Method for measuring equilibrium spin polarizability of alkali metal atoms based on triaxial magnetic field steady-state response

Abstract

A method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field is proposed. First, the device is adjusted to its normal operating state. Then, DC magnetic fields are applied in the x, y, and y, z directions, with the magnitude of the magnetic field in the z direction varied. The ratio of the device outputs in the two applications is fitted with the square of the applied magnetic field in the z direction to obtain the total relaxation rate. Next, the pressure broadening of the alkali metal gas cell is obtained at low temperature using the optical depth of the detection light. Then, at the normal operating temperature, the power of the detection light is varied, and the transfer coefficient is established using the pressure broadening and the fitting slope. Finally, a DC magnetic field is applied along the y-axis with varying magnitude, and the device output is fitted with the B... y‑fit The relationship between these factors, combined with the transfer coefficient, yields the final equilibrium spin polarization. This method does not disrupt the SERF states required for normal system operation, is unaffected by temperature, and has small measurement errors. It provides a more accurate measurement method for further optimizing SERF magnetic field measurement devices to improve their sensitivity.

Description

Technical Field

[0001] This invention relates to the field of SERF atomic magnetic field measurement and alkali metal atom spin polarizability detection technology, specifically to a method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field. Background Technology

[0002] Ultra-sensitive magnetic field measurements based on the spin-free exchange relaxation (SERF) effect of atomic spin benefit from the development of quantum technology and currently possess the world's highest magnetic field measurement sensitivity, reaching aT (1aT=10^27). -18 The order of magnitude is on the order of T. Based on the SERF atomic spin effect, applications can be made in fields such as heart and brain magnetometry, magnetic material analysis, magnetic anomaly detection, and fundamental physical science research.

[0003] The output of the SERF magnetic field measurement device is related to the equilibrium spin polarizability of alkali metal atoms. The device exhibits its maximum output response when the equilibrium spin polarizability reaches 0.5. Furthermore, the uniformity of the spatial distribution of polarizability within the alkali metal chamber is closely related to the device's differential sensitivity. Therefore, a method for measuring the equilibrium spin polarizability 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, including electron paramagnetic resonance (EPR), pump light intensity attenuation, near-resonance frequency (NRFM), and slowing factor methods. For SERF magnetic field measurement devices, EPR requires a magnetic field on the order of G, which disrupts the SERF state conditions and prevents 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 large optical depths, preventing complete transmission. The NRFM method requires low temperatures, which does not meet the operating conditions of SERF magnetic field measurement devices. The slowing factor method introduces significant errors when used at large optical depths. Currently, existing methods for detecting the spin polarizability of alkali metal atoms are difficult to implement under SERF state conditions, resulting in low accuracy. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field. By applying DC magnetic fields along the x, y, and y, z axes, the total relaxation rate within the alkali metal chamber at that location is obtained through fitting. The pressure broadening of the alkali metal chamber is obtained using the optical depth of the detection light, and the atomic number density is obtained by changing the power of the detection light, thereby calculating the transfer coefficient. Finally, by applying a DC magnetic field along the y-axis and fitting the data, the final equilibrium spin polarizability is obtained by combining the transfer coefficient. This method does not disrupt the SERF state required for normal system operation, is unaffected by temperature, and has small measurement errors. It provides a more accurate parameter measurement method for further optimizing SERF magnetic field measurement devices to improve their sensitivity.

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

[0007] A method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field is characterized by comprising the following steps:

[0008] Step 1: Adjust the SERF magnetic field measuring device to normal operating condition;

[0009] Step 2, by applying a DC magnetic field B along the x-axis x and the DC magnetic field B along the y-axis y The first output V1 of the SERF magnetic field measuring device is obtained by applying B. y and z-axis DC magnetic field B z The second output V2 of the SERF magnetic field measuring device is obtained;

[0010] Step 3, change B z The size of the response, the ratio of the two responses, and B are recorded. z The square of the value is used to fit the equation, and the total relaxation rate R is obtained from the slope of the fitting equation. tot ;

[0011] Step 4: Measure the pressure broadening at low temperature, which is 120℃±20℃;

[0012] Step 5: Change the detection optical power and calculate the transfer function K;

[0013] Step 6, apply B y And change B y The magnitude of the magnetometer's response is recorded.

