Method for measuring alkali metal atom equilibrium spin polarizability based on three-axis magnetic field steady-state response

Abstract

A method for measuring alkali metal atom equilibrium spin polarizability based on three-axis magnetic field steady-state response comprises the following steps: firstly, adjusting a device to a normal working state, then applying direct-current magnetic fields in x, y, y and z directions, changing the size of the magnetic field in the z direction, fitting the ratio of two outputs of the device with the square of the magnetic field applied in the z direction to obtain the size of the total relaxation rate, and finally measuring the alkali metal atom equilibrium spin polarizability. Obtaining the pressure broadening of the alkali metal air chamber by using the optical depth of the detection light at a low temperature, then changing the power of the detection light at a normal working temperature, establishing a transfer coefficient by using the pressure broadening and a fitting slope, and finally applying a direct-current magnetic field on a y axis and changing the size of the direct-current magnetic field, and fitting the relationship between the output of the device and the By-fit, so as to obtain the alkali metal air chamber. The final balance spin polarizability is obtained by combining the transfer coefficient, the SERF state required by normal work of the system is not damaged, the influence of temperature is avoided, the measurement error is small, and a more accurate measurement means is provided for further optimizing an SERF magnetic field measurement device to improve the sensitivity of the SERF magnetic field measurement device.

Description

Technical Field

[0001] The present invention relates to the technical field of SERF atomic magnetic field measurement of alkali metal atomic spin polarization detection, and particularly to a method for measuring the equilibrium spin polarization of alkali metal atoms based on a three-axis magnetic field steady-state response. Background Art

[0002] Ultra-high-sensitivity magnetic field measurement based on the spin exchange relaxation free regime (SERF) effect of atomic spins has benefited from the development of quantum technology and currently has the world's highest magnetic field measurement sensitivity, which can reach aT (1aT=10 -18 SERF-based atomic spin effects can be applied to fields such as cardio-cerebral magnetic measurement, magnetic material analysis, magnetic anomaly detection, and basic physics research.

[0003] The output of a SERF magnetic field measurement device is related to the equilibrium spin polarization of the alkali metal atoms. When the equilibrium spin polarization reaches 0.5, the device reaches its maximum output response. The uniformity of the spatial distribution of the polarization within the alkali metal chamber is also closely related to the device's differential sensitivity. Therefore, a method for measuring the equilibrium spin polarization of alkali metal atoms within an alkali metal chamber is needed.

[0004] Researchers have proposed various methods for measuring the spin polarizability of alkali metal atoms: electron paramagnetic resonance, pump light intensity attenuation, near-resonance frequency, and slowing-down factor methods. For SERF magnetic field measurement devices, the electron paramagnetic resonance method requires a G-level magnetic field for measurement. The presence of a large magnetic field disrupts the atomic SERF state, preventing the device from functioning properly. The pump light intensity attenuation method requires complete transmission of the pump light, but SERF magnetic field measurement devices operate at high temperatures and have a large optical depth, preventing complete transmission of the pump light. The near-resonance detection method requires low temperatures, which does not meet the operating conditions of SERF magnetic field measurement devices. The slowing-down factor method produces large errors when used at large optical depths. Currently available methods for measuring the polarizability of alkali metal atoms are difficult to implement under SERF state conditions and suffer from low accuracy. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention provides a method for measuring the equilibrium spin polarization rate of alkali metal atoms based on a steady-state response of a three-axis magnetic field. A DC magnetic field is applied along the x, y, and y, z axes to obtain the magnitude of the total relaxation rate in the alkali metal chamber at that position through fitting. The pressure broadening of the alkali metal chamber is obtained by utilizing the optical depth of the detection light, and the atomic number density is obtained by varying the power of the detection light, thereby calculating the transfer coefficient. Furthermore, a DC magnetic field is applied along the y axis and fitted to obtain the final equilibrium spin polarization rate in combination with the transfer coefficient. This method does not destroy the SERF state required for the normal operation of the system, is not affected by temperature, and has a small measurement error. This method provides a more accurate parameter measurement method for further optimizing a SERF magnetic field measurement device to improve its sensitivity.

