Magnetic field measurement method based on multi-focus array laser pumping atomic spinning

Abstract

A magnetic field measurement method based on multi-focus array laser pumping atomic spinning comprises the steps that pumping light is subjected to phase modulation through a spatial light modulator to generate a multi-focus circularly polarized light array, light intensity distribution of focuses of the multi-focus circularly polarized light array on a transverse plane is uniform, and the distances between the focuses of the multi-focus circularly polarized light array are consistent; therefore, the problem of non-uniform distribution of the laser in the transverse direction due to Gaussian light intensity is effectively compensated. In the longitudinal direction, according to the law of energy attenuation caused by the action of light and atoms, the focus light intensity is designed to be gradually enhanced along with the z-axis depth in combination with an anti-Lambert-W function, and a focus array is uniformly focused at the center of an alkali metal gas chamber by expanding the focus depth, so that the transverse and longitudinal polarizability uniformity of alkali metal atoms is remarkably improved, the optical frequency shift virtual magnetic field gradient is inhibited, and the stability of the alkali metal gas chamber is improved. And the common-mode rejection ratio, the signal-to-noise ratio and the response sensitivity of the SERF magnetic field measuring device are improved. The focus array is optimized in real time through detection feedback, efficient compensation and regulation are achieved, and the method is suitable for accurate measurement of the sub-fT-level weak magnetic field.

Description

Technical Field

[0001] The present invention relates to the technical field of SERF atomic magnetic field measurement, and in particular to a magnetic field measurement method based on multi-focus array laser pumping of atomic spins. By generating a multi-focus array inside an alkali metal gas chamber and generating focuses with increasing energy along the optical axis, the transverse and longitudinal polarizabilities of atoms in the alkali metal gas chamber can be improved. Background Art

[0002] The spin-exchange relaxation-free atomic spin magnetic field (SERF) measurement device, with its ultra-high sensitivity of sub-femtoliter, has become the most sensitive measurement device in the world's magnetic field measurement technology. It is widely used in cutting-edge basic scientific research such as high-precision monitoring of cardiac and brain magnetic signals, precise detection of geomagnetic anomalies, and dark matter exploration.

[0003] In the existing SERF magnetic field measurement technology, a circularly polarized laser beam is mainly used to pump the alkali metal atoms in the alkali metal gas chamber. However, the traditional pumping method will cause the pump laser to have a significant attenuation of light intensity when passing through the alkali metal gas chamber due to the high atomic density and high optical depth in the alkali metal gas chamber. At the same time, since the output laser is generally a Gaussian beam, the Gaussian light intensity distribution causes a large difference in transverse polarization between the center and edge of the light spot, thereby generating a strong optical frequency-shifted virtual magnetic field gradient. The two lead to lower longitudinal and transverse polarization rates in the alkali metal gas chamber, respectively, which limits the accuracy and sensitivity of the magnetic field measurement. Therefore, how to optimize the uniform transverse distribution of the pump light intensity, reduce the attenuation of the longitudinal light intensity, and increase the transverse and longitudinal polarization rates of atoms in the alkali metal gas chamber to achieve efficient pumping has become a technical problem that needs to be solved urgently.

[0004] In order to solve the problem of uneven transverse and longitudinal polarizabilities of atoms in the existing alkali metal gas cell, the present invention proposes a method of generating a multi-focal array through a spatial light modulator. The energy distribution of the focal points is uniform in the transverse distribution, and the spacing is equal, which compensates for the uneven intensity of Gaussian light in the transverse distribution. In the longitudinal direction, based on the attenuation W curve of the interaction between light and atoms, compensation is performed through the inverse Lambert-W function, so that the focal light intensity gradually increases with the longer the propagation direction of the pump light. By extending the focal depth, the focal array is evenly focused on the center of the alkali metal gas cell, thereby significantly improving the transverse and longitudinal polarizabilities of the alkali metal atoms in the gas cell. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art and provides a magnetic field measurement method based on multi-focal array laser pumping of atomic spins. By utilizing the phase control function of a spatial light modulator (SLM), a multi-focal array is generated in the transverse direction, effectively improving the uniformity of the transverse polarization rate. To further optimize the focal light intensity distribution in the z-direction, the present invention incorporates an inverse Lambert-W function compensation design, gradually increasing the focal light intensity along the z-axis to compensate for the energy attenuation caused by the interaction between light and atoms. Simultaneously, by extending the focal depth, the focal array uniformly covers the working area of ​​the alkali metal gas chamber, thereby significantly improving the transverse and longitudinal atomic polarization efficiency. The present invention also introduces a real-time optimization mechanism to dynamically adjust the phase pattern of the SLM based on feedback data to optimize the transverse and longitudinal parameters of the focal array. This process adjusts the focal array using real-time feedback signals, ensuring that the focal energy distribution can optimally adapt to changes in the atomic distribution within the atomic gas chamber, thereby improving the accuracy and sensitivity of magnetic field measurements. Therefore, the present invention not only solves the problem of uneven polarization rate caused by uneven transverse and longitudinal pump light intensity distribution, but also significantly improves the sensitivity and accuracy of magnetic field measurements.

