Method for determining overall symbol of measured magnetic field of double-beam CPT vector magnetometer

Abstract

According to the method for determining the overall symbol of the measured magnetic field of the double-beam CPT vector magnetometer, the symmetry of linearly polarized light is destroyed by using elliptically polarized light, so that the overall symbol of the measured magnetic field is determined under the condition that the high contrast of a linearly polarized light CPT signal is kept; modulation linear polarization polychromatic light of an external cavity semiconductor laser is converted into polychromatic elliptically polarized light through a wave plate, and then the polychromatic elliptically polarized light is input into a gas chamber and is subjected to frequency scanning to obtain an optical signal carrying magnetic field information, and the optical signal is converted into a voltage signal through a photoelectric diode and modulated and demodulated through a lock-in amplifier to obtain a plurality of dispersion signals; by observing the intensity of the signals on the two sides of the central peak and combining the rotation direction of the elliptically polarized light, the magnetic field component is determined to be in the front light propagation direction or the back light propagation direction, the overall symbol of the measured magnetic field of the CPT magnetometer is determined by using an all-optical method without the help of an additional device, and the method has relatively high continuation applicability and relatively high practical value.

Description

Technical Field

[0001] The invention relates to a method for determining the overall sign of a magnetic field measured by a double-beam CPT vector magnetometer, and belongs to the technical field of interaction between light and alkali metal atoms and optical pumping. Background Art

[0002] The CPT effect is a quantum coherence effect. The CPT effect and the Zeeman effect can be used to achieve absolute measurement of the external magnetic field (CPT, Coherent Population Trapping). The CPT magnetometer is essentially an absolute magnetometer, but it exhibits different characteristics when the detection light is linearly polarized light. Specifically, for a single-beam CPT magnetometer, when linearly polarized light is used as the detection light, the direction of the external magnetic field will cause the linear polarization direction to change the appearance of the atomic ensemble:

[0003]

[0004] where e line is the unit vector of linear polarization, is the spherical base, e x ,e y ,e z is an orthogonal basis, α is a vector e line The angle between the vector e and the magnetic field direction B. In the general case, when α≠90°, line The presence of the π-polarization component causes the amplitude and contrast of the central two-photon resonance to decrease. Therefore, the polarization direction of the light can be detected by modulating the linear polarization and observing the performance of the 0th-order peak of the CPT resonance signal to achieve measurement of the magnetic field plane.

[0005] In order to further determine the direction of the magnetic field, the straight line where the magnetic field is located can be determined by the dual-beam configuration. However, a new problem emerges: how to determine the specific direction of the magnetic field, that is, how to determine the overall sign of the measured magnetic field. Taking into account the optical pumping effect unique to circularly polarized light, the present invention uses elliptically polarized light for detection, which not only retains the unique characteristics of linearly polarized light in determining the plane of the magnetic field, but also successfully determines the overall sign of the measured magnetic field through the circularly polarized light pumping effect. The theory of the decomposition of circularly polarized light along the direction of the magnetic field is established, and the effectiveness of the invented method is analyzed from a theoretical perspective, realizing a method for determining the overall sign of the measured magnetic field of a dual-beam CPT vector magnetometer. Summary of the invention

[0006] The problem solved by the invention is: a method for determining the overall sign of a magnetic field measured by a double-beam CPT vector magnetometer (CPT, Coherent Population Trapping). The radio frequency signal (ECDL, External Cavity Diode Laser, EOM, electro-optic modulator) generated by the radio frequency signal generator is injected into the output beam of the ECDL laser through the EOM, and the laser is half-wave modulated to obtain a multi-color laser. The light intensity is weakened and the laser is changed to an elliptically polarized state through a light intensity modulator; the signals generated by the triangle wave signal generator and the sine wave signal generator are superimposed by an adder, and the radio frequency signal is modulated to realize the scanning and modulation of the multi-color light field. The optical signal is demodulated by a phase-locked amplifier through an alkali metal gas chamber to obtain multiple CPT dispersion signals; the wave plate is controlled by a stepper motor to adjust the polarization direction of each optical branch, the intensity of the 0-level peak CPT dispersion signal is observed, and the straight line where the magnetic field is located is solved; the magnitude relationship of the signal intensity on both sides of the 0-level peak is observed, and the overall sign of the measured magnetic field is determined according to the intrinsic spin angular momentum of the elliptically polarized light.

