An in-situ magnetic field gradient measurement method based on SERF inertial measurement

Abstract

A method for in-situ magnetic field gradient measurement based on SERF inertial measurement, where SERF (Spin-Exchange-Relaxation-Free) is spin-exchange relaxation free. The total magnetic field gradient in the atomic gas chamber is obtained according to the quadratic relationship between the transverse (longitudinal) relaxation rate of nucleons and the longitudinal (transverse) magnetic field gradient. The polarization rate gradient and the static magnetic field gradient are measured by reversing the pumping light helicity and changing the magnitude of the static current. At the same time, the remanent magnetic gradient can be obtained, which is beneficial to analyzing the source mechanism of the magnetic field gradient, reducing the magnetic field gradient and increasing the transverse relaxation time of nucleons, thereby improving the magnetic noise suppression ability of the SERF inertial measurement system and ultimately improving the inertial measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of in-situ total magnetic field gradient and component magnetic field gradient measurement in inertial measurement, and particularly to a method for measuring in-situ magnetic field gradient based on SERF inertial measurement, where SERF (Spin-Exchange-Relaxation-Free) is spin-exchange-relaxation-free. The total magnetic field gradient in the atomic gas chamber is obtained according to the quadratic relationship between the transverse (longitudinal) relaxation rate of nucleons and the longitudinal (transverse) magnetic field gradient. By reversing the helicity of the pumping light and changing the magnitude of the static current, the polarization rate gradient and the static magnetic field gradient can be measured, and the remanent magnetic field gradient can be obtained at the same time, which is beneficial to analyzing the source mechanism of the magnetic field gradient, reducing the magnetic field gradient and increasing the transverse relaxation time of nucleons, thereby improving the magnetic noise suppression ability of the SERF inertial measurement system and ultimately improving the inertial measurement accuracy. Background Art

[0002] Magnetic field inhomogeneity has a great influence on spin relaxation. Previous researchers have carried out theoretical and experimental studies on the influence of magnetic field gradient on atomic spin relaxation, and derived the theoretical expression of the transverse relaxation rate of spin-polarized atoms caused by magnetic field gradient. In addition, due to magnetic shielding, heating film magnetic field and coil inhomogeneity, the magnetic field inhomogeneity of the SERF gyroscope (SERF, Spin-Exchange-Relaxation-Free, spin-exchange-relaxation-free) will be caused, resulting in residual magnetic field relaxation. The above studies all show that the residual magnetic field gradient leads to equivalent magnetic field gradient relaxation, which is the main source of the transverse relaxation rate of inert gas nuclear spins. Therefore, the residual magnetic field gradient can cause rapid relaxation of nuclear spins. For experimental studies based on polarized inert gases, it is very important to understand these mechanisms and compensate for the influence of the residual magnetic field gradient on the spin relaxation time.

[0003] In addition, the error caused by the magnetic field comes from the nuclear spin relaxation rate and the spin exchange rate determining the low-frequency magnetic field sensitivity. On the one hand, in an atomic sensor system, magnetic shielding is usually used to shield the external magnetic field, and the magnetic shielding ability is limited by the conditions of the magnetic shielding system. In SERF inertial measurement, the magnetic shielding structure has the function of converging magnetic field lines, which will change the magnetic field lines inside the magnetic shielding, thereby reducing the magnetic field uniformity and introducing a magnetic field gradient. On the other hand, the non-orthogonality of the coils and the non-orthogonality of the light-magnetic field may cause the position of the gas chamber to move relative to the symmetry center of the coil system. Therefore, the gas chamber can sense the magnetic field gradient in the system, and the magnetic field gradient is compensated by the gradient field coil to suppress the low-frequency magnetic field noise. Summary of the Invention

[0004] The present invention provides a method for in-situ magnetic field gradient measurement based on SERF inertial measurement. Aiming at the problem of magnetic field gradient measurement in SERF inertial measurement, the sources of each magnetic field gradient are clarified, and the total magnetic field gradient, polarization magnetic field gradient, static magnetic field gradient and residual magnetic field gradient are measured respectively, which can solve the existing technical defects.

