Air chamber polarization enhanced magnetometer based on multi-focal plane holographic metasurface and measurement method

Abstract

The invention discloses a gas chamber polarization enhanced magnetometer based on a multi-focal plane holographic metasurface and a measurement method, and belongs to the technical field of magnetic field measurement. The magnetometer comprises a laser generation and control module, a 1 / 4 wave plate, a multi-focal plane holographic metasurface, an optical magnetic resonance module, an optical pump signal post-processing module and a reflector. Laser is collimated by the 1 / 4 wave plate and then enters the multi-focal-plane holographic metasurface, and the metasurface regulates and controls the phase of the incident light, so that a light field forms a plurality of focal planes at different depths in a gas chamber, the spatial uniformity of optical pumping is improved, and the alkali metal atom polarizability is enhanced. The transmission light enters the optical pump signal post-processing module and passes through the polarization splitting prism, the balance differential detector and the lock-in amplifier, magnetic resonance signals are extracted, and the magnetic field intensity is calculated. The optical pumping process is optimized, the stability and the signal-to-noise ratio of the magnetic measurement system are improved, the measurement error is reduced, and the method is suitable for the high-sensitivity magnetic field measurement fields such as geomagnetic detection and biological magnetic signal detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic field measurement, and particularly relates to a gas chamber polarization enhanced magnetometer based on a multi-focal plane holographic metasurface and a measurement method. Background Art

[0002] Magnetic field is an important physical quantity generated by moving charges, which widely affects the natural environment, industrial applications, and life sciences. Magnetic field measurement technology has become an important research direction in the fields of basic physics, geophysics, biomedicine, military defense, etc. High-precision magnetic measurement equipment is crucial for applications such as magnetic anomaly detection, resource exploration, and life health monitoring.

[0003] Currently, atomic magnetometers hold the highest magnetic field measurement sensitivity record and show broad application prospects in fields such as geophysical exploration, deep space exploration, and biomagnetic imaging. With the development of miniaturized unmanned aerial vehicle (UAV)-borne magnetometers and portable health monitoring devices, atomic magnetometers are gradually being chip-integrated. However, the existing optically pumped magnetometer technology still has the following key bottlenecks:

[0004] ① Optical pumping non-uniformity: Traditional optical pumping methods rely on the free propagation of lasers. As the laser penetrates deeper into the gas chamber, the optical power gradually attenuates, resulting in non-uniform polarization distribution of alkali metal atoms in the gas chamber, thus affecting the quality of magnetic resonance signals.

[0005] ② Limited polarization rate: Existing optical systems are difficult to efficiently utilize pump light, resulting in insufficient polarization rate of alkali metal atoms, thus limiting the sensitivity of the magnetometer.

[0006] ③ System integration issue: Existing systems usually adopt lens or fiber optic coupling schemes to regulate lasers, with relatively large device volumes, which is not conducive to portable applications.

[0007] To address the above problems, this paper proposes a gas chamber polarization enhanced magnetometer based on a multi-focal plane holographic metasurface. By designing special metasurface optical elements, this method enables multiple focal planes to be formed at the rear end of the gas chamber for the laser, achieving a more uniform optical pumping distribution, thereby improving the polarization uniformity of alkali metal atoms, increasing the optical pumping rate, and enhancing the sensitivity and stability of the magnetic measurement system. Compared with traditional methods, this scheme has higher integration and stability, providing a new solution for portable high-precision magnetic measurement. Summary of the Invention

[0008] The present invention provides a gas chamber polarization enhanced magnetometer and a measurement method based on a multi-focal plane holographic metasurface. By introducing the multi-focal plane holographic metasurface technology, with its characteristics of being thin, light, two-dimensional integration, and multi-functionality, and using sub-micron scale structures to precisely control the light propagation characteristics, the light field distribution in the gas chamber becomes more uniform, achieving efficient polarization enhancement, thereby improving the sensitivity and stability of the magnetic measurement system, and making the overall structure meet the design requirements of miniaturization, high sensitivity, and high integration.

