Gradient magnetic field imaging method and related device based on spatial light modulation

Abstract

The present invention provides a gradient magnetic field imaging method and related device based on spatial light modulation, including: making an incident detection laser beam be divided into two detection laser beams after being emitted; turning on a heating device; completing a magnetic field compensation operation; applying a calibration magnetic field signal; setting the first parameter value in the frequency control parameter as the frequency control parameter of a radio frequency driver; obtaining a corresponding gradient magnetic field value by processing with a data processor; setting the frequency control parameter of the radio frequency driver point by point according to a set of frequency control parameter values ​​corresponding to the second detection laser beam recorded in step 2, repeating step 6 and recording a corresponding set of gradient magnetic field values; making a one-to-one correspondence between a set of point-by-point position values ​​of a scanning light beam in step 2 and a set of gradient magnetic field values. The technical solution of the present invention is applied to solve the technical problem that the SERF atomic magnetometer imaging device in the prior art is difficult to simultaneously meet the requirements of high spatial resolution and high sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum precision magnetic field measurement, and in particular to a gradient magnetic field imaging method and related device based on spatial light modulation. Background Art

[0002] In application fields such as biomagnetic source imaging and localization, material characterization, and paleomagnetic distribution research based on extremely weak magnetic field imaging technology, magnetic sensors based on atomic spin coherence effects, especially Spin-Exchange Relaxation-Free (SERF) atomic magnetometers, have become an important development direction of the new generation of magnetic field imaging technology due to their advantages of high sensitivity, simple structure, and convenient operation. Their magnetic field measurement spatial resolution and sensitivity indicators directly determine the imaging quality.

[0003] For the field of biomagnetic measurement with high requirements for imaging quality, such as measuring weak currents in the cardiovascular system for diagnosing diseases such as atrial fibrillation, the magnetic field measurement requires a spatial resolution of sub-mm level and a sensitivity of sub-fT level at the same time. However, the spatial resolution that can be achieved by the existing array-type SERF atomic magnetometer imaging device is in the order of mm to cm, and there is an urgent need to further improve it. In practice, the operation of improving the spatial resolution by improving the hardware performance is relatively complex. Taking the volume of the atomic magnetometer as an example, further reducing the volume can effectively improve the spatial resolution, but if the resulting reduction in sensitivity reaches the order of hundreds of fT, it will be difficult to meet the above application requirements, and due to the processing technology limitations of the device components, there is a limit to the reduction of the atomic magnetometer volume. Summary of the Invention

[0004] The present invention provides a gradient magnetic field imaging method and related device based on spatial light modulation, which can solve the technical problem that the existing SERF atomic magnetometer imaging device is difficult to simultaneously meet the requirements of high spatial resolution and high sensitivity.

[0005] According to one aspect of the present invention, a gradient magnetic field imaging method based on spatial light modulation is provided. The gradient magnetic field imaging method based on spatial light modulation includes: Step 1, an acousto-optic device is arranged on the incident side of the detection light of the alkali metal atomic cell. A detection laser is arranged on the incident side of the acousto-optic device. A linear polarizer is arranged between the output side of the acousto-optic device and the alkali metal atomic cell. A combined prism is arranged on the pumping light incident side of the alkali metal atomic cell. An optical fiber collimator is arranged at the incident part of the combined prism. A polarization-maintaining optical fiber is arranged at the incident part of the optical fiber collimator and is connected to a pumping laser. A heating device is arranged outside the alkali metal atomic cell. A magnetic shielding device is arranged outside the heating device. A three-axis magnetic compensation coil is arranged inside the magnetic shielding device. A first mirror, a first half-wave plate, a first polarization beam splitter prism, a first group of photodetectors, a second mirror, a second half-wave plate, a second polarization beam splitter prism and a second group of photodetectors are arranged on the output side of the alkali metal atomic cell. The detection laser output by the detection laser is divided into two beams of detection laser after passing through the acousto-optic device. The first beam of detection laser is a stationary beam, and the second beam of detection laser is a scanning beam. The first beam of detection laser enters the first mirror, the first half-wave plate, the first polarization beam splitter prism and the first group of photodetectors in sequence after passing through the alkali metal atomic cell. The second beam of detection laser enters the second mirror, the second half-wave plate, the second polarization beam splitter prism and the second group of photodetectors in sequence after passing through the alkali metal atomic cell. The output end of the first group of photodetectors is connected to a first differential connector. The output end of the second group of photodetectors is connected to a second differential connector. The output ends of the first differential connector and the second differential connector are connected to the input end of a differential amplifier. The output end of the differential amplifier is connected to a data processor; Step 2, turn on the detection laser, the pumping laser and the RF driver of the acousto-optic device. Adjust the installation angle of the acousto-optic device so that a beam of incident detection laser is divided into a first beam of detection laser and a second beam of detection laser after being emitted. Adjust the amplitude control parameter of the RF driver so that the optical power densities of the first beam of detection laser and the second beam of detection laser after being emitted are equal. Continuously adjust the frequency control parameter of the RF driver. The second beam of detection laser performs a point-by-point scanning operation. Record the spot position of the first beam of detection laser on the output side of the detection light of the alkali metal atomic cell, a set of point-by-point position values of the second beam of detection laser for scanning, and a set of frequency control parameters corresponding to the second beam of detection laser; Step 3, turn on the heating device and heat the alkali metal atomic cell in the magnetic shielding device to a set temperature so that the atomic number density reaches the conditions required for the spin-exchange relaxation-free state. During the whole test process, the heating device keeps the device at the set temperature through current closed-loop control; Step 4, set the frequency control parameter of the RF driver to any parameter value recorded in Step 2. Adjust the driving current of the three-axis magnetic compensation coil to complete the magnetic field compensation operation so that the alkali metal atomic cell is in a zero magnetic field environment; Step 5, turn on the calibration signal current source connected to the three-axis magnetic compensation coil and apply a calibration magnetic field signal;Set the first parameter value in the set of frequency control parameters corresponding to the second detection laser recorded in step two as the frequency control parameter of the radio frequency driver; Step six, collect the optoelectronic signals of the first detection laser and the second detection laser through the first group of optoelectronic detectors and the second group of optoelectronic detectors respectively. The optoelectronic signals of the first detection laser and the second detection laser enter the differential amplifier after passing through the first differential connector and the second differential connector respectively, and the corresponding gradient magnetic field values are obtained by the data processor and recorded; Step seven, set the set of frequency control parameter values corresponding to the second detection laser recorded in step two point by point as the frequency control parameter of the radio frequency driver, repeat step six and record the corresponding set of gradient magnetic field values; Step eight, make the point-by-point position values of the set of scanning beams in step two correspond one by one with the set of gradient magnetic field values obtained in step seven, and the gradient magnetic field imaging result is obtained.

