Excitation type synchronous pulse broadband magnetic field scanning imaging method and device

Abstract

The invention relates to a magnetic field measurement technology, and aims to provide an excitation type synchronous pulse broadband magnetic field scanning imaging method and device. According to the method, in a broadband magnetic field scanning imaging process, based on response characteristics of fluorescence generated by a solid-state spin ensemble represented by an NV color center ensemble to a magnetic field, synchronous excitation is carried out by combining an alternating current excitation signal and a high-order dynamic decoupling sequence synchronized with microwave pulses, so that measurement of the external magnetic field by solid-state spin is realized. Through combination of synchronous current excitation and a high-order power decoupling sequence, magnetic field calibration without external reference is realized, the sensitivity and the signal-to-noise ratio of magnetic measurement are improved, and the precision and the imaging quality of magnetic field measurement are remarkably improved; absolute magnetic field information can be directly extracted from experimental data, so that errors caused by external interference are eliminated, and the method is suitable for long-term experiments and high-precision measurement requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic field measurement applications, and in particular to a technology of solid-state spin-based excitation synchronous pulse broadband magnetic field scanning imaging. Background Art

[0002] Magnetic resonance refers to the physical process in which particles with non-zero spin magnetic moments within a substance resonate with the electromagnetic field in a static magnetic field. This interaction mechanism enables researchers to analyze the composition of materials without destroying the sample structure. The technology is also being applied to the sensing and detection of precise physical quantities.

[0003] Under the influence of an external magnetic field, electrons within a substance, due to their inherent spin magnetic moment, experience Zeeman level splitting, where a single energy level expands into multiple sublevels with different magnetic quantum numbers. When electrons transition between energy levels, they must follow specific transition rules related to changes in magnetic quantum numbers. This quantum selection rule directly determines the possibilities of a particle's spin state evolution.

[0004] With the breakthrough of quantum information technology, solid-state spin systems have become an important direction for the research and development of new sensors due to their unique physical properties. Solid-state quantum systems represented by diamond nitrogen-vacancy (NV) color centers have shown significant advantages: their electron spin states can not only maintain microtesla-level magnetic field sensitivity at room temperature and pressure, but also have a quantum state maintenance time of up to milliseconds. The unique optical manipulation and signal reading capabilities of this system make it the only natural quantum probe that can currently realize magnetic resonance detection at the microscopic scale, showing broad application prospects in materials science, biomedicine and other fields. The structural stability and anti-interference ability of such solid-state systems further enhance their practical value in complex environments. In addition, NV color centers have the potential for high measurement bandwidth. The wider bandwidth can cover a larger magnetic field frequency range to meet different measurement scenarios and application requirements.

[0005] Current mainstream quantum magnetometer technology typically utilizes the photoinduced magnetic resonance properties of NV color centers for magnetic field sensing. Its operating principle is to initialize electron spin states through laser irradiation, coherently manipulate quantum states using microwave radiation, and ultimately interpret the external magnetic field by detecting differences in the populations of different spin states in the photoluminescence signal. This technology, through the interaction of quantum states with the electromagnetic field, converts magnetic field intensity into observable optical signal variations, thereby achieving highly sensitive magnetic field measurements.

[0006] Magnetic field scanning imaging using nitrogen-vacancy (NV) color centers in diamond is a cutting-edge method that combines quantum sensing with nanoscale precision detection. It can achieve high-sensitivity, high-resolution visualization of magnetic field distributions at room temperature and is widely used in high-density magnetic storage, spintronics, and two-dimensional materials research. During magnetic field scanning imaging, traditional magnetic field calibration methods typically rely on external calibration coils or additional calibration equipment, which can lead to the accumulation of measurement errors and inconvenience in calibration.

[0007] Therefore, it is necessary to propose new solutions to solve the above technical problems. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a method and device for excitation-type synchronous pulse broadband magnetic field scanning imaging.

[0009] To solve the technical problem, the solution of the present invention is:

[0010] A method for solid-state spin-based excitation synchronous pulse broadband magnetic field scanning imaging is provided, the method comprising:

[0011] The control readout module controls the switching device in the microwave magnetic field module to output two microwave pulses with an initial phase difference of π / 2. The control readout module triggers the current excitation module to output a sinusoidal AC signal. The sequence generator in the control readout module outputs a reference signal synchronized with the two microwave pulses to the signal acquisition device, and the signal acquisition device acquires the AC signal output in real time by the current excitation module.

[0012] The control readout module adjusts the trigger signal of the current excitation module, and by controlling the trigger time, the AC signal node displayed on the signal acquisition device is aligned with the center of the reference signal. After fixing the aligned parameters, a high-order kinetic decoupling sequence is obtained for synchronizing the AC excitation signal with the microwave pulse. Compared with the CPMG sequence (Carr-Purcell-Meiboom-Gill sequence), this sequence further adds synchronous excitation and reference sequences.

