A method for measuring polarization gradient relaxation of an atomic spin inertia measurement device

Abstract

A method for measuring polarization gradient relaxation of an atomic spin inertial measurement device, which realizes the measurement of polarization gradient relaxation through the following steps, can realize the in-situ measurement of polarization gradient in the atomic spin inertial measurement device, and provides strong support for the evaluation and suppression of the polarization gradient inside the gas chamber: Step 1, fix the working point parameters of the atomic spin inertial measurement device to have a response signal at a diagonal rate; Step 2, decouple the precession of the alkali metal electron spin and the noble gas nuclear spin; Step 3, use the free precession decay method to test the nuclear spin transverse relaxation rate R2 at the current P1; Step 4, test the non-polarization gradient relaxation term in the nuclear spin transverse relaxation; Step 5, test the total transverse relaxation at any pumping laser power point P, calculate the polarization gradient relaxation at the pumping laser power point P, and the polarization gradient relaxation at the P point is the difference between the total transverse relaxation rate and the non-polarization gradient relaxation rate at the P point.

Description

Technical Field

[0001] The present invention relates to the field of atomic gyroscopes, and in particular to a method for measuring polarization gradient relaxation of an atomic spin inertial measurement device. Background Art

[0002] The spin-exchange relaxation-free (SERF) atomic spin inertial measurement device based on the interaction between light magnetism and atoms has ultra-high theoretical measurement sensitivity, and has become one of the important development directions of future high-precision inertial measurement instruments with its unique volume and precision advantages. Atomic spin relaxation is an important error source that limits the performance improvement in SERF inertial measurement devices. There are mainly two types of atomic spins in SERF inertial measurement devices: alkali metal electron spins and noble gas nuclear spins. The relaxation time of each type of atom (the numerical values of the relaxation time and the relaxation rate are reciprocal to each other, the unit of the relaxation time: s, the unit of the relaxation rate: 1 / s) is mainly divided into the longitudinal relaxation time T1 and the transverse relaxation time T2. The longitudinal relaxation time characterizes the time length for the electron spin magnetic moment to dissipate in the spin polarization direction, and the transverse relaxation time characterizes the time length for the electron spin magnetic moment to naturally dissipate in the transverse plane corresponding to the polarization direction without external action. After applying a small magnetic field bias (2 nT) in the Y direction and then removing it, the nuclear spin precesses around the main magnetic field and freely precesses and decays around the main magnetic field direction with the transverse relaxation time as the characteristic time. By testing the free precession decay signals at different laser powers and fitting, the transverse relaxation rate of the nuclear spin at the corresponding power point can be obtained. Among them, polarization gradient relaxation is one of the main sources of noble gas nuclear spin transverse relaxation. The atomic spin polarization gradient is mainly caused by the attenuation of the pumping light when the laser interacts with the atoms, and is an unavoidable error source in SERF inertial measurement devices. The atomic spin polarization gradient will cause atomic decoherence, resulting in atomic relaxation and reducing the system sensitivity. At the same time, the atomic spin polarization gradient relaxation will affect the noble gas nuclear spin polarization efficiency, weaken the self-compensation ability of the nucleons to the external magnetic field, destroy the stability of the system, and limit the improvement of the system performance. In SERF inertial measurement devices, there has always been a lack of an effective evaluation method for evaluating atomic spin polarization gradient relaxation. The present invention provides a method for measuring polarization gradient relaxation of an atomic spin inertial measurement device, which provides strong support for the characterization and evaluation of atomic spin polarization gradient. Summary of the Invention

[0003] Aiming at the deficiencies existing in the prior art, the present invention provides a method for measuring polarization gradient relaxation of an atomic spin inertial measurement device.

