Diamond sensor

Abstract

This diamond sensor includes a diamond having a color center having electron spin, and a sensor head that accommodates the diamond, wherein: the diamond includes a reflective surface which reflects excitation light that has propagated through an optical system and has entered the inside of the diamond, and a flat surface that allows the excitation light to enter the inside of the diamond and allows radiation light emitted from the color center to exit the diamond; the reflective surface reflects the radiation light radiated from the color center that has been excited by the excitation light and causes the radiation light to condense in the direction of the optical system; a first off angle, which is an angle formed by a specific crystal plane of the diamond having a low index, is 3° or less with respect to a reference plane perpendicular to a predetermined reference direction fixed to the sensor head; and a surface roughness Ra of the flat surface is 20 nm or less.

Description

Diamond Sensor

[0001] The present disclosure relates to a diamond sensor. This application claims priority to Japanese Application No. 2024-027997, filed February 28, 2024, the entire contents of which are incorporated herein by reference.

[0002] Diamond sensors using NV centers (hereinafter referred to as NV centers) in diamond are known. When an NV center, which is composed of nitrogen (i.e., N) that has entered the substitution position of carbon (i.e., C) in diamond and a vacancy (i.e., V: Vacancy) adjacent to the nitrogen, becomes negatively charged, its ground state becomes a triplet state (i.e., spin S=1). A negatively charged NV center is an NV － Although the term "NV center" is used in the present specification, it will be abbreviated as "NV center" below for convenience. When a charged NV center is excited by laser light with a wavelength of approximately 530 nm (i.e., green light), it emits fluorescence with a wavelength of approximately 637 nm (i.e., red light). The intensity of the fluorescence changes depending on the spin state of the NV center, and the spin state of the NV center changes due to magnetic resonance between a magnetic field applied to the NV center and microwaves or radio waves, so it can be used as a magnetic sensor.

[0003] For detection, an optical system is used that transmits excitation light from a light source and irradiates the diamond containing NV centers, and a waveguide that transmits microwaves from a power source and irradiates the diamond. In addition, an optical system is also used that collects fluorescence from the NV centers of the diamond and transmits it to a photodetector. Patent Document 1 below discloses a corner cube-shaped diamond as a diamond containing NV centers.

[0004] International Publication No. 2022 / 210695

[0005] A diamond sensor according to one aspect of the present disclosure includes a diamond having a color center with electronic spin, and a sensor head that houses the diamond, wherein the diamond includes a reflective surface that reflects excitation light that is propagated through an optical system and enters the interior of the diamond, and a flat surface that allows the excitation light to enter the interior of the diamond and causes the radiation light emitted from the color center to exit the diamond, wherein the reflective surface reflects the radiation light emitted from the color center excited by the excitation light and focuses it in the direction of the optical system, and a first off angle, which is the angle formed by a specific crystal plane with a low index of the diamond with respect to a reference plane that is perpendicular to a predetermined reference direction fixed to the sensor head, is 3° or less, and the surface roughness Ra of the flat surface is 20 nm or less.

[0006] FIG. 1A is a left side view of a diamond sensor according to an embodiment of the present disclosure. FIG. 1B is a front view of the diamond sensor shown in FIG. 1A. FIG. 2 is a perspective view of the diamond shown in FIG. 1. FIG. 3 is a cross-sectional view showing the relationship between the diamond housed in the sensor head and the reference direction indicator. FIG. 4 is a cross-sectional view showing the angle formed between the crystal plane of the diamond and the bottom surface of the diamond formed by cutting. FIG. 5 is a perspective view showing the relationship between the four possible directions of the NV axis of the diamond and the magnetic field to be measured. FIG. 6 is a graph schematically showing the relationship between the signal strength and electromagnetic wave frequency observed in the state shown in FIG. 5. FIG. 7 is a graph schematically showing the relationship between the signal strength and electromagnetic wave frequency observed in a state where the magnetic field is slightly tilted from the state shown in FIG. 5. FIG. 8 is a graph schematically showing the relationship between the signal strength and electromagnetic wave frequency observed in a state where the magnetic field is significantly tilted from the state shown in FIG. 5. FIG. 9A is a front view of a diamond according to a first modified example. FIG. 9B is a plan view of the diamond shown in FIG. 9A. FIG. 9C is a right side view of the diamond shown in FIG. 9A. FIG. 10 is a cross-sectional view showing a diamond sensor according to a second modified example. FIG. 11 is a perspective view showing the diamond shown in FIG. 10. FIG. 12A is a front view showing a diamond according to a third modified example. FIG. 12B is a plan view of the diamond shown in FIG. 12A. FIG. 12C is a right side view of the diamond shown in FIG. 12A. FIG. 13A is a front view of the fabricated diamond. FIG. 13B is a plan view of the diamond shown in FIG. 13A. FIG. 13C is a right side view of the diamond shown in FIG. 13A. FIG. 14 is a table showing the results of an experiment in which multiple diamonds similar to the diamonds shown in FIGS. 13A to 13C were fabricated and excitation light was incident from the bottom surface. FIG. 15 is a table showing the results of an experiment in which multiple diamonds similar to the diamonds shown in FIGS. 13A to 13C were fabricated and excitation light was incident from the incident surface.

[0007] [Problem that the present disclosure aims to solve] If the crystal plane of diamond containing NV center cannot be accurately positioned relative to the measurement object (for example, magnetic field), the width of ODMR (Optical Detected Magnetic Resonance) spectrum will be widened and split into multiple parts.Therefore, in order to measure external field (magnetic field, electric field and temperature), it is necessary to sweep microwaves over a wide frequency range, and it becomes difficult to measure with high accuracy in a short time.For example, when diamond is incorporated into a case or the like to manufacture a diamond sensor, the crystal plane of the incorporated diamond cannot be easily identified from the outside of the case, and it is not easy to position the crystal plane of diamond at the appropriate position relative to the measurement object.

[0008] Therefore, an object of the present disclosure is to provide a diamond sensor that can easily position the crystal face of the diamond relative to the object to be measured with high precision.

[0009] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a diamond sensor that can easily position the crystal plane of diamond with high precision relative to the measurement object.

[0010] [Description of Embodiments of the Present Disclosure] The contents of the embodiments of the present disclosure will be listed and described below. At least some of the embodiments described below may be combined in any combination.

[0011] (1) A diamond sensor according to a first aspect of the present disclosure includes a diamond having a color center with an electronic spin and a sensor head containing the diamond, wherein the diamond includes a reflective surface that reflects excitation light propagated through an optical system and incident on the diamond, and a flat surface that allows the excitation light to enter the diamond and emit radiation emitted from the color center from the diamond, the reflective surface reflects radiation emitted from the color center excited by the excitation light and focuses it in the direction of the optical system, and the first off-angle, which is the angle formed by a specific low-index crystal plane of the diamond with respect to a reference plane perpendicular to a predetermined reference direction fixed to the sensor head, is 3° or less, and the surface roughness Ra of the flat surface is 20 nm or less. This allows the crystal plane of the diamond to be accurately and easily positioned relative to the measurement object. Therefore, high-precision measurements can be performed in a short time.