[0006] The technical solutions of the present invention are as follows: A magnetic field measurement method based on multi-focus array laser pumping of atomic spins, characterized by comprising the following steps: Step 1: In a multi-focal array laser-pumped atomic spin magnetic field measurement device, a spatial light modulator is used to initialize a focal array, wherein the focal array is a multi-focal circularly polarized light array formed by the spatial light modulator after phase-modulating the pump light and incident on the alkali metal gas chamber from the z-axis direction; Step 2, after the pumping light focus array pumps the alkali metal atoms in the polarized alkali metal gas cell, using a detection light path to detect the magnetic field signal response characteristics, the detection light passing through the alkali metal gas cell in the x-axis direction; Step 3: Extract the atomic longitudinal and transverse polarizability distributions and the optical frequency shift virtual magnetic field gradient information based on the polarization state change of the detected light; Step 4: determine whether the optical frequency shift virtual magnetic field gradient and the atomic transverse and longitudinal polarization uniformity meet the requirements. If not, dynamically adjust the phase mode of the spatial light modulator and optimize the parameters of the focal array and return to step 2. If yes, proceed to step 5. Step 5: Perform subsequent magnetic field measurements using the alkali metal gas cell after polarizability optimization and uniformity.

[0007] The magnetic field measurement device for multi-focus array laser-pumped atomic spins includes a pumping laser, a concave lens, a convex lens, a first 1 / 2 wave plate, a first polarization beam splitter prism, a first 1 / 4 wave plate and a spatial light modulator connected in sequence. The pumping light output by the spatial light modulator passes through the alkali metal gas chamber. The detection light incident side of the alkali metal gas chamber is connected to the detection laser in sequence through the second 1 / 4 wave plate, the photoelastic modulator, the polarizer, the second polarization beam splitter prism and the second 1 / 2 wave plate. The detection light exit side of the alkali metal gas chamber is connected to the three-axis compensation coil in sequence through the polarizer, the photodetector, the phase-locked amplifier, the host computer and the function generator. The phase-locked amplifier is connected to the photoelastic modulator through a modulation controller. The alkali metal gas chamber is located in a non-magnetic electric heating oven, the non-magnetic electric heating oven is located in the three-axis compensation coil, and the three-axis compensation coil is located in a magnetic shielding tube.

[0008] The initial focus array in step 1 is 10×10×10, with the focus uniformly distributed in the xy plane. The focus energy distribution in the z direction is compensated according to the inverse Lambert-W function.

[0009] In the longitudinal z-direction, based on the energy attenuation law caused by the interaction between light and atoms, the focal light intensity is designed to gradually increase with the depth of the z-axis in combination with the inverse Lambert-W function. The focal array is evenly focused on the center of the alkali metal gas cell by extending the focal depth. By ensuring that the light intensity gradually increases in the z-direction of the gas cell, the absorption and attenuation of the light intensity are effectively compensated, thereby improving the uniformity of the transverse and longitudinal polarizability of the alkali metal atoms, suppressing the virtual magnetic field gradient of the optical frequency shift, and improving the common mode rejection ratio, signal-to-noise ratio and response sensitivity.

[0010] Include the following expressions: , where I(z) is the z-axis light intensity, Rrel is the relaxation rate, W is the Lambert-W function, σ(v) is the light absorption cross-section, I(0) is the light intensity at z = 0, n is the alkali metal atomic density, and z is the z-axis coordinate.

[0011] Step 4 includes the following expression: The optical frequency shift virtual magnetic field gradient requirement is less than 0.7pT / cm; , where ΔP xy represents the inhomogeneity index of the polarizability in the transverse direction, i.e., in the xy plane, when the z value is the same. max It represents the maximum value of the polarizability of the measurement point on the transverse plane when the z value is the same, P min It represents the minimum value of the polarizability of the measurement point on the transverse plane when the z value is the same, P avg It represents the average value of the polarizability of all measurement points on the transverse plane when the z value is the same.

[0012] Step 3 includes combining the diffusion equations of light and atoms with the detection feedback data to evaluate the uniformity of the current focus array and the light field distribution effect.

