Temperature measurement method using temperature imaging system based on diamond NV color center

Abstract

The invention discloses a method for measuring temperature by using a temperature imaging system based on a diamond NV color center. The temperature imaging system comprises a laser source, a microwave signal source, a pulse signal generator, a fluorescence collection device, a scanning device and a computer; the scanning device comprises a tapered optical fiber solid-state quantum temperature probe, a device to be measured and an electric scanning device, and the electric scanning device is equipped with a tapered optical fiber solid-state quantum temperature probe for mobile scanning of the device to be measured; the optical fiber quantum temperature probe can measure 8 centrally symmetrical and mutually independent resonance peaks by scanning an ODMR spectrum, and obtain eight energy levels of an NV color center ensemble, the peak positions of the energy levels are obtained by fitting, the Hamiltonian of the NV color center system is numerically solved, the value of D is obtained, and then the temperature value is obtained according to the temperature dependence of D calibrated in advance; the application adopts a point-by-point scanning method to greatly improve the measurement resolution, the NV color center is extremely small, and the measurement sensitivity can be significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum precision sensing, and in particular relates to a method for measuring temperature using a temperature imaging system based on diamond NV color centers. Background Art

[0002] Color centers are a type of solid crystal defect, belonging to point defects. These defects can absorb and emit fluorescence of specific wavelengths, and then be distinguished by characteristic spectra. Different doping will result in different types and contents of diamond color centers. Among the various diamond defects that have been discovered, nitrogen vacancy defects are considered to be one of the defects with the most research potential due to their unique optical properties and electron spin characteristics.

[0003] Diamond NV color center refers to a diamond fixed structure carbon atom is replaced by a nitrogen atom, there is a vacancy in the adjacent four carbon atoms, the nitrogen atom and the remaining two carbon atoms and the vacancy form a stable structure, this structure has a luminescence defect, so it is called diamond NV color center. Diamond NV color center has two different charged states, namely NV 0 and NV - , N.V. 0 is an uncharged NV color center, while NV - It is a negatively charged NV color center. 3 A2 and excited states 3 E forms a spin triplet state, whose spin energy levels are m s =+1, m s =0, m s =-1. Without the effect of external static magnetic field, m in the ground state s = -1 and m s = +1, these two originally linearly independent states are degenerate. This state is related to m s = 0 state is 2.87GHz, which is the D value under zero field. Therefore, the NV color center can resonate with the 2.87GHz microwave signal, which is manifested as a significant decrease in the intensity of the fluorescence signal on a macroscopic scale. The crystal defects are spin-polarized and optically read out by pump light, and the magnetic resonance information is transferred to the detection light intensity. This technology is called optical detection magnetic resonance (ODMR) technology.

[0004] The research on temperature measurement using NV color center usually focuses on measuring the movement of D. In the room temperature range, the change of D value and temperature is approximately linear. The fiber quantum temperature probe obtains eight energy levels of the NV color center ensemble by scanning the ODMR spectrum. The peak position of the energy level is obtained by fitting. By numerically solving the D (zero field splitting, which is related to temperature) of the NV color center system, the precise measurement of temperature can be obtained according to the temperature dependence of D calibrated in advance.

