the same reference numerals are used to refer to the same parts. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated.

[0094] Reference Figure 3 The diamond optical-magnetic sensor 100 according to the embodiments of this disclosure is formed of diamond containing NV centers. The diamond optical-magnetic sensor 100 is formed as a tetrahedron. Figure 3 In the diagram, four points A, B, C, and D represent the vertices of the tetrahedron. Edges AD, BD, and CD represent the X-axis, Y-axis, and Z-axis, respectively. Lengths a, b, and c represent the lengths of edges AD, BD, and CD, respectively. Angle α represents the angle between edge AD and edge BD. Angle β represents the angle between edge BD and edge CD. Angle γ represents the angle between edge CD and edge AD. The crystal orientation of the diamond optical-magnetic sensor 100 is arbitrary and not necessarily defined by the X-axis, Y-axis, and Z-axis.

[0095] When using the diamond optical-magnetic sensor 100 to measure magnetic fields, for example, excitation light is incident perpendicularly to surface ABC. This irradiates the NV center inside the diamond optical-magnetic sensor 100, causing it to emit fluorescence. The three surfaces of the diamond optical-magnetic sensor 100 other than surface ABC (i.e., the incident surface) (i.e., surfaces ABD, BCD, and ACD) are ground into flat surfaces, allowing them to function as reflective surfaces without the need for mirrors (e.g., metal plating, metal vapor deposition, etc.). The fluorescence emitted in all directions is internally reflected by surfaces ABD, BCD, and ACD of the diamond optical-magnetic sensor 100 and output from surface ABC, which can then be detected by a detector.

[0096] The angles α, β, and γ of the diamond optical-magnetic sensor 100 are arbitrary. Preferably, all angles α, β, and γ are 90°. The shape of the diamond optical-magnetic sensor 100 in this case is called a corner prism. The sides a, b, and c of the diamond optical-magnetic sensor 100 preferably satisfy 0.5b ≤ a ≤ 1.5b and 0.5c ≤ a ≤ 1.5c.

[0097] Reference Figure 4 When using the diamond optical-magnetic sensor 100 to measure the magnetic field, the diamond optical-magnetic sensor 100 is configured with surface ABC (refer to...). Figure 3 It is positioned opposite the end of the optical fiber 102 (i.e., the output part of the excitation light). Figure 4 The lower right corner shows as Figure 3 Points A, B, C, and D are shown as vertices of the diamond optical-magnetic sensor 100.

[0098] The optical fiber 102 only needs to be configured to be close to (including touching) the diamond optical-magnetic sensor 100. Preferably, the optical fiber 102 is configured such that its optical axis is perpendicular to the surface ABC (i.e., the incident surface) of the diamond optical-magnetic sensor 100. Light emitted from a light source (e.g., a laser diode, etc.) (e.g., with a wavelength of approximately 532 nm) serves as the excitation light for the NV center 104 of the diamond optical-magnetic sensor 100, is transmitted through the optical fiber 102, and enters the diamond optical-magnetic sensor 100. As described above, the fluorescence emitted from the NV center 104 is reflected internally by the reflective surfaces of the diamond optical-magnetic sensor 100 (i.e., surfaces ABD, BCD, and ACD), output from surface ABC, and transmitted to the detector through the optical fiber 102.

[0099] At this point, when the refractive index of diamond is 2.4, since the critical angle for total internal reflection of a material with a refractive index of 2.4 is 24.6 degrees, the angle θ (degrees) between the reflecting surface 106 (i.e., surface ABD) of the diamond optical-magnetic sensor 100 and the perpendicular surface 108 perpendicular to the optical axis of the optical fiber 102 is preferably 20 ≤ θ ≤ 70 (45-25 ≤ θ ≤ 45+25). Regarding each reflecting surface, by setting θ within this range (i.e., forming the diamond optical-magnetic sensor 100 such that θ is within this range), light incident on each reflecting surface inside the diamond optical-magnetic sensor 100 can be reflected towards the front of the diamond optical-magnetic sensor 100 and towards the central axis of the optical fiber 102. Therefore, the proportion of excitation light used for excitation of the NV center can be increased, and the proportion of emitted fluorescence incident into the optical fiber 102 can be increased. More preferably, 24.6 ≤ θ ≤ 65.4 (45-20.4 ≤ θ ≤ 45+20.4). A further preferred value is 38≤θ≤52(45-(20.4 / 3)≤θ≤45+(20.4 / 3)).

[0100] The size of the diamond optical-magnetic sensor 100 is preferably one-third to three times the core diameter (i.e., the diameter of the fiber core) of the optical fiber 102. The size of the diamond optical-magnetic sensor 100 refers, for example, to the size of the circumcircle of the surface opposite the optical fiber 102 (i.e., the incident surface of the excitation light). Furthermore, the diamond optical-magnetic sensor 100 is preferably larger than or equal to the size inscribed in a circle with the core diameter of the optical fiber 102 and smaller than or equal to the size circumscribed in the circle. This allows the excitation light transmitted through the optical fiber 102 to efficiently enter the diamond optical-magnetic sensor 100, and the fluorescence emitted from the diamond optical-magnetic sensor 100 to efficiently enter the core of the optical fiber 102.

[0101] Alternatively, a focusing element can be configured between the diamond optical-magnetic sensor 100 and the optical fiber 102. For example, refer to... Figure 5 A focusing element 110 and a focusing element 112 are disposed between the diamond optical-magnetic sensor 100 and the optical fiber 102. Thus, the excitation light transmitted through and output from the end of the optical fiber 102 is focused by the focusing elements 110 and 112 and irradiates the diamond optical-magnetic sensor 100. Fluorescence emitted from the NV center of the diamond optical-magnetic sensor 100 is focused by the focusing elements 112 and 110 and incident on the end of the fiber core of the optical fiber 102, where it is transmitted.

