A method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device

Abstract

A method for measuring the three-dimensional polarization distribution of an atomic spin inertial measurement device. When the gas cell parameters and the operating temperature point are determined, first determine the method for measuring the electron polarization rate according to whether there are resolvable electron resonance peaks in the system, and measure the electron polarization rate based on the resonance peak frequency or the double compensation point; use the pumping beam and the detection beam that can cover the gas cell in combination with a digital micromirror to control the position of the beam unit passing through the gas cell, and use an array detector or a CCD to detect the light intensity information passing through the gas cell to obtain the electron polarization rate at different positions, and obtain the three-dimensional distribution inside the gas cell. This method does not require moving the detection light and has little impact on the system. At the same time, the area passed by the beam unit can be controlled by the digital micromirror, and the measurement resolution is high. After changing the working state, the three-dimensional distribution inside the gas cell can be quickly measured, providing strong support for the evaluation and suppression of the atomic polarization gradient in the SERF atomic spin inertial measurement device.

Description

Technical Field

[0001] The present invention relates to the field of atomic gyroscopes, and particularly to a method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device. Background Art

[0002] The Spin-Exchange Relaxation-Free (SERF) atomic spin inertia 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 the SERF inertial measurement device. Among them, the atomic spin polarization gradient is the dominant factor. In the SERF atomic spin inertia measurement system, the main source of the polarization gradient is the absorption of the pumping light during the polarization of alkali metal atoms, resulting in the attenuation of the alkali metal electron spin polarization rate along the propagation direction of the pumping light, and a polarization gradient appears 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 point of the SERF atomic spin inertia measurement system is 170°C to 200°C. At this time, the absorption of the pumping light by atoms is intense, and the polarization gradient in the gas chamber becomes an important error source.

[0003] When an external uniform magnetic field is applied, the nuclear spin of the inert gas and the electron spin of the alkali metal in the working state feel each other's magnetic fields. Therefore, when there is a gradient in the electron spin polarization rate, the combined magnetic field (external magnetic field + electron polarization equivalent magnetic field) felt by the nuclear spin has a gradient. Under the same external magnetic field, the precession frequencies of the nuclear spins are different. In the working state, the electron spin and the nuclear spin are coupled to each other, and their precession frequencies are affected by the electron polarization rate in the gas chamber. At the same time, the existence of the longitudinal gradient of the electron spin polarization will cause the transverse relaxation of the nuclear spin, weaken the self-compensation ability of the nuclear spin to the external magnetic field, destroy the stability of the system, and limit the improvement of the system performance. Measuring the three-dimensional polarization distribution in the gas chamber and evaluating the polarization gradient level in the gas chamber are the basis for suppressing the polarization gradient, and provide an evaluation means for reducing the relaxation of the SERF atomic spin inertia measurement system, enhancing the magnetic compensation ability, and improving the nuclear spin magnetic field.

[0004] In the SERF inertial measurement device, most of the test methods for the spatial distribution of electron spins are carried out by moving the detection light. The test accuracy is limited, the repeatability is poor, the resolution is low, and at the same time, the detection light needs to be moved, and a large space is required. The present invention provides a method for measuring the three-dimensional polarization distribution in the SERF inertial measurement device, which provides strong support for the characterization and evaluation of the atomic spin polarization gradient.

[0005] Extract the resonance peak frequencies and double compensation points at different positions by covering the pumping and detection beams of the gas chamber. Use an array detector or a CCD to receive the light intensities at different positions, obtain the polarizability information from the changes in light intensity, and extract and normalize the polarizability information to obtain the three-dimensional polarization distribution information in the gas chamber. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the present invention provides a method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device.

[0007] The technical solution of the present invention is as follows:

[0008] A method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device, characterized by comprising the following steps:

[0009] Step 1, fix the working point parameters of the atomic spin inertia measurement device, where the working point parameters include the gas chamber temperature and the pumping laser power, make the device work at the nuclear spin self-compensation point, and determine the initial position of the first digital micromirror on the pumping optical path and / or the initial position of the second digital micromirror on the detection optical path to fix the initial position of the beam unit passing through the gas chamber;

[0010] Step 2, apply a sinusoidal modulation magnetic field Bx in the X direction, change the modulation frequency, and determine whether there is a resolvable electron resonance peak in the system output. If so, go to step A3; if not, go to step B3;

[0011] Step A3, on the basis of the compensation point, change the Z-axis magnetic field Bz, measure the corresponding resonance peak frequency points at different Bz values, and fit to obtain the slowing factor Q;

[0012] Step A4, fit the electron polarizability according to the slowing factor Q Then go to step 5;