[0013] The high-order kinetic decoupling sequence is played using a control readout module to achieve coordinated operation of laser, microwave, and AC excitation; the excitation current in the sample to be tested is changed using a current excitation module, and then the current value is kept constant; the photocurrent signal is read and averaged to obtain the fluorescence intensity corresponding to the current value; after stepwise changing the excitation current, a curve of the relationship between the fluorescence intensity and the excitation current in the sample to be tested is obtained, and then the magnetic field corresponding to the specific value of the excitation current in the sample to be tested is calculated;

[0014] The above operation is repeated after stepping through the position of the sample to be tested to obtain the magnetic field size corresponding to scanning a new area in the sample under a specific excitation current value; and so on, finally completing the scanning of the sample to be tested according to the predetermined plan and obtaining complete magnetic image data.

[0015] As a preferred embodiment of the present invention, the calibration curve is analyzed according to a self-traceable magnetic field calibration method, which refers to calibrating the magnetic field generated by the sample current by a phase accumulation method of a spin system;

[0016] Specifically, based on the phase accumulation principle of the solid-state spin system, when the phase is π, the phase accumulation formula Inversely deduce the magnetic field B π The first peak of the fluorescence intensity and current curve corresponds to the current value I π , when the current in the sample to be tested is I, the magnetic field at that location is In the above formulas, is the angular coefficient of the gyromagnetic ratio, is the angle between the magnetic field and the principal axis of the NV color center; γ e =28.025Hz / nT, which is the gyromagnetic ratio of electrons; B is the amplitude of the AC magnetic field; is the total phase integration time, f is the frequency of the AC magnetic field, and n is (π) y The number of microwave pulses; B π It refers to the magnetic field corresponding to the phase accumulation of π, I π It refers to the current corresponding to the phase accumulation of π.

[0017] As a preferred embodiment of the present invention, the high-order dynamic decoupling sequence includes parameters of two microwave pulses in the x-direction and the y-direction; the two microwave pulses are generated by a 90-degree power splitter and the initial phase difference is fixed at π / 2, and the frequency and duration of the microwave pulses are determined by continuous wave spectrum experiments and Rabi oscillation experiments of the corresponding phases, respectively.

[0018] As a preferred solution of the present invention, a signal acquisition device is used to obtain a real-time current monitoring signal at the output end of the power amplifier in the current excitation module and display it on a screen.

[0019] The present invention further provides a device for implementing the aforementioned method of solid-state spin-based excitation synchronous pulse broadband magnetic field scanning imaging, comprising:

[0020] Laser modulation module, used to output pulsed laser to excite diamond containing NV color center ensemble to emit fluorescence;

[0021] A probe assembly, comprising the diamond as a magnetic sensitive unit, the fluorescence emitted by the diamond including magnetic field information of the sample to be tested;

[0022] A microwave magnetic field module is used to generate a uniform bias magnetic field near the magnetic sensitive unit; and is used to generate and combine two microwave pulses with an initial phase difference to generate a uniform microwave field at the probe assembly;

[0023] The current excitation module is used to output a sinusoidal AC signal to provide current excitation to the sample to be tested;

[0024] A control readout module is used to obtain a photocurrent signal converted from fluorescence from the probe assembly; and is used to modulate the two microwave pulses and the sinusoidal AC signal so that the nodes of the microwave pulses and the AC signal are aligned;

[0025] The data processing module is used to generate a high-order dynamic decoupling sequence based on the node alignment rules of microwave pulses and AC signals, and provide it to the control readout module for generating laser modulation signals, microwave pulse control signals and excitation current trigger signals; it is used to receive the signals obtained by the control readout module and generate a magnetic image based on the photocurrent signals converted by the probe assembly.

[0026] As a preferred solution of the present invention, the probe assembly further comprises a parabolic lens, a filter and a photodiode arranged in sequence; the magnetic sensitive unit is located on the optical path outside the parabolic lens, and the photodiode is connected to the control readout module via a coaxial line.

[0027] As a preferred embodiment of the present invention, the microwave magnetic field module includes a microwave source, a power divider, a combiner, a power amplifier, a radiating structure, and a pair of Helmholtz coils connected in sequence via a coaxial line; switching devices are respectively provided on the two branches between the power divider and the combiner, and each switching device is respectively connected to the control readout module via a coaxial line; the radiating structure is connected to the power amplifier via the coaxial line, and the magnetic sensitive unit is nested in the radiating structure; the pair of Helmholtz coils are respectively located on both sides of the magnetic sensitive unit and maintain a distance therebetween, and the magnetic sensitive unit is located on the centerline of the magnetic field.