[0005] On this basis, temperature sensing devices based on diamond NV color centers have been proposed one after another. The early detection methods based on ODMR were mainly designed based on the confocal optical path system. In order to improve the practicality of the measurement technology, technicians in this field have developed a fiber optic temperature sensor based on diamond NV color centers (Chinese patent CN 111307326 A), which mainly includes optical fiber, microwave transmission antenna and diamond containing NV color centers. The diamond containing NV color centers is located at the end face of the optical fiber. Temperature changes will cause changes in the ground state energy level of the NV color center, which is then used for temperature sensing. As the main sensing component, diamond itself has a very high thermal conductivity, which enables it to respond to temperature changes in the millisecond level. However, one thing that needs to be noted is that, although in principle the size of the diamond can be changed to meet the needs of different spatial resolutions, if the sensor device is used to measure micro devices (such as chips), the diamond size needs to reach about 10μm, but the core diameter of traditional multimode optical fiber is 50-62.5μm and the outer diameter of the cladding is 125μm; the core diameter of single-mode optical fiber is about 8.3μm, and the outer diameter of the cladding is about 125μm. The fiber diameter is an order of magnitude different from the diamond size. In the process of using fluorescence excitation and collection modules to excite NV color centers and collect fluorescence to convert optical signals into electrical signals, the fluorescence collection efficiency is sensitive to the relative size of the fiber diameter and the diamond. When light enters the optical fiber from a certain angle, if the incident angle of the interface between the core and the cladding exceeds the critical angle, the light will be completely reflected and ultimately constrained to propagate within the core. This will cause laser leakage problems, which will affect the laser excitation efficiency and fluorescence collection efficiency.

[0006] Chinese patent CN 109143121 B discloses a microwave field quantitative test system and method based on pulse modulation. The test system proposes the idea of ​​using tapered optical fiber to improve the fluorescence collection rate. Specifically, diamond particles containing NV color centers are fixed on the end face of the tapered optical fiber probe, and the microwave field is tested by laser coupling into the optical fiber. The design of the tapered optical fiber can improve the collection efficiency of the fluorescence signal. When the probe volume is very small, the design can achieve high spatial resolution magnetic field measurement at the chip level. The scheme uses pulse modulation to quantitatively test the microwave field. There is no scheme in the prior art that uses tapered optical fiber for temperature imaging system, and there is no scientific temperature calculation method based on this that can significantly improve the temperature measurement precision. Summary of the invention

[0007] The present invention aims to solve the problem of insufficient resolution and sensitivity of the optical fiber temperature measurement system in the prior art, and proposes a method for measuring temperature using a temperature imaging system based on diamond NV color centers. The method improves the measurement resolution and sensitivity by adopting a micron-scale tapered optical fiber quantum temperature probe containing diamond NV color centers, a photodetector, a spectrometer and a micron-scale stepping electric displacement platform.

[0008] The technical solution of the present invention is: a method for measuring temperature using a temperature imaging system based on diamond NV color centers, the temperature imaging system comprising a laser source, a microwave signal source, a pulse signal generator, a fluorescence collection device, a scanning device and a computer;

[0009] The laser source and the microwave signal source are electrically connected to the pulse signal generator respectively;

[0010] The scanning device includes a tapered optical fiber solid-state quantum temperature probe, a device to be tested, and an electric scanning device. The electric scanning device is equipped with a tapered optical fiber solid-state quantum temperature probe for performing mobile scanning on the device to be tested fixed on the electric scanning device.

[0011] The fluorescence collection device includes an excitation optical path, a photodetector, a voltage collection module, a low-noise amplifier and a filter, which is used to collect the red fluorescence generated by the diamond being excited. After the collection is completed, the processed signal is transmitted to the spectrum analyzer;

[0012] The pulse signal generator, the spectrum analyzer and the electric scanning device are electrically connected to the computer respectively;

[0013] The fiber quantum temperature probe can measure eight centrosymmetric and mutually independent resonance peaks by scanning the ODMR spectrum, and obtain eight energy levels of the NV color center ensemble. The peak positions of the energy levels are obtained by fitting, and the value of D is obtained by numerically solving the Hamiltonian containing D, E and vector B of the NV color center system. The calculation process is as follows:

[0014] Using the Hamiltonian formula and The expression of H′ is

[0015] Among them, H represents Hamiltonian, B represents the magnitude of magnetic field, D represents the zero-field splitting value, E represents crystal stress, θ represents the angle between NV axis and magnetic field, H′ represents a newly constructed Hamiltonian, and I represents the unit matrix;

[0016] Find the eigenvalue of H′, the characteristic polynomial is:

[0017]

[0018] The three eigenvalues ​​f1, f2, f3 of H′ satisfy:

[0019]

[0020] Let f u =f3-f1, f1=f2-f1, we can get

[0021]

[0022]

[0023] Comparing the constant terms we get:

[0024]

[0025] The given coordinate system is a coordinate system in which the direction vectors of the four NV axes are (1, 1, 1), (1, 1, -1), (1, -1, 1), (-1, 1, 1), respectively, which is called the NV coordinate system. The given direction angles α and β are: α represents the angle between the NV coordinate system and the z-axis, and β represents the angle between the NV axis and the x-axis.