[0014] Step 7, Fit the response to B y-fit B y-fit Is with B y The magnitude correlation coefficient is used to obtain the equilibrium spin polarization P0 using the fitting slope and K.

[0015] Step 1 includes setting the temperature of the alkali metal gas chamber to 160-200℃, adjusting the triaxial magnetic compensation coil, and using three-dimensional in-situ magnetic compensation technology to compensate for the residual magnetism of the system. First, the residual magnetism of the x-axis and z-axis is cross-compensated, and then the residual magnetism of the y-axis is compensated, so that the SERF magnetic field measuring device works in SERF state.

[0016] In step 2, B x =0.05nT, B y =0.5nT, B z =0.05nT; B in step 3 z The variation range is 0.05 nT to 0.25 nT; the B applied in step 6 y =0.1nT, B y The variation range is 0.1nT to 0.5nT.

[0017] Step 3 includes the following relation:

[0018] ,

[0019] Where β is the intermediate vector, β x It is the x-axis component of β, β y It is the y-axis component of β, β z γ is the z-axis component of β. e Where B is the gyromagnetic ratio, and R is the triaxial magnetic field. tot K is the total relaxation rate. OD It is the fitting slope, I out It measures the power of the emitted light from the alkali metal gas cell, I. in It measures the power of light incident on the alkali metal gas cell.

[0020] Step 5 includes the following relation:

[0021] ,

[0022] Where G is the conversion coefficient between the optical power received by the photodetector and the output voltage, α is the modulation angle of the photoelastic modulator, e is the natural constant, OD is the optical depth of the detection light, ξ is the attenuation coefficient of the glass on the detection light power, and ν pr It is the frequency of the light being detected, ν D1 It is the D1 line resonance frequency of alkali metal atoms, Γ D1 It is the pressure broadening of the D1 line of alkali metal atoms.

[0023] Step 7 includes the following relation:

[0024] ,

[0025] 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 measuring 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 inside a non-magnetic electric heating system, which is located inside a triaxial magnetic compensation coil. The triaxial magnetic compensation coil is located inside a magnetic shielding barrel, and the triaxial magnetic compensation coil is connected to a host computer via a function generator.

[0027] The detection optical path includes a detection laser, a second half-wave plate, a second polarizing beam splitter, a polarizer, a photoelastic modulator, a second quarter-wave plate, an 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 through a modulation controller.

[0028] The pump optical path includes a pump laser, a concave lens, a first convex lens, a reflector, a first half-wave plate, a first polarizing beam splitter, a first quarter-wave plate, and an alkali metal gas cell connected in sequence.

[0029] The technical effects of this invention are as follows: This invention is based on a method for measuring the equilibrium spin polarization of alkali metal atoms using a triaxial magnetic field steady-state response. First, the device is adjusted to its normal operating state. Then, 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 is obtained by fitting the ratio of the device outputs in the two steps to the square of the applied magnetic field in the z direction. Next, the pressure broadening value of the alkali metal gas cell is obtained at low temperature using the optical depth of the detection light. Then, at normal operating temperature, the number density of alkali metal atoms is obtained by changing the power of the detection light. 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 then compared with the B... y-fit The relationship between these parameters, combined with the transfer coefficient, yields the final equilibrium spin polarization. This method does not disrupt the SERF states required for normal system operation, is unaffected by temperature, and has small measurement errors. It provides a more accurate parameter measurement method for further optimizing the SERF magnetic field measurement device to improve its sensitivity.

[0030] The advantages of this invention compared with the prior art are: (1) By changing the magnitude of the magnetic field for fitting, the influence of inaccurate coil constant calibration and residual magnetic field can be reduced; (2) By 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, the error caused by directly calculating the density using temperature can be reduced; (3) This method will not destroy the SERF state of the system's normal operation; (4) This method can simultaneously measure the magnitude of the total relaxation rate and the equilibrium spin polarization rate of alkali metal atoms; (5) This method does not require additional modulation, is simple to operate, and has a small measurement error. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the SERF magnetic field measurement device involved in implementing the method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field according to the present invention. SERF stands for Spin Exchange Relaxation Free Regime.

