Optical pump magnetometer and magnetic field measurement method
By generating two circularly polarized beams of equal intensity using a liquid crystal polarization grating, and combining them with laser and atomic sensing modules, the accuracy and sensitivity of the optically pumped magnetometer are improved, solving the problems of large size, high cost, and high difficulty of traditional optically pumped magnetometers.
Patent Information
- Application Number
- CN202511758847.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-02-06
AI Technical Summary
Traditional optically pumped magnetometers are susceptible to nonlinear Zeeman effects under single circularly polarized optical pumping, resulting in asymmetrical magnetic resonance signals, inconsistent measurement results, and large component size, high cost, and high implementation difficulty.
Two beams of right-handed and left-handed circularly polarized light with equal intensity are generated using a liquid crystal polarization grating. Combined with a laser emission and control module and an atomic sensing and signal detection module, symmetrical magnetic resonance signal detection is achieved.
The component size and cost of the optically pumped magnetometer were reduced, the implementation difficulty was simplified, the measurement accuracy and sensitivity were improved, and the problem of misalignment was solved.
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Figure CN121477072A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of quantum sensing and precision measurement instrument technology, and in particular to an optically pumped magnetometer and a magnetic field measurement method. Background Technology
[0002] Optically pumped magnetometers, as a type of highly sensitive quantum magnetic sensor, operate based on the Zeeman splitting of atomic energy levels and the optical pumping effect. Traditional optically pumped magnetometers face a challenge: when pumped by a single circularly polarized light, the nonlinear Zeeman effect in geomagnetic environments causes asymmetry in the magnetic resonance signal, resulting in a significant rotational error. This means that after rotating the probe 180°, the measurement results for the same magnetic field are inconsistent, severely affecting measurement accuracy and application on moving platforms.
[0003] Existing technologies include using calcite crystals combined with waveplate components to generate two beams of left-handed and right-handed circularly polarized light with equal intensity, and using multiple devices such as PBS polarization beam splitters, mirrors, and λ / 4 waveplates to generate two beams of left-handed and right-handed circularly polarized light with equal intensity. However, these technologies suffer from problems such as large component size, high cost, and high implementation difficulty.
[0004] Therefore, no effective solution has yet been proposed to address the problems of large component size, high cost, and high implementation difficulty in existing technologies. Summary of the Invention
[0005] This application provides an optically pumped magnetometer and a magnetic field measurement method, which solves the problems of large component size, high cost, and high implementation difficulty in the prior art.
[0006] Firstly, this embodiment provides an optically pumped magnetometer, including a laser emission and control module, a polarization beam splitting and sampling module, and an atomic sensing and signal detection module, wherein:
[0007] The laser emission and modulation module is used to generate pump lasers of a specific wavelength and modulate the pump lasers to output linearly polarized light with adjustable intensity.
[0008] The polarization beam splitting and sampling module includes a liquid crystal polarization grating, which is used to diffract the linearly polarized light into right-hand circularly polarized light and left-hand circularly polarized light, wherein the intensity of the right-hand circularly polarized light and the intensity of the left-hand circularly polarized light are equal.
[0009] The atomic sensing and signal detection module is used to obtain symmetrical magnetic resonance signals using the right-hand circularly polarized light and the left-hand circularly polarized light.
[0010] In some embodiments, the laser emission and control module includes a laser, a liquid crystal variable phase delay unit, and an analyzer, wherein the laser is used to generate the pump laser, the liquid crystal variable phase delay unit is used to modulate the pump laser, and the analyzer is used to output the linearly polarized light.
[0011] In some embodiments, the atomic sensing and signal detection module includes an atomic gas cell, a Helmholtz coil, and a lock-in amplifier, wherein the Helmholtz coil is wound around the outside of the atomic gas cell to generate a radio frequency magnetic field, and the lock-in amplifier is used to extract the magnetic resonance signal generated after the right-hand circularly polarized light and the left-hand circularly polarized light pass through the atomic gas cell.
[0012] In some embodiments, the wavelength of the pump laser resonates with the absorption transition lines of alkali metal atoms inside the atomic chamber.
[0013] In some embodiments, the atomic sensing and signal detection module further includes a heating component and a temperature controller; wherein the heating component is used to heat the atomic gas chamber, and the temperature controller is used to control the temperature of the atomic gas chamber.