[0006] The technical solutions of the present invention are as follows: A method for measuring the equilibrium spin polarizability of alkali metal atoms based on a three-axis magnetic field steady-state response, characterized by comprising the following steps: Step 1: Adjust the SERF magnetic field measuring device to a normal working state; Step 2: Apply an x-axis DC magnetic field B x and the y-axis DC magnetic field B y The first output V1 of the SERF magnetic field measurement device is obtained by applying B y and the z-axis DC magnetic field B z Obtaining a second output V2 of the SERF magnetic field measurement device; Step 3, change B z The size of the two responses is recorded and compared with B z The square of the fitting is fitted, and the total relaxation rate R is obtained according to the fitting slope. tot ; Step 4, measuring the pressure broadening at low temperature, which is 120°C ± 20°C; Step 5: Change the detection optical power and calculate the transfer function K; Step 6: Apply B y And change B y The magnitude of , records the magnetometer response; Step 7, Fitting the response to B y-fit , B y-fit Yes and B y The size-dependent quantity, the equilibrium spin polarization P0, is obtained using the fitting slope and K.

[0007] Step 1 includes setting the temperature of the alkali metal gas chamber to 160-200°C, adjusting the three-axis magnetic compensation coil, and using three-dimensional in-situ magnetic compensation technology to compensate for the system residual magnetism. First, cross-compensate the x-axis residual magnetism and the z-axis residual magnetism, and then compensate for the y-axis residual magnetism, so that the SERF magnetic field measurement device operates in the SERF state.

[0008] Step 2Bx =0.05nT,B y =0.5nT,B z =0.05nT; B in step 3 z The range of variation is 0.05 nT to 0.25 nT; the B applied in step 6 y =0.1nT,B y The range of variation is 0.1nT~0.5nT.

[0009] Step 3 includes the following relationships: Where β is the intermediate vector, β x is the x-axis component of β, β y is the y-axis component of β, β z is the z-axis component of β, γ e is the gyromagnetic ratio, B is the triaxial magnetic field, R tot is the total relaxation rate, K OD is the fitting slope, I out is the power of the detection light emitted from the alkali metal gas cell, I in It is used to detect the power of light incident on the alkali metal gas cell.

[0010] Step 5 includes the following relationship: , Where G is the conversion coefficient between the light power received by the photodetector and the output voltage, α is the modulation angle of the photoelastic modulator, e is a natural constant, OD is the optical depth of the detection light, ξ is the attenuation coefficient of the glass to the detection light power, and ν pr is the frequency of the detection light, ν D1 is the D1 line resonance frequency of the alkali metal atom, Γ D1 It is the pressure broadening of the D1 line of alkali metal atoms.

[0011] Step 7 includes the following relationship: where V0 is the output of the device when a magnetic field is applied only along the y-axis, and P0 is the equilibrium spin polarization.

[0012] In step 1, the SERF magnetic field measurement device includes a detection optical path passing through the alkali metal gas chamber along the x-axis, and a pumping optical path passing through the alkali metal gas chamber along the z-axis. The alkali metal gas chamber is located in a non-magnetic electric heating system, and the non-magnetic electric heating system is located in a three-axis magnetic compensation coil. The three-axis magnetic compensation coil is located in a magnetic shielding barrel, and the three-axis magnetic compensation coil is connected to a host computer through a function generator.

[0013] The detection optical path includes a detection laser, a second 1 / 2 wave plate, a second polarization beam splitter, a polarizer, a photoelastic modulator, a second 1 / 4 wave plate, an alkali metal gas chamber, a polarizer, a second convex lens, a photodetector, a phase-locked amplifier and a host computer, which are connected in sequence. The phase-locked amplifier is connected to the photoelastic modulator through a modulation controller.

[0014] The pumping optical path includes a pumping laser, a concave lens, a first convex lens, a reflecting mirror, a first 1 / 2 wave plate, a first polarization beam splitter prism, a first 1 / 4 wave plate and an alkali metal gas chamber which are connected in sequence.