[0102] The magnification of the lens formed by the focusing element 110 and the focusing element 112 is preferably the reciprocal of the numerical aperture NA of the optical fiber 102 (i.e., 1 / NA). Furthermore, the size of the diamond optical-magnetic sensor 100 is preferably the core diameter of the optical fiber 102. The product of the numerical aperture NA (i.e., The range is between 80% and 120%. Thus, the excitation light transmitted through the optical fiber 102 can be efficiently injected into the diamond optical-magnetic sensor 100, and the fluorescence emitted from the diamond optical-magnetic sensor 100 can be efficiently injected into the core of the optical fiber 102.

[0103] The above description illustrates the transmission of excitation light and fluorescence via optical fiber 102, but it is not a limitation. An optical guide formed by bundling multiple optical fiber cores may also be used instead of optical fiber 102.

[0104] Figure 6 This indicates the optical path of the excitation light within the diamond optical-magnetic sensor 100. (Refer to...) Figure 6 Excitation light (refer to the arrow) transmitted from optical fiber 102 enters the diamond photomagnetic sensor 100 and passes through multiple reflective surfaces (i.e., Figure 1The excitation light (surfaces ABD, BCD, and ACD) is reflected inside the diamond optical-magnetic sensor 100 and irradiates the NV center 104. That is, excitation light from all directions, including not only from the front (i.e., the fiber optic 102 side), but also from the rear, top, bottom, left, and right, enters the NV center 104. Therefore, the irradiation power density of the excitation light entering the NV center can be increased. When absorption is low in the optical path up to the specific NV center, the irradiation power density of the excitation light can be increased by up to 6 times compared to the case where only excitation light comes from the front. This improves the sensitivity of the diamond optical-magnetic sensor.

[0105] Furthermore, the optical path of the excitation light that is reflected by multiple reflective surfaces and enters the NV center 104 is longer (for example, about twice as long) than the optical path that is not reflected and directly enters the NV center 104. Therefore, the optical path of the excitation light within the diamond photomagnetic sensor 100 can be made closer to the absorption length of diamond, thereby increasing the absorption efficiency of the excitation light (i.e., the quantum efficiency of absorption). That is, due to the increased number of excited NV centers, the emitted fluorescence intensity increases. This, in turn, improves the sensitivity of the diamond photomagnetic sensor.

[0106] Figure 7 This represents the optical path of fluorescence emitted from the NV center of the diamond photomagnetic sensor 100. (Refer to...) Figure 7 Inside the diamond photomagnetic sensor 100, the NV center 104, after being irradiated with excitation light, emits fluorescence in all directions (refer to the arrows). The fluorescence emitted forward (i.e., towards the fiber optic 102 side) directly enters the end of the fiber optic 102 (i.e., the output section of the excitation light). On the other hand, the fluorescence emitted backward and to the left, right, and up, down ... and up Figure 1 The light emitted from surfaces ABD, BCD, and ACD is reflected internally by the diamond optical-magnetic sensor 100 and output from the sensor 100, then enters the end of the optical fiber 102 (i.e., the excitation light output section). This allows the omnidirectionally emitted fluorescence to be focused forward, increasing the fluorescence focusing efficiency. Therefore, the sensitivity of the diamond optical-magnetic sensor can be improved.

[0107] Reference Figures 8-11 The effect of increasing the focusing efficiency of fluorescence brought about by the diamond optical-magnetic sensor 100 will be explained in more detail. Figure 8 This represents the optical path of fluorescence emitted from the interior of a rectangular (e.g., cubic) diamond. Here, the refractive index of the diamond is set to 1 and is not considered. In this case, the emitted light is emitted from an observation surface (i.e., the left-hand surface) within a range where the angle θ (degrees) relative to the central axis is 0 ≤ θ ≤ 45° (i.e., the shaded area). Therefore, based on the ratio of solid angles, 25% (=π / (4π)) of the emitted light can be detected.

[0108] exist Figure 9 In China, regarding Figure 8 For diamonds of the same shape, considering the diamond's refractive index n (i.e., approximately 2.5), the optical path of fluorescence emitted from within the diamond is shown. In this case, the emitted light from the observation surface (the left-hand surface) is emitted within the range where the angle θ (degrees) relative to the central axis is 0 ≤ θ ≤ 17 (i.e., the shaded area). Light with θ > 17 exceeds the critical angle and is therefore reflected by the left-hand surface. Thus, with... Figure 8 Unlike other substances, in reality, based on the ratio of solid angles, only about 2.3% (=0.3%) can be detected. 2 π / (4π)) of radiation.

[0109] exist Figure 10 In the context of placing a mirror on one facet of a diamond, and... Figure 9 Similarly, considering the refractive index n of diamond, the optical path of fluorescence emitted from within the diamond is shown. For convenience, the size of the diamond in the direction perpendicular to the observation plane is assumed to be n. Figure 9 1 / 2. In this case, with Figure 9 Similarly, light emitted from the observation surface (i.e., the left side) is emitted within a range where the angle θ (degrees) relative to the central axis is 0 ≤ θ ≤ 17 (i.e., the shaded area). Furthermore, light emitted backward within the same angular range is reflected forward by a mirror and emitted from the observation surface within the same angular range. Therefore, light emitted from the observation surface (i.e., the left side) is emitted... Figure 9 Approximately twice the light of the previous case. Based on the ratio of solid angles, approximately 4.5% (=(0.3)) can be detected. 2 The radiation of π)×2 / (4π)).

[0110] Figure 11 The optical path of fluorescence emitted from the interior of a diamond within a pyramidal prism is shown, taking into account the refractive index n of the diamond. In this case, with Figure 9 Similarly, light emitted from the observation surface (i.e., the left side) within a range where the angle θ (degrees) relative to the central axis is 0 ≤ θ ≤ 17 (i.e., the shaded area) is emitted. Furthermore, regarding light emitted from the rear and sides within the same angular range (i.e., the shaded area), the surfaces of the corner cube prism other than the observation surface function as reflective surfaces, reflecting the light forward and outputting it from the observation surface. Based on the ratio of the solid angle, approximately 35% (=((0.3)) can be detected. 2 The radiation of π)×2+0.6×2π) / (4π)).