[0013] Step B3, apply a square wave modulation magnetic field By on the Y axis, change the Z-axis magnetic field Bz, find two Z-axis magnetic field double compensation points Bz1 and Bz2 where the difference in the response of the steady-state signal to By is 0, and use the signal difference obtained from the free precession decay and a small range change in Bz to calculate the nuclear spin relaxation rate Rtotn and the electron spin relaxation rate Rtote;

[0014] Step B4, calculate the electron polarizability using Bz1, Bz2, Rtotn, and Rtote Then go to step 5;

[0015] Step 5, determine whether the beam unit has traversed the range of the gas chamber. If not, use the digital micromirror to change the position of the beam unit passing through the gas chamber, and return to step 2; if so, go to step 6;

[0016] Step 6: Based on the information on the electron polarizability distribution of the cross-sections of the pumping beam and the detection beam obtained in the detection optical path and the pumping optical path respectively, obtain the three-dimensional polarization distribution inside the gas chamber. The three-dimensional polarization distribution includes the YOZ plane covered by the detection beam and the XOY plane covered by the pumping beam. The polarization distribution refers to the distribution of the electron polarizability in the direction of the polarization principal axis, i.e., the Z direction. of the distribution.

[0017] In the said Step 1, it includes using the pumping laser to polarize the alkali metal electrons, and then hyperpolarizing the nuclear spins of the inert gas, so that the system is in a polarized state, and the device operates at the magnetic field self-compensation point to respond to the input of the external angular rate.

[0018] The resolvable electron resonance peaks in the said Step 2 meet the following judgment criteria: when the magnetic field modulation frequency changes by 1 Hz, the resonance peak amplitude changes by more than 0.5 mV; the change range of the modulation frequency is: 1 Hz < ω < 400 Hz, where ω is the modulation frequency.

[0019] The frequency corresponding to the electron transverse magnetic field response resonance peak conforms to the following relational expression:

[0020]

[0021] where ω represents the frequency, γ e is the electron gyromagnetic ratio, B z is the actively applied longitudinal main magnetic field, B n is the equivalent Feynman contact field generated by the nuclear spin for the electron spin, Lz is the longitudinal optical frequency shift, is the electron spin transverse relaxation rate, is the slowing-down factor of the alkali metal gas nucleons for the electrons, related to the electron spin polarizability and is abbreviated as Q.

[0022] The nuclear spin quantum number I e = 3 / 2 and I e = 5 / 2 for the alkali metal atoms, and the slowing-down factors are Q 3 / 2 and Q 5 / 2 respectively. The expression of the slowing-down factor related to the polarizability is:

[0023]

[0024]

[0025] The density ratio D r of the atoms with nuclear spin quantum number 3 / 2 to the atoms with nuclear spin quantum number 5 / 2 is 0.385, and the mixed slowing-down factor Q1 is

[0026]

[0027]

[0028]

[0029] wherein represents the nuclear magnetic field, represents the electron magnetic field, γ e is the electron gyromagnetic ratio, γ n is the nuclear spin gyromagnetic ratio, is the electron spin transverse relaxation rate, which is calibrated by varying Bz near the compensation point and fitting the relationship between the difference in the response of the signal to the square wave and Bz; is the nuclear spin longitudinal relaxation rate, which is measured by the free precession decay signal; B z1 、B z2 are respectively the small compensation point and the large compensation point of the Z-axis magnetic field, collectively referred to as the double compensation point,

[0030]

[0031]

[0032] By using the pumping light and detection light covering the gas chamber, the detector array or CCD, measuring the double compensation points at different positions, as well as the electron and nuclear relaxation rates at different positions, the electron and nuclear magnetic fields at different positions can be measured, and the spin polarization distributions of electrons and nuclei can be obtained.

[0033] The incident light of the first digital micromirror comes from the pumping laser connected through the second convex lens, the second polarizer, the liquid crystal, the first polarizer and the first convex lens in sequence. The reflected light of the first digital micromirror passes through the first λ / 2 wave plate, the first beam splitter, the first λ / 4 wave plate, the gas chamber, the second λ / 4 wave plate, the second λ / 2 wave plate and the second beam splitter in sequence and is connected to the first detector array or CCD. The first beam splitter is connected to the liquid crystal through the first photodetector and the power control system in sequence. The incident light of the second digital micromirror comes from the detection laser connected through the fourth convex lens and the third convex lens in sequence. The reflected light of the second digital micromirror passes through the third polarizer, the third λ / 2 wave plate, the third beam splitter, the gas chamber, the fourth λ / 2 wave plate and the fourth beam splitter in sequence and is connected to the second detector array or CCD. The third beam splitter is connected to the second photodetector. The second photodetector, the second detector array or CCD and the first detector array or CCD are respectively connected to the signal acquisition system, and the signal acquisition system extracts the polarization information of the alkali metal gas chamber.

[0034] A heating film, a coil, a ferrite and a shielding cylinder are sequentially arranged outward around the gas chamber.