[0032] Figure 2 This is a schematic flowchart illustrating the method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field, as described in this invention. Figure 2 The process includes step 1, adjusting the SERF magnetic field measuring device to normal operating condition; and step 2, applying a DC magnetic field B along the x-axis. x and the DC magnetic field B along the y-axis y The first output V1 of the SERF magnetic field measuring device is obtained by applying B. y and z-axis DC magnetic field B z Obtain the second output V2 of the SERF magnetic field measuring device; Step 3, change B z The size of the response, the ratio of the two responses, and B are recorded. z The square of the value is used to fit the equation, and the total relaxation rate R is obtained from the slope of the fitting equation. tot Step 4: Measure the pressure broadening at low temperature (120℃ ± 20℃); Step 5: Change the detection optical power and calculate the transfer function K; Step 6: Apply B y And change B y Measure the magnitude of the magnetometer and record its response; Step 7, fit the response to B. y-fit B y-fit Is with B y The magnitude correlation coefficient is used to obtain the equilibrium spin polarization P0 using the fitting slope and K.

[0033] The reference numerals in the attached diagram are explained as follows: 1-Pump laser; 2-Concave lens; 3-First convex lens; 4-Reflector; 5-First half-wave plate; 6-First polarizing beam splitter; 7-First quarter-wave plate; 8-Magnetic shielding barrel; 9-Triaxial magnetic compensation coil; 10-Non-magnetic electric heating system; 11-Alkali metal gas chamber; 12-Detection laser; 13-Second half-wave plate; 14-Second polarizing beam splitter; 15-Polarizer; 16-Photoelastic modulator; 17-Second quarter-wave plate; 18-Analyzer; 19-Second convex lens; 20-Photodetector; 21-Modulation controller; 22-Lock-in amplifier; 23-Function generator; 24-Host computer; xyz-Cartesian coordinate system (x-axis, y-axis, z-axis). Detailed Implementation

[0034] The following is in conjunction with the attached diagram ( Figures 1-2 The present invention will be described in conjunction with the embodiments.

[0035] Figure 1 This is a schematic diagram of the SERF magnetic field measuring device involved in implementing the method of measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field according to the present invention. Figure 2 This is a schematic flowchart illustrating the method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field, as described in this invention. (Reference) Figures 1 to 2 As shown, the method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field includes the following steps: Step 1, adjusting the SERF magnetic field measuring device to normal operating condition; Step 2, applying a DC magnetic field B along the x-axis... x and the DC magnetic field B along the y-axis y The first output V1 of the SERF magnetic field measuring device is obtained by applying B. y and z-axis DC magnetic field B z Obtain the second output V2 of the SERF magnetic field measuring device; Step 3, change B z The size of the response, the ratio of the two responses, and B are recorded. z The square of the value is used to fit the equation, and the total relaxation rate R is obtained from the slope of the fitting equation. tot Step 4: Measure the pressure broadening at low temperature (120℃ ± 20℃); Step 5: Change the detection optical power and calculate the transfer function K; Step 6: Apply B y And change B y Measure the magnitude of the magnetometer and record its response; Step 7, fit the response to B. y-fit B y-fit Is with B y The magnitude correlation coefficient is used to obtain the equilibrium spin polarization P0 using the fitting slope and K.

[0036] Step 1 includes setting the alkali metal gas chamber temperature to 160–200°C, adjusting the triaxial magnetic compensation coil, and using three-dimensional in-situ magnetic compensation technology to compensate for system residual magnetism. First, the x-axis and z-axis residual magnetism are cross-compensated, then the y-axis residual magnetism is compensated, so that the SERF magnetic field measuring device operates in SERF mode. Step 2 involves B... x =0.05nT, B y =0.5nT, B z =0.05nT; B in step 3 z The variation range is 0.05 nT to 0.25 nT; the B applied in step 6 y =0.1nT, B y The variation range is 0.1nT to 0.5nT.