[0015] The technical effects of the present invention are as follows: The present invention is based on a method for measuring the equilibrium spin polarization rate of alkali metal atoms based on a three-axis magnetic field steady-state response. First, the device is adjusted to a normal working state, and then a DC magnetic field is applied in the x, y and y, z directions. The magnitude of the magnetic field in the z direction is changed. The ratio of the output of the two devices is fitted with the square of the magnetic field applied in the z direction to obtain the magnitude of the total relaxation rate. Next, the optical depth of the detection light is used to obtain the value of the pressure broadening of the alkali metal gas chamber at low temperature. Then, the power of the detection light is changed at normal operating temperature to obtain the number density of alkali metal atoms. The transfer coefficient is calculated using the pressure broadening and the alkali metal number density. Finally, a DC magnetic field is applied to the y-axis and its magnitude is changed. The output of the fitting device is fitted with B y-fit The relationship between the two, combined with the transfer coefficient, is used to obtain the final equilibrium spin polarization rate, which can maintain the SERF state required for the normal operation of the system, is not affected by temperature, and has a small measurement error. This provides a more accurate parameter measurement method for further optimizing the SERF magnetic field measurement device to improve its sensitivity.

[0016] The advantages of the present invention over the prior art are: (1) changing the size of the magnetic field for fitting can reduce the influence of inaccurate coil constant calibration and residual magnetic field; (2) using the optical depth of the detection light and changing the power of the detection light to calculate the number density of alkali metal atoms can reduce the error caused by directly calculating the density using temperature; (3) this method will not destroy the SERF state of normal operation of the system; (4) this method can simultaneously measure the size of the total relaxation rate and the equilibrium spin polarization rate of the alkali metal atoms; (5) this method does not require additional modulation, is simple to operate, and has a small measurement error. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the structure of the SERF magnetic field measurement device involved in the method of measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to the present invention. SERF is the Spin Exchange Relaxation Free Regime.

[0018] Figure 2It is a schematic flow chart of the method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to the present invention. Figure 2 The method includes the following steps: 1. adjusting the SERF magnetic field measuring device to a normal working state; 2. applying an x-axis DC magnetic field B x and the y-axis DC magnetic field B y The first output V1 of the SERF magnetic field measurement device is obtained by applying B y and the z-axis DC magnetic field B z Get the second output V2 of the SERF magnetic field measuring device; Step 3, change B z The size of the two responses is recorded and compared with B z The square of the fitting is fitted, and the total relaxation rate R is obtained according to the fitting slope. tot ; Step 4, measure the pressure broadening at low temperature, the low temperature is 120℃±20℃; Step 5, change the detection light power and calculate the transfer function K; Step 6, apply B y And change B y The size of the magnetometer is recorded; Step 7, fit the response to B y-fit , B y-fit Yes and B y The size-dependent quantity, the equilibrium spin polarization P0, is obtained using the fitting slope and K.

[0019] The figure numbers are explained as follows: 1-pumping laser; 2-concave lens; 3-first convex lens; 4-reflecting mirror; 5-first 1 / 2 wave plate; 6-first polarization beam splitter prism; 7-first 1 / 4 wave plate; 8-magnetic shielding barrel; 9-three-axis magnetic compensation coil; 10-non-magnetic electric heating system; 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-second convex lens; 20-photodetector; 21-modulation controller; 22-phase-locked amplifier; 23-function generator; 24-host computer; xyz-three axes of Cartesian coordinate system (x-axis, y-axis, z-axis). DETAILED DESCRIPTION

[0020] Below is the attached figure ( Figure 1-Figure 2 ) and Examples illustrate the present invention.