[0004] The technical solution of the present invention is as follows:

[0005] A method for measuring polarization gradient relaxation of an atomic spin inertial measurement device, characterized by comprising the following steps:

[0006] Step 1: Fix the working point parameters of the atomic spin inertia measurement device to have a response signal at the diagonal rate. The working point parameters include the heating temperature and the pumping laser power point P1. The heating temperature is to heat the alkali metal gas cell to the target working temperature. The pumping laser at the power point P1 polarizes the alkali metal electrons, thereby hyperpolarizing the inert gas nuclear spins. Through three-axis magnetic field compensation, the device operates at the nuclear spin magnetic self-compensation point;

[0007] Step 2: Decouple the precession of the alkali metal electron spins and the inert gas nuclear spins;

[0008] Step 3: Use the free precession decay method to measure the nuclear spin transverse relaxation rate R2 at the current P1;

[0009] Step 4: Measure the non-polarized gradient relaxation term in the nuclear spin transverse relaxation;

[0010] Step 5: Measure the total transverse relaxation at any pumping laser power point P, and calculate the polarization gradient relaxation at the pumping laser power point P. The polarization gradient relaxation at the P point is the difference between the total transverse relaxation rate and the non-polarized gradient relaxation rate at the P point.

[0011] In step 2, it includes applying a magnetic field Bz with a bias ten times that of the magnetic self-compensation point in the main magnetic field direction Z to decouple the precession between the electron spins and the nuclear spins.

[0012] In step 3, it includes, based on Bz, applying a bias magnetic field By = 2 nT in the Y direction. The nuclear spin polarization rate Pn precesses around the main magnetic field direction, and there is a polarization rate projection Pnx of Pn in the X direction. By obtaining the output signal, the free precession decay curve of the change of Pnx in the X direction is obtained, and the envelope of the decay curve is fitted to obtain the nuclear spin transverse relaxation rate R at the current pumping power point. 2 .

[0013] In step 4, it includes quickly reducing the pumping laser power to 50% of the P1 point based on P1, and measuring the nuclear spin transverse relaxation rate R 2 , repeating to reduce the power point to 50% of the previous test point until R 2 tends to be invariant as the pumping laser power decreases; when the pumping laser power changes, the nuclear spin relaxation change caused by the change of the electron polarization distribution, and the other relaxation terms in R 2 are not affected by the pumping laser power. At this time, the measured transverse relaxation is the non-polarized gradient relaxation term.

[0014] The other relaxation terms include spin collision relaxation R sd , electric quadrupole relaxation R quad , and spin exchange relaxation R se, the spin collision relaxation is the collision relaxation between Ne atoms, and the spin exchange relaxation is the spin exchange relaxation between the inert gas Ne atoms and the alkali metal electrons:

[0015]

[0016] where T 2 is the nuclear spin transverse relaxation time, is the electron spin polarization gradient relaxation;

[0017]

[0018] where p Ne is the gas chamber pressure;

[0019]

[0020]

[0021]

[0022] where are the spin exchange relaxations of Rb and K atoms to Ne atoms respectively, are the exchange collision coefficients between Ne atoms and Rb and K atoms respectively, and n K and n Rb are the densities of K and Rb atoms respectively;

[0023]

[0024]

[0025]

[0026]

[0027]

[0028] where, are the spin collision relaxations of Rb to Ne, Ne to Rb, K to Ne, and Rb to Ne respectively. n K and n Rb and n Ne are the densities of K, Rb, and Ne atoms respectively, and υ NeRb and υ NeK are the spin collision velocities between Ne atoms and Rb and K atoms respectively;

[0029]

[0030] where Rp is the pumping rate, T is the temperature, α is a coefficient independent of the pumping power, and Dn is the diffusion coefficient of the inert gas Ne in the gas chamber, d is the diameter of the gas chamber, n K represents the density of alkali metal K atoms, W is the Lambert function, R rel is the electron relaxation rate of the alkali metal, R p0 is the pumping rate at the incident point, e is the natural constant, is the polarization gradient, σ v is the photon absorption cross-sectional area.