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

[0008] The method for determining the overall sign of the magnetic field measured by a double-beam CPT vector magnetometer is characterized by comprising the following steps:

[0009] Step 1, generating multi-color laser in a dual-beam CPT vector magnetometer system;

[0010] Step 2, the multi-color laser is coupled and collimated and then passes through a quarter wave plate to form multi-color elliptically polarized light;

[0011] Step 3, splitting the polychromatic elliptically polarized light into a first beam of polychromatic elliptically polarized light and a second beam of polychromatic elliptically polarized light, the first beam of polychromatic elliptically polarized light sequentially passes through a second 1 / 2 wave plate, an atomic gas chamber, a first photodetector and a phase-locked amplifier to connect to a data acquisition system, the second beam of polychromatic elliptically polarized light passes through a third 1 / 2 wave plate, a first reflector, a second reflector, an atomic gas chamber, a second photodetector and the phase-locked amplifier to connect to the data acquisition system, and the gas chamber probe located in a fixed magnetic field is used to respectively demodulate the two beams of polychromatic elliptically polarized light signals after passing through the atomic gas chamber in a mutually perpendicular manner by the phase-locked amplifier to obtain a plurality of CPT dispersion signals;

[0012] Step 4, using the first rotary stepping motor to adjust the second 1 / 2 wave plate, and using the second stepping motor to adjust the third 1 / 2 wave plate, to control the directions of the two beams of multi-color elliptically polarized light, and to obtain the straight line where the magnetic field is located;

[0013] Step 5: Observe the signal amplitudes on both sides of the central CPT signal to determine the overall sign of the measured magnetic field.

[0014] Step 1 includes connecting the input end of the first 1 / 2 wave plate to the ECDL laser, connecting the output end of the first 1 / 2 wave plate to a polarization beam splitter prism, connecting the polarization beam splitter prism to an electro-optic modulator via a fiber coupler and a first polarization-maintaining fiber in turn, connecting the electro-optic modulator to the 1 / 4 wave plate in step 2 via a second polarization-maintaining fiber and a laser collimator in turn, connecting the 1 / 4 wave plate to the second 1 / 2 wave plate via the transmission side of the beam splitter, connecting the 1 / 4 wave plate to the third 1 / 2 wave plate via the reflection side of the beam splitter, connecting the electro-optic modulator to the output end of the adder via a radio frequency signal generator, connecting the first input end of the adder to a triangle wave signal generator, connecting the second input end of the adder to a sine wave signal generator, and connecting the sine wave signal generator to the input end of the phase-locked amplifier.

[0015] The laser emitted by the ECDL laser is locked on the D1 line of the Rb87 atom in the atomic gas chamber, the RF signal generator generates a 3.417 GHz signal, and the electro-optic modulator modulates the RF signal into the optical signal to obtain a multi-color laser. The frequencies of the first beam of multi-color elliptically polarized light and the second beam of multi-color elliptically polarized light both satisfy the frequency difference of 6.834 GHz between the two hyperfine energy levels of the Rb87 atom D1 line.

[0016] Step 4 includes the following expressions:

[0017]

[0018] Where n is the direction vector B of the magnetic field and the normal vector of the plane (e1, e2). The elliptically polarized light is regarded as the superposition of linear polarized light and circular polarized light. The direction of linear polarized light is along the long axis of the elliptically polarized light. e1 is the direction vector of the linear polarized light in the first beam of multi-color elliptically polarized light. e2 is the direction vector of the linear polarized light in the second beam of multi-color elliptically polarized light. is the angle between e2 and the Z axis, θ is the angle between e1 and the Z axis, the first beam of multi-color elliptically polarized light enters the atomic gas cell along the X axis, and the second beam of multi-color elliptically polarized light enters the atomic gas cell along the Y axis.

