Vector magnetometer installation error elimination method based on double-beam CPT

Abstract

Based on a double-beam CPT vector magnetometer installation error elimination method, a model is established to analyze an angle relationship between two beams of orthogonal line polarized light and a standard three-axis magnetic field, so that angle output influenced by an installation error of an experimental probe device placed in a generation device platform is corrected; the CPT magnetometer is configured by adopting two linearly polarized light beams with mutually orthogonal propagation directions, and modeling analysis is performed on angle output of a proposed CPT magnetometer magnetic field vector according to a relation between three key vectors of a laser wave vector K, a polarization direction e and a magnetic field direction B and CPT resonance amplitude, so that an analytical solution of a magnetic field angle is obtained. The precondition of the model is that two light beams need to be orthogonally configured, and the light beams are difficult to realize in the actual situation. An installation error correction scheme is provided based on a double-beam measurement model, and how to obtain an installation error angle and correct magnetometer angle output when the system has an installation error is analyzed and discussed from a theoretical angle.

Description

Technical Field

[0001] The invention relates to a method for eliminating installation errors based on a double-beam CPT vector magnetometer, and belongs to the field of interaction and automatic control between light and alkali metal atoms. Background Art

[0002] CPT atomic magnetometer can be widely used in geophysics, medicine and basic physics (CPT, coherent population trapping, coherent population trapping), CPT magnetometer has high sensitivity potential It can achieve the advantages of miniaturization, vector measurement and geomagnetic environment measurement. In many application scenarios, understanding the vector component of the magnetic field is crucial to complete the specific information of the field. In general, the measurement of the two-dimensional magnetic field direction can be determined by changing the polarization direction of a single beam of light and observing the 0-level peak amplitude of the CPT resonance signal to determine the plane of the magnetic field. The polarization direction e of the linearly polarized light is orthogonal to the magnetic field direction B, so the linear polarization direction e can be obtained to achieve the vector measurement of the magnetic field. For the measurement of the three-dimensional magnetic field direction, it is only necessary to convert the three-dimensional magnetic field into a two-dimensional magnetic field. The typical magnetic compensation technology can easily realize the conversion of the magnetic field, but this method inevitably couples the magnetic compensation with the magnetic field to be measured.

[0003] The method of measuring magnetic field vector using dual beams can avoid the magnetic field coupling problem caused by traditional magnetic compensation methods, and achieve more accurate acquisition of magnetic field size and direction. However, for the dual beam magnetic field vector measurement method, it relies on the polarization rotation angle of the two beams of light to obtain the direction, and the vector result will be very dependent on the propagation direction of the two beams of light, and the inevitable installation error will lead to a decrease in the accuracy of the magnetic field direction. In view of this, the method of the present invention focuses on reducing the angular error of the dual beam CPT vector magnetometer and improving the angle measurement accuracy, strictly models the system, and realizes a method for eliminating installation errors based on the dual beam CPT vector magnetometer. Summary of the invention

[0004] In view of the defects or shortcomings of the prior art, the present invention proposes a method for eliminating installation errors based on a double-beam CPT vector magnetometer, which is beneficial to reducing the angular error of the double-beam CPT vector magnetometer and improving the angle measurement accuracy.

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

[0006] The method for eliminating installation errors of a double-beam CPT vector magnetometer is characterized by comprising the following steps:

[0007] Step 1, using a dual-beam CPT vector magnetometer measurement system to generate multi-color lasers;

[0008] Step 2, dividing the multicolor laser into a first beam of light and a second beam of light with equal light intensities, and adjusting the linear polarization directions of the two beams of light by controlling half-wave plates through respective stepper motors;

[0009] Step 3, based on the relationship between the laser wave vector, polarization direction, magnetic field direction and CPT resonance amplitude, the angle output of the magnetic field vector is modeled and analyzed, including establishing a Cartesian coordinate system XYZ, the wave vector K1 of the first beam of light is consistent with the X-axis direction, the wave vector K2 of the second beam of light is consistent with the Y-axis direction, and the linear polarization direction e of the first beam of light is 1 The angle between the second beam and the Z axis is θ, and the linear polarization direction of the second beam is e 2 The angle between the Z axis and For the unknown magnetic field direction B, the experiment is carried out by adjusting e 1 and e 2 , observe the amplitude of the 0-level peak of the CPT signal of both, and realize the polarization rotation angle Determination of B and e 1 , e 2 At the same time, vertically determine B;

[0010] Step 4, calculating the installation error angle by obtaining the polarization rotation angle when the CPT signal amplitude is maximum;

[0011] Step 5: Establish a magnetometer angle output correction model to eliminate installation errors.

