SERF atom magnetometer longitudinal polarization non-uniformity measurement and longitudinal polarization optimization method

Abstract

According to the SERF atom magnetometer longitudinal polarization non-uniformity measurement and longitudinal polarization optimization method, the electron spin polarization longitudinal non-uniformity of an SERF atom magnetometer is calculated by measuring magnetometer scale coefficients of a plurality of points in a gas chamber and through the relation between the SERF atom magnetometer scale coefficients and electron spin polarizability, and the method comprises the following steps of: calculating the electron spin polarization longitudinal non-uniformity of the SERF atom magnetometer along the pumping light direction of the SERF atom magnetometer; a plurality of measuring points are arranged, and the number and the distance of the measuring points are determined according to the size of the air chamber. And the detection light passes through the air chamber in a direction perpendicular to the pumping light, the detection light is adjusted to the positions of the measurement points in sequence, and the magnetometer scale coefficients under the measurement points are measured. The standard deviation and the average value of the magnetometer calibration coefficient are calculated, the standard deviation is divided by the average value, the larger the parameter is, the more non-uniform the electron spin polarization of the SERF atom magnetometer is, and otherwise, the more uniform the electron spin polarization of the SERF atom magnetometer is. And then, changing an optical parameter based on a non-uniformity measurement result, finding out a parameter when the longitudinal electron spin polarization performance is maximum, and completing longitudinal polarization optimization.

Description

Technical Field

[0001] The invention relates to the technical field of SERF magnetometers, and in particular to a method for measuring the inhomogeneity of electron spin longitudinal polarization of a SERF atomic magnetometer and a longitudinal polarization optimization method based on the inhomogeneity measurement result. Background Art

[0002] SERF atomic magnetometer (SERF, Spin-Exchange Relaxation-Free, spin-exchange relaxation-free) has a very high theoretical sensitivity and has great potential in the fields of human heart magnetometry and brain magnetometry. When the SERF atomic magnetometer is working, circularly polarized light is needed to polarize the electrons in the alkali metal atoms. The size of the electron spin polarization and the uniformity of the electron spin polarization directly affect the performance of the magnetometer. Therefore, it is very important to adjust the electron spin polarization to the optimum and improve the uniformity of the electron spin polarization. The uniformity of the electron spin polarization is divided into longitudinal uniformity and transverse uniformity. The present invention first measures the longitudinal inhomogeneity of the electron spin polarization, and then uses the longitudinal inhomogeneity of the electron spin polarization as one of the optimization indicators, while considering the uniformity of the longitudinal electron spin polarization and the size of the longitudinal electron spin polarization to optimize the electron spin polarization.

[0003] Existing solutions for measuring electron spin polarization of SERF atomic magnetometers either measure the overall size of electron spin polarization or measure the lateral distribution of electron spin polarization, and there is no method that focuses on the measurement of the longitudinal inhomogeneity of electron spin polarization. For example, CN113075594B, a dual-axis in-situ measurement system and method for electron polarizability of a SERF atomic magnetometer, implements electron spin polarization measurement in the detection direction and pumping direction, but does not measure the inhomogeneity of electron spin polarization. For another example, CN104215553B, an integrated measurement device for atomic density and polarizability of alkali metal vapor, and CN116449265A, a relaxation-based atomic magnetometer polarizability measurement method, do not measure the inhomogeneity of electron spin polarization. For example, CN113639883B, an alkali metal atomic magnetometer spin polarization spatial distribution in-situ measurement system and method, uses two CMOS cameras to measure the change in the transmitted light intensity of the pumping light. This method measures the lateral distribution of electron spin polarization, but cannot measure the longitudinal uniformity of electron spin polarization.

[0004] For the longitudinal polarization of SERF atomic magnetometer, there is no optimization method that considers both the longitudinal uniformity and polarization magnitude of electron spin polarization. For example, CN 115825824 A, a device and method for improving the uniformity of electron polarization rate of SERF atomic magnetometer, can reduce the electron spin polarization gradient by pump light detuning, but does not measure the longitudinal electron spin polarization inhomogeneity, nor optimize the longitudinal electron spin polarization. Summary of the invention

[0005] In view of the defects or shortcomings in the prior art, the present invention provides a method for measuring the longitudinal inhomogeneity of electron spin polarization of a SERF atomic magnetometer and a longitudinal polarization optimization method based on the inhomogeneity measurement result.