[0014] In some embodiments, the liquid crystal polarization grating is also used to diffract the linearly polarized light into 0th-order diffracted light, wherein the linear polarization state of the 0th-order diffracted light is the same as the linear polarization state of the linearly polarized light.
[0015] In some embodiments, the optically pumped magnetometer further includes an optical power stabilization control module; the optical power stabilization control module includes a controller, a voltage driver, a liquid crystal variable phase delay unit, and an analyzer, wherein the controller is used to generate a control signal for a driving voltage based on the 0th order diffracted light, the voltage driver is used to generate a corresponding driving voltage based on the control signal, the liquid crystal variable phase delay unit is used to modulate the pump laser according to the driving voltage to obtain modulated polarized light, and the analyzer is used to convert the modulated polarized light into intensity-adjustable linearly polarized light.
[0016] Secondly, this embodiment provides a method for measuring the magnetic field of an optically pumped magnetometer, used in the optically pumped magnetometer described in the first aspect above, the method comprising:
[0017] The laser emission and modulation module generates a pump laser of a specific wavelength and modulates the pump laser to output linearly polarized light with adjustable intensity.
[0018] The polarization beam splitting and sampling module diffracts the linearly polarized light into right-hand circularly polarized light and left-hand circularly polarized light, wherein the intensity of the right-hand circularly polarized light and the intensity of the left-hand circularly polarized light are equal.
[0019] The atomic sensing and signal detection module uses the right-hand circularly polarized light and the left-hand circularly polarized light to obtain a symmetrical magnetic resonance signal.
[0020] In some embodiments, the optically pumped magnetometer further includes an optical power stabilization control module; the method further includes:
[0021] The optical power stabilization control module modulates the pump laser based on the 0th order diffracted light emitted by the linearly polarized light, so that the power of the linearly polarized light is stabilized at a preset value.
[0022] Thirdly, this embodiment provides an airborne magnetic measurement device, including the optically pumped magnetometer described in the first aspect above.
[0023] Compared with related technologies, this embodiment provides an optically pumped magnetometer and a magnetic field measurement method. The optically pumped magnetometer includes a laser emission and modulation module, a polarization beam splitting and sampling module, and an atomic sensing and signal detection module. The laser emission and modulation module generates a pump laser of a specific wavelength and modulates the pump laser to output linearly polarized light with adjustable intensity. The polarization beam splitting and sampling module includes a liquid crystal polarization grating, which diffracts the linearly polarized light into right-handed and left-handed circularly polarized light, wherein the intensity of the right-handed and left-handed circularly polarized light is equal. The atomic sensing and signal detection module uses the right-handed and left-handed circularly polarized light to obtain a symmetrical magnetic resonance signal. By using a liquid crystal polarization grating to generate two beams of circularly polarized light with equal intensity and opposite polarization, the problem of directional error in the optically pumped magnetometer is solved, reducing the size and cost of the components and simplifying implementation.
[0024] Details of one or more embodiments of this application are set forth in the following drawings and description to make other features, objects and advantages of this application more readily apparent. Attached Figure Description
[0025] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:
[0026] Figure 1 This is a schematic diagram of the structure of the optically pumped magnetometer according to an embodiment of this application;
[0027] Figure 2 This is a schematic diagram of the liquid crystal polarization grating structure and polarization diffraction behavior according to an embodiment of this application;
[0028] Figure 3 This is a schematic diagram of the liquid crystal polarization grating structure and polarization diffraction behavior according to an embodiment of this application;
[0029] Figure 4 This is a flowchart of the magnetic field measurement method of the optically pumped magnetometer according to an embodiment of this application. Detailed Implementation
[0030] To better understand the purpose, technical solution, and advantages of this application, the application is described and illustrated below in conjunction with the accompanying drawings and embodiments.
[0031] Unless otherwise defined, the technical or scientific terms used in this application shall have the general meaning understood by one of ordinary skill in the art to which this application pertains. Words such as “a,” “an,” “an,” “the,” “the,” and “these” used in this application do not indicate quantitative limitation and may be singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that comprises a series of steps or modules (units) is not limited to the listed steps or modules (units) but may include steps or modules (units) not listed, or may include other steps or modules (units) inherent to these processes, methods, products, or devices. Words such as “connected,” “linked,” and “coupled” used in this application are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect. “Multiple” used in this application refers to two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can represent: A alone, A and B simultaneously, and B alone. Normally, the character " / " indicates that the objects before and after it are in an "or" relationship. The terms "first," "second," "third," etc., used in this application are merely to distinguish similar objects and do not represent a specific order of objects.
