Magnetic field source location detection method

Abstract

To provide a magnetic field source position detection method capable of improving detection accuracy while maintaining the portability of a diamond sensor.SOLUTION: A magnetic field source position detection method includes: a fluorescence intensity acquisition step of two-dimensionally scanning a sample in a state where excitation light from a laser light source is guided by an optical fiber and applied to a diamond, and acquiring intensity of fluorescence emitted from the diamond; and a position detection step of detecting a position of a magnetic field source in the sample on the basis of a change amount of the fluorescence intensity in the same direction as a scanning direction of the excitation light with respect to the acquired fluorescence intensity. The position detection step includes calculating a differential value only in the same direction as the scanning direction of the excitation light for a distribution image of the acquired two-dimensional fluorescence intensity, obtaining the square of the calculated differential value, and detecting the position of the magnetic field source in the sample on the basis of the obtained result.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for detecting the position of a magnetic field source, and more particularly to a method for detecting the position of a magnetic field source using a diamond sensor with an optical fiber. [Background technology]

[0002] As an example of a diamond sensor using optical fibers, the one described in Non-Patent Document 1 below is known. Specifically, as shown in Figure 2(a) of Non-Patent Document 1, the sensor comprises a laser light source that generates excitation light, a diamond having NV (Nitrogen-Vacancy) centers, a microwave source that sweeps the diamond by irradiating it with microwaves, and a detection unit that detects the intensity of fluorescence emitted from the diamond by irradiation with excitation light. The excitation light output from the laser light source is guided to the diamond by an optical fiber. In a diamond sensor with such a structure, the position of the magnetic field source is detected based on the amount of change in the detected fluorescence intensity. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Akihiro Kuwahata et al., “Magnetometer with nitrogen-vacancy center in a bulk diamond for detecting magnetic nanoparticles in biomedical applications”, Scientific Reports (2020) 10:2483, https: / / doi.org / 10.1038 / s41598-020-59064-6 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Recently, with the expanding applications of diamond sensors, there has been a demand for the development of portable diamond sensors. However, the aforementioned diamond sensors using optical fibers have problems in terms of portability for the following reasons. Specifically, when scanning a magnetic field source to be detected using such a diamond sensor, the optical fiber also vibrates slightly due to the influence of minute vibrations. This generates a large amount of background noise, resulting in poor detection accuracy. In order to maintain detection accuracy, methods such as rigidly fixing the optical fiber are being considered, but fixing the optical fiber creates a new problem that hinders the portability of the diamond sensor.

[0005] The present invention was made to solve these technical problems, and aims to provide a magnetic field source position detection method that can improve detection accuracy while maintaining the portability of the diamond sensor. [Means for solving the problem]

[0006] The magnetic field source position detection method according to the present invention is characterized by comprising: a fluorescence intensity acquisition step of scanning a sample in two dimensions while excitation light from a light source is guided through an optical fiber and irradiated onto a diamond, and acquiring the fluorescence intensity emitted from the diamond; and a position detection step of detecting the position of the magnetic field source in the sample based on the amount of change in fluorescence intensity in the same direction as the scanning direction of the excitation light with respect to the acquired fluorescence intensity.

[0007] In the magnetic field source position detection method according to the present invention, the position of the magnetic field source is detected based on the change in fluorescence intensity in the same direction as the scanning direction of the excitation light, thereby reducing background noise caused by minute vibrations of the optical fiber. Moreover, since there is no need to fix the optical fiber, the portability of the diamond sensor can be ensured. As a result, the accuracy of detecting the position of the magnetic field source can be improved while maintaining the portability of the diamond sensor.

[0008] In the magnetic field source position detection method according to the present invention, in the position detection step, it is preferable to calculate a differential value only in the same direction as the scanning direction of the excitation light for the acquired two-dimensional fluorescence intensity distribution image, and detect the position of the magnetic field source in the sample based on the calculated differential value. By doing so, background noise caused by minute vibrations of the optical fiber can be reduced, so that the detection accuracy of the position of the magnetic field source can be improved.