[0028] As a preferred embodiment of the present invention, the current excitation module includes an arbitrary waveform generator and a power amplifier connected in sequence via a coaxial line, and the output end of the power amplifier is connected to the sample to be tested, which is a wire, chip or magnetic material that can be excited by current.

[0029] As a preferred embodiment of the present invention, the control readout module includes a sequence generator, an acquisition card and a signal acquisition device; the sequence generator is respectively connected to the laser modulation module, the probe assembly, the microwave magnetic field module, the current excitation module and the data processing module through a coaxial line; the data processing module is a host computer; the signal acquisition device is respectively connected to the sequence generator and the monitoring port provided on the power amplifier through a coaxial line.

[0030] As a preferred solution of the present invention, the probe assembly is fixed below the end of the cantilever beam, and the head end of the cantilever beam is connected to a six-degree-of-freedom translation platform; the sample to be tested is placed on the three-dimensional translation platform.

[0031] Description of the invention principle:

[0032] This paper proposes an innovative solution that uses a combination of synchronous current excitation and high-order kinetic decoupling sequences to accurately calculate the phase accumulation formula, thereby inferring the relationship between the magnetic field and the excitation current. This provides a self-traceable magnetic field calibration method based on a solid-state spin system, eliminating the need for an external reference system and calibration equipment. Based on the response characteristics of the fluorescence generated by a solid-state spin ensemble represented by the NV color center ensemble to the magnetic field, this method combines high-order kinetic decoupling methods with synchronous excitation methods to achieve solid-state spin measurement of external magnetic fields.

[0033] Among them, the high-order dynamic decoupling sequence is based on the traditional CPMG(n) sequence, with the addition of AC synchronous excitation and reference sequence parts to suppress environmental noise and improve the sensitivity and signal-to-noise ratio of magnetic measurements. AC synchronous excitation uses an arbitrary waveform generator to generate a sinusoidal AC signal, which is applied to the sample through a high-power amplifier. In order to keep the current node in the sample aligned with the center of the microwave pulse, the control readout module outputs a signal synchronized with the microwave pulse to the signal acquisition device as a reference. The signal at the current monitoring end of the high-power amplifier is also connected to the signal acquisition device. By adjusting the trigger time of the AC excitation in the high-order dynamic decoupling sequence, it is ensured that the node of the AC signal is aligned with the center of the microwave synchronous reference signal, thereby optimizing the acquisition of the magnetic response signal.

[0034] The solid-state spin system in the present invention works based on the following self-traceable magnetic field calibration principle: the crystal orientation of the diamond is measured by the continuous wave spectrum, and the angle between the magnetic field and the main axis of the NV color center is estimated. The angular coefficient of the gyromagnetic ratio is obtained as The formula for phase accumulation is: where γ e =28.025Hz / nT is the gyromagnetic ratio of the electron, B is the amplitude of the AC magnetic field, is the total phase accumulation time, and f is the frequency of the AC magnetic field. Therefore, when the phase accumulation is π, the corresponding magnetic field B π =π 2 ·f / (α·γ e n). The relationship between fluorescence intensity and accumulation phase: F∝cosθ. Since the magnetic field is proportional to the current, the fluorescence intensity is also cosine-related to the current in the sample. The current value I corresponding to the first peak of the fluorescence intensity is the accumulation phase π. π Therefore, according to I π Value and B πThe value can be calculated that at any current I, the magnitude of the magnetic field at that location is

[0035] The solid-state spin ensemble uses a diamond NV color center ensemble. To achieve higher spatial resolution, the diamond is polished and thinned, then glued to a parabolic lens with UV glue for collection. After filtering out the green light through a filter, it is converted by a photodiode into a current input to control the acquisition interface of the readout module. The diamond is at the center of the radiation structure. The output of the microwave source is divided into two parts with an initial phase difference of π / 2 by a 90-degree power splitter, providing Microwave pulses and (π) y Microwave pulses ultimately generate uniform microwave manipulation of the electron spins of the diamond NV center at the radiating structure. The probe components—diamond, parabolic lens, filter, photodiode, and radiating structure—are fixed to the end of a cantilever beam. The head of the cantilever is fixed to a six-degree-of-freedom translation stage to adjust the angle between the principal axis of the diamond NV center and the magnetic field being measured.

[0036] Therefore, the innovative idea of the present invention compared with the existing technology lies in that, during the broadband magnetic field scanning imaging process, through the combination of synchronous current excitation and high-order dynamic decoupling sequence, magnetic field calibration without the need for external reference is achieved, the sensitivity and signal-to-noise ratio of magnetic measurement are improved, and the accuracy of magnetic field measurement and imaging quality are significantly improved.