[0012] (2) A diamond sensor according to a second aspect of the present disclosure includes a diamond having a color center with an electronic spin and a sensor head containing the diamond, wherein the diamond includes an incident surface that allows excitation light propagating through an optical system to enter the diamond, a reflective surface that reflects the radiated light emitted from the color center excited by the excitation light incident from the incident surface and focuses it toward the light-receiving optical system that guides it to the light-receiving element, and a flat surface that allows the radiated light to exit the diamond, the area of ​​the reflective surface being larger than the area of ​​the incident surface, and the reflective surface guides the radiated light emitted in different directions from the same position to the light-receiving optical system through multiple optical paths, the first off-angle, which is the angle formed by a specific crystal orientation with a low index of the diamond with respect to a reference plane perpendicular to a predetermined reference direction fixed to the sensor head, is 3° or less, and the surface roughness Ra of each of the flat surface and the incident surface is 20 nm or less. This allows the crystal plane of the diamond to be accurately and easily positioned relative to the measurement object. Therefore, high-precision measurements can be performed in a short time.

[0013] (3) In the above (1), the shape of the diamond may be a triangular pyramid, the flat surface may be the base of the triangular pyramid, and the second off-angle, which is the angle between the diamond's crystal plane {100} or crystal plane {111} and the base, may be 3° or less. As a result, when the base of the triangular pyramid diamond is positioned perpendicular to the reference direction, the off-angle of the crystal plane {100} or crystal plane {111} can be 3° or less with respect to the reference plane perpendicular to the reference direction, making it easy to store the diamond in the sensor head with high positional accuracy.

[0014] (4) In the above (2), the shape of the diamond may be a triangular pyramid truncated, the flat surface may be the bottom surface that is the lower base of the triangular pyramid truncated, and the second off-angle, which is the angle between the diamond's crystal plane {100} or crystal plane {111} and the bottom surface, may be 3° or less. As a result, when the bottom surface of the triangular pyramid truncated diamond is positioned perpendicular to the reference direction, the off-angle of the crystal plane {100} or crystal plane {111} with respect to the reference plane perpendicular to the reference direction can be 3° or less, making it easy to store the diamond in the sensor head with high positional accuracy.

[0015] (5) In the above (1) or (3), the sensor head may have a sensing surface, the shape of the diamond may be a triangular pyramid, and the third off-angle, which is the angle between the sensing surface and the base of the triangular pyramid, may be 1° or less. Thus, by precisely positioning the sensing surface of the sensor head relative to the measurement object, the crystal plane of the diamond can be precisely positioned relative to the measurement object, thereby improving the detection sensitivity of the diamond sensor.

[0016] (6) In the above (3) or (4), the fourth off angle may be 3° or less, and when the second off angle is the angle between the diamond crystal plane (001) and the bottom surface, the fourth off angle may be the angle between any one side of the bottom surface and the <100> direction of the diamond, or when the second off angle is the angle between the diamond crystal plane (111) and the bottom surface, the fourth off angle may be the angle between any one side of the bottom surface and the <1-10> direction of the diamond. This allows the diamond crystal plane to be positioned accurately relative to the measurement object. Also, it becomes easier to store the diamond in the sensor head with high positional accuracy.

[0017] (7) In the above (5), the fifth off-angle, which is the angle between one side of the sensing surface and one side of the bottom surface of the diamond, may be 1° or less. This allows the crystal plane of the diamond to be positioned accurately relative to the measurement target. It also makes it easier to accommodate the diamond in the sensor head with high positional accuracy.

[0018] (8) In (1) above, the diamond may be a triangular pyramid with each apex of the triangular base cut off, the first side formed by cutting off the apex may form an angle of 80° to 100° with respect to the base, and the exterior angle of the hexagon formed by cutting off the apex may be 57° to 63°. This makes it easier to grip the diamond that constitutes the diamond sensor, improves the processing accuracy of the diamond, and improves the detection accuracy of the diamond sensor.

[0019] (9) In (2) above, the diamond may be a truncated triangular pyramid with each vertex of the triangular base being removed, the first side formed by removing the vertices may form an angle of 80° to 100° with respect to the base, and the exterior angle of the hexagon formed by removing the vertices may be 57° to 63°. This makes it easier to grip the diamond that constitutes the diamond sensor, improves the processing accuracy of the diamond, and improves the detection accuracy of the diamond sensor.

[0020] (10) In any one of (1) to (9) above, the first off-angle may be 1° or less. This allows the crystal plane of the diamond to be positioned with greater precision relative to the object to be measured.

[0021] (11) In the above (10), the first off-angle may be 0.1° or less, thereby enabling the crystal plane of the diamond to be positioned with even greater precision relative to the object to be measured.

[0022] (12) In any one of the above (3), (4), (6), and (7), the second off-angle may be 1° or less. This allows the diamond to be accommodated in the sensor head with higher accuracy.

[0023] (13) In the above (12), the second off-angle may be 0.1° or less. This allows the diamond to be accommodated in the sensor head with even greater precision.

[0024] (14) In the above (6), the fourth off-angle may be 1° or less. This allows the crystal face of the diamond to be positioned with high precision relative to the measurement target. It also makes it easier to accommodate the diamond in the sensor head with high precision.

[0025] (15) In the above (5), the third off-angle may be 0.1° or less. This allows the diamond crystal plane to be positioned more accurately relative to the measurement object by accurately positioning the sensing surface relative to the measurement object, thereby further improving the detection sensitivity of the diamond sensor.

[0026] (16) In the above (7), the fifth off-angle may be 0.1° or less. This allows the crystal plane of the diamond to be positioned with greater precision relative to the measurement target. This also makes it easier to accommodate the diamond in the sensor head with greater positional precision.

[0027] (17) In the above (8) or (9), the exterior angle of the hexagon may be 59° or more and 61° or less. This makes it easier to grip the diamond that constitutes the diamond sensor, further improving the processing accuracy of the diamond and the detection accuracy of the diamond sensor.

[0028] (18) In any one of (8), (9), and (17) above, the maximum value of the diameter of the first side surface may be 50 μm or more and 40% or less of the length of one side of the triangle. This allows the diamond to be stably held. It also suppresses the reduction of NV centers, making it possible to balance the improvement of sensor accuracy due to the improvement of diamond processing accuracy with the reduction of fluorescence intensity.

[0029] (19) In any one of the above (8), (9), (17), and (18), the diamond may further include a second side surface formed by cutting each side of the bottom surface, which allows the diamond to be easily gripped using a two-point gripping jig when cutting the diamond.

