sensor

Abstract

The present invention provides a sensor capable of suppressing fluctuations in the magnetic field applied from a magnet to an element having a color center. [Solution] The sensor 1 comprises an element 10 that emits fluorescence when irradiated with excitation light and has a color center, an antenna 20 that radiates microwaves to the element 10, an optical system 30 that irradiates the element 10 with excitation light, a photosensor 40 that receives the fluorescence emitted from the element 10 and detects the intensity of the fluorescence, a magnet 50 that applies a bias magnetic field to the element 10, and a holder 60 that houses and fixes the element 10 and the magnet 50 so that the positional relationship between the element 10 and the magnet 50 is constant.

Description

[Technical Field]

[0001] This invention relates to a sensor. [Background technology]

[0002] Conventionally, optically detected magnetic resonance (ODMR) techniques using materials such as diamond containing nitrogen and lattice defects (NV centers) are known. In this technique, as described later, the magnetic field received by the object being measured can be measured based on the resonance frequency of the ODMR spectrum.

[0003] Patent Document 1 discloses a magnetic field measuring device comprising a magnetic resonance member (element), a high-frequency magnetic field generator for applying microwaves to the magnetic resonance member, a magnet for applying a static magnetic field to the magnetic resonance member, and an irradiation device for irradiating the magnetic resonance member with incident light of a specific wavelength. The magnetic resonance member is a material such as diamond containing an NV center. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-057947 [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent Document 1 discloses applying a bias magnetic field (static magnetic field) to a magnetic resonance element, such as a diamond element having an NV center, using a magnet. However, Patent Document 1 does not disclose a method for fixing the magnet. On the other hand, when the magnet is fixed to an optical table, there is a problem that the bias magnetic field applied from the magnet to the magnetic resonance element fluctuates over time. Therefore, it may be difficult to measure the magnetic field with high accuracy using conventional magnetic field measuring devices.

[0006] This invention has been made in view of the problems of the prior art. The object of this invention is to provide a sensor that can suppress fluctuations in the magnetic field applied from a magnet to an element having a color center. [Means for solving the problem]

[0007] A sensor according to an aspect of the present invention comprises an element that emits fluorescence upon irradiation with excitation light and has a color center, an antenna that radiates microwaves to the element, an optical system that irradiates excitation light to the element, and a photosensor that receives the fluorescence emitted from the element and detects the intensity of the fluorescence. The sensor comprises a magnet that applies a bias magnetic field to the element, and a holder that houses and fixes the element and the magnet such that the positional relationship between the element and the magnet is constant. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a sensor that can suppress fluctuations in the magnetic field applied from a magnet to an element having a color center. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view showing a sensor according to one embodiment. [Figure 2] This is a plan view showing an example of the inside of a sensor with the top panel removed. [Figure 3] This diagram schematically shows the structure of a diamond element having an NV center. [Figure 4] This figure shows the valence band and conduction band of a diamond element with an NV center. [Figure 5] This figure shows the energy levels between the ground state and excited state of a diamond element having an NV center. [Figure 6] This is the ODMR spectrum when no magnetic field is applied to the element (Bext=0). [Figure 7]It is a graph showing the relationship between the magnetic field applied to the element and the energy levels of the ground state (ms = -1, 0, +1). [Figure 8] It is the ODMR spectrum when no magnetic field is applied to the element (Bext = 0) and when a magnetic field is applied to the element (Bext > 0). [Figure 9] It is a perspective view showing an example of an antenna according to an embodiment. [Figure 10] It is the ODMR spectrum when the current in the bus bar is 0, when the current in the bus bar is positive, and when the current in the bus bar is negative in the state where a magnetic field is applied to the element. [Figure 11] It is a schematic diagram showing the state when the center of the diamond element having the NV center is arranged at a height of 2.5 mm from the surface of the bus bar. [Figure 12] It is a graph showing the relationship between the current in the bus bar and the magnetic flux density of the element when the center of the diamond element having the NV center is arranged at a height of 2.5 mm from the surface of the bus bar. [Figure 13] It is a schematic plan view showing the appearance of an apparatus according to a comparative example in which a magnet is attached to an optical surface plate to measure the transition of the resonance frequency of the element. [Figure 14] It is a graph showing the relationship between the elapsed time and the resonance frequency in the case where the current in the bus bar is 0 A and the ambient temperature is 25 °C for the apparatus according to the comparative example. [Figure 15] It is a graph showing the relationship between the elapsed time and the resonance frequency in the case where the current in the bus bar is 0 A and the ambient temperature is 25 °C for the apparatus according to this example. [Figure 16] It is the simulation result of Test Example 1. [Figure 17] It is the simulation result of Test Example 2. [Figure 18] It is a graph showing the relationship between the position of the diamond element and the magnetic flux density in Test Example 1 and Test Example 2.