[0012] The dual-beam CPT vector magnetometer measurement system in step 1 includes an ECDL laser connected to the incident side of the beam splitter through an optical isolator, a first half-wave plate, a polarization beam splitter prism, a fiber coupler, a first polarization-maintaining fiber, an electro-optic modulator, a second polarization-maintaining fiber and a laser collimator in sequence; the electro-optic modulator is connected to a triangular wave generator through a radio frequency signal generator; the transmission side of the beam splitter forms a first beam of light which is connected to a data acquisition system through a second half-wave plate, an atomic gas chamber and a first photodetector in sequence; the reflection side of the beam splitter forms a second beam of light which is connected to a data acquisition system through a third half-wave plate, a first reflector, a second reflector, an atomic gas chamber and a second photodetector in sequence; the second half-wave plate is connected to the first stepper motor; the third half-wave plate is connected to the second stepper motor; the atomic gas chamber is located in an oven; the oven is located in a coil; and the coil is located in a shielding layer.

[0013] The output light beam of the electro-optic modulator is transformed from monochromatic light to polychromatic light due to modulation, and the frequency difference of the first-order sideband light field generated is equal to 87 Rb hyperfine structure ground state energy level |5 2 S 1 / 2 ,F g =1> and |5 2 S 1 / 2 ,F g=2> frequency difference Δv hfs .

[0014] Step 3 includes the following expressions:

[0015]

[0016] Where n is e 1 and e 2 The normal vector of the plane formed, B, is consistent with the direction of n. When θ=0, B is in the same direction as the X-axis, and when θ=0, B is in the same direction as the Y-axis.

[0017] Step 4 includes the following expressions:

[0018]

[0019] where γ max is the polarization rotation angle when the CPT signal amplitude is maximum, δ x is the angle between the projection of K2 on the XOY plane and the coordinate axis Y, δz is the angle between the projection of K2 on the YOZ plane and the coordinate axis Y, is the magnitude of the magnetic field on the X axis, is the magnitude of the magnetic field on the Y axis.

[0020] Step 5 includes the following expression:

[0021] B=(b·tanθ-c,-tanθ·a,a),

[0022]

[0023] Among them, a, b, and c are all intermediate quantities.

[0024] The technical effects of the present invention are as follows: Based on the installation error elimination method of the dual-beam CPT vector magnetometer, the present invention establishes a model to analyze the angular relationship between two beams of orthogonal linear polarized light and the standard three-axis magnetic field, so as to realize the correction of the angle output affected by the installation error of the experimental probe device placed in the generating device platform. The dual-beam coherent population trapping (CPT) vector magnetometer magnetic field vector method uses two linear polarized beams with mutually orthogonal propagation directions to configure the CPT magnetometer, and according to the relationship between the three key vectors of the laser wave vector K, polarization direction e and magnetic field direction B and the CPT resonance amplitude, the angle output of the proposed CPT magnetometer magnetic field vector is modeled and analyzed, and then the analytical solution of the magnetic field angle is obtained. However, the prerequisite of this model is that the two beams need to be orthogonally configured, which is difficult to achieve in the actual situation. The present invention proposes a correction scheme for installation errors based on the dual-beam measurement model, and analyzes and discusses how to obtain the installation error angle and correct the magnetometer angle output when the system has an installation error from a theoretical perspective. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic flow chart of the method for eliminating installation errors of a double-beam CPT vector magnetometer according to the present invention. Figure 1 The method includes step 1, generating multicolor laser; step 2, using BS to split the laser into two beams of equal light intensity, and then adjusting the polarization direction through HWP (HWP, half-wave plate); step 3, modeling and analyzing the angular output of the magnetic field vector according to the relationship between the laser wave vector, polarization direction, magnetic field direction and CPT resonance amplitude (CPT, Coherent Population Trapping); step 4, calculating the installation error angle by obtaining the polarization rotation angle when the CPT signal amplitude is maximum; step 5, establishing a magnetometer angle output correction model to eliminate the installation error.