[0021] Figure 1 It is a structural schematic diagram of a SERF magnetic field measurement device involved in the method of measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to the present invention. Figure 2 This is a flow chart of the method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to the present invention. Figures 1 to 2As shown, the method for measuring the equilibrium spin polarization rate of alkali metal atoms based on the steady-state response of the three-axis magnetic field includes the following steps: Step 1, adjusting the SERF magnetic field measurement device to a normal working state; Step 2, applying an x-axis DC magnetic field B x and the y-axis DC magnetic field B y The first output V1 of the SERF magnetic field measurement device is obtained by applying B y and the z-axis DC magnetic field B z Get the second output V2 of the SERF magnetic field measuring device; Step 3, change B z The size of the two responses is recorded and compared with B z The square of the fitting is fitted, and the total relaxation rate R is obtained according to the fitting slope. tot ; Step 4, measure the pressure broadening at low temperature, the low temperature is 120℃±20℃; Step 5, change the detection light power and calculate the transfer function K; Step 6, apply B y And change B y The size of the magnetometer is recorded; Step 7, fit the response to B y-fit , B y-fit Yes and B y The size-dependent quantity, the equilibrium spin polarization P0, is obtained using the fitting slope and K.

[0022] Step 1 includes setting the temperature of the alkali metal gas chamber to 160-200°C, adjusting the three-axis magnetic compensation coil, and using three-dimensional in-situ magnetic compensation technology to compensate for the system residual magnetism. First, cross-compensate the x-axis residual magnetism and the z-axis residual magnetism, and then compensate the y-axis residual magnetism, so that the SERF magnetic field measurement device works in the SERF state. Step 2 B x =0.05nT,B y =0.5nT,B z =0.05nT; B in step 3 z The range of variation is 0.05 nT to 0.25 nT; the B applied in step 6 y =0.1nT,B y The range of variation is 0.1nT~0.5nT.

[0023] Step 3 includes the following relationships: Where β is the intermediate vector, β x is the x-axis component of β, β y is the y-axis component of β, β z is the z-axis component of β, γ e is the gyromagnetic ratio, B is the triaxial magnetic field, R tot is the total relaxation rate, K OD is the fitting slope, I out is the power of the detection light emitted from the alkali metal gas cell, I inIt is used to detect the power of light incident on the alkali metal gas cell.

[0024] Step 5 includes the following relationship: , Where G is the conversion coefficient between the light power received by the photodetector and the output voltage, α is the modulation angle of the photoelastic modulator, e is a natural constant, OD is the optical depth of the detection light, ξ is the attenuation coefficient of the glass to the detection light power, and ν pr is the frequency of the detection light, ν D1 is the D1 line resonance frequency of the alkali metal atom, Γ D1 It is the pressure broadening of the D1 line of alkali metal atoms.

[0025] Step 7 includes the following relationship: where V0 is the output of the device when a magnetic field is applied only along the y-axis, and P0 is the equilibrium spin polarization.

[0026] In step 1, the SERF magnetic field measurement device includes a detection optical path passing through the alkali metal gas cell along the x-axis and a pumping optical path passing through the alkali metal gas cell along the z-axis. The alkali metal gas cell is located within a non-magnetic electric heating system, which is located within a three-axis magnetic compensation coil. The three-axis magnetic compensation coil is located within a magnetic shielding barrel, and the three-axis magnetic compensation coil is connected to a host computer via a function generator. The detection optical path includes a detection laser, a second half-wave plate, a second polarization beam splitter prism, a polarizer, a photoelastic modulator, a second quarter-wave plate, the alkali metal gas cell, an analyzer, a second convex lens, a photodetector, a lock-in amplifier, and a host computer, connected in sequence. The lock-in amplifier is connected to the photoelastic modulator via a modulation controller. The pumping optical path includes a pump laser, a concave lens, a first convex lens, a reflector, a first half-wave plate, a first polarization beam splitter prism, a first quarter-wave plate, and the alkali metal gas cell, connected in sequence.

[0027] A method for measuring the equilibrium spin polarization of alkali metal atoms in a SERF magnetic field measurement device based on the steady-state response of a three-axis magnetic field is used to measure the equilibrium spin polarization of alkali metal atoms. A DC magnetic field is applied along the x-, y-, and y-z axes, and the total relaxation rate is obtained by fitting the ratio of the two steady-state responses with the square of the applied z-axis magnetic field. The number density of alkali metal atoms is determined using the optical depth of the detection light, and the pressure broadening of the alkali metal gas chamber is accurately measured at low temperatures. The transfer coefficient between the x-component of the atomic spin polarization and the device output response is then calculated. A DC magnetic field is then applied along the y-axis, varying its magnitude. The equilibrium spin polarization is then obtained by fitting the device's steady-state output response and combining the transfer coefficient. This method maintains the SERF state of the system, is unaffected by temperature, and offers minimal measurement error and uncertainty. The atomic equilibrium spin polarization is a critical parameter of a SERF magnetic field measurement device. Accurate measurement of the polarization ensures device optimization and is crucial for improving the device's differential measurement sensitivity.