[0009] The technical solution of the present invention is as follows:

[0010] A gas chamber polarization enhanced magnetometer based on a multi-focal plane holographic metasurface, characterized in that it includes a laser generation and control module, a quarter-wave plate, a multi-focal plane holographic metasurface, an optical magnetic resonance module, and an optical pump signal post-processing module connected in sequence. The multi-focal plane holographic metasurface performs spatial phase modulation on the circularly polarized light from the quarter-wave plate to form multiple focal planes with different depth distributions along the beam propagation direction in the alkali metal gas chamber in the optical magnetic resonance module, reducing the polarization gradient caused by uneven light intensity distribution in the gas chamber.

[0011] The spatial phase modulation of the multi-focal plane holographic metasurface includes splitting the incident laser into multiple depth layers along the beam propagation direction using the holographic lens principle, and integrating and encoding the phase information of multiple holographic lenses using a single metasurface to achieve precise phase modulation with sub-wavelength dimensions.

[0012] The laser generation and control module includes a laser and a laser controller, and the laser is connected to the laser controller and the quarter-wave plate respectively.

[0013] The optical magnetic resonance module includes an oven with the alkali metal gas chamber disposed therein, an electric heating wire and a radio frequency coil are arranged between the oven and the alkali metal gas chamber, and the electric heating wire is connected to the oven temperature control system.

[0014] The optical pump signal post-processing module includes a polarization beam splitter prism, a balanced differential detector, a lock-in amplifier, and a mirror. The input side of the polarization beam splitter prism is connected to the laser output side of the alkali metal gas chamber, the transmission side of the polarization beam splitter prism is connected to the first input end of the balanced differential detector, the reflection side of the polarization beam splitter prism is connected to the second input end of the balanced differential detector through the mirror, and the output end of the balanced differential detector is connected to the lock-in amplifier.

[0015] A measurement method for a gas chamber polarization enhanced magnetometer based on a multi-focal plane holographic metasurface, characterized by including the following steps:

[0016] Step 1, Laser Frequency Tuning and Locking: Adjust the operating parameters of the laser through a laser controller to make the laser wavelength match the resonance transition frequency of alkali metal atoms, ensure the stability of the optical pumping process, and improve the polarization rate.

[0017] Step 2, Temperature Monitoring and Regulation of the Alkali Metal Gas Chamber: Set the target heating temperature of the oven and the PID control parameters. The oven temperature control system measures the internal temperature of the oven through a thermistor, calculates the deviation between the target temperature and the actual temperature, and adjusts the power output of the electric heating wire according to PID control to keep the oven temperature stable, ensure that the evaporation of alkali metal atoms in the gas chamber reaches a steady state, and improve the signal-to-noise ratio of the magnetic resonance signal.

[0018] Step 3, Optical Pumping and Detection: The laser passes through a quarter-wave plate and a multi-focal plane holographic metasurface in sequence. The multi-focal plane holographic metasurface performs phase modulation on the incident light to form multiple focal planes at different depths in the alkali metal gas chamber, improving the uniformity of optical pumping. The modulated laser enters the alkali metal gas chamber at a fixed angle to uniformly polarize the alkali metal atoms in the gas chamber. The polarized atoms interact with the external magnetic field, causing changes in the optical signal during transmission. The transmitted light enters the optical pump signal post-processing module.

[0019] Step 4, Magnetic Field Signal Processing and Calculation: The optical pump signal post-processing module includes a polarization beam splitter prism, a photodetector, and a lock-in amplifier, which are used to extract the magnetic resonance signal and calculate the external magnetic field strength. After the outgoing laser enters the optical pump signal post-processing module, it is split by the polarization beam splitter prism and enters the photodetectors respectively, converted into electrical signals and processed. The lock-in amplifier modulates the radio frequency signal and applies it to the radio frequency coil, scans the magnetic resonance signal within a set frequency range, obtains the Larmor precession frequency, and calculates the external magnetic field strength.

[0020] The technical effects of the present invention are as follows: The present invention relates to a gas chamber polarization-enhanced magnetometer and a measurement method based on a multi-focal plane holographic metasurface. It adopts an optical field regulation scheme based on a multi-focal plane holographic metasurface. On the basis of a single-beam magnetometer, the incident laser is divided into multiple depth layers along the beam propagation direction through the principle of a holographic lens, and the phase information of multiple holographic lenses is integrated and encoded using a single metasurface to achieve precise phase modulation at the sub-wavelength scale. Thus, the optical field forms multiple accurately positioned focal planes in the gas chamber, realizing uniform focusing of laser energy, significantly improving the polarization rate and polarization uniformity of alkali metal atoms, thereby enhancing the amplitude and signal-to-noise ratio of the magnetic resonance signal, and greatly improving the sensitivity and stability of magnetic field measurement.

