CN116087845A - A three-dimensional distribution measurement method of electron spin polarizability based on electron paramagnetic resonance - Google Patents

Abstract

The method for measuring the three-dimensional distribution of the spin polarizability of the electron based on electron paramagnetic resonance uses a longitudinal uniform magnetic field coil and a longitudinal gradient magnetic field coil to distinguish the transverse distribution of the spin polarizability of the electron, applies an oscillating magnetic field in the x direction to generate electron paramagnetic resonance with the spin, changes the size of the longitudinal uniform magnetic field, makes the spin of the electron at different positions away from the x axis resonate with the oscillating magnetic field, ensures that the amplitude of the spin angle of a resonance signal is in direct proportion to the relative polarizability of a resonance point, reflects the three-dimensional distribution of the spin polarizability of the electron by measuring the resonance signals at different spatial positions, does not apply a big magnetic field of Gaussian magnitude to cause the atomic energy level to split, and is favorable for measuring the three-dimensional distribution of the spin polarizability of the electron at high temperature and high pressure.

Description

A three-dimensional distribution measurement method of electron spin polarizability based on electron paramagnetic resonance

technical field

The invention relates to a method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance, which belongs to the field of optically pumped atomic polarization.

Background technique

The sensitive elements of devices such as atomic magnetometers, atomic gyroscopes, and atomic clocks based on optically pumped atomic polarization are alkali metal gas cells. Due to the absorption of pumping light by alkali metals, there is a serious gradient in electron spin polarizability, which greatly affects the coherence between electron spin and nuclear spin. Accurately measuring the three-dimensional distribution of electronic polarizability has become an urgent problem to be solved.

At present, most of the studies on the three-dimensional distribution of electronic susceptibility are finite element simulations based on the Bloch-Diffusion equation. The simulation results are heavily dependent on preset parameters, and untrue preset parameters will produce very different simulation results. Some studies use the transmittance of the pumping light to reflect the longitudinal polarizability distribution, but this method cannot accurately measure the lateral distribution of the polarizability. In the previous research on the measurement of electron spin polarization by electron paramagnetic resonance, a large magnetic field was relied on to generate energy level splitting and measure the number of atomic layouts. This scheme has measurement defects for atomic gas chambers with high temperature and high pressure.

Contents of the invention

The problem solved by the present invention is: the present invention proposes a method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance. To distinguish, apply an oscillating magnetic field in the x direction and electron paramagnetic resonance occurs with the electron spin, change the size of the longitudinal uniform magnetic field, and make the electron spin at different positions from the x axis resonate with the oscillating magnetic field, and the amplitude of the optical rotation angle of the resonance signal It is proportional to the relative polarizability of the resonance point. By measuring the resonance signals at different spatial positions, it reflects the three-dimensional distribution of electron spin polarizability. It does not need to apply a large Gaussian magnetic field to split the atomic energy level, which is conducive to the measurement of high Three-dimensional distribution of electron spin polarizability under temperature and high pressure.

Technical solution of the present invention is as follows:

The method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance is characterized in that the transverse distribution of electron spin polarizability is distinguished by using a longitudinal uniform magnetic field coil and a longitudinal gradient magnetic field coil, and an oscillating magnetic field is applied in the x direction Electron paramagnetic resonance occurs with the electron spin, changing the size of the longitudinal uniform magnetic field, so that the electron spin at different positions from the x-axis resonates with the oscillating magnetic field, and the amplitude of the resonance signal optical rotation angle and the relative polarizability of the resonance point In direct proportion, the three-dimensional distribution of electron spin polarizability is reflected by measuring the resonance signals at different spatial positions. The spatial resolution of the method is less than 1 mm ³ .

