Superconducting coil magnetic field measuring device and method based on NV color center

Abstract

The invention discloses a superconducting coil magnetic field measurement device and method based on an NV color center, and belongs to the field of superconducting coil magnetic field measurement, and the device comprises a coaxial optical system, an imaging system and a fluorescence processing system. The method comprises the following steps: irradiating a to-be-detected sample with a first type of light, and adjusting the light paths of the first type of light and returned fluorescent light based on a light spot of reflected light of the to-be-detected sample; irradiating a second kind of light to the to-be-tested sample, and adjusting the second kind of light based on imaging of the imaging system; irradiating the to-be-detected sample with a first type of light, and carrying out photoelectric treatment based on the returned fluorescent light of the to-be-detected sample. The device is ingenious in design, and the measurement process can be conveniently and accurately regulated and controlled. The light return path is simple and reasonable in design, and the fluorescence collection efficiency is improved. The normal-temperature light path and the refrigerator are installed in a matched mode, the size and uniformity of the magnetic field in the superconducting coil can be measured, and the device has the advantages of being compact in occupied space, highly integrated, accurate in measurement result and the like.

Description

Technical Field

[0001] The present invention relates to the field of superconducting coil magnetic field measurement, and particularly to a superconducting coil magnetic field measurement device and method based on NV centers. Background Art

[0002] The NV center (nitrogen-vacancy center) is a point defect structure in diamond formed by a nitrogen atom replacing a carbon atom and accompanied by an adjacent vacancy. Its spin state can be manipulated by optical detection magnetic resonance (ODMR) technology. The NV center can be used to measure the magnetic field strength through optical detection magnetic resonance (ODMR) technology. By using a laser to excite the NV center for a long time, the NV center spin can be polarized to the ground state |m s = 0>, and the polarization rate can reach 90%. At this time, the fluorescence intensity remains at the maximum value. The microwave field will resonate with the NV center spin. When the microwave frequency satisfies the energy level difference between |m s = 0> and |m s = ±1>, the NV center can be flipped between the ground state |m s = 0> and |m s = ±1>, which is manifested as a decrease in fluorescence intensity. The external magnetic field will cause splitting between the |m s = ±1> state and the |m s = -1> state, and the splitting size is related to the magnetic field strength. Therefore, by changing the microwave frequency by sweeping the frequency and measuring the fluorescence intensity corresponding to different microwave field frequencies, the ODMR spectrum of the NV center can be obtained, and the magnetic field strength can be calculated through the spectrum line.

[0003] Due to its characteristics such as zero resistance, high current density, and strong diamagnetism, superconducting coils have a wide range of applications in many fields such as medical diagnosis and research equipment, frontier research, and quantum technology. However, because superconducting coils themselves require a low-temperature environment, it is difficult to measure the magnetic field distribution at the center of the coil by conventional methods. Especially for the magnetic field measurement of superconducting magnets in cryogenic refrigerators, it brings inconvenience to practical applications. Summary of the Invention

[0004] In view of the above technical problems, the present disclosure provides a superconducting coil magnetic field measurement device and method based on NV centers that can accurately measure the magnitude and uniformity of the magnetic field in a superconducting coil.

[0005] According to the first aspect of the present disclosure, there is provided a superconducting coil magnetic field measurement device based on NV centers, comprising:

[0006] A coaxial optical system for providing a first type of light and a second type of light to a sample to be measured, adjusting the optical paths of the first type of light and the fluorescence return light based on the reflected light of the first type of light from the sample to be measured, adjusting the second type of light based on the optical path of the fluorescence return light and the imaging of the second type of light by the sample in the imaging system, receiving the fluorescence return light of the first type of light from the sample to be measured and outputting it.

[0007] An imaging system for receiving the reflected light of the first type of light and the second type of light from the sample to be measured and imaging.

[0008] A fluorescence processing system for performing optoelectronic processing based on the fluorescence output by the coaxial optical system.

[0009] According to an embodiment of the present disclosure, the coaxial optical system includes a first fiber collimator; the first type of light is directly irradiated onto the sample to be measured through the first fiber collimator.

[0010] According to an embodiment of the present disclosure, the coaxial optical system includes a second fiber collimator and a dichroic mirror disposed coaxially with the incident optical path of the first type of light; the fluorescence return light of the sample to be measured is reflected by the dichroic mirror and irradiated onto the second fiber collimator; the second fiber collimator is used to connect the fluorescence processing system.

[0011] According to an embodiment of the present disclosure, the coaxial optical system includes a beam splitting flat plate disposed coaxially with the incident optical path of the first type of light; the second type of light is reflected by the beam splitting flat plate to the sample to be measured; the reflected light of the second type of light from the sample to be measured is reflected by the dichroic mirror to the imaging system.

[0012] According to an embodiment of the present disclosure, a detachable mirror is provided between the dichroic mirror and the second fiber collimator; the light reflected by the dichroic mirror is reflected by the detachable mirror to the imaging system.

[0013] According to an embodiment of the present disclosure, at least one first mirror is provided between the dichroic mirror and the second fiber collimator; the first mirror is used to adjust the optical path of the light reflected by the dichroic mirror.