[0021] In addition, by effectively reducing the polarization gradient caused by uneven light intensity distribution, the solution of the present invention reduces signal distortion caused by local over-pumping or insufficient polarization, and greatly improves the accuracy and repeatability of measurement. Compared with the traditional optical pumping method, this solution can improve the utilization efficiency of the pump light in the gas chamber, reduce the polarization gradient problem caused by uneven light intensity distribution, thereby improving the stability and repeatability of magnetic field measurement. A higher polarization rate in the gas chamber can enhance the amplitude of the nuclear magnetic resonance signal and improve the signal-to-noise ratio of the magnetometer, while a more uniform polarization distribution can reduce signal distortion caused by local insufficient polarization or over-pumping, making the magnetic field measurement more accurate and reliable, further reducing the system error, and improving the sensitivity of magnetic field measurement. Brief Description of the Drawings

[0022] Figure 1 is a schematic structural diagram of a gas chamber polarization-enhanced magnetometer based on a multi-focal plane holographic metasurface of the present invention.

[0023] Figure 2 is Figure 1 a schematic diagram of the principle of forming multiple focal planes by the multi-focal plane holographic metasurface in the alkali metal gas chamber in

[0024] Description of the reference numerals is as follows: 1 - Laser generation and control module; 2 - Laser; 3 - Laser controller; 4 - Quarter-wave plate; 5 - Multi-focal plane holographic metasurface; 6 - Opto-magnetic resonance module; 7 - Oven; 8 - Electric heating wire; 9 - Alkali metal gas chamber; 10 - Radio frequency coil; 11 - Oven temperature control system; 12 - Optical pump signal post-processing module; 13 - Polarizing beam splitter prism; 14 - Balanced differential detector; 15 - Phase-locked amplifier; 16 - Mirror; 17 - Circularly polarized light; 18 - First focal plane (i.e., front focal plane); 19 - Second focal plane (i.e., middle focal plane); 20 - Third focal plane (i.e., rear focal plane); 21 - Polarized atoms. Detailed Embodiments

[0025] The present invention will be described below with reference to the accompanying drawings ( Figure 1 - Figure 2 ).

[0026] Figure 1 is a schematic structural diagram of a gas chamber polarization-enhanced magnetometer based on a multi-focal plane holographic metasurface of the present invention. Figure 2 is Figure 1 a schematic diagram of the principle of forming multiple focal planes by the multi-focal plane holographic metasurface in the alkali metal gas chamber in. Refer to Figure 1 to Figure 2As shown in the figure, a gas cell polarization enhanced magnetometer based on a multi-focal plane holographic metasurface includes a laser generation and control module 1, a quarter-wave plate 4, a multi-focal plane holographic metasurface 5, an optical magnetic resonance module 6, and an optical pumping signal post-processing module 12 connected in sequence. The multi-focal plane holographic metasurface 5 performs spatial phase modulation on the circularly polarized light 17 from the quarter-wave plate 4 to form multiple focal planes with different depth distributions along the beam propagation direction in the alkali metal gas cell 9 in the optical magnetic resonance module 6 (for example, the first focal plane 18, i.e., the front focal plane, the second focal plane 19, i.e., the middle focal plane, and the third focal plane 20, i.e., the rear focal plane. The alkali metal atoms in the gas cell become polarized atoms 21 under the action of the light fields formed by the multiple focal planes), reducing the polarization gradient caused by the uneven light intensity distribution in the gas cell. The spatial phase modulation of the multi-focal plane holographic metasurface 5 includes splitting the incident laser into multiple depth layers along the beam propagation direction using the holographic lens principle, and integrating and encoding the phase information of multiple holographic lenses using a single metasurface to achieve precise phase modulation with sub-wavelength dimensions.