Include the following steps:

Step 1, apply the bias magnetic field B _z0 and the gradient magnetic field B _{z gradient} in the z-axis direction perpendicular to the direction of the probe light, dB _{z gradient} /dx=k, where k is the magnetic field gradient, and the total gradient magnetic field is B _z (x)= B _z0 + B _{z gradient} (x), the electron spin precession frequency distributed in the x-axis direction, that is, the detection light direction is ω _spin (x) = γ _e (B _z0 + kx)/q, where q is the electron spin spin ensemble slowing down factor, γ _e is the gyromagnetic ratio of electron spin ensemble;

Step 2, measuring the transmitted light intensity of the probe light;

Step 3, applying an oscillating magnetic field in the x direction to resonate with the electron spin;

Step 4, change the magnetic field strength value of B _z0 , so that the resonance plane of the electron spin moves from one side to the other side along the x direction of the alkali metal gas chamber, and the electron spin resonance point x=(ωq/γ _e -B _z0 ) /k, where ω is the frequency of the oscillating magnetic field in the x direction, and the resonance strength of each resonance point is recorded, and the resonance strength is proportional to the electron spin polarizability;

Step 5, changing the position of the probe light on the yoz plane, and repeatedly testing the transmitted light intensity and resonance intensity;

In step 6, the resonance intensity at each position is divided by the transmitted light intensity of the probe light to obtain the three-dimensional distribution of electron spin polarizability.

The bias magnetic field in the step 1 is a DC uniform magnetic field.

The step 2 includes that in the process of measuring the optical rotation angle by the balanced difference method, the output signal is proportional to the optical rotation angle or the transmitted light intensity. In order to ensure that the optical rotation angles at different measurement positions are comparable, firstly, the transmitted light of the probe light Strongly measure and normalize the output signal for the later stage.

The oscillating frequency of the oscillating magnetic field applied in step 3 is around γ _e B _z0 /q, so as to resonate with electron spins.

The resonance strength in step 4 is obtained by demodulating the output signal of the lock-in amplifier.

The step 2 includes extracting the electron spin ensemble polarizability x-axis component information <P _x > by the following formula:

Where <S _x > represents the optical rotation angle signal detected by the probe light, I is the transmitted light intensity, a is a constant proportional coefficient, and l is the width of the inner space of the alkali metal gas chamber on the x-axis.

The measuring device of the transmitted light intensity comprises a polarizing beam splitting prism, the input side of the polarizing beam splitting prism is connected to the transmitted light passing through the alkali metal gas chamber, and the reflection side of the polarizing beam splitting prism is connected to the negative side of the differential amplifier through the first photodetector. To the input end, the transmission side of the polarization splitter prism is connected to the positive input end of the differential amplifier, and the output end of the differential amplifier is connected to the data acquisition system.

The technical effect of the present invention is as follows: the present invention is based on the electron paramagnetic resonance three-dimensional distribution measurement method of electron spin polarizability, based on the fact that electron spins have different precession frequencies under different longitudinal magnetic fields, so the use of longitudinal uniform magnetic field coils and longitudinal gradient The magnetic field coil distinguishes the lateral distribution of the electron spin polarizability, and applies an oscillating magnetic field in the x direction. The oscillation frequency should be close to the Larmor precession frequency of the electron spin. Changing the size of the longitudinal uniform magnetic field can make the distance x The electron spins at different positions on the axis resonate with the oscillating magnetic field, and the amplitude of the optical rotation angle of the resonance signal is proportional to the electron spin polarizability at the resonance point. This method can measure the three-dimensional distribution of the transverse polarizability. The three-dimensional distribution of the polarizability of the electron spin in the atomic gas chamber can be measured by changing the incident position of the probe light on the yoz plane and repeating the test. This method can be used to study the three-dimensional distribution of spin polarizability of atomic vapor electrons in systems such as optically pumped magnetometers, SERF atomic gyroscopes, and optically pumped atomic clocks.

Compared with the prior art, the present invention has the advantages that the transverse distribution of electron spin polarizability is distinguished by using the longitudinal uniform magnetic field coil and the longitudinal gradient magnetic field coil, and the transverse polarizability distribution can be measured. The optical rotation angle detection scheme using the balanced differential after magnetic field modulation has a higher signal-to-noise ratio than the light absorption detection scheme. The three-dimensional distribution of electron spin polarizability at high temperature and high pressure can be measured without applying a large Gaussian magnetic field to split the atomic energy level.