[0026] Figure 2 Schematic diagram of the dual-beam magnetic field vector measurement principle. Figure 2 Where O is the origin, XYZ are the three axes of the Cartesian coordinate system (i.e., x-axis, y-axis, and z-axis), K1-x-axis direction light beam (x(K1)) is the first light beam, K2-y-axis direction light beam (y(K2)) is the second light beam, e1-linear polarization direction of the first light beam, e2-linear polarization direction of the second light beam, (e1, e2) is the plane formed by the polarization directions of the two beams, θ-is the angle between e1 and the z-axis (the linear polarization angle of the first light beam), φ is the angle between e2 and the z-axis (the linear polarization angle of the second light beam), n(B) is the normal vector of (e1, e2), n(B) = [e1×e2], n is the normal vector, n = [e1×e2], and B is the direction of the magnetic field.

[0027] Figure 3 This is a schematic diagram of installation error. Figure 3 Where δx is the angle between the projection of K2 on the XOY plane and the coordinate axis Y, and δz is the angle between the projection of K2 on the YOZ plane and the coordinate axis Y.

[0028] Figure 4 This is the structural schematic diagram of the dual-beam CPT vector magnetometer measurement system. Figure 4 The invention comprises an ECDL laser (ECDL, external-cavity diode laser) connected to the incident side of the beam splitter through an optical isolator, a first half-wave plate, a polarization beam splitter prism, a fiber coupler, a first polarization-maintaining fiber, an electro-optic modulator, a second polarization-maintaining fiber and a laser collimator, the electro-optic modulator is connected to a triangular wave generator through a radio frequency signal generator, the transmission side (first beam of light) of the beam splitter is connected to a data acquisition system through a second half-wave plate, an atomic gas chamber and a first photodetector (detecting the first beam of light) in sequence, the reflection side (second beam of light) of the beam splitter is connected to the data acquisition system through a third half-wave plate, a first reflector, a second reflector, an atomic gas chamber and a second photodetector (PD, detecting the second beam of light) in sequence, the second half-wave plate is connected to the first stepper motor, the third half-wave plate is connected to the second stepper motor, the atomic gas chamber is located in an oven, the oven is located in a coil (Helmholtz coil), and the coil is located in a shielding layer. DETAILED DESCRIPTION

[0029] Below is the attached figure ( Figure 1-Figure 4 ) and Examples illustrate the present invention.

[0030] Figure 1 It is a schematic flow chart of the method for eliminating installation errors of a double-beam CPT vector magnetometer according to the present invention. Figure 2 Schematic diagram of the dual-beam magnetic field vector measurement principle. Figure 3 This is a schematic diagram of installation error. Figure 4 This is the structural principle diagram of the double-beam CPT vector magnetometer measurement system. Figures 1 to 4 As shown, the method for eliminating installation errors based on a double-beam CPT vector magnetometer includes the following steps: step 1, using a double-beam CPT vector magnetometer measurement system to generate a multi-color laser; step 2, dividing the multi-color laser into a first beam of light and a second beam of light with equal light intensities, and adjusting the linear polarization directions of the two beams of light by controlling a half-wave plate through respective stepper motors; step 3, modeling and analyzing the angular output of the magnetic field vector according to the relationship between the laser wave vector, polarization direction, magnetic field direction and CPT resonance amplitude, including establishing a Cartesian coordinate system XYZ, the light wave vector K1 of the first beam of light is consistent with the X-axis direction, the light wave vector K2 of the second beam of light is consistent with the Y-axis direction, and the linear polarization direction e of the first beam of light is consistent with the X-axis direction.1 The angle between the second beam and the Z axis is θ, and the linear polarization direction of the second beam is e 2 The angle between the Z axis and For the unknown magnetic field direction B, the experiment is carried out by adjusting e 1 and e 2 , observe the amplitude of the 0-level peak of the CPT signal of both, and realize the polarization rotation angle Determine by B and e 1 , e 2 At the same time, B is determined vertically; step 4, the installation error angle is calculated by obtaining the polarization rotation angle when the CPT signal amplitude is maximum; step 5, a magnetometer angle output correction model is established to eliminate the installation error.