[0009] Further, in the magnetic field source position detection method according to the present invention, in the position detection step, it is preferable to obtain the square of the calculated differential value or the absolute value of the calculated differential value, and detect the position of the magnetic field source in the sample based on the obtained result. By doing so, background noise caused by minute vibrations of the optical fiber can be further reduced, so that the detection accuracy of the position of the magnetic field source can be further improved.

[0010] Furthermore, in the magnetic field source position detection method according to the present invention, in the fluorescence intensity acquisition step, it is preferable to two-dimensionally scan the sample with an external magnetic field applied in the scanning direction of the excitation light. By doing so, the signal-to-noise ratio can be increased, so that the detection accuracy of the position of the magnetic field source can be further improved.

Advantages of the Invention

[0011] According to the present invention, it is possible to improve the detection accuracy of the position of the magnetic field source while maintaining the portability of the diamond sensor.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic diagram showing the configuration of a diamond sensor used in the magnetic field source position detection method according to the embodiment. [Figure 2] It is a schematic diagram showing the scanning direction of the excitation light. [Figure 3] It is a flowchart showing the fluorescence intensity acquisition step. [Figure 4] It is a flowchart showing the position detection step. [Figure 5]This is a schematic diagram of a two-dimensional fluorescence intensity distribution to explain the calculation of differential values. [Figure 6] This is a schematic diagram illustrating the sensor head and the foreign object placed on the XY stage used in Comparative Example 1 and Example 1. [Figure 7] (a) is a figure showing the results of Comparative Example 1, and (b) is a figure showing the results of Example 1. [Figure 8] (a) is a figure showing the results of Comparative Example 2, (b) is a figure showing the results of Comparative Example 3, (c) is a figure showing the results of Example 2, and (d) is a figure showing the results of Comparative Example 4. [Figure 9] This is a flowchart showing the position detection process according to Examples 3 to 5. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments of the magnetic field source position detection method according to the present invention will be described with reference to the drawings. Prior to describing the embodiments, the configuration of the diamond sensor used in the magnetic field source position detection method will be described.

[0014] [About the configuration of the diamond sensor] The diamond sensor 1 used in the magnetic field source position detection method of this embodiment is a diamond sensor using an optical fiber, which scans a sample two-dimensionally and is a device for detecting the position of a magnetic field source in the sample. Here, "magnetic field source" refers to, for example, foreign matter in the sample, and therefore, detecting the position of a magnetic field source in the sample is equivalent to detecting foreign matter in the sample. By using this technology, it is possible to confirm whether or not there are defective products in the product and to easily identify the location where the defective products originate.

[0015] Figure 1 is a schematic diagram showing the configuration of a diamond sensor used in a magnetic field source position detection method according to an embodiment. As shown in Figure 1, the diamond sensor 1 mainly comprises an excitation light irradiation unit 2, a sensor unit 3 on which a diamond 31 is arranged, a microwave source 6, an external magnetic field 7, a sample mounting stage 8, a detection unit 4, and a control unit 5.

[0016] The excitation light irradiation unit 2 includes a laser light source 21 that generates excitation light to irradiate the diamond 31, a first lens 22 that guides the excitation light output from the laser light source 21 to the optical fiber 23, an optical fiber 23 that guides the excitation light towards the diamond 31, an optical fiber 24 connected to the optical fiber 23 via a fiber coupler (not shown), and a second lens 25 and a third lens 26 that are optically connected to the optical fiber 24. The laser light source 21 is controlled by the control unit 5 and outputs, for example, green excitation light (i.e., laser light).

[0017] The sensor unit 3 has a microwave irradiation substrate 32 on which a diamond 31 is arranged. The diamond 31 has multiple NV centers and emits fluorescence when irradiated with excitation light.

[0018] The microwave source 6 is controlled by the control unit 5 and irradiates and sweeps the diamond 31 with a variable-frequency microwave. The external magnetic field 7 consists of a permanent magnet and plays a role in improving the responsiveness to the magnetic field by applying a magnetic field of, for example, about 2-3 mT to the position of the diamond 31. Furthermore, by adjusting the polarity of the external magnetic field 7, a magnetic field can be applied to the sample 100 placed on the sample mounting stage 8 in a predetermined direction (for example, the X direction). The sample 100 is, for example, a product, and the magnet drawn on the sample 100 represents the magnetic field source 101.