[0111] As mentioned above, in Figure 9In the flat diamond shown, approximately 2.3% of the fluorescence emanating from the center of the NV (noise, radiance, and inflection) can be observed forward. Even with a reflective surface, the fluorescence is limited to approximately 4.5%. In contrast, using a diamond with a pyramidal prism, the fluorescence emanating laterally and rearward from the center of the NV can be focused forward, resulting in approximately 35% fluorescence. This represents an approximately 15-fold increase in focusing efficiency compared to the flat diamond.

[0112] In summary, the diamond optical-magnetic sensor 100 can improve the focusing efficiency of fluorescence, the absorption efficiency of excitation light, and the power density. Therefore, it is possible to realize a diamond optical-magnetic sensor with improved responsiveness and sensitivity.

[0113] (First variation)

[0114] The above description focuses on a diamond optical-magnetic sensor made of diamond, but it is not limited to this. Components other than diamond may also be included. The diamond optical-magnetic sensor in the first variation includes components other than diamond.

[0115] Reference Figure 12 The diamond optical-magnetic sensor 120 has a diamond 122 containing an NV center and a glass 124 containing the diamond 122. The shape of the glass 124 is consistent with... Figure 3 The diamond optical-magnetic sensor 100 shown has the same shape (e.g., a corner cube prism). Regarding the dimensions of each side of the glass 124 (i.e., Figure 3 The values ​​a, b, and c shown, and the angle (i.e., Figure 3 The conditions for α, β, and γ shown can also be the same as those shown for the diamond optical-magnetic sensor 100. As described above, in Figure 12 In this process, the excitation light incident on the incident surface 126 is reflected by the reflecting surface 128 inside the diamond optical-magnetic sensor 120 and concentrated within the single-dot dashed line (hereinafter referred to as the excitation light amplification region). Therefore, the diamond 122 only needs to be at least partially present within the excitation light amplification region, and the shape of the diamond 122 is arbitrary. By forming the area around the diamond with glass 124, the amount of diamond can be reduced, thereby lowering the cost of the diamond optical-magnetic sensor. Furthermore, since the glass can be machined into the shape of a pyramidal prism, the manufacture of the diamond optical-magnetic sensor becomes easier compared to machining the diamond itself.

[0116] As described above, the fluorescence emitted from the NV center of the diamond 122 is reflected by the reflecting surface 128 and output from the incident surface 126. The component containing the diamond 122 is not limited to glass. It can also be resin, as long as the transmittance of green light (i.e., wavelength about 490-560 nm) and red light (i.e., wavelength about 630-800 nm) is high. Furthermore, since the refractive index of glass 124 is smaller than that of diamond, it is preferable to process the surface of the reflecting surface 128 to be flat to provide the mirror (e.g., metal coating, metal vapor deposition, etc.).

[0117] (Second variation)

[0118] The above description addresses the case where the reflective surface is planar, but it is not a limitation. The diamond optical-magnetic sensor involved in the second variation has a curved reflective surface.

[0119] Reference Figure 13 The diamond optical-magnetic sensor 130 includes an NV center, a planar incident surface 132, and a curved reflecting surface 134. Excitation light is incident on the incident surface 132. The reflecting surface 134 is, for example, a curved surface connecting the focal point 136 of a parabolic or ellipsoidal surface. The reflecting surface 134 is concave when viewed from the incident surface 132 side. If the reflecting surface 134 is concave, the excitation light incident on the diamond optical-magnetic sensor 130 from the incident surface 132 is reflected forward (i.e., from the incident surface 132 side) inside the diamond optical-magnetic sensor 130. Therefore, the optical path of the excitation light is lengthened, which increases the absorption efficiency of the excitation light at the NV center. Fluorescence emitted from the NV center is focused forward (i.e., from the incident surface 132 side) by the reflecting surface 134 inside the diamond optical-magnetic sensor 130 and output from the incident surface 132. Therefore, the focusing efficiency of the fluorescence can be increased.

[0120] Alternatively, the reflective surface of a diamond optical-magnetic sensor can also be spherical. (See reference...) Figure 14 The diamond optical-magnetic sensor 140 includes an NV center, a planar incident surface 142, and a curved reflecting surface 144. The diamond optical-magnetic sensor 140 is a spherical cap without a center O, obtained by cutting away a sphere of radius r with a plane that does not pass through its center O. The reflecting surface 144 is a portion of the cut-off spherical surface (i.e., a spherical cap). Excitation light enters the diamond optical-magnetic sensor 140 from the incident surface 142. The excitation light entering the diamond optical-magnetic sensor 140 is reflected forward (i.e., towards the incident surface 142 side) by the reflecting surface 144 inside the diamond optical-magnetic sensor 140. Therefore, the optical path of the excitation light is lengthened, increasing the absorption efficiency of the excitation light at the NV center. Fluorescence emitted from the NV center is focused forward (i.e., towards the incident surface 142 side) by the reflecting surface 144 inside the diamond optical-magnetic sensor 140 and output from the incident surface 142. Therefore, the focusing efficiency of the fluorescence is increased. Regarding... Figure 14 The lengths d and e shown are preferably r > d > 3r / 4 and 3r / 2 > e > r / 2. Length d is the diameter of the incident surface 142, and length e is the height of the spherical cap (i.e., the maximum value of the vertical distance from the incident surface 142 to the spherical cap).

[0121] Regarding the diamond optical-magnetic sensor involved in the second modification, similarly to the first modification, it can also be formed as comprising a diamond containing an NV center and a glass containing that diamond. In this case, the glass containing the diamond is formed as follows: Figure 13 or Figure 14 The shape shown.

[0122] (Third variation)

[0123] The above description addresses the case where the incident surface of the excitation light is planar, but it is not a limitation. The diamond photomagnetic sensor involved in the third variation has a curved incident surface.