Embodiments for Carrying Out the Invention

[0010] The sensor according to this embodiment will be described in detail below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0011] Figure 1 is a perspective view showing a sensor 1 according to one embodiment. Figure 2 is a plan view showing an example of the interior of the sensor 1 with the top plate 63 removed. The sensor 1 according to this embodiment is a current sensor that measures the current flowing through a busbar B such as a power supply path or a power distribution board. As shown in Figures 1 and 2, the sensor 1 according to this embodiment includes an element 10, an antenna 20, a microwave generator 26, an optical system 30, a light sensor 40, a control calculation processing unit 45, a magnet 50, and a holder 60.

[0012] The element 10 according to this embodiment emits fluorescence upon irradiation with excitation light. The element 10 is a diamond element having an NV center and is positioned in close proximity to one side of the busbar B. The element 10 is a plate-shaped member with a rectangular shape in plan view. The element 10 is attached to the tip of the optical fiber 32 of the optical system 30 and has an irradiation surface 10a to which excitation light is irradiated. The element 10 has a first emission surface 10b on the side opposite to the irradiation surface 10a from which fluorescence is emitted. The element 10 also has a second emission surface 10c that connects the irradiation surface 10a and the first emission surface 10b and from which fluorescence is emitted. The irradiation surface 10a and the first emission surface 10b are parallel surfaces, and the second emission surface 10c is a surface perpendicular to the irradiation surface 10a and the first emission surface 10b and extends in the thickness direction of the element 10. The second emission surface 10c is formed from four surfaces, and the area of ​​each surface is smaller than the area of ​​the irradiation surface 10a and the first emission surface 10b.

[0013] Antenna 20 radiates microwaves onto element 10. Optical system 30 irradiates element 10 with excitation light. Photosensor 40 receives fluorescence emitted from element 10 and detects the intensity of the fluorescence. Control processing unit 45 controls microwave generator 26 and optical system 30 and calculates at least one physical quantity selected from the group consisting of magnetic field, electric field, temperature, strain, etc., of the object to be measured, based on the output signal detected by photosensor 40. Magnet 50 applies a bias magnetic field to element 10. Holder 60 is attached to the surface of busbar B and houses and fixes element 10 and magnet 50 so that the positional relationship between element 10 and magnet 50 is constant.

[0014] As shown in Figure 3, the NV center has a structure in which one carbon atom in the diamond crystal structure is replaced by a nitrogen atom, and a vacancy is located adjacent to the replaced nitrogen atom. Because the NV center has a long spin coherence time at room temperature and atmospheric pressure, it can perform highly sensitive measurements even under normal environmental conditions.

[0015] As shown in Figure 4, diamond is a wide-bandgap semiconductor with a bandgap width of approximately 5.5 eV, but its ground state is located 2.6 eV from the conduction band, and its excited states are also within the bandgap.

[0016] As shown in Figure 5, an NV center (NV) has one negative charge. - ) is the magnetic quantum number m in the ground state of spin S=1. S =-1,0,+1 results in a triplet state, m S The spin sub-levels of =±1 are degenerate when the magnetic field is 0. S When the element 10 is in the ground state of =0, if green excitation light is shone on it, the electrons transition from the ground state to the excited state and then return to the ground state while emitting red fluorescence. However, m S =0 and m S A microwave of 2.87 GHz, corresponding to the energy difference with ±1, is applied to element 10, and electrons m S When the state is ±1, and green excitation light is shone on element 10, the proportion of non-radiative transitions increases. In other words, the intensity of red fluorescence is due to the electrons mS is lower when excited from m = ±1 than when excited from m = 0. Therefore, as shown in Fig. 6, when the frequency of the microwave is the resonance frequency of the NV center, the intensity of the red fluorescence emitted from the NV center decreases. Thus, by utilizing the characteristics of ODMR, the spin state of the NV center can be detected with light and microwaves. S =0から励起された場合よりも、m