[0006] The technical solution of the present invention is as follows:

[0007] A method for measuring longitudinal inhomogeneity of electron spin polarization of a SERF atomic magnetometer, characterized in that it comprises the following steps:

[0008] Step 1, starting the SERF atomic magnetometer system, pumping light passes through the alkali metal atomic gas chamber along the y-axis direction, and presetting m detection light positions on the pumping light path in the alkali metal atomic gas chamber to be used as measurement points of the magnetometer calibration coefficient, where m is an integer greater than 1;

[0009] Step 2, detect the smooth x-axis direction passing through the alkali metal atomic gas chamber and align each measuring point one by one, and obtain the SERF atomic magnetometer scale coefficient corresponding to each measuring point. When adjusting, use the first translation stage, the second translation stage, the third translation stage, and the fourth translation stage to simultaneously adjust the positions of the second collimator, the aperture, the polarization beam splitter prism, and the differential photodetector, and measure point by point along the positive direction of the y-axis starting from the leftmost measurement point.

[0010] Step 3, calculate the average value and standard deviation of the calibration coefficient, calculate the size of the standard deviation divided by the average value, and the value of the calibration coefficient standard deviation divided by the average value is the longitudinal inhomogeneity of the electron spin polarization of the SERF atomic magnetometer.

[0011] During unidirectional pumping, the longitudinal inhomogeneity of electron spin polarization includes the following three situations: the magnetometer response first increases and then decreases, the magnetometer response keeps increasing, and the magnetometer response keeps decreasing.

[0012] During bidirectional pumping, the longitudinal inhomogeneity of electron spin polarization includes the following three situations: the magnetometer response first decreases and then increases, the magnetometer response first increases and then decreases, and the magnetometer response increases, decreases, increases, and decreases.

[0013] The larger the value of the scale factor standard deviation divided by the average value is, the more non-uniform the electron spin polarization of the SERF atomic magnetometer is, and vice versa, the more uniform it is.

[0014] The longitudinal polarization optimization method based on the non-uniformity measurement result is characterized by comprising the following steps:

[0015] Step 1, start the SERF atomic magnetometer system, first adjust the pumping light frequency to resonate with the D1 line frequency of the alkali metal atoms, and preset the pumping light frequency adjustment step.

[0016] Step 2, using the above method to measure the longitudinal inhomogeneity of the SERF atomic magnetometer electron spin polarization, through the measurement, both the average value of the scale coefficient at different positions and the longitudinal inhomogeneity of the SERF atomic magnetometer electron spin polarization can be obtained.

[0017] Step 3, change the pumping light frequency according to the preset frequency adjustment step size, and measure the longitudinal inhomogeneity of the SERF atomic magnetometer's electron spin polarization each time the frequency is adjusted to obtain the average value of the scale coefficient at different positions and the longitudinal inhomogeneity of the SERF atomic magnetometer's electron spin polarization. Normalize the average value of the scale coefficient under different frequency conditions, normalize the longitudinal inhomogeneity of the electron spin polarization under different frequency conditions, and then subtract the normalized longitudinal inhomogeneity of the electron spin polarization from 1 to obtain the normalized longitudinal uniformity of the electron spin polarization. Multiply the average value of the normalized scale coefficient and the normalized longitudinal uniformity of the electron spin polarization by a weight of 1 / 2, and then add them together to obtain the total optimized evaluation value, which is defined as the longitudinal electron spin polarization performance. Until the maximum value of the longitudinal electron spin polarization performance of the SERF atomic magnetometer is found.

[0018] Step 4, adjust the pumping laser frequency to the frequency at which the longitudinal electron spin polarization performance is maximized, and the SERF atomic magnetometer longitudinal electron spin polarization optimization is completed.

[0019] The SERF atomic magnetometer system includes a first laser for generating laser light, which is emitted after passing through a first polarization-maintaining optical fiber and a first collimator, and then converted into circularly polarized pump light through a quarter-wave plate to enter the alkali metal atom gas chamber to polarize the alkali metal atoms in the gas chamber. A second laser is used to generate another laser beam, which is emitted after passing through a second polarization-maintaining optical fiber and a second collimator fixed on a first displacement platform. After the emitted laser light passes through a linear polarizer and an aperture fixed on a second displacement platform, a linearly polarized detection light with a smaller spot area is incident on the alkali metal atom gas chamber perpendicular to the pump light direction. After the laser light is transmitted through the alkali metal atom gas chamber, it first passes through a half-wave plate and a polarization beam splitter prism, and then is converted into a photocurrent signal through a differential photodetector. Finally, the signal enters a signal processing system to obtain a magnetic field measurement result. The temperature control system is used to control the power of the electric heating oven to control the temperature of the alkali metal atom gas chamber.