[0030] [Details of the embodiments of the present disclosure] In the following embodiments, the same components are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0031] 1A and 1B, a diamond sensor 100 according to an embodiment of the present disclosure includes a diamond 102, an optical fiber 104, and a sensor head 106 housing the diamond 102 and the optical fiber 104. In FIGS. 1A and 1B, the diamond 102 and the optical fiber 104 are shown enlarged for convenience, and the magnification is not uniform. The diamond 102 is formed of a single crystal diamond containing an NV center composed of nitrogen (N) and a vacancy (V). The optical fiber 104 transmits excitation light 112 irradiated to the NV center of the diamond 102 and transmits fluorescence 114 emitted from the NV center to a detection device (not shown). The excitation light 112 is green light (i.e., wavelength 490 nm to 560 nm). The excitation light 112 is laser light generated, for example, by a semiconductor laser (e.g., emitted light wavelength 532 nm). The fluorescence 114 is detected by a detection device (e.g., a photodiode). The sensor head 106 includes a λ / 4 transformer 132 and a λ / 4 open stub 134 that function as resonators for irradiating microwaves onto the diamond 102. The λ / 4 open stub 134 is arranged to sandwich the diamond 102. The λ / 4 open stub 134 is bent at its center by approximately 90° and is arranged so as to form an angle of approximately 90° with the λ / 4 transformer 132 at the connection point with the λ / 4 transformer 132. Microwaves are generated by a microwave source (not shown) and transmitted to the λ / 4 transformer 132 by a coaxial cable 130.

[0032] The sensor head 106 has a prismatic shape, and a cross section perpendicular to its axis is rectangular. The sensor head 106 has, for example, a cross section perpendicular to its axis that is 5 mm wide x 10 mm high and 20 mm long. The sensor head 106 is formed, for example, from resin, and has a reference direction indicator 110 on its surface. As will be described later, the reference direction indicator 110 is used to identify the crystal plane of the diamond 102. The reference direction indicator 110 has a visible shape. For example, the reference direction indicator 110 is a linear convex or concave portion. The reference direction indicator 110 may also be a visible colored figure arranged on the surface of the sensor head 106. The sensor head 106 also has a sensing surface 108. FIG. 1B shows one horizontal side 116 of the sensing surface 108. The sensing surface 108 is a surface perpendicular to the axis of the sensor head 106. Therefore, the sensing surface 108 is perpendicular to the reference direction indicator 110, and the crystal plane of the diamond 102 can also be identified by the sensing surface 108. Note that as long as information for identifying the crystal plane of the diamond 102 is visibly displayed on the sensor head 106, any shape and color of information may be fixed to the sensor head 106.

[0033] Referring to FIG. 2 , the diamond 102 is a triangular pyramid having vertices A to D and a flat surface 120. The flat surface 120 is the base of the triangular pyramid. The diamond 102 is formed, for example, in a corner cube shape. FIG. 2 shows orthogonal X-, Y-, and Z-axes. That is, angles α, β, and γ are all 90°. The flat surface 120 is an equilateral triangle. The diamond 102 is positioned so that the flat surface 120 is perpendicular to the axis of the sensor head 106 (i.e., perpendicular to the reference direction indicator 110). The excitation light 112 output from the optical fiber 104 is incident on the flat surface 120. The incident excitation light 112 irradiates the NV center 122 in the diamond 102. The fluorescence 114 emitted from the NV center 122 is emitted in all directions. The emitted fluorescence 114 is reflected multiple times by the sides of the triangular pyramid, that is, the faces ABD, ACB, and ADC, and is emitted from the flat face 120. The fluorescence 114 emitted from the flat face 120 enters the optical fiber 104 and is transmitted to the detection device as described above.

[0034] The flat surface 120 is polished so that the excitation light 112 is efficiently incident on the flat surface 120. The three side surfaces (faces ABD, ACB, and ADC) of the triangular pyramid diamond 102 are polished so that the fluorescence 114 is efficiently reflected. The flat surface 120 and the three side surfaces have a surface roughness Ra of less than 20 nm, for example. This allows the excitation light 112 to efficiently incident on the flat surface 120. The fluorescence 114 is efficiently reflected and emitted from the flat surface 120.

[0035] The flat surface 120 of the diamond 102 is, for example, a crystal plane (001). The flat surface 120 may be a crystal plane (111). The flat surface 120 may be any low-index (relatively small Miller indices) crystal plane, including a crystal plane {100}, a crystal plane {110}, and a crystal plane {111}. The crystal plane {100} represents a crystal plane equivalent to the crystal plane (100) and the crystal plane (100). Similarly, the crystal plane {110} represents a crystal plane equivalent to the crystal plane (110) and the crystal plane (110), and the crystal plane {111} represents a crystal plane equivalent to the crystal plane (111). For example, if the flat surface 120 is a crystal plane (001), one side of the flat surface 120 is formed along, for example, the

[100] direction or the

[010] direction. For example, one side of the flat surface 120 formed along the

[100] direction (for example, side CD shown in FIG. 2) is arranged parallel to the side 116 of the sensing surface 108 shown in FIG. 1B. When the flat surface 120 is a crystal plane (011), one side of the flat surface 120 is formed along, for example, the

[100] direction or the [0-11] direction. For example, one side of the flat surface 120 formed along the

[100] direction (for example, side CD shown in FIG. 2) is arranged parallel to the side 116 of the sensing surface 108 shown in FIG. 1B. When the flat surface 120 is a crystal plane (111), one side of the flat surface 120 is formed along, for example, the [1-10] direction, the [10-1] direction, or the [01-1] direction. For example, one side of the flat surface 120 formed along the [1-10] direction (for example, side CD shown in FIG. 2) is arranged parallel to the side 116 of the sensing surface 108 shown in FIG. 1B. By forming the diamond 102 in this manner and disposing it on the sensor head 106, the detection accuracy of the fluorescence emitted from the NV center of the diamond 102 can be improved, as will be described later.

[0036] The sensor head 106 has a recess (not shown) for accommodating the corner cube-shaped diamond 102. The diamond 102 is placed in the recess, so that the crystal plane of the diamond 102 is aligned perpendicular to the reference direction indicator 110. Referring to FIG. 3 , depending on the precision of the recess for accommodating the diamond 102, the crystal plane of the diamond 102 may be tilted relative to a vertical plane 124, which is a reference plane perpendicular to the reference direction indicator 110. FIG. 3 illustrates a case in which the flat plane 120 is formed parallel to the crystal plane. For example, the tilt angle (hereinafter referred to as the off angle) θ1 is 3° or less. The off angle (first off angle) θ1 is the angle between the crystal plane (i.e., the flat plane 120) and the reference plane, with the vertical plane 124 relative to the reference direction indicator 110 being the reference plane. It refers to an in-plane angle (positive acute angle) perpendicular to the line where these two planes intersect. As a result, as will be described later, by arranging the reference direction indicator 110 of the diamond sensor 100 relative to the measurement object, the crystal plane of the diamond 102 can be accurately and easily positioned relative to the measurement object. Therefore, as will be described later, highly accurate measurements can be made in a short time.