[0017] On the other hand, as shown in Figs. 7 and 8, when a magnetic field parallel to the NV axis is applied to element 10, the levels of m = -1 and m = +1 are Zeeman split, and the resonance frequency varies in proportion to the magnetic field strength. Therefore, by obtaining the difference between the microwave frequency at the minimum fluorescence intensity at m = -1 and the microwave frequency at the minimum fluorescence intensity at m = +1, the magnetic field strength applied to element 10 can be measured. S =-1とm S =+1の準位がゼーマン分裂し、磁場強度に比例して共鳴周波数が変動する。そのため、m S =-1における蛍光強度極小値のマイクロ波周波数と、m S =+1における蛍光強度極小値のマイクロ波周波数と差を求めることにより、素子10に印加される磁場強度を測定することができる。

[0018] Antenna 20 radiates microwaves to element 10. Antenna 20 radiates microwaves with variable frequency to element 10. Microwaves are supplied to antenna 20 by a microwave generator 26. Antenna 20 is electrically connected to a power supply line 27 such as a coaxial cable, and a high-frequency current with variable frequency is supplied from the microwave generator 26 through the power supply line 27.

[0019] As shown in Figure 9, the antenna 20 is formed into a rectangular loop shape by bending, for example, a roughly rectangular plate-shaped conductor. Such an antenna 20 is low-cost and can reduce unevenness in the distribution of microwaves applied to the element 10. The element 10 is arranged inside the loop-shaped antenna 20. The antenna 20 includes a first metal plate 21, a second metal plate 22, a third metal plate 23, a fourth metal plate 24, and a fifth metal plate 25. The first metal plate 21, the second metal plate 22, the third metal plate 23, the fourth metal plate 24, and the fifth metal plate 25 are all flat plates. The first metal plate 21 is connected to the second metal plate 22, and the second metal plate 22 is connected to the third metal plate 23. The third metal plate 23 is connected to the fourth metal plate 24, and the fourth metal plate 24 is connected to the fifth metal plate 25.

[0020] In the planar direction, one end of the first metal plate 21 is a free end, and the other end of the first metal plate 21 is connected to the second metal plate 22. In the planar direction, one end of the second metal plate 22 is connected to the first metal plate 21, and the other end of the second metal plate 22 is connected to the third metal plate 23. In the planar direction, one end of the third metal plate 23 is connected to the second metal plate 22, and the other end of the third metal plate 23 is connected to the fourth metal plate 24. In the planar direction, one end of the fourth metal plate 24 is connected to the third metal plate 23, and the other end of the fourth metal plate 24 is connected to the fifth metal plate 25. In the planar direction, one end of the fifth metal plate 25 is connected to the fourth metal plate 24, and the other end of the fifth metal plate 25 is a free end.

[0021] The first metal plate 21 and the fifth metal plate 25, and the third metal plate 23 and the fifth metal plate 25 are arranged facing each other with a space in between. The second metal plate 22 and the fourth metal plate 24 are also arranged facing each other with a space in between. The first metal plate 21 has a feed point, to which a feed line 27 is connected. A high-frequency current is supplied from the microwave generator 26 to the antenna 20 via the feed line 27 and the feed point. The element 10 is arranged in the space enclosed by the second metal plate 22, the third metal plate 23 and the fourth metal plate 24. The third metal plate 23 is positioned facing the first emission surface 10b of the element 10 and covering the first emission surface 10b. The second metal plate 22 and the fourth metal plate 24 are positioned facing the second emission surface 10c of the element 10, respectively, and are positioned to cover each second emission surface 10c. The fifth metal plate 25 has a power supply line insertion hole 25a through which a power supply line 27 is inserted, and an optical fiber insertion hole 25b through which an optical fiber 32 is inserted. The power supply line insertion hole 25a is a power supply point connected to, for example, the outer conductor of a coaxial cable.

