SERF gyroscope pump light direction residual magnetic field measurement method

Abstract

The invention relates to an SERF gyroscope pump light direction residual magnetic field measurement method, which is characterized in that pump light is respectively adjusted to left-hand circular polarization and right-hand circular polarization in an SERF gyroscope system to perform pump polarization, and the characteristic that the light displacement is equal in size and opposite in direction and the residual magnetic field is kept unchanged in two states is utilized to measure the residual magnetic field in the SERF gyroscope pump light direction. The total magnetic fields obtained by testing in the two states are combined to calculate and eliminate optical displacement, so that the measurement of the residual magnetic field is realized. According to the invention, in-situ measurement of the residual magnetic field in the pumping light direction can be realized without adding a device or changing the system light path in the system light path, the operation in the test process is relatively simple, and the measurement result is relatively reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of SERF gyroscopes, and in particular relates to a method for measuring a residual magnetic field in a pump light direction of a SERF gyroscope. Background Art

[0002] SERF gyroscopes need to work in a near-zero field environment to ensure the measurement accuracy and stability of the SERF gyroscope. There are generally two methods used to achieve near-zero field, namely passive magnetic shielding and active magnetic compensation. Passive magnetic shielding generally uses 1J85 Permalloy soft magnetic material to process into a multi-layer magnetic shielding tube, and changes the direction of the external magnetic field through multiple layers of soft magnetic materials to achieve shielding. However, after a certain level of residual magnetism is achieved by this method, the shielding effect is not significantly improved by simply increasing the number of shielding tube layers, so an active magnetic compensation method is needed. The active magnetic compensation method is to generate a corresponding magnetic field by passing a certain current through a three-dimensional coil, which is equal to the residual magnetism in size and opposite in direction to offset the residual magnetic field. However, the premise of active magnetic compensation is that the size and direction of the residual magnetism need to be known in order to effectively compensate for it.

[0003] There are many ways to measure residual magnetism, including built-in high-precision magnetometers, atomic spin polarization signal measurement, etc., but these methods have certain limitations. For example, built-in high-precision magnetometers cannot measure residual magnetism in situ, and on the other hand, they take up a certain amount of space and affect the measurement of the SERF gyroscope itself. Using atomic spin polarization signals for residual magnetism measurement cannot effectively remove the influence of optical displacement on the test results, and sometimes the optical path needs to be changed. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention proposes a method for measuring the residual magnetic field in the direction of pump light of a SERF gyroscope, which does not require adding devices in the system optical path or changing the system optical path, can achieve in-situ measurement and has accurate measurement results.

[0005] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0006] A method for measuring residual magnetic field in pump light direction of a SERF gyroscope comprises the following steps:

[0007] Step 1: Active magnetic compensation is performed through the three-dimensional magnetic field coil in the SERF gyroscope to compensate the ambient magnetic field felt by the alkali metal gas chamber to as close to zero as possible;

[0008] Step 2: After the magnetic compensation is completed, a set fixed magnetic field is applied to the coil in the y direction;

[0009] Step 3: adjust the pump light to left-handed polarized light by rotating the λ / 4 wave plate in the pump light path, adjust its wavelength to wavelength λ, and record the wavelength value;

[0010] Step 4: Adjust the signal generator of the z-direction magnetic field coil in the control circuit, set its scanning mode to ramp scanning, and set the initial value and step size of the output voltage so that the corresponding magnetic field scanning range is -1000nT-1000nT;

[0011] Step 5: The signal generator outputs, and the data acquisition system is used to collect the output signal of the balanced detector; after at least one complete cycle is scanned, the collection of the detector output signal is stopped;

[0012] Step 6: Use the relationship between the detector output and the scanning magnetic field to fit the detector output data and the magnetic field scanning value obtained within a complete cycle to obtain L z ' - ;

[0013] Step 7: Adjust the pump light to right-handed circular polarization by rotating the λ / 4 wave plate in the pump light path, keep the wavelength unchanged, and keep the signal generator settings unchanged; after the signal generator outputs, synchronously collect the balanced detector signal; wait until at least one complete cycle is scanned, and stop collecting the detector output signal;

[0014] Step 8: Use the relationship between the detector output and the scanning magnetic field to fit the detector output data and the magnetic field scanning value obtained within a complete cycle to obtain L z ' + ;

[0015] Step 9: Change the pump light wavelength within the set wavelength range with a set step length, and repeat steps 3 to 8 at each wavelength to obtain L at different pump wavelengths. z ' - and L z ' + ;

[0016] Step 10: Fit the two sets of data using the light displacement formula to obtain the fitted theoretical light displacement data L z ″ - and L z ″ + , and then the two sets of data are calculated as follows:

[0017]

[0018] Then, take the obtained B z0 The average value of the data is the residual magnetic field in the direction of the pump light.