[0026] Assume the magnetic field direction vector is v = (sinαcosβ, sinαsinβ, cosα) and use the formula

[0027]

[0028] The cosine value of the angle between the magnetic field direction and the four NV axes is obtained and written in matrix form as

[0029]

[0030] c=(cosθ1, cosθ2, cosθ3, cosθ4)^T (3-11)

[0031] N·v=c (3-12)

[0032] Using the cosine value obtained from formula (3-9) combined with formula (3-7), formula (3-8) has five equations in total. The five unknowns can be solved to get D. The f in the equation u , f l There are 8 peaks, one pair in each direction. According to the temperature dependence of D calibrated in advance, precise measurement of temperature is obtained.

[0033] Furthermore, the laser source is used to generate a laser pulse signal, the microwave signal source is used to generate a high-frequency microwave signal, and the pulse signal generator is used to generate a TTL signal to control the laser source and the microwave signal source.

[0034] Furthermore, the laser source generates a duty-cycle controllable green laser with a wavelength of 532 nm using a modulation signal sent by a pulse signal generator.

[0035] Furthermore, the high-frequency microwave signal generated by the microwave signal source is modulated by a pulse modulation signal and connected to a high-frequency microwave coil, which is placed near the tapered optical fiber solid-state quantum temperature probe to stabilize the microwave field around the diamond NV color center.

[0036] Furthermore, the diameter of diamond particles can be adjusted between the submicron level and the submillimeter level, mainly to meet the needs of different spatial resolutions. In order to adapt to the diameter of diamond particles, the end face diameter of the tapered multimode optical fiber can be between the submicron level and 125 microns.

[0037] Furthermore, the tapered optical fiber solid-state quantum temperature probe is formed by fixing a diamond NV color center particle sample at the tip of a tapered multimode optical fiber, and the tapered multimode optical fiber is prepared by a manual taper method or an arc discharge method.

[0038] Furthermore, the excitation light path includes a convex lens, a reflector, a long-pass dichroic mirror, a first objective lens, a fiber adapter plate and a second objective lens; the laser emitted by the laser source passes through a group of convex lenses to adjust the transmitted laser into a beam of parallel light, and the parallel light reflected by the reflector is irradiated on the long-pass dichroic mirror, the mirror plane of the long-pass dichroic mirror is at an angle of 45° with the incident laser, and the long-pass dichroic mirror reflects the incident laser to the first objective lens in a direction of 90° to the incident angle, the first objective lens and the fiber adapter plate are used for focusing and coupling the pump laser, and the parallel laser used for excitation is coupled to the tapered multimode optical fiber, the laser is transmitted to the tapered surface of the tapered multimode optical fiber, and the NV color center in the diamond fixed at its front end is excited; the fluorescence radiated by the NV color center is collected by the tapered multimode optical fiber and transmitted to the fiber adapter plate and the first objective lens, penetrates the long-pass dichroic mirror and irradiates the second objective lens, and the second objective lens focuses the fluorescence on the photodetector to realize the conversion between the optical signal and the electrical signal.