[0037] In the above, it is assumed that the flat surface 120 of the diamond 102 is formed parallel to the crystal plane, but depending on the processing precision, the flat surface 120 may be misaligned with the crystal plane. Referring to Figure 4, the off-angle (second off-angle) θ2, which is the angle that the flat surface 120 forms with respect to the crystal plane 126, is 3° or less. As a result, when the flat surface 120 of the triangular pyramidal diamond 102 is arranged perpendicular to the reference direction marking 110, the off-angle of the crystal plane {100} or {111} with respect to the reference plane (vertical plane 124) perpendicular to the reference direction marking 110 can be 3° or less. Therefore, it becomes easy to accommodate the diamond 102 in the sensor head 106 with high positional precision.

[0038] Referring to FIG. 5, the orientation of the NV center contained in diamond 102, the direction of a magnetic field, which is an example of a measurement target, and the fluorescence intensity detected by ODMR will be described. There are four possible directions for the NV axis of the NV center. In FIG. 5, the bracketed [V] represents a vacancy, and the bracketed numbers [1] to [4] represent the four positions where nitrogen (N) can be located relative to [V]. FIG. 5 also shows the crystal orientation. Using a diamond containing N at equal ratios at positions [1] to [4], ODMR is performed with magnetic field B1, B2, or B3 applied as shown in FIG. 5, resulting in a graph with two valleys, as shown in FIG. 6. Magnetic fields B1, B2, and B3 are parallel to the <001>, <010>, and <100> directions, respectively. The graph shown in Figure 6 is obtained because the angle between the NV axis and magnetic field B1, B2, or B3 when N is at each of the positions [1] to [4] is 54.7°. That is, the same magnetic field strength is detected by the NV sensors when N is at each of the positions [1] to [4], so the frequency proportional to the magnetic field strength (i.e., the distance between the two valleys) is equal. The distance between the two valleys, i.e., the frequency difference, is proportional to the magnetic field strength. Therefore, because each valley is a monotonic valley with one minimum value, the distance between the two valleys can be calculated with high accuracy, and the magnetic field strength can also be calculated with high accuracy.

[0039] On the other hand, for example, by performing ODMR when magnetic field B1 is tilted relative to the NV center as indicated by the dashed arc-shaped arrow, a graph such as that shown in FIG. 7 is obtained. The dashed arrows in FIG. 5 represent the tilt in the plane including [1] and [2], or the tilt in the plane including [3] and [4]. In the graph shown in FIG. 7, the shape of each valley is not monotonic but includes multiple minimum values. Furthermore, its full width at half maximum (hereinafter simply referred to as the FWHM) is larger than that of FIG. 6. Therefore, the accuracy of calculating the distance between the two valleys decreases, and the accuracy of calculating the magnetic field strength also decreases. Therefore, it is necessary to sweep microwaves over a wide frequency range to measure the magnetic field, making it difficult to measure accurately in a short time. The same applies when magnetic fields B2 and B3 are each tilted relative to the NV center.

[0040] Furthermore, if the magnetic field B1 is tilted in a direction different from the direction indicated by the dashed arc-shaped arrow in FIG. 5 , the graph obtained by ODMR will be as shown in FIG. 8 . In the graph shown in FIG. 8 , the shape of each valley is not monotonic and contains more minimum values ​​than in FIG. 7 . Furthermore, the half-width is larger than that in FIG. 7 . Therefore, the accuracy of calculating the distance between the two valleys is further reduced, and the accuracy of calculating the magnetic field strength is further reduced. Therefore, it is necessary to sweep the microwave over a wider frequency range to measure the magnetic field, making it more difficult to measure accurately in a short time. The same applies when the magnetic fields B2 and B3 are tilted relative to the NV center.

[0041] Therefore, to improve the detection accuracy of the sensor and shorten the measurement time, it is important to accurately position the NV center relative to the measurement target (e.g., magnetic field). To achieve this, it is important to accurately position the crystal plane (e.g., crystal plane {100}) of the diamond 102 relative to the measurement target. As described above, a reference direction indicator 110 is provided on the sensor head 106, and the diamond 102 is positioned on the sensor head 106 so that the flat surface 120 is approximately perpendicular to the reference direction indicator 110. At this time, the diamond 102 is positioned so that the first off-angle θ1 is 3° or less. As described above, this allows the crystal plane of the diamond 102 to be accurately and easily positioned relative to the measurement target. Therefore, high-precision measurements can be performed in a short time. Note that when the diamond is positioned so that the crystal plane {111} or the crystal plane {110} of the diamond is perpendicular to the magnetic field of the measurement target, the angles between the magnetic field and the four NV axes are not the same, but the angles between the magnetic field and each NV axis are determined. The crystal plane {110} is a plane equivalent to the crystal plane (110). The shape of the graph obtained by ODMR (such as the number of valleys) is determined by using a diamond in which N is contained at the same ratio between [1] and [4]. Therefore, if the diamond crystal plane {111} or {110} can be precisely positioned perpendicular to the measurement target (magnetic field), the magnetic field strength can be easily calculated.

[0042] The first off-angle θ1 may be 1° or less. This allows the crystal plane of diamond 102 to be positioned with greater precision relative to the measurement object. The first off-angle θ1 may also be 0.1° or less. This allows the crystal plane of diamond 102 to be positioned with even greater precision relative to the measurement object.

[0043] The second off-angle θ2 may be 1° or less. This allows the diamond 102 to be accommodated in the sensor head 106 with greater precision. The second off-angle θ2 may be 1° or less. This allows the diamond 102 to be accommodated in the sensor head 106 with even greater precision.

[0044] As described above, the diamond 102 may be positioned relative to the sensing surface 108. For example, the off-angle (third off-angle), which is the angle between the sensing surface 108 and the flat surface 120, is 1° or less. This allows the crystal plane of the diamond 102 to be positioned relative to the measurement object with high precision by positioning the sensing surface 108 with high precision relative to the measurement object, thereby improving the detection sensitivity of the diamond sensor 100.

[0045] The third off-angle may be 0.1° or less. This allows the crystal plane of diamond 102 to be positioned more accurately with respect to the measurement object by precisely positioning sensing surface 108 with respect to the measurement object, thereby further improving the detection sensitivity of diamond sensor 100. The third off-angle may be 0.05° or less.

[0046] As described above, when the crystal plane (001) is used as the flat surface 120, one side of the flat surface 120 is formed, for example, along the <100> direction. Depending on the processing accuracy, the direction of one side of the flat surface 120 may be tilted with respect to the <100> direction. The off-angle (fourth off-angle), which represents the allowable range of tilt angles, is 3° or less. Furthermore, when the flat surface 120 is a crystal plane (111), one side of the flat surface 120 is formed, for example, along the <1-10> direction (including the [1-10] direction and its equivalent directions, such as the [10-1] direction and the [01-1] direction). Similarly, depending on the processing accuracy, the direction of one side of the flat surface 120 may be tilted with respect to the <1-10> direction. The fourth off-angle is 3° or less. This allows the crystal plane of the diamond 102 to be positioned accurately relative to the measurement target. Furthermore, it also makes it easier to accommodate the diamond 102 in the sensor head 106 with high positional accuracy.