[0031] The dual-beam CPT vector magnetometer measurement system in step 1 includes an ECDL laser connected to the incident side of the beam splitter through an optical isolator, a first half-wave plate, a polarization beam splitter prism, a fiber coupler, a first polarization-maintaining fiber, an electro-optic modulator, a second polarization-maintaining fiber and a laser collimator in sequence; the electro-optic modulator is connected to a triangular wave generator through a radio frequency signal generator; the transmission side of the beam splitter forms a first beam of light which is connected to a data acquisition system through a second half-wave plate, an atomic gas chamber and a first photodetector in sequence; the reflection side of the beam splitter forms a second beam of light which is connected to a data acquisition system through a third half-wave plate, a first reflector, a second reflector, an atomic gas chamber and a second photodetector in sequence; the second half-wave plate is connected to the first stepper motor; the third half-wave plate is connected to the second stepper motor; the atomic gas chamber is located in an oven; the oven is located in a coil; and the coil is located in a shielding layer.

[0032] The output light beam of the electro-optic modulator is transformed from monochromatic light to polychromatic light due to modulation, and the frequency difference of the first-order sideband light field generated is equal to 87 Rb hyperfine structure ground state energy level |5 2 S 1 / 2 ,F g =1> and |5 2 S 1 / 2 ,F g =2> frequency difference Δv hfs .

[0033] Step 3 includes the following expressions:

[0034]

[0035] Where n is e 1 and e 2 The normal vector of the plane formed, B, is consistent with the direction of n. When θ=0, B is in the same direction as the X-axis, and when θ=0, B is in the same direction as the Y-axis.

[0036] Step 4 includes the following expressions:

[0037]

[0038] where γ max is the polarization rotation angle when the CPT signal amplitude is maximum, δ x is the angle between the projection of K2 on the XOY plane and the coordinate axis Y, δz is the angle between the projection of K2 on the YOZ plane and the coordinate axis Y, is the magnitude of the magnetic field on the X axis, is the magnitude of the magnetic field on the Y axis.

[0039] Step 5 includes the following expression:

[0040] B=(b·tanθ-c,-tanθ·a,a),

[0041]

[0042] Among them, a, b, and c are all intermediate quantities.

[0043] The problem solved by the present invention is: a method for eliminating installation errors of a dual-beam CPT vector magnetometer. The spatial light is converted into optical fiber light through an optical fiber coupling head, and then injected into an electro-optical phase modulator to modulate the laser. The radio frequency signal is then used to achieve half-wave modulation of the laser frequency to obtain a multi-color laser. The BS is used to achieve light splitting to obtain two beams of light with equal light intensity. 1 , K 2 , and then the linear polarization direction of the dual beams is adjusted by the HWP controlled by a high-precision stepper motor. The dual-beam magnetic field measurement is modeled and analyzed based on the magnetic field direction B, light propagation direction K, and linear polarization direction e, and the analytical solution of the magnetic field direction is obtained; the linear polarization beam K is rotated 2 , observe the maximum value of the CPT signal amplitude to obtain the theoretical installation error angle; further analyze the installation error angle together with the double-beam measurement model to obtain the correction model of the magnetometer angle output.

[0044] Principle and coordinate system reference of magnetic field vector measurement system of CPT vector magnetometer Figure 4 .

[0045] According to the experimental design, two lasers are needed to meet the frequency difference between the two hyperfine energy levels of the D1 line of the Rb87 atom. In this experiment, the laser beam passes through an optical isolator, a half-wave plate, and a polarization beam splitter in turn to achieve optical power adjustment. The spatial light is then converted into fiber light through a fiber coupling head and injected into the electro-optic phase modulator to achieve laser modulation. A triangular wave signal generator is used to generate a scanning signal to modulate the RF signal with a frequency of 3.417 GHz generated by the RF signal generator. The RF output signal is connected to the electro-optic modulator to achieve half-wave modulation of the laser frequency. At this time, the output beam of the electro-optic modulator is transformed from monochromatic light to polychromatic light due to modulation, and the frequency difference of the first-order sideband light field generated is exactly equal to 87 Rb hyperfine structure ground state energy level |5 2 S 1 / 2 ,F g =1> and |5 2 S 1 / 2 ,F g =2. Frequency difference Δν hfs , the conditions are met.