[0027] The laser generation and control module 1 includes a laser 2 and a laser controller 3. The laser 2 is respectively connected to the laser controller 3 and the quarter-wave plate 4. The optical magnetic resonance module 6 includes an oven 7 with the alkali metal gas cell 9 disposed therein. An electric heating wire 8 and a radio frequency coil 10 are provided between the oven 7 and the alkali metal gas cell 9. The electric heating wire 8 is connected to an oven temperature control system 11. The optical pumping signal post-processing module 12 includes a polarization beam splitter prism 13, a balanced differential detector 14, a lock-in amplifier 15, and a mirror 16. The input side of the polarization beam splitter prism 13 is connected to the laser output side of the alkali metal gas cell 9. The transmission side of the polarization beam splitter prism 13 is connected to the first input end of the balanced differential detector 14. The reflection side of the polarization beam splitter prism 13 is connected to the second input end of the balanced differential detector 14 through the mirror 16. The output end of the balanced differential detector 14 is connected to the lock-in amplifier 15.

[0028] The present invention discloses a gas cell polarization enhanced magnetometer and a measurement method based on a multi-focal plane holographic metasurface, belonging to the technical field of magnetic field measurement. The magnetometer includes a laser generation and control module, a quarter-wave plate, a multi-focal plane holographic metasurface, an optical magnetic resonance module, an optical pumping signal post-processing module, and a mirror. The laser is collimated by the quarter-wave plate and then incident on the multi-focal plane holographic metasurface. The metasurface performs phase modulation on the incident light, causing the light field to form multiple focal planes at different depths in the gas cell, improving the spatial uniformity of optical pumping and enhancing the polarization rate of alkali metal atoms. The transmitted light enters the optical pumping signal post-processing module, passes through the polarization beam splitter prism, the balanced differential detector, and the lock-in amplifier, extracts the magnetic resonance signal, and calculates the magnetic field strength. The present invention optimizes the optical pumping process, improves the stability and signal-to-noise ratio of the magnetic measurement system, reduces the measurement error, and is applicable to high-sensitivity magnetic field measurement fields such as geomagnetic exploration and biomagnetic signal detection.

[0029] A gas chamber polarization enhanced magnetometer based on a multi-focal plane holographic metasurface, comprising: a laser generation and control module, a quarter-wave plate, a multi-focal plane holographic metasurface, an optical magnetic resonance module, an optical pumping signal post-processing module, and a mirror;

[0030] The laser generation and control module includes a laser and a laser controller, and the laser controller adjusts the laser to ensure stable output of laser with a specific wavelength and power;

[0031] The quarter-wave plate is used to adjust the divergence angle of the laser so that its beam characteristics are suitable for phase modulation by the multi-focal plane holographic metasurface;

[0032] The multi-focal plane holographic metasurface performs spatial phase modulation on the incident laser through a precisely designed sub-micron structure. Using the geometric phase principle, by adjusting the size, shape, period, and rotation angle of the nanostructure, the phase information of multiple holographic lenses is integrated on a single metasurface, enabling the laser to form multiple precise focal planes at different depths in the alkali metal gas chamber, thereby optimizing the optical pumping uniformity and increasing the atomic polarization rate;

[0033] The optical magnetic resonance module includes an alkali metal gas chamber, and the polarized atoms undergo Larmor precession under the action of an external magnetic field and affect the polarization state of the transmitted light;

[0034] The transmitted light enters the optical pumping signal post-processing module, and the optical pumping signal post-processing module receives the signal and generates a radio frequency magnetic field to drive the optical magnetic resonance module to obtain the Larmor precession frequency, so as to calculate the magnetic field strength.

[0035] The operating parameters of the laser generation and control module include the operating temperature, operating current, and output wavelength of the laser to ensure that the pump light matches the resonance transition frequency of the alkali metal atoms.

[0036] The multi-focal plane holographic metasurface precisely regulates the phase of the incident light through periodic nanostructures, enabling it to form multiple focal planes at different depths in the alkali metal gas chamber, improving the optical pumping uniformity, enhancing the atomic polarization process, and reducing the influence of the polarization gradient on the magnetic measurement signal.

[0037] The optical magnetic resonance module includes: an alkali metal gas chamber, an oven, an oven temperature control system, a radio frequency coil skeleton, and a radio frequency coil;

[0038] The alkali metal gas chamber: is filled with alkali metal atom gas and buffer gas and has windows to allow laser transmission;

[0039] The oven: wraps the alkali metal gas chamber and provides a stable heating environment to maintain the evaporation state of the alkali metal atoms;

[0040] The oven temperature control system: uses an electric heating wire and a thermistor to achieve temperature monitoring and feedback control, so as to maintain the internal temperature of the alkali metal gas cell stable and improve the stability of the optical pumping process;

[0041] The radio frequency coil: is fixed on the radio frequency coil support skeleton and is driven by a lock-in amplifier, and is used to provide an alternating magnetic field to excite the atoms to undergo Larmor precession.