[0020] The half wave plate is used to zero the differential signal of the differential photodetector under zero magnetic field conditions. The magnetic shielding barrel is used to shield the external geomagnetic field and the interfering magnetic field. The coil is used to compensate for the residual magnetic field in conjunction with the current source, and a calibration magnetic field can be applied to calibrate the scale factor of the magnetometer.

[0021] The technical effects of the present invention are as follows: the present invention provides a method for measuring the longitudinal unevenness of electron spin polarization of a SERF atomic magnetometer and a method for optimizing the longitudinal polarization of electron spin. By measuring the magnetometer scale coefficients of multiple points in the gas chamber, the longitudinal unevenness of the electron spin polarization of the SERF atomic magnetometer is calculated through the relationship between the SERF atomic magnetometer scale coefficient and the electron spin polarization rate, including setting multiple measurement points along the pumping light direction of the SERF atomic magnetometer, and the number and spacing of the measurement points are determined according to the size of the gas chamber. The detection light passes through the gas chamber perpendicular to the pumping light direction, and the detection light is adjusted to the position of each measurement point in turn, and the size of the magnetometer scale coefficient at each measurement point is measured. The standard deviation and average value of the magnetometer scale coefficient are calculated, and the standard deviation is divided by the average value, which is defined as the longitudinal unevenness of the electron spin polarization of the SERF atomic magnetometer. The larger the parameter, the more uneven the SERF atomic magnetometer electron spin polarization, and vice versa, the more uniform it is.

[0022] Then, based on the average value of the scale coefficient at different positions measured in the method for measuring the longitudinal inhomogeneity of electron spin polarization and the longitudinal inhomogeneity of the electron spin polarization of the magnetometer, a calculation method for judging the quality of the electron spin longitudinal polarization is proposed. Keep the pumping light power unchanged, change the pumping light frequency according to the preset frequency adjustment step, and measure the longitudinal inhomogeneity of the electron spin polarization of the SERF atomic magnetometer once each time the frequency is adjusted to obtain the average value of the scale coefficient at different positions and the longitudinal inhomogeneity of the electron spin polarization of the SERF atomic magnetometer. The average value of the scale coefficient under different frequency conditions is normalized, and the longitudinal inhomogeneity of the electron spin polarization under different frequency conditions is normalized. Then, the normalized longitudinal inhomogeneity of the electron spin polarization is subtracted from 1 to obtain the normalized longitudinal uniformity of the electron spin polarization. The average value of the normalized scale coefficient and the normalized longitudinal uniformity of the electron spin polarization are multiplied by a weight of 1 / 2, and then added to obtain the total optimized evaluation value, which is defined as the longitudinal electron spin polarization performance. Until the maximum value of the SERF atomic magnetometer longitudinal electron spin polarization performance is found, the pumping laser frequency is adjusted to the frequency of the maximum value of the longitudinal electron spin polarization performance, and the SERF atomic magnetometer longitudinal electron spin polarization optimization is completed.

[0023] The characteristics of the present invention are as follows:

[0024] 1. The present invention can measure the longitudinal uniformity of the electron spin polarization of the SERF atomic magnetometer and can provide a quantitative inhomogeneity result.

[0025] 2. The present invention optimizes the longitudinal electron spin polarization by taking into account the longitudinal uniformity and polarization size of the electron spin polarization, and proposes a criterion for judging the quality of the optimization.

[0026] 3. The measurement method in the present invention is an in-situ measurement under the working state of the SERF atomic magnetometer and does not destroy the normal working state of the SERF atomic magnetometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is a flow chart of a method for measuring longitudinal inhomogeneity of electron spin polarization of SERF atomic magnetometer in the present invention. SERF is spin-exchange relaxation-free. Figure 1 The method comprises step 1, setting up the corresponding configuration of the magnetometer; step 2, turning on two lasers in the magnetometer system; step 3, heating the alkali metal atom gas chamber using a temperature control system and an electric heating oven; step 4, compensating for the residual magnetic field; step 5, adjusting the detection light position to a preset measurement point; step 6, measuring the magnetometer scale coefficient; step 7, judging whether the measurement of all measurement points is completed, if not, returning to step 5, if yes, entering step 8; step 8, calculating the longitudinal inhomogeneity of the electron spin polarization of the SERF atomic magnetometer.