[0035] The technical effects of the present invention are as follows: For a method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device of the present invention, when the gas cell parameters and the operating temperature point are determined, first, the method for measuring the electron polarization rate is determined according to whether there is a resolvable electron resonance peak in the system, and the electron polarization rate is measured based on the resonance peak frequency or the double compensation point; the pumping beam and the detection beam that can cover the gas cell are combined with a digital micromirror to control the position of the beam unit passing through the gas cell, and an array detector or a CCD is used to detect the light intensity information passing through the gas cell to obtain the electron polarization rate at different positions, thereby obtaining the three-dimensional distribution inside the gas cell. This method does not require moving the detection light and has little impact on the system. At the same time, the area passed by the beam unit can be controlled by the digital micromirror, and the measurement resolution is high. After changing the working state, the three-dimensional distribution inside the gas cell can be quickly measured, providing strong support for the evaluation and suppression of the atomic polarization gradient in the SERF atomic spin inertia measurement device. Description of the Drawings

[0036] Figure 1 It is a schematic flow chart for implementing a method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device of the present invention. Figure 1It includes Step 1: Fix the working point parameters such as the gas cell temperature and the pumping laser power. The device operates at the nuclear spin self-compensation point, determine the initial position of the digital micromirror to fix the initial position of the beam unit passing through the gas cell; Step 2: Apply a sinusoidal modulation magnetic field Bx in the X direction, vary the modulation frequency, and determine whether there is a resolvable electron resonance peak in the system with an error range less than 1 Hz. If so, enter Step A3; if not, enter Step B3; Step A3: Use the digital micromirror to control the position of the beam unit passing through the gas cell and perform the electron polarizability test. If there is a resonance peak, based on the compensation point, vary the magnetic field Bz in the Z direction and measure the corresponding resonance peak frequency points at different Bz values. Fit the slope of the resonance peak frequency points and the Z-axis magnetic field to calculate the slowing-down factor Q; Step A4: Fit the electron polarizability according to the slowing-down factor, and then enter Step 5; Step B3: If there is no electron resonance peak, apply a square-wave modulation magnetic field By in the Y axis, vary the magnetic field Bz in the Z axis, and find two Z-axis magnetic field compensation points Bz1 and Bz2 where the difference in the response of the steady-state signal to By is 0. Use the difference in the signal obtained from the free precession decay and a small range of variation of Bz to calculate the nuclear spin relaxation rate Rtotn and the electron spin relaxation rate Rtote; Step B4: Calculate the electron polarizability based on the measured parameters Bz1, Bz2, Rtotn, and Rtote, and then enter Step 5; Step 5: Whether the beam unit has traversed the range of passing through the gas cell. If not, use the digital micromirror to change the position of the beam unit passing through the gas cell and return to Step 2. If so, enter Step 6; Step 6: According to the electron polarizability distribution information of the cross-sections of the pumping beam and the detection beam obtained in the detection optical path and the pumping optical path respectively, obtain the three-dimensional polarization distribution inside the gas cell. The three-dimensional polarization distribution includes the YOZ plane covered by the detection beam and the XOY plane covered by the pumping beam. The polarization distribution refers to the distribution of the electron polarizability in the direction of the polarization principal axis (Z direction).

[0037] Figure 2 Schematic diagram of the system structure used for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device according to the present invention.

[0038] Figure 3 Schematic diagram of the relationship curve between the slowing-down factor and the electron polarizability. Figure 3 The abscissa of (Z-direction electron polarizability or longitudinal electron polarizability), the abscissa scale values are 0, 0.2, 0.4, ···, 1; the ordinate is the slowing-down factor Q, and the ordinate scale values are 5, 6, ···, 11.

[0039] The reference numerals are listed as follows: 1 - pumping laser; 2 - first convex lens; 3 - first polarizer; 4 - liquid crystal; 5 - second polarizer; 6 - second convex lens; 7 - first digital micromirror device; 8 - first λ / 2 wave plate; 9 - first beam splitter; 10 - first photodetector; 11 - power control system (the reflection end of the first beam splitter 9 is connected to the feedback end of the power control system 11, and the control end of the power control system 11 is connected to the liquid crystal 4); 12 - first λ / 4 wave plate; 13 - second λ / 4 wave plate; 14 - second λ / 2 wave plate; 15 - second beam splitter; 16 - first detector array (or CCD, charge coupled device); 17 - detection laser; 18 - third convex lens; 19 - fourth convex lens; 20 - second digital micromirror device; 21 - third polarizer; 22 - third A / 2 wave plate; 23 - third beam splitter; 24 - second photodetector; 25 - fourth λ / 2 wave plate; 26 - fourth beam splitter; 27 - second detector array (or CCD); 28 - shielding cylinder; 29 - ferrite; 30 - coil; 31 - heating film; 32 - gas chamber (or alkali metal gas chamber); 33 - signal acquisition system (the output end of the fourth beam splitter 26 is connected to the second detector array 27 or CCD, the second detector array 27 is connected to the signal acquisition system 33, and the signal acquisition system 33 extracts the polarization information of the alkali metal gas chamber 32). Detailed implementation manners

[0040] The present invention will be described below in conjunction with the accompanying drawings ( Figures 1 - 3 ). and embodiments.