[0037] Compared with the prior art, the technical effects of the present invention are:

[0038] 1. The present invention is based on the synchronous excitation detection technology of the solid-state spin ensemble and the high-order dynamic decoupling sequence, which can realize high-sensitivity, high-bandwidth, contactless sample magnetic field detection working in room temperature and atmospheric environment; through the design of the solid-state spin ensemble magnetic sensor probe and the sample stage, high-spatial-resolution scanning imaging of the magnetic field around the sample is achieved; based on the self-traceable calibration method of the solid-state spin system, the relationship between the magnetic field generated by the current in the sample and the current magnitude is calibrated.

[0039] 2. Self-traceable calibration. This method achieves high-precision magnetic field calibration without relying on an external reference system or additional calibration equipment. Leveraging the inherent physical properties of the spin system, this method can directly extract absolute magnetic field information from experimental data, eliminating errors caused by external interference. It is suitable for long-term experiments and high-precision measurements.

[0040] 3. High spatial resolution. The present invention uses diamond NV ensemble scanning imaging, which has higher spatial resolution than CCD imaging. By reducing the thickness of the diamond and the diameter of the laser spot focused on the diamond, the spatial resolution of the imaging is further improved, achieving more precise magnetic field distribution measurement.

[0041] 4. High sensitivity. This method, based on the diamond NV color center ensemble and employing a high-order kinetic decoupling sequence, achieves highly sensitive measurements of the weak magnetic field surrounding the sample. By optimizing the pulse sequence design, it effectively suppresses ambient noise and prolongs the coherence time of the NV color center, thereby improving the signal-to-noise ratio of the magnetic measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic structural diagram of a scanning imaging device provided in Example 1 of the present invention.

[0043] Figure 2 Schematic diagram of the high-order kinetic decoupling sequence.

[0044] Figure 3 Schematic diagram of the change of fluorescence with sample current. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0046] Part I Overview of the Technical Solution of the Invention

[0047] The present invention first provides a device for solid-state spin-based excitation synchronous pulse broadband magnetic field scanning imaging, comprising: a laser modulation module, a probe assembly, a microwave magnetic field module, a current excitation module, a control readout module, and a data processing module.

[0048] The laser modulation module is used to output pulsed laser to excite diamond containing NV color center ensemble to emit fluorescence.

[0049] The probe assembly includes the diamond as a magnetic sensitive unit, and the fluorescence emitted by the diamond includes the magnetic field information of the sample to be tested. The probe assembly also includes a parabolic lens, a filter and a photodiode arranged in sequence; the magnetic sensitive unit is located on the optical path outside the parabolic lens, and the photodiode is connected to the control readout module via a coaxial line. In order to adjust the position of the probe assembly in the magnetic field, the entire probe assembly is fixed below the end of the cantilever beam, and the head end of the cantilever beam is connected to a six-degree-of-freedom translation stage. The sample to be tested is placed on the three-dimensional translation stage, and the position of the sample can be adjusted during the scanning process through the three-dimensional translation stage.

[0050] The microwave magnetic field module is used to generate a uniform bias magnetic field near the magnetic sensitive unit and to generate and combine two microwave pulses with an initial phase difference to produce a uniform microwave field at the probe assembly. The microwave magnetic field module includes a microwave source, a power divider, a combiner, a power amplifier, a radiating structure, and a pair of Helmholtz coils, all connected in sequence via a coaxial line. Switching devices are provided on each of the two branches between the power divider and combiner, and each switching device is connected to the control readout module via a coaxial line. For example, the switching device can be a ZASWA-2-50DRA+ model RF switch. The end of the radiating structure is connected to the power amplifier via a coaxial line, and the magnetic sensitive unit is nested within the radiating structure. A pair of Helmholtz coils are located on either side of the magnetic sensitive unit, separated by a distance, and the magnetic sensitive unit is located on the centerline of the magnetic field.

[0051] The current excitation module is used to output a sinusoidal AC signal to provide current excitation to the sample under test. The current excitation module consists of an arbitrary waveform generator and a power amplifier connected in sequence via a coaxial cable. The output of the power amplifier is connected to the sample under test. The sample under test can be a wire, chip, or magnetic material that can be excited by current. The magnetic field generated by the current excitation is used as the measurement object, and the location of sample defects is determined based on the distribution of the magnetic field.