[0019] The sample mounting stage 8 is for placing and fixing the sample 100 and is located below the diamond 31. This sample mounting stage 8 has a rectangular base 81 and an XY stage 82 which is positioned on the upper surface of the base 81 and is movable in the X-axis and Y-axis directions relative to the base 81. The sample 100 is placed on the upper surface of the XY stage 82 and can move in the X-axis and Y-axis directions as the XY stage 82 moves. The distance between the upper surface of the XY stage 82 and the bottom surface of the diamond 31 can be adjusted as needed, but is, for example, 0.8 mm.

[0020] The detection unit 4 includes an optical fiber 41 connected to optical fibers 23 and 24 via a fiber coupler (not shown), an optical fiber 45 connected to optical fiber 41 via a first mirror 42, a filter 43 and a second mirror 44, a photodetector 46 for detecting light guided by optical fiber 45, and a voltmeter 47.

[0021] The filter 43 is configured to transmit only the red fluorescence emitted from the diamond 31, and not transmit any other light. The photodetector 46 has, for example, a photodiode that converts the emission intensity of the diamond 31 into a voltage intensity, detects the fluorescence guided by the optical fiber 45, and outputs the detected fluorescence signal to the control unit 5. The voltmeter 47 converts the voltage signal (analog signal) from the photodiode into a digital signal to send to the control unit 5, and outputs the converted signal to the control unit 5.

[0022] The control unit 5 is composed of a microcomputer that combines, for example, a CPU (Central Processing Unit) that performs calculations, a ROM (Read-Only Memory) as a secondary storage device that stores the program for the calculations, and a RAM (Random Access Memory) as a temporary storage device that stores the progress of calculations and temporary control variables. By executing the stored program, it performs control of each component that makes up the diamond sensor 1, and calculations related to the detection of the position of the magnetic field source 101.

[0023] For example, the control unit 5 is electrically connected to the laser light source 21 and the microwave source 6, respectively, and controls their operating timing, output, operating time, etc. The control unit 5 also detects the position of the magnetic field source 101 in the sample 100 based on the fluorescence signal detected by the photodetector 46. More specifically, the control unit 5 detects the position of the magnetic field source 101 in the sample 100 based on the change in fluorescence intensity detected by the photodetector 46.

[0024] [Background to the present invention] Now, let me explain the background leading to this invention.

[0025] The inventors of this application used the diamond sensor 1 with the optical fiber described above to scan a sample 100 in two dimensions, but were unable to detect the position of the magnetic field source 101 in the sample 100. The reason for this is thought to be the large fluctuation in the intensity of the entire acquired two-dimensional fluorescence image. More specifically, when scanning in two dimensions using the diamond sensor 1, the optical fibers 23, 24, 41, and 45 also vibrate slightly due to the influence of minute vibrations that occur. When the optical fibers 23, 24, 41, and 45 vibrate, the efficiency at which fluorescence emitted from the diamond 31 reaches the detection unit 4 changes, and therefore the fluctuation in background intensity becomes large. In other words, the background noise is large due to the minute vibration of the optical fibers. As a result, it is thought that the detection accuracy is negatively affected. Here, "background" refers to the sample.

[0026] To improve the detection accuracy of the diamond sensor 1, it is necessary to reduce background noise caused by minute vibrations in the optical fiber. As mentioned above, methods to firmly fix the optical fiber are being considered to suppress minute vibrations in the optical fiber, but fixing the optical fiber creates a new problem that hinders the portability of the diamond sensor.

[0027] Therefore, the inventors of this invention have diligently conducted research and have found that the accuracy of detecting the position of the magnetic field source in the sample can be improved by detecting the change in fluorescence intensity in the same direction as the scanning direction of the excitation light, relative to the acquired fluorescence intensity, and have completed the present invention.

[0028] [Regarding the magnetic field source location detection method according to the embodiment] To achieve the above, the magnetic field source position detection method according to this embodiment includes a fluorescence intensity acquisition step and a position detection step.

[0029] First, in the fluorescence intensity acquisition process, the laser light source 21 irradiates the diamond 31 with excitation light according to the command of the control unit 5. The excitation light is, for example, a 532 nm green laser light with a power of, for example, 2 mW. The green excitation light is then guided through the first lens 22, optical fiber 23 and optical fiber 24, and further passes through the second lens 25 and third lens 26 before irradiating the diamond 31.