[0005] The technical solution of the present invention is as follows:

[0006] A method for in-situ magnetic field gradient measurement based on SERF inertial measurement, characterized by comprising the following steps:

[0007] Step 1, the atomic gas cell is heated to the normal working state by AC heating;

[0008] Step 2, the pumping laser polarizes electrons, and the electrons hyperpolarize atoms by spin-exchange collision with atoms so that the SERF inertial measurement device operates in the SERF state, and the detection laser detects the signal of the inertial measurement device by detecting alkali metal electrons;

[0009] Step 3, in-situ measurement of the total magnetic field gradient of the atomic gas cell is carried out through a gradient coil to obtain the total magnetic field gradient ΔB total ;

[0010] Step 4, measure the polarization magnetic field gradient, static magnetic field gradient and residual magnetic field gradient respectively.

[0011] In the said Step 1, it includes heating the atomic gas cell to above 170 °C to increase the atomic density. The inert gas inside the atomic gas cell is used to sense inertia and resist the external interference magnetic field, and the alkali metal electrons inside the atomic gas cell are used for spin-exchange collision to polarize the nuclear spins of the inert gas.

[0012] The pumping laser in the said Step 2 comes from a pumping laser, and the pumping laser is a distributed Bragg reflector laser DBR. The detection laser in the said Step 2 comes from a detection laser, and the detection laser is a distributed feedback laser DFB.

[0013] The said Step 3 includes the following relational expressions: where represents the nuclear transverse relaxation rate, represents the electric quadrupole relaxation, represents the spin destruction relaxation, represents the polarization of alkali metal electrons by spin-exchange collision 21 The nuclear spin exchange rate of Ne, represents the transverse magnetic field gradient relaxation. By applying a longitudinal gradient magnetic field using a gradient coil and measuring the transverse relaxation time under different longitudinal gradient magnetic field conditions, the quadratic parabola relationship between the longitudinal magnetic field gradient and the transverse relaxation time can be obtained according to the following formula:

[0014]

[0015] Among them, V is the volume of the atomic gas cell, is the longitudinal magnetic field gradient, D Ne-Ne is the diffusion coefficient of the atomic gas cell, which is inversely proportional to the gas pressure; R is the radius of the atomic gas cell, γ n is the nuclear gyromagnetic ratio, and the minimum value of the transverse relaxation rate reflects the total magnetic field gradient ΔB of the gas cell total .

[0016] The fourth step includes the following formula for the polarizability:

[0017]

[0018] Among them is the longitudinal electron polarizability, R p is the equivalent pumping rate of the pumping light, s z is the electron spin curl, is the longitudinal relaxation rate of the nuclear spin, is the longitudinal relaxation rate of the mixed alkali metal atoms, is the equivalent spin exchange rate between the atom and the mixed alkali metal, is the equivalent spin exchange rate between the mixed alkali metal and the atom. The magnitude of the electron spin magnetic field is calculated by the following formula:

[0019]

[0020] Among them, B p (z) is the magnitude of the electron spin magnetic field, k0 is the Fermi contact constant, g s is the Landé factor, u B is the Bohr magneton, n e is the alkali metal atom density. At the magnetic compensation point B c the measured magnetic field gradient ΔB total1 , after changing the direction of the pumping light curl, the measured total magnetic field gradient is ΔB total2 , after changing the magnitude of the magnetic field δB z in the z-axis direction, the measured total magnetic field gradient is ΔB total3 . The principle of changing the direction of the pumping light curl is to add a half-wave plate in the incident direction of the pumping light, and after placing the optical axis of the wave plate at 45°, the following formula is obtained:

[0021]

[0022] Among them, G 1 / 2λ is the Jones matrix of the half-wave plate, E s is the Jones matrix of the right-handed circularly polarized light, θ is the angle between the wave plate and the optical axis, here θ = 45°, and i is the imaginary unit;