[0046] This scheme requires that the experimental beams be two beams of equal intensity in order to achieve the purpose of measuring the direction of the magnetic field using dual beams. After the multicolor laser is generated, it needs to be transmitted to the laser collimator through a polarization-maintaining fiber, and the laser spot diameter is adjusted to 5mm. The laser is divided into two beams of equal intensity using BS, and the intensity of both beams is adjusted to 50 microwatts. Both beams pass through the HWP (half-wave plate) controlled by a high-precision stepper motor to achieve the adjustment of the linear polarization direction in the experiment.

[0047] In the experiment, the propagation directions of the two linearly polarized light beams are arranged orthogonally. 1 , K 2 They correspond to the coordinate axes X and Y respectively, and the direction of the coordinate axis Z is determined by the right-hand rule. 1 ,e 2 The angles with the Z axis are For the unknown magnetic field direction B, the polarization directions of the two beams are adjusted separately in the experiment, and the amplitude of the 0-level peak of the CPT signal of the two beams is observed to realize the polarization rotation angle. According to the previous conclusion, the magnetic field direction B should be consistent with the linear polarization direction e 1 , e 2 At the same time, a Cartesian coordinate system is established as shown in the figure. According to the constraints, the direction of the straight line where the magnetic field is located can be easily determined. In the figure, X, Y, and Z satisfy the right-hand coordinate system. K 1 ,K 2 are the propagation directions of the two beams of light, and their linear polarization directions are represented by e 1 , e 2. Double beam magnetic field vector measurement principle reference Figure 2 .

[0048] pass Figure 2 The Cartesian coordinate system shown in the figure provides a general analysis of the magnetic field vector measurement method: First, when When the polarization direction vectors of the two beams of light can be expressed as e 1 =(0,y 1 ,y 1 ·cotθ), In order to simplify the calculation of the direction vector, let x 1 =y 1 =1, that is, e 1 =(0,1,cotθ), in For the plane formed by the polarization directions of the two beams (e 1 , e 2 ), let’s assume that its normal vector is n=(n x , n y , n z ), and the normal vector satisfies n=[e 1 ×e 2 ], we can further get the equation:

[0049]

[0050] This equation is an underdetermined equation. Let n z =1, and the normal vector is further obtained as:

[0051]

[0052] The direction of the magnetic field B and the linear polarization direction e 1 , e 2 At the same time, it is perpendicular, that is, the direction vector of the magnetic field is perpendicular to the plane (e 1 ,e 2 ) is consistent with the normal vector n. For θ=0,cotθ→∞, the magnetic field direction B can be expressed as That is, it can be considered that the magnetic field direction B coincides with the coordinate axis Y. When , the direction of the magnetic field B coincides with the coordinate axis X.

[0053] The prerequisite of the magnetic field normal vector is that two beams need to be orthogonal, which is difficult to achieve in actual situations. The present invention analyzes and discusses the method of obtaining the installation error angle and correcting the magnetometer angle output when there is an installation error from a theoretical perspective.

[0054] The double beam installation error involved in the experiment is as follows: Figure 3 As shown, where δ x ,δ zThey represent the linearly polarized beam K 2 Projected to the YOZ plane, the angle between the XOY plane and the coordinate axis Y. The experimental probe device is placed on the standard three-axis magnetic field generating device platform, and the linear polarized beam K is continuously rotated. 1 The polarization direction e 1 . The beam K 1 After aligning with the X-axis of the magnetic field coordinate, only the Y-axis magnetic field is applied. Due to the installation error, the linearly polarized beam K 2 The polarization direction e 2 , the CPT signal amplitude does not remain unchanged. At this time, the polarization rotation angle γ when the CPT signal amplitude is maximum is recorded. max , which can be parsed as:

[0055]

[0056] Further, the polarization direction e 2 Restore to the initial position and keep it unchanged, apply a fixed magnetic field along the Y axis, and change the X axis magnetic field at the same time. When the CPT signal amplitude reaches the maximum, record the X and Y axis magnetic field magnitudes Based on this x It can be expressed as:

[0057]

[0058] Substituting into the above formula, we can get δ z Finally, we get the beam K 2 Installation error angle δ with Y axis x , δ z .

[0059] Get beam K 2 After the installation error angle with the Y axis, assume that B = (X 0 ,Y 0 ,Z 0 ), combined with the two beams K 1 , K 2 Polarization angles of the output You can get:

[0060] B=(b·tanθ-c,-tanθ·a,a) (5)

[0061] in

[0062]

[0063] Each term in the equation is a known term, and when the installation error angle δ x ,δ z When =0, the magnetic field B is consistent with its normal vector n, which further verifies the generality of the modified model.