[0032] Figure 1 A schematic diagram of the structure of an optically pumped magnetometer in one embodiment provided in this application. Figure 1 As shown, this optically pumped magnetometer includes a laser emission and control module 10, a polarization beam splitting and sampling module 20, and an atomic sensing and signal detection module 30, wherein:
[0033] The laser emission and modulation module 10 is used to generate a pump laser of a specific wavelength and modulate the pump laser to output linearly polarized light with adjustable intensity; the polarization beam splitting and sampling module 20 includes a liquid crystal polarization grating 201, which is used to diffract the linearly polarized light into right-hand circularly polarized light and left-hand circularly polarized light, wherein the intensity of the right-hand circularly polarized light and the intensity of the left-hand circularly polarized light are equal; the atomic sensing and signal detection module 30 is used to obtain a symmetrical magnetic resonance signal using the right-hand circularly polarized light and the left-hand circularly polarized light.
[0034] Specifically, the pump laser is a laser of a specific wavelength and polarization state, used to achieve highly uniform directional alignment, i.e., polarization, of the alkali metal atoms inside the atomic gas chamber 301 of the optically pumped magnetometer. The liquid crystal polarization grating 201 is a diffractive optical element that achieves spatial modulation of the polarization state and phase of the incident light by periodically arranging the orientation of liquid crystal molecules. The liquid crystal polarization grating 201 is thin, light, and highly transparent, effectively improving the utilization rate of the light source while reducing its size. The magnetic resonance signal is the signal when the frequency of the radio frequency magnetic field at which the alkali metal atoms inside the atomic gas chamber 301 of the optically pumped magnetometer are located is equal to the Larmor precession frequency of the alkali metal atoms. This magnetic resonance signal exhibits symmetry.
[0035] Figure 2 This embodiment of the present application provides a schematic diagram of the structure and polarization diffraction behavior of a liquid crystal polarization grating 201. Each rod-shaped element represents a liquid crystal molecule whose optical axis rotates periodically in the x-direction and changes continuously by 180 degrees within one period. When incident light passes through the optical axis of the liquid crystal molecules at different rotation angles, different polarization states are generated. Therefore, this spatial structure can introduce a continuously changing geometric phase into the incident light. Under the control of this phase, the liquid crystal polarization grating 201 can not only deflect the light beam but also be sensitive to the polarization state of the incident light, thereby achieving polarization chiral splitting. Therefore, the liquid crystal polarization grating 201 can diffract the linearly polarized light 210 into right-handed circularly polarized light 220 and left-handed circularly polarized light 230, wherein the intensity of the right-handed circularly polarized light 220 is equal to the intensity of the left-handed circularly polarized light 230, and the polarization rotation direction of the right-handed circularly polarized light 220 is opposite to that of the left-handed circularly polarized light 230. The deflection angle between right-handed circularly polarized light 220° and left-handed circularly polarized light 230° The equation for a planar grating is satisfied:
[0036] ;
[0037] in, The wavelength of linearly polarized light 210. This is the period of the liquid crystal polarization grating 201. The deflection angle... This will affect the volume of the optically pumped magnetometer, which can be addressed by changing the period of the liquid crystal polarization grating 201. Adjustments will be made.
[0038] The core of this liquid crystal polarization grating 201 is a thin liquid crystal film, typically a few micrometers to tens of micrometers thick, attached to a glass or plastic substrate. This makes the liquid crystal polarization grating 201 relatively thin and flat, suitable for integration into modern devices with strict requirements on size and weight. Through optical alignment technology, the arrangement pattern of liquid crystal molecules can be precisely designed, thereby producing diffraction beams with different diffraction angles and efficiencies. Its functionality can be customized as needed, offering high flexibility. The fabrication process of this liquid crystal polarization grating 201 is simple, allowing for large-area production at a relatively low cost.
[0039] The liquid crystal polarization grating 201 can directly and conveniently convert linearly polarized light 210 with arbitrary polarization direction into two beams of left-handed circularly polarized light 230 and right-handed circularly polarized light 220 with equal intensity and opposite rotation, thus satisfying the optical pumping function. It does not require polarization direction adjustment of the incident light incident on the liquid crystal polarization grating 201, nor does it require additional polarization adjustment of the left-handed circularly polarized light 230 and right-handed circularly polarized light 220 emitted from the liquid crystal polarization grating 201. This simplifies the optical path structure, reduces the implementation difficulty, and is conducive to the miniaturization and portability of the optically pumped magnetometer.