[0019] The technical effects of the present invention are as follows: The method for determining the overall sign of the magnetic field measured by the dual-beam CPT vector magnetometer of the present invention can achieve the determination of the overall sign of the magnetic field measured by the CPT magnetometer by an all-optical method without the aid of additional devices, and has strong extended applicability and high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flow chart of a method for determining the overall sign of a magnetic field measured by a double-beam CPT vector magnetometer. Figure 1 The method comprises the steps of: 1, generating a multi-color laser; 2, passing the optical path through a 1 / 2 wave plate and a PBS (polarization beam splitter prism), adjusting the laser power, and obtaining elliptically polarized light through a 1 / 4 wave plate after coupling and collimation; 3, modulating the multi-color light, and obtaining a plurality of CPT dispersion signals (CPT, Coherent Population Trapping) through an air chamber probe located in a fixed magnetic field and demodulating the signals using a phase-locked amplifier; 4, adjusting the 1 / 2 wave plate using a rotary stepping motor, controlling the polarization direction of the dual-beam elliptical light, and obtaining the straight line where the magnetic field is located; and 5, observing the signal amplitudes on both sides of the central CPT signal to determine the overall sign of the measured magnetic field.

[0021] Figure 2 It is a schematic diagram of the double-beam magnetic field vector measurement principle involved in the method for determining the overall sign of the magnetic field measured by the double-beam CPT vector magnetometer of the present invention. Figure 2 O-coordinate origin, XYZ-coordinate tri-axis, K1-wave vector of the first beam of elliptically polarized light, which is consistent with the X direction (X(K1)), K2-wave vector of the second beam of elliptically polarized light, which is consistent with the Y direction (Y(K2)), B-magnetic field or magnetic field direction, n(B)-normal vector of magnetic field B, e1-linear polarization direction contained in the first beam of light, e2-linear polarization direction contained in the second beam of light, θ-angle between Z axis and e1, The angle between the axis and e2.

[0022] Figure 3 The invention discloses a schematic diagram of the structure of a double-beam CPT vector magnetometer system involved in the method for determining the overall sign of a magnetic field measured by the double-beam CPT vector magnetometer.

[0023] The reference numerals are as follows: 1-ECDL laser (ECDL, External Cavity Diode Laser, external cavity semiconductor laser), 2-first 1 / 2 wave plate; 3-polarization beam splitter prism; 4-fiber coupler; 5-first polarization-maintaining fiber; 6-electro-optic modulator; 7-second polarization-maintaining fiber; 8-laser collimator; 9-1 / 4 wave plate; 10-beam splitter prism; 11-second 1 / 2 wave plate; 12-atomic gas chamber; 13-oven; 14-magnetic field coil; 15-ferrite shielding layer; 16-Permalloy shielding layer; 17-first photodetector; 18-phase-locked amplifier; 19-data acquisition system; 20-sine wave signal generator; 21-adder; 22-RF signal generator; 23-triangle wave signal generator; 24-first stepper motor; 25-third 1 / 2 wave plate; 26-second stepper motor; 27-first reflector; 28-second reflector; xyz-three axes of rectangular coordinate system (i.e., x-axis, y-axis and z-axis). DETAILED DESCRIPTION

[0024] Below is the attached figure ( Figure 1-Figure 3 ) and Examples illustrate the present invention.

[0025] Figure 1 The present invention is a flow chart of a method for determining the overall sign of a magnetic field measured by a double-beam CPT vector magnetometer. Figure 2 It is a schematic diagram of the double-beam magnetic field vector measurement principle involved in the method for determining the overall sign of the magnetic field measured by the double-beam CPT vector magnetometer of the present invention. Figure 3 The figure is a schematic diagram of the structure of a double-beam CPT vector magnetometer system involved in the method for determining the overall sign of the magnetic field measured by the double-beam CPT vector magnetometer of the present invention. Figures 1 to 3 As shown, the method for determining the overall sign of the magnetic field measured by the double-beam CPT vector magnetometer comprises the following steps: step 1, generating a multi-color laser in the double-beam CPT vector magnetometer system; step 2, the multi-color laser is coupled and collimated and then passes through a 1 / 4 wave plate to form a multi-color elliptically polarized light; step 3, the multi-color elliptically polarized light is split into a first beam of multi-color elliptically polarized light and a second beam of multi-color elliptically polarized light, the first beam of multi-color elliptically polarized light passes through a second 1 / 2 wave plate 11, an atomic gas chamber 12, a first photodetector 17 and a phase-locked amplifier 18 in sequence to connect to a data acquisition system 19, and the second beam of multi-color elliptically polarized light passes through a third 1 / 2 wave plate 25, a first reflector 27, a second The reflector 28, the atomic gas chamber 12, the second photodetector 29 and the phase-locked amplifier 18 are connected to the data acquisition system 19. The gas chamber probe is located in a fixed magnetic field, and the phase-locked amplifier 18 is used to demodulate the two beams of multi-color elliptically polarized light signals that pass through the atomic gas chamber 12 in a perpendicular manner to obtain multiple CPT dispersion signals; step 4, using the first rotary stepping motor 24 to adjust the second 1 / 2 wave plate 11, and using the second stepping motor 26 to adjust the third 1 / 2 wave plate 25, to control the directions of the two beams of multi-color elliptically polarized light and obtain the straight line where the magnetic field is located; step 5, observing the signal amplitudes on both sides of the central CPT signal to determine the overall sign of the measured magnetic field.