[0124] Reference Figure 15 The diamond optical-magnetic sensor 150 includes an NV center, a curved incident surface 152, and a curved reflecting surface 154. Both the incident surface 152 and the reflecting surface 154 are spherical caps, and the diamond optical-magnetic sensor 150 is shaped by joining two spherical caps on a plane. Excitation light enters the diamond optical-magnetic sensor 150 from the incident surface 152. The excitation light entering the diamond optical-magnetic sensor 150 is reflected forward (i.e., to the incident surface 152 side) by the reflecting surface 154 inside the diamond optical-magnetic sensor 150. Therefore, the optical path of the excitation light is lengthened, which increases the absorption efficiency of the excitation light at the NV center. Fluorescence emitted from the NV center is focused forward (i.e., to the incident surface 152 side) by the reflecting surface 154 inside the diamond optical-magnetic sensor 150 and output from the incident surface 152. Therefore, the focusing efficiency of the fluorescence can be increased.

[0125] If the reflecting surface 154 is as follows Figure 14 As shown, two spherical defects are formed by cutting away a sphere of radius r, then regarding... Figure 15 The lengths d and e shown are preferably r > d > 3r / 4 and 3r / 2 > e > r / 2. If the diamond optical-magnetic sensor 150 has such a shape, when the excitation light is incident on the incident surface 152 parallel to the axis perpendicular to the joint surface of the incident surface 152 and the reflecting surface 154, the excitation light can be focused inside the diamond optical-magnetic sensor 150.

[0126] Regarding the diamond optical-magnetic sensor involved in the third modification, similarly to the first modification, it can also be formed as comprising a diamond containing an NV center and a glass containing that diamond. In this case, the glass containing the diamond is formed as follows: Figure 15 The shape shown.

[0127] (Fourth variation)

[0128] The above description addresses the case where the diamond optical-magnetic sensor is tetrahedral, but it is not a limitation. The fourth variation involves a diamond optical-magnetic sensor that is a polyhedron with five or more pentahedrons.

[0129] Reference Figure 16 The diamond optical-magnetic sensor 160 includes an NV center and is formed as a triangular prism (i.e., a pentahedron), having an incident surface 162 and four reflecting surfaces other than the incident surface 162 (i.e., reflecting surfaces 164, etc.). Excitation light enters the diamond optical-magnetic sensor 160 from the incident surface 162. The excitation light entering the diamond optical-magnetic sensor 160 is reflected forward (i.e., on the incident surface 162 side) by multiple reflecting surfaces such as the reflecting surfaces 164 inside the diamond optical-magnetic sensor 160. Therefore, the optical path of the excitation light becomes longer, which can increase the absorption efficiency of the excitation light from the NV center. The fluorescence emitted from the NV center is focused forward (i.e., on the incident surface 162 side) by multiple reflecting surfaces such as the reflecting surfaces 164 inside the diamond optical-magnetic sensor 160 and is output from the incident surface 162. Therefore, the focusing efficiency of the fluorescence can be increased.

[0130] When using a diamond optical-magnetic sensor 160 to measure magnetic fields. Figure 16 The angle δ shown is preferably 90 degrees. The incident surface 162 is preferably a square, that is, the lengths h and i of the two orthogonal sides are equal. In addition, the following relationship is preferably satisfied with respect to the lengths f, g, h, and i.

[0131] g×(1 / 1.4-0.5)≤f≤g×(1 / 1.4+0.5)

[0132] h×(1 / 1.4-0.5)≤f≤h×(1 / 1.4+0.5)

[0133] i×(1 / 1.4-0.5)≤f≤i×(1 / 1.4+0.5)

[0134] Diamond optical-magnetic sensors can also be polyhedrons with more than one hexahedron. Alternatively, they can also be... Figure 13 as well as Figure 14 The reflective surface of the curved surface shown is a polyhedron approximated by multiple planes.

[0135] Regarding the diamond optical-magnetic sensor involved in the fourth modification, similarly to the first modification, it can also be formed as comprising a diamond containing an NV center and a glass containing that diamond. In this case, the glass containing the diamond is formed as a polyhedron with five or more pentahedrons (e.g., Figure 16 (The triangular prism shown).

[0136] (Fifth variation)

[0137] In the above description, the case of detecting fluorescence output from the surface into which the excitation light is incident (i.e., the case where the direction of the excitation light incident on the diamond optical-magnetic sensor is opposite to the direction of the fluorescence output from the diamond optical-magnetic sensor) was explained, but it is not limited to this. In the diamond optical-magnetic sensor according to the fifth modified example, the direction of the excitation light incident is the same as the direction of the fluorescence output, and fluorescence output from a surface different from the surface into which the excitation light is incident is detected.

[0138] Reference Figure 17 The fifth variation involves a diamond optical-magnetic sensor 400 formed from diamond containing an NV center, shaped as a generally triangular pyramid (specifically a truncated pyramid) with flat minute portions 402. The diamond optical-magnetic sensor 400 can be, for example, made by... Figure 3 The diamond optical-magnetic sensor 100 shown is formed by cutting out the portion containing vertex D with a predetermined plane.

[0139] Reference Figure 18 The excitation light to the diamond optical-magnetic sensor 400 is irradiated by the optical fiber 408 onto the micro-part 402. For example, the excitation light is irradiated perpendicularly from the optical fiber 408 onto the surface of the micro-part 402. Thus, the excitation light irradiated from the optical fiber 408 enters the diamond optical-magnetic sensor 400 from the micro-part 402. Fluorescence is emitted from the NV center 104 by the excitation light entering the interior of the diamond optical-magnetic sensor 400. The emitted fluorescence is reflected by the reflective surface 404, output from the output surface 410, and enters the optical fiber 102. The fluorescence entering the optical fiber 102 is transmitted to the detector through the optical fiber 102.