[0014] According to an embodiment of the present disclosure, the fluorescence processing system includes a photodetector; the photodetector is used to receive the fluorescence output by the coaxial optical system, count the fluorescence photons and convert them into electrical signals.

[0015] Another aspect of the embodiments of the present disclosure provides a method for measuring the magnetic field of a superconducting coil based on an NV center, which is applied to a device for measuring the magnetic field of a superconducting coil based on an NV center. The method includes:

[0016] Irradiating a first type of light onto the sample to be measured, and adjusting the optical paths of the first type of light and the fluorescence return light based on the spot of the reflected light from the sample to be measured.

[0017] Irradiate the sample to be measured with a second type of light, and adjust the second type of light based on the optical path of the fluorescence retroreflection and the imaging of the sample on the second type of light in the imaging system.

[0018] Irradiate the sample to be measured with a first type of light, and perform optoelectronic processing based on the fluorescence retroreflection of the sample to be measured.

[0019] According to an embodiment of the present disclosure, irradiating the sample to be measured with a first type of light and adjusting the first type of light based on the reflected light spot of the sample to be measured received includes: irradiating the sample to be measured with a first type of light, and adjusting the angle and / or position of the first type of light based on the reflected light spot of the sample to be measured; adjusting the first type of light to be focused on the sample to be measured based on the optoelectronic signal power of the reflected light;

[0020] Irradiating the sample to be measured with the second type of light and adjusting the second type of light based on the imaging of the fluorescence retroreflection optical path of the sample to be measured and the imaging system includes: irradiating the sample to be measured with the second type of light, and adjusting the position and / or angle of the second type of light based on the imaging of the imaging system.

[0021] According to an embodiment of the present disclosure, the method for measuring the magnetic field of a superconducting coil based on an NV color center includes: emitting a first type of light and microwaves with time sequence control to the sample to be measured, and receiving a fluorescence signal and performing optoelectronic processing.

[0022] The above one or more embodiments have the following beneficial effects:

[0023] The magnetic field measurement device of the superconducting coil based on the NV color center according to the embodiment of the present disclosure is provided with a coaxial optical system, an imaging system, and a fluorescence processing system. The normal temperature optical path of the device is separated from the magnetic field system of the refrigerator where the sample to be measured is located, and can be installed on the optical window of the refrigerator through a cage system fixing frame. The normal temperature optical path is installed in cooperation with the refrigerator, and can measure the magnitude and uniformity of the magnetic field in the superconducting coil. The laser optical path and the fluorescence optical path of the device are ingeniously designed, and can conveniently and accurately control the measurement process. The retroreflection optical path is designed simply and reasonably, improving the fluorescence collection efficiency.

[0024] In the optical path design of the measurement device according to the embodiment of the present disclosure, a beam splitter flat plate and other designs are used to achieve precise positioning of the sample at the excitation position; at least one first reflector is designed, which is easy to adjust the fluorescence retroreflection optical path and improves the fluorescence collection efficiency. The illumination imaging optical path adopts off-axis illumination, making the imaging effect better. By adjusting the relative position of the incident laser and the sample to be measured, the measurement of the magnetic field uniformity at the center of the superconducting coil can be achieved.

[0025] The embodiments of the present disclosure are based on an NV - center - based superconducting coil magnetic field measurement device, which is easy to build and debug, has a high degree of integration, and a simple measurement method. It can achieve high - spatial - resolution measurement of the central magnetic field of the superconducting coil by adjusting the position of the NV center. Based on the spin and optical properties of the NV center, this superconducting coil magnetic field measurement method has high sensitivity and high spatial resolution. Description of the Drawings

[0026] Through the following description of the embodiments of the present disclosure with reference to the drawings, the above - mentioned content and other objects, features, and advantages of the present disclosure will become clearer. In the drawings:

[0027] Figure 1 Schematically shows an application scenario diagram of an NV - center - based superconducting coil magnetic field measurement device according to an embodiment of the present disclosure.

[0028] Figure 2 Schematically shows a structural block diagram of an NV - center - based superconducting coil magnetic field measurement device according to an embodiment of the present disclosure.

[0029] Figure 3 Schematically shows a design diagram of an NV - center - based superconducting coil magnetic field measurement device according to an embodiment of the present disclosure.

[0030] Figure 4 Schematically shows a measurement schematic diagram of an NV - center - based superconducting coil magnetic field according to an embodiment of the present disclosure.

[0031] Figure 5 Schematically shows a coaxial frame structure diagram of an NV - center - based superconducting coil magnetic field measurement device according to an embodiment of the present disclosure.

[0032] Figure 6 Schematically shows a flowchart of an NV - center - based superconducting coil magnetic field measurement method according to an embodiment of the present disclosure.

[0033] In the figure, 100 is an NV - center - based superconducting coil magnetic field measurement device.

[0034] 200 is a refrigerator; 201 is an NV center (sample to be measured); 202 is a superconducting coil; 203 is a cryogenic objective lens.

[0035] 300 is a control and analysis device.

[0036] 110 is a coaxial optical system; 120 is an imaging system; 130 is a fluorescence processing system.