[0026] Step 1 includes connecting the input end of the first 1 / 2 wave plate 2 to the ECDL laser 1, connecting the output end of the first 1 / 2 wave plate 2 to the polarization beam splitter prism 3, connecting the polarization beam splitter prism 3 to the electro-optic modulator 6 through the fiber coupler 4 and the first polarization-maintaining fiber 5 in turn, connecting the electro-optic modulator 6 to the 1 / 4 wave plate 9 in step 2 through the second polarization-maintaining fiber 7 and the laser collimator 8 in turn, connecting the 1 / 4 wave plate 9 to the second 1 / 2 wave plate 11 through the transmission side of the beam splitter 10, connecting the 1 / 4 wave plate 9 to the third 1 / 2 wave plate 25 through the reflection side of the beam splitter 10, connecting the electro-optic modulator 6 to the output end of the adder 21 through the RF signal generator 22, connecting the first input end of the adder 21 to the triangle wave signal generator 23, connecting the second input end of the adder 21 to the sine wave signal generator 20, and connecting the sine wave signal generator 20 to the input end of the phase-locked amplifier 18.

[0027] The laser emitted by the ECDL laser 1 is locked on the D1 line of the Rb87 atom in the atomic gas chamber, the RF signal generator 22 generates a 3.417 GHz signal, and the electro-optic modulator 6 modulates the RF signal into the optical signal to obtain a multi-color laser. The frequencies of the first beam of multi-color elliptically polarized light and the second beam of multi-color elliptically polarized light both satisfy the frequency difference of 6.834 GHz between the two hyperfine energy levels of the Rb87 atomic D1 line.

[0028] Step 4 includes the following expressions:

[0029]

[0030] Where n is the direction vector B of the magnetic field and the normal vector of the plane (e1, e2). The elliptically polarized light is regarded as the superposition of linear polarized light and circular polarized light. The direction of linear polarized light is along the long axis of the elliptically polarized light. e1 is the direction vector of the linear polarized light in the first beam of multi-color elliptically polarized light. e2 is the direction vector of the linear polarized light in the second beam of multi-color elliptically polarized light. is the angle between e2 and the Z axis, θ is the angle between e1 and the Z axis, the first beam of multi-color elliptically polarized light enters the atomic gas cell along the X axis, and the second beam of multi-color elliptically polarized light enters the atomic gas cell along the Y axis.

[0031] The present invention relates to a method for determining the overall sign of a magnetic field measured by a double-beam CPT vector magnetometer. The symmetry of linearly polarized light is destroyed by elliptically polarized light to achieve the determination of the overall sign of the measured magnetic field while retaining the high contrast of the linearly polarized light CPT signal. In order to ensure the feasibility of determining the overall sign of the measured magnetic field, the difference in the magnetic field measurement signal obtained when the overall direction of the magnetic field is opposite and the effectiveness of the invention are analyzed from a theoretical perspective. As the probe part of a coherent population trapping (CPT) vector magnetometer, the modulated linearly polarized polychromatic light of an external cavity semiconductor laser (ECDL) is converted into polychromatic elliptically polarized light through a wave plate and then input into an air chamber and subjected to frequency scanning to obtain an optical signal carrying magnetic field information and obtain multiple dispersion signals after being converted into a voltage signal by a photodiode and modulated and demodulated by a phase-locked amplifier. By observing the signal intensity on both sides of the central peak and combining the handedness of the elliptically polarized light, it is determined that the magnetic field component is in the direction of propagation along the light or against the light, thereby achieving the determination of the overall sign of the magnetic field. This method can determine the overall sign of the magnetic field measured by the CPT magnetometer using an all-optical method without the aid of additional devices, and has strong extended applicability and high practical value.