[0023]

[0024]

[0025]

[0026] where ΔB DC is the static magnetic field gradient obtained by solution, and ΔB DC1 and ΔB DC2 are the static magnetic field gradients before and after the magnitude of the magnetic field δB z changes along the z-axis. ΔB r is the residual magnetic field gradient, and ΔB p1 and ΔB p2 are the magnetic field gradients of the electron polarization rate before and after the direction of the pumping light helicity changes. ΔB p is the magnetic field gradient of the electron polarization rate obtained by solution.

[0027] The pumping laser comes from a pumping laser, and the pumping laser emitted by the pumping laser irradiates the atomic gas cell after passing through a second spot expander, a third linear polarizer, a second liquid crystal phase retarder, a fourth linear polarizer, a second half-wave plate, an optical isolator, and a 1 / 4 wave plate connected in series in sequence. The optical isolator is connected to the second liquid crystal phase retarder through a third photodetector and a second electronic control unit in sequence; the detection laser comes from a detection laser, and the detection laser emitted by the detection laser enters the input end of a polarization beam splitter after passing through a first spot expander, a first linear polarizer, a first liquid crystal phase retarder, a second linear polarizer, a first half-wave plate, a Glan-Taylor prism, a beam splitting prism, an atomic gas cell, and a third half-wave plate connected in series in sequence. The transmission end of the polarization beam splitter is connected to the first input end of a differential node through a first photodetector, the reflection end of the polarization beam splitter is connected to the second input end of the differential node through a second photodetector, the output end of the differential node is connected to a host computer through a DAQ data acquisition card, and the Glan-Taylor prism is connected to the first liquid crystal phase retarder through a fourth photodetector and a first electronic control unit in sequence; a heating film, a three-axis active magnetic compensation coil, a gradient coil, a ferrite, and a permalloy are sequentially arranged outside the atomic gas cell.

[0028] The technical effects of the present invention are as follows: A method for in-situ magnetic field gradient measurement based on SERF inertial measurement of the present invention heats, polarizes electrons with a pumping laser, hyperpolarizes atoms with electrons, and in-situ measures the total magnetic field gradient of an atomic gas cell with a gradient coil. By steps of respectively measuring the polarization magnetic field gradient, the static magnetic field gradient, and the residual magnetic field gradient, etc., the sources of each magnetic field gradient are clarified and measured, so as to reduce the magnetic field gradient, and finally suppress the magnetic noise error and drift of SERF inertial measurement. The research object of the present invention can ultimately be used for ultra-high-precision inertial and sensitivity measurement. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of a SERF inertial measurement device used to implement a method for in-situ magnetic field gradient measurement based on SERF inertial measurement of the present invention.

[0030] Figure 2 It is a schematic diagram of the simulation fitting of the axial gradient coil and its magnetic field-displacement change. Figure 2 In the left figure of the simulation fitting in [reference], the magnetic field of the gradient coil is simulated by the finite element simulation software Comsol. By applying a current of 1 mA to the gradient coil, the corresponding gradient magnetic field is obtained, and thus its theoretical coil constant is obtained. Through Figure 2 It can be seen from the right figure in [reference] that the coil constant of the longitudinal gradient coil in the X-axis is 3.856 nT / cm / mA, the coil constant in the Y-axis is 3.842 nT / cm / mA, and the coil constant in the z-axis is 7.694 nT / cm / mA (nT / cm / mA).