[0040] The laser emission and modulation module 10 is used to generate a pump laser of a specific wavelength and apply an adjustable phase delay to the biorthogonal polarization components of the pump laser to obtain modulated polarized light, and then convert the modulated polarized light into linearly polarized light 210 with adjustable intensity. The polarization beam splitting and sampling module 20 includes a liquid crystal polarization grating 201, which is used to diffract the linearly polarized light 210 into right-handed circularly polarized light 220 and left-handed circularly polarized light 230, wherein the intensity of the right-handed circularly polarized light 220 is equal to the intensity of the left-handed circularly polarized light 230, and the polarization rotation direction of the right-handed circularly polarized light 220 is opposite to that of the left-handed circularly polarized light 230. The atomic sensing and signal detection module 30 is used to detect the magnetic resonance signal when the frequency of the radio frequency magnetic field of the alkali metal atoms inside the atomic gas chamber 301 of the optically pumped magnetometer is equal to the Larmor precession frequency of the alkali metal atoms. Therefore, the optically pumped magnetometer provided in this embodiment solves the problem of the rotation difference of the optically pumped magnetometer by using the liquid crystal polarization grating 201 to generate two circularly polarized lights with equal intensity and opposite rotation, thereby reducing the size and cost of the components and reducing the difficulty of implementation.
[0041] In one embodiment, the laser emission and control module 10 includes a laser 102, a liquid crystal variable phase delay 105, and an analyzer 106, wherein the laser 102 is used to generate a pump laser, the liquid crystal variable phase delay 105 is used to modulate the pump laser, and the analyzer 106 is used to output linearly polarized light 210.
[0042] Specifically, the laser 102 is a device for generating pump laser, the liquid crystal variable phase retarder 105 is a device for controlling the phase delay of light through voltage, and the analyzer 106 is a device for generating linearly polarized light 210. The laser 102 is controlled by a control box 101 to generate pump laser of a specific wavelength. The control box 101 controls the generation of pump laser of a specific wavelength by adjusting the current and temperature. The pump laser is transmitted through a polarization-maintaining fiber 103, and the polarization state of the pump laser remains unchanged during transmission. The pump laser is output by a collimator 104, which collimates the output of the pump laser. The pump laser passes through the liquid crystal variable phase retarder 105, which applies an adjustable phase delay to the biorthogonal polarization components of the pump laser under voltage drive, generating modulated polarized light. The modulated polarized light passes through the analyzer 106, which converts the modulated polarized light into linearly polarized light 210 with adjustable intensity. The transmission axis of the analyzer 106 forms a 45-degree angle with the fast axis direction of the liquid crystal variable phase delay unit 105.
[0043] In one embodiment, the atomic sensing and signal detection module 30 includes an atomic gas cell 301, a Helmholtz coil 302, and a lock-in amplifier 307. The Helmholtz coil 302 is wound around the outside of the atomic gas cell 301 to generate a radio frequency magnetic field, and the lock-in amplifier 307 is used to extract the magnetic resonance signal generated after the right-hand circularly polarized light 220 and the left-hand circularly polarized light 230 pass through the atomic gas cell 301.