[0032] A principle and coordinate system setting for determining the overall symbol system of the magnetic field measured by a double-beam CPT vector magnetometer Figure 3 shown.

[0033] The CPT magnetometer utilizes the interference effect between atomic energy levels. For rubidium 87 atoms, it is necessary to generate polychromatic light that satisfies the frequency difference of hyperfine energy levels. The present invention uses an ECDL laser to generate the D1 line of the Rb87 atom, and inputs it into the electro-optical modulator after attenuating the light intensity. The laser frequency is half-wave modulated using the 3.417GHz electrical signal generated by the radio frequency signal generator, and the resulting frequency difference of the two sideband lights is equal to 6.834GHz, which roughly satisfies the hyperfine energy level difference. The signals generated by the triangle wave signal generator and the sine wave signal generator are superimposed by an adder, input into the radio frequency signal generator, and the radio frequency signal is modulated to achieve small-range scanning (MHz) and modulation of the polychromatic light field. When the laser passes through the gas chamber containing Rb87 atoms, the CPT phenomenon caused by the Zeeman effect can be seen, and the absolute value information of the magnetic field can be obtained by comparing the frequency difference of the zero-crossing point of the dispersion signal. In the invention, Figure 3 As shown, the propagation directions of the two elliptically polarized light beams are configured orthogonally. The wave vectors K1 and K2 of the two light beams correspond to the coordinate axes X and Y respectively, and the direction of the coordinate axis Z is determined by the right-hand rule. For elliptically polarized light, it can be simply regarded as the superposition of linear polarized light and circular polarized light, and the linear polarization direction is along the long axis of the elliptical light. For the linear polarization part, the angles between the polarization directions e1 and e2 of the two light beams and the Z axis are θ, For the unknown magnetic field direction B, the polarization directions of the two beams are adjusted respectively during the experiment, and the amplitude of the 0-level peak of the CPT signal of the two beams is observed. When the amplitude reaches the maximum, it is the required angle, and then the polarization rotation angle θ is achieved. According to the relevant conclusions, the magnetic field direction B should be perpendicular to both the linear polarization directions e1 and e2, such as Figure 2 A Cartesian coordinate system is established as shown. According to the constraints, the direction of the straight line where the magnetic field is located can be easily determined uniquely. Figure 2 X, Y, and Z satisfy the right-hand coordinate system. K1 and K2 are the propagation directions of the two beams of light, and their linear polarization directions are represented by e1 and e2 respectively.

[0034] pass Figure 2 The Cartesian coordinate system is shown in the figure. A general analysis of the magnetic field vector measurement method is performed, and the normal vector can be obtained as:

[0035]

[0036] Among them, The direction of the magnetic field B is perpendicular to both the linear polarization directions e1 and e2, that is, the direction vector of the magnetic field is consistent with the normal vector n of the plane (e1, e2), thereby determining the straight line where the magnetic field is located.

[0037] Considering the circular polarization component of elliptically polarized light, the circular polarization can determine the overall direction of the magnetic field. Specifically, for the CPT system, the quantization axis direction (vector B) will affect the performance of the circular polarization direction e:

[0038]

[0039] in is the spherical base, e x ,e y ,e z is an orthogonal basis, and β is the angle between the magnetic field direction and the light propagation direction.