[0042] The oven temperature control system adopts a PID control strategy (PID is proportional integral derivative), and adjusts the heating power in real time according to the measured internal temperature of the oven to reduce the influence of temperature fluctuations on the magnetic measurement signal.

[0043] The optical pumping signal post-processing module includes: a polarization beam splitter prism, a balanced differential detector, and a lock-in amplifier;

[0044] The polarization beam splitter prism splits the transmitted light into two mutually perpendicular light beams, one of which propagates in the original direction, and the other is adjusted by a mirror and then is parallel to the first light beam and the two are incident on the balanced differential detector for light intensity detection;

[0045] The balanced differential detector performs differential processing on the two light signals to improve the signal-to-noise ratio and reduce the influence of light intensity fluctuations on the measurement results;

[0046] The lock-in amplifier amplifies and filters the output signal of the balanced differential detector and applies a radio frequency scan to extract the characteristic frequency of the magnetic resonance signal and calculate the magnetic field strength.

[0047] The radio frequency magnetic field generated by the radio frequency coil has an adjustable frequency range and is connected to the lock-in amplifier, enabling the system to measure magnetic resonance signals in different magnetic field environments and adapt to the measurement requirements of different magnetic field strengths.

[0048] A measurement method of a gas cell polarization enhanced magnetometer based on a multi-focal plane holographic metasurface, including:

[0049] Step 1: Laser frequency tuning and locking;

[0050] Adjust the working parameters of the laser through a laser controller to make the laser wavelength match the resonance transition frequency of the alkali metal atoms, ensure the stability of the optical pumping process, and improve the polarization rate.

[0051] Step 2: Monitoring and regulation of the alkali metal gas cell temperature;

[0052] Set the target heating temperature and PID control parameters of the oven. The oven temperature control system measures the internal temperature of the oven through a thermistor, calculates the deviation between the target temperature and the actual temperature, and adjusts the power output of the electric heating wire according to PID control to keep the oven temperature stable, ensuring that the evaporation of alkali metal atoms in the gas chamber reaches a steady state and improving the signal-to-noise ratio of the magnetic resonance signal.

[0053] Step 3: Optical pumping and detection;

[0054] The laser passes through a quarter-wave plate and a multi-focal plane holographic metasurface in sequence. The multi-focal plane holographic metasurface performs phase modulation on the incident light, enabling it to form multiple focal planes at different depths in the alkali metal gas chamber, thereby improving the uniformity of optical pumping. The modulated laser enters the alkali metal gas chamber at a fixed angle, uniformly polarizing the alkali metal atoms in the chamber. The polarized atoms interact with the external magnetic field, causing changes in the optical signal during transmission. The transmitted light then enters the optical pumping signal post-processing module.

[0055] Step 4: Magnetic field signal processing and calculation;

[0056] The optical pumping signal post-processing module includes a polarization beam splitter prism, a photodetector, and a lock-in amplifier, which are used to extract the magnetic resonance signal and calculate the external magnetic field strength. After the outgoing laser enters the optical pumping signal post-processing module, it is split by the polarization beam splitter prism and then enters the photodetectors respectively, where it is converted into electrical signals and processed. The lock-in amplifier modulates the radio frequency signal and applies it to the radio frequency coil, scans the magnetic resonance signal within a set frequency range, obtains the Larmor precession frequency, and calculates the external magnetic field strength.

[0057] Reference Figure 1 As shown, a gas chamber polarization-enhanced magnetometer based on a multi-focal plane holographic metasurface includes: a laser generation and control module 1, a quarter-wave plate 4, a multi-focal plane holographic metasurface 5, an optical magnetic resonance module 6, an optical pumping signal post-processing module 12, and a mirror 16; the laser generation and control module 1 is used to generate a stable pump light, which passes through the quarter-wave plate 4 and the multi-focal plane holographic metasurface 5 in sequence along the optical path direction; the multi-focal plane holographic metasurface 5 performs spatial phase modulation on the incident light beam, enabling it to form multiple focal planes inside the gas chamber, improving the optical field uniformity and optimizing the atomic polarization rate; the laser after the action of the optical magnetic resonance module 6 enters the optical pumping signal post-processing module 12, and the optical pumping signal post-processing module 12 receives the transmitted optical signal and processes it to extract the magnetic resonance signal and calculate the Larmor precession frequency corresponding to the magnetic field strength.