[0044] Specifically, the atomic gas chamber 301 is a device for containing gaseous atoms, the Helmholtz coil 302 is a device for generating a radio frequency magnetic field, and the lock-in amplifier 307 is a device for extracting signals of a specific frequency. The atomic gas chamber 301 is filled with alkali metal atoms and a buffer gas, wherein the alkali metal atoms can be cesium, rubidium, potassium, etc., and the buffer gas can be nitrogen, neon, argon, etc. The Helmholtz coil 302 is wound around the outside of the atomic gas chamber 301. The linearly polarized light 210 output by the analyzer 106 is diffracted by the liquid crystal polarization grating 201 into right-hand circularly polarized light 220 and left-hand circularly polarized light 230. The right-hand circularly polarized light 220 and the left-hand circularly polarized light 230 pass through the atomic gas chamber 301, where the alkali metal atoms are polarized. After passing through the atomic gas chamber 301, the right-hand circularly polarized light 220 and the left-hand circularly polarized light 230 are converged by the plano-convex lens 305 and received by the first photodetector 306 and converted into a first electrical signal. The lock-in amplifier 307 extracts the first electrical signal, and the Helmholtz coil 302 generates a corresponding radio frequency magnetic field according to the first electrical signal. The input terminal of the lock-in amplifier 307 is connected to the output terminal of the first photodetector 306, and the output terminal of the lock-in amplifier 307 is connected to the Helmholtz coil 302. When the frequency of the radio frequency magnetic field is equal to the Larmor precession frequency of the alkali metal atoms inside the atomic gas chamber 301, a magnetic resonance effect occurs. After the right-hand circularly polarized light 220 and the left-hand circularly polarized light 230 pass through the atomic gas chamber 301, the light intensity after being converged by the plano-convex lens 305 is also significantly reduced. At this time, the first electrical signal is a magnetic resonance signal. The magnetic resonance signal has symmetry, and the lock-in amplifier 307 extracts the symmetrical magnetic resonance signal.
[0045] In one embodiment, the wavelength of the pump laser resonates with the absorption transition line of the alkali metal atoms inside the atomic gas chamber 301.
[0046] Specifically, the pump laser is used to make the spins of the alkali metal atoms inside the atomic gas chamber 301 highly consistent and oriented, i.e., polarized. Therefore, the wavelength of the pump laser resonates with the absorption transition line of the alkali metal atoms inside the atomic gas chamber 301.
[0047] In one embodiment, the atomic sensing and signal detection module 30 further includes a heating component 303 and a temperature controller 304; wherein the heating component 303 is used to heat the temperature of the atomic gas chamber 301, and the temperature controller 304 is used to control the temperature of the atomic gas chamber 301.
[0048] Specifically, the heating element 303 is a resistance heating element 303, and the temperature controller 304 is a digital temperature controller 304. The heating element 303 is used to heat the temperature of the atomic gas chamber 301, and the temperature controller 304 is used to control the temperature of the atomic gas chamber 301. The temperature setting of the atomic gas chamber 301 is related to the type of alkali metal atoms inside the atomic gas chamber 301, and the temperature range is 80 degrees to 130 degrees.
[0049] In one embodiment, the liquid crystal polarization grating 201 is further used to diffract the linearly polarized light 210 into 0th-order diffracted light 310, wherein the linear polarization state of the 0th-order diffracted light 310 is the same as that of the linearly polarized light 210.
[0050] Specifically, Figure 3 This is a schematic diagram of the structure and polarization diffraction behavior of a liquid crystal polarization grating 201 in one embodiment of this application. Each rod-shaped element represents a liquid crystal molecule whose optical axis rotates periodically in the x-direction and changes continuously by 180 degrees within one period. The liquid crystal polarization grating 201 can diffract the linearly polarized light 210 into 0th-order diffracted light 310. The intensity of the 0th-order diffracted light 310 is expressed as:
[0051] ;
[0052] in The wavelength of linearly polarized light 210. The thickness of the liquid crystal layer. The birefringence of the liquid crystal material is... , For unusual light refractive index, The refractive index is the ordinary light refractive index. By selecting a liquid crystal material and adjusting the thickness of the liquid crystal layer, the intensity of the 0th-order diffracted light 310 is designed to be non-zero. The intensity of this 0th-order diffracted light 310 can be controlled within 5%–10% of the intensity of the linearly polarized light 210. The linear polarization state of this 0th-order diffracted light 310 is the same as that of the linearly polarized light 210.
[0053] In one embodiment, the optically pumped magnetometer further includes an optical power stabilization control module; the optical power stabilization control module includes a controller 402, a voltage driver 403, a liquid crystal variable phase delay 105, and an analyzer 106, wherein the controller 402 is used to generate a control signal for a driving voltage based on the 0th order diffracted light 310, the voltage driver 403 is used to generate a corresponding driving voltage based on the control signal, the liquid crystal variable phase delay 105 is used to modulate the pump laser according to the driving voltage to obtain modulated polarized light, and the analyzer is used to convert the modulated polarized light into linearly polarized light with adjustable intensity.