[0040] Based on the symmetry of the spherical basis, we can assume that circularly polarized light can be expressed as e when propagating in the same direction as the magnetic field. +1 When the propagation direction of circularly polarized light is in the same direction as the magnetic field direction B (β = 0°), e = e +1 , the direction of the light field received by the atomic ensemble remains the same as the initial direction; when the propagation direction of the circularly polarized light is opposite to the direction of the magnetic field B (β = 180°), e = -e -1, the direction of the light field received by the atomic ensemble is opposite to the initial one. Considering the characteristics of circularly polarized light, it has a pumping effect on the atomic ensemble. When circularly polarized light produces the CPT phenomenon, the intensity of the magnetically insensitive peak is no longer symmetrical due to the optical pumping effect. The specific intensity depends on the spin angular momentum of the light field felt by the atomic ensemble. According to the above theory, if left-handed circularly polarized light is used for excitation, its spin angular momentum is +1. When there is a measured magnetic field, m is observed. F = +1, +2, +3 CPT resonance peak intensity is higher than m F = -1, -2, -3 CPT resonance peak intensity, it is considered that the overall direction of the measured magnetic field is consistent with the direction of light propagation; and the observed m F = +1, +2, +3 CPT resonance peak intensity is lower than m F =-1, -2, -3 of the CPT resonance peak intensity, it is considered that the overall direction of the measured magnetic field is opposite to the direction of light propagation. Further combined with the straight line where the measured magnetic field is located in step 4, the overall sign of the measured magnetic field is obtained by observing the intensity distribution of the dispersion signal. The advantage of the present invention compared with the prior art is that the magnetic field vector measurement can be realized by configuring a CPT magnetometer with dual-beam linear polarized light, but it can ultimately only determine the straight line where the measured magnetic field is located, and does not have the ability to determine the overall sign of the magnetic field. The present invention proposes a method for determining the overall sign of the magnetic field measured by a dual-beam CPT vector magnetometer. A method for determining the overall sign of the magnetic field measured by a dual-beam CPT vector magnetometer. The radio frequency signal generated by the radio frequency signal generator is injected into the output beam of the ECDL laser through the EOM, and the laser is half-wave modulated to obtain a multi-color laser. The light intensity is weakened and the laser is changed to an elliptically polarized state through a light intensity modulator; the signals generated by the triangle wave signal generator and the sine wave signal generator are superimposed by an adder, and the radio frequency signal is modulated to realize the scanning and modulation of the multi-color light field. The optical signal is demodulated by a phase-locked amplifier through an alkali metal gas chamber to obtain multiple CPT dispersion signals; the wave plate is controlled by a stepper motor to adjust the polarization direction of each optical branch, the intensity of the 0-level peak CPT dispersion signal is observed, and the straight line where the magnetic field is located is solved; the magnitude relationship of the signal intensity on both sides of the 0-level peak is observed, and the overall sign of the measured magnetic field is determined according to the intrinsic spin angular momentum of the elliptically polarized light.

[0041] This method requires five steps to implement a method for determining the overall sign of the magnetic field measured by a double-beam CPT vector magnetometer.

[0042] Step 1: Multicolor laser generation

[0043] To meet the principle of CPT magnetometer, two laser frequencies need to be generated to meet the frequency difference between the two hyperfine energy levels of the D1 line of Rb87 atom (approximately 6.834 GHz). Usually, the ECDL laser is locked on the D1 line, and then a RF signal generator is used to generate a 3.417 GHz signal. The RF signal is modulated into the optical signal through an electro-optical modulator (EOM) to obtain a multi-color laser.

[0044] Step 2: Ellipsometry Preparation

[0045] Polarization devices are used to make the ECDL laser line polarization purer. The intensity of polarized light is reduced to a suitable level through the light intensity adjustment system composed of a λ / 2 wave plate and a polarization beam splitter prism. The light intensity is usually 20uW. The light passes through a λ / 4 wave plate to generate elliptically polarized light, providing an optical basis for the dual-beam vector magnetometer.

[0046] Step 3: Modulate and demodulate the CPT signal to obtain the dispersion signal

[0047] The signal generated by the RF signal generator is frequency modulated by a triangular wave function and a sine wave function. The triangular wave function is used to realize the frequency scanning function; the sine wave function modulates the optical signal, and the sine wave function signal is used as the reference signal input of the phase-locked amplifier, and the corresponding dispersion signal is demodulated. Since the dispersion signal has a one-to-one correspondence with the CPT signal, and the zero crossing point of the dispersion signal coincides with the peak point of the CPT signal, the dispersion signal can be used to measure the magnetic field. In the case of an external magnetic field, due to the Zeeman multiplicity of the ground state, multiple CPT resonances are formed. For the magnetic quantum number m of the alkali metal atom F = ±1, ±2, ±3 Zeeman sublevel frequency differences will change with the change of magnetic field, and the frequency shift will change. F = 0, the Zeeman sublevel frequency difference remains unchanged and is always equal to the hyperfine level frequency difference.