[0031] The atomic spin inertia measurement device includes a pumping laser and a detection laser. The pumping laser is sequentially connected to a first convex lens, a first polarizer, a liquid crystal, a second polarizer, a second convex lens and a reflector. The reflector is connected to a first beam splitter through a first 1 / 2 wave plate. The transmission side of the first beam splitter is sequentially connected to a 1 / 4 wave plate, a gas chamber and a fourth photodetector through the gas chamber. The reflection side of the first beam splitter is sequentially connected to a first photodetector, a power control system and the liquid crystal. The detection laser is sequentially connected to a third polarizer, a second 1 / 2 wave plate, a second beam splitter, a gas chamber, a Wollaston prism and a second photodetector. The second photodetector is connected to a signal acquisition system. The reflection end of the second beam splitter is connected to a third photodetector. The third photodetector and the fourth photodetector are respectively connected to the signal acquisition system. A heating film, a coil, a ferrite and a shielding cylinder are sequentially arranged around the gas chamber from the inside to the outside.

[0032] The technical effects of the present invention are as follows: A method for measuring the polarization gradient relaxation of an atomic spin inertia measurement device according to the present invention can accurately measure the polarization gradient relaxation at different pumping light power operating points and evaluate the polarization gradient level inside the gas chamber. When parameters such as the gas chamber temperature, the density ratio inside the gas chamber, and the air pressure are fixed, only one calibration of the non-polarization gradient relaxation term needs to be performed (changing 3 to 5 pumping power points and performing a rapid measurement of R 2 ), and the test of R 2 at the current pumping power operating point is performed, and the polarization gradient relaxation at the current operating point can be calculated. Compared with the traditional methods of compensating the magnetic field gradient with a gradient coil and measuring the electron polarization rate gradient with an array detection light, the method proposed by the present invention can quickly measure and directly separate the polarization gradient relaxation. This method does not require adding an additional coil or changing the detection optical path, and can realize the in-situ measurement of the polarization gradient in the atomic spin inertia measurement device, providing strong support for the evaluation and suppression of the polarization gradient inside the gas chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic flow chart of a method for measuring the polarization gradient relaxation of an atomic spin inertia measurement device according to the present invention. Figure 1It includes the following steps: Step 1, fix the working point parameters such as the heating temperature and the pumping laser power (power point: P1), and the device works at the nuclear spin self-compensation point; Step 2, apply a magnetic field Bz with a bias ten times that of the self-compensation point in the direction of the main magnetic field to decouple the electron spin from the nuclear spin; Step 3, use the free precession decay signal to measure the total transverse relaxation rate R of the current working point 2 ; Step 4, reduce the power to 50% of the P1 point and measure R 2 , repeat this step, reduce the power to 50% of the previous test point until R 2 remains unchanged as the pumping light power decreases, and obtain the non-polarized gradient relaxation rate; Step 5, measure R 2 at any power working point P, and obtain the polarized gradient relaxation of the working point P by subtracting the non-polarized gradient relaxation rate from R 2 .

[0034] Figure 2 is a schematic diagram of the system structure used in the method for measuring the polarized gradient relaxation of an atomic spin inertia measurement device according to the present invention Figure 2 The system in is a SERF atomic spin inertia measurement system (SERF, Spin-Exchange Relaxation-Free, without spin exchange relaxation). Figure 2 The system in successively includes a pumping optical path (from the pumping laser 1 - mirror 7 - the fourth photodetector 26) from the outside to the inside, a detection optical path (from the detection laser 25 - the second photodetector 17), a shielding cylinder 16, a ferrite 15, a coil 14, a heating film 13, and a gas chamber 20. The pumping optical path includes a first convex lens 2, a first polarizer 3, a liquid crystal 4, a second polarizer 5, a second convex lens 6, a mirror 7, a first 1 / 2 wave plate 8 (λ / 2), a first beam splitter 9, a 1 / 4 wave plate (λ / 4), a fourth photodetector 26. The reflection end of the first beam splitter 9 is connected to the feedback end of the power control system 11 through a first photodetector 10, and the control end of the power control system 11 is connected to the liquid crystal 4; the detection optical path includes a third polarizer 24, a second 1 / 2 wave plate 23 (λ / 2), a second beam splitter 21, a Wollaston prism 19, and a second photodetector 17; the output end of the Wollaston prism 19 is connected to the second photodetector 17, and the second photodetector 17 is connected to the signal acquisition system 18; the reflection end of the second beam splitter 21 is connected to a third photodetector 22, and the third photodetector 22 and the fourth photodetector 26 are respectively connected to the signal acquisition system 18 Detailed implementation mode