[0054] Specifically, the controller 402 is a proportional-integral-derivative controller 402, and the voltage driver 403 is a device that generates the driving voltage. The liquid crystal variable phase delayer 105 is a phase delayer based on nematic liquid crystal, and its driving voltage is an AC square wave voltage in the range of 0-10V with a frequency of 1-10kHz. The 0th-order diffracted light 310 is converted into a second electrical signal by the second photodetector 401. The controller 402 receives the second electrical signal and compares it with a preset reference voltage. After proportional, integral, and differential operations, it generates a control signal for the driving voltage. The voltage driver 403 receives the control signal, generates a corresponding AC square wave driving voltage, and applies it to the indium tin oxide electrode of the liquid crystal variable phase delay unit 105. The liquid crystal variable phase delay unit 105 applies an adjustable phase delay to the biorthogonal polarization component of the pump laser according to the driving voltage, obtaining modulated polarized light. The analyzer 106 converts the modulated polarized light into linearly polarized light 210 with adjustable intensity, so that the power of the linearly polarized light 210 is stabilized at a preset value. The output terminal of the second photodetector 401 is connected to the input terminal of the controller 402, the output terminal of the controller 402 is connected to the input terminal of the voltage driver 403, and the output terminal of the voltage driver 403 is connected to the liquid crystal variable phase delay unit 105. The 0th-order diffracted light 310 is designed to be non-zero, and together with the liquid crystal variable phase retarder 105, it is used to stabilize the power of the linearly polarized light 210 at a preset value. This effectively reduces the impact of large laser power fluctuations and improves the measurement accuracy of the optically pumped magnetometer. A purely electronic control scheme is adopted, avoiding the use of costly acousto-optic modulators, electro-optic modulators, or precision mechanical components, thus reducing costs. Furthermore, the fast response speed of the liquid crystal variable phase retarder 105 improves the reliability of the optically pumped magnetometer.
[0055] This embodiment provides a method for measuring the magnetic field of an optically pumped magnetometer. Figure 4 This is a flowchart of the magnetic field measurement method in this embodiment, as follows: Figure 4 As shown, the process includes the following steps:
[0056] In step S410, the laser emission and control module 10 generates a pump laser of a specific wavelength and modulates the pump laser to output linearly polarized light 210 with adjustable intensity.
[0057] Specifically, the control box 101 of the laser emission and control module 10 controls the laser 102 to generate a pump laser of a specific wavelength by adjusting the current and temperature. This pump laser is transmitted through a polarization-maintaining fiber 103, and its polarization state remains unchanged during transmission. The pump laser is output by a collimator 104, which collimates the output of the pump laser. The pump laser passes through a liquid crystal variable phase delay unit 105, which, under voltage drive, applies an adjustable phase delay to the biorthogonal polarization components of the pump laser, generating modulated polarized light. This modulated polarized light then passes through an analyzer 106, which converts the modulated polarized light into linearly polarized light 210 with adjustable intensity.
[0058] In step S420, the polarization beam splitting and sampling module 20 diffracts the linearly polarized light 210 into right-handed circularly polarized light 220 and left-handed circularly polarized light 230, wherein the intensity of the right-handed circularly polarized light 220 and the intensity of the left-handed circularly polarized light 230 are equal.
[0059] Specifically, the liquid crystal polarization grating 201 of the polarization beam splitter and sampling module 20 diffracts the linearly polarized light 210 into right-hand circularly polarized light 220 and left-hand circularly polarized light 230, wherein the intensity of the right-hand circularly polarized light 220 and the intensity of the left-hand circularly polarized light 230 are equal.
[0060] In step S430, the atomic sensing and signal detection module 30 uses right-handed circularly polarized light 220 and left-handed circularly polarized light 230 to obtain a symmetrical magnetic resonance signal.