[0030] When green excitation light is shone on the diamond 31, red fluorescence is emitted from the NV center. The emitted red fluorescence and a portion of the green excitation light are guided to the filter 43 via the optical fiber 24, optical fiber 41, and first mirror 42. The filter 43 is configured to transmit only the red fluorescence emitted from the diamond 31 and not transmit other light. Therefore, the red fluorescence passes through the filter 43, but the green excitation light and other light are blocked. The red fluorescence that has passed through the filter 43 is then guided to the photodetector 46 via the second mirror 44 and optical fiber 45.

[0031] Next, the microwave source 6, in accordance with the command of the control unit 5, irradiates the microwave irradiation substrate 32 with microwaves and sweeps. When the microwaves are swept, the electron spins of the NV centers undergo photodetectable magnetic resonance, and the red fluorescence emitted from the diamond 31 rapidly weakens. That is, the red fluorescence intensity decreases rapidly at the resonance frequency. The photodetector 46 detects the red fluorescence and outputs the intensity of the detected fluorescence to the control unit 5.

[0032] Next, the relative positions of the sample 100 and the diamond 31 are moved, and the fluorescence emitted from the diamond 31 is detected while scanning the sample 100 two-dimensionally with excitation light through the diamond 31. In this embodiment, the sample 100 is scanned by fixing the sensor unit 3 on which the diamond 31 is placed and moving the sample 100. However, the sample 100 may also be scanned by fixing the sample 100 and moving the sensor unit 3, or the sample 100 may be scanned by moving both the sample 100 and the sensor unit 3. Compared to moving the sample 100, moving the sensor unit 3 allows for a wider detection field.

[0033] In this embodiment, the sample 100 is scanned with excitation light by moving the XY stage 82. Specifically, the sample 100 is moved in the X direction of the XY stage 82 relative to the diamond 31. For example, as shown by the arrow in Figure 2, the excitation light is scanned along the X direction of the XY stage 82 from one end to the other of the sample 100. After reaching the other end of the sample 100, the position of the sample 100 is adjusted on the XY stage 82 so that the excitation light is shifted in the Y direction of the XY stage 82 and returned to the one end of the sample 100. By repeating this operation, the fluorescence emitted from the diamond 31 is detected while continuously scanning the entire main surface of the sample 100 with laser light.

[0034] The scanning of the excitation light and acquisition of the fluorescence intensity are performed under control by the control unit 5, for example, according to the flowchart shown in Figure 3.

[0035] First, in step S101, the control unit 5 starts scanning the excitation light with the scan count N set to 0 (zero). In step S102, following step S101, the control unit 5 moves the Y-direction stage to the scanning start point. At this time, y=0. As the Y-direction stage moves, the sample 100 placed on the XY stage 82 also moves.

[0036] In step S103, following step S102, the control unit 5 moves the X-direction stage to the scanning start point. At this time, x=0. As the X-direction stage moves, the sample 100 placed on the XY stage 82 also moves.

[0037] In step S104, following step S103, the fluorescence intensity is acquired. At this time, the detection unit 4 detects the fluorescence emitted from the diamond 31 at the scanning start point (x=0, y=0) and acquires the intensity of the detected fluorescence.

[0038] In step S105, following step S104, the control unit 5 moves the stage Δx in the X direction, making x equal to x + Δx. In step S106, following step S105, the control unit 5 determines whether x > x_max. x_max is a value that is pre-set based on, for example, the dimensions of the sample 100 in the X direction, and is stored in the control unit 5.

[0039] If it is determined that x is less than or equal to x_max, the process returns to step S104 described above, and fluorescence is acquired at the point (x=x+Δx, y=0). On the other hand, if it is determined in step S106 that x is greater than x_max, the process proceeds to step S107 described above.

[0040] In step S107, the control unit 5 moves the stage Δy in the Y direction, making y equal to y + Δy. In step S108, following step S107, the control unit 5 determines whether y > y_max. y_max is a value that is pre-set based on, for example, the dimensions of the sample 100 in the Y direction, and is stored in the control unit 5.