[0035] The following will describe the present invention in conjunction with the accompanying drawings ( Figure 1 - Figure 2 ) and embodiments

[0036] Figure 1Schematic flow chart of the polarization gradient relaxation measurement method for an atomic spin inertial measurement device according to the present invention. Figure 2 It is a schematic structural diagram of the system used for the polarization gradient relaxation measurement method of an atomic spin inertial measurement device according to the present invention. Refer to Figures 1 to 2 As shown, a polarization gradient relaxation measurement method for an atomic spin inertial measurement device is characterized by including the following steps: Step 1, fix the working point parameters of the atomic spin inertial measurement device to have a response signal at a diagonal rate. The working point parameters include the heating temperature and the pumping laser power point P1. The heating temperature is to heat the alkali metal gas cell to the target working temperature, and the pumping laser at the power point P1 polarizes the alkali metal electrons, thereby hyperpolarizing the inert gas nuclear spins. Through three-axis magnetic field compensation, the device works at the nuclear spin magnetic self-compensation point; Step 2, decouple the precession of the alkali metal electron spins and the inert gas nuclear spins; Step 3, use the free precession decay method to test the nuclear spin transverse relaxation rate R 2 ; Step 4, test the non-polarization gradient relaxation term in the nuclear spin transverse relaxation; Step 5, test the total transverse relaxation at any pumping laser power point P, calculate the polarization gradient relaxation at the pumping laser power point P, and the polarization gradient relaxation at point P is the difference between the total transverse relaxation rate at point P and the non-polarization gradient relaxation rate.

[0037] In step 2, it includes applying a magnetic field Bz with a bias ten times that of the magnetic self-compensation point in the main magnetic field direction Z to decouple the precession between the electron spins and the nuclear spins. In step 3, on the basis of Bz, apply a bias magnetic field By = 2 nT in the Y direction. The nuclear spin polarization rate Pn precesses around the main magnetic field direction, and there is a polarization rate projection Pnx of Pn in the X direction. By obtaining the output signal, the free precession decay curve of the change of Pnx in the X direction is obtained, and the envelope of the decay curve is fitted to obtain the nuclear spin transverse relaxation rate R 2 at the current pumping power point. In step 4, it includes quickly reducing the pumping laser power to 50% of the P1 point on the basis of P1, and testing the nuclear spin transverse relaxation rate R 2 , repeat reducing the power point to 50% of the previous test point until R 2 tends to be invariant as the pumping laser power decreases; when the pumping laser power changes, the change in the nuclear spin relaxation caused by the change in the electron polarization distribution, and the other relaxation terms in R 2 are not affected by the pumping laser power. At this time, the measured transverse relaxation is the non-polarization gradient relaxation term.

[0038] The other relaxation terms include spin collision relaxation R sd , electric quadrupole relaxation r quad , and spin exchange relaxation R se, the spin collision relaxation is the collision relaxation between Ne atoms, and the spin exchange relaxation is the spin exchange relaxation between the inert gas Ne atoms and the alkali metal electrons:

[0039] where T 2 is the nuclear spin transverse relaxation time, is the electron spin polarization gradient relaxation;

[0040]

[0041] where p Ne is the gas chamber pressure;

[0042]

[0043]

[0044]

[0045] where are the spin exchange relaxations of Rb and K atoms with respect to Ne atoms, respectively, are the exchange collision coefficients between Ne atoms and Rb and K atoms, respectively, and n K and n Rb are the densities of K and Rb atoms, respectively;

[0046]

[0047]

[0048]

[0049]

[0050]

[0051] where, are the spin collision relaxations of Rb with respect to Ne, Ne with respect to Rb, K with respect to Ne, and Rb with respect to Ne, respectively. n K and n Rb and n Ne are the densities of K, Rb, and Ne atoms, respectively, and υ NeRb and υ NeK are the spin collision velocities between Ne atoms and Rb and K atoms, respectively;

[0052]

[0053] where Rp is the pumping rate, T is the temperature, α is a coefficient independent of the pumping power, and D nis the diffusion coefficient of the inert gas Ne in the gas chamber, d is the diameter of the gas chamber, n K represents the density of the alkali metal K atoms, W is the Lambert function, R rel is the electron relaxation rate of the alkali metal, R p0 is the pumping rate at the incident point, e is the natural constant, is the polarization gradient, σ v is the photon absorption cross-sectional area.