[0028] The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field comprises the following steps: Step 1: Build a SERF magnetic field measurement device, set the alkali metal gas chamber temperature to 160-200°C, adjust the three-axis magnetic compensation coil, and use three-dimensional in-situ magnetic compensation technology to compensate for the system's residual magnetism (cross-compensating the magnetic fields in the x and z directions, and finally compensating the magnetic field in the y direction) to make the device operate in the SERF state; Step 2: Apply a DC magnetic field on the x-axis, y-axis, and y-z-axis, respectively, to obtain two outputs V1 and V2 of the device. Change the magnitude of the magnetic field applied on the z-axis, fit V1 / V2 to the square of the z-axis magnetic field, and obtain the magnitude of the total relaxation rate based on the fitting slope. Step 3: Change the frequency of the detection light at low temperature (around 120°C) and use the relationship between the optical depth of the detection light and the frequency detuning to obtain the pressure broadening of the alkali metal gas cell; Step 4: Under normal operating temperature, the power of the detection light incident on the alkali metal gas cell is changed, and the optical depth of the detection light is used to fit the power of the detection light incident on and exiting the alkali metal gas cell, and information on the number density of alkali metal atoms is obtained based on the slope of the fitted power. Step 5: Calculate the transfer coefficient K between the x-direction component of the atomic spin polarizability and the device output response based on the pressure broadening and alkali metal atomic number density obtained in Steps 3 and 4; Step 6: Apply a DC magnetic field along the y-axis and change its magnitude. Fit the output of the device to B. y-fit The relationship between the transfer coefficient K and the equilibrium spin polarization P0 is represented by the slope. Step 7: Calculate the equilibrium spin polarization P0 based on the transfer coefficient K obtained in step 5 and the product of the transfer coefficient K obtained in step 6 and the equilibrium spin polarization P0.

[0029] In step 2, the magnitude of the magnetic field applied in the x direction is 0.05 nT, the magnitude of the magnetic field applied in the y direction is 0.5 nT, and the magnitude of the magnetic field applied in the z direction is 0.05~0.05~0.25 nT; in step 6, the magnitude of the magnetic field applied in the y direction is 0.1~0.1~0.5 nT.

[0030] It mainly includes the following relationships: , Where V1 and V2 are the outputs of the device applying DC magnetic field on the x, y and y, z axes respectively, β = Bγ e / R tot , B = [β x , β y , β z ] T is the magnitude of the magnetic field applied on the three axes, γ e is the gyromagnetic ratio, R tot is the total relaxation rate.

[0031] , Among them I out and I in is the power of the detection light exiting and entering the alkali metal gas cell, and its fitting slope K OD Contains information about the number density of alkali metal atoms; K is the transfer coefficient, G is the conversion coefficient between the light power received by the photodetector and the output voltage, α is the modulation angle of the photoelastic modulator, OD is the optical depth of the detection light, ξ is the attenuation coefficient of the glass to the detection light power, ν pr is the frequency of the detection light, ν D1 is the D1 line resonance frequency of the alkali metal atom, Γ D1 is the pressure broadening value of the D1 line of alkali metal atoms.

[0032] , Where V0 is the output of the device when the magnetic field is applied only in the y-axis, P0 is the equilibrium spin polarization, and B y-fit =γ e R tot β y / (R 2 tot +(γ e B y ) 2 ) is a term related to the magnitude of the magnetic field applied on the y-axis.