[0047] The fourth off-angle may be 1° or less. This allows the crystal face of the diamond 102 to be positioned with high precision relative to the object to be measured. It also makes it easier to accommodate the diamond 102 in the sensor head 106 with high precision. The fourth off-angle may be 0.1° or less.

[0048] When placing the diamond 102 in the sensor head 106, as described above, it is placed so that one side of the flat surface 120 is parallel to the side 116 of the sensing surface 108. Depending on the placement accuracy, one side of the flat surface 120 may be tilted with respect to the side 116. The off-angle (fifth off-angle), which represents the allowable tilt angle, is 1° or less. This allows the crystal face of the diamond 102 to be positioned with precision relative to the object to be measured. It also makes it easier to accommodate the diamond 102 in the sensor head 106 with precision.

[0049] The fifth off-angle may be 0.1° or less. This allows the crystal plane of the diamond 102 to be positioned with greater precision relative to the measurement target. It also makes it easier to accommodate the diamond 102 in the sensor head 106 with greater positional precision. The fifth off-angle may be 0.05° or less.

[0050] In the above description, the sensor head 106 is described as being in the shape of a prism with a rectangular cross section (see FIG. 1B ), but is not limited to this. The sensor head 106 may be in the shape of a prism with a square cross section. The sensor head 106 may also be in the shape of a cylinder with a circular or elliptical cross section.

[0051] (First Modification) In the above, the diamond 102 has been described as a triangular pyramid, but this is not limiting. Referring to FIGS. 9A to 9C, the diamond 102A used in the diamond sensor 100 may have a shape in which each apex of the base of the triangular pyramid is cut off. That is, in the diamond 102A shown in FIG. 2, a portion of the diamond 102 from apex B for a length L1 is cut off perpendicular to the line connecting apex A and apex B in the plan view. The first side surface 202 formed by the cut-off is perpendicular to the bottom surface 200 (corresponding to the flat surface 120 in FIG. 2) (angle θ3 is 90°). Similarly, a portion of the diamond 102 from apex C for a length L2 and a portion of the diamond 102 from apex D for a length L2 are cut off perpendicular to the bottom surface 200. The first side surface 204 and the first side surface 206 formed by the cut-off are each perpendicular to the bottom surface 200. The length L1 is greater than the length L2.

[0052] The above-described cutting is performed to facilitate gripping of the diamond. Specifically, by gripping the first side surface 202, the first side surface 204, and the first side surface 206 using a three-point gripping tool, the diamond 102A can be stably gripped. The areas of the first side surface 202, the first side surface 204, and the first side surface 206 need only be large enough to be easily gripped. For example, the length L3 of one of the three sides of the first side surface 202 that is also included in the bottom surface 200 is 50 μm or more. The same applies to the first side surface 204 and the first side surface 206. Note that when the angles α, β, and γ shown in FIG. 2 are 90°, the length L3 is the maximum across length of the first side surface 202 if the first side surface 202 is perpendicular to the bottom surface 200. The across length is the distance between two points on the periphery of the figure. However, if the first side surface 202 is not perpendicular to the bottom surface 200, the maximum value of the diameter of the first side surface 202 may differ from the length L3. Furthermore, if the angles α, β, and γ shown in FIG. 2 are less than 90°, the maximum value of the diameter of the first side surface 202 may differ from the length L3 even if the first side surface 202 is perpendicular to the bottom surface 200. Therefore, to facilitate gripping, the maximum value of the diameter of the first side surface 202 needs only to be 50 μm or more.

[0053] On the other hand, as the amount of NV center removed from the triangular pyramid increases, the number of NV centers in the diamond decreases, resulting in a decrease in the detected fluorescence intensity. Furthermore, the area of ​​the fluorescence reflecting surface decreases, which also reduces the fluorescence intensity. Therefore, there is an allowable range for the amount of removal, and the maximum length across the first side surface 202 (e.g., length L3) is 40% or less of one side of the base of the original triangular pyramid (length L4). The same applies to each of the first side surface 204 and the first side surface 206. This allows for a stable grip of the diamond. Furthermore, the reduction in NV centers can be suppressed, making it possible to balance the improvement in sensor accuracy due to improved diamond processing accuracy with the reduction in fluorescence intensity.

[0054] The base 200 is hexagonal, with the angle θ4 between two adjacent sides being 120°, and the exterior angle θ5 being 60°. After cutting, the sides (triangles) of the triangular pyramid become pentagonal sides 210, 212, and 214. Figures 9A to 9C show the crystal orientation of diamond 102A. That is, the base 200 is the crystal plane (001), and the direction of side CD, one side of the base, is the <100> direction. The reason for the difference in cutting amounts (L1 > L2) as described above is to enable identification of sides in the <100> direction. If the sides in the <100> direction can be identified by another method, such as marking the surface of the diamond, length L1 may be equal to length L2.

[0055] Diamond 102A is arranged in sensor head 106 so that bottom surface 200 serves as the excitation light incidence surface and the fluorescence emission surface, and side surfaces 210, 212, and 214 serve as fluorescence reflection surfaces. Therefore, as described above, bottom surface 200, side surfaces 210, 212, and 214 are polished to a surface roughness Ra of less than 20 nm. This allows excitation light to efficiently enter bottom surface 200, and fluorescence to be efficiently reflected by side surfaces 210, 212, and 214 and emitted from bottom surface 200.

[0056] When fabricating diamonds for use in diamond sensors, triangular pyramids (e.g., corner cubes) of approximately 1 mm are fabricated using laser processing, taking into account the crystal planes. In this process, triangular pyramids are difficult to grasp and difficult to precisely machine relative to the crystal planes. Therefore, polishing the excitation light incident surface and the fluorescence reflection surface is not easy. As described above, diamond 102A has first side surface 202, first side surface 204, and first side surface 206 perpendicular to bottom surface 200, making it easy to grasp, improving the diamond's machining accuracy and the detection accuracy of the diamond sensor. That is, diamond 102A can be stably grasped by these three surfaces using a jig. Therefore, it is easy to precisely machine relative to the crystal planes and polish the bottom surface 200, etc. Furthermore, it is also easy to precisely position diamond 102A in sensor head 106.

[0057] Depending on the processing accuracy when producing diamond 102A from diamond 102, there is a possibility that diamond 102A will not be formed as described above. A tolerance range is set for using diamond 102A in diamond sensor 100. For example, the tolerance range for angle θ3 is 90°±10°, i.e., 80° to 100°. The tolerance range for angle θ5 is 60°±3°, i.e., 57° to 63°. This makes it easier to grasp the diamond that makes up the diamond sensor, improving the processing accuracy of the diamond and the detection accuracy of the diamond sensor.

[0058] The allowable range of the exterior angle θ5 may be 60°±1°, i.e., 59° to 61°, which makes it easier to hold the diamond that constitutes the diamond sensor, further improving the processing accuracy of the diamond and the detection accuracy of the diamond sensor.

[0059] The allowable range of angle θ3 may be 90°±5°, i.e., 85° to 95°, or 90°±1°, i.e., 89° to 91°, which makes it easier to hold the diamond that constitutes the diamond sensor, further improving the processing accuracy of the diamond and the detection accuracy of the diamond sensor.