[0037] 1. First fiber collimator; 2. First filter; 3. Diaphragm; 4. Beam splitter flat; 5. White light source; 6. Dichroic mirror; 7. First mirror; 8. Optical window; 9. Second filter set; 10. Removable mirror; 11. Plano-convex lens; 12. Camera; 13. Second fiber collimator. 17. Cryogenic objective; 18. Sample to be measured; 19. Superconducting coil.

[0038] 201, 213. Five-axis optical adjustment mounts; 204. Coaxial rotary quick-release mount; 205. Orthogonal steering plate; 206. Coaxial cube; 207. Coaxial right-angle adjustment mount; 209. Spring-loaded quick-release coaxial plate; 210. Rotary quick-release mount; 211. Coaxial displacement stage; 214. Coaxial orthogonal steering plate; 220, 221, 222. Coaxial struts.

[0039] It should be noted that, for clarity, in the drawings used to describe the embodiments of the present disclosure, the dimensions of the overall / local structure or the overall / local region may be enlarged or reduced, that is, these drawings are not drawn to actual scale. Detailed implementation manners

[0040] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure. However, obviously, one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0041] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0042] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0043] Embodiments of the present disclosure provide a superconducting coil magnetic field measurement device based on NV centers, comprising: a coaxial optical system for providing a first type of light and a second type of light to a sample to be measured, adjusting the optical paths of the first type of light and the fluorescence return light based on the reflected light of the first type of light by the sample to be measured, adjusting the second type of light based on the optical path of the fluorescence return light and the imaging of the sample on the second type of light in the imaging system, and receiving and outputting the fluorescence return light of the first type of light by the sample to be measured; an imaging system for receiving the reflected light of the first type of light and the second type of light by the sample to be measured and imaging; and a fluorescence processing system for performing optoelectronic processing based on the fluorescence output by the coaxial optical system.

[0044] Figure 1 FIG. schematically shows an application scenario diagram of a superconducting coil magnetic field measurement device based on NV centers according to an embodiment of the present disclosure. It should be noted that Figure 1 The shown is only an example where the embodiments of the present disclosure can be applied to help those skilled in the art understand the technical content of the present disclosure, but it does not mean that the embodiments of the present disclosure cannot be used in other devices, systems, environments or scenarios.

[0045] As Figure 1 shown, the application scenario according to this embodiment includes a superconducting coil magnetic field measurement device 100 based on NV centers, a refrigerator 200, and a control and analysis device 300. The refrigerator 200 provides a low-temperature environment for the superconducting coil 202 inside, making it in a superconducting state. Since the superconducting coil 202 is in the refrigerator 200, it is very difficult to accurately measure its magnetic field. In the prior art, an integrated customized design is generally required to achieve magnetic field measurement in a refrigerator environment. This makes the measurement device unable to be flexibly used for low-temperature magnetic field measurement in various scenarios. In the embodiments of the present application, a test light is emitted to the window of the refrigerator 200 through an independent superconducting coil magnetic field measurement device based on NV centers. The test light is irradiated onto the sample to be measured 201 through an objective lens 203, etc., and the fluorescence return light of the sample to be measured is received and analyzed, realizing the convenient measurement of the magnitude and uniformity of the magnetic field in the superconducting coil. In addition, 100 can also be connected to the control and analysis device 300 to control the measurement process and further analyze the measurement data.

[0046] The following will be based on Figure 1 the described scenario and in combination with Figures 2 - 5 to describe in detail the superconducting coil magnetic field measurement device based on NV centers of the embodiments of the present disclosure.

[0047] Figure 2 FIG. schematically shows a structural block diagram of a superconducting coil magnetic field measurement device based on NV centers according to an embodiment of the present disclosure.

[0048] As Figure 2As shown, the superconducting coil magnetic field measurement device 100 based on NV color centers in this embodiment includes a coaxial optical system 110, an imaging system 120, and a fluorescence processing system 130.

[0049] The coaxial optical system 110 is configured to provide a first type of light and a second type of light to the sample to be measured, adjust the optical paths of the first type of light and the fluorescence return light based on the reflected light of the first type of light from the sample to be measured, adjust the second type of light based on the optical path of the fluorescence return light and the imaging of the sample on the second type of light in the imaging system 120, receive the fluorescence return light of the first type of light from the sample to be measured, and output it.

[0050] The first type of light is emitted to the sample to be measured. The sample to be measured can simultaneously generate reflected light of the first type of light for the first type of light, and can also generate fluorescence return light when excited by the first type of light. Since the reflected light of the first type of light and the fluorescence return light propagate along the same optical path, therefore, the optical path of the fluorescence return light can be adjusted by adjusting the reflected light of the first type of light. Moreover, since the fluorescence return light of the sample to be measured is often much weaker than the reflected light of the first type of light. Therefore, adjusting the optical path of the fluorescence return light based on the reflected light of the first type of light from the sample to be measured is more intuitive and has stronger operability. In this embodiment, the coaxial optical system 110 can emit laser light to the sample to be measured, and adjust the optical path of the fluorescence return light based on the reflected light generated by the sample to be measured for the laser light, so that the return light optical path is unobstructed and collimated, meeting the measurement requirements. After the optical path of the fluorescence return light is adjusted, the coaxial optical system 110 emits white light to the sample to be measured, and the reflected light of the white light from the sample is reflected to the imaging system 120 through the optical path of the fluorescence return light. The above white light is adjusted based on the imaging of the imaging system 120, so that the position and incident direction of the white light source meet the imaging requirements.