[0052] The control readout module is used to obtain the photocurrent signal converted from the fluorescence from the probe assembly; and is used to modulate the two microwave pulses and the sinusoidal AC signal so that the nodes of the microwave pulses and the AC signal are aligned. The control readout module includes a sequence generator, an acquisition card, and a signal acquisition device; the sequence generator is connected to the laser modulation module, the probe assembly, the microwave magnetic field module, the current excitation module, and the data processing module via coaxial cables. As an example, the sequence generator can be an ASG8000 model digital delay pulse generator, and the signal acquisition device can be an oscilloscope. The oscilloscope is connected to the sequence generator and the monitoring port of the power amplifier via coaxial cables, thereby obtaining the real-time current at the output end and displaying the monitoring signal together with the microwave synchronization reference signal on the screen.

[0053] The data processing module receives signals from the control readout module. It generates a high-order kinetic decoupling sequence based on the node alignment rules of the microwave pulse and AC signal, and provides this sequence to the control readout module for generating laser pulse control signals, microwave pulse control signals, and excitation current trigger signals. It also generates a magnetic image based on the photocurrent signal converted by the probe assembly. For example, the data processing module is a host computer with complex computing, control, and human-computer interaction capabilities.

[0054] By using the above-mentioned device, the present invention can realize a method for solid-state spin-based excitation synchronous pulse broadband magnetic field scanning imaging, comprising:

[0055] The control readout module controls the switching device in the microwave magnetic field module to output two microwave pulses with an initial phase difference of π / 2. The control readout module triggers the current excitation module to output a sinusoidal AC signal. The sequence generator in the control readout module outputs a reference signal synchronized with the two microwave pulses to an oscilloscope, and the oscilloscope is used to obtain the AC signal output in real time by the current excitation module.

[0056] The trigger signal of the current excitation module is adjusted by using a control readout module, and the AC signal node displayed on the oscilloscope is aligned with the center of the reference signal by controlling the trigger time. After the aligned parameters are fixed, a high-order dynamic decoupling sequence is obtained to achieve synchronous excitation of the AC signal and the microwave pulse. Compared with the CPMG sequence, this sequence further adds the content of synchronous excitation and reference sequence. Among them, the high-order dynamic decoupling sequence includes the parameters of two microwave pulses in the x-direction and y-direction. The two microwave pulses are generated by a 90-degree power divider and the initial phase difference is fixed at π / 2. The frequency and duration of the microwave pulses are determined by continuous wave spectrum experiments and Rabi oscillation experiments of the corresponding phases, respectively.

[0057] The high-order kinetic decoupling sequence is played by the control readout module, the excitation current in the sample to be tested is changed through the current excitation module, and then the current value is fixed; the photocurrent signal is read and the average value is taken as the fluorescence intensity corresponding to the current value; after the excitation current is changed step by step, a curve of the relationship between the fluorescence intensity and the excitation current in the sample to be tested is obtained, and then the magnetic field size corresponding to the excitation current in the sample to be tested at a specific value is calculated; wherein, the calibration curve is analyzed according to the self-traceable magnetic field calibration method, which refers to calibrating the magnetic field size generated by the sample current through the phase accumulation method of the spin system; specifically including: based on the phase accumulation principle of the solid-state spin system, when the phase is π, the phase accumulation formula Inversely deduce the magnetic field B π The first peak of the fluorescence intensity and current curve corresponds to the current value I π , when the current in the sample to be tested is I, the magnetic field at that location is In the above formulas, is the angular coefficient of the gyromagnetic ratio, is the angle between the magnetic field and the principal axis of the NV color center; γ e =28.025Hz / nT, which is the gyromagnetic ratio of electrons; B is the amplitude of the AC magnetic field; is the total phase integration time, f is the frequency of the AC magnetic field, and n is (π) y The number of microwave pulses; B π It refers to the magnetic field corresponding to the phase accumulation of π, I π It refers to the current corresponding to the phase accumulation of π.

[0058] The above operation is repeated after stepping through the position of the sample to be tested to obtain the magnetic field size corresponding to scanning a new area in the sample under a specific excitation current value; and so on, finally completing the scanning of the sample to be tested according to the predetermined plan and obtaining complete magnetic image data.

[0059] Part II: A Specific Example

[0060] The experimental setup of this embodiment is as follows Figure 1 As shown, the device is used to realize calibration based on NV color center ensemble self-traceability, and diamond magnetic scanning imaging is realized by synchronous excitation combined with high-order dynamic decoupling sequence.

[0061] The laser modulation module can adopt existing technology, and can output initial uniform pulse laser and can be regulated in conjunction with the CPMG sequence.

