An optically pumped atomic magnetometer device for deep space weak magnetic and zero magnetic detection

Abstract

The present application provides an optically pumped atomic magnetometer device for deep space weak magnetic and zero magnetic detection, which includes a magnetometer probe and an electronics box, and uses internal modulation or external modulation to achieve laser constant power control. The internal modulation scheme is: the circuit realizes laser constant power control by synchronously controlling the laser drive temperature and current. The external modulation scheme is: adding an optical power control device such as an acousto-optic modulator or an electrically adjustable attenuator at the output end of the laser to perform closed-loop control of the laser power. The optically pumped magnetometer with stable optical power adopts low-frequency modulation and narrow-linewidth Mz magnetic resonance methods, and can accurately measure weak magnetic field scalars equivalent to the Mz resonance line width from the earth's magnetic field intensity to the Mz resonance line width for a long time. By adding a small compensation magnetic field to the magnetometer probe and its modulation solution scheme, near-zero magnetic field intensity detection can also be achieved. It is suitable for deep space weak magnetic field environment detection such as the earth's high orbit, the moon, Mars, asteroids, various satellites, and interplanetary space, and can also be applied to medical and basic scientific research.

Description

Technical Field

[0001] The present application belongs to the field of magnetic field detection and control, and specifically relates to an optically pumped atomic magnetometer device for deep space weak magnetic and zero magnetic detection. Background Art

[0002] In deep space exploration missions, magnetic field detection devices and technologies have important applications, among which the ability to accurately detect zero and weak fields is of great significance. For example, the magnetic field on Mercury is around 300nT, the magnetic field on Venus is mostly less than 50nT, the magnetic field on the moon is in the order of 100nT, the magnetic field on Mars is generally less than 10nT, the magnetic field in the heliosphere is less than 10nT, and the magnetic field between the stars is sometimes close to zero field. In order to achieve the goals of deep space exploration missions and maximize the value of the payload, this requires that the magnetic field detection device be accurate, stable, have a large measurement range, and be able to measure zero and weak fields.

[0003] Fluxgate magnetometers have been used in previous deep space exploration missions. In 2011, Juno carried a fluxgate magnetometer with a magnetic field measurement range from ±1600nT to ±160000nT. However, the fluxgate has various drift problems, which limits its measurement accuracy.

[0004] Atomic magnetometers have been widely used because they have the inherent physical properties of atoms and the ability to accurately measure magnetic fields over a long period of time. In terms of weak field measurements, the CPT magnetometer carried by the European ESA's JUICE Jupiter exploration mission has an accuracy of 0.2nT in the range of 300nT to 1200nT. Optically pumped atomic magnetometers (OPAMs) are an important type of atomic magnetometer. Their advantages are simple structure, high sensitivity, and a long history of application. However, in actual use, OPAMs are extremely sensitive to changes in the wavelength and power of lasers. Changes in these factors will make the results of magnetic field measurements no longer accurate. In addition, optically pumped atomic magnetometers are rarely used in the field of deep space weak field measurements. At present, there is no mature technology in China to accurately measure deep space weak fields using optically pumped atomic magnetometers. Summary of the invention

[0005] The purpose of this application is to improve the accuracy of OPAM magnetic field measurement results.

[0006] In order to achieve the above-mentioned purpose, the present application proposes an optically pumped atomic magnetometer device for deep space weak magnetic and zero magnetic detection, including a magnetometer probe and an electronics box;

[0007] The magnetometer probe comprises:

[0008] The front optical path is located at the input end of the magnetometer probe, receives the laser signal from the laser, and provides a stable light source for the atomic gas chamber;

[0009] The atomic gas chamber receives the laser signal from the front circuit, and the laser signal is transmitted to the photoelectric detector behind the atomic gas chamber after a series of effects;

[0010] Photoelectric detector, used to convert optical signals into electrical signals and transmit them to the electronics box;

[0011] A heating / temperature measuring component, used to cooperate with the electronics box to heat the atomic gas chamber and stabilize it to a set temperature; and

[0012] The modulation coil is located around the atomic gas chamber and is used to generate the magnetic resonance modulation magnetic field required by the magnetometer;

[0013] The magnetometer probe also includes:

[0014] A compensation coil, located outside the atomic chamber, is used to generate a compensation magnetic field;