[0060] The maximum value of the diameter of the first side surface 202 may be 100 μm or more. The maximum value of the diameter of the first side surface 202 may be 150 μm or more, or even 200 μm or more. The same applies to each of the first side surface 204 and the first side surface 206. Increasing the area of ​​each of the first side surface 202, the first side surface 204, and the first side surface 206 makes it easier to grasp the diamond 102A. However, as the amount of the triangular pyramid cut away increases, the detected fluorescence intensity decreases, as described above. Therefore, the maximum value of the diameter of the first side surface 202 may be 30% or less of one side of the base of the original triangular pyramid (length L4), or may be 20% or less. The same applies to each of the first side surface 204 and the first side surface 206. If it is possible to grasp the diamond 102A, the detection accuracy of the diamond sensor improves as the amount of cutting away decreases.

[0061] (Second Modification) In the above, as shown in FIG. 1A, the case where the excitation light 112 is incident on the bottom surface of the diamond 102 (flat surface 120 in FIG. 2) has been described, but this is not limited thereto. Referring to FIG. 10, a diamond sensor 150 according to a second modification irradiates the excitation light 112 on the side opposite the bottom surface of the triangular pyramidal diamond 152. The diamond sensor 150 is configured similarly to the diamond sensor 100, except for the incident direction of the excitation light 112 on the diamond. That is, the diamond sensor 150 includes a diamond 152, an optical fiber 104, an optical fiber 154, and a sensor head 156 that houses the diamond 152, the optical fiber 104, and the optical fiber 154. The diamond 152 is formed from a diamond single crystal containing an NV center. The optical fiber 154 transmits the excitation light 112 that is irradiated on the NV center of the diamond 152. The optical fiber 104 transmits the fluorescence 114 emitted from the NV center in the diamond 152. The excitation light 112 is, for example, laser light generated by a semiconductor laser (e.g., emitted light wavelength 532 nm). The fluorescence 114 is detected by a detection device (e.g., a photodiode). The sensor head 156 is prismatic (the cross section perpendicular to the axis is square) and is made of, for example, resin. Similar to the diamond sensor 100, a reference direction indicator 110 is arranged on the surface of the sensor head 156.

[0062] Referring to FIG. 11 , diamond 152 is a triangular pyramid truncated by removing apex A from diamond 102 shown in FIG. 2 . Excitation light 112 enters diamond 152 from incident surface 160, which is formed by removing apex A. NV centers 122 in diamond 152 are irradiated by the incident excitation light 112. Fluorescence emitted from NV centers 122 is emitted in all directions. The emitted fluorescence is reflected multiple times by three trapezoidal surfaces, which are the side surfaces of the triangular pyramid, and then emitted from flat surface 120. Fluorescence 114 emitted from flat surface 120 enters optical fiber 104 and is transmitted to the detection device as described above. Of the two base surfaces (i.e., incident surface 160 and flat surface 120) of diamond 152, which is a triangular pyramid truncated, incident surface 160, which has a relatively smaller area, is referred to as the upper base, and flat surface 120, which has a relatively larger area, is referred to as the lower base.

[0063] The incident surface 160 is polished so that the excitation light 112 efficiently enters the diamond 152 from the incident surface 160. The three trapezoidal faces of the diamond 152, which is a truncated triangular pyramid, are polished so that the fluorescent light 114 is efficiently reflected. The flat surface 120 that outputs the fluorescent light 114 is also polished. The incident surface 160, the flat surface 120, and the three trapezoidal faces have a surface roughness Ra of less than 20 nm, for example. This allows the excitation light 112 to efficiently enter the diamond 152. The fluorescent light 114 is efficiently reflected and exits from the flat surface 120.

[0064] The crystal plane and crystal orientation of the diamond 152 are the same as those of the diamond 102. That is, the flat surface 120 is a crystal plane {100}. The flat surface 120 may also be a crystal plane {111}. For example, if the flat surface 120 is a crystal plane (001), one side of the flat surface 120 (e.g., side CD) is formed along the <100> direction, for example. The sensor head 156 has a recess for accommodating the diamond 152, and by arranging the diamond 152 in the recess, the crystal plane of the diamond 152 is arranged perpendicular to the reference direction indicator 110.

[0065] Depending on the precision of the recess formed in the sensor head 156 to accommodate the diamond 152, the crystal face of the diamond 152 can be tilted relative to a reference plane perpendicular to the reference direction indicator 110 (see FIG. 3). Assuming that the flat surface 120 is formed parallel to the crystal face, the first off-angle θ1 (see FIG. 3) is 3° or less. As a result, similar to the diamond sensor 100, by positioning the reference direction indicator 110 of the diamond sensor 150 relative to the measurement object, the crystal face of the diamond 152 can be positioned accurately and easily relative to the measurement object. Therefore, high-precision measurements can be performed in a short time.

[0066] Furthermore, depending on the processing precision, the flat surface 120 may be misaligned with the crystal plane (see FIG. 4). The second off-angle θ2 (see FIG. 4), which is the angle that the flat surface 120 forms with respect to the crystal plane, is 3° or less. As a result, when the flat surface 120 of the diamond 152 is positioned perpendicular to the reference direction marking 110, the off-angle of the crystal plane {100} or {111} with respect to the reference plane perpendicular to the reference direction marking 110 can be 3° or less. This makes it easy to accommodate the diamond 152 in the sensor head 156 with high positional precision.

[0067] The first off-angle θ1 may be 1° or less. The first off-angle θ1 may be 0.1° or less. This allows the crystal plane of diamond 152 to be positioned with high precision relative to the measurement object.

[0068] The second off angle θ2 may be equal to or less than 1°. The second off angle θ2 may be equal to or less than 1°. This allows the diamond 152 to be accommodated in the sensor head 156 with even greater precision.

[0069] As described above, when the crystal plane (001) is used as the flat surface 120 of the diamond 152, one side of the flat surface 120 is formed, for example, along the <100> direction. Depending on the processing accuracy, the direction of one side of the flat surface 120 may be tilted with respect to the <100> direction. The off-angle (fourth off-angle), which represents the allowable tilt angle, is 3° or less. Furthermore, when the flat surface 120 is a crystal plane (111), one side of the flat surface 120 is formed, for example, along the <110> direction. Similarly, depending on the processing accuracy, the direction of one side of the flat surface 120 may be tilted with respect to the <110> direction. The fourth off-angle, which represents the allowable tilt angle, is 3° or less. This allows the crystal plane of the diamond 152 to be positioned accurately relative to the measurement target. Furthermore, it becomes easier to accommodate the diamond 152 in the sensor head 156 with high positional accuracy.

[0070] The fourth off angle may be equal to or less than 1°, or may be equal to or less than 0.1°, which allows the crystal plane of diamond 102 to be positioned with high precision relative to the object to be measured.

[0071] In the above description, the sensor head 156 is described as being in the shape of a prism with a square cross section, but this is not limiting. The sensor head 156 may be in the shape of a prism with a rectangular cross section. The sensor head 156 may also be in the shape of a cylinder with a circular or elliptical cross section.