[0037] Step 3 includes the following relation:

[0038] ,

[0039] Where β is the intermediate vector, β xIt is the x-axis component of β, β y It is the y-axis component of β, β z γ is the z-axis component of β. e Where B is the gyromagnetic ratio, and R is the triaxial magnetic field. tot K is the total relaxation rate. OD It is the fitting slope, I out It measures the power of the emitted light from the alkali metal gas cell, I. in It measures the power of light incident on the alkali metal gas cell.

[0040] Step 5 includes the following relation:

[0041] ,

[0042] Where G is the conversion coefficient between the optical power received by the photodetector and the output voltage, α is the modulation angle of the photoelastic modulator, e is the natural constant, OD is the optical depth of the detection light, ξ is the attenuation coefficient of the glass on the detection light power, and ν pr It is the frequency of the light being detected, ν D1 It is the D1 line resonance frequency of alkali metal atoms, Γ D1 It is the pressure broadening of the D1 line of alkali metal atoms.

[0043] Step 7 includes the following relation:

[0044] ,

[0045] 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.

[0046] 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 pump 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 triaxial magnetic compensation coil. The triaxial magnetic compensation coil is located within a magnetic shielding container, and the triaxial magnetic compensation coil is connected to a host computer via a function generator. The detection optical path includes, in sequence, a detection laser, a second half-wave plate, a second polarizing beam splitter, 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. The lock-in amplifier is connected to the photoelastic modulator via a modulation controller. The pump optical path includes, in sequence, a pump laser, a concave lens, a first convex lens, a mirror, a first half-wave plate, a first polarizing beam splitter, a first quarter-wave plate, and the alkali metal gas cell.

[0047] A method based on the triaxial magnetic field steady-state response for measuring the equilibrium spin polarizability of alkali metal atoms is used to measure the equilibrium spin polarizability of alkali metal atoms in a SERF magnetic field measurement device. By applying DC magnetic fields along the x and y axes and y and z axes, the total relaxation rate is obtained by fitting the ratio of two steady-state responses with the square of the applied magnetic field magnitude along the z axis. The number density of alkali metal atoms is obtained using the optical depth of the detection light, and the pressure broadening of the alkali metal gas cell is accurately measured at low temperature. The transfer coefficient between the x-axis component of the atomic spin polarizability and the device's output response is then calculated. Next, a DC magnetic field is applied along the y-axis, and its magnitude is varied. By fitting the steady-state output response of the device and combining it with the transfer coefficient, the equilibrium spin polarizability is obtained. This method does not disrupt the SERF state of the system, is unaffected by temperature, has small measurement errors, and low measurement uncertainty. The atomic equilibrium spin polarizability is a crucial parameter of the SERF magnetic field measurement device; accurate measurement of the polarizability ensures the optimization process of the device and is of great significance for improving the differential measurement sensitivity of the device.

[0048] A method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field includes the following steps:

[0049] Step 1: Set up the SERF magnetic field measurement device, set the temperature of the alkali metal gas chamber to 160-200℃, adjust the triaxial magnetic compensation coil, and use three-dimensional in-situ magnetic compensation technology to compensate for the residual magnetism of the system (cross-compensate the magnetic fields in the x and z directions, and finally compensate the magnetic field in the y direction) so that the device works in SERF state.

[0050] Step 2: Apply DC magnetic fields to the x and y axes and the y and z axes respectively to obtain two outputs V1 and V2 of the device. Change the magnitude of the magnetic field applied to the z axis, fit V1 / V2 with the square of the magnitude of the magnetic field on the z axis, and obtain the magnitude of the total relaxation rate based on the fitting slope.

[0051] Step 3: Change the frequency of the detection light at a low temperature (around 120°C) and use the relationship between the optical depth of the detection light and frequency detuning to obtain the pressure broadening of the alkali metal gas cell.

[0052] Step 4: Under normal operating temperature, change the power of the detection light incident on the alkali metal gas cell, use the optical depth of the detection light to fit the power of the detection light incident on and out of the alkali metal gas cell, and obtain the information of the alkali metal atom number density based on its slope.

[0053] Step 5: Based on the pressure broadening and alkali metal atom number density obtained in Steps 3 and 4, calculate the transfer coefficient K between the x-direction component of atomic spin polarizability and the device output response.