[0062] The probe assembly, consisting of a magnetic sensing unit 410, a parabolic lens 420, a filter 430, and a photodiode 440, is fixed to the end of a cantilever beam 480 for measuring magnetic fields. The head end of the cantilever beam 480 is fixed to a six-degree-of-freedom translation stage 490, facilitating fine-tuning of the angle between the principal axis of the diamond NV color center and the magnetic field. The sample 510 under test is fixed to a three-dimensional translation stage 520, and scanning imaging is achieved by varying the relative position between the sample and the magnetic sensing unit 410. Before the formal scanning experiment, the three-dimensional translation stage 520 is positioned directly below the probe assembly. A pair of Helmholtz coils 470 are positioned on either side of the probe assembly, maintaining a certain distance between them. The magnetic sensing unit 410 is positioned at the magnetic field midline. Preliminary scanning tests are conducted to adjust the height of the three-dimensional translation stage 520 and the distance between the magnetic sensing unit 410 and the center of the radiating structure 170, ultimately determining the relative positions of the various components of the device for optimal experimental results.

[0063] The magnetic sensing unit 410 is a diamond containing an NV color center ensemble. Laser light 450 from a laser modulation module is focused onto the diamond to polarize or read out the state of the electron spins in the NV color center ensemble. The radiation structure 170 radiates microwaves to manipulate the electron spins. A pair of Helmholtz coils 470 provides a uniform bias magnetic field for the NV color center. Fluorescence 460 emitted by the diamond passes through a parabolic lens 420 to improve collection efficiency. A filter 430 removes the green laser component. With the assistance of a bias transistor, a photodiode 440 converts the fluorescence into photocurrent, which is ultimately transmitted to the control and readout module for processing.

[0064] In the microwave module, the microwave output by the microwave source 110 is divided into two branches with approximately equal power and a phase difference of π / 2 by a 90-degree power splitter 120, providing Microwave pulses and (π) yMicrowave pulses. The sequence generator 310 in the control readout module outputs two signals 320, which are used to control the switch devices 130 on the two branches. After the output signals are adjusted, the microwave pulses from the two branches are input to the combiner 140 to combine into one output. The microwave power is then amplified to the watt level by the power amplifier 150. Finally, it is output to the radiating structure 170 through the isolator 160 and radiated into the air, applying uniform microwave manipulation to the magnetic sensitive unit 410.

[0065] In the excitation module, the arbitrary waveform generator 210 outputs a sinusoidal AC signal, which is amplified by the power amplifier 220 to provide excitation to the sample under test 510; the oscilloscope 250 monitors the current signal 240 in the sample in real time through the monitoring port 230 provided at the output end of the power amplifier.

[0066] Sequencer 310 outputs a reference signal 330 synchronized with the microwave pulse to oscilloscope 250 and a trigger signal 340 to arbitrary waveform generator 210. By adjusting trigger signal 340, the start time of AC signal output is controlled, thereby aligning the AC node on the oscilloscope with the center of the microwave pulse displayed by reference signal 330, achieving synchronous excitation of the excitation current. The specific implementation principles of this process are as follows:

[0067] Compared with the existing CPMG(n) sequence, the high-order dynamic decoupling sequence proposed in this invention adds two additional parts: AC synchronous excitation and reference sequence (such as Figure 2 shown), where n is (π) y The number of microwave pulses. The high-order dynamic decoupling sequence can be divided into two parts, including the microwave part (the left half in the figure) and the microwave-free part (the right half in the figure, i.e., the reference sequence). The reference sequence is used to eliminate time-related influencing factors such as temperature changes, electronic noise, etc. In addition, the laser is divided into two paths, one of which is Figure 2 As shown, the laser beam hits the diamond. The other laser beam (reference beam) is directly converted into photocurrent by the photodiode and transmitted to the control readout module. During the two acquisitions in the sequence, the laser intensity of the reference beam is read out simultaneously with the fluorescence intensity to cancel the laser noise. In the microwave sequence, the 532nm laser is first turned on to polarize the spins of most of the diamond NV color center electrons to the |0> state. The microwave pulse with an initial phase of 0° After flipping it to the equal superposition state of |0> and |1>, the spin begins to precess freely under the action of the magnetic field to be measured and accumulates the phase θ; during the free precession time, whenever the direction of the magnetic field to be measured changes, an initial phase of 90° (π) is applied. y Microwave pulse; second The microwave pulse will reflect the accumulated phase information on the occupancy of the system, so that the fluorescence intensity F∝cosθ; the fluorescence intensity and reference laser intensity obtained by the first readout are F1 and L1 respectively. Compared with the part with microwave sequence, the microwave remains off in the part without microwave sequence. The fluorescence intensity and reference laser intensity obtained by this readout are F2 and L2 respectively. After processing, the final result of the fluorescence intensity is F=(F1 / L1) / (F2 / L2). It can be seen from the above description that the present invention uses the control readout module to play the high-order kinetic decoupling sequence to achieve the coordinated work of laser, microwave and AC excitation, eliminate the errors caused by external interference, and ensure the high-precision measurement requirements in long-term experiments.