Description of drawings

Fig. 1 is a schematic flowchart of implementing the method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to the present invention. Figure 1 includes step 1, applying a gradient magnetic field and a DC magnetic field in the z direction; step 2, measuring the transmitted light intensity of the probe light; step 3, applying an oscillating magnetic field in the x direction to resonate with the electron spin; step 4, changing the DC uniform magnetic field Intensity, so that the resonance plane of the electron spin moves from one side to the other along the x direction of the gas cell, and record the resonance intensity of each resonance point; step 5, change the position of the probe light on the yoz plane, and repeat the test of the transmitted light intensity and resonance intensity; step 6, dividing the resonance intensity at each position by the transmitted light intensity of the probe light to obtain the three-dimensional distribution of electron spin polarizability.

Fig. 2 is a schematic diagram of the principle of a three-dimensional distribution measurement device for electron spin polarizability based on electron paramagnetic resonance. Figure 2 includes the resonant magnetic field along the x-axis, the gradient magnetic field Bz along the z-axis, the polarizability distribution along the x-direction, the pumping beam and the detection beam. In the Cartesian coordinate system, the incident direction of the pumping light is parallel to the z-axis , the incident direction of the probe light is parallel to the x-axis. Figure 2 includes PBS (polarization beam splitter, polarization beam splitter), two PDs (Photodetector, photodetector), differential amplifier, and data acquisition system.

Detailed ways

The present invention will be described below in conjunction with the accompanying drawings (FIG. 1-FIG. 2) and embodiments.

Fig. 1 is a schematic flowchart of implementing the method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to the present invention. Fig. 2 is a schematic diagram of the principle of a three-dimensional distribution measurement device for electron spin polarizability based on electron paramagnetic resonance. Referring to Figures 1 to 2, the method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance uses longitudinal uniform magnetic field coils and longitudinal gradient magnetic field coils to distinguish the lateral distribution of electron spin polarizability. When an oscillating magnetic field is applied in the x direction, electron paramagnetic resonance occurs with the electron spin, and the size of the longitudinal uniform magnetic field is changed, so that the electron spin at different positions from the x axis resonates with the oscillating magnetic field, and the amplitude of the optical rotation angle of the resonance signal is related to the resonance point. The relative polarizability is proportional to the size, and the three-dimensional distribution of electron spin polarizability is reflected by measuring the resonance signals at different spatial positions. The spatial resolution is less than 1mm ³ .

Including the following steps: Step 1, applying a bias magnetic field B _z0 and a gradient magnetic field B _{z gradient} in the z-axis direction perpendicular to the direction of the probe light, dB _{z gradient} /dx=k, where k is the magnetic field gradient, and the total gradient magnetic field is B _z (x) = B _z0 + B _{z gradient} (x), the electron spin precession frequency distributed in the x-axis direction, that is, the probe light direction is ω _spin (x) = γ _e (B _z0 + kx)/q, where q is the slowing down factor of the electron spin ensemble, and γ _e is the gyromagnetic ratio of the electron spin ensemble; step 2, measuring the transmitted light intensity of the probe light; step 3, applying an oscillating magnetic field in the x direction to generate resonance with the electron spin; step 4. Change the magnetic field strength value of B _z0 , so that the resonance plane of the electron spin moves from one side to the other side along the x direction of the alkali metal gas chamber, and the electron spin resonance point x=(ωq/γ _e -B _z0 )/ k, where ω is the frequency of the oscillating magnetic field in the x direction, record the resonance strength of each resonance point, and the resonance strength is proportional to the electron spin polarizability; step 5, change the position of the probe light on the yoz plane, and repeat the test of the transmitted light intensity and resonance intensity; step 6, dividing the resonance intensity at each position by the transmitted light intensity of the probe light to obtain the three-dimensional distribution of electron spin polarizability.

The bias magnetic field in the step 1 is a DC uniform magnetic field. The step 2 includes that in the process of measuring the optical rotation angle by the balanced difference method, the output signal is proportional to the optical rotation angle or the transmitted light intensity. In order to ensure that the optical rotation angles at different measurement positions are comparable, firstly, the transmitted light of the probe light Strongly measure and normalize the output signal for the later stage. The oscillating frequency of the oscillating magnetic field applied in step 3 is around γ _e B _z0 /q, so as to resonate with electron spins. The resonance strength in step 4 is obtained by demodulating the output signal of the lock-in amplifier.

