A method for measuring a residual magnetic field in a direction of a pumping light of a SERF gyroscope

Abstract

The application relates to a SERF gyroscope pump light direction residual magnetic field measuring method, which is characterized in that: in a SERF gyroscope system, pump light is adjusted to left-handed circular polarization and right-handed circular polarization respectively to carry out pump polarization, the characteristics that the light displacement size is equal and the direction is opposite in the two states while the residual magnetic field remains unchanged are utilized, total magnetic fields obtained by testing in the two states are combined to eliminate the light displacement, and thus the measurement of the residual magnetic field is realized. The application can realize in-situ measurement of the pump light direction residual magnetic field without adding devices in the system light path or changing the system light path, the test process operation is relatively simple, and the measurement result is relatively reliable.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of SERF gyroscopes, and particularly relates to a method for measuring a residual magnetic field in a pump light direction of a SERF gyroscope. BACKGROUND

[0002] A SERF gyroscope needs to work in a near-zero field environment to ensure the measurement accuracy and stability of the SERF gyroscope. There are two methods commonly used to achieve a near-zero field, namely passive magnetic shielding and active magnetic compensation. The passive magnetic shielding generally adopts a 1J85 permalloy soft magnetic material to process a multi-layer magnetic shielding cylinder, and changes the direction of the external magnetic field through the multi-layer soft magnetic material to achieve shielding. However, after a certain residual magnetic level is reached by using this method, the shielding effect cannot be obviously improved by simply increasing the number of shielding cylinder layers, and therefore the active magnetic compensation method needs to be used. The active magnetic compensation method is to generate a corresponding magnetic field by passing a certain current through the three-dimensional coil, and the magnetic field is equal in size and opposite in direction to the residual magnetic field to offset the residual magnetic field. However, the premise of the active magnetic compensation is to know the size and direction of the residual magnetic field, so as to effectively compensate it.

[0003] There are many methods for measuring the residual magnetic field, including built-in high-precision magnetometers and using atomic spin polarization signals for measurement. However, these methods have certain limitations. For example, the built-in high-precision magnetometer cannot achieve in-situ measurement of the residual magnetic field, and on the other hand, it will occupy a certain space and also affect the measurement of the SERF gyroscope itself. The use of atomic spin polarization signals for residual magnetic field measurement cannot effectively separate the influence of optical displacement on the test results, and sometimes the optical path needs to be changed. SUMMARY

[0004] The present application proposes a method for measuring the residual magnetic field in the pump light direction of a SERF gyroscope, which does not need to add devices or change the system optical path, can achieve in-situ measurement, and the measurement result is accurate.

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

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

[0007] Step one, actively compensate the magnetic field by using the three-dimensional magnetic field coil in the SERF gyroscope, and compensate the environmental magnetic field sensed by the alkali metal cell to near zero as much as possible;

[0008] Step two, after the magnetic compensation is completed, a fixed magnetic field is applied to the y-direction coil;

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

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

[0011] Step five, the signal generator outputs, and at the same time, the output signal of the balanced detector is collected by using the data acquisition system; after at least one complete cycle of scanning is completed, the collection of the output signal of the detector is stopped;

[0012] Step six, the detector output data and the magnetic field scanning value in one complete cycle are fitted by using the relationship between the detector output and the scanning magnetic field, and L z ′ - is obtained;

[0013] Step seven, adjust the pump light to be right-handed circularly polarized light by rotating the λ / 4 wave plate in the pump light path, and the wavelength remains unchanged, and the signal generator setting is also unchanged; after the signal generator outputs, the balanced detector signal is collected synchronously; after at least one complete cycle of scanning is completed, the collection of the output signal of the detector is stopped;

[0014] Step eight, the detector output data and the magnetic field scanning value in one complete cycle are fitted by using the relationship between the detector output and the scanning magnetic field, and L z ′ + is obtained;

[0015] Step nine, change the wavelength of the pump light in the set wavelength range with the set step, repeat steps three to eight at each wavelength, and obtain L z ′ - and L z ′ + at different pump wavelengths;