[0061] Specifically, the right-hand circularly polarized light 220 and the left-hand circularly polarized light 230 output by the polarization beam splitting and sampling module 20 pass through the atomic gas chamber 301. The alkali metal atoms inside the atomic gas chamber 301 are polarized. After passing through the atomic gas chamber 301, the right-hand circularly polarized light 220 and the left-hand circularly polarized light 230 are converged by the plano-convex lens 305 and received by the first photodetector 306 and converted into a first electrical signal. The lock-in amplifier 307 extracts the first electrical signal, and the Helmholtz coil 302 generates a corresponding radio frequency magnetic field according to the first electrical signal. The input terminal of the lock-in amplifier 307 is connected to the output terminal of the first photodetector 306, and the output terminal of the lock-in amplifier 307 is connected to the Helmholtz coil 302. When the frequency of the radio frequency magnetic field is equal to the Larmor precession frequency of the alkali metal atoms inside the atomic gas chamber 301, a magnetic resonance effect occurs. The intensity of the right-handed circularly polarized light 220 and the left-handed circularly polarized light 230, after passing through the atomic gas chamber 301 and being converged by the plano-convex lens 305, is significantly reduced. At this time, the first electrical signal is a magnetic resonance signal. This magnetic resonance signal is symmetrical. The lock-in amplifier 307 extracts this symmetrical magnetic resonance signal to obtain the frequency of the radio frequency magnetic field corresponding to the peak value of the symmetrical magnetic resonance signal. Therefore, the strength of the magnetic field to be measured can be obtained according to the formula, which is expressed as:
[0062] ;
[0063] in The strength of the magnetic field to be measured. The frequency of the radio frequency magnetic field corresponding to the peak value of this symmetrical magnetic resonance signal. It is the gyromagnetic ratio of the alkali metal atoms inside the atomic gas chamber 301.
[0064] By using two beams of right-handed circularly polarized light 220 and left-handed circularly polarized light 230 with the same intensity for symmetrical pumping, the dependence of the atomic polarization vector on the pump light direction can be effectively canceled. This makes the initial precession condition of the atomic magnetic moment no longer sensitive to the orientation of the optically pumped magnetometer relative to the Earth's magnetic field. Therefore, the measured magnetic field strength is independent of the orientation, and the orientation difference is greatly suppressed or even eliminated, ensuring the measurement accuracy and sensitivity of the optically pumped magnetometer.
[0065] Through steps S410 to S430 above, compared with related technologies, this application generates a pump laser of a specific wavelength through the laser emission and modulation module 10, and modulates the pump laser to output linearly polarized light 210 with adjustable intensity; the polarization beam splitting and sampling module 20 diffracts the linearly polarized light 210 into right-handed circularly polarized light 220 and left-handed circularly polarized light 230, wherein the intensity of the right-handed circularly polarized light 220 and the intensity of the left-handed circularly polarized light 230 are equal; the atomic sensing and signal detection module 30 uses the right-handed circularly polarized light 220 and the left-handed circularly polarized light 230 to obtain a symmetrical magnetic resonance signal. This approach can reduce the size and cost of components and the difficulty of implementation while solving the problem of directional error in optically pumped magnetometers, thereby improving the measurement accuracy of optically pumped magnetometers.
[0066] In one embodiment, the optically pumped magnetometer further includes an optical power stabilization control module; the magnetic field measurement method of the optically pumped magnetometer further includes: the optical power stabilization control module modulates the pump laser according to the 0th order diffracted light 310 diffracted by the linearly polarized light, so that the power of the linearly polarized light 210 is stabilized at a preset value.
[0067] Specifically, the 0th-order diffracted light 310 is converted into a second electrical signal by the second photodetector 401. The proportional-integral-differential controller 402 receives the second electrical signal and compares it with a preset reference voltage. After proportional, integral, and differential operations, it generates a control signal for the driving voltage. The voltage driver 403 receives the control signal, generates a corresponding AC square wave driving voltage, and applies it to the indium tin oxide electrode of the liquid crystal variable phase delay device 105. The liquid crystal variable phase delay device 105 applies an adjustable phase delay to the biorthogonally polarized components of the pump laser according to the driving voltage, so that the power of the linearly polarized light 210 is stabilized at a preset value.
[0068] This embodiment provides an airborne magnetic measurement device, which includes the optically pumped magnetometer of any of the above embodiments.
[0069] Specifically, this airborne magnetic surveying equipment is an integrated aircraft system for high-precision measurement of the Earth's magnetic field, with the optically pumped magnetometer serving as its core sensor. Airborne magnetic surveying is a geophysical exploration method that involves mounting a geomagnetic magnetometer on an aircraft to map large-scale geological areas by measuring changes in the Earth's magnetic field. The optically pumped magnetometer plays a crucial role as the magnetic induction unit, utilizing the principle of atomic energy level transitions in a magnetic field to convert weak geomagnetic field signals into electrical signals. Its extremely high sensitivity and sampling rate determine the final detection accuracy and resolution of the entire airborne magnetic surveying system.
[0070] It should be understood that the specific embodiments described herein are merely illustrative of the application and not intended to limit it. All other embodiments derived by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.