[0041] Figure 1 It is a schematic flow chart of a method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device according to the present invention. Figure 2 It is a schematic structural diagram of a system used for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device according to the present invention. Figure 3 It is a schematic diagram of the relationship curve between the slowing factor and the electron polarizability. Refer to Figures 1 to 3As shown, a method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device includes the following steps: Step 1, fix the working point parameters of the atomic spin inertia measurement device, where the working point parameters include the gas cell temperature and the pumping laser power, make the device work at the nuclear spin self-compensation point, and determine the initial position of the first digital micromirror on the pumping optical path and / or the initial position of the second digital micromirror on the detection optical path to fix the initial position of the beam unit passing through the gas cell; Step 2, apply a sinusoidal modulation magnetic field Bx in the X direction, vary the modulation frequency, and determine whether there is a resolvable electron resonance peak in the system output. If so, go to Step A3; if not, go to Step B3; Step A3, on the basis of the compensation point, vary the magnetic field Bz in the Z direction, measure the corresponding resonance peak frequency points at different Bz values, and fit to obtain the slowing factor Q; Step A4, fit the electron polarization rate according to the slowing factor Q Then go to Step 5; Step B3, apply a square wave modulation magnetic field By on the Y axis, vary the magnetic field Bz in the Z axis, find two Z-axis magnetic field double compensation points Bz1 and Bz2 where the difference in the response of the steady-state signal to By is 0, and use the difference in the signals obtained from the free precession decay and the small-range variation of Bz to calculate the nuclear spin relaxation rate Rtotn and the electron spin relaxation rate Rtote; Step B4, calculate the electron polarization rate using Bz1, Bz2, Rtotn, and Rtote Then go to Step 5; Step 5, determine whether the beam unit has traversed the range of the gas cell. If not, use the digital micromirror to change the position of the beam unit passing through the gas cell and return to Step 2. If so, go to Step 6; Step 6, according to the electron polarization rate distribution information of the pumping beam and the detection beam cross-sections obtained in the detection optical path and the pumping optical path respectively, obtain the three-dimensional polarization distribution inside the gas cell. The three-dimensional polarization distribution includes the YOZ plane covered by the detection beam and the XOY plane covered by the pumping beam, and the polarization distribution refers to the distribution of the electron polarization rate in the polarization principal axis direction, i.e., in the Z direction of the distribution.

[0042] In Step 1, it includes polarizing alkali metal electrons using the pumping laser, and then hyperpolarizing the nuclear spin of the inert gas, so that the system is in a polarized state, and the device works at the magnetic field self-compensation point to respond to the external angular rate input. The resolvable electron resonance peak in Step 2 meets the following judgment criteria: when the magnetic field modulation frequency changes by 1 Hz, the resonance peak amplitude changes by more than 0.5 mV; the change range of the modulation frequency is: 1 Hz < ω < 400 Hz, where ω is the modulation frequency. The frequency corresponding to the electron transverse magnetic field response resonance peak conforms to the following relational expression:

[0043]

[0044] where ω represents the frequency, γ e is the electron gyromagnetic ratio, B zis the actively applied longitudinal main magnetic field, B n is the equivalent Feynman contact field generated by nuclear spin for electron spin, Lz is the longitudinal optical frequency shift, is the electron spin transverse relaxation rate, is the slowing-down factor of alkali metal gas nucleons on electrons, related to the electron spin polarization rate and is abbreviated as Q.

[0045] Nuclear spin quantum number I e = 3 / 2 and I e = 5 / 2 of the alkali metal atoms have slowing-down factors of Q 3 / 2 and Q 5 / 2 , and the expression of the slowing-down factor and the polarization rate is:

[0046]

[0047]

[0048] The density ratio D of atoms with nuclear spin quantum number 3 / 2 to atoms with nuclear spin quantum number 5 / 2 r = 0.385, and the mixed slowing-down factor Q1 is

[0049]

[0050]

[0051]

[0052] where represents the nucleon magnetic field, represents the electron magnetic field, γ e is the electron gyromagnetic ratio, γ n is the nuclear spin gyromagnetic ratio, is the electron spin transverse relaxation rate, which is calibrated by varying Bz near the compensation point and fitting the relationship between the difference in the response of the signal to the square wave and Bz; is the nuclear spin longitudinal relaxation rate, which is measured by the free precession decay signal; b z1 、B z2 are the small compensation point and the large compensation point of the Z-axis magnetic field respectively, collectively referred to as the double compensation point,

[0053]

[0054]

[0055] By using the pumping light and detection light that cover the gas chamber, a detector array or a CCD, measuring the double compensation points at different positions, as well as the electron and nucleon relaxation rates at different positions, the electron and nucleon magnetic fields at different positions can be measured, and the spin polarization distributions of electrons and nucleons can be obtained.