[0006] Further, the acousto-optic device includes an acousto-optic modulator or an acousto-optic deflector.

[0007] Further, the included angle α between the first detection laser and the second detection laser can be obtained according to calculation, where is the Bragg diffraction angle, λ is the incident light wavelength, f s is the acoustic wave frequency, n s is the refractive index of the acousto-optic crystal, v s is the acoustic wave velocity.

[0008] Further, the combined prism is composed of a linear polarizer, a reflecting prism and a quarter-wave plate. The linear polarizer and the quarter-wave plate are respectively arranged on the sides of the reflecting prism, and the combined prism is used to convert the incident linearly polarized light into circularly polarized light.

[0009] Further, the first group of optoelectronic detectors includes a first optoelectronic detector and a second optoelectronic detector. The output ends of the first optoelectronic detector and the second optoelectronic detector are both connected to the first differential connector. The second group of optoelectronic detectors includes a third optoelectronic detector and a fourth optoelectronic detector. The output ends of the third optoelectronic detector and the fourth optoelectronic detector are both connected to the second differential connector.

[0010] Further, the detection laser frequency output by the detection laser is at the detuning frequency of the D1 line of the alkali metal atomic absorption spectrum where the output signal amplitude is the largest, and the pumping laser frequency of the pumping laser is the resonance frequency value of the D1 absorption spectrum.

[0011] According to another aspect of the present invention, a gradient magnetic field imaging system based on spatial light modulation is provided. The gradient magnetic field imaging system based on spatial light modulation uses the gradient magnetic field imaging method as described above for gradient magnetic field imaging.

[0012] Furthermore, the gradient magnetic field imaging system includes an acousto-optic device, a radio frequency driver, a detection laser, an alkali metal atomic gas cell, a linear polarizer, a combined prism, an optical fiber collimator, a polarization-maintaining optical fiber, a heating device, a magnetic shielding device, a three-axis magnetic compensation coil, a first mirror, a first half-wave plate, a first polarization beam splitter prism, a first group of photodetectors, a second mirror, a second half-wave plate, a second polarization beam splitter prism, a second group of photodetectors, a first differential connector, a second differential connector, a differential amplifier, and a data processor. The acousto-optic device is arranged on the incident side of the detection light of the alkali metal atomic gas cell, the detection laser is arranged on the incident side of the acousto-optic device, the linear polarizer is arranged between the output side of the acousto-optic device and the alkali metal atomic gas cell, the radio frequency driver is used to drive the acousto-optic device, the combined prism is arranged on the incident side of the pumping light of the alkali metal atomic gas cell, the optical fiber collimator is arranged at the incident position of the combined prism, the polarization-maintaining optical fiber is arranged at the incident position of the optical fiber collimator, and the polarization-maintaining optical fiber is connected to the pumping laser. The heating device is arranged outside the alkali metal atomic gas cell, the magnetic shielding device is arranged outside the heating device, the three-axis magnetic compensation coil is arranged inside the magnetic shielding device, the first mirror, the first half-wave plate, the first polarization beam splitter prism, the first group of photodetectors, the second mirror, the second half-wave plate, the second polarization beam splitter prism, and the second group of photodetectors are all arranged on the output side of the alkali metal atomic gas cell. The detection laser output by the detection laser is divided into two beams of detection laser after passing through the acousto-optic device. The first beam of detection laser is a stationary beam, and the second beam of detection laser is a scanning beam. The first beam of detection laser enters the first mirror, the first half-wave plate, the first polarization beam splitter prism, and the first group of photodetectors in sequence after passing through the alkali metal atomic gas cell. The second beam of detection laser enters the second mirror, the second half-wave plate, the second polarization beam splitter prism, and the second group of photodetectors in sequence after passing through the alkali metal atomic gas cell. The output end of the first group of photodetectors is connected to the first differential connector, the output end of the second group of photodetectors is connected to the second differential connector, the output ends of the first differential connector and the second differential connector are connected to the input end of the differential amplifier, and the output end of the differential amplifier is connected to the data processor.

[0013] According to another aspect of the present invention, there is provided a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the gradient magnetic field imaging method based on spatial light modulation as described above.

[0014] According to still another aspect of the present invention, there is provided a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the steps of a gradient magnetic field imaging method based on spatial light modulation as described above.