[0041] If it is determined that y is less than or equal to y_max, the process returns to step S103 described above, and then fluorescence is acquired at the point (x=x+Δx, y=y+Δy) (step S104). On the other hand, if it is determined in step S108 that y is greater than y_max, the process proceeds to step S109 described above.

[0042] In step S109, the control unit 5 counts the number of scans and sets N to N+1. In step S110, following step S109, the control unit 5 determines whether N == N_max. N_max is a value that is pre-set based on the overall dimensions of the sample 100 and is stored in the control unit 5. If it is determined in step S110 that N == N_max, the process returns to step S102, and steps S102 to S109 described above are repeated. On the other hand, if it is determined in step S110 that N == N_max, the process proceeds to step S111.

[0043] In step S111, the control unit 5 terminates the scanning of the excitation light and saves the data output from the detection unit 4 (i.e., the fluorescence intensity of each acquired point).

[0044] Then, in the position detection step following the fluorescence intensity acquisition step, the position of the magnetic field source 101 in the sample 100 is detected based on the change in fluorescence intensity in the same direction as the scanning direction of the excitation light, relative to the acquired fluorescence intensity. At this time, the control unit 5 first calculates the differential value of the acquired two-dimensional fluorescence intensity distribution image (i.e., two-dimensional magnetic field distribution image) only in the same direction as the scanning direction of the excitation light. After that, the control unit 5 calculates the square of the calculated differential value and detects the position of the magnetic field source 101 in the sample 100 based on the result.

[0045] The position detection process will now be explained in detail based on Figure 4. The process shown in Figure 4 is performed, for example, under the control of the control unit 5.

[0046] First, in step S201, the control unit 5 sets i to 0 (zero) and starts detection. In step S202, following step S201, the control unit 5 sets i to i+1 and calculates the derivative value of the i-th image with respect to the X direction only. Here, the "i-th image" refers to, for example, the fluorescence intensity images of each point acquired in the fluorescence intensity acquisition step. For example, the control unit 5 designates the fluorescence intensity images of points (x=0,y=0), (x=x+Δx,y=0), (x=x+Δx,y=y+Δy), etc., acquired sequentially in the fluorescence intensity acquisition step as the 1st image, 2nd image, 3rd image, etc., and calculates the derivative value of each fluorescence intensity image with respect to the X direction only.

[0047] In step S203, following step S202, the control unit 5 calculates the square of the derivative value calculated in step S202. In step S204, following step S203, the control unit 5 determines whether i == N_acc. N_acc is the number of integrations and is set based on, for example, the total number of points acquired in the fluorescence intensity acquisition step.

[0048] Then, in step S204, if it is determined that i == N_acc, the process returns to step S202, where the calculation of the derivative value in the X direction only for the next fluorescence intensity image (step S202) and the calculation of the square of the calculated derivative value (step S203) are performed. On the other hand, if it is determined in step S204 that i == N_acc, the process proceeds to step S205.

[0049] In step S205, the control unit 5 removes noise by performing an averaging operation on N_acc data points. In step S206, following step S205, the control unit 5 performs image processing by binarizing the image using half of the maximum intensity I_max as the threshold. This completes the detection process (step S207).

[0050] Here, based on FIG. 5, the calculation of the differential value (differentiation process) in step S202 will be described. FIG. 5 is a schematic diagram of a two-dimensional fluorescence intensity distribution for explaining the calculation of the differential value. The schematic diagram of the two-dimensional fluorescence intensity distribution shown in FIG. 5 is the one obtained in the above-described fluorescence intensity acquisition step, that is, a two-dimensional magnetic field distribution image (also referred to as a distribution image of two-dimensional fluorescence intensity). Note that c in FIG. 5 ij represents the fluorescence intensity at each point (x i , y j ). Also, the fluorescence intensity is proportional to the magnetic field intensity.

[0051] For example, when calculating the differential value only in the X direction (the scanning direction of the excitation light) with respect to the two-dimensional magnetic field distribution image, the difference between adjacent points in the X direction is taken, and the differential value at the point (x i , y j ) is calculated as c'ij as follows. That is, c' ij = (c i(j+1) - c i(j-1) ) / Δx = c i(j+1) - c i(j-1) (here, Δx = 1). Mathematically, Δx = 2 is appropriate, but in the subsequent processing, the coefficient part that applies to the whole has no meaning (that is, it does not affect the results such as the SNR), so it is processed with only a simple difference as Δx = 1. Therefore, for example, when x = 2 and y = 2, c' 22 = c 23 - c 21 .