[0031] Figure 3 It is a schematic diagram of the total magnetic field gradient measurement result. Figure 3 It includes obtaining the relationship between the nuclear transverse relaxation rate by changing the longitudinal magnetic field gradient under three temperature conditions of 170 °C, 180 °C, and 190 °C, so as to measure the total magnetic field gradient in-situ. Figure 3 It can be seen from [reference] that the total magnetic field gradient at 170 °C is -14.86 nT / cm, the total magnetic field gradient under the condition of 180 °C is -25.62 nT / cm, and the total magnetic field gradient under the condition of 190 °C is -43.02 nT / cm. The transverse relaxation rate is the reciprocal of the transverse relaxation time. Figure 3 In [reference], the ordinate is the nuclear transverse relaxation rate (1 / s), and the scale values of the ordinate are 0, 0.01, 0.02, ···, 0.05; the abscissa is the longitudinal magnetic field gradient dBz / dz (nT / cm), Bz represents the longitudinal magnetic field, that is, the magnetic field in the z-axis direction, and the scale values of the abscissa are -150, -100, -50, 0, 50, 100. Figure 3 In [reference], there is a quadratic parabola relationship between the transverse relaxation rate and the longitudinal magnetic field gradient.

[0032] The reference numerals are listed as follows: 1 - detection laser; 2 - first spot expander (including two lenses); 3 - first linear polarizer; 4 - first liquid crystal phase retarder; 5 - second linear polarizer; 6 - first half-wave plate; 7 - Glan-Taylor prism; 8 - beam splitter prism; 9 - first electronic control unit (ECU); 10 - pump laser; 11 - second spot expander (including two lenses); 12 - third linear polarizer; 13 - second liquid crystal phase retarder; 14 - fourth linear polarizer; 15 - second half-wave plate; 16 - optical isolator; 17 - 1 / 4 wave plate; 18 - ferrite; 19 - permalloy; 20 - atomic cell; 21 - three-axis active magnetic compensation coil and gradient coil; 22 - heating film; 23 - third half-wave plate; 24 - first photodetector; 25 - second photodetector; 26 - polarization beam splitter; 27 - host computer; 28 - second electronic control unit (ECU); 29 - third photodetector; 30 - fourth photodetector; 31 - DAQ data acquisition card. Detailed implementation manners

[0033] The present invention will be described below with reference to the accompanying drawings ( Figures 1-3 ).

[0034] Figure 1 FIG. is a schematic structural diagram of a SERF inertial measurement device used to implement a method for in-situ magnetic field gradient measurement based on SERF inertial measurement according to the present invention. Figure 2 FIG. is a schematic simulation fitting diagram of an axial gradient coil and its magnetic field-displacement change. Figure 3 FIG. is a schematic diagram of the total magnetic field gradient measurement result. Referring to Figures 1 to 3 as shown, a method for in-situ magnetic field gradient measurement based on SERF inertial measurement includes the following steps: Step 1, the atomic cell is heated to the normal working state by AC heating; Step 2, the pump laser polarizes electrons, and the electrons hyperpolarize atoms through spin-exchange collisions with atoms so that the SERF inertial measurement device operates in the SERF state, and the detection laser detects the signal of the inertial measurement device by detecting alkali metal electrons; Step 3, the total magnetic field gradient of the atomic cell is measured in-situ by the gradient coil to obtain the total magnetic field gradient ΔB total ; Step 4, the polarization magnetic field gradient, the static magnetic field gradient, and the residual magnetic field gradient are measured respectively.

[0035] In step 1, the atomic gas cell is heated to above 170 °C to increase the atomic density. The inert gas inside the atomic gas cell is used to sense inertia and resist the external interference magnetic field. The alkali metal electrons inside the atomic gas cell are used to polarize the nuclear spins of the inert gas through spin-exchange collisions. The pumping laser in step 2 comes from a pumping laser, and the pumping laser is a distributed Bragg reflector laser DBR. The detection laser in step 2 comes from a detection laser, and the detection laser is a distributed feedback laser DFB. Step 3 includes the following relational expressions: where represents the nuclear transverse relaxation rate, represents the electric quadrupole relaxation, represents the spin-destruction relaxation, represents the polarization of the alkali metal electrons through spin-exchange collisions 21 the nuclear spin-exchange rate of Ne, represents the transverse magnetic field gradient relaxation. By applying a longitudinal gradient magnetic field using a gradient coil and measuring the transverse relaxation time under different longitudinal gradient magnetic field conditions, the quadratic parabola relationship between the longitudinal magnetic field gradient and the transverse relaxation time can be obtained according to the following formula:

[0036]

[0037] where V is the volume of the atomic gas cell, is the longitudinal magnetic field gradient, D Ne-Ne is the diffusion coefficient of the atomic gas cell, which is inversely proportional to the air pressure; R is the radius of the atomic gas cell, γ n is the nuclear gyromagnetic ratio, and the minimum value of the transverse relaxation rate reflects the total magnetic field gradient ΔB of the gas cell total .

[0038] Step 4 includes the following polarizability calculation formula:

[0039]

[0040] where is the electron longitudinal polarizability, R p is the equivalent pumping rate of the pumping light, s z is the electron spin curl, is the nuclear spin longitudinal relaxation rate, is the longitudinal relaxation rate of the mixed alkali metal atoms, is the equivalent spin-exchange rate between the atoms and the mixed alkali metal, is the equivalent spin-exchange rate between the mixed alkali metal and the atoms. The magnitude of the electron spin magnetic field is calculated by the following formula:

[0041]

[0042] where B p(z) is the magnitude of the electron spin magnetic field, k0 is the Fermi contact constant, g s is the Landé factor, u B is the Bohr magneton, n e is the alkali metal atom density, and the magnetic field gradient ΔB c measured at the magnetic compensation point B total1 , the total magnetic field gradient measured after changing the direction of the pumping light helicity is ΔB total2 , and the magnitude of the varying magnetic field in the z-axis is δB z , and the total magnetic field gradient measured after that is ΔB total3 , and the principle of changing the direction of the pumping light helicity is to add a half-wave plate in the direction of the pumping light entering the cell, and after placing the optical axis of the wave plate at 45°, the following formula is obtained:

[0043]

[0044] where G 1 / 2λ is the Jones matrix of the half-wave plate, Es is the Jones matrix of the right-handed circularly polarized light, θ is the angle between the wave plate and the optical axis, here θ = 45°, and i is the imaginary unit;

[0045]

[0046]

[0047]

[0048] where ΔB DC is the static magnetic field gradient obtained by solving, ΔB DC1 and ΔB DC2 are the static magnetic field gradients before and after the magnitude of the varying magnetic field in the z-axis is δB z , ΔB r is the residual magnetic field gradient, ΔB p1 and ΔB p2 are the magnetic field gradients of the electron polarizability before and after changing the direction of the pumping light helicity, and ΔB p is the magnetic field gradient of the electron polarizability obtained by solving.

[0049] The pumping laser comes from a pumping laser 10. The pumping laser emitted by the pumping laser 10 irradiates the atomic gas cell 20 after passing through a second spot expander assembly 11, a third linear polarizer 12, a second liquid crystal phase retarder 13, a fourth linear polarizer 14, a second half-wave plate 15, an optical isolator 16, and a quarter-wave plate 17 connected in series in sequence. The optical isolator 16 is connected to the second liquid crystal phase retarder 13 through a third photodetector 29 and a second electronic control unit 28 in sequence. The detection laser comes from a detection laser 1. The detection laser emitted by the detection laser 1 enters the input end of a polarization beam splitter 26 after passing through a first spot expander assembly 2, a first linear polarizer 3, a first liquid crystal phase retarder 4, a second linear polarizer 5, a first half-wave plate 6, a Glan-Taylor prism 7, a beam splitting prism 8, the atomic gas cell 20, and a third half-wave plate 23 in sequence. The transmission end of the polarization beam splitter 26 is connected to the first input end of a differential node through a first photodetector 24, and the reflection end of the polarization beam splitter 26 is connected to the second input end of the differential node through a second photodetector 25. The output end of the differential node is connected to a host computer 27 through a DAQ data acquisition card 31. The Glan-Taylor prism 7 is connected to the first liquid crystal phase retarder 4 through a fourth photodetector 30 and a first electronic control unit 9 in sequence. An outer periphery of the atomic gas cell 20 is sequentially provided with a heating film 22, a three-axis active magnetic compensation coil, a gradient coil 21, a ferrite 18, and a permalloy 19 outward.