[0058] As an illustrative example, the laser generation and control module 1 includes: a laser controller 3 and a laser 2. The laser controller 3 is used to control the frequency, power and temperature of the laser 2 to ensure the stability of the laser and to ensure that the pump light matches the resonance transition of the alkali metal atoms. As a preferred illustrative example, the quarter-wave plate 4 is used to adjust the polarization state of the laser so that the light beam incident on the multi-focal plane holographic metasurface 5 is circularly polarized light, improving the modulation efficiency of the metasurface on the optical field and avoiding affecting the polarization process due to the light beam deviating from the focal plane.

[0059] As an illustrative example, the optical magnetic resonance module 6 includes: an oven 7, an electric heating wire 8, an alkali metal gas cell 9, a radio frequency coil 10 and an oven temperature control system 11. The oven 7 houses the alkali metal gas cell 9 and provides heat through the electric heating wire 8 to adjust the temperature of the gas cell to maintain and stabilize the appropriate vapor pressure of the alkali metal atoms and to ensure the stability and density uniformity of the atomic vapor in the gas cell. The alkali metal gas cell 9 contains alkali metal atomic vapor and buffer gas, and the laser beam penetrates it to achieve optical pumping polarization. The radio frequency coil 10 is arranged around the alkali metal gas cell 9. When the radio frequency field frequency is the same as the Larmor precession frequency of the alkali metal atoms, optical magnetic resonance will occur, and this signal is transmitted to the lock-in amplifier 15. The oven temperature control system 11 realizes precise adjustment of the internal temperature of the oven 7 through feedback control of the electric heating wire 8 and the temperature sensor to improve the quality of the magnetic resonance signal.

[0060] As an illustrative example of an application, the multi-focal plane holographic metasurface 5 is composed of a plurality of periodically arranged sub-wavelength nanostructures. These nanostructures usually take the form of cuboids or cylinders and can be designed based on various modulation mechanisms such as geometric phase, resonance phase or propagation phase. By precisely controlling the size, shape, orientation angle and periodic layout of the nanostructures, the phase information of a plurality of holographic lenses with different focal lengths is superimposed on the same metasurface, so that the incident light forms a plurality of independent focal planes at different longitudinal depths. This can not only compensate for the gradual attenuation of the optical power in the gas cell, but also enhance the optical field effect in the deep region of the gas cell, so that the alkali metal atoms obtain a more uniform polarization state throughout the gas cell range, greatly improving the amplitude and consistency of the magnetic resonance signal.

[0061] As an example, the optical pumping signal post-processing module 12 includes: a polarization beam splitter prism 13, a balanced differential detector 14, and a lock-in amplifier 15. The polarization beam splitter prism 13 is used to split the transmitted light according to the polarization state, so that one beam of light propagates along the original direction, and the other beam of light enters the balanced differential detector 14 after deflection, so as to improve the signal extraction accuracy. The balanced differential detector 14 performs differential detection on the two beam signals, effectively suppressing the light source fluctuation and background noise, and improving the signal-to-noise ratio of the signal. The lock-in amplifier 15 amplifies and filters the differential signal output by the balanced differential detector 14, and extracts the magnetic resonance signal by the lock-in amplification method, calculates the Larmor precession frequency, and estimates the external magnetic field strength.

[0062] As an example of the effect, the multi-focal plane holographic metasurface 5 makes the optical pumping more uniform through precise optical field control, effectively improving the stability and sensitivity of the magnetic resonance signal. This scheme reduces the non-uniformity of the optical field during propagation, makes the response of the magnetic resonance signal more stable, and improves the anti-interference ability and measurement accuracy of the system. In addition, this design has a high integration level, occupies a small space, simplifies the optical system, reduces the volume and complexity of the traditional lens system, helps the miniaturization development of high-precision magnetic field measurement equipment, and provides a better solution for portable and integrated magnetic measurement systems.