[0052] For reference, for example, when calculating the differential value only in the Y direction with respect to the two-dimensional magnetic field distribution image, the difference between adjacent points in the Y direction is taken, and the differential value at the point (x i , y j ) is calculated as c'ij as follows. That is, c' ij = (c (i+1)j - c (i-1)j ) / Δx = c (i+1)j - c (i-1)j (here, Δx = 1). Therefore, for example, when x = 2 and y = 2, c' 22 = c 32 - c 12 .

[0053] Furthermore, for example, when calculating the derivative values ​​in the X and Y directions for a 2D magnetic field distribution image, the difference between adjacent points in the X direction and adjacent points in the Y direction is taken, and the point (x i ,y j The derivative c'ij of ) is calculated as follows: That is, c' ij =={(c i(j+1) -c i(j-1) )+(c (i+1)j -c (i-1)j )} / Δx=(c i(j+1) -c i(j-1) )+(c (i+1)j -c (i-1)j ) becomes (here, Δx=1). Therefore, for example, in the case of x=2, y=2, c' 22 =(c 23 -c 21 )+(c 32 -c 12 )

[0054] In the magnetic field source position detection method according to this embodiment, the position of the magnetic field source 101 in the sample 100 is detected based on the change in fluorescence intensity in the same direction as the scanning direction of the excitation light, thereby reducing background noise caused by minute vibrations of the optical fibers 23, 24, 41, and 45. Moreover, since there is no need to fix the optical fibers 23, 24, 41, and 45, the portability of the diamond sensor 1 can be ensured. As a result, the detection accuracy of the position of the magnetic field source 101 can be improved while maintaining the portability of the diamond sensor 1.

[0055] In particular, the differential value is calculated only in the same direction as the scanning direction of the excitation light for the acquired two-dimensional fluorescence intensity distribution image, the square of the calculated differential value is taken, and the position of the magnetic field source 101 in the sample 100 is detected based on the result. This further reduces background noise caused by minute vibrations of the optical fiber, thereby further improving the detection accuracy of the position of the magnetic field source 101.

[0056] Furthermore, in the fluorescence intensity acquisition process, it is preferable to use an external magnetic field 7 to scan the sample two-dimensionally while applying the external magnetic field in the scanning direction of the excitation light. Specifically, the polarity of the external magnetic field 7 is adjusted to apply the magnetic field to the sample 100 in the X direction. Then, with the magnetic field applied in the X direction, the sample 100 is scanned with the excitation light. In this way, the signal-to-noise ratio (SNR) can be increased (in other words, the SNR can be improved), and the detection accuracy of the position of the magnetic field source 101 can be further enhanced.

[0057] In this embodiment, instead of calculating the square of the derivative value (step S203), the absolute value of the calculated derivative value may be obtained. In this case as well, the same effect can be obtained.

[0058] [Comparative Examples and Examples] To verify the effectiveness of the magnetic field source position detection method of this embodiment, the inventors of the present invention performed the following comparative examples and examples.

[0059] [Comparative Example 1] In Comparative Example 1, the diamond sensor 1 shown in Figure 1 was modified as shown in Figure 6. More specifically, in order to facilitate the scanning of the excitation light, the optical fiber 24, the second lens 25 and the third lens 26, the sensor unit 3 having the diamond 31, and the external magnetic field 7 were combined into a single unit in the sensor head 9.

[0060] Next, using the diamond sensor 1 equipped with the sensor head 9, the foreign object 102 placed on the XY stage 82 was scanned (number of scans N=9) according to the flowchart shown in Figure 3, the fluorescence emitted from the diamond 31 was detected, and a two-dimensional magnetic field distribution image was obtained. The foreign object 102 was, for example, a minute metal foil measuring 1 mm × 1 mm × 10 μm. The distance between the top surface of the XY stage 82 and the bottom surface of the diamond 31 was 0.8 mm.