[0050] The present invention aims at the problem of magnetic field gradient measurement in SERF inertial measurement, clarifies the sources of each magnetic field gradient, and measures the total magnetic field gradient, the polarization magnetic field gradient, the static magnetic field gradient, and the residual magnetic field gradient respectively, and it can solve the existing technical defects.

[0051] A method for in-situ magnetic field gradient measurement based on SERF inertial measurement in the present invention includes the following steps:

[0052] Step 1: The atomic gas cell is heated to a normal working state by an alternating current heating method.

[0053] Step 2: The pumping laser polarizes electrons, and the electrons hyperpolarize atoms by spin-exchange collisions with atoms, so that the SERF inertial measurement device reaches the SERF state where it can work normally. The detection laser detects the signal of the inertial measurement device by detecting alkali metal electrons.

[0054] Step 3: The total magnetic field gradient of the atomic gas cell is measured in-situ through the gradient coil, and the total magnetic field gradient is obtained as ΔB total1 ;

[0055] Step 4: Measure the polarization magnetic field gradient, the static magnetic field gradient, and the residual magnetic field gradient respectively.

[0056] In Step 1, the atomic cell is heated to above 170°C to increase the atomic density. The inert gas inside the atomic cell is used to sense inertia and resist external interference magnetic fields, and the alkali metal electrons are used to polarize the nuclear spins of the inert gas through spin-exchange collisions. In Step 2, the pumping laser is a distributed Bragg reflector laser (DBR), and the detection laser is a distributed feedback laser (DFB).

[0057] In Step 3, the nuclear transverse relaxation rate is affected by the relaxation due to the electric quadrupole moment spin-destruction relaxation The alkali metal electrons are polarized through spin-exchange collisions 21 The spin-exchange rate of the Ne nuclear spin transverse magnetic field gradient relaxation .

[0058]

[0059] Among them, is the relaxation due to the electric quadrupole moment, is the transverse magnetic field gradient relaxation, is the spin-destruction relaxation, is the polarization of the alkali metal electrons through spin-exchange collisions 21 The spin-exchange rate of the Ne nuclear spin

[0060] In Step 4, the polarization magnetic field gradient is considered to have the same circular polarization state s of the left-handed circularly polarized pumping light and the right-handed circularly polarized pumping light z . The atoms reach almost the same polarization rate under left-handed and right-handed circular polarization pumping. Therefore, by changing the polarization state of the pumping light from left-handed circular polarization to right-handed circular polarization, the direction of the magnetic field gradient of the electron polarization rate can be reversed

[0061] The pumping light beam is generated by a distributed Bragg reflector (DBR) laser with a central frequency of 770.108 nm (K atom D1 resonance line). The quarter-wave plate in the pumping path converts the linearly polarized laser into a circular polarization state, and a pair of plano-convex lenses are used to expand the pumping light beam. The detection light beam is generated by a distributed feedback (DFB) laser with a central frequency of 795.311 nm (about 0.3 nm on the blue side of the Rb D1 resonance line). A Glan-Taylor polarizer (GT-5, Thorlabs) can purify the laser into a better linearly polarized laser

[0062] The gradient coil described above adopts a first-order longitudinal gradient coil as shown in Figure 2 dBz / dz, and the processing technology uses a flexible printed circuit board (FPC)

[0063] The transverse (longitudinal) magnetic field gradient relaxation is in a quadratic parabolic relationship with the longitudinal (transverse) magnetic field gradient.