[0068] The present invention adopts a self-traceable calibration method to realize the calibration of the relationship between the magnetic field generated by the current in the sample and the current size. Specifically, it refers to the calibration of the magnetic field size generated by the sample current by the phase accumulation method of the spin system. For example, the crystal orientation of the diamond is

[110] measured by the continuous wave spectrum, and the angle between the magnetic field and the main axis of the NV color center is estimated to be 35.3°, resulting in an angular coefficient of α≈0.82. The formula for the phase accumulation is where γ e =28.025nT / Hz is the gyromagnetic ratio of the electron, B is the amplitude of the AC magnetic field, is the total phase accumulation time, and f is the frequency of the AC magnetic field. Therefore, when the phase accumulation is π, the corresponding magnetic field B π =π 2 ·f / (α·γ e ·n). The relationship between fluorescence intensity and accumulation phase: F∝cosθ, because the magnetic field is proportional to the current, the fluorescence intensity is also in a cosine relationship with the current in the sample. Figure 3 As shown. The accumulation phase is π corresponding to the first peak of fluorescence intensity, that is Figure 3 (I π ,F π ) point. According to I π Value and B π The value can be calculated that at any current I, the magnitude of the magnetic field at that location is

[0069] Based on the above description, the excitation-type synchronous pulse broadband magnetic field scanning imaging method in this example can be performed according to the following steps:

[0070] (1) Synchronous excitation: The arbitrary waveform generator 210 receives a trigger signal from the sequence generator 310 and starts to output an AC signal; the trigger time is adjusted and the AC signal is collected so that the AC signal node displayed by the oscilloscope 250 is synchronously aligned with the microwave pulse represented by the reference signal. After alignment, the trigger parameters are fixed to obtain a high-order dynamic decoupling sequence, which is then uploaded to the host computer;

[0071] (2) Downloading and playing sequence: The sequence generating device 310 downloads the high-order dynamic decoupling sequence stored in the host computer.

[0072] (3) Then, the output voltage of the arbitrary waveform generator 210 is set to change the current in the sample; the current size is fixed, and the sequence is started to control the coordinated operation of the laser, microwave, and AC excitation; the sequence generator 310 plays the sequence multiple times in a loop and obtains the corresponding measurement results of the probe assembly, and takes the average value as the fluorescence intensity corresponding to the excitation current.

[0073] (4) Current sweep: Repeat step (3) to sweep the current value within the appropriate range and step of the sample. Obtain a curve showing the relationship between fluorescence intensity and excitation current. Calculate the magnetic field magnitude corresponding to a specific current value in the sample using the self-traceable magnetic field calibration method.

[0074] (5) Scanning and imaging: The computer controls the three-dimensional translation stage 520 to move one step, repeating steps (1) to (4) to obtain the magnetic field magnitude corresponding to scanning a new region of the sample under a specific excitation current value. This process is repeated in this manner until the sample is scanned according to the predetermined plan and complete magnetic image data is obtained.

[0075] The foregoing description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be conceived by a person skilled in the art within the technical scope disclosed in the present invention are intended to be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for solid-state spin-based excitation synchronous pulse broadband magnetic field scanning imaging, characterized in that: The method comprises: The control readout module controls the switching device in the microwave magnetic field module to output two microwave pulses with an initial phase difference of π / 2. The control readout module triggers the current excitation module to output a sinusoidal AC signal. The sequence generator in the control readout module outputs a reference signal synchronized with the two microwave pulses to the signal acquisition device, and the signal acquisition device acquires the AC signal output in real time by the current excitation module. The control readout module is used to adjust the trigger signal of the current excitation module. By controlling the trigger time, the AC signal node displayed on the signal acquisition device is aligned with the center of the reference signal. After fixing the aligned parameters, a high-order dynamic decoupling sequence is obtained for synchronizing the AC excitation signal with the microwave pulse. Compared with the CPMG sequence, this sequence further includes synchronous excitation and reference sequences. The high-order kinetic decoupling sequence is played using a control readout module to achieve coordinated operation of laser, microwave, and AC excitation; the excitation current in the sample to be tested is changed using a current excitation module, and then the current value is kept constant; the photocurrent signal is read and averaged to obtain the fluorescence intensity corresponding to the current value; after stepwise changing the excitation current, a curve of the relationship between the fluorescence intensity and the excitation current in the sample to be tested is obtained, and then the magnetic field corresponding to the specific value of the excitation current in the sample to be tested is calculated; The above operation is repeated after stepping through the position of the sample to be tested to obtain the magnetic field size corresponding to scanning a new area in the sample under a specific excitation current value; and so on, finally completing the scanning of the sample to be tested according to the predetermined plan and obtaining complete magnetic image data.