[0033] The pumping light is emitted by a distributed Bragg laser (DBL) with a frequency matching the D1 line resonance peak of alkali metal atoms. It passes through a beam expansion system consisting of concave and convex lenses, outputting a pumping laser beam with a diameter comparable to the diameter of the alkali metal gas chamber. This light is converted by a quarter-wave plate into circularly polarized light before entering the alkali metal gas chamber to polarize the alkali metal atoms. The detection light, emitted by a DBL with a frequency detuned to 150 GHz from the D1 line resonance peak of alkali metal atoms, is converted by a polarizer into linearly polarized light before entering the alkali metal gas chamber for optical rotation angle detection. The system includes a magnetic shielding and three-axis magnetic compensation system to shield against external magnetic fields and generate the magnetic field signals required for measurement. A non-magnetic electric heating system is included to heat the alkali metal gas chamber to the temperature required for the SERF state. A signal acquisition system is also included to collect the optical rotation angle information carried by the detection light.

[0034] The alkali metal atoms in the alkali metal gas chamber are one of potassium, rubidium and cesium, and the interior is filled with buffer gas helium and quenching gas nitrogen.

[0035] The pump laser emits laser light that passes through a concave lens, a first convex lens, a reflector, a first half-wave plate, a first polarization beam splitter, and a first quarter-wave plate, converting it into circularly polarized pump light before entering the alkali metal gas chamber to polarize the alkali metal atoms. The detection laser emits laser light that passes through a second half-wave plate, a second polarization beam splitter, a polarizer, a photoelastic modulator, a second quarter-wave plate, the alkali metal gas chamber, an analyzer, and a second convex lens before entering a photodetector. The optical signal is converted into an electrical signal and then transmitted via a coaxial cable to a lock-in amplifier. The lock-in amplifier is connected to a modulation controller and a host computer, respectively, and the modulation controller is connected to the photoelastic modulator. The magnetic field measurement device is sequentially arranged from the center of the alkali metal gas chamber outward, comprising a non-magnetic electric heating system, a three-axis magnetic compensation coil, and a magnetic shielding barrel.

[0036] The photoelastic modulator is driven by a modulation controller. The electrical signal and the reference signal of the modulation controller are demodulated by a phase-locked amplifier to obtain the DC component, the first harmonic component and the second harmonic component of the detection electrical signal, and are fed back to the host computer for real-time display.

[0037] The principle of the method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field is as follows: Assuming the pumping light direction is along the z-axis and the detection light direction is along the x-axis, the output equation of the device can be expressed as: , Where P0 = R op / R tot is the value of the equilibrium spin polarization in the absence of a magnetic field, β = Bγ e / R tot , B = [B x , B y , Bz ] T is the external magnetic field, R tot = R op + R rel is the total relaxation rate, K is the transfer coefficient between the polarizability along the detection light direction and the response of the magnetometer, which is related to the pressure broadening of the alkali metal cell and the alkali metal number density.

[0038] When a DC magnetic field is applied in the x, y and y, z directions and the magnitude of the magnetic field in the z direction is changed, the total relaxation rate can be calculated by the slope of the following expression: , By using the optical depth of the detection light and changing the power of the detection light, the following expression can be obtained: , Among them, I out is the power of the detection light exiting the alkali metal gas cell, I in is the power of the detection light incident on the alkali metal gas cell, and the slope K OD The information about the pressure broadening of the alkali metal cell and the number density of alkali metal atoms can be used to establish a relationship with the transfer coefficient: , Where G is the conversion coefficient between the optical power input to the photodetector and the output voltage, α is the modulation angle of the photoelastic modulator, OD is the optical depth of the detection light, ξ is the attenuation coefficient of the glass to the detection light power, and ν pr is the frequency of the detection light, ν D1 is the D1 line resonance frequency of the alkali metal atom, Γ D1 is the pressure broadening value of the D1 line of alkali metal atoms.

[0039] When a DC magnetic field is applied in the y direction and the magnitude of the magnetic field in the y direction is changed, the following expression can be obtained: , Where V0 is the output of the device when the magnetic field is applied only on the y-axis, B y-fit It is related to the magnitude of the y-axis magnetic field. The equilibrium spin polarization P0 can be obtained based on the slope of the above formula and the value of the transfer coefficient K.