[0140] The minute portion 402 is a portion with an area smaller than the reflecting surface 404, which only needs to meet the optical incidence conditions into the diamond optical-magnetic sensor 400, and may not be planar as described later. The minute portion 402 is preferably a size of sub-μm or larger, allowing the laser (i.e., excitation light) to penetrate it. Furthermore, the position of the minute portion 402 is preferably such that the emitted light (i.e., fluorescence) from the NV center caused by the excitation light incident on the diamond optical-magnetic sensor 400 is reflected by the reflecting surface and focused towards the optical system receiving the emitted light. Furthermore, focusing refers to the function of concentrating light with an extended angle in a direction toward the target.

[0141] The above description describes the case where the minute portion 402 for receiving excitation light is flat, but it is not limited to this. (See reference...) Figure 19The diamond optical-magnetic sensor 420 has a minute portion 422 and a reflective surface 424. The reflective surface 424, like the reflective surface 404, is approximately triangular. The minute portion 422 is not flat but a smooth curved surface. Therefore, as shown by the solid arrow, the excitation light incident on the minute portion 422 mainly enters the interior of the diamond optical-magnetic sensor 420. As shown by the dashed arrow, light incident on the portion other than the minute portion 422 (i.e., the reflective surface 424) is mainly reflected and cannot enter the interior of the diamond optical-magnetic sensor 420. Thus, the shape of the minute portion can also be non-flat, as long as it allows the excitation light to enter the interior of the diamond optical-magnetic sensor 420. The fluorescence emitted from the NV center 104 by the excitation light incident on the diamond optical-magnetic sensor 420 is reflected by the reflective surface 424 and output from the opposite side of the excitation light's incident side.

[0142] (Sixth variation)

[0143] In the fifth variation, a case was described where the diamond optical-magnetic sensor containing the NV center is a roughly triangular pyramid with a small portion, but it is not limited to this. (See also...) Figure 20 The diamond optical-magnetic sensor 430 involved in the sixth modification has a minute portion 432 and a reflective surface 434, both of which are integrally formed as smooth curved surfaces. Therefore, as shown by the solid arrow, the excitation light incident on the minute portion 432 mainly enters the interior of the diamond optical-magnetic sensor 430. As shown by the dashed arrow, light incident on the portion other than the minute portion 432 (i.e., the reflective surface 434) is mainly reflected and cannot enter the interior of the diamond optical-magnetic sensor 430. The fluorescence emitted from the NV center 104 by the excitation light incident on the diamond optical-magnetic sensor 430 is reflected by the reflective surface 434 and output from the side opposite to the side where the excitation light was incident.

[0144] Furthermore, similar to the fifth variation, the minute portion can also be flat. (See also...) Figure 21 The diamond optical-magnetic sensor 440 has a minute portion 442 and a reflective surface 444. The reflective surface 444 is a smooth curved surface, while the minute portion 442 is a flat surface. The optical paths for excitation light and fluorescence are... Figure 20 same.

[0145] (Seventh variation)

[0146] In the fifth and sixth modifications, cases where the entire diamond optical-magnetic sensor is made of diamond were described, but this is not a limitation. (See reference...) Figure 22 The diamond optical-magnetic sensor 450 involved in the seventh modification includes a glass 452 and a diamond 122, the glass 452 having a minute portion 454 and a reflective surface 456. The diamond optical-magnetic sensor 450 and... Figure 12Similarly, the interior of glass 452 contains diamond 122, including the NV center. The shape of glass 452 is similar to... Figure 17 as well as Figure 18 The diamond photomagnetic sensor 400 shown has the same shape (i.e., a truncated pyramid). Therefore, as indicated by the solid arrow, the excitation light incident on the minute portion 454 is primarily incident on the interior of the glass 452 and into the diamond 122. As indicated by the dashed arrow, light incident on the portion outside the minute portion 454 (i.e., the reflecting surface 456) is primarily reflected and cannot enter the interior of the glass 452, thus not reaching the diamond 122. The fluorescence emitted from the NV center of the diamond 122 by the excitation light incident on the glass 452 is reflected by the reflecting surface 456 and output from the opposite side of the excitation light's incident side.

[0147] Even tiny portions formed in glass can be non-flat. (See reference) Figure 23 The diamond optical-magnetic sensor 460 includes a glass 462 and a diamond 122. The glass 462 has a minute portion 464 and a reflective surface 466. The diamond 122, containing the NV center, is located within the glass 462. The shape of the glass 462 is similar to... Figure 19 The diamond photomagnetic sensor 420 shown is identical. That is, the minute portion 464 is not flat, but a smooth curved surface. The optical paths for excitation light and fluorescence are the same as... Figure 22 same.

[0148] As mentioned above, diamond 122 only needs to be present in at least a portion of the excitation light amplification region (i.e., Figure 12 The size of the interior (within the single-dot dashed line) is sufficient, and the shape of the diamond 122 is arbitrary. By forming the area around the diamond using glass, the amount of diamond can be reduced, thus lowering the cost of the diamond optical-magnetic sensor. Furthermore, since only glass needs to be machined, the manufacture of the diamond optical-magnetic sensor is easier compared to machining the diamond itself.

[0149] (Eighth variation)

[0150] The shape of the diamond-containing glass is not limited to the shapes described above. (See reference...) Figure 24 The diamond optical-magnetic sensor 470 involved in the eighth modification includes a glass 472 and a diamond 122. The glass 472 has a minute portion 474 and a reflective surface 476. The glass 472 contains a diamond 122 including an NV center. The shape of the glass 472 is similar to... Figure 20The diamond photomagnetic sensor 430 shown has the same shape. That is, the minute portion 474 of the glass 472 and the reflective surface 476 are formed as a whole as a smooth curved surface. Therefore, as shown by the solid arrow, the excitation light incident on the minute portion 474 mainly enters the interior of the glass 472 and into the diamond 122. As shown by the dashed arrow, the light incident on the portion other than the minute portion 474 (i.e., the reflective surface 476) is mainly reflected and cannot enter the interior of the glass 472, and will not enter the diamond 122. The fluorescence emitted from the NV center of the diamond 122 by the excitation light incident on the glass 472 is reflected by the reflective surface 476 and output from the opposite side of the side where the excitation light is incident.