[0015] Applying the technical solution of the present invention, a gradient magnetic field imaging method based on spatial light modulation is provided. Aiming at the requirements of high spatial resolution and high sensitivity in magnetic field imaging applications, considering the problem that traditional array-type SERF atomic magnetometers imaging devices are difficult to meet the above requirements simultaneously, an incident detection laser beam is divided into two beams. After passing through an alkali metal atomic gas cell, one of the beams performs a fast scan and is processed through a differential amplifier together with the other stationary laser beam to obtain a gradient imaging result. This device and method are of great significance for high-performance magnetic field imaging applications and can achieve high spatial resolution and high-sensitivity gradient magnetic field measurement. In addition, the two beams of light on the output side of each polarization beam splitter pass through a group of photodetectors and a differential connector and then output a signal, whose function is to eliminate the common-mode noise of the two beams of light and improve the signal-to-noise ratio of the signal. The two differential connectors altogether obtain two output signals, which are respectively connected to the two input ends of the differential amplifier to obtain one output signal, whose function is to further eliminate the common-mode noise of the two output signals and further improve the signal-to-noise ratio of the signal. Therefore, compared with the prior art, the gradient magnetic field imaging method based on spatial light modulation provided by the present invention realizes high spatial resolution and high-sensitivity gradient magnetic field imaging based on the spatial modulation of the detection laser beam, and can effectively solve the problem that existing SERF atomic magnetometers imaging devices are difficult to meet the requirements of high spatial resolution and high sensitivity simultaneously, providing technical support for high-quality magnetic field imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings included are used to provide a further understanding of the embodiments of the present invention, which form a part of the specification, are used to illustrate the embodiments of the present invention, and are used to explain the principles of the present invention together with the text description. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 FIG. shows a schematic structural diagram of a gradient magnetic field imaging system based on spatial light modulation provided according to a specific embodiment of the present invention.

[0018] Among them, the above-mentioned accompanying drawings include the following reference numerals:

[0019] 1 - Detection laser; 2 - Pump laser; 3 - Polarization-maintaining fiber; 4 - Fiber collimator; 5 - Combined prism; 6 - Acousto-optic device; 7 - Zero-order transmitted light (the first detection laser beam); 8 - First-order diffracted light (the second detection laser beam); 9 - Linear polarizer; 10 - Alkali metal atomic gas cell; 11 - Heating device; 121 - First reflector; 122 - Second reflector; 131 - First half-wave plate; 132 - Second half-wave plate; 141 - First polarization beam splitter prism; 142 - Second polarization beam splitter prism; 151 First group of photodetectors; 152 - Second group of photodetectors; 161 - First differential connector; 162 - Second differential connector; 17 - Differential amplifier; 18 - Data processor; 19 - Magnetic shielding device; 20 - Three-axis magnetic compensation coil. Detailed implementation manners

[0020] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually illustrative only and in no way limits the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] Unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that, for the sake of convenience of description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationship. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the authorization specification. In all the examples shown and discussed here, any specific values should be construed as merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, further discussion thereof is not required in subsequent drawings.

[0023] As Figure 1As shown, according to a specific embodiment of the present invention, a gradient magnetic field imaging method based on spatial light modulation is provided. The gradient magnetic field imaging method based on spatial light modulation includes: Step 1, an acousto-optic device is arranged on the incident side of the detection light of the alkali metal atomic cell. A detection laser is arranged on the incident side of the acousto-optic device. A linear polarizer is arranged between the output side of the acousto-optic device and the alkali metal atomic cell. A combined prism is arranged on the pumping light incident side of the alkali metal atomic cell. An optical fiber collimator is arranged at the incident part of the combined prism. A polarization-maintaining fiber is arranged at the incident part of the optical fiber collimator and is connected to a pumping laser. A heating device is arranged outside the alkali metal atomic cell. A magnetic shielding device is arranged outside the heating device. A three-axis magnetic compensation coil is arranged inside the magnetic shielding device. A first mirror, a first half-wave plate, a first polarization beam splitter prism, a first group of photodetectors, a second mirror, a second half-wave plate, a second polarization beam splitter prism, and a second group of photodetectors are arranged on the output side of the alkali metal atomic cell. The detection laser output by the detection laser is divided into two beams of detection laser after passing through the acousto-optic device. The first beam of detection laser is a stationary beam, and the second beam of detection laser is a scanning beam. The first beam of detection laser enters the first mirror, the first half-wave plate, the first polarization beam splitter prism, and the first group of photodetectors in sequence after passing through the alkali metal atomic cell. The second beam of detection laser enters the second mirror, the second half-wave plate, the second polarization beam splitter prism, and the second group of photodetectors in sequence after passing through the alkali metal atomic cell. The output end of the first group of photodetectors is connected to a first differential connector. The output end of the second group of photodetectors is connected to a second differential connector. The output ends of the first differential connector and the second differential connector are connected to the input end of a differential amplifier. The output end of the differential amplifier is connected to a data processor; Step 2, turn on the detection laser, the pumping laser, and the RF driver of the acousto-optic device. Adjust the installation angle of the acousto-optic device so that a beam of incident detection laser is divided into a first beam of detection laser and a second beam of detection laser after exiting. Adjust the amplitude control parameter of the RF driver so that the optical power densities of the first beam of detection laser and the second beam of detection laser after exiting are equal. Continuously adjust the frequency control parameter of the RF driver. The second beam of detection laser performs a point-by-point scanning operation. Record the spot position of the first beam of detection laser on the output side of the detection light of the alkali metal atomic cell, a set of point-by-point position values of the second beam of detection laser for scanning, and a set of frequency control parameters corresponding to the second beam of detection laser; Step 3, turn on the heating device and heat the alkali metal atomic cell in the magnetic shielding device to a set temperature so that the atomic number density reaches the conditions required for the non-spin-exchange relaxation state. During the whole test process, the heating device keeps the device at the set temperature through current closed-loop control; Step 4, set the frequency control parameter of the RF driver to any parameter value recorded in Step 2. Adjust the drive current of the three-axis magnetic compensation coil to complete the magnetic field compensation operation so that the alkali metal atomic cell is in a zero magnetic field environment; Step 5, turn on the calibration signal current source connected to the three-axis magnetic compensation coil and apply a calibration magnetic field signal;Set the first parameter value in the set of frequency control parameters corresponding to the second detection laser recorded in step two as the frequency control parameter of the radio frequency driver; Step six, collect the optoelectronic signals of the first detection laser and the second detection laser through the first group of optoelectronic detectors and the second group of optoelectronic detectors respectively. The optoelectronic signals of the first detection laser and the second detection laser enter the differential amplifier after passing through the first differential connector and the second differential connector respectively, and the corresponding gradient magnetic field value is obtained by the data processor and recorded; Step seven, set the set of frequency control parameter values corresponding to the second detection laser recorded in step two point by point as the frequency control parameter of the radio frequency driver, repeat step six and record the corresponding set of gradient magnetic field values; Step eight, make the set of point-by-point position values of the set of scanning beams in step two correspond one by one with the set of gradient magnetic field values obtained in step seven, that is, obtain the gradient magnetic field imaging result.;