[0051] The imaging system 120 is configured to receive the reflected light of the first type of light and the second type of light from the sample to be measured and perform imaging.

[0052] The fluorescence processing system 130 is configured to perform optoelectronic processing based on the fluorescence output by the coaxial optical system.

[0053] In this embodiment, the first type of light is used to excite the sample to be measured under specific conditions, so that the sample to be measured generates fluorescence return light, for example, it can be laser light. The second type of light can be white light or light of other colors, such as red light, yellow light, etc., and can be used to provide surface illumination for the sample to be measured, provide illumination light for microscopic imaging to facilitate imaging by the imaging system, enable the sample to be adjusted by observing the sample imaging, and move the focus of the laser on the surface of the sample to the desired measurement position. In some embodiments, white light is specifically used as the light source. In this embodiment, the first type of light and the second type of light are incident on the sample to be measured coaxially.

[0054] In this embodiment, the imaging system 120 can be a camera, such as a CMOS camera, a CCD camera, etc. When visible light irradiates the surface of the sample to be measured, the camera forms an image based on the reflected light of the sample to be measured received. Since the wavelengths of some lasers are within the visible light range, when a laser is used to irradiate the sample to be measured, the reflected light image of the laser can be observed in the image displayed by the imaging system 120. The imaging system is used to receive the image of the sample surface and display it on a computer for observation and calibration.

[0055] In this embodiment, the fluorescence processing system 130 can specifically be a photodetector, which converts the fluorescence optical signal output by the coaxial optical system into an electrical signal. The photodetector can specifically be a single-photon detector. Based on the photoelectric effect, when a single photon is incident on the photosensitive material of the detector, it will excite the generation of photoelectrons, and then through the amplification mechanism inside the detector, the electrical signal generated by the photoelectrons is amplified to a detectable level, thereby realizing the detection of a single photon. Further, the electrical signal can be used for computer processing.

[0056] According to an embodiment of the present disclosure, the coaxial optical system includes a first fiber collimator; the first type of light is directly irradiated onto the sample to be measured through the first fiber collimator.

[0057] As Figure 3 , Figure 4 shown, the device in this embodiment includes a laser, and the first type of light is laser light; an acousto-optic modulator (AOM) can be arranged between the laser and the first fiber collimator, and the laser is connected to the acousto-optic modulator and the acousto-optic modulator is connected to the first fiber collimator through optical fibers. Further, the optical fiber can specifically use a single-mode optical fiber. The first fiber collimator is used to convert the excitation light into parallel light and then irradiate it onto the sample to be measured. The acousto-optic modulator modulates the laser based on a pulsed electrical signal to make it into time-sequential laser light. In this embodiment, the laser light emitted by the laser is irradiated onto the sample to be measured along a straight path through the first fiber collimator.

[0058] According to an embodiment of the present disclosure, the coaxial optical system includes a second fiber collimator and a dichroic mirror arranged coaxially with the incident optical path of the first type of light; the fluorescence return light of the sample to be measured is reflected by the dichroic mirror and irradiated onto the second fiber collimator; the second fiber collimator is used to connect to the fluorescence processing system.

[0059] In this embodiment, the dichroic mirror can transmit the first type of light (such as the excitation light for the sample to be measured), reflect fluorescence (i.e., the fluorescence return light of the sample to be measured) and the second type of light (such as visible light), so the dichroic mirror can be used for splitting the above two types of light. The second fiber collimator is used to couple the fluorescence into the optical fiber, and the optical fiber can be used to transmit the fluorescence and finally connect to the fluorescence processing system. In this embodiment, the optical fiber can use a single-mode optical fiber.

[0060] According to an embodiment of the present disclosure, the coaxial optical system comprises a spectroscopic plate coaxially arranged on the incident optical path of the first type of light. The second type of light is reflected to the sample to be tested by the spectroscopic plate; and the reflected light of the second type of light of the sample to be tested is reflected to the imaging system by the dichroic mirror.

[0061] In this embodiment, the spectroscopic plate (or flat beam splitter) can transmit the first type of light and reflect the second type of light at the same time, so that the first type of light and the second type of light are emitted to the sample to be tested along the same optical path. The second type of light is mainly used to provide illumination for the sample. By observing the imaging of the second type of light reflected by the sample to be tested and the imaging of the reflected first type of light, it is helpful to move the sample and adjust the focus of the first type of light irradiated on the sample surface. This provides conditions for accurately calibrating the excitation position of the sample to be tested. For example, using laser as the first type of light and white light as the second type of light, the sample image and the laser incident point on the sample surface can be seen in the imaging system.

[0062] According to one embodiment of the present disclosure, a detachable reflector is provided between the dichroic mirror and the second fiber collimator; the light reflected by the dichroic mirror is reflected toward the imaging system via the detachable reflector.