[0015] The electronic learning box comprises:

[0016] The gas chamber temperature control circuit is used to transmit signals to the heating / temperature measuring components in the magnetometer probe to heat the atomic gas chamber and stabilize it at a set temperature;

[0017] An IV conversion circuit is used to convert the output signal of the photodetector in the magnetometer probe into a voltage signal and output it to the signal conditioning circuit;

[0018] A signal conditioning circuit, used for dividing the voltage signal into two AC signals and inputting the signals into the first loop and the second loop respectively;

[0019] In the first loop, the AC signal is demodulated into an Mz resonance signal through a first phase-locked amplifier circuit, and then locked at the zero point of the Mz resonance signal through a first closed-loop controller;

[0020] The first signal source has two outputs, one output is output as a reference source to the first phase-locked amplifier circuit to demodulate the Mz resonance signal; the other output and the output signal of the first closed-loop controller are added by the first adder, and then the added signal is frequency modulated by the DDS output to generate two signals, one signal is output to the modulation current source, and the modulation current source controls the modulation coil to generate a modulation field; the other signal of the DDS output is output to the magnetic field solver, when the measured magnetic field strength solved by the magnetic field solver is less than the set magnetic field strength, the magnetic field solver outputs a signal to the bias controller, and the bias controller controls the bias current source to output current to the compensation coil to generate a compensation magnetic field;

[0021] In the second loop, the AC signal enters the second phase-locked amplifier circuit and is then output to the second closed-loop controller and the third closed-loop controller respectively; the third closed-loop controller generates a temperature control signal for the laser, and the laser temperature controller controls the laser temperature; the signal output by the second closed-loop controller and the signal of the second signal source are added by the second adder to generate a current control signal for the laser, and the laser current is controlled by the laser current source;

[0022] The second signal source has two outputs, one output is output as a reference source to the second phase-locked amplifier, and the other output is output to the second adder.

[0023] As an improvement of the above device, when measuring a weak magnetic field, the reference signal output by the first information source to the first phase-locked amplifier circuit is a low-frequency signal, the frequency of which is lower than the Mz magnetic resonance line width;

[0024] When measuring a large magnetic field, the reference signal output by the first information source to the first phase-locked amplifier circuit is a high-frequency signal.

[0025] As an improvement of the above device, the set magnetic field strength is the magnetic field strength B corresponding to the resonance line width Ω. w :

[0026] B w =Ω / γ

[0027] Here, γ is the atomic gyromagnetic ratio.

[0028] As an improvement of the above device, the compensation magnetic field strength generated by the compensation coil is 2B w .

[0029] As an improvement of the above device, when using a compensation coil, first add a magnetic field along the laser direction, and the magnetometer measures the magnetic field Y1. Then add a magnetic field in the opposite direction, and the magnetometer measures the magnetic field Y2. The actual magnetic field is:

[0030]

[0031] As an improvement of the above device, the electronic box further comprises: a modulation circuit;

[0032] The signal conditioning circuit separates a voltage signal into a DC signal, which passes through a modulation circuit to stabilize the laser power.

[0033] As an improvement of the above device, the modulation circuit includes an internal modulation circuit and / or an external modulation circuit;

[0034] The internal modulation circuit comprises: a fourth closed-loop controller;

[0035] The DC signal controls the laser current source through a fourth closed-loop controller to stabilize the laser power;

[0036] The external modulation circuit includes: a fifth closed-loop controller and an acousto-optic modulator / electrically adjustable attenuator;

[0037] The DC signal controls the acousto-optic modulator / electrically adjustable attenuator through a fifth closed-loop controller to stabilize the laser power.

[0038] As an improvement of the above device, a double beam of left-handed circularly polarized light and right-handed circularly polarized light enters the atomic gas chamber, which is used to reduce the probe steering error of the magnetometer.

[0039] Compared with the prior art, the advantages of this application are:

[0040] 1. Compared with the traditional optically pumped atomic magnetometer which is mostly used to measure large magnetic fields, this device can be applied to a variety of measurement scenarios, not only to measure large fields, but also to measure near-zero fields and weak fields. When measuring near-zero fields and weak fields, the detection limit of the Mz magnetometer is reduced to about 50nT, and it can measure about 0nT when adding a compensation field.