[0013] The technical effects of the present invention are as follows: The present invention provides a magnetic field measurement method based on multi-focal array laser pumping of atomic spins. The multi-focal array is generated by a spatial light modulator, which significantly solves the problems of poor uniformity of transverse and longitudinal polarization rates in the gas chamber and large optical frequency shift virtual magnetic field gradient caused by uneven transverse and longitudinal light intensity distribution of the pumping light in traditional Gaussian beams. Through the generation of a transverse multi-focal array and the design of longitudinal light intensity energy compensation based on the inverse Lambert-W function, the present invention effectively improves the uniformity of the transverse and longitudinal polarization rates of atoms in the alkali metal gas chamber, significantly reduces the optical frequency shift virtual magnetic field gradient, and improves the polarization uniformity. In addition, the present invention dynamically adjusts the transverse spacing and longitudinal energy distribution of the focal array according to the detection signal through a feedback optimization mechanism, so that the focal array can more accurately adapt to the atomic distribution characteristics and response requirements in the gas chamber. The extended depth of focus design ensures that the focal array evenly covers the working area of ​​the alkali metal gas chamber, thereby significantly improving the magnetic field measurement sensitivity and accuracy of the device.

[0014] Compared with the prior art, the present invention has the following advantages: (1) Compared with the traditional Gaussian beam pumped SERF magnetic field measurement device, the problem of excessive virtual magnetic field gradient of optical frequency shift caused by uneven transverse light intensity distribution in the gas chamber is solved, and the uniformity of transverse polarizability is improved.

[0015] (2) In the longitudinal direction, the inverse Lambert-W function is combined to compensate the focal light intensity, so that the light intensity gradually increases along the z-axis, compensating for the energy attenuation caused by the interaction between light and atoms, improving the longitudinal polarization efficiency, and ensuring that the focal array evenly covers the working area of ​​the gas chamber.

[0016] (3) The present invention dynamically adjusts the phase mode of the spatial light modulator based on the detection signal, optimizes the lateral spacing and longitudinal energy distribution of the focal array through a feedback optimization mechanism, and significantly improves the adaptability of the pumping light field to the atoms in the gas chamber.

[0017] (4) By optimizing the transverse and longitudinal light field distribution, the present invention significantly improves the transverse and longitudinal polarizability of atoms in the gas chamber, thereby enhancing the signal-to-noise ratio of the magnetic field signal and significantly improving the sensitivity and accuracy of magnetic field measurement. It is suitable for extremely weak magnetic field measurements at the sub-fetT level. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a schematic structural diagram of a magnetic field measurement device for multi-focus array laser pumped atomic spins involved in a magnetic field measurement method based on multi-focus array laser pumped atomic spins of the present invention.

[0019] Figure 2 The present invention is a flowchart of a magnetic field measurement method based on multi-focus array laser pumping of atomic spins. Figure 2 The method includes step 1, initializing the focal array using a spatial light modulator; step 2, starting the device and detecting the magnetic field signal response characteristics; step 3, extracting the atomic longitudinal and transverse polarizability distribution and the optical frequency shift virtual magnetic field gradient information; step 4, dynamically optimizing the parameters of the focal array according to the feedback data; step 5, judging whether the optical frequency shift virtual magnetic field gradient and the atomic transverse and longitudinal polarization uniformity meet the requirements, if not, returning to step 3, if yes, entering step 6; step 6, using the alkali metal gas chamber after the polarizability optimization uniformity to perform subsequent magnetic field measurements.

[0020] The figure numbers are explained as follows: 1-pumping laser; 2-concave lens; 3-convex lens; 4-first 1 / 2 wave plate; 5-first polarization beam splitter prism; 6-first 1 / 4 wave plate; 7-spatial light modulator; 8-magnetic shielding tube; 9-three-axis compensation coil; 10-non-magnetic electric heating oven; 11-alkali metal gas chamber; 12-detection laser; 13-second 1 / 2 wave plate; 14-second polarization beam splitter prism; 15-polarizer; 16-photoelastic modulator; 17-second 1 / 4 wave plate; 18-polarizer; 19-photodetector; 20-phase-locked amplifier; 21-host computer; 22-function generator; 23-modulation controller; xyz-three axes of the rectangular coordinate system (i.e., x-axis, y-axis, and z-axis). DETAILED DESCRIPTION

[0021] Below is the attached figure ( Figure 1-Figure 2 ) and Examples illustrate the present invention.