[0019] Moreover, in step 2, the fixed magnetic field is set to be 10nT.

[0020] Moreover, in step nine, the step length is set to 5 pm, and the wavelength range is set to: 794.94nm-794.99nm

[0021] The advantages and positive effects of the present invention are:

[0022] 1. The measurement method of the present invention can realize the test by simply adjusting the 1 / 4 wave plate in the pump optical path of the SERF gyroscope. Compared with other residual magnetism measurement methods, it does not need to add devices in the system optical path or change the system optical path, and the test process is relatively simple.

[0023] 2. The present invention can realize in-situ measurement of the residual magnetic field in the direction of the pump light, and the measurement result is relatively reliable.

[0024] 3. The testing method of the present invention can simultaneously measure the system optical displacement and the residual magnetic field in the pump light direction, and effectively separate the optical displacement and the residual magnetic field.

[0025] 4. The present invention has good compatibility with the detection method of the detection light path of the SERF gyro system. Regardless of whether the detection light path adopts differential detection, photoelastic modulation or Faraday modulation, the method of the invention is applicable.

[0026] 5. The present invention calculates the residual magnetic field through theoretical fitting data of two sets of light displacements, which avoids the influence of accidental measurement errors on the overall test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A diagram of a system device for measuring the residual magnetic field in the direction of the internal pump light of a SERF gyroscope using the method of the present invention;

[0028] Figure 2 The balanced detector output obtained by scanning the z-direction magnetic field under a pump light of a certain wavelength vs. the pump light direction scanning magnetic field test data and the corresponding fitting curve schematic diagram;

[0029] Figure 3 The optical displacement results and theoretical curves of left-handed and right-handed circularly polarized pump light are measured respectively; DETAILED DESCRIPTION

[0030] The structure of the present invention is further described below with reference to the accompanying drawings and by way of examples. It should be noted that the present examples are descriptive rather than restrictive.

[0031] A method for measuring residual magnetic field in the direction of pump light of a SERF gyroscope, see Figure 1The invention point is: in the SERF gyroscope system, the pump light is adjusted to left-handed circular polarization and right-handed circular polarization respectively to perform pump polarization, and the characteristic that the light displacement in the two states is equal in magnitude and opposite in direction while the residual magnetic field remains unchanged is utilized. The total magnetic field (light displacement + residual magnetic field) obtained by testing in the two states is combined and calculated to eliminate the light displacement, thereby realizing the measurement of the residual magnetic field.

[0032] The SERF gyro system is an existing system, see Figure 1 , mainly including: pump light laser 1, first 1 / 2 wave plate 2, first polarization beam splitter prism 3, first lens 4, second lens 5, first 45° reflector 6, first polarizer 7, 1 / 4 wave plate 8, detection light laser 9, second polarizer 10, filter 11, Glan prism 12, second 1 / 2 wave plate 13, second polarization beam splitter prism 14, second 45° reflector 15, balanced detector 16, shielding device 17, three-dimensional magnetic field coil 18, heating and heat preservation device 19, atomic gas chamber 20. The atomic gas chamber 20 contains alkali metal Rb, inert gas Xe and buffer gas N2.

[0033] The basic principle of the measurement method is as follows:

[0034] The Bloch equation for the time evolution of the SERF gyroscope electron spin polarization is:

[0035]

[0036] in, is the electron spin polarizability of the alkali metal atom; γ e is the spin magnetic ratio of the electron spin of the alkali metal atom; Q is the slowing factor, which reflects the maintenance of the electron spin polarization by the nuclear spin in the alkali metal atom through hyperfine coupling; B is the ambient magnetic field; λM n is the polarization field factor of the inert gas nuclear spin; is the nuclear spin polarization of the noble gas atoms; is the light displacement; R is the angular velocity of the carrier system relative to the inertial system; p is the optical pumping rate of the pump light, reflecting the polarization effect of the pump light on the electron spin; R m is the optical pumping rate of the detection light, reflecting the polarization effect of the detection light on the electron spin; is the nuclear spin polarization rate, which reflects the polarization effect of the nuclear spin of the inert gas atom on the electronic spin of the alkali metal atom; R tot is the total relaxation rate of the electron spin of the alkali metal atom; The angular momentum transfer direction of the photons of the pump laser; To detect the angular momentum of the laser photons and transfer the orientation;