[0039] Furthermore, the fluorescence passes through the second objective lens and passes through a long-pass filter before being focused on the photodetector to filter out noise signals.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] 1. When measuring temperature using the system disclosed in the present application, the microwave signal frequency is changed by a programmable microwave source, and after applying an external magnetic field, ODMR technology can be used to measure 8 centrally symmetrical and mutually independent resonance peaks, and eight energy levels of the NV color center ensemble are obtained. The peak positions of the energy levels are obtained by fitting, and the Hamiltonian of the NV color center system is numerically solved to obtain the value of D. Then, based on the temperature dependence of D calibrated in advance, a relatively precise temperature value can be obtained. The present invention uses a point-by-point scanning method to greatly improve the measurement resolution, and the NV color center is extremely small, which greatly improves the measurement sensitivity.

[0042] 2. This application performs a taper process on a conventional multimode optical fiber to make a tapered multimode optical fiber, and then fixes a diamond NV color center particle sample at the tapered end to form a tapered optical fiber solid-state quantum temperature probe. Compared with a temperature probe made of conventional optical fiber materials, since the size of the tapered tip is closer to the size of a small particle of diamond, it can effectively prevent laser leakage, which helps to improve the laser excitation efficiency and fluorescence collection efficiency;

[0043] 3. The temperature imaging system disclosed in the present application utilizes a tapered optical fiber solid-state quantum temperature probe for temperature measurement. Based on the high fluorescence collection efficiency of the probe, the measurement sensitivity can be significantly improved, high spatial resolution temperature measurement and scanning can be achieved, and high-precision temperature measurement of tiny devices can be performed to meet the needs of higher precision experiments and applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic block diagram of the structure of a micron-scale high-resolution temperature imaging system based on diamond NV color centers;

[0045] Figure 2 It is a detailed diagram of the process of laser transmission from the laser source to the spectrum analyzer;

[0046] Figure 3 This is a schematic diagram of the structure of a tapered optical fiber solid-state quantum temperature probe;

[0047] Figure 4 This is a comparison chart of the fluorescence collection efficiency of tapered fiber and untapered fiber;

[0048] Figure 5 This is a physical picture of the arc discharge method equipment;

[0049] Among them, 1-conical fiber solid-state quantum temperature probe, 2-first objective lens, 3-laser source, 4-long-pass dichroic mirror; 5-filter, 6-photodetector, 7-voltage acquisition module, 8-low noise amplifier, 9-filter, 10-pulse signal generator, 11-microwave signal source, 12-high-frequency microwave coil, 13-device to be tested, 14-electric scanning device, 15-computer, 16-spectrometer, 17-convex lens, 18-reflector, 19-fiber adapter plate, 20-second objective lens;

[0050] 11- Diamond NV color center particle sample, 12- Tapered multimode optical fiber. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0052] Embodiment 1

[0053] In order to improve the resolution and sensitivity of temperature sensing, a micron-level high-resolution temperature imaging system based on diamond NV color centers is disclosed in this embodiment, including a laser source 3, a microwave signal source 11, a pulse signal generator 10, a fluorescence collection device, a scanning device and a computer 15;

[0054] The laser source 3 and the microwave signal source 11 are electrically connected to the pulse signal generator 10 respectively. The laser source 3 is used to generate a laser pulse signal, the microwave signal source 11 is used to generate a high-frequency microwave signal, and the pulse signal generator 10 is used to generate a TTL signal to control the laser source and the microwave signal source;

[0055] The scanning device for detecting, scanning and imaging the temperature field comprises a tapered optical fiber solid-state quantum temperature probe 1, a device to be tested 13 and an electric scanning device 14. The electric scanning device 14 is a two-dimensional electrically controlled displacement platform, which is a micron-level stepping electric displacement platform. The device to be tested 13 is fixed on the displacement platform. The electric scanning device 14 is equipped with the tapered optical fiber solid-state quantum temperature probe 1 and is used to perform mobile scanning on the device to be tested 13. The device to be tested referred to in this embodiment is a micro chip to be tested.