[0041] 2. Compared with the traditional optically pumped atomic magnetometer, this device adds an internally modulated or externally modulated laser power stabilization link, and uses a double beam to reduce the steering difference, further improving the accuracy.

[0042] 3. The experimental system designed based on the principle of Mz atomic magnetometer has a simple and reliable system structure, which can more easily meet the reliability and life requirements of space payloads. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The figure shows the schematic diagram of the structure of the optically pumped atomic magnetometer device for deep space weak magnetic and zero magnetic detection;

[0044] Figure 2 Shown is a schematic diagram of a weak field measurement embodiment (compensation circuit omitted);

[0045] Figure 3 Shown is a schematic diagram of the Mz resonance signal;

[0046] Figure 4 Shown is a diagram of the magnetic field measurement linearity result in Example 2;

[0047] Figure 5 Shown is a diagram of the magnetic field measurement stability result in Example 2;

[0048] Figure 6 FIG. 1 is a schematic diagram of an internal modulation system in Example 3 (the compensation circuit is omitted);

[0049] Figure 7FIG. 1 is a schematic diagram of an external modulation system in Example 3 (with the compensation circuit omitted);

[0050] Figure 8 Shown is a schematic diagram of magnetic field solution. DETAILED DESCRIPTION

[0051] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0052] Example 1

[0053] like Figure 1 As shown, the present application provides an optically pumped atomic magnetometer device for deep space weak magnetic and zero magnetic detection, which can measure not only large fields but also near zero fields and weak fields. The device includes: a magnetometer probe, an optical fiber and an electronics box.

[0054] The magnetometer probe is used to receive laser signals, sense magnetic fields, and output magnetic field information to the electronics box in the form of electrical signals. It includes: front optical path, atomic gas chamber, photoelectric detector, heating and temperature measurement components, modulation coil and compensation coil.

[0055] The front optical path, located at the input end of the magnetometer probe, receives the laser signal from the optical fiber and provides a stable light source for the atomic gas chamber.

[0056] The atomic gas chamber receives the laser signal from the front circuit, and the laser signal is transmitted to the photodetector behind the atomic gas chamber after a series of effects. The double beams of left-handed circularly polarized light and right-handed circularly polarized light enter the atomic gas chamber to reduce the probe steering error of the Mz magnetometer.

[0057] Photoelectric detector converts light signals into electrical signals and transmits them to the electronics box outside the probe.

[0058] The heating / temperature measuring component cooperates with the gas and room temperature control circuit in the electronics box to heat the atomic gas chamber and stabilize it to the set temperature.

[0059] The modulation coil is located around the atomic gas chamber and is used to generate the magnetic resonance modulation magnetic field required by the Mz magnetometer to achieve weak magnetic field scalar measurement.

[0060] The above-mentioned front optical path, atomic gas chamber, photoelectric detector, heating / temperature measurement component and modulation coil are all components of existing mature magnetometer probes.

[0061] The compensation coil is located outside the atomic chamber and can generate a compensation magnetic field to extend the range of the magnetometer to near zero field. When the magnetic field to be measured is smaller than the magnetic field B corresponding to the resonance line width Ω w When using compensation coil to generate 2B w The compensation magnetic field is less than B w To zero magnetic field detection.

[0062] The main functions of the electronics box are: regulating the corresponding devices; processing the electrical signal containing magnetic field information from the magnetometer probe, feeding it back to other parts to complete the system closed loop, and finally obtaining the magnetic field strength information. It includes: air and room temperature control circuit, bias current source, IV conversion circuit, signal conditioning circuit, phase-locked amplifier circuit, closed-loop controller, signal source, magnetic field solver, bias controller, laser, acousto-optic modulator and electrically adjustable attenuator, etc.

[0063] The gas and air temperature control circuit is used to transmit signals to the heating / temperature measuring components in the magnetometer probe to heat the atomic gas chamber and stabilize it at a set temperature.

[0064] The IV conversion circuit is used to convert the output signal of the photodetector in the magnetometer probe into a voltage signal and output it to the signal conditioning circuit.