[0040] 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 method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field, characterized in that: The following steps are involved: Step 1: Adjust the SERF magnetic field measuring device to a normal working state; Step 2: Apply an x-axis DC magnetic field B x and the y-axis DC magnetic field B y The first output V1 of the SERF magnetic field measurement device is obtained by applying B y and the z-axis DC magnetic field B z Obtaining a second output V2 of the SERF magnetic field measurement device; Step 3, change B z The size of the two responses is recorded and compared with B z The square of the fitting is fitted, and the total relaxation rate R is obtained according to the fitting slope. tot ; Step 4, measuring the pressure broadening at low temperature, which is 120°C ± 20°C; Step 5: Change the detection optical power and calculate the transfer function K; Step 6: Apply B y And change B y The magnitude of , records the magnetometer response; Step 7, Fitting the response to B y-fit , B y-fit Yes and B y The size-dependent quantity, the equilibrium spin polarization P0, is obtained using the fitting slope and K.

2. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to claim 1, characterized in that: Step 1 includes setting the temperature of the alkali metal gas chamber to 160-200°C, adjusting the three-axis magnetic compensation coil, and using three-dimensional in-situ magnetic compensation technology to compensate for the system residual magnetism. First, cross-compensate the x-axis residual magnetism and the z-axis residual magnetism, and then compensate for the y-axis residual magnetism, so that the SERF magnetic field measurement device operates in the SERF state.

3. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to claim 1, characterized in that: Step 2B x =0.05nT,B y =0.5nT,B z =0.05nT; B in step 3 z The range of variation is 0.05nT~0.25nT; the B applied in step 6 y =0.1nT,B y The range of variation is 0.1nT~0.5nT.

4. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to claim 1, characterized in that: Step 3 includes the following relationships: Where β is the intermediate vector, β x is the x-axis component of β, β y is the y-axis component of β, β z is the z-axis component of β, γ e is the gyromagnetic ratio, B is the triaxial magnetic field, R tot is the total relaxation rate, K OD is the fitting slope, I out is the power of the detection light emitted from the alkali metal gas cell, I in It is used to detect the power of light incident on the alkali metal gas cell.

5. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to claim 4, characterized in that: Step 5 includes the following relationship: ， Where G is the conversion coefficient between the light power received by the photodetector and the output voltage, α is the modulation angle of the photoelastic modulator, e is a natural constant, OD is the optical depth of the detection light, ξ is the attenuation coefficient of the glass to the detection light power, and ν pr is the frequency of the detection light, ν D1 is the D1 line resonance frequency of the alkali metal atom, Γ D1 It is the pressure broadening of the D1 line of alkali metal atoms.

6. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to claim 5, characterized in that: Step 7 includes the following relationship: where V0 is the output of the device when a magnetic field is applied only along the y-axis, and P0 is the equilibrium spin polarization.

7. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to claim 1, characterized in that: In step 1, the SERF magnetic field measurement device includes a detection optical path passing through the alkali metal gas chamber along the x-axis, and a pumping optical path passing through the alkali metal gas chamber along the z-axis. The alkali metal gas chamber is located in a non-magnetic electric heating system, and the non-magnetic electric heating system is located in a three-axis magnetic compensation coil. The three-axis magnetic compensation coil is located in a magnetic shielding barrel, and the three-axis magnetic compensation coil is connected to a host computer through a function generator.

8. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to claim 7, characterized in that: The detection optical path includes a detection laser, a second 1 / 2 wave plate, a second polarization beam splitter, a polarizer, a photoelastic modulator, a second 1 / 4 wave plate, an alkali metal gas chamber, a polarizer, a second convex lens, a photodetector, a phase-locked amplifier and a host computer, which are connected in sequence. The phase-locked amplifier is connected to the photoelastic modulator through a modulation controller.

9. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a three-axis magnetic field according to claim 7, characterized in that: The pumping optical path includes a pumping laser, a concave lens, a first convex lens, a reflecting mirror, a first 1 / 2 wave plate, a first polarization beam splitter prism, a first 1 / 4 wave plate and an alkali metal gas chamber which are connected in sequence.

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