[0056] The tapered fiber solid-state quantum temperature probe 1 is formed by fixing a diamond NV color center particle sample 11 on the tapered end of a tapered multimode optical fiber 12, and the tapered multimode optical fiber 12 is a quasi-adiabatic tapered optical fiber made of multimode optical fiber. During scanning, the device under test 13 can be controlled to perform micron-level electric scanning by controlling the electric displacement platform control box through a computer program.

[0057] The structure of the tapered optical fiber solid-state quantum temperature probe 1 is as follows Figure 3 As shown, the size of each tip of the tapered optical fiber quantum temperature probe 1 used matches the size of the corresponding diamond NV color center particle sample 11; in this embodiment, the diameter of the diamond particle is 12 μm, and the end face diameter of the tapered multimode optical fiber is 16-21 μm.

[0058] The tapered multimode optical fiber proposed in this embodiment can be prepared by a manual tapering method or an arc discharge method.

[0059] Manual taper method: First, use a wire stripper to strip off the coating of the multimode optical fiber for about 2-3 cm, and then use a lab paper dipped in anhydrous alcohol solution to wipe off the coating residue; then, place the optical fiber at the tip of a candle flame to heat it, hold one end tightly with your hand, and use tweezers to stretch the other end at a constant speed until it breaks. When pulling, make sure to do it in a closed environment, because air flow will affect the flame temperature and quality. Finally, use a fiber cleaver to quickly cut the end face flat to form a flat end face, which will help fix the diamond particles and improve the collection efficiency.

[0060] Arc discharge method: First, use a wire stripper to strip off the coating of the multimode optical fiber for about 2-3 cm, and then place the multimode optical fiber with the coating removed on the optical fiber holder. Figure 5 As shown, a pair of electrodes are placed in a front-to-back position, with the tips about 1mm apart; the size and time of arc discharge are controlled by setting the current size and current time, and the speed of the motor is controlled to control the speed of the clamp moving away, thereby melting the optical fiber to obtain a tapered optical fiber. This method can obtain an optical fiber with a stable tapered length, and the tapered length range is controlled in the range of 60μm-400μm, with higher accuracy.

[0061] The laser source 3 uses the modulation signal emitted by the pulse signal generator 10 to generate a green laser with a controllable duty cycle of 532nm. Considering that the size of the sample to be tested is extremely small and the temperature sensing ability is extremely strong, the laser temperature will directly affect the temperature detected by the probe. Therefore, a controllable duty cycle laser is required to control the temperature generated by the laser at the end of the optical fiber to be lower than the room temperature. The green laser with controllable duty cycle is injected into the optical path and finally focused to the conical solid-state optical fiber quantum temperature probe 1 through the objective lens to complete the conversion of the photoelectric signal.

[0062] The high-frequency microwave signal generated by the microwave signal source 11 is modulated by a pulse modulation signal and connected to the high-frequency microwave coil 12. The high-frequency microwave coil 12 is placed near the tapered optical fiber solid-state quantum temperature probe 1 so that the microwave field around the diamond NV color center remains unchanged.

[0063] The fluorescence collection device includes an excitation optical path, a photodetector 6, a voltage collection module 7, a low-noise amplifier 8 and a filter 9. The diamond NV color center generates a sideband fluorescence pulse signal under the alternating action of laser and microwave signals. After the diamond is excited to produce red fluorescence, the fluorescence collection device is used to collect the red fluorescence generated by the excited diamond. After the collection is completed, the processed signal is transmitted to the spectrometer 16 for further analysis and processing.

[0064] The pulse signal generator 10 , the spectrum analyzer 16 and the electric scanning device 14 are electrically connected to the computer 15 , respectively.