[0065] The signal conditioning circuit is used to divide the voltage signal into a DC signal and an AC signal and input them into different loops respectively. The AC signal enters two loops respectively: one AC signal is demodulated into an Mz resonance signal by the first phase-locked amplifier circuit, and locked at the zero point of the Mz resonance signal by the first closed-loop controller. One output of the first signal source is passed as a reference source to the first phase-locked amplifier circuit to demodulate the Mz resonance signal, and the other output and the output signal of the first closed-loop controller are added by the first adder. The DDS output (the waveform output generated by the Direct Digital Synthesis technology) performs frequency modulation on the added signal and then outputs it to the modulation current source. The modulation current source controls the modulation coil to generate a modulation field. The DDS outputs another signal to the magnetic field solver. When the solved magnetic field strength to be measured is less than B w When , the bias controller controls the bias current source to output current to the compensation coil to generate a compensation magnetic field.

[0066] Another AC signal enters the second phase-locked amplifier circuit, passes through the second closed-loop controller and the third closed-loop controller respectively, generates signals for controlling the current and temperature of the laser, and realizes laser wavelength locking. One output of the second signal source is passed to the second phase-locked amplifier as a reference source, and the other output is added to the output signal of the second closed-loop controller to modulate the laser current. The internal and external modulation modes are selected by the switch T / F: in the internal modulation mode, the DC signal stabilizes the laser power through the fourth closed-loop controller. In the external modulation mode, the DC signal controls the acousto-optic modulator / electrically adjustable attenuator through the fifth closed-loop controller, thereby stabilizing the laser power.

[0067] In the above device, when measuring a large magnetic field, the reference signal sent by the first information source to the first phase-locked amplifier circuit is a high-frequency signal, such as the geomagnetic magnitude, and the magnetic field measurement range of the device is not limited to a small field. When measuring a weak magnetic field, the reference signal sent by the first information source to the first phase-locked amplifier circuit is a low-frequency signal, and the frequency is lower than the Mz magnetic resonance line width.

[0068] In the above device, the compensation coil can be added selectively. When measuring near-zero field, the compensation coil is used to generate a compensation magnetic field. When measuring weak field, the compensation coil may not be used. When adding the compensation coil, a magnetic field B can be added along the Z-axis direction. offset , the magnetometer measures the magnetic field Y1, and then adds the magnetic field B in reverse offset , the magnetometer measures the magnetic field Y2, then the actual magnetic field is:

[0069]

[0070] The coordinate system in this application takes the center of the atomic gas chamber as the origin, the Z axis is the laser direction (the same as the central axis direction of the atomic gas chamber, for example, if the atomic gas chamber is a cylinder, the Z axis direction is the line connecting the centers of the two circular bottom edges), the Y axis is the vertical direction, and the X axis is the horizontal direction.

[0071] In the above device, internal modulation and external modulation are used to stabilize the laser power. When the switch points to T, the internal modulation mode is used: the laser power is stabilized by controlling the laser temperature and current. When the power changes, the laser current is slowly adjusted to stabilize the laser power, and the wavelength fluctuation caused by the temperature compensation current change is locked by temperature. When the switch points to F, the external modulation mode is used: the laser power is stabilized by controlling the acousto-optic modulator / electrically adjustable attenuator added after the laser. The temperature control in the external modulation scheme can also choose not to use closed-loop control, but to select a fixed temperature.

[0072] In the above device, the bias controller determines whether a compensation magnetic field needs to be added according to the DDS output. Figure 1 As shown, if the magnetic field strength calculated according to the DDS output frequency is less than the magnetic field strength corresponding to the resonance line width Ω, the magnetic field solver transmits a signal to the bias controller, and the bias controller controls the bias current source to generate a compensation magnetic field B offset , where B offset =2B w , B w is the magnetic field strength corresponding to the resonance line width, B w =Ω / γ, where γ is the atomic gyromagnetic ratio, rubidium atom γ=7Hz / nT, cesium atom γ=3.5Hz / nT, helium atom γ=28Hz / nT.

[0073] The specific application method and magnetic field solution method are as follows Figure 8 As shown: Figure 8 In the XYZ rectangular coordinate system shown, the magnetic field to be measured The components of the three axes XYZ are Add a bias field in the Z axis Then the scalar magnetic field value Y1 measured by the magnetometer is:

[0074]

[0075] Rapidly reverse the bias field, and the scalar magnetic field value Y2 measured by the magnetometer is:

[0076]

[0077] From the above two formulas, we can get:

[0078]

[0079] Magnetic field strength to be measured B 2 for:

[0080]

[0081] Therefore, according to Y1, Y2, The value of can be used to obtain the total magnetic field strength B to be measured:

[0082]

[0083] If the DDS output frequency is greater than the resonance linewidth Ω, there is no need to generate a compensation magnetic field and weak field measurement can be performed directly.