[0061] Next, the acquired two-dimensional magnetic field distribution image was processed using the following conventional method, and the results are shown in Figure 7(a).

[0062] The conventional method differs from the position detection process of this embodiment in steps S202 and S203 shown in Figure 4. Specifically, in the conventional method, instead of steps S202 and S203 shown in Figure 4, the following steps are sequentially provided between steps 201 and S204: "Calculation of the average intensity I_mean of the entire i-th image, with i set to i+1", "Calculation of the difference between the intensity of each point and I_mean", and "Calculation of the absolute value of the intensity of each point". Steps S204 to S207 are the same as in this embodiment.

[0063] [Example 1] In Example 1, similar to Comparative Example 1, a diamond sensor 1 equipped with a sensor head 9 was used to scan a foreign object 102 placed on an XY stage 82 (number of scans N=9) to acquire a two-dimensional magnetic field distribution image. Position detection as described in this embodiment was then performed on the acquired two-dimensional magnetic field distribution image. Specifically, in Example 1, position detection was performed on the acquired two-dimensional magnetic field distribution image using the flowchart shown in Figure 4, and the results are shown in Figure 7(b).

[0064] As can be seen by comparing Figure 7(a) and Figure 7(b), in Comparative Example 1, the background noise was large and the foreign object 102 (i.e., the magnetic field source) could not be detected, but in Example 1, the foreign object 102 could be detected.

[0065] Furthermore, as an indicator of detection effectiveness, the detection performance of Comparative Example 1 and Example 1 was compared using the ratio of the signal intensity of the foreign object to the background intensity (i.e., the degree of fluctuation in the signal intensity of the non-foreign object area) (S / N ratio). The S / N ratio is calculated as S / N = (maximum absolute value of the signal intensity of the foreign object) / (standard deviation of the signal intensity of the non-foreign object area). The S / N ratio of Comparative Example 1 was approximately 1. Therefore, in Comparative Example 1, the signal intensity of the foreign object and the background intensity were almost equal, making it impossible to identify the location of the foreign object (in other words, the location of the magnetic field source). On the other hand, the S / N ratio of Example 1 was 39.

[0066] The results from Comparative Example 1 and Example 1 demonstrate that the magnetic field source position detection method of this embodiment can reduce background noise.

[0067] [Comparative Example 2, Comparative Example 3, Example 2, and Comparative Example 4] Furthermore, the inventors of the present invention conducted Comparative Examples 2, 3, 2, and 4 to clarify the effect of calculating the differential value only in the same direction as the scanning direction of the excitation light. In these comparative examples and examples, a two-dimensional magnetic field distribution image obtained by the same method was subjected to image processing using the conventional method (Comparative Example 2), differential value calculation in the XY direction (Comparative Example 3), differential value calculation only in the X direction (i.e., the same direction as the scanning direction of the excitation light) (2), and differential value calculation only in the Y direction (Comparative Example 4), and the fluctuation of the background intensity in each case was compared. In addition, in order to compare only the background intensity, a two-dimensional magnetic field distribution image was obtained without placing any foreign objects (i.e., a magnetic field source), and the fluctuations of Comparative Examples 2, 3, 2, and 4 were compared.

[0068] Specifically, first, using the diamond sensor 1 equipped with the aforementioned sensor head 9, the XY stage 82 was scanned according to the flowchart shown in Figure 3 (number of scans N=1) with no foreign matter placed on it (i.e., no foreign matter 102 as shown in Figure 6), and fluorescence emitted from the diamond was detected to obtain a two-dimensional magnetic field distribution image.

[0069] Next, the acquired two-dimensional magnetic field distribution images were processed using the conventional method described above to obtain Comparative Example 2, the differential values ​​in both the X and Y directions were calculated to obtain Comparative Example 3, the differential value in the X direction only was calculated to obtain Example 2, and the differential value in the Y direction only was calculated to obtain Comparative Example 4.

[0070] Figure 8(a) shows the results for Comparative Example 2, Figure 8(b) shows the results for Comparative Example 3, Figure 8(c) shows the results for Example 2, and Figure 8(d) shows the results for Comparative Example 4. As can be seen by comparing these figures, when the differential value in the X direction only was calculated for a two-dimensional magnetic field distribution image, the signal-to-noise ratio could be increased and background noise could be reduced.