[0063] Refer to Figure 1 As shown in the figure; the working temperature and driving current of the laser 2 are set by the laser controller 3, so that the wavelength of the output laser is stabilized near the Rb atomic D1 transition line (794.979 nm), and the laser power is adjusted to an appropriate level to ensure that the pump light effectively acts on the alkali metal atoms in the gas chamber and realizes polarization, while avoiding the non-linear effects that may be caused by too high light intensity.

[0064] In the experimental environment, the target temperature of the oven 7 is set to 80 - 120 °C by the oven temperature control system 11. The oven temperature control system monitors the real-time temperature inside the oven through the built-in thermistor, and uses the PID control strategy to dynamically adjust the output power of the electric heating wire 8 to ensure that the alkali metal atoms in the alkali metal gas chamber 9 evaporate to a stable vapor density, improving the stability and repeatability of the magnetic resonance signal.

[0065] The light beam emitted by the laser 2 passes through the quarter-wave plate 4 and the multi-focal plane holographic metasurface 5 in sequence. The quarter-wave plate 4 realizes the polarization conversion of the light beam and reduces the spot divergence; the multi-focal plane holographic metasurface 5 performs spatial control on the phase of the incident light beam to form multiple focal planes at different depths in the alkali metal gas chamber 9. As Figure 2As shown, the length of the alkali metal gas cell 9 is 8 mm. It is fixed approximately 4 mm away from the alkali metal gas cell 9 using holographic multi-focal planes, with focal lengths of 5 mm, 8 mm, and 11 mm respectively, forming three focal planes, thereby achieving more uniform optical pumping inside the entire gas cell, improving the uniformity of alkali metal atom polarization, and reducing signal distortion caused by uneven polarization.

[0066] The polarized atoms undergo Larmor precession under the action of an external magnetic field, generating optical magnetic resonance and causing changes in the transmitted light intensity. The transmitted light enters the optical pumping signal post-processing module 12 and is polarized and split into two beams by the polarization beam splitter 13. One beam propagates in the original direction, and the other beam is adjusted in direction by the mirror 16 and then enters the balanced differential detector 14 in parallel with the former. The balanced differential detector 14 performs differential operations on the intensity signals of the two beams of light to effectively suppress noise, enhance signal contrast, and improve detection sensitivity.

[0067] The lock-in amplifier 15 applies an alternating radio frequency signal to the radio frequency coil 10 within a certain frequency range and scans the differential change in the light intensity signal received from the balanced differential detector 14. When the amplitude of the detected magnetic resonance signal reaches an extreme value, the corresponding radio frequency is the Larmor precession frequency ω, and the external magnetic field strength can be calculated through the following formula:

[0068] ω = γB0

[0069] where γ = 7 Hz / nT is the gyromagnetic ratio of rubidium atoms, and B0 is the external magnetic field strength.

[0070] According to the radio frequency field frequency ω corresponding to the peak value of the measured magnetic resonance signal, the external magnetic field strength B0 can be calculated through the above formula, and the measurement accuracy can be improved by combining the results of multiple measurements. Compared with traditional optical pumping magnetometers, the present invention uses a multi-focal plane holographic metasurface to improve the spatial uniformity of optical pumping, thereby enhancing the signal stability, sensitivity, and anti-interference ability of the magnetic measurement system, and is applicable to high-precision magnetic measurement application scenarios such as geomagnetic measurement and biomagnetic field detection.

[0071] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art.

[0072] The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the purpose of the present application and the scope protected by the claims, and all belong to the protection scope of the present application.

[0073] Those of ordinary skill in the art will realize that the units and algorithm steps of each example described in combination with the embodiments disclosed in the embodiments of the present application can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. A professional technician can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present application.

[0074] Those skilled in the art can clearly understand that for the convenience and conciseness of description, the specific working processes of the systems, devices, and units described above can refer to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0075] In the embodiments provided in the present application, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the system embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces, and the indirect couplings or communication connections of devices or units can be in electrical, mechanical, or other forms.

[0076] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place, or distributed to multiple network units; some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0077] In addition, the functional units in each embodiment of the present application can be integrated into a processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit.