[0022] Figure 1 The present invention is a schematic structural diagram of a magnetic field measurement device for multi-focus array laser pumped atomic spins involved in a magnetic field measurement method based on multi-focus array laser pumped atomic spins of the present invention. Figure 2 This is a flow chart of a method for measuring magnetic field based on multi-focus array laser pumping of atomic spins according to the present invention. Figures 1 to 2As shown, a magnetic field measurement method based on multi-focal array laser pumping of atomic spins includes the following steps: Step 1, in a magnetic field measurement device for multi-focal array laser pumping of atomic spins, initializing a focal array using a spatial light modulator, wherein the focal array is a multi-focal circularly polarized light array formed by the spatial light modulator phase-modulating the pumping light and then incident on an alkali metal gas chamber from the z-axis direction; Step 2, after the pumping light focal array pumps the polarized alkali metal atoms in the alkali metal gas chamber, detecting the magnetic field signal response characteristics using a detection optical path, wherein the detection light passes through the alkali metal gas chamber from the x-axis direction; Step 3, extracting the atomic longitudinal and transverse polarizability distribution and optical frequency-shifted virtual magnetic field gradient information based on the change in the polarization state of the detection light; Step 4, determining whether the optical frequency-shifted virtual magnetic field gradient and the atomic transverse and longitudinal polarization uniformity meet requirements; if not, dynamically adjusting the phase mode of the spatial light modulator and optimizing the parameters of the focal array and then returning to Step 2; if yes, proceeding to Step 5; Step 5, performing subsequent magnetic field measurements using the alkali metal gas chamber after the polarizability optimization uniformity.

[0023] The multi-focus array laser pumped atomic spin magnetic field measurement device comprises a pumping laser 1, a concave lens 2, a convex lens 3, a first 1 / 2 wave plate 4, a first polarization beam splitter prism 5, a first 1 / 4 wave plate 6 and a spatial light modulator 7 connected in sequence. The pumping light output by the spatial light modulator 7 passes through an alkali metal gas cell 11, and the incident side of the detection light of the alkali metal gas cell 11 passes through a second 1 / 4 wave plate 17, a photoelastic modulator 16, a polarizer 15, a second polarization beam splitter prism 14 and a second 1 / 2 wave plate 17 in sequence. 3 is connected to the detection laser 12. The detection light output side of the alkali metal gas chamber 11 is connected to the three-axis compensation coil 9 through the polarizer 18, the photodetector 19, the lock-in amplifier 20, the host computer 21 and the function generator 22 in sequence. The lock-in amplifier 20 is connected to the photoelastic modulator 16 through the modulation controller 23. The alkali metal gas chamber 11 is located in the non-magnetic electric heating oven 10, the non-magnetic electric heating oven 10 is located in the three-axis compensation coil 9, and the three-axis compensation coil 9 is located in the magnetic shielding tube 8.

[0024] The initial focal array in step 1 is 10×10×10, with a uniform distribution of focal points in the xy plane. The focal energy distribution in the z direction is compensated according to the inverse Lambert-W function. In the longitudinal z direction, the energy attenuation caused by the interaction between light and atoms is combined with the inverse Lambert-W function to design a focal intensity that gradually increases with depth along the z axis. By extending the focal depth, the focal array is uniformly focused on the center of the alkali metal gas cell. By ensuring that the light intensity gradually increases in the z direction of the gas cell, the absorption and attenuation of the light intensity are effectively compensated, thereby improving the uniformity of the transverse and longitudinal polarizability of the alkali metal atoms, suppressing the virtual magnetic field gradient caused by optical frequency shift, and improving the common-mode rejection ratio, signal-to-noise ratio, and response sensitivity.

[0025] Include the following expressions: , where I(z) is the z-axis light intensity, Rrel is the relaxation rate, W is the Lambert-W function, σ(v) is the light absorption cross-section, I(0) is the light intensity at z = 0, n is the alkali metal atomic density, and z is the z-axis coordinate.

[0026] Step 4 includes the following expression: The optical frequency shift virtual magnetic field gradient requirement is less than 0.7pT / cm; , where ΔP xy represents the inhomogeneity index of the polarizability in the transverse direction, i.e., in the xy plane, when the z value is the same. max It represents the maximum value of the polarizability of the measurement point on the transverse plane when the z value is the same, P min It represents the minimum value of the polarizability of the measurement point on the transverse plane when the z value is the same, P avg It represents the average value of the polarizability of all measurement points on the transverse plane when the z value is the same.

[0027] Step 3 includes combining the diffusion equations of light and atoms with the detection feedback data to evaluate the uniformity of the current focus array and the light field distribution effect.