[0024] Applying this configuration method, a gradient magnetic field imaging method based on spatial light modulation is provided. Aiming at the requirements of high spatial resolution and high sensitivity in magnetic field imaging applications, considering the problem that traditional array-type SERF atomic magnetometer imaging devices are difficult to meet the above requirements at the same time, an incident detection laser beam is divided into two beams. After passing through the alkali metal atomic gas cell, one of the beams performs fast scanning and is processed through a differential amplifier with the other stationary laser beam to obtain a gradient imaging result. This device and method are of great significance for high-performance magnetic field imaging applications and can achieve high spatial resolution and high-sensitivity gradient magnetic field measurement; In addition, the two beams of light on the output side of each polarization beam splitter pass through a group of optoelectronic detectors and a differential connector and then output a signal, the function of which is to eliminate the common-mode noise of the two beams of light and improve the signal-to-noise ratio of the signal. The two differential connectors obtain two output signals in total, which are respectively connected to the two input ends of the differential amplifier to obtain one output signal, the function of which is to further eliminate the common-mode noise of the two output signals and further improve the signal-to-noise ratio of the signal. Therefore, compared with the prior art, the gradient magnetic field imaging method based on spatial light modulation provided by the present invention realizes high spatial resolution and high-sensitivity gradient magnetic field imaging based on the spatial modulation of the detection laser, and can effectively solve the problem that the existing SERF atomic magnetometer imaging device is difficult to meet the requirements of high spatial resolution and high sensitivity at the same time, providing technical support for high-quality magnetic field imaging.

[0025] Furthermore, in the present invention, in order to make the output signal amplitude maximum and achieve the purpose of optimal sensitivity, the detection laser and the pumping laser each output a linearly polarized laser beam. The frequency of the detection laser output by the detection laser is at the detuning frequency of the D1 line of the alkali metal atomic absorption spectrum where the output signal amplitude is maximum, and the pumping laser frequency of the pumping laser is the resonance frequency value of the D1 absorption spectrum.

[0026] The pumping laser propagates through a polarization-maintaining optical fiber and enters an optical fiber collimator. After exiting, it passes through a combined prism. The combined prism is composed of a linear polarizer, a reflecting prism, and a quarter-wave plate. The linear polarizer and the quarter-wave plate are respectively arranged on the sides of the reflecting prism. The combined prism is used to convert the incident linearly polarized light into circularly polarized light, and this circularly polarized light enters the alkali metal atomic gas cell to pump the atoms and polarize the atoms.

[0027] The function of the linear polarizer is to improve the polarization degree of the incident linearly polarized light. The half-wave plate can be rotated, and its function is to adjust the light intensities of the two beams of light on the output side of the polarization beam splitter prism before the calibration magnetic field signal is applied to make them equal. The function of the polarization beam splitter prism is to decompose a beam of incident light into two beams of linearly polarized light with orthogonal polarization degrees.

[0028] The two beams of light on the output side of each polarization beam splitter prism pass through a group of photodetectors and a differential connector and then output a signal, which is used to eliminate the common-mode noise of the two beams of light and improve the signal-to-noise ratio of the signal. The two differential connectors altogether obtain two output signals, which are respectively connected to the two input ends of a differential amplifier to obtain an output signal, which is used to further eliminate the common-mode noise of the two output signals and further improve the signal-to-noise ratio of the signal. The output end of the differential amplifier is connected to a data collector to process and record the signal to obtain gradient magnetic field imaging information. As a specific embodiment of the present invention, the first group of photodetectors includes a first photodetector and a second photodetector, and the output ends of the first photodetector and the second photodetector are both connected to the first differential connector. The second group of photodetectors includes a third photodetector and a fourth photodetector, and the output ends of the third photodetector and the fourth photodetector are both connected to the second differential connector.