[0016] Step ten, fit the two groups of data respectively by using the optical shift formula, obtain the fitted theoretical optical shift data L z ″ - and L z ″ + , and then calculate the two groups of data as follows:

[0017]

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

[0019] And, in step two, the fixed magnetic field is set to 10 nT

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

[0021] The present application has the advantages and positive effects that:

[0022] 1. The measurement method of the present application can realize testing by adjusting the 1 / 4 wave plate in the pump light path of the SERF gyroscope, and compared with other residual magnetism measurement methods, it does not need to increase devices in the system light path or change the system light path, and the testing process is relatively simple to operate.

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

[0024] 3. The testing method of the present application can realize measurement of the system light displacement and the residual magnetic field in the pump light direction at the same time, and effectively separates the light displacement and the residual magnetic field.

[0025] 4. The present application has good compatibility to the detection mode of the detection light path of the SERF gyroscope system, and no matter whether the detection light path adopts differential detection, photoelastic modulation or Faraday modulation, the method of the present application is usable.

[0026] 5. The present application calculates the residual magnetic field through the theoretical fitting data of two groups of light displacement, and this method avoids the influence of accidental measurement error on the overall test result. DETAILED DESCRIPTION

[0027] Figure 1 It is a system device diagram for measuring the residual magnetic field in the pump light direction of the SERF gyroscope by using the method of the present application;

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

[0029] Figure 3 It is the light displacement result and the theoretical curve schematic diagram respectively measured under the conditions of left-handed and right-handed circularly polarized pump light; DETAILED DESCRIPTION

[0030] The structure of the present application will be further described below by combining the drawings and through embodiments. It should be noted that the present embodiment is descriptive rather than limiting.

[0031] A SERF gyroscope pump light direction residual magnetic field measurement method, please refer to Figure 1The application point is that in the SERF gyroscope system, the pump light is adjusted to left-handed circular polarization and right-handed circular polarization respectively for pumping polarization, the characteristics that the light displacement size is equal and the residual magnetic field remains unchanged in the two states are used, the total magnetic field (light displacement + residual magnetic field) obtained by testing in the two states is combined to calculate and eliminate the light displacement, and thus the measurement of the residual magnetic field is realized.

[0032] The SERF gyroscope system is an existing system, please refer to Figure 1 The SERF gyroscope system mainly comprises a pump light laser 1, a first 1 / 2 wave plate 2, a first polarization light splitting prism 3, a first lens 4, a second lens 5, a first 45° mirror 6, a first polarizer 7, a 1 / 4 wave plate 8, a probe light laser 9, a second polarizer 10, a filter 11, a Glan prism 12, a second 1 / 2 wave plate 13, a second polarization light splitting prism 14, a second 45° mirror 15, a balanced detector 16, a shielding device 17, a three-dimensional magnetic field coil 18, a heating and heat preservation device 19 and an atomic cell 20. The atomic cell 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 of the electronic spin polarization of the SERF gyroscope with time evolution is:

[0035]

[0036] Among them, is the electronic spin polarization rate of the alkali metal atom; γ e is the electronic spin gyromagnetic ratio of the alkali metal atom; Q is a slowing factor, reflecting the maintenance effect of the nuclear spin of the alkali metal atom on the electronic spin polarization through hyperfine coupling; B is the environmental magnetic field; λM n is the polarization field factor of the nuclear spin of the inert gas; is the nuclear spin polarization rate of the inert gas atom; is the light displacement; is the rotation angular velocity of the carrier system to the inertial system; R p is the optical pumping rate of the pump light, reflecting the polarization effect of the pump light on the electronic spin; R m is the optical pumping rate of the probe light, reflecting the polarization effect of the probe light on the electronic spin; is the nuclear spin polarization rate, reflecting 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 electronic spin of the alkali metal atom; is the photon angular momentum transmission direction of the pump laser; is the photon angular momentum transmission direction of the probe laser;