[0054] The atomic spin inertia measurement device includes a pumping laser 1 and a detection laser 25. The pumping laser 1 is sequentially connected to a first convex lens 2, a first polarizer 3, a liquid crystal 4, a second polarizer 5, a second convex lens 6, and a mirror 7. The mirror 7 is connected to a first beam splitter 9 through a first 1 / 2 wave plate 8. The transmission side of the first beam splitter 9 sequentially passes through a 1 / 4 wave plate 12 and a gas chamber 20 and is connected to a fourth photodetector 26. The reflection side of the first beam splitter 9 sequentially passes through a first photodetector 10 and a power control system 11 and is connected to the liquid crystal 5. The detection laser 25 is sequentially connected to a third polarizer 24, a second 1 / 2 wave plate 23, a second beam splitter 21, the gas chamber 20, a Wollaston prism 19, and a second photodetector 17. The second photodetector 17 is connected to a signal acquisition system 18. The reflection end of the second beam splitter 21 is connected to a third photodetector 22. The third photodetector 22 and the fourth photodetector 26 are respectively connected to the signal acquisition system 18. An outer periphery of the gas chamber 20 is sequentially provided with a heating film 13, a coil 14, a ferrite 15, and a shielding cylinder 16 from inside to outside.

[0055] A method for measuring the polarization gradient relaxation of an atomic spin inertia measurement device. When the gas chamber parameters and the working temperature point are determined, the free precession decay curve of atoms is tested at the working point of the pumping laser power to obtain the total transverse relaxation rate of the nuclear spin. In the transverse relaxation of the nuclear spin, only the polarization gradient relaxation is related to the pumping light power. The pumping laser power is reduced until the total transverse relaxation rate tends to be constant as the pumping laser power decreases. The relaxation rate in the flat region is the non-polarization gradient relaxation term in the total relaxation. The difference between the transverse relaxation rate at the system working point and the non-polarization gradient relaxation rate is the atomic spin polarization gradient relaxation at the current working point. This method does not require adding an extra coil or changing the detection optical path, and can realize in-situ measurement of the polarization gradient relaxation. By rapidly changing the pumping laser power, the separation measurement of the polarization gradient relaxation can be realized, providing strong support for the evaluation and suppression of the polarization gradient in the gas chamber of the SERF atomic spin inertia measurement device.

[0056] A method for measuring the polarization gradient relaxation of an atomic spin inertia measurement device. The measurement steps are as follows:

[0057] Step 1: Fix the working point parameters such as the heating temperature and the pumping laser power (working point P1). Through three-axis magnetic field compensation, make the device in the normal gyro working state (nuclear spin self-compensation point), and there is a response signal to the angular rate. Heat the alkali metal gas cell in the atomic spin inertia measurement device to the target working temperature, polarize the alkali metal electrons with the pumping laser, and then hyperpolarize the nuclear spins of the inert gas, so that the system is in a polarized state. The device works at the magnetic field self-compensation point and can respond to the external angular rate input.

[0058] Step 2: Decouple the precession of the electron spin and the nuclear spin. Apply a magnetic field Bz with a bias ten times that of the magnetic field self-compensation point in the Z direction of the main magnetic field direction to decouple the precession between the electron spin and the nuclear spin.