[0029] The acousto-optic device includes an acousto-optic modulator or an acousto-optic deflector. The acousto-optic device is used to divide a beam of incident detection laser into two beams. One beam is the transmitted light, which remains stationary in position during the operation of the device, and the other beam is the diffracted light, which performs a fast scan. Its beam splitting principle is based on the Bragg diffraction law of the acousto-optic crystal. For the acousto-optic device, it can be an acousto-optic modulator or an acousto-optic deflector, where: using one of the acousto-optic modulators can achieve the spatial one-dimensional scanning function, using two acousto-optic modulators placed orthogonally can achieve the spatial two-dimensional scanning function, and using one acousto-optic deflector can also achieve the spatial two-dimensional scanning function. In practice, it can be set according to the application scenario.

[0030] The Bragg diffraction law is expressed as: where is the Bragg diffraction angle, n s is the refractive index of the acousto-optic crystal, λ and λ s respectively represent the wavelengths of the incident laser and the control acoustic wave. When is small enough to satisfy When approximating:

[0031] The angle α between the first detection laser beam and the second detection laser beam can be obtained according to (Formula 1).

[0032] Wherein, is the Bragg diffraction angle, λ is the wavelength of the incident light, λ s is the acoustic wave wavelength, f s is the acoustic wave frequency, n s is the refractive index of the acousto-optic crystal, v s is the acoustic wave velocity. It can be seen from Formula 1 that by controlling the acoustic wave frequency, the size of the Bragg diffraction angle can be changed to achieve fast scanning of the diffracted light. This device changes the Bragg diffraction angle by adjusting the frequency control parameter of the acousto-optic device radio frequency driver.

[0033] According to another aspect of the present invention, a gradient magnetic field imaging system based on spatial light modulation is provided. This gradient magnetic field imaging system based on spatial light modulation uses the gradient magnetic field imaging method as described above for gradient magnetic field imaging.

[0034] Applying this configuration method, a gradient magnetic field imaging system based on spatial light modulation is provided. For the requirements of high spatial resolution and high sensitivity in magnetic field imaging applications, considering the problem that traditional array-type SERF atomic magnetometer imaging devices are difficult to meet the above requirements at the same time, a beam of incident detection laser is divided into two beams. After passing through the alkali metal atomic gas cell, one beam performs fast scanning and is processed through a differential amplifier with another stationary laser beam to obtain a gradient imaging result. This device and method are of great significance for high-performance magnetic field imaging applications; in addition, the two beams of light on the output side of each polarization beam splitter pass through a group of photodetectors and a differential connector and then output a signal, the function of which is to eliminate the common-mode noise of the two beams of light and improve the signal-to-noise ratio. The two differential connectors obtain two output signals in total, which are respectively connected to the two input ends of the differential amplifier to obtain an output signal, the function of which is to further eliminate the common-mode noise of the two output signals and further improve the signal-to-noise ratio. Therefore, compared with the prior art, the gradient magnetic field imaging system based on spatial light modulation provided by the present invention realizes high-spatial-resolution and high-sensitivity gradient magnetic field imaging based on the spatial modulation of the detection laser, and can effectively solve the problem that existing SERF atomic magnetometer imaging devices are difficult to meet the requirements of high spatial resolution and high sensitivity at the same time, providing technical support for high-quality magnetic field imaging.

[0035] Furthermore, in the present invention, in order to implement gradient magnetic field imaging based on spatial light modulation, the gradient magnetic field imaging system includes an acousto-optic device 6, a radio frequency driver, a detection laser 1, an alkali metal atomic gas cell 10, a linear polarizer 9, a combined prism 5, an optical fiber collimator 4, a polarization-maintaining optical fiber 3, a heating device 11, a magnetic shielding device 19, a three-axis magnetic compensation coil 20, a first mirror 121, a first half-wave plate 131, a first polarization beam splitter prism 141, a first group of photodetectors 151, a second mirror 122, a second half-wave plate 132, a second polarization beam splitter prism 133, a second group of photodetectors 134, a first differential connector 161, a second differential connector 162, a differential amplifier 17, and a data processor 18. The acousto-optic device 6 is arranged on the incident side of the detection light of the alkali metal atomic gas cell. The detection laser is arranged on the incident side of the acousto-optic device. The linear polarizer is arranged between the output side of the acousto-optic device and the alkali metal atomic gas cell. The radio frequency driver is used to drive the acousto-optic device. The combined prism is arranged on the incident side of the pumping light of the alkali metal atomic gas cell. The optical fiber collimator is arranged at the incident position of the combined prism. The polarization-maintaining optical fiber is arranged at the incident position of the optical fiber collimator. The polarization-maintaining optical fiber is connected to the pumping laser. The heating device is arranged outside the alkali metal atomic gas cell. The magnetic shielding device is arranged outside the heating device. The three-axis magnetic compensation coil is arranged inside the magnetic shielding device. The first mirror, the first half-wave plate, the first polarization beam splitter prism, the first group of photodetectors, the second mirror, the second half-wave plate, the second polarization beam splitter prism, and the second group of photodetectors are all arranged on the output side of the alkali metal atomic gas cell. The detection laser output by the detection laser is divided into two beams of detection laser after passing through the acousto-optic device. The first beam of detection laser is a stationary beam, and the second beam of detection laser is a scanning beam. The first beam of detection laser enters the first mirror, the first half-wave plate, the first polarization beam splitter prism, and the first group of photodetectors in sequence after passing through the alkali metal atomic gas cell. The second beam of detection laser enters the second mirror, the second half-wave plate, the second polarization beam splitter prism, and the second group of photodetectors in sequence after passing through the alkali metal atomic gas cell. The output end of the first group of photodetectors is connected to the first differential connector. The output end of the second group of photodetectors is connected to the second differential connector. The output ends of the first differential connector and the second differential connector are connected to the input end of the differential amplifier. The output end of the differential amplifier is connected to the data processor.