[0063] In this embodiment, when the second type of light needs to be adjusted, a detachable reflector is provided between the dichroic mirror and the second optical fiber collimator. When the second type of light is irradiated onto the surface of the sample to be tested, the second type of light reflected by the sample to be tested is continuously reflected to the imaging system via the dichroic mirror and the detachable reflector. According to the imaging of the reflected second type of light in the imaging system, the position and incident angle of the second type of light can be adjusted to achieve accurate off-axis illumination of the sample to be tested.

[0064] According to one embodiment of the present application, at least one first reflector is provided between the dichroic mirror and the second optical fiber collimator; the first reflector is used to adjust the optical path of the light reflected by the dichroic mirror. The at least one first reflector mentioned in this embodiment can be used to adjust the reflected light of the sample to be tested reflected by the dichroic mirror. That is, the reflected light of the sample to be tested reflected by the dichroic mirror is continuously reflected by at least one first reflector and finally emitted to the second optical fiber collimator. By changing the angle and / or position of the reflector, the fine adjustment of the reflected light path can be achieved. Therefore, the reflector group mentioned in the present application can be either only one first reflector or two or more first reflectors. For example, when a first reflector is used at an angle of 45° to the light emitted by the dichroic mirror, a 90° change in the propagation direction of the light path emitted from the dichroic mirror can be achieved, and when another first reflector is used at an angle of 90° to the aforementioned first reflector, a 180° change in the propagation direction of the light path emitted from the dichroic mirror can be achieved. The first reflector is used to adjust the fluorescence light path and improve the collection efficiency of fluorescence.

[0065] According to an embodiment of the present application, the fluorescence processing system includes a photodetector; the photodetector is configured to receive the fluorescence output by the coaxial optical system, count the fluorescence photons and convert them into electrical signals. The photodetector may specifically be a single-photon detector.

[0066] As Figure 4 shown, in this embodiment, a photodetector is arranged to be connected to the coaxial optical system, and the photodetector is used for fluorescence counting; the photodetector is connected to a computer through a lock-in amplifier. A microwave source is provided, and the microwave source is used to apply microwaves to the NV color center; the photodetector, the lock-in amplifier, the computer, and the microwave source can be connected through RF cables;

[0067] The pulse generator is configured to generate pulse signals, which are controlled by a computer; the pulse generator is controlled by a computer program to correctly output a pulse sequence to an acousto-optic modulator, a microwave source, and a lock-in amplifier, so as to realize optical excitation, microwave driving, and optically detected magnetic resonance ODMR and Ramsey interference measurement of a sample, and further obtain the magnitude of the magnetic field at a point to be measured. The computer is used for processing data and controlling the acousto-optic modulator.

[0068] As Figure 3 shown, according to an embodiment of the present application, a superconducting coil magnetic field measuring device based on an NV color center includes: a coaxial optical system, an imaging system, and a fluorescence processing system.

[0069] The coaxial optical system includes a laser optical path 14. In this embodiment, a laser with a central wavelength of 532 nm is used. This part of the laser optical path specifically further includes a first fiber collimator 1, a first filter 2, and a diaphragm 3. The first fiber collimator 1, the first filter 2, the diaphragm 3, the optical window 8, and the cryogenic objective lens 17 are on the same optical axis. The incident laser exits from the first fiber collimator 1, passes through the first filter 2, the diaphragm 3, the optical window 8, and the cryogenic objective lens 17, and irradiates the sample 18 to be measured. The diaphragm 3 is used to control the light flux of the incident laser. By changing the size of the diaphragm aperture, the laser flux entering the coaxial optical system can be controlled, so as to adjust the irradiation laser intensity and the imaging brightness of the imaging system. The first filter 2 may be a band-pass filter, which is used to filter out unnecessary wavelength components in the incident laser.

[0070] In this embodiment, the coaxial optical system includes a fluorescence optical path 15, which specifically includes a dichroic mirror 6, two first reflectors 7, and a second fiber collimator 13. The dichroic mirror 6 is disposed between the aperture 3 and the optical window 8 in the laser optical path. The dichroic mirror 6 forms a 45° angle with the laser optical path. The two first reflectors 7 form a 90° angle with each other. The reflected light of the sample to be measured is continuously reflected by the dichroic mirror 6 and the two first reflectors 7 and then enters the second fiber collimator 13. In this embodiment, a second filter set 9 is further disposed between the first reflector 7 and the second fiber collimator 13. The second filter set 9 may include a 532 nm band-pass filter for filtering the laser; a 650 nm long-pass filter for filtering the fluorescence. The 650 nm long-pass filter is used to transmit light with a wavelength greater than 650 nm and block light with a wavelength less than 650 nm; the 532 nm band-pass filter transmits light with a wavelength near 532 nm and blocks light of other wavelengths. In actual use, the type of filter to be used is selected according to the specific light to be filtered. It can be seen from this embodiment that the reflected light emitted by the sample to be measured is continuously reflected to the second fiber collimator 13 after passing through the dichroic mirror 6. The fluorescence collection effect of this embodiment is high, so that the measurement device and the measurement method have high sensitivity and high spatial resolution.