[0071] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties.
[0072] Obviously, the accompanying drawings are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar situations based on these drawings without any creative effort. Furthermore, it is understood that although the work done in this development process may be complex and lengthy, for those skilled in the art, certain design, manufacturing, or production modifications made based on the technical content disclosed in this application are merely conventional technical means and should not be considered as insufficient disclosure of this application.
[0073] The term "embodiment" in this application refers to a specific feature, structure, or characteristic described in connection with an embodiment that may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily imply the same embodiment, nor does it imply that it is mutually exclusive with or independent of other embodiments. It will be clearly or implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.
[0074] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of patent protection. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.
Claims
1. An optically pumped magnetometer, characterized in that, The laser emission and regulation module, the polarization light splitting and sampling module, the atomic sensing and signal detection module, wherein: The laser emission and regulation module is used for generating pump laser of specific wavelength, and modulating the pump laser to output linearly polarized light with adjustable intensity; The polarization light splitting and sampling module includes a liquid crystal polarization grating, which is used to diffract the linearly polarized light into right circularly polarized light and left circularly polarized light, wherein the intensity of the right circularly polarized light is equal to that of the left circularly polarized light; The atomic sensing and signal detection module is used to obtain symmetrical magnetic resonance signals by using the right circularly polarized light and the left circularly polarized light.
2. The optically pumped magnetometer of claim 1, wherein, The laser emission and regulation module includes a laser, a liquid crystal variable phase retarder, and a polarizer, wherein the laser is used to generate the pump laser, the liquid crystal variable phase retarder is used to modulate the pump laser, and the polarizer is used to output the linearly polarized light.
3. The optically pumped magnetometer of claim 1, wherein, The atomic sensing and signal detection module includes an atomic cell, a Helmholtz coil, and a lock-in amplifier, wherein the Helmholtz coil is wound outside the atomic cell to generate a radio frequency magnetic field, and the lock-in amplifier is used to extract the magnetic resonance signals generated by the right circularly polarized light and the left circularly polarized light after passing through the atomic cell.
4. The optically pumped magnetometer of claim 3, wherein, The wavelength of the pump laser resonates with the absorption transition line of alkali atoms inside the atomic cell.
5. The optically pumped magnetometer of claim 3, wherein, The atomic sensing and signal detection module further includes a heating assembly and a temperature controller, wherein the heating assembly is used to heat the temperature of the atomic cell, and the temperature controller is used to control the temperature of the atomic cell.
6. The optically pumped magnetometer of claim 1, wherein, The liquid crystal polarization grating is also used to diffract the linearly polarized light into 0-order diffracted light, wherein the linear polarization state of the 0-order diffracted light is the same as that of the linearly polarized light.
7. The optically pumped magnetometer of claim 6, wherein, The optically pumped magnetometer further includes a light power stabilization control module; the light power stabilization control module includes a controller, a voltage driver, a liquid crystal variable phase retarder, and a polarizer, wherein the controller is used to generate a control signal for driving voltage according to the 0-order diffracted light, the voltage driver is used to generate a corresponding driving voltage according to the control signal, the liquid crystal variable phase retarder is used to modulate the pump laser according to the driving voltage to obtain modulated polarized light, and the polarizer is used to convert the modulated polarized light into linearly polarized light with adjustable intensity.
8. A method of magnetic field measurement of an optically pumped magnetometer, characterized by, The method for the optically pumped magnetometer of any one of claims 1 to 7, the method comprising: The laser emission and regulation module generates pump laser of specific wavelength, and modulates the pump laser to output linearly polarized light with adjustable intensity; The polarization light splitting and sampling module diffracts the linearly polarized light into right circularly polarized light and left circularly polarized light, wherein the intensity of the right circularly polarized light is equal to that of the left circularly polarized light; The atomic sensing and signal detection module obtains symmetrical magnetic resonance signals by using the right circularly polarized light and the left circularly polarized light.
9. The magnetic field measuring method according to claim 8, characterized in that, The optically pumped magnetometer further includes a light power stabilization control module; the method further comprises: The light power stabilizing control module modulates the pump laser according to the 0th order diffracted light of the linearly polarized light, so as to stabilize the power of the linearly polarized light at a preset value.
10. An airborne magnetic survey apparatus, characterized by, An optically pumped magnetometer comprising the light source of any one of claims 1 to 7.