[0036] According to another aspect of the present invention, there is provided a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method for gradient magnetic field imaging based on spatial light modulation as described above.

[0037] According to another aspect of the present invention, there is provided a computer-readable storage medium storing a computer program, characterized in that when the computer program is executed by a processor, it implements the steps of a gradient magnetic field imaging method based on spatial light modulation as described above.

[0038] For a further understanding of the present invention, the following combines Figure 1 to elaborate in detail on the gradient magnetic field imaging method based on spatial light modulation provided by the present invention.

[0039] Figure 1 It is a schematic structural diagram of a gradient magnetic field imaging device based on spatial light modulation of the present invention. Referring to Figure 1 As shown, the gradient magnetic field imaging device based on spatial light modulation includes an acousto-optic device 6, the acousto-optic device 6 is located on the incident side of the detection light of the alkali metal atomic gas cell 10, a detection laser 1 is arranged on the incident side of the acousto-optic device 6, a linear polarizer 9 is arranged between the output side and the alkali metal atomic gas cell 10, a combined prism 5 is arranged on the pumping light incident side of the alkali metal atomic gas cell 10, an optical fiber collimator 4 is arranged at the incident point of the combined prism, a polarization-maintaining optical fiber 3 is arranged at the incident point of the optical fiber collimator 4 and is connected to a pumping laser 2, the outside of the alkali metal atomic gas cell 10 is wrapped by a heating device 11 and is located inside a magnetic shielding device 19, a three-axis magnetic compensation coil 20 is arranged inside the magnetic shielding device 19, a mirror 12 (mirror one and mirror two) is arranged on the output side of the alkali metal atomic gas cell 10, a half-wave plate 13 (half-wave plate one and half-wave plate two), a polarization beam splitter prism 14 (polarization beam splitter prism one and polarization beam splitter prism two) is arranged at the output of the half-wave plate 13, a photodetector 15 (first group of photodetectors and second group of photodetectors) is respectively arranged at the output of the polarization beam splitter prism one and the polarization beam splitter prism two, the output ends of the first group of photodetectors and the second group of photodetectors are respectively connected to differential connectors (differential connector one and differential connector two), the output end of the differential connector one and the output end of the differential connector two are connected to two input ends of a differential amplifier 17, and the output end of the differential amplifier 17 is connected to a signal collector 18.

[0040] Step 1: Place the acousto-optic device on the incident side of the detection light of the alkali metal atomic cell. Set a detection laser on the incident side of the acousto-optic device. Place a linear polarizer between the output side of the acousto-optic device and the alkali metal atomic cell. Set a combined prism on the pump light incident side of the alkali metal atomic cell. Set an optical fiber collimator at the incident point of the combined prism. There is a polarization-maintaining fiber connected to the pump laser at the incident point of the optical fiber collimator. Set a heating device outside the alkali metal atomic cell. Set a magnetic shielding device outside the heating device. Install a three-axis magnetic compensation coil inside the magnetic shielding device. Set a first mirror, a first half-wave plate, a first polarization beam splitter prism, a first group of photodetectors, a second mirror, a second half-wave plate, a second polarization beam splitter prism, and a second group of photodetectors on the output side of the alkali metal atomic cell. The detection laser output by the detection laser is divided into two beams of detection laser after passing through the acousto-optic device. The first beam of detection laser is a stationary beam, and the second beam of detection laser is a scanning beam. The first beam of detection laser enters the first mirror, the first half-wave plate, the first polarization beam splitter prism, and the first group of photodetectors in sequence after exiting the alkali metal atomic cell. The second beam of detection laser enters the second mirror, the second half-wave plate, the second polarization beam splitter prism, and the second group of photodetectors in sequence after exiting the alkali metal atomic cell. Connect the output end of the first group of photodetectors to the first differential connector. Connect the output end of the second group of photodetectors to the second differential connector. Connect the output ends of the first differential connector and the second differential connector to the input end of the differential amplifier. Connect the output end of the differential amplifier to the data processor

[0041] Step 2: Turn on the detection laser 1, the pump laser 2, and the RF driver of the acousto-optic device 6. Adjust the installation angle of the acousto-optic device 6 so that one incident detection laser is divided into two beams after exiting. Adjust the amplitude control parameter of the RF driver so that the optical power densities of the two beams after exiting are equal. Continuously adjust the frequency control parameter of the RF driver. At this time, the first-order diffracted light performs a point-by-point scanning operation. Record the spot position of the stationary beam on the output side of the detection light of the alkali metal atomic cell, the point-by-point position values of a group of scanning beams, and a group of corresponding frequency control parameters

[0042] Step 3: Turn on the heating device 11 and heat the alkali metal atomic cell 10 in the magnetic shielding device 19 to a certain temperature so that the atomic number density reaches the conditions required for the spin-exchange relaxation-free state. During the entire test process, the heating device 11 maintains the device at a constant temperature through current closed-loop control

[0043] Step 4: Set the frequency control parameter of the radio frequency driver to any one of the parameter values recorded in Step 1, adjust the driving current of the three-axis magnetic compensation coil 20 to complete the magnetic field compensation operation, and make the alkali metal atomic gas cell 10 in a zero magnetic field environment. The magnetic field compensation principle is based on the quasi-static response of the Bloch equation of atoms at high density and low magnetic field. Through Step 3 and Step 4, the alkali metal atomic gas cell enters the spin-exchange relaxation-free state;