[0028] Figure 2 It is a flow chart of the SERF atomic magnetometer electron spin longitudinal polarization optimization method based on the inhomogeneity measurement results. Figure 2 The method includes step 1, setting up the corresponding configuration of the magnetometer; step 2, turning on the two lasers in the magnetometer system; step 3, using the temperature control system and the electric heating oven to heat the alkali metal atom gas chamber; step 4, adjusting the pumping light laser frequency; step 5, using the current source to apply current to the magnetic compensation coil to compensate for the residual magnetic field and the virtual magnetic field caused by the optical frequency shift; step 6, adjusting the position of the detection light so that the light spot of the detection light is aligned with the preset measurement point; step 7: measuring the scale coefficient of the magnetometer and recording it; step 8, judging whether the measurement of all measurement points is completed, if not, returning to step 6, if yes, entering step 9. ; Step 9, according to the recorded magnetometer scale coefficients at each measuring point, calculate the average values ​​of the scale coefficients at different positions and the longitudinal non-uniformity of the SERF atomic magnetometer electron spin polarization; Step 10, weighted calculation to obtain the SERF atomic magnetometer longitudinal electron spin polarization performance; Step 11, determine whether the maximum value of the SERF atomic magnetometer longitudinal electron spin polarization performance is found, if not, return to step 4, if yes, enter step 12; Step 12, adjust the pumping laser frequency to the frequency of the maximum value of the longitudinal electron spin polarization performance, and the SERF atomic magnetometer longitudinal electron spin polarization optimization is completed.

[0029] Figure 3 The present invention is a schematic diagram of a SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement and longitudinal electron spin polarization optimization device.

[0030] Figure 4 It is the simulation result of the SERF atomic magnetometer scale factor changing with electron spin polarization. Figure 4 The horizontal axis is the electron spin polarization (i.e. polarization rate, the scale value is from 0 to 1), and the vertical axis is the scale coefficient (normalized, the scale value is from 0 to 1).

[0031] The accompanying drawings are marked as follows: 1-first laser; 2-first polarization-maintaining fiber; 3-first collimator; 4-quarter wave plate; 5-second laser; 6-second polarization-maintaining fiber; 7-second collimator; 8-first translation stage; 9-linear polarizer; 10-second translation stage; 11-aperture; 12-alkali metal atom gas chamber; 13-electric heating oven; 14-magnetic shielding barrel; 15-coil; 16-half wave plate; 17-polarization beam splitter; 18-third translation stage; 19-differential photodetector; 20-fourth translation stage; 21-temperature control system; 22-signal processing system; 23-current source; xyz-three axes of the rectangular coordinate system (i.e., x-axis, y-axis, and z-axis). DETAILED DESCRIPTION

[0032] Below is the attached figure ( Figure 1-Figure 4 ) and Examples illustrate the present invention.

[0033] Figure 1 It is a schematic flow chart of a method for measuring longitudinal inhomogeneity of electron spin polarization of a SERF atomic magnetometer in the present invention. Figure 2 It is a flow chart of the SERF atomic magnetometer electron spin longitudinal polarization optimization method based on the inhomogeneity measurement results. Figure 3 The present invention is a schematic diagram of a SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement and longitudinal electron spin polarization optimization device. Figure 4 This is the simulation result of the SERF atomic magnetometer scale factor changing with electron spin polarization. Figures 1 to 4As shown, a method for measuring longitudinal inhomogeneity of electron spin polarization of a SERF atomic magnetometer comprises the following steps: step 1, starting the SERF atomic magnetometer system, pumping light along the y-axis direction through an alkali metal atomic gas chamber, presetting m detection light positions on the pumping light path in the alkali metal atomic gas chamber to be used as measurement points of the magnetometer scale coefficient size respectively, where m is an integer greater than 1; step 2, detecting light along the x-axis direction through the alkali metal atomic gas chamber and aligning each measurement point one by one, and obtaining the SERF atomic magnetometer scale coefficient corresponding to each measurement point respectively; step 3, calculating the average value and standard deviation of the scale coefficient, calculating the size of the standard deviation divided by the average value, and the value of the scale coefficient standard deviation divided by the average value is the longitudinal inhomogeneity of electron spin polarization of the SERF atomic magnetometer.