[0084] Example 2

[0085] like Figure 2 As shown, the optically pumped magnetometer device of this embodiment does not adopt internal and external modulation and has no laser power stabilization measures, that is, relative to Example 1, it does not include the fourth closed-loop controller, the fifth closed-loop controller and the acousto-optic modulator / electrically adjustable attenuator.

[0086] Use Figure 2 The Mz magnetometer system shown in the figure, the magnetometer probe is placed in the shielding tube, the air chamber heating circuit is turned on, and the air chamber temperature is heated to the target temperature. The VCSEL laser (Vertical-Cavity Surface-Emitting Laser) is turned on, the frequency is scanned, and the wavelength is locked. A test field B is applied along the laser direction. test . Turn on the other instrument switches, and the first signal source uses a frequency less than half of the resonance line width, for example, 200Hz for a line width of 400Hz. The lock-in amplifier obtains the resonance signal, such as Figure 3 The closed-loop controller is locked at zero to achieve frequency tracking.

[0087] The linearity of the magnetometer was tested in the weak field range, and the minimum magnetic field was close to the magnetic field B corresponding to the Mz resonance line width. w , so that B test The range ranges from 50nT to 1500nT, which can cover most of the weak field requirements of deep space exploration. The magnetic field measured by the magnetometer is recorded and fitted to obtain the linearity of the magnetometer, such as Figure 4 As shown: The test results show that the magnetometer has good linearity and the residual error is less than 0.1nT.

[0088] Keep generating test field B test The current on the coil is constant, and the magnetic field measurement value is recorded within 7 hours. The result after data processing and filtering is as follows Figure 5 As shown: the magnetic field change level is less than 0.1nT and the system stability is good.

[0089] Example 3

[0090] Figure 6 and Figure 7 Shown is a schematic structural diagram of Example 3.

[0091] Internal modulation: using Figure 6 The device shown performs internal modulation on the laser power. The second signal source modulates the laser current. The change of the laser current will change the laser power and wavelength, and the change of temperature will change the wavelength. The AC signal of the electronics box outputs an error signal through the second phase-locked amplifier circuit to perform closed-loop control on the temperature to achieve laser wavelength locking. When the laser power changes, the laser current is slowly adjusted by the fourth closed-loop controller to stabilize the laser power, and the wavelength change caused by the temperature compensation current is quickly adjusted, so that the power of the laser output is stabilized.

[0092] External modulation: using Figure 7 The device shown performs external modulation on the laser power. The input end of the acousto-optic modulator / electrically adjustable attenuator is connected to the output end of the laser through an optical fiber, and its output is connected to the input of the magnetometer probe through an optical fiber. The acousto-optic modulator / electrically adjustable attenuator is adjusted through the fifth closed-loop controller using the DC signal of the signal conditioning circuit to keep the laser output power constant.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application is described in detail with reference to the embodiments, a person skilled in the art should understand that any modification or equivalent replacement of the technical solution of the present application does not depart from the spirit and scope of the technical solution of the present application and should be included in the scope of the claims of the present application.