[0071] In this embodiment, a detachable reflector 10 is disposed in the fluorescence optical path 15, specifically between the second filter set 9 and the second fiber collimator 13, and can form a 45° angle with the fluorescence optical path 15. A plano-convex lens 11 is disposed between the detachable reflector 10 and the camera 12. The plano-convex lens 11 can cooperate with the cryogenic objective lens 17 to achieve microscopic imaging of the surface of the sample to be measured. In this embodiment, the cryogenic objective lens is a high numerical aperture objective lens, which can effectively improve the resolution, increase the brightness, reduce the aberration, and can better adapt to the optical characteristics of the sample at low temperature. The plano-convex lens 11 cooperates with the cryogenic objective lens 17 to achieve clear imaging of the sample surface.

[0072] In this embodiment, the coaxial optical system includes a visible light optical path 16, which is specifically provided with a white light source 5 and a beam splitter flat plate 4. The beam splitter flat plate 4 is disposed between the aperture 3 and the dichroic mirror 6 in the laser optical path, and the beam splitter flat plate 4 forms a 45° angle with the laser optical path 14. The white light emitted by the white light source 5 is reflected by the beam splitter flat plate 4 and irradiates the sample to be measured 18 along the laser optical path 14. The design of this embodiment enables the white light and the laser to irradiate the sample to be measured 18 along the same optical path, which is beneficial to accurately observing and adjusting the measurement point (laser excitation point) of the sample to be measured 18 with the help of the imaging system, and ensuring the accurate coincidence of the laser point and the target excitation point.

[0073] In this embodiment, the sample to be measured 18 is arranged in the sample adjustment system. Specifically, a low-temperature displacement stage can be set to carry and fix the low-temperature scanning stage, and at the same time be responsible for position adjustment, and is fixed at the bottom of the cryostat sample rod. The low-temperature scanning stage is arranged above the low-temperature displacement stage and is responsible for the support of the sample and finer position adjustment; the low-temperature objective lens 17 is used to focus the laser, collect fluorescence, and is used for microscopic imaging.

[0074] According to an embodiment of the present application, as Figure 5 Schematically shows a coaxial frame structure diagram of a superconducting coil magnetic field measurement device based on NV centers implemented according to the present disclosure.

[0075] In this embodiment, the coaxial optical system is stably installed on the optical window of the cryostat through a coaxial support rod. The first fiber collimator 1 is installed on the five-axis optical adjustment frame 201 to facilitate the adjustment of the incident laser angle; the five-axis optical adjustment frame 201, the aperture 3, and the band-pass filter 2 are installed above the coaxial cube 206 through the coaxial support rod 220 to form a laser incident module. Inside the coaxial cube 206, a coaxial cube rotary stage is installed, and the dichroic mirror 6 is closely fitted and installed on the coaxial cube rotary stage through a specially designed mirror mount to ensure an accurate angle of 45 degrees with the laser.

[0076] Two first reflecting mirrors 7 are installed on two coaxial right-angle adjustment frames 207 to achieve precise adjustment of the fluorescence path; the second fiber collimator 13 is installed on the five-axis optical adjustment frame 213; the five-axis optical adjustment frame 213 and the coaxial right-angle adjustment frame 207 are connected by a coaxial support rod 221. In addition, the second filter set 9 is installed on the coaxial support rod 221 through a spring-type quick-release coaxial plate 209 and is located between the coaxial right-angle adjustment frame 207 and the five-axis optical adjustment frame 213.

[0077] The white light source 5 is installed on the coaxial support rod 220 of the laser incident module and is positioned by the orthogonal turning plate 205 of the coaxial system; in front of it, the flat beam splitter 4 is firmly connected to the same coaxial support rod 220 through the coaxial rotary quick-release frame 204. The camera 12 is installed between the filter set 9 and the five-axis optical adjustment frame 213 in the fluorescence collection module through the coaxial support rod 222 and the coaxial orthogonal turning plate 214. A coaxial displacement stage 211 is installed between the camera 12 and the coaxial orthogonal turning plate 214, and an optical element mounting bracket of the plano-convex lens 11 is installed on the coaxial displacement stage 211.

[0078] The bottom of the coaxial optical system is connected to a coaxial interface reserved on the cold head plug of the cryocooler through a precision coaxial support rod. This interface is designed with an optical window 8 to facilitate the passage of light. The low-temperature translation stage is installed at the bottom of the cold head plug, and the low-temperature scanning stage is installed on the low-temperature translation stage. The sample to be measured is fixed on the sample holder and installed on the low-temperature scanning stage; the low-temperature objective lens 17 is installed on the coaxial support rod in the plug through the low-temperature translation stage, maintaining a certain distance from the sample to be measured. When adjusting the position of the sample to be measured (NV color center) through the low-temperature translation stage, the objective lens moves up and down synchronously with the sample to be measured.

[0079] The coaxial frame structure of the above device in this embodiment can be implemented using a cage system. The cage system is an optical experimental system based on modular and standardized design, usually consisting of a series of precisely machined building blocks that can be quickly assembled and aligned to construct a large optomechanical system. This system has optical elements with unified dimensions and interfaces, which can be interconnected through standardized cage structure components (such as cage plates and cage rods).

[0080] Based on the above superconducting coil magnetic field measurement device based on NV color centers, the present disclosure also provides a superconducting coil magnetic field measurement method based on NV color centers. The following will be combined with Figure 6 to describe this method in detail.