[0056] The incident light of the first digital micromirror 7 comes from the pumping laser 1 which is connected in sequence through the second convex lens 6, the second polarizer 5, the liquid crystal 4, the first polarizer 3 and the first convex lens 2. The reflected light of the first digital micromirror 7 passes through the first λ / 2 wave plate 8, the first beam splitter 9, the first λ / 4 wave plate 12, the gas chamber 32, the second λ / 4 wave plate 13, the second λ / 2 wave plate 14 and the second beam splitter 15 in sequence to be connected to the first detector array 16 or the CCD. The first beam splitter 9 is connected to the liquid crystal 4 through the first photodetector 10 and the power control system 11 in sequence. The incident light of the second digital micromirror 20 comes from the detection laser 17 which is connected through the fourth convex lens 19 and the third convex lens 18 in sequence. The reflected light of the second digital micromirror 20 passes through the third polarizer 21, the third λ / 2 wave plate 22, the third beam splitter 23, the gas chamber 32, the fourth λ / 2 wave plate 25 and the fourth beam splitter 26 in sequence to be connected to the second detector array 27 or the CCD. The third beam splitter 23 is connected to the second photodetector 24. The second photodetector 24, the second detector array 27 or the CCD and the first detector array 16 or the CCD are respectively connected to the signal acquisition system 33, and the signal acquisition system 33 extracts the polarization information of the alkali metal gas chamber 32. A heating film 31, a coil 30, a ferrite 29 and a shielding cylinder 28 are sequentially arranged outward around the gas chamber 32.

[0057] The advantages of the present invention compared with the prior art are as follows: The polarization rate distribution at different positions inside the gas chamber can be accurately measured, and the polarization gradient level inside the gas chamber can be evaluated. After the modulation magnetic field is applied, it can be quickly removed without affecting the working state of the system. Compared with the traditional method of moving the detection light to measure the Z-direction polarization distribution, this method can measure the three-dimensional distribution without moving the position of the detection light, and can simultaneously measure the polarization distributions along the X, Y, and Z directions, which is beneficial to improving the accuracy and miniaturization of the SERF inertial measurement system. Using a CCD can increase the test resolution of this method. The method proposed by the present invention can quickly measure the three-dimensional polarization rate distribution inside the gas chamber, obtain the atomic polarization rate gradient level inside the gas chamber, and provide strong support for the evaluation and suppression of the polarization gradient inside the gas chamber.

[0058] A method for measuring the three-dimensional polarization distribution of an atomic spin inertial measurement device, and the measurement steps are as follows:

[0059] Step 1: Fix the working point parameters such as the heating temperature and the pumping laser power. The device is in the normal gyro working state (nuclear spin self-compensation point) and has 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 using the pumping laser, and then hyperpolarize the inert gas nuclear spins, 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.

[0060] Step 2: Apply a sinusoidal modulation magnetic field Bx in the transverse direction (X direction), vary the modulation frequency, and determine whether there is a resolvable electron resonance peak in the system. The judgment criterion is that when the magnetic field modulation frequency changes by 1 Hz, the resonance peak amplitude changes by more than 0.5 mV.

[0061] Step 3: Conduct the test of the electron polarization rate and measure the polarization distribution of the detection light cross-section. If it is resolvable, calculate the electron polarization rate by the method of varying the main magnetic field to measure the resonance peak frequency. There is a transverse magnetic field with different modulation frequencies (0.01 Hz - 400 Hz). The atoms precess with the modulation magnetic field, and the precession amplitude is demodulated by a lock-in amplifier. The modulation frequency corresponding to the maximum point of this amplitude is the electron resonance peak frequency. Vary the Z-axis magnetic field Bz, measure the corresponding frequencies of the electron resonance peaks under different magnetic fields, and fit to obtain the electron slowing factor Q.

[0062] If it is not resolvable, calculate and measure the electron polarization rate using the double compensation point method. Apply a square wave modulation magnetic field in the Y axis, vary the Z-axis main magnetic field, observe the change of the signal difference with the By square wave, and find the main magnetic fields Bz1 and Bz2 corresponding to the signal difference of 0. Then change Bz, measure the steady-state signal difference under the input of the Y-direction square wave magnetic field By, and calculate the electron relaxation rate. Measure the nuclear spin relaxation rate through the free precession decay signal.