[0151] Furthermore, even minute portions of glass can be flat. (See reference) Figure 25 The diamond optical-magnetic sensor 480 includes a glass 482 and a diamond 122. The glass 482 has a minute portion 484 and a reflective surface 486. The glass 482 contains the diamond 122, which includes the NV center. The shape of the glass 482 is... Figure 21 The diamond photomagnetic sensor 440 shown has the same shape. Glass 482 is a smooth curved surface, and the minute portion 484 is a flat surface. The optical paths for excitation light and fluorescence are the same as... Figure 24 same.

[0152] Furthermore, from the viewpoints of light transmittance, ease of processing, and ease of handling, the aforementioned glass is preferably quartz glass. Glass is capable of transmitting over 90% of excitation light and fluorescence, and is further preferably a material with a high refractive index. This is because, at the reflective surface of the glass (e.g., Figure 22 The critical angle for total internal reflection (such as the reflective surface 456) increases, resulting in more focused fluorescence. Additionally, this is because at the glass-diamond interface (e.g., the...)... Figure 22 The boundary between glass 452 and diamond 122 has less internal reflection, making it easier for light (i.e., excitation light) to penetrate into the diamond.

[0153] A sensor unit can be constructed using the diamond optical-magnetic sensor described above. Specifically, as described above, the sensor unit includes: a diamond optical-magnetic sensor containing an NV center; an irradiation unit that irradiates excitation light onto the diamond optical-magnetic sensor; a detection unit that detects emitted light from the NV center of the diamond optical-magnetic sensor; and an optical waveguide that transmits the excitation light and the emitted light. Thus, a sensor unit with fast response and high sensitivity can be achieved.

[0154] The above description focuses on diamond optical-magnetic sensors containing NV centers, but is not limited to this. Any diamond optical-magnetic sensor with a color center possessing electron spin is acceptable. A color center with electron spin is a center that forms a spin triplet state and emits light when excited; the NV center is a representative example. Furthermore, color centers with electron spin are known to exist in silicon-hole centers (i.e., Si-V centers), germanium-hole centers (i.e., Ge-V centers), and tin-hole centers (i.e., Sn-V centers). Therefore, diamonds containing these types of centers can be used instead of diamonds containing NV centers to construct diamond optical-magnetic sensors.

[0155] The above description illustrates the transmission of excitation light and fluorescence to a diamond photomagnetic sensor via optical fiber, but it is not limited to this. Excitation light and fluorescence can also be transmitted spatially. For example, refer to... Figure 26 The excitation light output from the light source 500 is collimated into parallel light by the collimating lens 502, reflected by the dichroic mirror 504, and focused by the collimating lens 506 to illuminate the diamond optical-magnetic sensor 100. The fluorescence emitted from the NV center of the diamond optical-magnetic sensor 100 is collimated into parallel light by the collimating lens 506, passed through the dichroic mirror 504, focused by the collimating lens 508, and detected by the photodetector 510.

[0156] Example 1

[0157] The effectiveness of this disclosure is demonstrated below through examples. A diamond optical-magnetic sensor uses materials cut to... Figure 3 The elements of the corner cube prism shown are compared with the flat element as a comparative example.

[0158] Type Ib diamond was used, with an electron beam acceleration energy of 3 MeV and an electron beam dose of 3 × 10⁻⁶. 18 pcs / cm 2 Electrons were injected into the diamond, which was then annealed at 800°C for about 1 hour to produce a diamond containing an NV center. This diamond was then cut into a pyramidal prism with a 1mm bevel to fabricate a diamond optical-magnetic sensor. Additionally, a diamond optical-magnetic sensor was fabricated as a comparative example by cutting it into a cube with a 1mm side length.

[0159] use Figure 27 The measuring apparatus shown irradiates a diamond photomagnetic sensor with an NV center with excitation light, and measures the fluorescence intensity emitted from the NV center. (Refer to...) Figure 27The structure (i.e., the irradiation system) in the measuring apparatus for irradiating the diamond optical-magnetic sensor 210 with excitation light includes a light source 200, a collimating lens 202, a dichroic mirror 204, a spherical lens 206, and an optical fiber 208. The structure (i.e., the observation system) for observing the fluorescence emitted from the diamond optical-magnetic sensor 210 includes the optical fiber 208, the spherical lens 206, the dichroic mirror 204, an LPF (Long Pass Filter) 212, and a photodetector 214. The structure (i.e., the microwave system) for irradiating the diamond optical-magnetic sensor 210 with microwaves includes a coaxial cable 220, a microwave irradiation unit 222, and a terminating resistor 224.

[0160] The excitation light source 200 uses an LD (laser diode) element (specifically, an L515A1 manufactured by Thorlabs) to generate a 5mW green laser (i.e., excitation light). The excitation light output from the source 200 is focused by a collimating lens 202 and then incident on a dichroic mirror 204. The collimating lens 202 is an LA1116-A manufactured by Thorlabs, and the dichroic mirror 204 is an SO6-RG manufactured by Suruga Seiki Co., Ltd. The excitation light (i.e., green light) incident on the dichroic mirror 204 is reflected by the mirror. The reflected light is focused by a spherical lens 206 and then incident on an optical fiber 208 (specifically, the fiber core). After propagation in the optical fiber 208, it illuminates the diamond photomagnetic sensor 210. The spherical lens 206 is an MS-08-4.35P1 (8mm in diameter) manufactured by Opto Sigma. Fiber 208 uses a digital optical cable with a core diameter of φ0.9mm.