[0022] The optical system 30 irradiates the element 10 with excitation light. The optical system 30 irradiates the element 10 with green light as the excitation light. The optical system 30 includes a light source 31 and an optical fiber 32. The light source 31 may include, for example, a laser diode and emit laser light. The light emitted from the light source 31 may have a peak in intensity that shows its maximum value in the range of 500 nm to 560 nm. The optical fiber 32 guides the light emitted from the light source 31 to the element 10. Specifically, the light source 31 is provided at one end of the optical fiber 32, and the element 10 is provided at the other end of the optical fiber 32. The light emitted from the light source 31 irradiates the element 10. In this embodiment, the optical fiber 32 also includes a multimode fiber, and the red fluorescence emitted from the element 10 passes through the optical fiber 32 and is guided to the photosensor 40 via a dichroic mirror (not shown).

[0023] The light sensor 40 receives the fluorescence emitted from the element 10 and detects the intensity of the fluorescence. The light sensor 40 may include a photodiode, and the red fluorescence emitted from the element 10 may be detected by the photodiode. The light sensor 40 outputs an output signal corresponding to the detected fluorescence intensity to the control processing unit 45.

[0024] The control processing unit 45 controls the microwave generator 26 and the optical system 30, and calculates at least one physical quantity selected from the group consisting of magnetic field, electric field, temperature, and strain of the object to be measured, based on the output signal detected by the optical sensor 40. The control processing unit 45 is equipped with a computer including a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and loads a program stored in ROM into RAM and executes it with the CPU.

[0025] The magnet 50 applies a bias magnetic field to the element 10. The magnet 50 is <111> A bias magnetic field is applied parallel to the direction. As shown in Figure 2, in this embodiment, the magnet 50 includes a pair of magnets, a first magnet 51 and a second magnet 52. The pair of magnets are arranged so as to sandwich the element 10 with a space between them.

[0026] As shown in the upper part of Figure 10, when a bias magnetic field is applied to element 10, as described above, m S = +1 and m SThe -1 energy level undergoes Zeeman splitting, and the splitting width increases in proportion to the strength of the bias magnetic field. On the other hand, as shown in the middle of Figure 10, when a positive current is passed through busbar B in Figure 1 from left to right, the splitting width decreases depending on the magnitude of the magnetic field generated when the current is passed. Also, as shown in the lower part of Figure 10, when a negative current is passed through busbar B in Figure 1 from right to left, the splitting width increases depending on the magnitude of the magnetic field generated when the current is passed. In this case, if the bias magnetic field applied to element 10 is small compared to the current flowing through busbar B, the resonance frequencies will overlap when a large positive current flows through busbar B. Therefore, by applying a sufficiently large bias magnetic field to element 10 relative to the current flowing through busbar B, the direction of the current can be detected. The magnitude of the bias magnetic field of magnet 50 can be adjusted as appropriate depending on the current detection range.

[0027] Here, as shown in Figure 11, when element 10 having an NV center is positioned 2.5 mm from the surface of busbar B, the relationship between the current flowing through busbar B and the magnetic flux density applied to element 10 was evaluated. The results are shown in Figure 12. As shown in Figure 12, when a current of 1000 A flows through busbar B, the magnetic flux density applied to element 10 is 14.5 mT. In this case, when a bias magnetic field is applied to element 10 with a magnetic flux density of 14.5 mT, even when a current of -1000 A to +1000 A flows through busbar B, the two resonance frequencies that appear due to Zeeman splitting do not intersect, making it possible to detect currents of ±1000 A. Since the two resonance frequencies that appear due to Zeeman splitting change depending on the direction of the current flowing through busbar B, the current flowing through busbar B can be detected by comparing them with the resonance frequency when the current flowing through busbar B is 0 A.

[0028] The magnet 50 may include at least one of a permanent magnet and an electromagnet. The permanent magnet may include at least one selected from the group consisting of neodymium magnets, samarium cobalt magnets, ferrite magnets, and alnico magnets. These magnets should be selected based on conditions such as the magnetic field strength applied to the element 10, the distance between the first magnet 51 and the second magnet 52, the size of the magnet 50, and the operating temperature range of the magnet 50. For example, neodymium magnets have a strong magnetic force, so a large bias magnetic field can be applied to the element 10. Samarium cobalt magnets have a weaker magnetic force compared to neodymium magnets, but their Curie temperature is higher than that of neodymium magnets, and they can maintain a high magnetic force even in high-temperature environments, thus having good temperature characteristics. Therefore, when forming the same magnetic field strength with samarium cobalt magnets as when using neodymium magnets in the element 10, the distance between the magnets 50 can be reduced, and thus the size of the sensor 1 can be reduced.