[0034] During unidirectional pumping, the longitudinal non-uniformity of electron spin polarization includes the following three situations: the magnetometer response first increases and then decreases, the magnetometer response keeps increasing, and the magnetometer response keeps decreasing. During bidirectional pumping, the longitudinal non-uniformity of electron spin polarization includes the following three situations: the magnetometer response first decreases and then increases, the magnetometer response first increases and then decreases, and the magnetometer response increases, decreases, increases, and decreases. The larger the value of the scale factor standard deviation divided by the average value, the more non-uniform the SERF atomic magnetometer electron spin polarization is, and vice versa, the more uniform it is.

[0035] refer to Figures 1 to 4As shown, the SERF atomic magnetometer electron spin longitudinal polarization optimization method based on the inhomogeneity measurement result includes the following steps: Step 1, starting the SERF atomic magnetometer system, first adjusting the pumping light frequency to the resonance with the alkali metal atom D1 line frequency, and presetting the pumping light frequency adjustment step; Step 2, using the above method to measure the longitudinal inhomogeneity of the SERF atomic magnetometer electron spin polarization, through which both the average value of the scale coefficient at different positions and the longitudinal inhomogeneity of the SERF atomic magnetometer electron spin polarization can be obtained; Step 3, changing the pumping light frequency according to the preset frequency adjustment step, each time the frequency is adjusted, the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement is performed, and the average value of the scale coefficient at different positions and the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity are obtained. Normalize the average values ​​of the scale coefficients under different frequency conditions, normalize the longitudinal non-uniformity of the electron spin polarization under different frequency conditions, and then subtract the normalized longitudinal non-uniformity of the electron spin polarization from 1 to obtain the normalized longitudinal uniformity of the electron spin polarization. Multiply the average value of the normalized scale coefficient and the normalized longitudinal uniformity of the electron spin polarization by a weight of 1 / 2, and then add them together to obtain the total optimized evaluation value, which is defined as the longitudinal electron spin polarization performance. Until the maximum value of the longitudinal electron spin polarization performance of the SERF atomic magnetometer is found; Step 4, adjust the pumping laser frequency to the frequency of the maximum value of the longitudinal electron spin polarization performance, and the longitudinal electron spin polarization optimization of the SERF atomic magnetometer is completed.

[0036] The SERF atomic magnetometer system includes a first laser 1 for generating laser light, which is emitted after passing through a first polarization-maintaining optical fiber 2 and a first collimator 3, and then converted into circularly polarized pump light by a quarter wave plate 4 to enter an alkali metal atom gas chamber 12 to polarize the alkali metal atoms in the gas chamber. A second laser 5 is used to generate another laser beam, which is emitted after passing through a second polarization-maintaining optical fiber 6 and a second collimator 7 fixed on a first displacement stage 8. After the emitted laser light passes through a linear polarizer 9 and an aperture 11 fixed on a second displacement stage 10, a linearly polarized detection light with a smaller spot area is perpendicular to the pump light direction and enters the alkali metal atom gas chamber 12. After the laser light is transmitted through the alkali metal atom gas chamber 12, it first passes through a half wave plate 16 and a polarization beam splitter prism 17, and then is converted into a photocurrent signal by a differential photodetector 19. Finally, the signal enters a signal processing system 22 to obtain a magnetic field measurement result. A temperature control system 21 is used to control the power of an electric heating oven 13 to control the temperature of the alkali metal atom gas chamber 12.

[0037] The half wave plate 16 is used to zero the differential signal of the differential photodetector 19 under zero magnetic field conditions. The magnetic shielding barrel 14 is used to shield the external geomagnetic field and the interfering magnetic field. The coil 15 is used to compensate for the residual magnetic field in conjunction with the current source 23, and a calibration magnetic field can be applied to calibrate the scale factor of the magnetometer.

[0038] A method for measuring the longitudinal inhomogeneity of electron spin polarization of a SERF atomic magnetometer is disclosed. The magnetometer calibration coefficients at multiple points in a gas chamber are measured. The longitudinal inhomogeneity of electron spin polarization of the SERF atomic magnetometer is calculated through the relationship between the SERF atomic magnetometer calibration coefficient and the electron spin polarization rate. Multiple measurement points are set along the pumping light direction of the SERF atomic magnetometer. The number and spacing of the measurement points are determined according to the size of the gas chamber. The detection light passes through the gas chamber perpendicular to the pumping light direction, and the detection light is adjusted to the position of each measurement point in turn, and the magnetometer calibration coefficient at each measurement point is measured. The standard deviation and average value of the magnetometer calibration coefficient are calculated, and the standard deviation is divided by the average value, which is defined as the longitudinal inhomogeneity of electron spin polarization of the SERF atomic magnetometer. The larger the parameter is, the more inhomogeneous the SERF atomic magnetometer electron spin polarization is, and vice versa, the more uniform it is.