Claims

1. An optically pumped atomic magnetometer device for deep space weak magnetic and zero magnetic detection, including a magnetometer probe and an electronics box; The magnetometer probe comprises: The front optical path is located at the input end of the magnetometer probe, receives the laser signal from the laser, and provides a stable light source for the atomic gas chamber; The atomic gas chamber receives the laser signal from the front circuit, and the laser signal is transmitted to the photoelectric detector behind the atomic gas chamber after a series of effects; Photoelectric detector, used to convert optical signals into electrical signals and transmit them to the electronics box; Heating / temperature measuring components, used to cooperate with the electronics box to heat the atomic gas chamber and stabilize it to the set temperature; and a modulation coil, located around the atomic gas chamber, for generating the magnetic resonance modulation magnetic field required for the magnetometer; It is characterized in that The magnetometer probe also includes: A compensation coil, located outside the atomic chamber, is used to generate a compensation magnetic field; The electronic learning box comprises: The gas chamber temperature control circuit is used to transmit signals to the heating / temperature measuring components in the magnetometer probe to heat the atomic gas chamber and stabilize it at a set temperature; An IV conversion circuit is used to convert the output signal of the photodetector in the magnetometer probe into a voltage signal and output it to the signal conditioning circuit; A signal conditioning circuit, used for dividing the voltage signal into two AC signals and inputting the signals into the first loop and the second loop respectively; In the first loop, the AC signal is demodulated into an Mz resonance signal through a first phase-locked amplifier circuit, and then locked at the zero point of the Mz resonance signal through a first closed-loop controller; The first signal source has two outputs, one output is output as a reference source to the first phase-locked amplifier circuit to demodulate the Mz resonance signal; the other output and the output signal of the first closed-loop controller are added by the first adder, and then the added signal is frequency modulated by the DDS output to generate two signals, one signal is output to the modulation current source, and the modulation current source controls the modulation coil to generate a modulation field; the other signal of the DDS output is output to the magnetic field solver, when the measured magnetic field strength solved by the magnetic field solver is less than the set magnetic field strength, the magnetic field solver outputs a signal to the bias controller, and the bias controller controls the bias current source to output current to the compensation coil to generate a compensation magnetic field; In the second loop, the AC signal enters the second phase-locked amplifier circuit and is then output to the second closed-loop controller and the third closed-loop controller respectively; the third closed-loop controller generates a temperature control signal for the laser, and the laser temperature controller controls the laser temperature; the signal output by the second closed-loop controller and the signal of the second signal source are added by the second adder to generate a current control signal for the laser, and the laser current is controlled by the laser current source; The second signal source has two outputs, one output is output as a reference source to the second phase-locked amplifier, and the other output is output to the second adder.

2. The optically pumped atomic magnetometer device for deep space weak magnetic field and zero magnetic field detection according to claim 1 is characterized in that: When measuring a weak magnetic field, the reference signal output by the first signal source to the first phase-locked amplifier circuit is a low-frequency signal, the frequency of which is lower than the Mz magnetic resonance line width; When measuring a large magnetic field, the reference signal output by the first information source to the first phase-locked amplifier circuit is a high-frequency signal.

3. The optically pumped atomic magnetometer device for deep space weak magnetic field and zero magnetic field detection according to claim 1 is characterized in that: The set magnetic field strength is the magnetic field strength B corresponding to the resonance line width Ω w : B w =Ω / g Here, γ is the atomic gyromagnetic ratio.

4. The optically pumped atomic magnetometer device for deep space weak magnetic field and zero magnetic field detection according to claim 3 is characterized in that: The compensation magnetic field strength generated by the compensation coil is 2B w .

5. The optically pumped atomic magnetometer device for deep space weak magnetic field and zero magnetic field detection according to claim 4 is characterized in that: When using a compensation coil, first add a magnetic field along the laser direction, and the magnetometer measures the magnetic field Y1. Then add a magnetic field in the opposite direction, and the magnetometer measures the magnetic field Y2. The actual magnetic field is:

6. The optically pumped atomic magnetometer device for deep space weak magnetic field and zero magnetic field detection according to claim 1 is characterized in that: The electronic box also includes: a modulation circuit; The signal conditioning circuit separates a DC signal from the voltage signal and passes through a modulation circuit to stabilize the laser power.

7. The optically pumped atomic magnetometer device for deep space weak magnetic field and zero magnetic field detection according to claim 6 is characterized in that: The modulation circuit includes an internal modulation circuit and / or an external modulation circuit; The internal modulation circuit comprises: a fourth closed-loop controller; The DC signal controls the laser current source through a fourth closed-loop controller to stabilize the laser power; The external modulation circuit includes: a fifth closed-loop controller and an acousto-optic modulator / electrically adjustable attenuator; The DC signal controls the acousto-optic modulator / electrically adjustable attenuator through a fifth closed-loop controller to stabilize the laser power.

8. The optically pumped atomic magnetometer device for deep space weak magnetic field and zero magnetic field detection according to claim 1 is characterized in that: What enters the atomic gas chamber is a double beam of left-handed circularly polarized light and right-handed circularly polarized light, which is used to reduce the probe steering error of the magnetometer.

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