[0054] Step 6: Apply a DC magnetic field along the y-axis and change its magnitude; the output of the fitting device is compared with B. y-fitThe relationship between them is that the slope is the product of the transfer coefficient K and the equilibrium spin polarization P0;

[0055] 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.

[0056] 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.

[0057] The main relationships include the following:

[0058] ,

[0059] Where V1 and V2 are the outputs of the devices that apply DC magnetic fields along the x, y, and y, z axes, respectively, and β = Bγ e / R tot B = [β] x , β y , β z ] T γ is the magnitude of the magnetic field applied along the three axes. e R is the gyromagnetic ratio. tot The total relaxation rate is denoted as .

[0060] ,

[0061] Among them I out and I in It measures the power of light emitted from and incident on the alkali metal gas cell, and its fitting slope K OD This includes information on the number density of alkali metal atoms; K is the transfer coefficient, G is the conversion coefficient between the optical 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 on the detection light power, and ν pr It is the frequency of the light being detected, ν D1 It is the D1 line resonance frequency of alkali metal atoms, Γ D1 It is the pressure broadening value of the D1 line of alkali metal atoms.

[0062] ,

[0063] Where V0 is the output of the device when a magnetic field is applied only along the y-axis, P0 is the equilibrium spin polarization, and B... y-fit =γ e R tot β y / (R 2 tot +(γe B y ) 2 ) is a term related to the magnitude of the magnetic field applied along the y-axis.

[0064] The pump light is emitted by a distributed Bragg laser with the same frequency as the D1 line resonance peak of the alkali metal atoms. After passing through a beam expander system composed of concave and convex lenses, the output pump laser is approximately the same diameter as the alkali metal gas cell. This output laser is then converted into circularly polarized light by a quarter-wave plate and enters the alkali metal gas cell to polarize the alkali metal atoms. The detection light is emitted by a distributed Bragg laser with a frequency detuned to the D1 line resonance peak of the alkali metal atoms at 150 GHz. This light is converted into linearly polarized light by a polarizer and incident on the alkali metal gas cell for optical rotation angle detection. The system includes a magnetic shielding and triaxial magnetic compensation system to shield against external magnetic fields and generate the magnetic field signal required for measurement. A non-magnetic electric heating system is included to heat the alkali metal gas cell to the temperature required for the SERF state. A signal acquisition system is included to acquire the optical rotation angle information carried by the detection light.

[0065] The alkali metal atoms in the alkali metal chamber are one of potassium, rubidium, or cesium, and the chamber is filled with buffer gas helium and quenching gas nitrogen.

[0066] The pump laser emits laser light that sequentially passes through a concave lens, a first convex lens, a reflector, a first half-wave plate, a first polarizing beam splitter, and a first quarter-wave plate, converting it into circularly polarized pump light that enters the alkali metal gas cell to polarize alkali metal atoms. The detection laser emits laser light that sequentially passes through a second half-wave plate, a second polarizing beam splitter, a polarizer, a photoelastic modulator, a second quarter-wave plate, the alkali metal gas cell, an analyzer, and a second convex lens before entering a photodetector. The photodetector converts the optical signal into an electrical signal, which is then transmitted to a lock-in amplifier via a coaxial cable. The lock-in amplifier is connected to a modulation controller and a host computer, and the modulation controller is connected to the photoelastic modulator. The magnetic field measuring device, arranged sequentially from the center of the alkali metal gas cell outwards, includes a non-magnetic electric heating system, a triaxial magnetic compensation coil, and a magnetic shielding barrel.

[0067] The photoelastic modulator is driven by a modulation controller. The electrical signal and the reference signal of the modulation controller are demodulated by a lock-in amplifier to obtain the DC component, first harmonic component and second harmonic component of the detection electrical signal, and then fed back to the host computer for real-time display.

[0068] The principle of this invention, based on the steady-state response measurement of triaxial magnetic field to determine the equilibrium spin polarizability of alkali metal atoms, is as follows:

[0069] If the pump light direction is set along the z-axis and the detection light direction is set along the x-axis, then the output equation of the device can be expressed as:

[0070] ,

[0071] Where, P0 = Rop / R tot This 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 B z ] T It is an external magnetic field, R tot = R op + R rel It is the total relaxation rate, and K is the transfer coefficient between the polarizability along the direction of the detection light and the response of the magnetometer, which is related to the pressure broadening of the alkali metal gas cell and the alkali metal number density.