[0064] The reverse polarization magnetic field gradient is assumed to have substantially the same circular polarization state values ​​for the left-handed circularly polarized pump light and the right-handed circularly polarized pump light. The atoms achieve almost the same polarization rate under left-handed and right-handed circularly polarized pumping. By changing the polarization state of the pump light from left-handed circular polarization to right-handed circular polarization, the direction of the magnetic field gradient of the electronic polarizability can be reversed. The principle of changing the rotation direction of the pump light is to add a half-wave plate in the direction of the pump light entering the barrel, and the wave plate optical axis is placed at 45°.

[0065]

[0066] G 1 / 2λ is the half-wave plate Jones matrix, E s is the Jones matrix of right circularly polarized light.

[0067] Repeat step 3 and test the total magnetic field gradient to be ΔB. total2 , at magnetic compensation point B c The magnetic field gradient measured under total1 , the total magnetic field gradient relationship is as follows:

[0068]

[0069] Where ΔB DC The static magnetic field gradient is mainly generated by the inhomogeneity of the magnetic field coil, ΔB r The residual magnetic field gradient is mainly determined by the shielding performance of the magnetic shielding system, ΔB p1 and ΔB p2 They are all electronic polarization gradient magnetic fields. Similarly, the total magnetic field gradient of the test is ΔB total3 , when one of the magnetic field gradients is changed, the entire internal gradient will change.

[0070] Assume that the z-axis starts at the magnetic compensation point B c The magnetic field gradient measured under total1 , then the z-axis changes the magnetic field to δB z The magnetic field gradient is measured to be ΔB total3 Because the static magnetic field gradient is mainly generated by the non-uniformity of the coil, the static magnetic field gradient after the change is

[0071]

[0072] When one of the magnetic field gradients is changed, the entire internal gradient will change, and the total magnetic field gradient ΔB total1 and ΔB total3 They are

[0073]

[0074] Finally, the magnetic field gradient of the polarizability and the static magnetic field gradient are obtained, and then the residual magnetic field gradient is obtained.

[0075] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art. It is hereby pointed out that the above description helps those skilled in the art to understand the present invention, but does not limit the protection scope of the present invention. Any implementation that makes equivalent substitutions, modifications and improvements, and / or simplifies the above description without departing from the essence of the present invention falls within the protection scope of the present invention.