[0028] A magnetic field measurement method based on laser-pumped atomic spins using a multi-focal array aims to provide an efficient and accurate atomic pumping solution for magnetic field measurement devices. The pump light is phase-modulated by a spatial light modulator (SLM), generating a multi-focal circularly polarized light array. The focal points exhibit uniform intensity distribution and consistent spacing in the transverse plane, effectively compensating for the uneven Gaussian intensity distribution of the laser in the transverse direction. In the longitudinal direction, based on the energy attenuation caused by the interaction between light and atoms and incorporating an inverse Lambert-W function, the focal intensity gradually increases with z-axis depth. By extending the focal depth, the focal array is uniformly focused on the center of the alkali metal gas chamber, significantly improving the uniformity of the transverse and longitudinal polarizability of the alkali metal atoms, suppressing the virtual magnetic field gradient of optical frequency shifts, and enhancing the common-mode rejection ratio, signal-to-noise ratio, and response sensitivity of the SERF magnetic field measurement device. Real-time optimization of the focal array through detection feedback enables efficient compensation and regulation, making it suitable for precise measurement of sub-femtoliter weak magnetic fields.

[0029] A magnetic field measurement method based on multi-focus array laser pumping of atomic spins, comprising a pumping optical path, a detection optical path, and a magnetically shielded gas chamber system. The pumping optical path comprises a pumping laser (1), a beam expansion device composed of a concave lens (2) and a convex lens (3), a first 1 / 2 wave plate (4), a first polarization beam splitter prism (5), a first 1 / 4 wave plate (6), and a spatial light modulator (7); the pumping laser (1) emits a laser beam, which is expanded by the beam expansion device spot, and then sequentially passes through the first 1 / 2 wave plate (4), the first polarization beam splitter prism (5), and the first 1 / 4 wave plate (6) to convert the linearly polarized light into circularly polarized light, and then passes through the spatial light modulator (7) to perform phase modulation, thereby decomposing the circularly polarized light into a multi-focus array, wherein the focus light intensity on the xy plane is almost the same, the spacing between the focuses is almost equal, and as the pumping light propagation distance in the z direction increases, the light intensity of the focus light gradually increases, and at the same time, the focus is uniformly focused on the center of the alkali metal gas chamber (11) and the focal depth is increased, thereby pumping the polarized alkali metal atoms in the alkali metal gas chamber (11); The detection optical path portion includes a detection laser (12) emitting a detection laser beam, which passes through a second 1 / 2 wave plate (13), a second polarization beam splitter (14), a polarizer (15), a photoelastic modulator (16), a second 1 / 4 wave plate (17) and finally reaches a polarizer (18), detects the change in the polarization state of the detection laser before and after the alkali metal atoms are pumped by the pumping laser, converts the optical signal into an electrical signal through a photodetector (19), and then passes through a phase-locked amplifier (20), a host computer (21), a function generator (22), and a modulation controller (23) in sequence; The magnetic shielding gas chamber system comprises a magnetic shielding tube (8), a three-axis compensation coil (9), a non-magnetic electric heating oven (10), and an alkali metal gas chamber (11); the alkali metal gas chamber is placed in the non-magnetic electric heating oven (10), the outer layer is wrapped with the three-axis compensation coil (9), and finally placed in the magnetic shielding tube (8) to shield external electromagnetic information interference.

[0030] The distribution of the focus array in the xy plane has been optimized to ensure uniform focus spacing, and the focus light intensity compensates for the uneven intensity of Gaussian light in the lateral distribution; The energy distribution of the focal array in the z-direction is based on the energy attenuation caused by the interaction between light and atoms, and is designed with the inverse Lambert-W function to gradually increase the distribution of focal light intensity. The inverse Lambert-W function is used for compensation, so that the focal light intensity gradually increases with the depth of the z-axis.

[0031] By utilizing the optimized focus array design, the focus is uniformly focused on the working area of ​​the alkali metal gas chamber (11), thereby enhancing the polarization efficiency of the pumping light on the alkali metal atoms in the gas chamber and significantly improving the transverse polarization rate and the longitudinal polarization rate.

[0032] By using feedback data, the phase mode of the spatial light modulator is adjusted in real time, the parameters of the focal array are optimized, and the uniformity of the pump light intensity distribution in the gas chamber is significantly improved. This solves the problem of uneven lateral light intensity distribution caused by the Gaussian distribution of a single laser beam in the lateral direction. The energy attenuation law caused by the interaction between light and atoms is compensated in the longitudinal direction, ensuring the optimal atomic polarization effect and improving the SERF magnetic field measurement performance.