[0065] The excitation optical path that the laser light passes through when it is transmitted from the laser source 3 to the spectrometer 16 is as follows: Figure 2As shown, the laser emitted by the laser source 3 first passes through a group of convex lenses 17, which can adjust the transmitted laser into a beam of parallel light; then it is reflected by a reflector 18 (the reflector can be used to adjust the height and direction of the optical path), and the reflected parallel light is irradiated on the long-pass dichroic mirror 4, and the mirror plane of the long-pass dichroic mirror 4 is at an angle of 45° with the incident laser; since the wavelength of the incident laser is less than the starting wavelength of the long-pass dichroic mirror 4, the long-pass dichroic mirror 4 is equivalent to a reflector for the incident laser, which can reflect the incident laser to the first objective lens 2 at a direction of 90° to the incident angle; the first objective lens 2 and the fiber adapter plate 19 are used for focusing and coupling the pump laser, so that the optical fiber used for excitation can be focused on the first objective lens 2. The parallel laser is coupled into the tapered multimode optical fiber, and the laser is transmitted to the tapered surface of the tapered multimode optical fiber to excite the NV color center crystal fixed at its front end; the fluorescence radiated by the NV color center is collected by the tapered optical fiber and transmitted to the optical fiber adapter plate 19 and the first objective lens 2, and the wavelength range of the fluorescence is 600-800nm, and the wavelength is greater than the starting wavelength of the long-pass dichroic mirror 4. The long-pass dichroic mirror 4 has little obstruction and reflectivity to the light of this wavelength, and can penetrate the long-pass dichroic mirror 4 to irradiate the second objective lens 20; the second objective lens 20 focuses the fluorescence on the photodetector 6. The photodetector used in this embodiment is an avalanche photodiode APD, that is, it is finally collected by the APD to complete the conversion between the optical signal and the electrical signal.

[0066] A long-pass filter 5 is installed in front of the photodetector 6 to filter stray light that is not completely filtered out by the long-pass dichroic mirror 4 in the optical path system.

[0067] The method for measuring temperature using the above temperature imaging system is as follows:

[0068] The research on temperature measurement using NV color center usually focuses on measuring the movement of D. At room temperature, the change of D value and temperature T is approximately linear, which is: dD / dT=74.2kHz / K. The fiber quantum temperature probe can measure 8 centrosymmetric and independent resonance peaks by scanning the ODMR spectrum, and obtain the eight energy levels of the NV color center ensemble. The peak position of the energy level is obtained by fitting. The value of D is obtained by numerically solving the Hamiltonian containing D (zero field splitting, related to temperature), E (crystal stress, ignoring the relationship with temperature) and vector B of the NV color center system, which solves the problem of large error in the temperature value calculated by the double peak center frequency. The following describes how to obtain the value of D based on the 8 peaks.

[0069] Using the Hamiltonian formula and The expression of H′ is

[0070] Among them, H represents Hamiltonian, B represents the magnitude of magnetic field, D represents the zero-field splitting value, E represents crystal stress, θ represents the angle between NV axis and magnetic field, H′ represents a newly constructed Hamiltonian, and I represents the unit matrix;

[0071] Find the eigenvalue of H′, the characteristic polynomial is:

[0072]

[0073] The three eigenvalues ​​f1, f2, f3 of H′ satisfy:

[0074]

[0075] Let f u =f3-f1, f1=f2-f1, we can get

[0076]

[0077]

[0078] Comparing the constant terms we get:

[0079]

[0080] The coordinate system we give is a coordinate system in which the direction vectors of the four NV axes are (1, 1, 1), (1, 1, -1), (1, -1, 1), (-1, 1, 1), which is called the NV coordinate system. The given direction angles α and β are α, α represents the angle between the NV coordinate system and the z-axis, and β represents the angle between the NV axis and the x-axis.

[0081] Assume the magnetic field direction vector is v = (sinαcosβ, sinαsinβ, cosα) and use the formula

[0082]

[0083] The cosine value of the angle between the magnetic field direction and the four NV axes is obtained and written in matrix form as

[0084]

[0085] c=(cosθ1, cosθ2, cosθ3, cosθ4)^T (3-11)

[0086] N·v=c (3-12)

[0087] Using the cosine value obtained from formula (3-9) combined with formula (3-7), formula (3-8) has five equations in total. The five unknowns can be solved to get D. The f in the equation u , f lThere are 8 peaks, one pair in each direction. According to the temperature dependence of D calibrated in advance, precise measurement of temperature is obtained.