[0063] Step 4: Calculate the electron polarization rate respectively through the parameters measured in the two cases in Step 3.

[0064] Step 5: Use the digital micromirror in the optical path to control the beam unit to pass through the gas cell, and use an array detector or a CCD to measure the detection light intensity of the corresponding pixel points. Repeat Steps 3 - 4 to make the beam unit traverse through the gas cell, and solve the electron polarization rate distribution on the beam cross-section.

[0065] Step 6: Execute Steps 2 - 5 respectively in the detection light and pumping optical paths to obtain the electron polarization rate distribution information of the pumping light and detection light cross-sections, and obtain the three-dimensional polarization distribution inside the gas cell.

[0066] The principle of the present invention is as follows:

[0067] The position of the beam unit passing through the gas cell is controlled by a digital micromirror, and according to whether the resonance peak can be resolved, the resonance peak or the double compensation point method is selected to measure the polarizability at the corresponding position. The intensity of the beam unit passing through the gas cell is detected by an array detector or a CCD, and the slowing-down factor and the double compensation point at different positions are measured, and the polarizability distribution on different cross-sections is calculated. In the system, the diameters of the pumping beam and the detection beam cover the alkali metal gas cell, and the longitudinal electronic polarizability in each gas cell unit cell is related to the optical pumping rate R op at that place and the longitudinal electron relaxation rate R rel .

[0068]

[0069] Due to the absorption of the pumping light by the unpolarized atoms, there is an optical pumping rate gradient along the propagation direction of the pumping light. The optical pumping rate R p (z) is expressed by the attenuation equation as the pumping light passes through the path length z in the gas cell:

[0070]

[0071] where P e (z) is the electron spin polarizability at the path length z where the pumping light passes through the gas cell, σ v is the photon absorption cross-section area, and n K represents the density of alkali metal K atoms.

[0072] There is a transverse sinusoidal magnetic field with different modulation frequencies ω (1 Hz < ω < 400 Hz) applied, and the peak-to-peak value is B x0 . The atoms precess with the modulation magnetic field, and the precession amplitude is demodulated by a lock-in amplifier. The modulation frequency corresponding to the maximum point of this amplitude is the resonance peak frequency of the electrons. When there is a resolvable electron resonance peak in the system, the response amplitude of the system to the x-direction magnetic field is:

[0073]

[0074] where is the transverse electron polarizability, is the electron polarizability, is the slowing-down factor of the alkali metal gas nucleons on the electrons, which is related to the electron spin polarizability. γ e is the electron gyromagnetic ratio, B z is the actively applied longitudinal main magnetic field, B n is the equivalent Feynman contact field generated by the nuclear spin on the electron spin, and Lz is the longitudinal optical frequency shift. The optical frequency shift is small and can be ignored. is the electron spin transverse relaxation rate.

[0075] The resonance peak corresponding frequency of the electron transverse magnetic field response

[0076]

[0077] The electron Larmor precession frequency in the SERF atomic spin inertia measurement system is

[0078]

[0079] It can be seen from the above formula that the slope of the change of the frequency corresponding to the electron resonance peak with Bz and the slowdown factor are inversely proportional. is the polarizability function, which can be abbreviated as Q, and the nuclear spin is I e = 3 / 2 and I e = 5 / 2 of the alkali metal atoms, the slowdown factors are Q 3 / 2 and Q 5 / 2 , and the expressions of the slowdown factor and the polarizability are:

[0080]

[0081]

[0082] The Rb atoms filled inside the gas cell are natural Rb, including 72.2% of 85 Rb and 27.8% of 87 Rb, the density of K atoms is n K , and the density of Rb atoms is n Rb . The atoms with a nuclear spin of 3 / 2 are composed of K and 87 Rb, and its density is n 3 / 2 = n K + 0.278n Rb , the atoms with a nuclear spin of 5 / 2 are mainly composed of 85 Rb, n 5 / 2 = 0.722n Rb , the density ratio D of the atoms with a nuclear spin of 3 / 2 to the atoms with a nuclear spin of 5 / 2 r = n 3 / 2 / n 5 / 2 = (n K + 0.278n Rb ) / 0.722n Rb , the density ratio of K and Rb atoms is D r0 = n K / n Rb , D r0 is usually less than 0.01, then n K < 0.01n Rb , Dr is mainly determined by the proportion of 85 Rb and 87 Rb, and is affected by D r0has less impact. The density ratio of atoms with nuclear spin 3 / 2 to atoms with nuclear spin 5 / 2 is:

[0083]

[0084] The mixing slowdown factor Q1 is

[0085]

[0086] The slowdown factors at different polarizabilities are as Figure 3 shown. The horizontal axis is the electronic polarizability, and the vertical axis is the slowdown factor. The electronic polarizability and the slowdown factor correspond one by one.