[0161] The fluorescence emitted from the diamond photomagnetic sensor 210, which is incident on the optical fiber 208, propagates within the fiber 208, is then shaped into parallel light by the spherical lens 206, and incident on the dichroic mirror 204. The fluorescence (i.e., red light) incident on the dichroic mirror 204 passes through the dichroic mirror 204 and is incident on the LPF 212. The fluorescence after passing through the LPF 212 is detected by the photodetector 214. The LPF 212 allows light with wavelengths above a predetermined wavelength to pass through, while blocking (e.g., reflecting) light with wavelengths lower than the predetermined wavelength. The LPF 212 uses a LOPF-25C-593 manufactured by Opto Sigma. The photodetector 214 uses a photodiode (specifically, an S6967 manufactured by Hamamatsu Photonics Co., Ltd.). The emitted light from the diamond is red light, which passes through the LPF 212, but the wavelength of the excitation light is shorter than the wavelength of the emitted light from the diamond, and therefore does not pass through the LPF 212. This prevents the excitation light emitted from the light source 200 from being detected by the photodetector 214 and thus becoming noise, which would reduce the detection sensitivity.

[0162] Microwaves (1W) generated by a microwave generating device (not shown) are transmitted to a diamond optical-magnetic sensor 210 using a coaxial cable 220 and a microwave irradiation unit 222. The coaxial cable 220 uses a coaxial cable with a characteristic impedance of 50Ω. (Refer to...) Figure 28 The microwave irradiation section 222 is a coplanar circuit, with conductors 302 and 304 formed mutually insulated on the surface of an electrically insulating flexible substrate 300. Conductors 302 and 304 are formed of copper foil, and a 50Ω terminating resistor 224 (see reference) is used in region 306. Figure 27 The process terminates. Diamond optical-magnetic sensor 210 (refer to...) Figure 27 The device is positioned in region 308. The frequency of the microwave irradiating the diamond optical-magnetic sensor 210 is varied in the range of 2.74 GHz to 2.94 GHz, and excitation light is irradiated onto the diamond optical-magnetic sensor 210. The output voltage of the photodetector 214 is measured as an observation of the generated fluorescence.

[0163] The measurement results are shown in Figure 29 as well as Figure 30 . Figure 29 This indicates the results of using a diamond with a pyramidal prism as a diamond optical-magnetic sensor 210. Figure 30 The results show the comparative example of using a flat diamond as a diamond photomagnetic sensor 210. The vertical axis represents the voltage (V) of fluorescence intensity, and the horizontal axis represents the microwave frequency. Black circles plot the measurement data.

[0164] according to Figure 29 The results show a fluorescence intensity of approximately 2440 mV, which, as the spin detection contrast ratio (i.e., the rate of decrease in red light brightness, the value obtained by dividing the size of the valley in the graph by the fluorescence intensity), is approximately 2%. Therefore, multiplying these together yields a signal intensity of approximately 50 mV. On the other hand, according to... Figure 30 The graph shows a fluorescence intensity of approximately 520 mV, resulting in a contrast ratio of approximately 0.3%. Multiplying these values ​​yields a signal intensity of approximately 1.7 mV. Therefore, by using a diamond photomagnetic sensor with a pyramidal prism, the fluorescence intensity can be increased by approximately 5 times, and the contrast ratio can be increased by approximately 6 times. Consequently, the signal intensity can be significantly increased by approximately 30 times.

[0165] Example 2

[0166] Similar to Example 1, diamond optical-magnetic sensors using cut diamonds... Figure 3 The cornerstone prism shown is compared to a flat element, which was used to conduct experiments on transmitting excitation light and fluorescence via spatial transmission.

[0167] The diamond optical-magnetic sensor was fabricated in the same manner as in Example 1. Specifically, type Ib diamond was used, with an electron beam acceleration energy of 3 MeV and an electron beam dose of 3 × 10⁻⁶. 18 pcs / cm 2 Electrons were injected, followed by annealing at 800°C for approximately 1 hour to generate diamond containing NV centers. This diamond was then cut into a pyramidal prism with a 1mm bevel, and a tiny portion (i.e., the entry point for excitation light into the diamond) was formed at the vertex to fabricate a diamond optical-magnetic sensor. Additionally, a comparative diamond optical-magnetic sensor was fabricated by cutting it into a cube with a 1mm side length.

[0168] use Figure 31 The measuring apparatus shown irradiates the vertex (i.e., the minute portion) of the diamond photomagnetic sensor with the NV center with excitation light (reference). Figure 18 The fluorescence intensity emitted from the NV center was measured. (Refer to...) Figure 31 The structure in the measuring apparatus for irradiating the diamond optical-magnetic sensor 210 with excitation light (i.e., the irradiation system) includes a light source 200 and a collimating lens 202. The structure for observing the fluorescence emitted from the diamond optical-magnetic sensor 210 (i.e., the observation system) includes an LPF 212 and a photodetector 214. The structure for irradiating the diamond optical-magnetic sensor 210 with microwaves (i.e., the microwave system) includes a coaxial cable 220, a λ / 4 variable 520, and a λ / 4 open-circuit stub 522.

[0169] The light source 200, collimating lens 202, and photodetector 214 use the same components as in Embodiment 1. The LPF 212 differs from that in Embodiment 1, using an FGL590 manufactured by Thorlabs. The coaxial cable 220 uses the same 50Ω characteristic impedance coaxial cable as in Embodiment 1. The λ / 4 variable resistor 520 is constructed from microstrip lines with an impedance of 20Ω. The λ / 4 open-circuit stub 522 is constructed from parallel two-wire lines with an impedance of 300Ω. The λ / 4 variable resistor 520 functions as an impedance converter, accurately switching impedance between the coaxial cable 220 and the λ / 4 open-circuit stub 522 (which acts as a resonator), enabling efficient microwave irradiation of the diamond photomagnetic sensor 210.

[0170] A 5mW green light was used as the excitation light. The excitation light spot was reduced to a diameter of 20μm to achieve a power density of 3W / mm². 2A 1W microwave was swept in the frequency range of 2.74GHz to 2.94GHz to irradiate the diamond photomagnetic sensor 210 with excitation light, and the resulting fluorescence was measured. The result showed that the response speed was 30 μs for both the diamond cut into a cornerstone prism and the diamond of the comparative example. The photocurrent in the photodiode of the photodetector 214, corresponding to the fluorescence intensity, was 10 μA in the case of the diamond of the comparative example, and 100 μA in the case of the diamond cut into a cornerstone prism.