[0029] The first magnet 51 and the second magnet 52 in this embodiment are ring-shaped magnets. The ring-shaped magnets have through holes, and the optical fiber 32 is inserted through the through hole of the first magnet 51. The ring-shaped magnets surround the optical fiber 32. This allows for efficient use of space, and thus the size of the sensor 1 can be reduced.

[0030] The holder 60 houses and secures the element 10 and the magnet 50. By securing the element 10 and the magnet 50 in the same holder 60, the positional relationship between the element 10 and the magnet 50 in the holder 60 becomes constant. With this configuration, fluctuations in the bias magnetic field applied to the element 10 by the magnet 50 can be suppressed.

[0031] The holder 60 includes a base plate 61, a plurality of support columns 62, and a top plate 63. The base plate 61 is attached in contact with the surface of the busbar B. In this embodiment, the base plate 61 is integrally formed with the plurality of support columns 62, and the plurality of support columns 62 support the top plate 63. The holder 60 also has an element housing section 64, a power supply line insertion section 65, an optical fiber insertion section 66, and a magnet housing section 67. The element housing section 64, the power supply line insertion section 65, the optical fiber insertion section 66, and the magnet housing section 67 are spaces formed between the base plate 61, the support columns 62, and the top plate 63.

[0032] The holder 60 houses the element 10 and the antenna 20. The element housing section 64 houses the element 10, and the position of the element 10 is fixed relative to the position of the holder 60. The antenna 20 is also housed in the element housing section 64, and the antenna 20 is fixed to the holder 60. The feed line 27 is inserted through the feed line insertion section 65. The optical fiber 32 is inserted through the optical fiber insertion section 66. The tip of the optical fiber 32 is positioned in the element housing section 64. The magnet housing section 67 houses the magnet 50, and the position of the magnet 50 is fixed so that the magnet 50 does not move relative to the holder 60. The magnet housing section 67 has a first magnet housing section 67a and a second magnet housing section 67b.

[0033] The first magnet housing 67a houses the first magnet 51 and fixes the position of the magnet 50 so that it does not move relative to the holder 60. The first magnet housing 67a has a recess in which the first magnet 51 is housed. The recess of the first magnet housing 67a is configured to sandwich the first magnet 51 in the width direction, and the length of the first magnet 51 in the width direction is approximately the same as the length of the first magnet housing 67a in the width direction. Therefore, the first magnet 51 can be fixed to the first magnet housing 67a by fitting the first magnet 51 into the recess of the first magnet housing 67a. Alternatively, the first magnet 51 may be fixed to the first magnet housing 67a using an adhesive or the like.

[0034] The second magnet housing 67b houses the second magnet 52 and fixes the position of the second magnet 52 so that it does not move relative to the holder 60. The second magnet housing 67b has a recess in which the second magnet 52 is housed. The recess of the second magnet housing 67b is configured to sandwich the second magnet 52 in the width direction, and the length of the second magnet 52 in the width direction is approximately the same as the length of the second magnet housing 67b in the width direction. Therefore, the second magnet 52 can be fixed to the second magnet housing 67b by fitting the second magnet 52 into the recess of the second magnet housing 67b. Alternatively, the second magnet 52 may be fixed to the second magnet housing 67b using an adhesive or the like.

[0035] The element housing section 64 is located between the first magnet housing section 67a and the second magnet housing section 67b. The element 10 is attached to the tip of the optical fiber 32. The first magnet 51 and the second magnet 52 are ring-shaped magnets, and the optical fiber 32 is inserted through a through-hole in the first magnet 51 and held by the first magnet 51. The tip of the optical fiber 32 is located in the element housing section 64. Therefore, the position of the element 10 is fixed in the element housing section 64 so that the element 10 does not move relative to the holder 60.

[0036] In this embodiment, the holder 60 has a rectangular parallelepiped shape and is made of a resin material, but the shape of the holder 60 and the material used to form it are not particularly limited. For example, the holder 60 may be made of a material such as ceramic.