[0072] 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 determined by the slope of the following expression.

[0073] ,

[0074] By utilizing the optical depth of the detection light and changing its power, the following expression can be obtained:

[0075] ,

[0076] Among them, I out It measures the power of the light emitted from the alkali metal gas cell, I. in It measures the power of light incident on the alkali metal gas cell, and the slope K. OD Information including the pressure broadening of the alkali metal chamber and the atomic number density of the alkali metal can be used to establish their relationship with the transfer coefficient:

[0077] ,

[0078] 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 for the detection light power, and ν pr It is the frequency of the light being detected, ν D1 It is the D1 line resonance frequency of alkali metal atoms, Γ D1 It is the pressure broadening value of the D1 line of alkali metal atoms.

[0079] When a DC magnetic field is applied in the y-direction and the magnitude of the y-direction magnetic field is changed, the following expression can be obtained:

[0080] ,

[0081] Where V0 is the output of the device when a magnetic field is applied only along the y-axis, and B y-fitThe equilibrium spin polarization P0 can be obtained from the slope of the above formula and the value of the transfer coefficient K, which is related to the magnitude of the y-axis magnetic field.

[0082] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field, characterized in that, Includes the following steps: Step 1: Adjust the SERF magnetic field measuring device to normal operating condition; Step 2, by applying a DC magnetic field B along the x-axis x and the DC magnetic field B along the y-axis y The first output V1 of the SERF magnetic field measuring device is obtained by applying B. y and z-axis DC magnetic field B z The second output V2 of the SERF magnetic field measuring device is obtained; Step 3, change B z The size of the response, the ratio of the two responses, and B are recorded. z The square of the value is used to fit the equation, and the total relaxation rate R is obtained from the slope of the fitting equation. tot ; Step 4: Measure the pressure broadening at low temperature, which is 120℃±20℃; 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 the magnetometer's response is recorded. Step 7, Fit the response to B y-fit B y-fit Is with B y The magnitude correlation quantity is used to obtain the equilibrium spin polarization P0 using the fitting slope and K; Step 3 includes the following relation: , Where β is the intermediate vector, β x It is the x-axis component of β, β y It is the y-axis component of β, β z γ is the z-axis component of β. e Where B is the gyromagnetic ratio, and R is the triaxial magnetic field. tot K is the total relaxation rate. OD It is the fitting slope, I out It measures the power of the emitted light from the alkali metal gas cell, I. in It is used to detect the power of light incident on the alkali metal gas cell; Step 5 includes the following relation: ， Where G is the conversion coefficient between the optical power received by the photodetector and the output voltage, α is the modulation angle of the photoelastic modulator, e is the natural constant, OD is the optical depth of the detection light, ξ is the attenuation coefficient of the glass on the detection light power, and ν pr It is the frequency of the light being detected, ν D1 It is the D1 line resonance frequency of alkali metal atoms, Γ D1 It is a pressure broadening of the D1 line of alkali metal atoms; Step 7 includes the following relation: , 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.

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

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

4. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field according to claim 1, characterized in that, In step 1, the SERF magnetic field measuring 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 inside a non-magnetic electric heating system, which is located inside a triaxial magnetic compensation coil. The triaxial magnetic compensation coil is located inside a magnetic shielding barrel, and the triaxial magnetic compensation coil is connected to a host computer via a function generator.

5. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field according to claim 4, characterized in that, The detection optical path includes a detection laser, a second half-wave plate, a second polarizing beam splitter, a polarizer, a photoelastic modulator, a second quarter-wave plate, an 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 through a modulation controller.

6. The method for measuring the equilibrium spin polarizability of alkali metal atoms based on the steady-state response of a triaxial magnetic field according to claim 4, characterized in that, The pump optical path includes a pump laser, a concave lens, a first convex lens, a reflector, a first half-wave plate, a first polarizing beam splitter, a first quarter-wave plate, and an alkali metal gas cell connected in sequence.

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