[0039] A method for measuring longitudinal inhomogeneity of electron spin polarization of a SERF atomic magnetometer comprises the following steps:

[0040] Step 1: Build the magnetometer configuration.

[0041] Step 2, turn on the two lasers in the magnetometer system.

[0042] Step 3, heating the alkali metal atom gas chamber using a temperature control system and an electric heating oven.

[0043] Step 4: Compensate for the residual magnetic field.

[0044] Step 5: Adjust the detection light position to the preset measurement point.

[0045] Step 6, measure the magnetometer scale factor.

[0046] Step 7, determine whether the measurement of all measurement points is completed, if not, return to step 5, if yes, go to step 8.

[0047] Step 8, calculate the longitudinal inhomogeneity of the electron spin polarization of the SERF atomic magnetometer.

[0048] The magnetometer configuration in step 1 includes: the SERF atomic magnetometer system includes a first laser 1 for generating laser light, which is emitted after passing through a first polarization-maintaining optical fiber 2 and a first collimator 3, and then converted into circularly polarized pump light by a quarter wave plate 4 to enter the alkali metal atom gas chamber 12 to polarize the alkali metal atoms in the gas chamber. A second laser 5 is used to generate another laser beam, which is emitted after passing through a second polarization-maintaining optical fiber 6 and a second collimator 7 fixed on a first displacement stage 8. After the emitted laser light passes through a linear polarizer 9 and an aperture 11 fixed on a second displacement stage 10, a linearly polarized detection light with a smaller spot area is perpendicular to the pump light direction and enters the alkali metal atom gas chamber 12. After the laser light is transmitted through the alkali metal atom gas chamber 12, it first passes through a half wave plate 16 and a polarization beam splitter prism 17, and then is converted into a photocurrent signal by a differential photodetector 19. Finally, the signal enters a signal processing system 22 to obtain a magnetic field measurement result. A temperature control system 21 is used to control the power of the electric heating oven 13 to control the temperature of the alkali metal atom gas chamber 12.

[0049] The half wave plate 16 is used to zero the differential signal of the differential photodetector 19 under zero magnetic field conditions. The magnetic shielding barrel 14 is used to shield the external geomagnetic field and the interfering magnetic field. The coil 15 is used to compensate for the residual magnetic field in conjunction with the current source 23, and a calibration magnetic field can be applied to calibrate the scale factor of the magnetometer.

[0050] In step 5, the number and spacing of the measurement points are designed according to the size of the gas chamber, the detection light is incident perpendicular to the pumping light direction, the spot position is aligned with the preset measurement point, and the detection light spot position is adjusted to each measurement point. During the adjustment, the first displacement stage 8, the second displacement stage 10, the third displacement stage 18, and the fourth displacement stage 20 are used to simultaneously adjust the positions of the collimator 7, the aperture 11, the polarization beam splitter prism 17, and the differential photodetector 19, and the measurement is performed point by point along the positive direction of the y-axis starting from the leftmost measurement point.

[0051] In step 6, a magnetic field of known magnitude is applied to the magnetometer, and the response output of the magnetometer is divided by the magnitude of the calibrated magnetic field to obtain the scale factor of the magnetometer.

[0052] The theoretical basis of step 8 is that, first, the output signal of the SERF atomic magnetometer is,

[0053]

[0054] Where Vout is the output signal, K PD is the photoelectric conversion coefficient of the photodetector, K1 is the amplification factor of the signal processing system, l is the optical path length of the detection light, n is the number density of alkali metal atoms, c is the speed of light, r e is the classical electron radius, f D1 is the oscillator strength, v is the detection light frequency, v D1is the D1 line frequency of alkali metal atoms, Г D1 is the pressure broadening of alkali metal atoms, Ф probe is the optical power of the detection light, tr is the transmittance of the gas cell glass, σ(v) is the photon absorption cross section, R pump is the pumping rate, R rel is the relaxation rate, γ e is the electron gyromagnetic ratio, B x is the magnetic field to be measured, and the suffix (1) of the formula means that the formula is numbered 1.

[0055] It can be seen that when other conditions remain unchanged, including K PD , K1, l, n, v, Г D1 , Ф probe ,σ(v), the magnitude of the magnetometer output signal is only related to This term is related. Below, we analyze the relationship between this term and the steady-state electron spin polarization.