[0072] (Third Modification) In the above, the case where the diamond 152 is a triangular pyramid has been described, but this is not limiting. Referring to Figures 12A to 12C, the diamond 152A used in the diamond sensor 150 may have a shape in which the vertices of the base (lower base) of the triangular pyramid shown in Figure 11 have been removed. That is, the diamond 152A is the diamond 102A shown in Figures 9A to 9C with a predetermined portion including the vertex A removed. The height H2 of the removed portion may be determined so that the incident surface 220 formed by the removal is approximately the same size as the cross section of the optical fiber 154. This makes it easier to grasp the diamond that constitutes the diamond sensor, improving the processing accuracy of the diamond and the detection accuracy of the diamond sensor.

[0073] In the above, for diamonds having an incident surface for excitation light (diamond 152 in FIG. 11 and diamond 152A in FIGS. 12A to 12C), the case where excitation light is incident from the incident surface as shown in FIG. 10 has been described, but this is not limited to this. The diamonds shown in FIG. 11 and FIGS. 12A to 12C may also be used in the configurations shown in FIGS. 1A and 1B. That is, diamond 102 may be replaced with the diamond in FIG. 11 or FIGS. 12A to 12C, and excitation light may be incident from a flat surface (i.e., bottom surface). Similarly, for diamond 152B shown in FIGS. 13A to 13C described below, excitation light may be incident from the incident surface as shown in FIG. 10, or from a flat surface (i.e., bottom surface) as shown in FIG. 1A.

[0074] In the above, a case where a diamond having an NV center is used in a diamond sensor has been described, but this is not limiting. Any diamond having a color center with electronic spin will suffice. A color center with electronic spin is a center that forms a spin triplet state and emits light when excited, with the NV center being a representative example. In addition, it is known that color centers with electronic spin also exist in silicon-vacancy centers (i.e., Si-V centers), germanium-vacancy centers (i.e., Ge-V centers), and tin-vacancy centers (i.e., Sn-V centers). Therefore, diamonds containing these may be used in place of diamonds containing NV centers to construct diamond sensors.

[0075] The effectiveness of the diamond sensor of the present disclosure will be demonstrated below by way of examples. Diamond 152A shown in Figures 12A to 12C was produced by laser processing a diamond single crystal, and diamond 152B shown in Figures 13A to 13C was produced by further cutting along each side of the bottom surface.

[0076] Figures 13A to 13C show vertices A to D of a triangular pyramid (corner cube) before the vertices are cut off. Referring to Figure 2, angles α, β, and γ are all 90°. The length L4 of one side of the base of the triangular pyramid is 1.732 mm. The height H1 from the base to vertex A before cutting is 0.707 mm. The height H2 of the cut portion including vertex A is 0.035 mm. The length L1 of the cut portion including vertex B is 0.6 mm. The length L2 of the cut portion including vertex C and the cut portion including vertex D are each 0.4 mm.

[0077] In the diamond 152A shown in Figures 12A to 12C, one side of the bottom surface 200 was cut off perpendicular to the bottom surface 200 along side CD. This formed the rectangular second side surface 222 shown in Figures 13A to 13C. The width W of the cut-off portion was 0.1 mm. Similarly, the sides of the bottom surface 200 were cut off perpendicular to the bottom surface 200 along sides BC and DB. This cut formed rectangular second side surfaces 224 and 226. This allows the diamond to be easily gripped using a two-point gripping jig when polishing the diamond. That is, the parallel first and second side surfaces (e.g., first side surface 202A and second side surface 222) are gripped by the jig.

[0078] By cutting, the bottom surface 200, first side surface 202, first side surface 204, and first side surface 206 shown in FIGS. 12A to 12C are respectively formed into the bottom surface 200A, first side surface 202A, first side surface 204A, and first side surface 206A shown in FIGS. 13A to 13C. The bottom surface 200A is hexagonal, and the first side surfaces 202A, first side surfaces 204A, and first side surfaces 206A are each pentagonal. Of the five sides of the first side surface 202A, the length L5 of one side included in the bottom surface 200A is 0.462 mm. Similarly, the length of one side of the five sides of the first side surface 204A included in the bottom surface 200A and the length of one side of the five sides of the first side surface 206A included in the bottom surface 200A are each 0.231 mm.

[0079] As described above, the bottom surface 200A, the first side surface 202A, the first side surface 204A, the first side surface 206A, and the incident surface 220 were polished to a surface roughness Ra of less than 20 nm. The other surfaces were not polished.

[0080] Because first side surface 202A, first side surface 204A, and first side surface 206A are all pentagonal, the maximum value of the across length of each surface may differ from the length of the side included in bottom surface 200A. For example, the maximum across length of first side surface 202A is length L6. Note that when angles α, β, and γ shown in FIG. 2 are less than 90°, even if first side surface 202A is perpendicular to bottom surface 200A, the maximum across length of first side surface 202A may differ from length L6. In either case, to facilitate gripping of diamond 152B, it is sufficient that the maximum across length of each of first side surface 202A, first side surface 204A, and first side surface 206A be 50 μm or more.

[0081] On the other hand, if the portion cut from the triangular pyramid becomes larger, the number of NV centers in the diamond decreases, and the detected fluorescence intensity decreases. Therefore, the maximum value of the diameter length of each of the first side surfaces 202A, 204A, and 206A needs only to be 40% or less of one side of the base of the original triangular pyramid (length L4).

[0082] Diamonds similar to those in Example 1 were fabricated. Specifically, diamonds with a base face of (001), one side of the base face oriented in the <100> direction, and a triangular pyramid with a hypotenuse length of 550 μm before the apex was removed were processed to fabricate multiple diamonds with the shapes shown in FIGS. 13A to 13C. Measurement results using the fabricated diamonds are shown in FIG. 14. In FIG. 14, the off-angle (θ2) between the base face and the crystal plane, and the off-angle between the base and the crystal direction were measured using X-ray diffraction. The angle θ3 between the base face and the side face, the exterior angle θ5 of the hexagonal base, and the maximum diameter of the side face were measured using an optical microscope. The off-angle between the sensor head and the base face and the off-angle between the sensor head and the base face were measured using an optical microscope and a surface profilometer (manufactured by Zygo). The off-angle between the sensor head and the crystal plane was measured using X-ray diffraction. Excitation light was incident on the bottom face of each diamond, and the fluorescence intensity was measured as a photodiode current value. In addition, ODMR measurements were performed by sweeping the frequency while irradiating microwaves in continuous wave (CW) mode, and measuring the half-width when a 1 mT magnetic field was applied perpendicular to the sensor head. From these results, it was found that samples with an off-angle between the sensor head and the crystal plane of more than 3 degrees had a very large half-width of ODMR, making it difficult to obtain high-precision magnetic sensitivity. The larger the maximum diameter of the side, the better the polishing accuracy, and the smaller the off-angle between the sensor head and the crystal plane. It was found that the smaller the off-angle between the sensor head and the crystal plane, the smaller the half-width and the more sensitive the measurement.