[0059] Step 3: Use the free precession decay method to measure the nuclear spin transverse relaxation rate at the current pumping working point P1. On the basis of Bz, apply a magnetic field bias By = 2 nT in the Y direction. The nuclear spin Pn precesses around the main magnetic field direction. At this time, there is a polarization rate projection Pnx in the X direction. Obtain the change curve (free precession decay curve) of the X-direction polarization rate projection through the output signal. Fit the envelope of the decay curve to obtain the nuclear spin transverse relaxation rate R at the current pumping power point. 2 。

[0060] Step 4: Measure the non-polarized gradient relaxation term in the transverse relaxation. On the basis of P1, quickly reduce the pumping laser power to 50% of the P1 point, and measure the nuclear spin transverse relaxation rate R. 2 Repeat reducing the power point to 50% of the previous test point until R 2 tends to be invariant as the pumping laser power decreases. When the pumping laser power changes, the nuclear spin relaxation change caused by the change of the electron polarization distribution, and the other relaxation terms (spin collision relaxation, electric quadrupole relaxation, spin exchange relaxation) in R 2 are not affected by the laser power. At this time, the measured transverse relaxation is the non-polarized gradient relaxation term.

[0061] Step 5: Measure the total transverse relaxation at any power point P, and calculate the polarization gradient relaxation at the working point P. The polarization gradient relaxation at the P point is the difference between the total transverse relaxation rate and the non-polarized gradient relaxation rate at the current working laser power point P. By measuring R 2 at each power point, the polarization gradient relaxation at the current working point can be obtained.

[0062] The principle of the present invention lies in:

[0063] The longitudinal and transverse relaxation R 2 of the nuclear spin in the SERF atomic spin inertia measurement system can be expressed as

[0064]

[0065] where T 2 is the nuclear spin transverse relaxation time, and R quad is the electric quadrupole relaxation, and R se is the exchange relaxation between the noble gas Ne atoms and the alkali metal electrons, and R sd is the collision relaxation between Ne atoms, and is the electron spin polarization gradient relaxation.

[0066] The expressions for each relaxation are as follows:

[0067] A. Electric quadrupole relaxation R quad

[0068]

[0069] where p Ne is the gas chamber pressure.

[0070] B. Spin exchange relaxation R se

[0071]

[0072]

[0073]

[0074] where is the spin exchange relaxation of Rb and K atoms with Ne atoms, are the exchange collision coefficients between Ne atoms and Rb and K atoms, respectively.

[0075] C. Spin collision relaxation R sd

[0076]

[0077]

[0078]

[0079]

[0080]

[0081] where, are the spin collision relaxations of Rb with Ne, Ne with Rb, K with Ne, and Rb with Ne, respectively. n K 、n Rb 、n Ne are the densities of K, Rb, and Ne atoms, respectively. υ NeRb 、υ NeKThey are the spin collision velocities between Ne atoms and Rb and K atoms respectively.

[0082] D. Polarization gradient relaxation

[0083] In the SERF atomic spin inertial measurement system, the main source of the polarization gradient is the absorption of the pumping light during the polarization of alkali metal atoms, which causes the attenuation of the electron spin polarization rate of alkali metals along the propagation direction of the pumping light, resulting in a polarization gradient in the gas chamber. In addition, the relaxation effect of the gas chamber wall on electrons and the diffusion effect of atoms in the gas chamber are also the causes of the polarization gradient. Among them, the diffusion effect is mainly related to the gas chamber temperature and pressure, and the relaxation of the gas chamber wall on electrons is mainly related to the gas chamber diameter and pressure. Both are not affected by the pumping laser power. Usually, the operating temperature of the SERF atomic spin inertial measurement system is 170°C to 200°C. At this time, the absorption of the pumping light by atoms is intense, and the absorption of the pumping light by polarized alkali metal electrons can be expressed by the following pumping rate R p (z) The attenuation equation with the path length z of the pumping light passing through the gas chamber is expressed as:

[0084]

[0085] where P e (z) is the electron spin polarization rate at the incident distance z, σ v is the photon absorption cross section, and n K represents the density of alkali metal K atoms. The Lambert W function can be used to solve equation (1), and the variation of the pumping light intensity I(z) and the pumping rate R p (z) with the incident distance z can be obtained as:

[0086]

[0087] where h is the Planck constant, v is the pumping laser frequency, I(0) is the light intensity at the incident distance of 0, that is, the light intensity at the incident point. e is the natural constant, R p0 is the pumping rate at the incident point, R rel is the relaxation rate of alkali metal electrons. σ v is the photon absorption cross section, z is the length of the path of the pumping light passing through the gas chamber, and n K represents the density of alkali metal K atoms. W is the Lambert function, which is the inverse function of f(w) = w*e w , that is, Y = X*e X , X = W(Y)

[0088] Along the propagation direction of the pumping light (Z direction), the electron spin polarization rate gradient can be expressed as

[0089]

[0090] where z 1 and z 2 are two position points along the Z direction, is the polarizability at this point.