[0033] A magnetic field measurement method based on multi-focus array laser pumping of atomic spins, comprising the following steps: Step 1: Initialize the focal array: Use the phase control function of the spatial light modulator to generate an initial 10×10×10 multi-focal array. Ensure that the focal spots are evenly distributed in the lateral direction (xy plane) of the alkali metal gas cell. The longitudinal (z-direction) energy distribution is compensated according to the inverse Lambert-W function. Step 2, Initial Measurement: Focus the focal array on the center of the alkali metal gas chamber, activate the magnetic shielding tube and three-axis compensation coil to shield against external magnetic field interference; turn on the detection laser, and use the photodetector to detect the distribution of the transverse or longitudinal polarizability of the alkali metal atoms in the gas chamber and the magnetic field signal response characteristics; Step 3, Data Acquisition and Feedback: Based on the changes in the polarization state of the detected light, the transverse and longitudinal polarizability distributions of the atoms in the alkali metal gas chamber and the virtual magnetic field gradient of the optical frequency shift are extracted. The uniformity of the current focal array and the light field distribution effect are evaluated by combining the diffusion equations of light and atoms with the detection feedback data. Step 4, focal array optimization: dynamically adjust the phase pattern of the spatial light modulator based on the feedback data to optimize the parameters of the focal array; Step 5, measurement after optimization: apply the optimized focal array to the gas cell again and repeat steps 2 and 3 to determine whether the optical frequency shift virtual magnetic field gradient and the atomic transverse and longitudinal polarization uniformity meet the requirements. If not, return to step 4; Step 6: Perform subsequent magnetic field measurements.

[0034] Step 3 includes determining whether the optical frequency shift virtual magnetic field gradient is less than 0.7 pT / cm and whether the atomic polarization uniformity is greater than 80%.

[0035] Optimizing the focus array parameters in step 4 involves both lateral and longitudinal optimization. Lateral optimization primarily involves recalculating the focal distance using the diffusion equation and optimizing the lateral distribution of the focal points to achieve a more uniform polarization within the cell. Longitudinal optimization involves adjusting the inverse Lambert-W function compensation parameters to further optimize the z-direction focal intensity distribution, compensate for energy attenuation, and improve longitudinal polarization efficiency.

[0036] A magnetic field measurement method based on multi-focus array laser pumping of atomic spins includes a pumping optical path system, namely a pumping system, a detection optical path part, namely a detection system, and a magnetic shielding gas chamber system part.

[0037] The pumping system comprises a pumping laser (1), wherein the pumping laser (1) is expanded by a beam expansion device light spot composed of the concave lens (2) and the convex lens (3), and then sequentially passes through the first 1 / 2 wave plate (4), the first polarization beam splitter (5), and the first 1 / 4 wave plate (6) to convert the linearly polarized light into circularly polarized light, and then passes through the spatial light modulator (7) to perform phase modulation, thereby decomposing a beam of circularly polarized light into a multi-focus array, wherein the focus light intensity on the xy plane is almost the same, the spacing between the focuses is almost equal, and as the pumping light propagation distance in the z direction increases, the light intensity of the focus light reaching the target gradually increases, and at the same time, the focus is uniformly focused on the center of the alkali metal gas chamber (11) and the focal depth is increased, thereby pumping the polarized alkali metal atoms in the alkali metal gas chamber (11).

[0038] The detection system includes a detection laser (12), wherein the detection laser (12) emits a beam of detection laser light which passes through the second 1 / 2 wave plate (13), the second polarization beam splitter (14), the polarizer (15), the photoelastic modulator (16), the second 1 / 4 wave plate (17) and finally reaches the analyzer (18), and detects the change in polarization state of the detection laser light after the pumping laser pumps the alkali metal atoms. The optical signal is converted into an electrical signal by the photodetector (19), and then passes through the phase-locked amplifier (20), the host computer (21), the function generator (22) and the modulation controller (23) in sequence to measure and control the final magnetic field measurement information.

[0039] The magnetic shielding air chamber system comprises a magnetic shielding cylinder (8), a three-axis compensation coil (9), a non-magnetic electric heating oven (10), and an alkali metal air chamber (11); the alkali metal air chamber is placed in the non-magnetic electric heating oven (10), the outer layer is wrapped with the three-axis compensation coil (9), and finally placed in the magnetic shielding cylinder (8) to shield external electromagnetic information interference.

[0040] A magnetic field measurement method based on multi-focus array laser pumping of atomic spins. The principle is as follows: The pump light phase modulates circularly polarized light through a spatial light modulator to generate a multi-focal array. The distribution of the focal array in the xy plane is optimized to ensure uniform focal spacing and nearly uniform focal intensity. The energy distribution of the focal array in the z direction is based on the attenuation W curve of the interaction between light and atoms. It is designed using an inverse Lambert-W function compensation function, so that the focal intensity gradually increases with the depth of the z-axis propagation, compensating for the energy attenuation caused by optical absorption. The optimized focus array design enables uniform focus on the working area of ​​the alkali metal gas cell, enhancing the polarization efficiency of the pump light on the alkali metal atoms in the gas cell and significantly improving the transverse and longitudinal polarization rates. The spin motion of atoms in the SERF state can be described by the classic Bloch equation: , where P is the electron spin polarization vector, t is time, D is the diffusion coefficient, ▽ 2 is the Laplace operator, describing the diffusion behavior of the polarization vector in space, q(P) is the slowing factor, γ e is the gyromagnetic ratio of the electron, B is the external magnetic field, R op is the optical pumping efficiency, s is the circular polarization of the pumping light, its direction is along the z axis, R rel represents the optical pumping rate R op The total relaxation rate outside.