[0088] Comparative example: Comparison of fluorescence collection efficiency between tapered multimode fiber and conventional untapered fiber

[0089] Optical fiber is a cylindrical waveguide. Light is transmitted in the core, and its refractive index is about 1.47. The cladding is outside the core, and its refractive index is slightly lower than that of the core, about 1.42. When light enters the optical fiber from a certain angle, if the incident angle of the interface between the core and the cladding exceeds the critical angle, the light will be completely reflected, and the light will eventually be confined to propagate in the core. After the multimode optical fiber is tapered, the cladding becomes thinner, and even air becomes a new cladding (with a refractive index of 1), which is quite different from the refractive index of the core in the optical fiber, so the light is strongly bound at this time. The fluorescence collection efficiency is sensitive to the relative size of the tapered tip of the optical fiber and the diamond. When the size of the tapered tip is close to the size of the diamond, laser leakage can be prevented, and the laser excitation efficiency and fluorescence collection efficiency can be improved. Under the same time conditions, the fluorescence collection efficiency of the same sample at the same position was tested using a 532nm pump beam, and the number of collected fluorescence photons was recorded. Figure 4 This is a comparison chart of the fluorescence collection efficiency of tapered optical fiber and ordinary non-tapered optical fiber. It can be seen that the spectrum mainly covers the wavelength range of 600-800nm, and the fluorescence is strongest at 700nm. Since the filter filters out all light except red light, there is a cutoff point with a wavelength shorter than 600nm. The tapered optical fiber can clearly observe the NV-zero phonon line at 637nm (marked with an *), at which time the NV color center in the diamond can be effectively excited and captured. The non-tapered optical fiber cannot clearly show the spectral characteristics, and the fluorescence collection efficiency is low. The fluorescence intensity count collected by the tapered optical fiber reached nearly 6000, which is more than 12 times that of the non-tapered optical fiber, which can greatly improve the fluorescence collection efficiency.

[0090] This is the main reason for using tapered optical fiber in Example 1. Such a design can significantly improve the measurement sensitivity, achieve high spatial resolution temperature measurement and scanning, and perform high-precision temperature measurement on tiny devices to meet the needs of higher-precision experiments and applications.

[0091] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for measuring temperature using a temperature imaging system based on diamond NV color centers, characterized in that: The temperature imaging system includes a laser source, a microwave signal source, a pulse signal generator, a fluorescence collection device, a scanning device and a computer; The laser source and the microwave signal source are electrically connected to the pulse signal generator respectively; The scanning device includes a tapered optical fiber solid-state quantum temperature probe, a device to be tested, and an electric scanning device. The electric scanning device is equipped with a tapered optical fiber solid-state quantum temperature probe for performing mobile scanning on the device to be tested fixed on the electric scanning device. The fluorescence collection device includes an excitation optical path, a photodetector, a voltage collection module, a low-noise amplifier, and a filter. It is used to collect the red fluorescence generated by the excited diamond and transmit the processed signal to the spectrometer after the collection is completed. The pulse signal generator, the spectrum analyzer and the electric scanning device are electrically connected to the computer respectively; The fiber quantum temperature probe can measure eight centrosymmetric and independent resonance peaks by scanning the ODMR spectrum, obtaining the eight energy levels of the NV color center ensemble. The peak positions of the energy levels are obtained by fitting, and the value of D is obtained by numerically solving the Hamiltonian containing D, E, and vector B of the NV color center system. The calculation process is as follows: Using the Hamiltonian formula and The expression of H′ is obtained as Where H represents the Hamiltonian, B represents the magnitude of the magnetic field, D represents the zero-field splitting value, E represents the crystal stress, θ represents the angle between the NV axis and the magnetic field, H′ represents a newly constructed Hamiltonian, and I represents the unit matrix; Find the eigenvalue of H′, the characteristic polynomial is: The three eigenvalues ​​f1, f2, f3 of H′ satisfy: Let f u =f3-f1,f l =f2-f1, we can get Comparing the constant terms we get: The given coordinate system is a coordinate system in which the direction vectors of the four NV axes are (1, 1, 1), (1, 1, -1), (1, -1, 1), and (-1, 1, 1), respectively. This is called the NV coordinate system, and the given direction angles α and β are: α represents the angle between the NV coordinate system and the z-axis, and β represents the angle between the NV axis and the x-axis. Assume that the magnetic field direction vector is v = (sinαcosβ, sinαsinβ, cosα) and use the formula Calculate the cosine value of the angle between the magnetic field direction and the four NV axes and write it in matrix form: c=(cosθ1, cosθ2, cosθ3, cosθ4)^T (3-11) N·v=c (3-12) Using the cosine value obtained from formula (3-9) combined with formula (3-7), formula (3-8) has five equations in total. The five unknowns can be solved to get D. The f in the equation is u , f l There are 8 peaks, one pair in each direction. The temperature value is obtained according to the temperature dependence of D dD / dT = 74.2kHz / K, which has been calibrated in advance.