[0037] The system keeps still during the measurement, so the effect of the earth rotation angular velocity can be ignored. The probe light is assumed to be ideal linearly polarized light, i.e. s m = 0, L x = 0, and the pump laser is ideal circularly polarized light, The above equation can be further simplified as

[0038]

[0039] The x direction is assumed to be the probe light direction, the z direction is the pump light direction, and the y direction is perpendicular to both the x and z directions. The steady-state solution of the above equation is The steady-state solution is

[0040]

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

[0042] Since the probe light is along the x axis, the voltage signal measured by the photodetector is only related to the spin polarization of the electrons in the x axis, and is proportional to the spin polarization. That is,

[0043]

[0044] In the equation, B z is composed of the residual magnetic field and the scanning magnetic field, i.e.

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

[0046] where B z0 is the z-direction residual magnetic field, and B z ' is the scanning magnetic field. The z-direction magnetic field and the optical displacement term are recombined, i.e.

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

[0048] The detector output signal of the SERF gyroscope system at this time can be written as

[0049]

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

[0051] Optical displacement is equivalent to a virtual magnetic field, and its expression is:

[0052]

[0053] In the formula, in

[0054] r e λ is the classical electron radius, approximately 2.82 × 10⁻¹⁵ m; c is the speed of light; f is the resonance intensity, which is related to the laser frequency; r e ν is the classical electron radius, approximately 2.82 × 10⁻¹⁵ m; ν is the laser frequency; ν₀ is the transition frequency of the hyperfine level. Γ is the photon spin vector; Φ is the photon flux; G To broaden the Doppler; Γ L To broaden the scope of pressure.

[0055] Assuming the pump light is an ideally polarized laser, when its polarization is left-handed circularly polarized, its photon spin vector is: When the laser polarization is right-handed circularly polarized, its photon spin vector is: Therefore, it can be known that when left-handed and right-handed circularly polarized pump light act on the same system, the magnitude of the optical displacement in the pump light direction is equal and the direction is opposite, while the remanence of the system in that direction will not change.

[0056] Therefore, the pump light was adjusted to be left-handed circularly polarized light and right-handed circularly polarized light, and L was measured under both conditions. z ′, and denoted as L respectively. z ′ - and L z ′ + .

[0057] L z ′ - =B z0 +(-L z )

[0058] L z ′ + =B z0 +(+L z )

[0059] From this, we can obtain

[0060]

[0061] Thus, the measurement of the residual magnetic field is realized.

[0062] In the method, L z ′ + and L z ′ - are obtained at each pump light wavelength, then the optical displacement data when left-handed circular polarization and the optical displacement data when right-handed circular polarization are fitted respectively by using an optical displacement formula, and the theoretical optical displacement curve is obtained.

[0063] The SERF gyroscope pump light direction residual magnetic field measurement method comprises the following specific steps:

[0064] Step one, active magnetic compensation is performed through three-dimensional magnetic field coils in the SERF gyroscope, and the environmental magnetic field sensed by the alkali metal cell is compensated to near zero point as much as possible;

[0065] Step two, after the magnetic compensation is completed, a fixed magnetic field of about 10 nT is applied to the y-direction coil;

[0066] Step three, the pump light is adjusted to left-handed circularly polarized light by rotating the λ / 4 wave plate in the pump light path, and the wavelength is adjusted to wavelength λ, and the wavelength value is recorded;

[0067] Step four, the signal generator for controlling the z-direction magnetic field coil in the control circuit is adjusted, the scanning mode is set to a ramp scanning mode, and the initial value and the step of the output voltage are set, so that the corresponding magnetic field scanning range is -1000 nT-1000 nT;

[0068] Step five, the signal generator outputs, and at the same time, the output signal acquisition of the balanced detector is performed by using a data acquisition system; after one cycle of scanning is completed, the acquisition of the detector output signal is stopped;

[0069] Step six, the obtained detector output data and the magnetic field scanning value are fitted by using the relationship between the detector output and the scanning magnetic field, and L z ′ - is obtained.