[0071] Furthermore, the inventors of the present invention calculated the standard deviation of the entire image as the degree of fluctuation in background intensity for Comparative Example 2, Comparative Example 3, Example 2, and Comparative Example 4, and summarized the results in Table 1.

[0072] [Table 1]

[0073] As shown in Table 1, it was found that only in Example 2 could the fluctuation in background intensity (in other words, background noise) be significantly reduced.

[0074] [Examples 3, 4, and 5] In Examples 3, 4, and 5, the inventors of the present invention, similar to Example 1, used a diamond sensor 1 equipped with a sensor head 9 to scan a foreign object 102 placed on an XY stage 82 according to the flowchart shown in Figure 3 (number of scans N=9) and acquired a two-dimensional magnetic field distribution image. Next, position detection was performed on the acquired two-dimensional magnetic field distribution image using the flowchart shown in Figure 9.

[0075] The flowchart for position detection shown in Figure 9 follows the same steps S201, S202, S204, S205, and S207 as the flowchart in Figure 4, but differs in steps S303 and S306. Here, only the differing steps S303 and S306 will be explained.

[0076] The additional processing in step S303 is divided into three patterns. Example 3 is a pattern in which no additional processing is performed on the derivative value calculated in step S302 (i.e., the derivative value calculated in step S302 is used as is), Example 4 is a pattern in which the absolute value is taken from the derivative value calculated in step S302, and Example 5 is a pattern in which the absolute value is taken from the derivative value calculated in step S302 and the difference with the average value of the overall image intensity is taken.

[0077] On the other hand, step S306 is a step in which the signal-to-noise ratio is calculated based on the results of steps S301 to S305.

[0078] In Examples 3, 4, and 5, the additional processing in step S303 was varied into three patterns, and the signal-to-noise ratio (SNR) for each was calculated. The detection performance (i.e., SNR) of these examples was then compared. For comparison, the SNRs for Comparative Example 1 and Example 1 were also calculated. The results are summarized in Table 2.

[0079] [Table 2]

[0080] As shown in Table 2, all of Examples 1 and 3-5 showed an improvement in the signal-to-noise ratio compared to Comparative Example 1, but Example 1 was found to have the greatest improvement in the signal-to-noise ratio.

[0081] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of symbols]

[0082] 1: Diamond sensor, 2: Excitation light irradiation unit, 3: Sensor unit, 4: Detection unit, 5: Control unit, 6: Microwave source, 7: External magnetic field, 8: Sample mounting stage, 9: Sensor head, 21: Laser light source, 22: First lens, 23, 24, 41, 45: Optical fiber, 25: Second lens, 26: Third lens, 31: Diamond, 32: Microwave irradiation substrate, 42: First mirror, 43: Filter, 44: Second mirror, 46: Photodetector, 47: Voltmeter, 81: Base, 82: XY stage, 100: Sample, 101: Magnetic field source

Claims

1. A fluorescence intensity acquisition step involves guiding excitation light from a light source through an optical fiber and irradiating a diamond with it, scanning the sample in two dimensions, and acquiring the intensity of the fluorescence emitted from the diamond. A position detection step is performed to detect the position of the magnetic field source in the sample based on the amount of change in fluorescence intensity in the same direction as the scanning direction of the excitation light, with respect to the acquired fluorescence intensity. A method for detecting the position of a magnetic field source, characterized by including the following:

2. The magnetic field source position detection method according to claim 1, wherein in the position detection step, the differential value is calculated only in the same direction as the scanning direction of the excitation light for the acquired two-dimensional fluorescence intensity distribution image, and the position of the magnetic field source in the sample is detected based on the calculated differential value.

3. The magnetic field source position detection method according to claim 2, wherein in the position detection step, the square of the calculated differential value or the absolute value of the calculated differential value is obtained, and the position of the magnetic field source in the sample is detected based on the obtained result.

4. The magnetic field source position detection method according to any one of claims 1 to 3, wherein in the fluorescence intensity acquisition step, the sample is scanned two-dimensionally while an external magnetic field is applied in the scanning direction of the excitation light.

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