Claims

1. A method for in-situ magnetic field gradient measurement based on SERF inertial measurement, characterized in that, It includes the following steps: Step 1: The atomic gas cell is heated to the normal working state by AC heating. Step 2: The pumping laser polarizes electrons. The electrons hyperpolarize atoms through spin-exchange collisions with atoms, enabling the SERF inertial measurement device to operate in the SERF state. The detection laser detects the signal of the inertial measurement device by detecting alkali metal electrons. Step 3: In-situ measurement of the total magnetic field gradient of the atomic gas cell is performed by a gradient coil to obtain the total magnetic field gradient ΔB total ; Step 4: Measure the polarization magnetic field gradient, static magnetic field gradient, and residual magnetic field gradient respectively. The following relational expressions are included in Step 3: where represents the transverse relaxation rate of nucleons, represents the quadrupole relaxation, represents the spin-destruction relaxation, represents the polarization of alkali metal electrons through spin-exchange collisions 21 the nuclear spin-exchange rate of Ne, represents the transverse magnetic field gradient relaxation. By applying a longitudinal gradient magnetic field using a gradient coil and measuring the transverse relaxation time under different longitudinal gradient magnetic field conditions, the quadratic parabolic relationship between the longitudinal magnetic field gradient and the transverse relaxation time can be obtained according to the following formula: where V is the volume of the atomic cell, is the longitudinal magnetic field gradient, D Ne-Ne is the diffusion coefficient of the atomic cell, which is inversely proportional to the gas pressure; R is the radius of the atomic cell, γ n is the nuclear gyromagnetic ratio, and the minimum value of the transverse relaxation rate is the total magnetic field gradient ΔB of the cell total ; The following polarization rate calculation formula is included in Step 4: where is the electronic longitudinal polarizability, R p is the equivalent pumping rate of the pumping light, s z is the electronic spin curl, is the longitudinal relaxation rate of the nuclear spin, is the longitudinal relaxation rate of the mixed alkali metal atoms, is the equivalent spin exchange rate between the atom and the mixed alkali metal, is the equivalent spin exchange rate between the mixed alkali metal and the atom. The magnitude of the electron spin magnetic field is calculated by the following formula: Among which B p (z) is the magnitude of the electron spin magnetic field, k0 is the Fermi contact constant, g s is the Landé factor, μ B is the Bohr magneton, n e is the alkali metal atom density, and the magnetic field gradient ΔB c measured at the magnetic compensation point B total1 , and the total magnetic field gradient measured after changing the direction of the pumping light helicity is ΔB total2 , the magnitude of the varying magnetic field in the z-axis is δB z , and the total magnetic field gradient measured after that is ΔB total3 , the principle of changing the direction of the pumping light helicity is to obtain the following formula by adding a half-wave plate in the direction of the pumping light entering the cell and placing the optical axis of the wave plate at 45°: where G 1 / 2λ is the Jones matrix of a half-wave plate, and E s is the Jones matrix of a right-handed circularly polarized light. θ is the angle between the wave plate and the optical axis, where θ = 45°, and i is the imaginary unit; where ΔB DC is the static magnetic field gradient obtained by solution, ΔB DC1 and ΔB DC2 are the static magnetic field gradients before and after the magnitude of the magnetic field δB z varies along the z-axis, ΔB r is the residual magnetic field gradient, ΔB p1 and ΔB p2 are the magnetic fields of the electron polarizability gradient before and after the direction of the pumping light helicity changes, ΔB p is the magnetic field of the electron polarizability gradient obtained by solution.

2. The in-situ magnetic field gradient measurement method based on SERF inertial measurement according to claim 1, wherein In Step 1, the atomic gas cell is heated to above 170 °C to increase the atomic density. The inert gas inside the atomic gas cell is used to sense inertia and resist external interference magnetic fields. The alkali metal electrons inside the atomic gas cell are used for spin-exchange collisions to polarize the nuclear spins of the inert gas.

3. The method for in-situ magnetic field gradient measurement based on SERF inertial measurement according to claim 1, characterized in that The pumping laser in Step 2 comes from a pumping laser, and the pumping laser is a distributed Bragg reflector laser DBR. The detection laser in Step 2 comes from a detection laser, and the detection laser is a distributed feedback laser DFB.

4. The method for in-situ magnetic field gradient measurement based on SERF inertial measurement according to claim 1, wherein, The pumping laser comes from a pumping laser. The pumping laser emitted by the pumping laser irradiates the atomic gas cell after passing through a second spot expander assembly, a third linear polarizer, a second liquid crystal phase retarder, a fourth linear polarizer, a second half-wave plate, an optical isolator, and a 1 / 4 wave plate in series. The optical isolator is connected to the second liquid crystal phase retarder through a third photodetector and a second electronic control unit in sequence. The detection laser comes from a detection laser. The detection laser emitted by the detection laser enters the input end of a polarization beam splitter after passing through a first spot expander assembly, a first linear polarizer, a first liquid crystal phase retarder, a second linear polarizer, a first half-wave plate, a Glan-Taylor prism, a beam splitting prism, the atomic gas cell, and a third half-wave plate in series. The transmission end of the polarization beam splitter is connected to the first input end of a differential node through a first photodetector. The reflection end of the polarization beam splitter is connected to the second input end of the differential node through a second photodetector. The output end of the differential node is connected to a host computer through a DAQ data acquisition card. The Glan-Taylor prism is connected to the first liquid crystal phase retarder through a fourth photodetector and a first electronic control unit in sequence. An insulating film, a three-axis active magnetic compensation coil, a gradient coil, a ferrite, and a permalloy are sequentially arranged outside the atomic gas cell.

Images