The step 2 includes extracting the electron spin ensemble polarizability x-axis component information <P _x > by the following formula:

Where <S _x > represents the optical rotation angle signal detected by the probe light, I is the transmitted light intensity, a is a constant proportional coefficient, and l is the width of the inner space of the alkali metal gas chamber on the x-axis. The measuring device of the transmitted light intensity includes a polarizing beam splitting prism, the input side of the polarizing beam splitting prism is connected to the transmitted light passing through the alkali metal gas chamber, and the reflection side of the polarizing beam splitting prism is connected to the negative side of the differential amplifier through the first photodetector. To the input end, the transmission side of the polarization splitter prism is connected to the positive input end of the differential amplifier, and the output end of the differential amplifier is connected to the data acquisition system.

The invention proposes a method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance. The lateral distribution of electron spin polarizability is differentiated using longitudinal uniform magnetic field coils and longitudinal gradient magnetic field coils. An oscillating magnetic field is applied in the x-direction to undergo electron paramagnetic resonance with electron spins. Changing the size of the longitudinal uniform magnetic field makes the electron spins at different positions away from the x-axis resonate with the oscillating magnetic field, and the amplitude of the optical rotation angle of the resonance signal is proportional to the relative polarizability of the resonance point. The three-dimensional distribution of electron spin polarizability is reflected by measuring resonance signals at different spatial positions.

The measurement principle and coordinate system setting of the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance are shown in Figure 2. The kinetic equations of atomic polarization pumped by light and Larmor precession of atoms in an external magnetic field can be approximately described by the following Bloch equation:

In the Cartesian coordinate system in Figure 2, the incident direction of the pumping light is parallel to the z-axis, and the incident direction of the probe light is parallel to the x-axis; t is time; electron spin ensemble polarization <P>=<P _x ,P _y , P _z >, where P _x , P _y , P _z are the three coordinate axis components of electron polarizability; γ _e is the gyromagnetic ratio of electron spin ensemble; q is the slowing down factor of electron spin ensemble; The pumping rate R of the pulsed laser; the external magnetic field B=<B _x (t),B _y (t),B _z (t)> and its three-axis components B _x (t),B _y (t),B _z (t); In order to describe the relaxation process of the longitudinal and transverse polarizability of atoms, the longitudinal relaxation rate Γ ₁ and the transverse relaxation rate Γ ₂ of the electron spin are introduced. This equation describes the dynamical evolution of the electron spin ensemble under light pumping, atomic relaxation, and Larmor precession in a magnetic field.

在系统的x轴施加振荡磁场B_x(t)＝B₁cos(ωt)，B₁为振荡磁场幅值，ω为振荡磁场角速率，y轴不施加磁场，即B_y(t)＝0，z轴施加直流磁场B_z(t)＝B_z0，带入式(2)可得出系统x向极化率的磁场响应<P_x>：Where <P _± >=<P _x >±<P _y >, <B _± >(t)=<B _x >(t)±<B _y >(t). The longitudinal component of the electron spin is

Apply an oscillating magnetic field on the x-axis of the system B _x (t) = B ₁ cos(ωt), B ₁ is the amplitude of the oscillating magnetic field, ω is the angular rate of the oscillating magnetic field, and no magnetic field is applied on the y-axis, that is, By _y (t) = 0 , the z-axis applies a DC magnetic field B _z (t) = B _z0 , which can be inserted into the formula (2) to obtain the magnetic field response <P _x > of the x-direction polarizability of the system:

当z轴施加的磁场与x轴施加的振荡磁场B_x(t)＝B₁cos(ωt)共振时，即γ_eB_z0＝ωq，共振信号达到最大值：in

When the magnetic field applied on the z-axis resonates with the oscillating magnetic field B _x (t)=B ₁ cos(ωt) applied on the x-axis, that is, γ _e B _z0 =ωq, the resonance signal reaches its maximum value:

Similar to the principle of nuclear magnetic resonance imaging, by adding a spatial gradient to the magnetic field _Bz , the spatial variation information of electron spin polarization along the direction of the probe laser can be obtained, as shown in Figure 2. Apply a bias magnetic field B _z0 and a gradient magnetic field B _{z gradient} on the z axis perpendicular to the direction of the detection laser, the magnetic field gradient is dB _{z gradient} /dx=k, then the total gradient magnetic field is B _z (x) = B _z0 + B _{z gradient} (x). Under such a gradient, the electron spin precession frequency distributed in the x direction is ω _spin (x)=γ _e (B _z0 +kx)/q. Keep the gradient magnetic field unchanged, and set the frequency of the oscillating field in the x direction as ω. At this time, the electron spin resonance point is x=(ωq/γ _e -B _z0 )/k, and the size of B _z0 is scanned to move the resonance point from one side of the atomic gas cell to the other side along the probe laser. Keeping the applied magnetic field constant, when the electron spin resonates with the applied oscillating magnetic field, the oscillation intensity of <P _x > is only related to and proportional to the longitudinal polarizability <P _z > ₀ of the electron spin. The probe light is a beam of linearly polarized light parallel to the x-axis, and the <P _x > component information of the electron spin can be extracted by using the balanced difference method:

Among them, <S _x > represents the optical rotation angle signal detected by the probe light, I is the projected light intensity, and a is a constant proportional coefficient. The phase-locked amplification technique is used to extract the oscillation amplitude of each resonance point along the direction of the probe light and divide it by the corresponding transmitted light intensity I to obtain the relative distribution of the longitudinal polarizability of the electron spin. Since the diameter of the probe beam is only a few millimeters or less, the spatial resolution of the method is less than 1 mm ³ .

This method requires six steps to realize the three-dimensional distribution measurement of electron spin polarizability based on electron paramagnetic resonance.

Step 1: Apply a gradient magnetic field and a DC magnetic field in the z direction

Apply a bias magnetic field B _z0 and a gradient magnetic field B _{z gradient} on the z axis perpendicular to the direction of the detection laser, the magnetic field gradient is dB _{z gradient} /dx=k, then the total gradient magnetic field is B _z (x) = B _z0 + B _{z gradient} (x). Under such a gradient, the electron spin precession frequency distributed in the x direction is ω _spin (x)=γ _e (B _z0 +kx)/q.

Step 2: Measure the transmitted light intensity of the probe light

In the process of measuring the optical rotation angle by the balanced difference method, the output signal is proportional to the optical rotation angle and the transmitted light intensity. In order to ensure that the optical rotation angles at different measurement positions are comparable, the transmitted light intensity of the probe light is measured first, and the output signal is normalized in the later stage.

Step 3: Apply an oscillating magnetic field in the x direction to resonate with the electron spin

The applied oscillation frequency should be around γ _e B _z0 /q in order to resonate with electron spins.

Step 4: Change the intensity of the z-axis DC uniform magnetic field, so that the resonance plane of the electron spin moves from one side to the other side along the x direction of the gas cell, and the electron spin resonance point is x=(ωq/γ _e -B _z0 )/k. Record the resonance intensity of each resonance point. The resonance strength is proportional to the electron spin polarizability, which can be obtained by demodulating the output signal of the lock-in amplifier.

Step 5: Change the position of the probe light on the yoz plane, and repeat the test of the transmitted light intensity and resonance intensity

Step 6: The resonance intensity at each position is divided by the transmitted light intensity of the probe light to obtain the three-dimensional distribution of electron spin polarizability.

The lateral distribution of electron spin polarizability is differentiated using longitudinal uniform magnetic field coils and longitudinal gradient magnetic field coils. Apply an oscillating magnetic field in the x direction, and its oscillation frequency should be close to the Larmor precession frequency of electron spins. Changing the size of the longitudinal uniform magnetic field makes the electron spins at different positions away from the x-axis resonate with the oscillating magnetic field, and the amplitude of the optical rotation angle of the resonance signal is proportional to the relative polarizability of the resonance point. The three-dimensional distribution of electron spin polarizability can be reflected by measuring the resonance signals at different spatial positions.