[0083] Using diamonds prepared in the same manner as in Example 2, excitation light was incident on the incident surface of each diamond (see incident surface 220 in Figures 13A to 13C), and fluorescence intensity was measured. The results are shown in Figure 15. The measurement method for each item was the same as in Example 2. Samples 21 to 27 and 31 to 33 in Figure 15 correspond to Samples 1 to 7 and Samples 11 to 13 in Figure 14, respectively. The measured values ​​for the diamonds themselves are the same as those in Figure 14. The measured values ​​(off-angle) for the arrangement of the sensor head and diamond differ from those in Figure 14 depending on the arrangement of the diamond on the sensor head. From these results, it was found that samples with an off-angle between the sensor head and the crystal plane of more than 3 degrees have a very large half-width of ODMR, making it difficult to obtain high-precision magnetic sensitivity, and that the smaller the off-angle between the sensor head and the crystal plane, the smaller the half-width of ODMR, making high-sensitivity measurement possible.

[0084] Although the present disclosure has been described above by explaining the embodiments, the above-described embodiments are merely examples, and the present disclosure is not limited to only the above-described embodiments. The scope of the present disclosure is defined by the claims in the scope of the claims, taking into consideration the description of the detailed description of the invention, and includes all modifications within the meaning and scope equivalent to the wordings described therein.

[0085] 100, 150 Diamond sensor 102, 102A, 152, 152A, 152B Diamond 104, 154 Optical fiber 106, 156 Sensor head 108 Sensing surface 110 Reference direction indicator 112 Excitation light 114 Fluorescence 116 Side 120 Flat surface 122 NV center 124 Vertical surface 126 Crystal surface 130 Coaxial cable 132 λ / 4 transformer 134 λ / 4 open stub 160, 220 Incident surface 200, 200A Bottom surface 202, 204, 206, 202A, 204A, 206A First side surface 210, 212, 214 Side surface 222, 224, 226 Second side surface A, B, C, D Vertex α, β, γ, θ3, θ4, θ5 Angle θ1, θ2 Off angle H1, H2 Height L1, L2, L3, L4, L5, L6 Length W Width

Claims

1. A diamond sensor comprising: a diamond having a color center with electronic spin; and a sensor head that houses the diamond, wherein the diamond comprises: a reflective surface that reflects excitation light that is propagated through an optical system and enters the interior of the diamond; and a flat surface that allows the excitation light to enter the interior of the diamond and causes radiation emitted from the color center to exit the diamond, wherein the reflective surface reflects the radiation emitted from the color center excited by the excitation light and focuses it in the direction of the optical system, wherein a first off angle, which is the angle formed by a specific crystal plane with a low index of the diamond with respect to a reference plane perpendicular to a predetermined reference direction fixed to the sensor head, is 3° or less, and the surface roughness Ra of the flat surface is 20 nm or less.

2. A diamond sensor comprising: a diamond having a color center with electronic spin; and a sensor head that houses the diamond, wherein the diamond comprises: an incident surface that allows excitation light propagated through an optical system to enter the interior of the diamond; a reflecting surface that reflects radiated light emitted from the color center excited by the excitation light that entered from the incident surface and focuses the radiated light in the direction of a light-receiving optical system that guides the radiated light to a light-receiving element; and a flat surface that causes the radiated light to exit the diamond, wherein the area of ​​the reflecting surface is larger than the area of ​​the incident surface, and the reflecting surface guides the radiated light radiated in different directions from the same position to the light-receiving optical system via multiple optical paths; a first off angle, which is the angle formed by a specific crystal orientation with a low index of the diamond with respect to a reference plane perpendicular to a predetermined reference direction fixed to the sensor head, is 3° or less; and the surface roughness Ra of each of the flat surface and the incident surface is 20 nm or less.

3. A diamond sensor as described in claim 1, wherein the shape of the diamond is a triangular pyramid, the flat surface is the base of the triangular pyramid, and a second off angle, which is the angle between the diamond's crystal plane {100} or crystal plane {111} and the base, is 3° or less.

4. A diamond sensor as described in claim 2, wherein the shape of the diamond is a triangular pyramid truncated, the flat surface is the bottom surface which is the lower base of the triangular pyramid truncated, and a second off angle, which is the angle between the diamond's crystal plane {100} or crystal plane {111} and the bottom surface, is 3° or less.

5. A diamond sensor as described in claim 1 or claim 3, wherein the sensor head has a sensing surface, the shape of the diamond is a triangular pyramid, and the third off angle, which is the angle between the sensing surface and the base of the triangular pyramid, is 1° or less.

6. A diamond sensor as described in claim 3 or claim 4, wherein the fourth off angle is 3° or less, and the fourth off angle is the angle formed between any one side of the bottom surface and the <100> direction of the diamond when the second off angle is the angle formed between the crystal plane (001) of the diamond and the bottom surface, and the fourth off angle is the angle formed between any one side of the bottom surface and the <1-10> direction of the diamond when the second off angle is the angle formed between the crystal plane (111) of the diamond and the bottom surface.

7. A diamond sensor as described in claim 5, wherein a fifth off angle, which is the angle formed between one side of the sensing surface and any one side of the bottom surface of the diamond, is 1° or less.

8. A diamond sensor as described in claim 1, wherein the diamond has a shape in which each vertex of the triangular base of a triangular pyramid has been removed, a first side formed by removing the vertices forms an angle of 80° or more and 100° or less with respect to the base, and an exterior angle of a hexagon formed by removing the vertices is 57° or more and 63° or less.

9. The diamond sensor of claim 2, wherein the diamond has a shape in which each vertex of the triangular base, which is the lower base of a triangular truncated pyramid, is removed, the first side formed by removing the vertices forms an angle of 80° or more and 100° or less with the base, and the exterior angle of the hexagon formed by removing the vertices is 57° or more and 63° or less.

10. A diamond sensor according to any one of claims 1 to 9, wherein the first off angle is 1° or less.

11. The diamond sensor according to claim 10, wherein the first off angle is 0.1° or less.

12. A diamond sensor according to any one of claims 3, 4, 6 and 7, wherein the second off angle is 1° or less.

13. The diamond sensor according to claim 12, wherein the second off angle is 0.1° or less.

14. The diamond sensor according to claim 6, wherein the fourth off angle is 1° or less.

15. The diamond sensor according to claim 5, wherein the third off angle is 0.1° or less.

16. The diamond sensor according to claim 7, wherein the fifth off angle is 0.1° or less.

17. A diamond sensor according to claim 8 or claim 9, wherein the exterior angles of the hexagon are between 59° and 61°.

18. A diamond sensor as described in any one of claims 8, 9 and 17, wherein the maximum value of the diameter length of the first side is 50 μm or more and 40% or less of the length of one side of the triangle.

19. A diamond sensor as described in any one of claims 8, 9, 17 and 18, wherein the diamond further includes second side surfaces formed by cutting off each side of the bottom surface.

Images