[0037] During the measurement, the system remains stationary, so the influence of the earth's rotation angular velocity can be ignored. It is assumed that the detection light is an ideal linearly polarized light, that is, s m =0,L x =0, the pump laser is an ideal circularly polarized light, The above formula can be further simplified to

[0038]

[0039] Assume that the x direction is the direction of the detection light, the z direction is the direction of the pump light, and the y direction is perpendicular to both the x and z directions. Find the steady-state solution of the above equation: available

[0040]

[0041] in, B x , B y and B z are the magnitudes of the magnetic field in the x, y and z directions respectively, L z is the optical displacement in the z direction.

[0042] Since the detection light is along the x-axis, the voltage signal measured by the photodetector is only related to the spin polarization rate of the electrons in the x-axis direction and is proportional to it.

[0043]

[0044] In the formula, B z It consists of two parts: residual magnetic field and scanning magnetic field, namely

[0045] B z =B z0 +B z '

[0046] Among them B z0 is the residual magnetic field in z direction, B z ′ is the scanning magnetic field. Recombining the z-direction magnetic field and the optical displacement term, we get

[0047] B z +L z =B z0 +B z ′+L z =B z ′+L z '

[0048] At this time, the SERF gyro system detector output signal can be written as

[0049]

[0050] In the experiment, a small magnetic field in the y direction is given, and the z direction magnetic field is scanned over a large range at the same time to obtain the output of the SERF gyro system detector. Then, the total magnetic field L at the wavelength of the pump light can be obtained by fitting the above formula. z ′, which includes the residual magnetic field and the optical displacement.

[0051] The optical displacement is equivalent to a virtual magnetic field, which is expressed as

[0052]

[0053] In the formula, in

[0054] r e is the classical electron radius, about 2.82×10-15m; c is the speed of light; f is the resonance intensity, which is related to the frequency of the laser; r e is the classical electron radius, about 2.82×10-15m; ν is the laser frequency; ν0 is the transition frequency of the hyperfine energy level; is the photon spin vector; Φ is the photon flux; Γ G is the Doppler broadening; Γ L Widen for pressure.

[0055] Assuming that the pump light is an ideal polarized laser, when its polarization is left-handed circular polarization, its photon spin vector is When the laser polarization is right-hand circular polarization, its photon spin vector is Therefore, it can be known that when left-handed circularly polarized pump light and right-handed circularly polarized pump light act on the same system, the optical displacements in the direction of the pump light generated are equal in magnitude and opposite in direction, and the remanent magnetism of the system in that direction will not change.

[0056] Therefore, the pump light is adjusted to be left-handed circularly polarized light and right-handed circularly polarized light, and L is measured in the two cases respectively. z ′, and are denoted as L z ' - and L z ' + .

[0057] L z ' - =B z0 +(-L z )

[0058] L z ' + =B z0 +(+L z )

[0059] From this we can get

[0060]

[0061] This enables the measurement of the residual magnetic field.

[0062] In the method, L is first obtained at each pump light wavelength. z ' + and L z ' - , and then use the optical displacement formula to fit the optical displacement data of left-handed circular polarization and right-handed circular polarization respectively to obtain the theoretical optical displacement curve. Then calculate the fitted theoretical curve data to obtain the residual magnetic field data under different pump light wavelengths, and finally take the average value of all residual magnetic field data, which is the actual measured residual magnetic field.

[0063] The method for measuring the residual magnetic field in the pump light direction of a SERF gyroscope of the present invention comprises the following specific steps:

[0064] Step 1: Active magnetic compensation is performed through the three-dimensional magnetic field coil in the SERF gyroscope to compensate the ambient magnetic field felt by the alkali metal gas chamber to as close to zero as possible;

[0065] Step 2: After the magnetic compensation is completed, a fixed magnetic field of about 10nT is applied to the coil in the y direction;

[0066] Step 3: adjust the pump light to left-handed polarized light by rotating the λ / 4 wave plate in the pump light path, adjust its wavelength to wavelength λ, and record the wavelength value;