[0056] The steady-state electron spin polarization P is,

[0057]

[0058] In magnetometers, the electron spin polarization is usually changed by changing the pumping rate R pump Therefore, R in formula (2) pump After replacing P and ignoring the diffusion effect and magnetic field gradient, the R inside the gas chamber along the propagation direction of the pumping light is rel It can be considered as uniform, so the relationship between the steady-state electron spin polarization P and the magnetometer scale coefficient S is:

[0059]

[0060] According to the above formula (3), the simulation results of the SERF atomic magnetometer scale factor when the electron spin polarization changes can be obtained, such as Figure 4As shown. It can be seen that when the electron spin polarization changes, the magnetometer output response will also change. Although the change trend is not monotonic, the output response can still be used to determine whether the electron spin polarization is uniform. If the electron spin polarization is uniform in the longitudinal direction, then the responses at different positions will be almost equal. If the electron spin polarization is not uniform in the longitudinal direction, the following situations may occur. During unidirectional pumping, the pump light propagation direction is set along the positive direction of the y-axis. The electron spin polarization decreases with the propagation distance of the pump light. When the electron spin polarization is not uniform in the longitudinal direction, the following three situations will occur: the magnetometer response increases first and then decreases, the magnetometer response increases all the time, and the magnetometer response decreases all the time. During bidirectional pumping, the electron spin polarization is low in the middle and high on both sides. When the electron spin polarization is not uniform in the longitudinal direction, the following three situations will occur: the magnetometer response decreases first and then increases, the magnetometer response increases first and then decreases, and the magnetometer response increases, decreases, increases, and decreases. In summary, the above six situations cover the situations that occur when the electron spin polarization is longitudinally non-uniform during unidirectional pumping and counter-pumping.

[0061] The calculation method of step 8 is to obtain the SERF atomic magnetometer calibration coefficient corresponding to each measurement point, calculate the average value and standard deviation of the calibration coefficient, calculate the standard deviation divided by the average value, and divide the value of the calibration coefficient standard deviation by the average value as the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity. Thus, the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity is measured.

[0062] The SERF atomic magnetometer electron spin longitudinal polarization optimization method based on the inhomogeneity measurement results includes the following steps:

[0063] Step 1: Build the magnetometer configuration.

[0064] Step 2, turn on the two lasers in the magnetometer system.

[0065] Step 3, heating the alkali metal atom gas chamber using a temperature control system and an electric heating oven.

[0066] Step 4: Adjust the pumping laser frequency.

[0067] Step 5: Use a current source to apply current to the magnetic compensation coil to compensate for the residual magnetic field and the virtual magnetic field caused by the optical frequency shift.

[0068] Step 6: Adjust the position of the detection light so that the light spot of the detection light is aligned with the preset measurement point.

[0069] Step 7: Measure the scale factor of the magnetometer and record it.

[0070] Step 8, determine whether the measurement of all measurement points is completed, if not, return to step 6, if yes, go to step 9.

[0071] Step 9, according to the recorded magnetometer scale factor at each measuring point, calculate the average value of the scale factor at different positions and the longitudinal inhomogeneity of the electron spin polarization of the SERF atomic magnetometer.

[0072] Step 10, weighted calculation to obtain the longitudinal electron spin polarization performance of the SERF atomic magnetometer.

[0073] Step 11, determining whether the maximum value of the longitudinal electron spin polarization performance of the SERF atomic magnetometer is found, if not, returning to step 4, if yes, proceeding to step 12.

[0074] Step 12, adjusting the pumping laser frequency to the frequency at which the longitudinal electron spin polarization performance is maximized, and the longitudinal electron spin polarization optimization of the SERF atomic magnetometer is completed.

[0075] Among them, steps 1, 2, 3, 5, 6, 7, 8, and 9 are the same as the operation methods in the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement method, and will not be described in detail here.

[0076] The calculation method of step 10 is to obtain the SERF atomic magnetometer scale coefficient corresponding to each measurement point, calculate the average value and standard deviation of the scale coefficient, calculate the size of the standard deviation divided by the average value, and divide the value of the scale coefficient standard deviation by the average value as the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity. Thus, the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity is measured. Then, the scale coefficient average value under different frequency conditions is normalized, the electron spin polarization longitudinal inhomogeneity under different frequency conditions is normalized, and then the normalized electron spin polarization longitudinal inhomogeneity is subtracted from 1 to obtain the normalized electron spin polarization longitudinal uniformity, and the normalized scale coefficient average value and the normalized electron spin polarization longitudinal uniformity are each multiplied by a weight of 1 / 2, and then added to obtain a total optimized evaluation value, which is defined as the longitudinal electron spin polarization performance.