[0037] Next, an evaluation apparatus for a comparative example, as shown in Figure 13, was assembled, and the transition of the element's resonance frequency was evaluated. In the evaluation apparatus, sensors A and B, each containing a diamond element with NV centers on both sides of a busbar, were attached, and a pair of neodymium magnets were fixed to an optical platen so as to sandwich sensors A, B, and the busbar. Figure 14 shows the results of measuring the transition of the resonance frequency using the evaluation apparatus when the busbar current was 0A and the ambient temperature was 25°C. In Figure 14, "HIGH" indicates the resonance frequency on the high-frequency side, and "LOW" indicates the resonance frequency on the low-frequency side (see Figure 10).

[0038] As shown in Figure 14, even though no current was flowing through the busbar, the resonance frequencies of both Sensor A and Sensor B fluctuated over time. In other words, the results in Figure 14 indicate that the bias magnetic field of the element fluctuates over time. Furthermore, it was confirmed that the bias magnetic field also fluctuated after the device was transported due to the shift in the position of the magnet. From these results, it is thought that the bias magnetic field fluctuated over a long period of time due to the loosening of the fixing screws, etc., since the magnet is fixed to the optical base plate. If the magnetic field strength of the element fluctuates, it may affect the detection accuracy.

[0039] On the other hand, in the sensor 1 according to this embodiment, the holder 60 holds the element 10 and the magnet 50 so that the positional relationship between the element 10 and the magnet 50 remains constant. By fixing the element 10 and the magnet 50 within the same holder 60, fluctuations in the positional relationship between the element 10 and the magnet 50 can be suppressed compared to the case where the magnet 50 is fixed to an optical base plate. Therefore, for example, when a samarium-cobalt magnet is held inside the holder 60, fluctuations in the bias magnetic field applied to the element 10 can be suppressed, as shown in Figure 15. Furthermore, in the sensor 1 according to this embodiment, it is not necessary to place the magnet 50 outside the holder 60, so the sensor 1 can be made smaller.

[0040] Next, the magnetic flux density in the conditions described in Test Example 1 and Test Example 2 was evaluated by simulation. Figure 16 shows the simulation results for Test Example 1. Figure 17 shows the simulation results for Test Example 2. Figure 18 is a graph showing the relationship between the position of the diamond and the magnetic flux density in Test Example 1 and Test Example 2. The values ​​in Figures 16 and 17 represent the magnetic flux density (in mT). In Figure 18, the center of the diamond element is set to a distance of 2.5 mm.

[0041] [Test Example 1] A pair of plate-type neodymium magnets (30 mm long, 30 mm wide, and 10 mm thick) were placed on an optical base plate with a gap of 113 mm between them, so that element 10 was positioned in the center.

[0042] [Test Example 2] A pair of ring-shaped samarium-cobalt magnets (outer diameter 6.5 mm, inner diameter 3.53 mm, thickness 2.0 mm) were placed in the holder described in this embodiment with a gap of 18.5 mm between them, so that element 10 is positioned in the center.

[0043] Figures 16 to 18 confirm that even when a small magnet is fixed inside the miniaturized holder, the same magnetic flux density as when it is installed on an optical base plate can be applied to element 10. Fixing the magnet inside the holder reduces the volume of the magnet that applies the bias magnetic field, thus contributing to the miniaturization of sensor 1.

[0044] Sensor 1, configured as described above, irradiates the NV center of element 10 with green excitation light and simultaneously radiates microwaves to the NV center of element 10 while modulating the frequency of the microwaves. By utilizing the characteristics of ODMR, the magnetic field around busbar B can be measured.

[0045] In this embodiment, the case where sensor 1 is a current sensor has been described. Sensor 1 can be used, for example, as a battery sensor to evaluate the remaining battery level of an electric vehicle by measuring the current flowing through busbar B. However, sensor 1 may also measure at least one physical quantity selected from the group consisting of magnetic field, electric field, temperature, strain, etc., using ODMR.