The contents not described in detail in the description of the present invention belong to the prior art known to those skilled in the art. It is pointed out here that the above description is helpful for those skilled in the art to understand the present invention, but does not limit the protection scope of the present invention. Any equivalent replacement, modification and improvement and/or simplified implementation of the above descriptions without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims (9)

1. A method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance, characterized in that, using a longitudinal uniform magnetic field coil and a longitudinal gradient magnetic field coil to distinguish the lateral distribution of electron spin polarizability, applying Electron paramagnetic resonance occurs between the oscillating magnetic field and the electron spin, changing the size of the longitudinal uniform magnetic field, so that the electron spin at different positions from the x-axis resonates with the oscillating magnetic field, and the amplitude of the optical rotation angle of the resonance signal and the relative polarization of the resonance point The three-dimensional distribution of electron spin polarizability is reflected by measuring the resonance signals at different spatial positions. 2 . The method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to claim 1 , wherein the spatial resolution is less than 1 mm ³ . 3. the three-dimensional distribution measurement method of electron spin polarizability based on electron paramagnetic resonance according to claim 1, is characterized in that, comprises the following steps: Step 1, apply the bias magnetic field B _z0 and the gradient magnetic field B _{z gradient} in the z-axis direction perpendicular to the direction of the probe light, dB _{z gradient} /dx=k, where k is the magnetic field gradient, and the total gradient magnetic field is B _z (x)= B _z0 + B _{z gradient} (x), the electron spin precession frequency distributed in the x-axis direction, that is, the detection light direction is ω _spin (x) = γ _e (B _z0 + kx)/q, where q is the electron spin spin ensemble slowing down factor, γ _e is the gyromagnetic ratio of electron spin ensemble; Step 2, measuring the transmitted light intensity of the probe light; Step 3, applying an oscillating magnetic field in the x direction to resonate with the electron spin; Step 4, change the magnetic field strength value of B _z0 , so that the resonance plane of the electron spin moves from one side to the other side along the x direction of the alkali metal gas chamber, and the electron spin resonance point x=(ωq/γ _e -B _z0 ) /k, where ω is the frequency of the oscillating magnetic field in the x direction, and the resonance strength of each resonance point is recorded, and the resonance strength is proportional to the electron spin polarizability; Step 5, changing the position of the probe light on the yoz plane, and repeatedly testing the transmitted light intensity and resonance intensity; In step 6, the resonance intensity at each position is divided by the transmitted light intensity of the probe light to obtain the three-dimensional distribution of electron spin polarizability. 4. The method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to claim 3, wherein the bias magnetic field in the step 1 is a DC uniform magnetic field. 5. The method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to claim 3, characterized in that, in the step 2, the output signal It is proportional to the optical rotation angle or the transmitted light intensity. In order to ensure the comparability of the optical rotation angle at different measurement positions, the transmitted light intensity of the probe light is measured first, and the output signal is normalized in the later stage. 6. The method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to claim 3, characterized in that, in the step 3, the oscillation frequency of the applied oscillating magnetic field is near γ _e B _z0 /q, in order to resonate with electron spins. 7. The method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to claim 3, wherein the resonance strength in the step 4 is obtained by demodulating the output signal of a lock-in amplifier. 8. The method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to claim 3, wherein said step 2 includes extracting electron spin ensemble polarizability x-axis by the following formula Component information <P _x >:

Where <S _x > represents the optical rotation angle signal detected by the probe light, I is the transmitted light intensity, a is a constant proportional coefficient, and l is the width of the inner space of the alkali metal gas chamber on the x-axis. 9. The method for measuring the three-dimensional distribution of electron spin polarizability based on electron paramagnetic resonance according to claim 3, wherein the measuring device of the transmitted light intensity comprises a polarization beamsplitter prism, and the input of the polarization beamsplitter prism The side is connected to the transmitted light passing through the alkali metal gas chamber, the reflection side of the polarization beam splitter is connected to the negative input end of the differential amplifier through the first photodetector, and the transmission side of the polarization beam splitter is connected to the positive input end of the differential amplifier , the output terminal of the differential amplifier is connected to the data acquisition system.

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