[0077] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A method for measuring longitudinal inhomogeneity of electron spin polarization of a SERF atomic magnetometer, characterized in that: The following steps are involved: Step 1, starting the SERF atomic magnetometer system, pumping light passes through the alkali metal atomic gas chamber along the y-axis direction, and presetting m detection light positions on the pumping light path in the alkali metal atomic gas chamber to be used as measurement points of the magnetometer calibration coefficient, where m is an integer greater than 1; Step 2, detecting the smooth x-axis direction passing through the alkali metal atomic gas chamber and aligning each measuring point one by one, and obtaining the SERF atomic magnetometer calibration coefficient corresponding to each measuring point; Step 3, calculate the average value and standard deviation of the calibration coefficient, calculate the size of the standard deviation divided by the average value, and the value of the calibration coefficient standard deviation divided by the average value is the longitudinal inhomogeneity of the electron spin polarization of the SERF atomic magnetometer.

2. The SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement method according to claim 1, characterized in that: During unidirectional pumping, the longitudinal inhomogeneity of electron spin polarization includes the following three situations: the magnetometer response first increases and then decreases, the magnetometer response keeps increasing, and the magnetometer response keeps decreasing.

3. The SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement method according to claim 1, characterized in that: During bidirectional pumping, the longitudinal inhomogeneity of electron spin polarization includes the following three situations: the magnetometer response first decreases and then increases, the magnetometer response first increases and then decreases, and the magnetometer response increases, decreases, increases, and decreases.

4. The SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement method according to claim 1, characterized in that: The larger the value of the scale factor standard deviation divided by the average value is, the more non-uniform the electron spin polarization of the SERF atomic magnetometer is, and vice versa, the more uniform it is.

5. The SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement method according to claim 1, characterized in that: The SERF atomic magnetometer system includes a first laser, a first polarization-maintaining optical fiber, a first collimator, a quarter-wave plate, and an alkali metal atom gas chamber connected in series in sequence, wherein the alkali metal atom gas chamber is located in an electric heating oven, the electric heating oven is located in a coil, the coil is located in a magnetic shielding barrel, the coil is connected to a current source, the electric heating oven is connected to a temperature control system, and the first laser emits pumping light.

6. The SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement method according to claim 1, characterized in that: The detection light comes from a second laser, and the second laser is connected to a signal processing system in sequence through a second collimator, a linear polarizer, an aperture, an alkali metal atom gas chamber, a half-wave plate, a polarization beam splitter prism and a differential photodetector. The second collimator is arranged on a first displacement stage, the aperture is arranged on a second displacement stage, the polarization beam splitter prism is arranged on a third displacement stage, and the differential photodetector is arranged on a fourth displacement stage.

7. A SERF atomic magnetometer electron spin longitudinal polarization optimization method based on inhomogeneity measurement results, characterized in that: The following steps are involved: Step 1, start the SERF atomic magnetometer system, first adjust the pumping light frequency to resonate with the D1 line frequency of the alkali metal atom, and preset the pumping light frequency adjustment step; Step 2, using the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity measurement method as described in any one of claims 1 to 6, by measuring, both the average value of the scale coefficient at different positions and the SERF atomic magnetometer electron spin polarization longitudinal inhomogeneity can be obtained; Step 3, change the pumping light frequency according to the preset frequency adjustment step size, and measure the longitudinal inhomogeneity of the SERF atomic magnetometer's electron spin polarization each time the frequency is adjusted to obtain the average value of the scale coefficient at different positions and the longitudinal inhomogeneity of the SERF atomic magnetometer's electron spin polarization; normalize the average value of the scale coefficient under different frequency conditions, normalize the longitudinal inhomogeneity of the electron spin polarization under different frequency conditions, and then subtract the normalized longitudinal inhomogeneity of the electron spin polarization from 1 to obtain the normalized longitudinal uniformity of the electron spin polarization, multiply the normalized scale coefficient average value and the normalized longitudinal uniformity of the electron spin polarization by a weight of 1 / 2, and then add them together to obtain the total optimized evaluation value, which is defined as the longitudinal electron spin polarization performance. Until the maximum value of the longitudinal electron spin polarization performance of the SERF atomic magnetometer is found; Step 4, adjust the pumping laser frequency to the frequency at which the longitudinal electron spin polarization performance is maximized, and the SERF atomic magnetometer longitudinal electron spin polarization optimization is completed.

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