[0087] By changing the magnitude of the longitudinal main magnetic field Bz and measuring the slope of the resonance peak frequency and the main magnetic field, the slowdown factor can be fitted, and then the electronic polarizability can be calculated.

[0088] When the electronic relaxation rate Rtote of the system is relatively large, the linewidth at the electronic resonance peak is large, and the top of the resonance peak is flat. It is difficult to measure the polarizability by identifying the resonance peak. This patent also proposes a method for measuring the polarizability using double compensation points for SERF inertial measurement devices with large electronic relaxation. When the compensation magnetic field is applied in the Z direction, the inertial measurement sensitivity of the system is the highest. Define the deviation of the Z-axis magnetic field Bz from B c as δB z = B c - B z . The transverse electronic polarizability for the Y-direction magnetic field B y has the following relationship with δB z :

[0089]

[0090] K(By) is the scaling coefficient of the steady-state response of the electronic transverse polarizability to the square-wave modulated magnetic field By. The Z-direction applied magnetic field corresponding to the difference of the DC steady-state response of the system to By being 0 is called the compensation point of the system. At this time

[0091] K By (δB z ) = 0

[0092] When a square-wave magnetic field By is applied in the Y direction and the difference of the steady-state signal is 0, the value of δB z is as follows:

[0093]

[0094]

[0095] δB z2 = 0 = Bc -B z2

[0096] where γ e is the electron gyromagnetic ratio, and γ n is the nuclear spin gyromagnetic ratio. is the electron spin transverse relaxation rate, which can be calibrated by varying Bz near the compensation point and fitting the relationship between the response difference of the signal to the square wave and Bz. is the nuclear spin longitudinal relaxation rate, which can be measured from the free precession decay signal. B z1 and B z2 are the small and large compensation points of the Z-axis magnetic field, collectively called the double compensation points, and their values are respectively:

[0097]

[0098]

[0099] Thus, based on the Z-axis magnetic field compensation points B z1 and B z2 , the magnitudes of the electron magnetic field and the nucleon magnetic field can be obtained:

[0100]

[0101]

[0102] Therefore, by using the pumping light, detection light, and detector array covering the gas chamber to measure the double compensation points at different positions, as well as the electron and nucleon relaxation rates at different positions, the electron and nucleon magnetic fields at different positions can be measured, and the spin polarization distributions of electrons and nucleons can be obtained.

[0103] In the SERF atomic spin inertial measurement device, first, it is determined whether there is a resolvable electron resonance peak in the system. By measuring the resonance peak frequency or double compensation points at different positions, the electron polarization rate is obtained. By controlling the positions of the pumping and detection beam units passing through the gas chamber with a digital micromirror device, and combining the detection signals of the array detector or CCD, the slowing factor and double compensation points at different positions can be obtained, and then the three-dimensional distribution of the atomic polarization rate in the gas chamber can be obtained. After changing the working state (different temperatures or pumping laser powers), repeating the measurement steps can obtain the three-dimensional distribution in the gas chamber under different conditions, which is convenient for subsequent polarization gradient suppression.

[0104] 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 specified 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 is an equivalent replacement, modification and improvement, and / or simplification of the above description without departing from the essential content of the present invention falls within the protection scope of the present invention.

Claims

1. A method for measuring the three-dimensional polarization distribution of an atomic spin inertia measurement device, characterized in that, It includes the following steps: Step 1: Fix the working point parameters of the atomic spin inertia measurement device. The working point parameters include the gas chamber temperature and the pumping laser power, so that the device works at the nuclear spin self-compensation point, and determine the initial position of the first digital micromirror on the pumping optical path and / or the initial position of the second digital micromirror on the detection optical path, so as to fix the initial position of the beam unit passing through the gas chamber; Step 2: Apply a sinusoidal modulation magnetic field Bx in the X direction, change the modulation frequency, and judge whether there is a distinguishable electron resonance peak in the system output. If so, go to step A3; if not, go to step B3; Step A3: Based on the self-compensation point, change the Z-direction magnetic field Bz, measure the corresponding resonance peak frequency points at different Bz values, and fit to obtain the slowdown factor Q; Step A4, fitting the electronic polarizability according to the slowdown factor Q Then proceed to Step 5; Step B3, apply a square-wave modulated magnetic field By along the Y-axis, vary the magnetic field Bz along the Z-axis, and find two Z-axis magnetic field double compensation points B where the difference in the response of the steady-state signal to By is 0 z1 and B z2 , and measure the longitudinal relaxation rate of nuclear spins using free precession decay and calculate the transverse relaxation rate of electron spins using the signal difference obtained from a small range of variation of Bz Step B4, using B z1 , B z2 , and calculate the electronic polarizability Then proceed to Step 5; Step 5: Whether the beam unit has traversed the range of the gas chamber. If not, use the digital micromirror to change the position of the beam unit passing through the gas chamber, and return to step 2. If so, go to step 6; Step 6: Obtain the three-dimensional polarization distribution inside the gas chamber according to the information on the electron polarizability distribution of the cross-sections of the pump beam and the detection beam obtained in the detection optical path and the pump optical path respectively. The three-dimensional polarization distribution includes the YOZ plane covered by the detection beam and the XOY plane covered by the pump beam. The polarization distribution refers to the distribution of the electron polarizability in the direction of the polarization principal axis, i.e., in the Z direction. distribution.