[0081] Figure 6 Schematically shows a flowchart of a superconducting coil magnetic field measurement method based on NV color centers according to an embodiment of the present disclosure.

[0082] As Figure 6 shown, the superconducting coil magnetic field measurement method based on NV color centers in this embodiment includes:

[0083] S601: Irradiate the sample to be measured with a first type of light, and adjust the optical paths of the first type of light and the fluorescence return light based on the spot of the reflected light from the sample to be measured.

[0084] S602: Irradiate the sample to be measured with a second type of light, and adjust the second type of light based on the optical path of the fluorescence return light and the imaging of the second type of light by the sample in the imaging system.

[0085] S603: Irradiate the sample to be measured with a first type of light, and perform photoelectric processing based on the fluorescence return light of the sample to be measured.

[0086] According to an embodiment of the present application, S601 irradiates the sample to be measured with a first type of light and adjusts the first type of light based on the received spot of the reflected light from the sample to be measured, including: irradiating the sample to be measured with a first type of light, and adjusting the angle and / or position of the first type of light based on the spot of the reflected light from the sample to be measured; adjusting the focus of the first type of light to the sample to be measured based on the power of the photoelectric signal of the reflected light;

[0087] S602 irradiates the sample to be measured with a second type of light, and adjusts the second type of light based on the fluorescence retroreflection optical path of the sample to be measured and the imaging of the imaging system, including: irradiating the sample to be measured with the second type of light, and adjusting the position and / or angle of the second type of light based on the imaging of the imaging system.

[0088] According to an embodiment of the present application, the method includes: emitting a first type of light and microwaves with time sequence control to the sample to be measured, receiving the fluorescence signal and performing optoelectronic processing.

[0089] As Figure 5 shown, in this embodiment, the first type of light is irradiated to the sample to be measured, and the angle and / or position of the first type of light are adjusted based on the reflected light spot of the sample to be measured; the first type of light is focused on the sample to be measured based on the optoelectronic signal power of the reflected light; the specific process is implemented as follows.

[0090] Turn on the laser. After the laser is incident on the coaxial optical system, place the photosensitive card in front of the fiber collimator in the fluorescence collection optical path. By adjusting the five-axis optical adjustment frame 201 in the laser incident module, the two coaxial right-angle adjustment frames 207 in the fluorescence collection module, and the coaxial cube rotating table, a circular light spot is exactly irradiated in front of the second fiber collimator 13; adjust the low-temperature displacement stage to make the light spot converge into a point and enter the second fiber collimator 13 and be coupled into the single-mode fiber. Observe the output power of the single-mode fiber through an optical power meter, and adjust the above-mentioned low-temperature displacement stage, coaxial right-angle adjustment frame 207, five-axis optical adjustment frame 213, and the focal length of the second fiber collimator 13 to make the output optical power reach the maximum. At this time, confocal is formed. At this time, the output light is mainly the reflected light of the laser, and there may be a small amount of fluorescence, but the laser accounts for the majority. One or more of the above adjustment steps can be adjusted according to actual needs.

[0091] In this embodiment, irradiating the sample to be measured with the second type of light, and adjusting the position and / or angle of the second type of light based on the imaging of the imaging system. The specific process is implemented as follows.

[0092] Turn off the laser, turn on the white light source 5, and adjust the coaxial rotating quick-release frame 204 in front of the white light source 5 so that the white light is reflected onto the sample surface; install the rotating quick-release frame 210 equipped with the detachable mirror 10 in front of the camera 12 and the coaxial displacement stage 211, and adjust the angle of the detachable mirror 10 and the coaxial displacement stage 211 so that the camera can receive a clear image; adjust the position and angle of the white light source 5 to achieve off-axis illumination, so as to avoid the light source being too bright and interfering with the imaging effect; at this time, turn on the laser (with the power reduced), and the landing point of the excitation light incident on the sample surface can be seen; by adjusting the low-temperature displacement stage, ensure that the target excitation point coincides precisely with the laser point.

[0093] According to an embodiment of the present application, a first type of light and microwaves with timing control are emitted to the sample to be measured, and the fluorescence signal is received and subjected to optoelectronic processing. The specific implementation process is as follows.

[0094] Turn off the white light source 5, remove the rotating quick-release bracket 210 in front of the camera 12, so that fluorescence can be incident on the second fiber collimator 13; the second filter group 9 is installed on the coaxial support rod 221 and fixed by the spring-type quick-release coaxial plate 209. Its position is in the middle of the coaxial right-angle adjustment frame 207 and the five-axis optical adjustment frame 213. The second filter group 9 is mainly used to filter out the laser light in the light. Connect the single-mode fiber for fluorescence collection to the photodetector. The photodetector can convert the optical signal into an electrical signal, which is displayed on the computer as the photon count arriving within a period of time; adjust the cryogenic displacement stage, coaxial right-angle adjustment frame 207, five-axis optical adjustment frame 213, and the focal length of the second fiber collimator 13 to make the photodetector count reach the maximum, achieving the maximum coupling efficiency. The photodetector is specifically a single-photon detector.

[0095] Connect the photodetector to the lock-in amplifier through a cable to perform lock-in amplification on the signal to improve the contrast; the lock-in amplifier is connected to the computer through a cable, and the signal is analyzed and processed by the computer.