[0064] This method requires five steps to implement the installation error elimination method based on the double-beam CPT vector magnetometer.

[0065] Step 1: Multicolor laser generation

[0066] According to the experimental design, two lasers that meet the frequency difference of the two hyperfine energy levels of the D1 line of the Rb87 atom are needed. In this experiment, the laser beam passes through an optical isolator, a half-wave plate, and a polarization beam splitter in turn to achieve optical power adjustment. The spatial light is then converted into fiber light through a fiber coupling head and injected into the electro-optic phase modulator to achieve laser modulation. A triangular wave signal generator is used to generate a scanning signal to modulate the RF signal with a frequency of 3.417 GHz generated by the RF signal generator. The RF output signal is connected to the electro-optic modulator to achieve half-wave modulation of the laser frequency. At this time, the output beam of the electro-optic modulator is transformed from monochromatic light to polychromatic light due to modulation, and the frequency difference of the first-order sideband light field generated by it is exactly equal to the ground state energy level of the 87Rb hyperfine structure|5 2 S 1 / 2 ,F g =1> and |5 2 S 1 / 2 ,F g =2> frequency difference Δv hfs , the conditions are met.

[0067] Step 2: Get a dual-beam laser

[0068] This scheme requires that the experimental beams be two beams of equal intensity in order to achieve the purpose of measuring the direction of the magnetic field using dual beams. After the multicolor laser is generated, it needs to be transmitted to the laser collimator through a polarization-maintaining fiber, and the laser spot diameter is adjusted to 5mm. The laser is divided into two beams of equal intensity using BS, and the intensity of both beams is adjusted to 50 microwatts. Both beams pass through the HWP (half-wave plate) controlled by a high-precision stepper motor to achieve the adjustment of the linear polarization direction in the experiment.

[0069] Step 3: Dual-beam magnetic field measurement modeling and analysis

[0070] In the experiment, the propagation directions of the two linearly polarized light beams are arranged orthogonally. 1 , K 2 They correspond to the coordinate axes X and Y respectively, and the direction of the coordinate axis Z is determined by the right-hand rule. 1 , e 2 The angles with the Z axis are For the unknown magnetic field direction B, the polarization directions of the two beams are adjusted separately in the experiment, and the amplitude of the 0-level peak of the CPT signal of the two beams is observed to realize the polarization rotation angle. According to the previous conclusion, the magnetic field direction B should be consistent with the linear polarization direction e1 , e 2 At the same time, vertically, a Cartesian coordinate system is established as shown in the figure. According to the constraints, the direction of the straight line where the magnetic field is located can be easily determined. In the figure, X, Y, and Z satisfy the right-hand coordinate system. K 1 , K 2 are the propagation directions of the two beams of light, and their linear polarization directions are represented by e 1 , e 2 . Double beam magnetic field vector measurement principle reference Figure 2 .

[0071] pass Figure 2 The Cartesian coordinate system shown in the figure can be used to perform a general analysis of the magnetic field vector measurement method to obtain the normal vector expression, see the above formula (2).

[0072] Step 4: Obtain the installation error angle

[0073] The prerequisite for the analytical expression of the magnetic field normal vector is that the two beams need to be orthogonal, which is difficult to achieve in actual situations. This article discusses from a theoretical perspective how to obtain the installation error angle and correct the magnetometer angle output when there is an installation error. Figure 3 .

[0074] The double beam installation error involved in the experiment is as follows: Figure 3 As shown, where δ x ,δ z They represent the linearly polarized beam K 2 Projected to the YOZ plane, the angle between the XOY plane and the coordinate axis Y. The experimental probe device is placed on the standard three-axis magnetic field generating device platform, and the linear polarized beam K is continuously rotated. 1 The polarization direction e 1 . The beam K 1 After aligning with the X-axis of the magnetic field coordinate, only the Y-axis magnetic field is applied. Due to the installation error, the linearly polarized beam K 2 The polarization direction e 2 , the CPT signal amplitude does not remain unchanged. At this time, the polarization rotation angle γ when the CPT signal amplitude is maximum is recorded. max , we can get the analytical expression, see the above formulas (3) and (4).