[0171] The present disclosure has been described above by way of example, but the above-described embodiments are merely examples and the present disclosure is not limited to the above-described embodiments. The scope of the present disclosure is as set forth in the claims, based on the detailed description of the invention, and includes all modifications within the meaning and scope of the statements herein.

[0172] Explanation of reference numerals in the attached figures

[0173] 100, 120, 130, 140, 150, 160, 210, 400, 420, 430, 440, 450, 460, 470, 480: Diamond optical-magnetic sensors;

[0174] 102, 208, 408: Fiber optic cables;

[0175] 104: NV Center;

[0176] 106, 404, 424, 434, 444, 456, 466, 476, 486: Reflective surfaces;

[0177] 108: Vertical plane;

[0178] 110, 112: Concentrating elements;

[0179] 122: Diamond;

[0180] 124, 452, 462, 472, 482: Glass;

[0181] 126, 132, 142, 152, 162: Incident surfaces;

[0182] 128, 134, 144, 154, 164: Reflective surfaces;

[0183] 136: Focus;

[0184] 200, 500: Light source;

[0185] 202, 502, 506, 508: Collimating lenses;

[0186] 204, 504: Dichroic mirrors;

[0187] 206: Spherical lens;

[0188] 212: LPF;

[0189] 214, 510: Photodetectors;

[0190] 220: Coaxial cable;

[0191] 222: Microwave irradiation section;

[0192] 224: Terminating resistor;

[0193] 300: Flexible substrate;

[0194] 302, 304: Conductors;

[0195] 306, 308: Areas;

[0196] 402, 422, 432, 442, 454, 464, 474, 484: minute parts;

[0197] 410: Output surface;

[0198] 520: λ / 4 variable;

[0199] 522: λ / 4 open circuit stub;

[0200] A, B, C, D: Points;

[0201] a, b, c, d, e, f, g, h, i: length;

[0202] O: Center;

[0203] r: radius;

[0204] α, β, γ, δ, θ: angle.

Claims

1. A diamond optical-magnetic sensor, wherein, The diamond optical-magnetic sensor includes: Diamond, which has color centers with electron spin; and A reflective surface that reflects the excitation light that propagates through the optical system and enters the interior of the diamond. The reflective surface reflects the emitted light from the color center excited by the excitation light, focusing it towards the optical system. The optical system includes optical fibers and lenses. The excitation light, propagating via the optical fiber, is output from the lens and incident on the diamond. The reflective surface focuses the emitted light from the color center onto the lens. The magnification of the lens is the reciprocal of the numerical aperture of the optical fiber. The size of the circumcircle of the diamond face opposite the optical fiber is in the range of more than 80% and less than 120% of the product of the core diameter and the numerical aperture of the optical fiber.

2. The diamond optical-magnetic sensor according to claim 1, wherein, The excitation light is emitted from the output of the optical system and then into the diamond. The reflective surface focuses the emitted light onto the output section of the optical system.

3. A diamond optical-magnetic sensor, wherein, The diamond optical-magnetic sensor includes: Diamond has color centers with electron spin; A tiny portion that allows excitation light propagating through an optical system to penetrate into the interior of the diamond; as well as A reflective surface that reflects the emitted light from the color center excited by the excitation light incident from the minute portion, focusing the light in a direction that guides it to the light-receiving optical system of the light-receiving element. The reflective surface has an area larger than the tiny portion. The reflective surface guides the emitted light, which is emitted from the same position in different directions, to the light-receiving optical system through multiple optical paths. The optical system includes optical fibers and lenses. The excitation light, propagating via the optical fiber, is output from the lens and incident on the diamond. The reflective surface focuses the emitted light from the color center onto the lens. The magnification of the lens is the reciprocal of the numerical aperture of the optical fiber. The size of the circumcircle of the diamond face opposite the optical fiber is in the range of more than 80% and less than 120% of the product of the core diameter and the numerical aperture of the optical fiber.

4. The diamond optical-magnetic sensor according to claim 3, wherein, The excitation light is emitted from the output of the optical fiber through the tiny portion and into the diamond. The emitted light is focused by the reflective surface onto the output section of the optical fiber.

5. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The diamond photomagnetic sensor further includes a component containing the diamond and allowing the excitation light and the emitted light to pass through. The reflective surface is formed on the component.

6. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The reflective surface is formed in the diamond.

7. The diamond optical-magnetic sensor according to claim 5, wherein, As the component, a material with a refractive index closer to that of diamond is selected.

8. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The reflecting surface includes a curved surface or multiple planes connecting the focal point.

9. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The diamond has a flat surface and a spherical cap. The reflective surface is formed by the spherical cap.

10. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The diamond has two spherical caps. The reflective surface is formed by the first of the two spherical caps.

11. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The diamond is formed as a polyhedron. The reflective surface is formed by multiple faces of the polyhedron.

12. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The reflective surface has a plane. The angle between the plane perpendicular to the incident axis of the excitation light and the plane, forming the incident side of the excitation light, is 20° or more and 70° or less.

13. The diamond optical-magnetic sensor according to claim 12, wherein, The angle between the vertical plane and the plane is greater than 30° and less than 50°.

14. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The diamond has a pyramidal prism.

15. The diamond optical-magnetic sensor according to claim 7, wherein, The component containing the diamond has a pyramidal prism.

16. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The optical system includes optical fibers. The size of the diamond is more than one-third and less than three times the core diameter of the optical fiber.

17. The diamond optical-magnetic sensor according to any one of claims 1 to 4, wherein, The optical system includes optical fibers. The diamond is larger than or equal to the size of a circle inscribed in the circle with the core diameter of the optical fiber and smaller than or equal to the size of the circle circumscribed in the circle.

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