[0096] The computer controls the signal generator to generate three pulses to control the laser switch, microwave switch, and signal collection respectively. It is used for the excitation and coherent regulation of the sample.

[0097] Set the acousto-optic modulator to change the continuous laser signal into a pulsed laser signal. Set the photodetector to perform photon counting on the fluorescence and convert the optical signal into an electrical signal and output it to the lock-in amplifier; set the microwave source to generate microwaves of a specific frequency; use the signal generator to control the microwave and laser pulses by executing the pulsed file programmed by the computer to make the pulses meet the requirements of coherent manipulation.

[0098] Through the photodetector and computer program, observe the fluorescence photon count and adjust the coaxial structure optomechanical component to make the coaxial optical system reach the best measurement state. Control the pulse card through the computer to achieve the correct output of the three-pulse sequence, thereby realizing the excitation of the sample by the laser, the radiation of the microwave, and the optically detected magnetic resonance spectrum. The realization of magnetic field measurement mainly utilizes the splitting size between the |m s = +> and |m s = -1> states of the NV color center, which causes the peak shift of the optically detected magnetic resonance spectrum (ODMR) with the change of the magnetic field. By measuring the ODMR through the computer program and obtaining the peak information through fitting, the corresponding magnetic field strength can be obtained. Adjust the position of the NV color center, and repeat the above measurement steps to measure the magnetic field strength at different positions in the uniform magnetic field region of the superconducting coil 19.

[0099] The embodiments of the present disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although the embodiments have been described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should fall within the scope of the present disclosure.

Claims

1. A superconducting coil magnetic field measurement device based on NV color centers, characterized in that: Include: A coaxial optical system, used for providing a first type of light and a second type of light to a sample to be tested, adjusting the optical path of the first type of light and fluorescent return light based on the reflected light of the first type of light by the sample to be tested, adjusting the second type of light based on the optical path of the fluorescent return light and the imaging of the second type of light by the sample in the imaging system, and receiving and outputting the fluorescent return light of the first type of light by the sample to be tested; An imaging system, used for receiving the reflected light of the sample to be tested based on the first type of light and the second type of light and imaging; The fluorescence processing system is used for performing photoelectric processing based on the fluorescence output by the coaxial optical system.

2. The device according to claim 1, characterized in that The coaxial optical system comprises a first optical fiber collimator; the first type of light is directly emitted to the sample through the first optical fiber collimator.

3. The device according to claim 1, characterized in that The coaxial optical system comprises a second fiber collimator and a dichroic mirror arranged in the incident light path of the first type of light; the fluorescent return light of the sample to be tested is reflected by the dichroic mirror and emitted to the second fiber collimator; the second fiber collimator is used to connect to the fluorescence processing system.

4. The device according to claim 1, characterized in that The coaxial optical system comprises a beam splitter plate arranged coaxially with the incident optical path of the first type of light; The second type of light is reflected to the sample to be tested through the beam splitter; and the reflected light of the second type of light of the sample to be tested is reflected to the imaging system through the dichroic mirror.

5. The device according to claim 3, characterized in that A detachable reflector is arranged between the dichroic mirror and the second optical fiber collimator; the light reflected by the dichroic mirror is reflected toward the imaging system via the detachable reflector.

6. The device according to claim 4, characterized in that At least one first reflector is disposed between the dichroic mirror and the second optical fiber collimator; the first reflector is used to adjust the optical path of the light reflected by the dichroic mirror.

7. The device according to claim 1, characterized in that The fluorescence processing system comprises a photodetector; the photodetector is used to receive the fluorescence output by the coaxial optical system, count the fluorescence photons and convert them into electrical signals.

8. A method for measuring the magnetic field of a superconducting coil based on NV color centers, applied to the device of claims 1-7, characterized in that: The method comprises: irradiating the sample to be tested with a first type of light, and adjusting the optical paths of the first type of light and the fluorescent return light based on the light spot of the reflected light from the sample to be tested; irradiating the sample to be tested with a second type of light, and adjusting the second type of light based on the optical path of the fluorescent return light and the imaging of the second type of light by the sample in the imaging system; The first type of light is irradiated onto the sample to be tested, and photoelectric processing is performed based on the fluorescent return light of the sample to be tested.

9. The method according to claim 8, characterized in that The step of irradiating the first type of light to the sample to be tested and adjusting the first type of light based on the received reflected light spot of the sample to be tested comprises: irradiating the first type of light to the sample to be tested and adjusting the angle and / or position of the first type of light based on the reflected light spot of the sample to be tested; adjusting the focus of the first type of light to the sample to be tested based on the photoelectric signal power of the reflected light; The step of irradiating the sample to be tested with the second type of light and adjusting the second type of light based on the fluorescence return light path of the sample to be tested and the imaging of the imaging system comprises: irradiating the sample to be tested with the second type of light and adjusting the position and / or angle of the second type of light based on the imaging of the imaging system.

10. The method according to claim 8, characterized in that Include: The first type of light and microwaves are emitted to the sample to be tested under time sequence control, and the fluorescent signal is received and photoelectrically processed.

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