[0046] Furthermore, although the element 10 according to this embodiment is a diamond element having an NV center, it may also be an element having a color center such as an SnV center, a SiV center, or a GeV center. An SnV center is a structure in which one carbon atom in the diamond crystal is replaced by tin (Sn), and a vacancy is adjacent to the replaced Sn. A SiV center is a structure in which one carbon atom in the diamond crystal is replaced by Si, and a vacancy is adjacent to the replaced Si. A GeV center is a structure in which one carbon atom in the diamond crystal is replaced by Ge, and a vacancy is adjacent to the replaced Ge.

[0047] As described above, the sensor 1 according to this embodiment includes an element 10 that emits fluorescence upon irradiation with excitation light and has a color center, an antenna 20 that radiates microwaves to the element 10, and an optical system 30 that irradiates the element 10 with excitation light. The sensor 1 also includes a photosensor 40 that receives the fluorescence emitted from the element 10 and detects the intensity of the fluorescence, and a magnet 50 that applies a bias magnetic field to the element 10. The sensor 1 includes a holder 60 that houses and fixes the element 10 and the magnet 50 so that the positional relationship between the element 10 and the magnet 50 is constant.

[0048] In the sensor 1 according to this embodiment, the holder 60 houses and fixes the element 10 and the magnet 50 such that the relative positions of the element 10 and the magnet 50 remain constant. Therefore, compared to the case where the magnet 50 is fixed to an optical base plate, fluctuations in the relative positions of the element 10 and the magnet 50 can be suppressed. As a result, fluctuations in the magnetic field applied from the magnet 50 to the element 10 having a color center can be suppressed.

[0049] Magnet 50 may include a samarium-cobalt magnet. Compared to neodymium magnets, samarium-cobalt magnets have a higher Curie temperature and can maintain high magnetic force even in high-temperature environments, thus exhibiting good temperature characteristics. Therefore, the decrease in magnetic force can be suppressed.

[0050] The optical system 30 includes an optical fiber 32, and the element 10 may be attached to the end of the optical fiber 32. With this configuration, the excitation light can be reliably irradiated onto the element 10, and the intensity of the fluorescence emitted from the element 10 can be increased. The magnet 50 may also include a ring-shaped magnet surrounding the optical fiber 32. With this configuration, space can be used effectively, and the size of the sensor 1 can be reduced.

[0051] In this embodiment, the optical fiber 32 includes a multimode fiber, and the red fluorescence emitted from the element 10 is guided through the optical fiber 32 to the photosensor 40 via a dichroic mirror (not shown). However, the method of receiving fluorescence is not limited to this method. For example, the photosensor 40 may be positioned to face the second emission surface 10c. With this arrangement, fluorescence from the element 10 can be detected by the photosensor 40 without using a dichroic mirror. Therefore, the detection mechanism can be miniaturized in the sensor 1 using the element 10 having a color center.

[0052] Furthermore, the third metal plate 23 of the antenna 20 may be provided with a through-hole through which the fluorescence emitted from the element 10 passes. The antenna 20 is formed from a plate-shaped member with a through-hole, and the through-hole of the plate-shaped member may be positioned between the element 10 and the photosensor 40 such that the first emission surface 10b and the photosensor 40 face each other. With this configuration, the photosensor 40 can detect fluorescence emitted from the front of the element 10, rather than from the side. Therefore, the sensor 1 according to this embodiment can effectively detect the fluorescence intensity of the element 10 having a color center, and can improve the signal-to-noise ratio, for example.

[0053] Although this embodiment has been described above, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment. [Explanation of symbols]

[0054] 1 sensor 10 elements 20 antennas 30 Optical system 32 optical fibers 40 Light Sensors 50 magnets 60 holder

Claims

1. An element that emits fluorescence upon irradiation with excitation light and has a color center, The element is provided with an antenna that emits microwaves, An optical system for irradiating the element with the excitation light, A light sensor that receives the fluorescence emitted from the element and detects the intensity of the fluorescence, A magnet for applying a bias magnetic field to the element, A holder that houses and fixes the aforementioned button and the magnet such that the relative position of the button and the magnet is constant, A sensor equipped with the following features.

2. The sensor according to claim 1, wherein the magnet includes a samarium-cobalt magnet.

3. The optical system includes optical fibers, The element is attached to the tip of the optical fiber, The sensor according to claim 1 or 2, wherein the magnet includes a ring-shaped magnet surrounding the optical fiber.

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