[0091]

[0092] Polarization gradient relaxation and the polarization gradient The relationship can be expressed as

[0093]

[0094] where α is a coefficient independent of the pumping power, D n is the diffusion coefficient of the inert gas Ne in the gas chamber, d is the diameter of the gas chamber, n K represents the density of the alkali metal K atoms, W is the Lambert function, R rel is the electron relaxation rate of the alkali metal, and R p0 is the pumping rate at the incident point.

[0095] Taking the derivative of Equation (5) with respect to the pumping rate Rp gives:

[0096]

[0097] According to Equation (6), when there is no incident pumping light, i.e., Rp0 = 0, and That is, when the pumping light power at the incident point tends to 0, the polarization gradient relaxation gradually decreases and tends to 0, and the downward trend slows down until it remains unchanged, that is, a flat region appears. In the SERF atomic spin inertia measurement device, when the pumping light power is reduced, the measured relaxation rate approaches the non-polarization gradient relaxation rate, that is, the relaxation rate corresponding to the flat region is the non-polarization gradient relaxation rate. Therefore, the measurement of the atomic spin polarization gradient relaxation in the system can be achieved by measuring the difference between the transverse relaxation rate at the working point and the non-polarization gradient relaxation measured after quickly reducing the pumping power point.

[0098] The advantages of the present invention compared with the prior art are as follows: The polarization gradient relaxation at different pumping light power working points can be accurately measured, and the polarization gradient level inside the gas chamber can be evaluated. When parameters such as the gas chamber temperature, the density ratio inside the gas chamber, and the air pressure are fixed, only one calibration of the non-polarization gradient relaxation term is required (changing 3 to 5 pumping power points and quickly measuring R 2 ), and the current pumping power working point R 2Through the test, the polarization gradient relaxation at the current operating point can be calculated. Compared with the traditional methods of using gradient coils to compensate the magnetic field gradient and using array detection light to measure the electron polarizability gradient, the method proposed in the present invention can quickly measure and directly separate the polarization gradient relaxation. This method does not require the addition of extra coils or the change of the detection optical path, and can realize the in-situ measurement of the polarization gradient in the atomic spin inertia measurement device, providing strong support for the evaluation and suppression of the polarization gradient inside the gas chamber.

[0099] The content not detailedly described 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 made by equivalent substitution, modification and improvement, and / or simplification of the above description without departing from the substantial content of the present invention falls within the protection scope of the present invention.

Claims

1. A method for measuring polarization gradient relaxation of an atomic spin inertial measurement device, characterized in that, it includes the following steps: Step 1, fix the working point parameters of the atomic spin inertial measurement device to have a response signal at a diagonal rate. The working point parameters include the heating temperature and the pumping laser power point P1. The heating temperature is to heat the alkali metal gas cell to the target working temperature, and the pumping laser at the power point P1 polarizes the alkali metal electrons, and then hyperpolarizes the inert gas nuclear spins. By three-axis magnetic field compensation, the device works at the nuclear spin magnetic field self-compensation point; Step 2, decouple the precession of the alkali metal electron spin and the inert gas nuclear spin; Step 3, use the free precession decay method to measure the nuclear spin transverse relaxation rate R at the current P1 2 ; Step 4, test the non-polarization gradient relaxation term in the nuclear spin transverse relaxation; Step 5, test the total transverse relaxation at any pumping laser power point P, calculate the polarization gradient relaxation at the pumping laser power point P. The polarization gradient relaxation at point P is the difference between the total transverse relaxation rate and the non-polarization gradient relaxation rate at point P.