[0041] From the Bloch equation, we know that the relaxation time is: , According to the classical diffusion theory, the diffusion distance is: , The distribution of the focus array in the xy plane is optimized to avoid crosstalk between adjacent channels caused by atomic diffusion effects between pumping light focuses. Therefore, the distance between adjacent focuses should be greater than the diffusion distance L. D .

[0042] In the z direction, the pump beam is strongly absorbed when passing through the alkali metal gas cell. Therefore, its intensity decreases significantly with increasing distance. The intensity of the pump light in the gas cell along the pump light direction, I(z), can be calculated using the following equation: , Where I(Z) is the light intensity distributed along the z axis, n is the number density of alkali metal atoms, σ(v) is the light absorption cross-sectional area of ​​alkali metal atoms, z > represents the polarizability. s represents the polarization state of light. Considering that the pump light is completely circularly polarized, s = 1 or -1. In this case, Equation (4) has no general solution, but can be expressed by the following transcendental equation: , Where I(0) is the light intensity at z=0. This transcendental equation can be solved using the Lambert-W equation, which is as follows: , Where W represents the Lambert-W function, which is f(w)=We W ​Inverse function. Due to the interaction between light and atoms, an energy attenuation model is established. By calculating the attenuation of light intensity in the gas cell and adjusting the design based on the energy consumption of the interaction between light intensity distribution and atoms, the longitudinal distribution of light is ensured to be consistent. Formula (4) describes the change in light intensity when light propagates along the z direction in the gas cell. From formula (6), it can be seen that when circularly polarized pump light passes through the alkali metal gas cell, the attenuation of its light intensity is mainly affected by the optical depth and relaxation rate. To further optimize the light intensity distribution, an inverse Lambert-W function is used for compensation design. Formula (6) is used to compensate for the attenuation effect of light intensity, thereby ensuring that the light intensity gradually increases in the z direction of the gas cell, effectively compensating for the absorption and attenuation of light intensity, and improving the polarization efficiency of atoms.

[0043] Further considering converting the pumping light intensity into the pumping rate, using formula (6), the longitudinal attenuation of the pumping rate in the alkali metal gas chamber can be expressed as follows: , Where A is the pump light spot area, h is the Planck constant, and v is the frequency of the incident pump light. Combined with formula (7), the longitudinal (z-direction) distribution of the atomic spin polarization in the alkali metal gas chamber under steady-state conditions can be calculated, which can be expressed as follows: , P(z) is the polarizability in the z direction. Through the above compensation design, the energy distribution of the focal array in the z direction matches the absorption law of light, achieving uniform polarization pumping, thereby improving the uniformity of the longitudinal polarizability of the atoms in the gas chamber.

[0044] Since the Gaussian light generated by the traditional laser beam has uneven intensity in the lateral distribution, a multi-focus distribution on the lateral plane is adopted. After optimization design, the focus spacing is uniform and the focus light intensity compensates for the uneven intensity of the Gaussian light in the lateral distribution.

[0045] In the feedback optimization phase of step 4, the lateral polarizability distribution data is collected in real time through the detection optical path to construct a two-dimensional polarizability map. If the polarizability of a local area is detected to be lower than the set threshold, the focus density and light intensity weight of the area are recalculated. For example, the number of focuses in the low polarizability area is increased or the local focus intensity is increased. At the same time, the focus spacing is iteratively corrected through the diffusion equation to ensure that the optimized array meets the following requirements: , where ΔP xy Represents the inhomogeneity index of polarizability in the transverse direction (xy plane) when the z value is the same, P max It represents the maximum value of the polarizability of the measurement point on the transverse plane when the z value is the same, P min It represents the minimum value of the polarizability of the measurement point on the transverse plane when the z value is the same, Pavg It represents the average value of the polarizability of all measurement points on the transverse plane when the z value is the same. Combined with the real-time polarization modulation of the photoelastic modulator (16), the transverse light intensity drift caused by the temperature fluctuation of the gas chamber or the change of the atomic density is synchronously compensated, the uniformity of the focus array is further stabilized, and the sensitivity and accuracy of the magnetic field measurement are improved.