2. The method according to claim 1, characterized in that The calibration curve is analyzed based on a self-traceable magnetic field calibration method, which refers to calibrating the magnetic field generated by the sample current by a phase accumulation method of a spin system; Specifically, based on the phase accumulation principle of the solid-state spin system, when the phase is π, the phase accumulation formula Inversely deduce the magnetic field B π The first peak of the fluorescence intensity and current curve corresponds to the current value I π , when the current in the sample to be tested is I, the magnetic field at that location is In the above formulas, is the angular coefficient of the gyromagnetic ratio, is the angle between the magnetic field and the principal axis of the NV color center; γ e =28.025Hz / nT, which is the gyromagnetic ratio of electrons; B is the amplitude of the AC magnetic field; is the total phase integration time, f is the frequency of the AC magnetic field, and n is (π) y The number of microwave pulses; B π It refers to the magnetic field corresponding to the phase accumulation of π, I π It refers to the current corresponding to the phase accumulation of π.

3. The method according to claim 1, characterized in that The high-order dynamic decoupling sequence includes parameters of two microwave pulses in the x-direction and the y-direction; the two microwave pulses are generated by a 90-degree power splitter and the initial phase difference is fixed at π / 2. The frequency and duration of the microwave pulses are determined by continuous wave spectrum experiments and Rabi oscillation experiments of the corresponding phases, respectively.

4. The method according to claim 1, wherein The real-time current monitoring signal at the output of the power amplifier in the current excitation module is obtained using a signal acquisition device and displayed on the screen.

5. A device for implementing the method according to any one of claims 1 to 4, characterized in that: include: Laser modulation module, used to output pulsed laser to excite diamond containing NV color center ensemble to emit fluorescence; A probe assembly, comprising the diamond as a magnetic sensitive unit, the fluorescence emitted by the diamond including magnetic field information of the sample to be tested; A microwave magnetic field module is used to generate a uniform bias magnetic field near the magnetic sensitive unit; and is used to generate and combine two microwave pulses with an initial phase difference to generate a uniform microwave field at the probe assembly; The current excitation module is used to output a sinusoidal AC signal to provide current excitation to the sample to be tested; A control readout module is used to obtain a photocurrent signal converted from fluorescence from the probe assembly; and for modulating the two microwave pulses and the sinusoidal AC signal so that the nodes of the microwave pulses and the AC signal are aligned; The data processing module is used to generate a high-order dynamic decoupling sequence based on the node alignment rules of microwave pulses and AC signals, and provide it to the control readout module for generating laser modulation signals, microwave pulse control signals and excitation current trigger signals; it is used to receive the signals obtained by the control readout module and generate a magnetic image based on the photocurrent signals converted by the probe assembly.

6. The device according to claim 5, characterized in that The probe assembly further comprises a parabolic lens, a filter and a photodiode which are arranged in sequence; the magnetic sensitive unit is located on the optical path outside the parabolic lens, and the photodiode is connected to the control readout module via a coaxial line.

7. The device according to claim 5, characterized in that The microwave magnetic field module includes a microwave source, a power divider, a combiner, a power amplifier, a radiation structure, and a pair of Helmholtz coils connected in sequence via a coaxial line. Switching devices are respectively provided on the two branches between the power divider and the combiner, and each switching device is connected to the control readout module via a coaxial line. The radiation structure is connected to the power amplifier via the coaxial line, and the magnetic sensitive unit is nested in the radiation structure. The pair of Helmholtz coils are respectively located on both sides of the magnetic sensitive unit and maintain a distance therebetween. The magnetic sensitive unit is located on the center line of the magnetic field.

8. The device according to claim 5, characterized in that The current excitation module includes an arbitrary waveform generator and a power amplifier connected in sequence through a coaxial line. The output end of the power amplifier is connected to a sample to be tested. The sample to be tested is a wire, a chip or a magnetic material that can be excited by current.

9. The device according to claim 5, characterized in that The control readout module includes a sequence generator, an acquisition card and a signal acquisition device; the sequence generator is respectively connected to the laser modulation module, the probe assembly, the microwave magnetic field module, the current excitation module and the data processing module through a coaxial line; the data processing module is a host computer; the signal acquisition device is respectively connected to the sequence generator and the monitoring port provided on the power amplifier through a coaxial line.

10. The device according to claim 5, characterized in that The probe assembly is fixed below the end of the cantilever beam, and the head end of the cantilever beam is connected to a six-degree-of-freedom displacement platform; the sample to be measured is placed on the three-dimensional displacement platform.

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