2. The method for measuring polarization gradient relaxation of an atomic spin inertial measurement device according to claim 1, characterized in that, in step 2, a magnetic field Bz with a bias ten times that of the magnetic field self-compensation point is applied in the main magnetic field direction Z to decouple the precession between the electron spin and the nuclear spin.

3. The method for measuring polarization gradient relaxation of an atomic spin inertial measurement device according to claim 2, characterized in that, In step 3, a bias magnetic field By = 2 nT is applied in the Y direction on the basis of Bz. The nuclear spin polarization rate Pn precesses around the direction of the main magnetic field. There is a polarization rate projection Pnx of Pn in the X direction. The free precession decay curve of the change of Pnx in the X direction is obtained through the output signal. The envelope of the decay curve is fitted to obtain the nuclear spin transverse relaxation rate R at the current pumping power point 2 .

4. The method for measuring polarization gradient relaxation of an atomic spin inertial measurement device according to claim 1, characterized in that, Step 4 includes rapidly reducing the pumping laser power to 50% of the P1 point based on P1 and measuring the nuclear spin transverse relaxation rate R 2 , repeating the reduction of the power point to 50% of the previous test point until R 2 tends to be invariant as the pumping laser power decreases; when the pumping laser power changes, the change in the nuclear spin relaxation caused by the change in the electron polarization distribution, R 2 the other relaxation terms are not affected by the pumping laser power, and the measured transverse relaxation at this time is the non-polarization gradient relaxation term.

5. The method for measuring polarization gradient relaxation of an atomic spin inertial measurement device according to claim 4, characterized in that, Said other relaxation terms include spin collision relaxation R sd , electric quadrupole relaxation R quad , and spin exchange relaxation R se , where the spin collision relaxation is the collision relaxation between Ne atoms, and the spin exchange relaxation is the spin exchange relaxation between inert gas Ne atoms and alkali metal electrons: where T 2 is the nuclear spin transverse relaxation time, and is the electron spin polarization gradient relaxation; where p Ne is the air chamber air pressure; wherein are respectively the spin-exchange relaxation of Rb and K atoms to Ne atoms are respectively the exchange collision coefficients between Ne atoms and Rb and K atoms, n K and n Rb are respectively the densities of K and Rb atoms; Among them, are respectively the spin collision relaxations of Rb to Ne, Ne to Rb, K to Ne, and Ne to K, n K , n Rb , n Ne are respectively the densities of K, Rb, and Ne atoms, υ NeRb , v NeK are respectively the spin collision velocities between Ne atoms and Rb and K atoms; Among them, Rp is the pumping rate, T is the temperature, α is a coefficient independent of the pumping power, D n is the diffusion coefficient of the inert gas Ne in the gas chamber, d is the diameter of the gas chamber, n K represents the density of the alkali metal K atoms, W is the Lambert function, R rel is the electron relaxation rate of the alkali metal, R p0 is the pumping rate at the incident point, e is the natural constant, is the polarization gradient, σ v is the photon absorption cross section area.

6. The method for measuring polarization gradient relaxation of an atomic spin inertial measurement device according to claim 1, characterized in that, the atomic spin inertial measurement device includes a pumping laser and a detection laser. The pumping laser is sequentially connected to a first convex lens, a first polarizer, a liquid crystal, a second polarizer, a second convex lens and a reflector. The reflector is connected to a first beam splitter through a first 1 / 2 wave plate. The transmission side of the first beam splitter is sequentially connected to a 1 / 4 wave plate, a gas cell and a fourth photodetector through the gas cell. The reflection side of the first beam splitter is sequentially connected to a first photodetector, a power control system and the liquid crystal. The detection laser is sequentially connected to a third polarizer, a second 1 / 2 wave plate, a second beam splitter, a gas cell, a Wollaston prism and a second photodetector. The second photodetector is connected to a signal acquisition system. The reflection end of the second beam splitter is connected to a third photodetector. The third photodetector and the fourth photodetector are respectively connected to the signal acquisition system. The periphery of the gas cell is sequentially provided with a heating film, a coil, a ferrite and a shielding cylinder from the inside to the outside.

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