2. The method for measuring the three-dimensional polarization distribution of the atomic spin inertia measurement device according to claim 1, wherein In step 1, it includes polarizing alkali metal electrons with the pumping laser, and then hyperpolarizing the nuclear spins of inert gases, so that the system is in a polarized state, and the device works at the magnetic field self-compensation point to respond to the external angular rate input.

3. The method for measuring the three-dimensional polarization distribution of the atomic spin inertia measurement device according to claim 1, wherein The distinguishable electron resonance peak in step 2 meets the following judgment criteria: when the magnetic field modulation frequency changes by 1 Hz, the resonance peak amplitude changes by more than 0.5 mV; the change range of the modulation frequency is: 1 Hz < ω < 400 Hz, where ω is the modulation frequency.

4. The method for measuring the three-dimensional polarization distribution of the atomic spin inertial measurement device according to claim 1, wherein The resonance peak frequency points in step A3 meet the following relational formula: where ω represents the frequency, γ e is the electron gyromagnetic ratio, B z is the longitudinally applied main magnetic field, B n is the equivalent Feynman contact field generated by nuclear spin for electron spin, Lz is the longitudinal optical frequency shift, is the electron spin transverse relaxation rate, is the slowing-down factor of alkali metal gas nucleons on electrons, related to the electron spin polarization rate and is abbreviated as Q.

5. The method for measuring the three-dimensional polarization distribution of the atomic spin inertia measurement device according to claim 1, characterized in that, Nuclear spin quantum number I e = 3 / 2 and I e = 5 / 2 of the alkali metal atoms, the slowing down factors are Q 3 / 2 and Q 5 / 2 , the expression of the slowing down factor and the polarizability is as follows: Density ratio D of an atom with a nuclear spin quantum number of 3 / 2 and an atom with a nuclear spin quantum number of 5 / 2 r = 0.385, and the mixing slowdown factor Q1 is 6. The three-dimensional polarization distribution measurement method of the atomic spin inertia measurement device according to claim 1, characterized in that Among them represents the nuclear magnetic field, represents the electron magnetic field, γ e is the electron gyromagnetic ratio, γ n is the nuclear spin gyromagnetic ratio, is the electron spin transverse relaxation rate, which is calibrated by varying Bz near the self-compensation point and fitting the relationship between the response difference of the signal to the square wave and Bz; is the nuclear spin longitudinal relaxation rate, which is measured by the free precession decay signal; B z1 、B z2 are the small compensation point and the large compensation point of the Z-axis magnetic field respectively, collectively referred to as the double compensation point, By using the pumping light, detection light, and detector array covering the gas chamber, measure the double compensation points at different positions, as well as the electron and nucleon relaxation rates at different positions, so as to measure the electron and nucleon magnetic fields at different positions and obtain the spin polarization distributions of electrons and nucleons.

7. The method for measuring the three-dimensional polarization distribution of the atomic spin inertia measurement device according to claim 1, wherein The incident light of the first digital micromirror comes from the pumping laser connected in sequence through the second convex lens, second polarizer, liquid crystal, first polarizer, and first convex lens. The reflected light of the first digital micromirror passes through the first λ / 2 wave plate, first beam splitter, first λ / 4 wave plate, gas chamber, second λ / 4 wave plate, second λ / 2 wave plate, and second beam splitter to connect to the first detector array. The first beam splitter is connected to the liquid crystal through the first photodetector and the power control system in sequence. The incident light of the second digital micromirror comes from the detection laser connected in sequence through the fourth convex lens and third convex lens. The reflected light of the second digital micromirror passes through the third polarizer, third λ / 2 wave plate, third beam splitter, gas chamber, fourth λ / 2 wave plate, and fourth beam splitter to connect to the second detector array. The third beam splitter is connected to the second photodetector. The second photodetector, second detector array, and first detector array are respectively connected to the signal acquisition system, and the signal acquisition system extracts the polarization information of the alkali metal gas chamber.

8. The method for measuring the three-dimensional polarization distribution of the atomic spin inertia measurement device according to claim 1, characterized in that A heating film, a coil, a ferrite, and a shielding cylinder are sequentially arranged outward around the gas chamber.

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