[0048] Step 4: Determine the straight line where the magnetic field to be measured is located

[0049] In the invention, the propagation directions of the two elliptically polarized light beams are orthogonally arranged. The wave vectors K1 and K2 of the two light beams correspond to the coordinate axes X and Y respectively, and the direction of the coordinate axis Z is determined by the right-hand rule. For elliptically polarized light, it can be simply regarded as the superposition of linear polarized light and circular polarized light, and the linear polarization direction is along the long axis of the elliptically polarized light. For the linearly polarized part, the angles between the polarization directions e1 and e2 of the two light beams and the Z axis are θ, For the unknown magnetic field direction B, the polarization directions of the two beams are adjusted respectively during the experiment, and the amplitude of the 0-level peak of the CPT signal of the two beams is observed. When the amplitude reaches the maximum, it is the required angle, and then the polarization rotation angle θ is achieved. According to the relevant conclusions, the magnetic field direction B should be perpendicular to both the linear polarization directions e1 and e2, such as Figure 2 The Cartesian coordinate system is established as shown. 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. K1 and K2 are the propagation directions of the two beams of light, and their linear polarization directions are represented as e1 and e2 respectively.

[0050] pass Figure 2 The Cartesian coordinate system shown in the figure is used to analyze the magnetic field vector measurement method in general, and the normal vector can be obtained as:

[0051]

[0052] Among them, The direction of the magnetic field B is perpendicular to both the linear polarization directions e1 and e2, that is, the direction vector of the magnetic field is consistent with the normal vector n of the plane (e1, e2).

[0053] Step 5: Observe the signal strength to determine the overall sign of the measured magnetic field

[0054] Considering the CPT signal excited by elliptically polarized light, elliptically polarized light can be simply regarded as the superposition of linearly polarized light and circularly polarized light. The linearly polarized light part is used to determine the straight line where the measured magnetic field is located in step 4, while the circularly polarized light can determine the overall direction of the magnetic field.

[0055] Specifically, for the CPT system, the quantization axis direction (vector B) will affect the performance of the circular polarization direction e:

[0056]

[0057] in is the spherical base, e x ,e y ,e z is an orthogonal basis, and β is the angle between the magnetic field direction and the light propagation direction.

[0058] Based on the symmetry of the spherical basis, we can assume that circularly polarized light can be expressed as e when propagating in the same direction as the magnetic field. +1 When the propagation direction of circularly polarized light is in the same direction as the magnetic field direction B (β = 0°), e = e +1 , the direction of the light field received by the atomic ensemble remains the same as the initial direction; when the propagation direction of the circularly polarized light is opposite to the direction of the magnetic field B (β = 180°), e = -e -1, the direction of the light field received by the atomic ensemble is opposite to the initial one. Considering the characteristics of circularly polarized light, it has a pumping effect on the atomic ensemble. When circularly polarized light produces the CPT phenomenon, the intensity of the magnetically insensitive peak is no longer symmetrical due to the optical pumping effect. The specific intensity depends on the spin angular momentum of the light field felt by the atomic ensemble. According to the above theory, if left-handed circularly polarized light is used for excitation, its spin angular momentum is +1. When there is a measured magnetic field, m is observed. F = +1, +2, +3 CPT resonance peak intensity is higher than m F = -1, -2, -3 CPT resonance peak intensity, it is considered that the overall direction of the measured magnetic field is consistent with the direction of light propagation; and the observed m F = +1, +2, +3 CPT resonance peak intensity is lower than m F =-1, -2, -3 CPT resonance peak intensity, it is considered that the overall direction of the measured magnetic field is opposite to the light propagation direction. Further combined with the straight line where the measured magnetic field is located in step 4, the overall sign of the measured magnetic field is obtained by observing the intensity distribution of the dispersion signal.

[0059] The laser is adjusted to the appropriate light intensity and elliptical polarization state, and the laser frequency is modulated after the dual-beam vector measurement configuration is performed. Multiple dispersion signals are observed through the phase-locked amplifier, and then the high-precision stepper motors of each branch are started to adjust the direction of the long axis of the elliptical light until the intensity of the 0-level peak CPT signal of each branch reaches the maximum, thereby determining the straight line where the magnetic field is located. Further observation of the CPT signal m in the two branches F =+1, +2, +3 and m F =-1, -2, -3 CPT resonance peak intensity relationship, combined with the elliptical light intrinsic spin angular momentum, ultimately determine the overall sign of the measured magnetic field.