[0067] Step 4: Adjust the signal generator of the z-direction magnetic field coil in the control circuit, set its scanning mode to ramp scanning, and set the initial value and step size of the output voltage so that the corresponding magnetic field scanning range is -1000nT-1000nT;

[0068] Step 5: The signal generator outputs, and the data acquisition system is used to collect the output signal of the balanced detector; after one cycle of scanning is completed, the collection of the detector output signal is stopped;

[0069] Step 6: Use the relationship between the detector output and the scanning magnetic field to fit the obtained detector output data and the magnetic field scanning value to obtain L z ' - ;

[0070] Step 7: Adjust the pump light to right-hand circular polarization by rotating the λ / 4 wave plate in the pump light path, keep the wavelength unchanged, and keep the signal generator settings unchanged; after the signal generator outputs, synchronously collect the balanced detector signal; after a cycle scan is completed, stop collecting the detector output signal at the same time;

[0071] Step 8: Use the relationship between the detector output and the scanning magnetic field to fit the obtained detector output data and the magnetic field scanning value to obtain L z ' + ;

[0072] Step 9: Change the pump light wavelength in the range of 794.94nm-794.99nm with a step length of 5pm. Repeat steps 3 to 8 at each wavelength to obtain L at different pump wavelengths. z ' - and L z ' + .

[0073] Step 10: Fit the two sets of data using the light displacement formula to obtain the fitted theoretical light displacement data L z ″ - and L z ″ + , and then the two sets of data are calculated as follows:

[0074]

[0075] Then, take the obtained B z0 The average value of the data is the residual magnetic field in the direction of the pump light.

[0076] In step 5 and step 7, multiple scanning cycles can also be collected synchronously, and the data within a complete cycle can be intercepted from the collected data for fitting. The fitting formula adopts the SERF gyro system detector output signal formula described in the technical solution. In step 3 and step 7, the λ / 4 wave plate 8 is adjusted to make the pump light left-handed or right-handed circularly polarized, and the subsequent test steps need to be performed after the signal is stable.

[0077] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for measuring residual magnetic field in pump light direction of SERF gyroscope, characterized in that: The steps include: Step 1: Active magnetic compensation is performed through the three-dimensional magnetic field coil in the SERF gyroscope to compensate the ambient magnetic field felt by the alkali metal gas chamber to as close to zero as possible; Step 2: After the magnetic compensation is completed, a set fixed magnetic field is applied to the coil in the y direction; Step 3: adjust the pump light to left-handed polarized light by rotating the λ / 4 wave plate in the pump light path, adjust its wavelength to wavelength λ, and record the wavelength value; Step 4: Adjust the signal generator of the z-direction magnetic field coil in the control circuit, set its scanning mode to ramp scanning, and set the initial value and step size of the output voltage so that the corresponding magnetic field scanning range is -1000nT-1000nT; Step 5: The signal generator outputs, and the data acquisition system is used to collect the output signal of the balanced detector; after at least one complete cycle is scanned, the collection of the detector output signal is stopped; Step 6: Use the relationship between the detector output and the scanning magnetic field to fit the detector output data and the magnetic field scanning value obtained within a complete cycle to obtain L z ' - ; Step 7: Adjust the pump light to right-handed circular polarization by rotating the λ / 4 wave plate in the pump light path, keep the wavelength unchanged, and keep the signal generator settings unchanged; after the signal generator outputs, synchronously collect the balanced detector signal; wait until at least one complete cycle is scanned, and stop collecting the detector output signal; Step 8: Use the relationship between the detector output and the scanning magnetic field to fit the detector output data and the magnetic field scanning value obtained within a complete cycle to obtain L z ' + ; Step 9: Change the pump light wavelength within the set wavelength range with a set step length, and repeat steps 3 to 8 at each wavelength to obtain L at different pump wavelengths. z ' - and L z ' + ; Step 10: Fit the two sets of data using the light displacement formula to obtain the fitted theoretical light displacement data L z ″ - and L z ″ + , and then the two sets of data are calculated as follows: Then, take the obtained B z0 The average value of the data is the residual magnetic field in the direction of the pump light.

2. The method for measuring residual magnetic field in pump light direction of SERF gyroscope according to claim 1, characterized in that: In step 2, the fixed magnetic field is set to be 10 nT.

3. The method for measuring residual magnetic field in pump light direction of SERF gyroscope according to claim 1, characterized in that: In step nine, the step size is set to 5 pm, and the wavelength range is set to: 794.94nm-794.99nm.

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