[0075] Step 5: Magnetometer installation error angle correction

[0076] Get beam K 2 After the installation error angle with the Y axis, assume that B = (X 0 ,Y 0 ,Z 0 ), combined with the two beams K 1 , K 2Polarization angles of the output The above formulas (5), (6), (7) and (8) can be obtained.

[0077] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A method for eliminating installation errors based on a double-beam CPT vector magnetometer, characterized in that: The following steps are involved: Step 1, using a dual-beam CPT vector magnetometer measurement system to generate multi-color lasers; Step 2, dividing the multicolor laser into a first beam of light and a second beam of light with equal light intensities, and adjusting the linear polarization directions of the two beams of light by controlling half-wave plates through respective stepper motors; Step 3, based on the relationship between the laser wave vector, polarization direction, magnetic field direction and CPT resonance amplitude, the angle output of the magnetic field vector is modeled and analyzed, including establishing a Cartesian coordinate system XYZ, the light wave vector K1 of the first beam is consistent with the X-axis direction, the light wave vector K2 of the second beam is consistent with the Y-axis direction, the angle between the linear polarization direction e1 of the first beam and the Z axis is θ, and the angle between the linear polarization direction e2 of the second beam and the Z axis is For the unknown magnetic field direction B, the polarization rotation angle θ is achieved by adjusting e1 and e2 respectively and observing the amplitude of the 0-level peak of the CPT signal of both. Determine B by making B perpendicular to e1 and e2 at the same time; Step 4, calculating the installation error angle by obtaining the polarization rotation angle when the CPT signal amplitude is maximum; Step 5: Establish a magnetometer angle output correction model to eliminate installation errors.

2. The method for eliminating installation errors based on a double-beam CPT vector magnetometer according to claim 1 is characterized in that: The dual-beam CPT vector magnetometer measurement system in step 1 includes an ECDL laser connected to the incident side of the beam splitter through an optical isolator, a first half-wave plate, a polarization beam splitter prism, a fiber coupler, a first polarization-maintaining fiber, an electro-optic modulator, a second polarization-maintaining fiber and a laser collimator in sequence; the electro-optic modulator is connected to a triangular wave generator through a radio frequency signal generator; the transmission side of the beam splitter forms a first beam of light which is connected to a data acquisition system through a second half-wave plate, an atomic gas chamber and a first photodetector in sequence; the reflection side of the beam splitter forms a second beam of light which is connected to a data acquisition system through a third half-wave plate, a first reflector, a second reflector, an atomic gas chamber and a second photodetector in sequence; the second half-wave plate is connected to the first stepper motor; the third half-wave plate is connected to the second stepper motor; the atomic gas chamber is located in an oven; the oven is located in a coil; and the coil is located in a shielding layer.

3. The method for eliminating installation errors based on a double-beam CPT vector magnetometer according to claim 2 is characterized in that: The output light beam of the electro-optic modulator is transformed from monochromatic light to polychromatic light due to modulation, and the frequency difference of the first-order sideband light field generated is equal to 87 Rb hyperfine structure ground state energy level |5 2 S 1 / 2 ,F g =1> and |5 2 S 1 / 2 ,F g =2> frequency difference Δv hfs .

4. The method for eliminating installation errors based on a double-beam CPT vector magnetometer according to claim 1 is characterized in that: Step 3 includes the following expressions: Where n is the normal vector of the plane formed by e1 and e2, and B is in the same direction as n. When θ=0, B is in the same direction as the X-axis, and when θ=0, B is in the same direction as the Y-axis.

5. The method for eliminating installation errors based on a double-beam CPT vector magnetometer according to claim 1 is characterized in that: Step 4 includes the following expressions: where γ max is the polarization rotation angle when the CPT signal amplitude is maximum, δ x is the angle between the projection of K2 on the XOY plane and the coordinate axis Y, δz is the angle between the projection of K2 on the YOZ plane and the coordinate axis Y, is the magnitude of the magnetic field on the X axis, is the magnitude of the magnetic field on the Y axis.

6. The method for eliminating installation errors based on a double-beam CPT vector magnetometer according to claim 1, characterized in that: Step 5 includes the following expression: B=(b·tanθ-c,-tanθ·a,a), Among them, a, b, and c are all intermediate quantities.

Images