[0078] The above are only the preferred embodiments of the present invention. It should be understood that the description of the above embodiments is only for helping to understand the method and its core idea of the present invention, and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An air chamber polarization enhanced magnetometer based on a multi-focal plane holographic metasurface, characterized in that: The method comprises a laser generation and control module, a quarter wave plate, a multi-focal plane holographic metasurface, an optical magnetic resonance module and an optical pump signal post-processing module which are connected in sequence. The multi-focal plane holographic metasurface performs spatial phase control on the circularly polarized light from the quarter wave plate, and then forms a plurality of focal planes distributed at different depths along the propagation direction of the light beam in an alkali metal gas chamber in the optical magnetic resonance module, thereby reducing the polarization gradient caused by uneven light intensity distribution in the gas chamber.

2. The gas chamber polarization enhanced magnetometer based on multi-focal plane holographic metasurface according to claim 1, characterized in that: The spatial phase control of the multi-focal holographic metasurface includes using the principle of holographic lenses to split the incident laser into multiple depth layers along the beam propagation direction, and using a single metasurface to integrate and encode the phase information of multiple holographic lenses to achieve precise phase control at a sub-wavelength size.

3. The gas chamber polarization enhanced magnetometer based on multi-focal plane holographic metasurface according to claim 1, characterized in that: The laser generation and control module comprises a laser and a laser controller, and the laser is connected to the laser controller and the 1 / 4 wave plate respectively.

4. The gas chamber polarization enhanced magnetometer based on multi-focal plane holographic metasurface according to claim 1, characterized in that: The optical magnetic resonance module includes an oven in which the alkali metal gas chamber is placed, an electric heating wire and a radio frequency coil are arranged between the oven and the alkali metal gas chamber, and the electric heating wire is connected to the oven temperature control system.

5. The gas chamber polarization enhanced magnetometer based on multi-focal plane holographic metasurface according to claim 1, characterized in that: The optical pump signal post-processing module includes a polarization beam splitter prism, a balanced differential detector, a phase-locked amplifier and a reflector. The input side of the polarization beam splitter prism is connected to the laser output side of the alkali metal gas chamber, the transmission side of the polarization beam splitter prism is connected to the first input end of the balanced differential detector, the reflection side of the polarization beam splitter prism is connected to the second input end of the balanced differential detector through the reflector, and the output end of the balanced differential detector is connected to the phase-locked amplifier.

6. A measurement method of an air chamber polarization enhanced magnetometer based on a multi-focal plane holographic metasurface, characterized in that: The following steps are involved: Step 1, laser frequency tuning and locking: adjust the laser operating parameters through the laser controller to make the laser wavelength match the resonant transition frequency of the alkali metal atoms, ensure the stability of the optical pumping process, and improve the polarizability; Step 2, alkali metal gas chamber temperature monitoring and control: set the target heating temperature and PID control parameters of the oven, the oven temperature control system measures the internal temperature of the oven through the thermistor, calculates the deviation between the target temperature and the actual temperature, and controls the power output of the electric heating wire according to the PID regulation to keep the oven temperature stable, ensure that the evaporation of the alkali metal atoms in the gas chamber reaches a steady state, and improve the signal-to-noise ratio of the magnetic resonance signal; Step 3, optical pumping and detection: The laser passes through a quarter wave plate and a multi-focal holographic metasurface in sequence. The multi-focal holographic metasurface performs phase control on the incident light, so that it forms multiple focal planes at different depths in the alkali metal gas chamber, thereby improving the uniformity of optical pumping. The regulated laser enters the alkali metal gas chamber at a fixed angle, so that the alkali metal atoms in the gas chamber are uniformly polarized. The polarized atoms interact with the external magnetic field, causing the optical signal to change during the transmission process. The transmitted light enters the optical pump signal post-processing module; Step 4, magnetic field signal processing and calculation: The optical pump signal post-processing module includes a polarization beam splitter, a photodetector and a phase-locked amplifier, which are used to extract magnetic resonance signals and calculate the external magnetic field strength. After the emitted laser enters the optical pump signal post-processing module, it is split by the polarization beam splitter, and enters the photodetector respectively, converted into an electrical signal and processed. The phase-locked amplifier modulates the radio frequency signal and applies it to the radio frequency coil, scans the magnetic resonance signal within the set frequency range, obtains the Larmor precession frequency, and calculates the external magnetic field strength.

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