[0070] Step seven, the pump light is adjusted to right-handed circularly polarized light by rotating the λ / 4 wave plate in the pump light path, and the wavelength remains unchanged, and the signal generator setting is unchanged; after the signal generator outputs, the balanced detector signal acquisition is performed synchronously; after one cycle of scanning is completed, the acquisition of the detector output signal is stopped.

[0071] Step eight, fitting the obtained detector output data and magnetic field scanning values by using the relationship between the detector output and the scanning magnetic field to obtain L z +

[0072] Step nine, changing the pump light wavelength in the range of 794.94nm-794.99nm with a step of 5pm, repeating steps three to eight at each wavelength to obtain L z - and L z at different pump wavelengths. + .

[0073] Step ten, fitting the two groups of data by using the optical shift formula to obtain the fitted theoretical optical shift data L z - and L z . + Then, calculating the two groups of data as follows:

[0074]

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

[0076] In the step five and step seven, multiple scanning periods can also be collected synchronously, and the data in a complete period is cut from the collected data for fitting. The fitting formula uses the detector output signal formula of the SERF gyroscope system described in the technical solution. In the step three and step seven, the pump light is left-handed or right-handed circularly polarized by adjusting the λ / 4 wave plate 8, and the subsequent test steps are performed after the signal is stable.

[0077] Although the embodiments and drawings of the present application are disclosed for the purpose of illustration, those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit of the present application and the appended claims, therefore, the scope of the present application is not limited to the disclosed embodiments and drawings.​​​​

Claims

1. A method of measuring a residual magnetic field of a direction of a pump light of a SERF gyroscope, characterized by: Comprising the following steps: Step one, through the SERF gyroscope three-dimensional magnetic field coil active magnetic compensation, alkali metal chamber as far as possible to compensate the environmental magnetic field to near zero; Step two, after the end of the magnetic compensation, in the y direction coil to apply a set of fixed magnetic field; Step three, by rotating the pump light path of λ / 4 wave plate to adjust the pump light for left-handed circularly polarized light, and its wavelength is adjusted to the wavelength λ, and the wavelength value is recorded; Step four, adjust the signal generator in the control circuit to control the z direction magnetic field coil, set its scanning mode to the ramp scan, and set the initial value and step of the output voltage, so that its corresponding magnetic field scanning range is-1000nT—1000nT; Step five, signal generator output, at the same time, use the data acquisition system to collect the output signal of the balanced detector; after at least one complete cycle scanning, stop the acquisition of the detector output signal at the same time; Step six, the detector output data and magnetic field scan values obtained in one complete cycle are fitted using the relationship between the detector output and the scanning magnetic field to obtain L z - ​​ Step seven, through the rotating pump light path of λ / 4 wave plate to adjust the pump light for right-handed circularly polarized, the wavelength remains unchanged, the signal generator settings are unchanged; after the signal generator output, the balanced detector signal acquisition is carried out synchronously; after at least one complete cycle scanning, stop the acquisition of the detector output signal at the same time; Step eight, the detector output data and magnetic field scan values obtained over one complete cycle are fitted using the relationship between the detector output and the scan magnetic field to obtain L z + ​​ Step nine, change the pump light wavelength in the set wavelength range with a set step, repeat steps three to eight at each wavelength to obtain L z - and L z + ;​​ Step 10: Fit the two sets of data using the optical displacement formula to obtain the fitted theoretical optical displacement data L. z " - and L z " + Then perform the following calculations on the two sets of data: Then, the obtained B z0 The average value of the data is the remanent field in the direction of the pump light.

2. The SERF gyroscope pump light direction residual magnetic field measurement method of claim 1, wherein: In step two, the set of fixed magnetic field is 10nT fixed magnetic field.

3. The SERF gyroscope pump light direction residual magnetic field measurement method of claim 1, wherein: In step nine, the step is set to 5pm, and the set of wavelength range is: 794.94nm-794.99nm.

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