[0060] 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 determining the overall sign of a magnetic field measured by a double-beam CPT vector magnetometer, characterized in that: The following steps are involved: Step 1, generating multi-color laser in a dual-beam CPT vector magnetometer system; Step 2, the multi-color laser is coupled and collimated and then passes through a quarter wave plate to form multi-color elliptically polarized light; Step 3, splitting the polychromatic elliptically polarized light into a first beam of polychromatic elliptically polarized light and a second beam of polychromatic elliptically polarized light, the first beam of polychromatic elliptically polarized light sequentially passes through a second 1 / 2 wave plate, an atomic gas chamber, a first photodetector and a phase-locked amplifier to connect to a data acquisition system, the second beam of polychromatic elliptically polarized light passes through a third 1 / 2 wave plate, a first reflector, a second reflector, an atomic gas chamber, a second photodetector and the phase-locked amplifier to connect to the data acquisition system, and the gas chamber probe located in a fixed magnetic field is used to respectively demodulate the two beams of polychromatic elliptically polarized light signals after passing through the atomic gas chamber in a mutually perpendicular manner by the phase-locked amplifier to obtain a plurality of CPT dispersion signals; Step 4, using the first rotary stepping motor to adjust the second 1 / 2 wave plate, and using the second stepping motor to adjust the third 1 / 2 wave plate, to control the directions of the two beams of multi-color elliptically polarized light, and to obtain the straight line where the magnetic field is located; Step 5: Observe the signal amplitudes on both sides of the central CPT signal to determine the overall sign of the measured magnetic field.

2. The method for determining the overall sign of the magnetic field measured by the double-beam CPT vector magnetometer according to claim 1 is characterized in that: Step 1 includes connecting the input end of the first 1 / 2 wave plate to the ECDL laser, connecting the output end of the first 1 / 2 wave plate to a polarization beam splitter prism, connecting the polarization beam splitter prism to an electro-optic modulator via a fiber coupler and a first polarization-maintaining fiber in turn, connecting the electro-optic modulator to the 1 / 4 wave plate in step 2 via a second polarization-maintaining fiber and a laser collimator in turn, connecting the 1 / 4 wave plate to the second 1 / 2 wave plate via the transmission side of the beam splitter, connecting the 1 / 4 wave plate to the third 1 / 2 wave plate via the reflection side of the beam splitter, connecting the electro-optic modulator to the output end of the adder via a radio frequency signal generator, connecting the first input end of the adder to a triangle wave signal generator, connecting the second input end of the adder to a sine wave signal generator, and connecting the sine wave signal generator to the input end of the phase-locked amplifier.

3. The method for determining the overall sign of the magnetic field measured by the double-beam CPT vector magnetometer according to claim 2 is characterized in that: The laser emitted by the ECDL laser is locked on the D1 line of the Rb87 atom in the atomic gas chamber, the RF signal generator generates a 3.417 GHz signal, and the electro-optic modulator modulates the RF signal into the optical signal to obtain a multi-color laser. The frequencies of the first beam of multi-color elliptically polarized light and the second beam of multi-color elliptically polarized light both satisfy the frequency difference of 6.834 GHz between the two hyperfine energy levels of the Rb87 atom D1 line.

4. The method for determining the overall sign of the magnetic field measured by the double-beam CPT vector magnetometer according to claim 1 is characterized in that: Step 4 includes the following expressions: Where n is the direction vector B of the magnetic field and the normal vector of the plane (e1, e2). The elliptically polarized light is regarded as the superposition of linear polarized light and circular polarized light. The direction of linear polarized light is along the long axis of the elliptically polarized light. e1 is the direction vector of the linear polarized light in the first beam of multi-color elliptically polarized light. e2 is the direction vector of the linear polarized light in the second beam of multi-color elliptically polarized light. is the angle between e2 and the Z axis, θ is the angle between e1 and the Z axis, the first beam of multi-color elliptically polarized light enters the atomic gas cell along the X axis, and the second beam of multi-color elliptically polarized light enters the atomic gas cell along the Y axis.

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