[0044] Step 5: Turn on the calibration signal current source connected to the three-axis magnetic compensation coil 20, apply a calibration magnetic field signal, and set the first parameter value in the set of frequency control parameters corresponding to the second detection laser recorded in Step 2 as the frequency control parameter of the radio frequency driver;

[0045] Step 6: Collect the optoelectronic signals of the two outgoing light beams through two sets of optoelectronic detectors 15, enter the differential amplifier 17 after passing through the differentiator 16 respectively, and obtain the corresponding gradient magnetic field value through the processing of the data processor 18 and record it;

[0046] Step 7: Sequentially set the set of frequency control parameter values corresponding to the second detection laser recorded in Step 2 as the frequency control parameter of the radio frequency driver, repeat Step 6 and record a set of corresponding gradient magnetic field values;

[0047] Step 8: Make the set of point-by-point position values of the set of scanning light beams in Step 2 correspond one by one with the set of gradient magnetic field values in Step 7, and the gradient magnetic field imaging result is obtained.

[0048] In summary, the present invention proposes a gradient magnetic field imaging device and method based on spatial light modulation. This method uses an acou-optic device (acou-optic modulator or acou-optic deflector) to perform spatial modulation on the detection laser to achieve high-spatial-resolution and high-sensitivity gradient magnetic field measurement.

[0049] For the sake of description, spatial relative terms such as "above...", "over...", "on the upper surface of...", "above" etc. can be used here to describe the spatial position relationship of a device or feature shown in the figure with other devices or features. It should be understood that spatial relative terms are intended to include different orientations in use or operation in addition to the orientation described in the figure for the device. For example, if the device in the figure is inverted, the device described as "above other devices or structures" or "over other devices or structures" will be positioned as "below other devices or structures" or "under other devices or structures" afterwards. Thus, the exemplary term "above..." can include both the orientations of "above..." and "below...". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and corresponding interpretations are made for the spatial relative descriptions used here.

[0050] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Without additional declaration, the above terms have no special meaning, so it should not be construed as a limitation on the protection scope of the present invention.

[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A gradient magnetic field imaging method based on spatial light modulation, characterized in that: The gradient magnetic field imaging method based on spatial light modulation comprises: Step 1, an acousto-optic device is arranged on the incident side of the detection light of the alkali metal atom gas chamber, a detection laser is arranged on the incident side of the acousto-optic device, a linear polarizer is arranged between the exit side of the acousto-optic device and the alkali metal atom gas chamber, a combined prism is arranged on the pumping light incident side of the alkali metal atom gas chamber, a fiber collimator is arranged at the incident position of the combined prism, a polarization-maintaining fiber is arranged at the incident position of the fiber collimator and connected to the pumping laser, a heating device is arranged on the outside of the alkali metal atom gas chamber, a magnetic shielding device is arranged on the outside of the heating device, a three-axis magnetic compensation coil is arranged inside the magnetic shielding device, a first reflector, a first half-wave plate, a first polarization beam splitter prism, a first group of photodetectors, a second reflector, a second half-wave plate, a second polarization beam splitter prism and a second group of photodetectors are arranged on the exit side of the alkali metal atom gas chamber, and the detection laser output by the detection laser is transmitted through the detection laser. The acousto-optic device is then divided into two detection laser beams, the first detection laser beam is a stationary beam, and the second detection laser beam is a scanning beam. The first detection laser beam is emitted from the alkali metal atom gas chamber and then sequentially enters the first reflector, the first half wave plate, the first polarization beam splitter prism and the first group of photodetectors. The second detection laser beam is emitted from the alkali metal atom gas chamber and then sequentially enters the second reflector, the second half wave plate, the second polarization beam splitter prism and the second group of photodetectors. The output end of the first group of photodetectors is connected to the first differential connector, the output end of the second group of photodetectors is connected to the second differential connector, the output end of the first differential connector and the output end of the second differential connector are connected to the input end of the differential amplifier, and the output end of the differential amplifier is connected to the data processor; Step 2, turning on the detection laser, the pumping laser and the radio frequency driver of the acousto-optic device, adjusting the installation angle of the acousto-optic device so that a beam of incident detection laser is divided into a first beam of detection laser and a second beam of detection laser after being emitted, adjusting the amplitude control parameters of the radio frequency driver so that the optical power densities of the first beam of detection laser and the second beam of detection laser after being emitted are equal, continuously adjusting the frequency control parameters of the radio frequency driver, the second beam of detection laser performs a point-by-point scanning operation, and recording the spot position of the first beam of detection laser on the alkali metal atom gas chamber detection light emission side, a set of point-by-point position values ​​of scanning the second beam of detection laser, and a set of frequency control parameters corresponding to the second beam of detection laser; Step 3, turning on the heating device to heat the alkali metal atom gas chamber in the magnetic shielding device to a set temperature so that the atomic number density reaches the condition required for a state without spin exchange relaxation. During the entire test process, the heating device maintains the device at the set temperature through current closed-loop control; Step 4, setting the frequency control parameter of the RF driver to any parameter value recorded in step 2, adjusting the driving current of the three-axis magnetic compensation coil, completing the magnetic field compensation operation, and placing the alkali metal atom gas chamber in a zero magnetic field environment; Step 5, turning on the calibration signal current source connected to the three-axis magnetic compensation coil to apply a calibration magnetic field signal; setting the first parameter value in the set of frequency control parameters corresponding to the second detection laser beam recorded in the step 2 as the frequency control parameter of the RF driver; Step six, collecting the photoelectric signals of the first detection laser beam and the second detection laser beam through the first group of photodetectors and the second group of photodetectors respectively, the photoelectric signals of the first detection laser beam and the second detection laser beam respectively pass through the first differential connector and the second differential connector and enter the differential amplifier, and are processed by the data processor to obtain the corresponding gradient magnetic field value and record it; Step 7, setting the frequency control parameter values ​​corresponding to the second detection laser beam recorded in step 2 as the frequency control parameters of the RF driver point by point, repeating step 6 and recording the corresponding set of gradient magnetic field values; Step eight, one-to-one correspondence is made between the point-by-point position values ​​of a set of scanning light beams in step two and a set of gradient magnetic field values ​​obtained in step seven, so as to obtain a gradient magnetic field imaging result.