[0046] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A magnetic field measurement method based on multi-focus array laser pumping of atomic spins, characterized in that: The following steps are involved: Step 1: In a multi-focal array laser-pumped atomic spin magnetic field measurement device, a spatial light modulator is used to initialize a focal array, wherein the focal array is a multi-focal circularly polarized light array formed by the spatial light modulator after phase-modulating the pump light and incident on the alkali metal gas chamber from the z-axis direction; Step 2, after the pumping light focus array pumps the alkali metal atoms in the polarized alkali metal gas cell, using a detection light path to detect the magnetic field signal response characteristics, the detection light passes through the alkali metal gas cell in the x-axis direction; Step 3: Extract the atomic longitudinal and transverse polarizability distributions and the optical frequency shift virtual magnetic field gradient information based on the polarization state change of the detected light; Step 4: determine whether the optical frequency shift virtual magnetic field gradient and the atomic transverse and longitudinal polarization uniformity meet the requirements. If not, dynamically adjust the phase mode of the spatial light modulator and optimize the parameters of the focal array and return to step 2. If yes, proceed to step 5. Step 5: Perform subsequent magnetic field measurements using the alkali metal gas cell after polarizability optimization and uniformity.

2. The magnetic field measurement method based on multi-focus array laser pumping of atomic spins according to claim 1, characterized in that: The magnetic field measurement device for multi-focus array laser-pumped atomic spins includes a pumping laser, a concave lens, a convex lens, a first 1 / 2 wave plate, a first polarization beam splitter prism, a first 1 / 4 wave plate and a spatial light modulator connected in sequence. The pumping light output by the spatial light modulator passes through the alkali metal gas chamber. The detection light incident side of the alkali metal gas chamber is connected to the detection laser in sequence through the second 1 / 4 wave plate, the photoelastic modulator, the polarizer, the second polarization beam splitter prism and the second 1 / 2 wave plate. The detection light exit side of the alkali metal gas chamber is connected to the three-axis compensation coil in sequence through the polarizer, the photodetector, the phase-locked amplifier, the host computer and the function generator. The phase-locked amplifier is connected to the photoelastic modulator through a modulation controller. The alkali metal gas chamber is located in a non-magnetic electric heating oven, the non-magnetic electric heating oven is located in the three-axis compensation coil, and the three-axis compensation coil is located in a magnetic shielding tube.

3. The magnetic field measurement method based on multi-focus array laser pumping of atomic spins according to claim 1, characterized in that: The initial focus array in step 1 is 10×10×10, with the focus uniformly distributed in the xy plane. The focus energy distribution in the z direction is compensated according to the inverse Lambert-W function.

4. The magnetic field measurement method based on multi-focus array laser pumping of atomic spins according to claim 3, characterized in that: In the longitudinal z-direction, based on the energy attenuation law caused by the interaction between light and atoms, the focal light intensity is designed to gradually increase with the depth of the z-axis in combination with the inverse Lambert-W function. The focal array is evenly focused on the center of the alkali metal gas cell by extending the focal depth. By ensuring that the light intensity gradually increases in the z-direction of the gas cell, the absorption and attenuation of the light intensity are effectively compensated, thereby improving the uniformity of the transverse and longitudinal polarizability of the alkali metal atoms, suppressing the virtual magnetic field gradient of the optical frequency shift, and improving the common mode rejection ratio, signal-to-noise ratio and response sensitivity.

5. The magnetic field measurement method based on multi-focus array laser pumping of atomic spins according to claim 3, characterized in that: Include the following expressions: , where I(z) is the z-axis light intensity, Rrel is the relaxation rate, W is the Lambert-W function, σ(v) is the light absorption cross-section, I(0) is the light intensity at z = 0, n is the alkali metal atomic density, and z is the z-axis coordinate.

6. The magnetic field measurement method based on multi-focus array laser pumping of atomic spins according to claim 1, characterized in that: Step 4 includes the following expression: The optical frequency shift virtual magnetic field gradient requirement is less than 0.7pT / cm; , where ΔP xy represents the inhomogeneity index of the polarizability in the transverse direction, i.e., in the xy plane, when the z value is the same. max It represents the maximum value of the polarizability of the measurement point on the transverse plane when the z value is the same, P min It represents the minimum value of the polarizability of the measurement point on the transverse plane when the z value is the same, P avg It represents the average value of the polarizability of all measurement points on the transverse plane when the z value is the same.

7. The magnetic field measurement method based on multi-focus array laser pumping of atomic spins according to claim 1, characterized in that: Step 3 includes combining the diffusion equations of light and atoms with the detection feedback data to evaluate the uniformity of the current focus array and the light field distribution effect.

Images