2. The method for measuring temperature using a temperature imaging system based on diamond NV color centers according to claim 1, wherein: The laser source is used to generate a laser pulse signal, the microwave signal source is used to generate a high-frequency microwave signal, and the pulse signal generator is used to generate a TTL signal to control the laser source and the microwave signal source.

3. The method for measuring temperature using a temperature imaging system based on diamond NV color centers according to claim 1, wherein: The laser source uses the modulation signal sent by the pulse signal generator to generate a controllable duty cycle green laser with a wavelength of 532nm.

4. The method for measuring temperature using a temperature imaging system based on diamond NV color centers according to claim 1, wherein: The high-frequency microwave signal generated by the microwave signal source is modulated by a pulse modulation signal and connected to a high-frequency microwave coil. The high-frequency microwave coil is placed near the tapered fiber solid-state quantum temperature probe to maintain the stability of the microwave field around the diamond NV color center.

5. The method for measuring temperature using a temperature imaging system based on diamond NV color centers according to claim 1, wherein: The tapered fiber solid-state quantum temperature probe is formed by fixing a diamond NV color center particle sample at the tip of a tapered multimode optical fiber; the tapered multimode optical fiber is prepared by a manual taper method or an arc discharge method.

6. The method for measuring temperature using a temperature imaging system based on diamond NV color centers according to claim 1, wherein: The excitation light path includes a convex lens, a reflector, a long-pass dichroic mirror, a first objective lens, a fiber adapter plate, and a second objective lens; The laser emitted by the laser source passes through a set of convex lenses to adjust the transmitted laser into a beam of parallel light. After being reflected by the reflector, the parallel light is irradiated on the long-pass dichroic mirror. The mirror plane of the long-pass dichroic mirror is at a 45° angle to the incident laser. The long-pass dichroic mirror reflects the incident laser at a direction of 90° to the incident angle to the first objective lens. The first objective lens and the fiber adapter plate are used to focus and couple the pump laser, and the parallel laser used for excitation is coupled into the tapered multimode optical fiber. The laser is transmitted to the tapered surface of the tapered multimode optical fiber, exciting the NV color center in the diamond fixed at its front end; the fluorescence radiated by the NV color center is collected by the tapered multimode optical fiber and transmitted to the fiber adapter plate and the first objective lens, penetrating the long-pass dichroic mirror and irradiating the second objective lens. The second objective lens focuses the fluorescence on the photodetector, realizing the conversion between optical signals and electrical signals.

7. The method for measuring temperature using a temperature imaging system based on diamond NV color centers according to claim 6, wherein: The fluorescence passes through the second objective lens and passes through a long-pass filter to filter out noise signals before being focused on the photodetector.

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