2. The gradient magnetic field imaging method based on spatial light modulation according to claim 1, characterized in that: The acousto-optic device includes an acousto-optic modulator or an acousto-optic deflector.

3. The gradient magnetic field imaging method based on spatial light modulation according to claim 1, characterized in that: The angle α between the first detection laser beam and the second detection laser beam can be determined according to Calculate and obtain, where is the Bragg diffraction angle, λ is the wavelength of incident light, f s is the sound wave frequency, n s is the refractive index of the acousto-optic crystal, v s is the speed of sound waves.

4. The gradient magnetic field imaging method based on spatial light modulation according to claim 3, characterized in that: The combined prism is composed of a linear polarizer, a reflecting prism and a quarter wave plate. The linear polarizer and the quarter wave plate are respectively arranged on the side of the reflecting prism. The combined prism is used to convert incident linear polarized light into circular polarized light.

5. The gradient magnetic field imaging method based on spatial light modulation according to claim 4, characterized in that: The first group of photodetectors includes a first photodetector and a second photodetector, and the output ends of the first photodetector and the second photodetector are both connected to the first differential connector. The second group of photodetectors includes a third photodetector and a fourth photodetector, and the output ends of the third photodetector and the fourth photodetector are both connected to the second differential connector.

6. The gradient magnetic field imaging method based on spatial light modulation according to claim 1, characterized in that: The detection laser frequency output by the detection laser is the detuning frequency of the alkali metal atomic absorption line D1 line which makes the output signal amplitude maximum, and the pumping laser frequency of the pumping laser is the resonance frequency value of the D1 absorption line.

7. A gradient magnetic field imaging system based on spatial light modulation, characterized in that: The gradient magnetic field imaging system based on spatial light modulation uses the gradient magnetic field imaging method based on spatial light modulation as claimed in any one of claims 1 to 6 to perform gradient magnetic field imaging.

8. The gradient magnetic field imaging system based on spatial light modulation according to claim 7, characterized in that: The gradient magnetic field imaging system comprises an acousto-optic device, a radio frequency driver, a detection laser, an alkali metal atom gas chamber, a linear polarizer, a combined prism, a fiber collimator, a polarization-maintaining fiber, a heating device, a magnetic shielding device, a three-axis magnetic compensation coil, a first reflector, a first half-wave plate, a first polarization beam splitter prism, a first group of photodetectors, a second reflector, a second half-wave plate, a second polarization beam splitter prism, a second group of photodetectors, a first differential connector, a second differential connector, a differential amplifier and a data processor. The acousto-optic device is arranged on the detection light incident side of the alkali metal atom gas chamber, and the detection laser is arranged on the The incident side of the acousto-optic device, the linear polarizer is arranged between the exit side of the acousto-optic device and the alkali metal atom gas chamber, the radio frequency driver is used to drive the acousto-optic device, the combined prism is arranged on the pumping light incident side of the alkali metal atom gas chamber, the fiber collimator is arranged at the incident position of the combined prism, the polarization-maintaining fiber is arranged at the incident position of the fiber collimator, the polarization-maintaining fiber is connected to the pumping laser, the heating device is arranged outside the alkali metal atom gas chamber, the magnetic shielding device is arranged outside the heating device, the three-axis magnetic compensation coil is arranged inside the magnetic shielding device, and the The first reflector, the first half wave plate, the first polarization beam splitter prism, the first group of photodetectors, the second reflector, the second half wave plate, the second polarization beam splitter prism and the second group of photodetectors are all arranged on the exit side of the alkali metal atom gas chamber. The detection laser output by the detection laser is divided into two detection laser beams after passing through the acousto-optic device. The first detection laser beam is a stationary beam, and the second detection laser beam is a scanning beam. The first detection laser beam enters the first reflector, the first half wave plate, the first polarization beam splitter prism and the first group of photodetectors in sequence after exiting the alkali metal atom gas chamber. The second detection laser beam enters the second reflector, the second half wave plate, the second polarization beam splitter prism and the second group of photodetectors in sequence after exiting the alkali metal atom gas chamber. The output end of the first group of photodetectors is connected to the first differential connector, the output end of the second group of photodetectors is connected to the second differential connector, the output end of the first differential connector and the output end of the second differential connector are connected to the input end of the differential amplifier, and the output end of the differential amplifier is connected to the data processor.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: The processor executes the computer program to implement the steps of the gradient magnetic field imaging method based on spatial light modulation according to any one of claims 1 to 6.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of a gradient magnetic field imaging method based on spatial light modulation are implemented as described in any one of claims 1 to 6.

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