Method for suppressing environmental interference of very low frequency atomic magnetometer based on polarization selective reception

Abstract

The application provides a very low frequency atomic magnetometer environment interference suppression method based on polarization selection reception, wherein a precession main magnetic field B e and -B e are respectively applied by a main magnetic field coil in z direction and -z direction in front and back two regions of a gas chamber e and -B e regions are detected by using detection laser in x direction; external very low frequency signals are detected by interaction with atoms polarized in z direction to make the atoms produce precession signals in xOy plane, so that the signals are detected by light detection; when the external signals are linear polarization, according to the selection rule of angular momentum conservation, the precession signals of atoms in B e and -B e regions are offset, so that the system does not respond to linear polarization signals; for circular polarization signals, only atoms in B e or -B e region have precession signals, so that the detection of circular polarization signals is realized. The technical scheme of the application is applied to solve the technical problem of environmental magnetic noise interference of a very low frequency atomic magnetometer in an actual application scene in the prior art.

Description

Technical Field

[0001] This invention relates to the field of quantum sensing technology, and in particular to a method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception. Background Technology

[0002] In recent years, with the continuous development of quantum precision measurement technology, atomic magnetometer technology based on the atomic spin precession effect has achieved remarkable success in the field of high-sensitivity measurement of weak magnetic fields. Especially in femtosecond-level magnetic field measurements, compared to its competitor, the superconducting quantum interference device (SQUID), the atomic magnetometer demonstrates significant advantages in engineering applications such as small-size integration and room-temperature operation, while maintaining comparable measurement sensitivity. It also shows enormous potential application value in fields such as communication, exploration, and magnetic imaging. Particularly in the field of very low frequency (VLF) communication, compared to traditional VLF magnetic induction coil technology, the sensitivity of the VLF atomic magnetometer can be three orders of magnitude higher within the same effective sensing volume. VLF atomic magnetometer technology based on atomic magnetometers will bring revolutionary development to this field. However, performance testing of VLF atomic magnetometers is primarily conducted in heavily shielded laboratory environments, such as multi-layered magnetically shielded rooms. In unshielded environments similar to those used in VLF atomic magnetometer applications, the performance is limited by the influence of ambient magnetic field noise. Therefore, noise suppression technology in unshielded environments is an important issue that needs to be addressed in the application of very low frequency atomic magnetometers. Summary of the Invention

[0003] This invention provides a method for suppressing environmental interference in very low frequency atomic magnetometers based on polarization-selective reception, which can solve the technical problem of environmental magnetic noise interference caused by existing very low frequency atomic magnetometers in practical application scenarios.

[0004] According to one aspect of the present invention, a method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception is provided. The method includes: polarizing alkali metal atoms in an atomic gas chamber along the direction of the driving laser (z-direction) using a driving laser; providing a zero-field environment by compensating for the external magnetic field at the atomic gas chamber through a triaxial magnetic field coil and a triaxial magnetic sensor, and using the main magnetic field B... e Coil and Main Magnetic Field - B e The coil applies a precessing main magnetic field B of equal magnitude and opposite direction along the z-direction and -z-direction in two regions before and after the gas chamber, respectively. e and -B e The x-direction utilizes a detection laser to simultaneously measure B. e With -B eThe precession of the spin projection signal of atoms in the x-direction is detected. The precession amplitude is proportional to the amplitude of the external very low frequency (VLF) signal, and the frequency is the same as the external VLF signal. Atoms are manipulated by pump and probe lasers. The pump laser is σ+ circularly polarized light, which resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF = +1, the atom will be pumped to m under the action of the circularly polarized pump laser. f =F max Polarization is achieved at the quantum state with the largest magnetic quantum number, with the system's quantization axis along the driving laser direction, and the polarized atom spin pointing in the positive z direction; for a main magnetic field of B e In the region where the polarized atomic spins point towards B... e Similarly, along the positive z-direction, for a principal magnetic field of -B e In the region where the polarized atomic spins point in the same direction as -B e Conversely, also along the positive z-direction, very low frequency electromagnetic signals propagating in the xy-plane along the z-direction are absorbed by polarized atoms, causing the polarization vector to deviate from the z-direction and begin precessing around the z-axis at a frequency γBe, where γ is the gyromagnetic ratio of alkali metal atoms. The detection laser is linearly polarized, and its frequency is significantly detuned to the resonance frequency of the alkali metal atoms. Therefore, the absorption of the detection laser by the atomic ensemble is negligible, and dichroism plays a dominant role. The detection laser signal changes with the precession of atomic spin. When the received very low frequency signal is linearly polarized, according to the transition selection rule, polarized atoms in both magnetic field regions can absorb the electromagnetic signal, resulting in precession. Since the precession magnetic fields in the two regions are opposite, according to the right-hand rule, the precession directions of the atoms in the two regions are also opposite. Therefore, the precession of the detection light after passing through the two regions will cancel each other out, ultimately resulting in no signal. When the received signal is σ... - For circularly polarized signals, according to the transition selection rule, only B... e The atoms in the region will interact with the electromagnetic field under this polarization, thereby generating a precession signal, -B e There is no atomic precession signal in the region, and the detection laser passes through B. e With -B e B will be detected after the region. e The atomic precession of the region enables the detection of very low frequency signals; when the received signal is σ + For circularly polarized signals, according to the transition selection rule, only -B e The atoms in the region will interact with the electromagnetic field under this polarization, thereby generating a precession signal, B. e There is no atomic precession signal in the region, and the detection laser passes through B. e With -B e -B will be detected after the region. e The precession of atoms in the region enables the detection of very low frequency signals, thereby completing the environmental interference suppression of the very low frequency atomic magnetometer based on polarization-selective reception.

[0005] Furthermore, the pump laser generated by the pump laser passes sequentially through a first Glanthall prism and a quarter-wave plate before entering the atomic gas chamber. Through interaction with the alkali metal atoms in the atomic gas chamber, polarization of the alkali metal atoms is achieved. The probe laser generated by the probe laser passes sequentially through a second half-wave plate, a second Glanthall prism, and a second reflector before entering the atomic gas chamber. The detection laser emitted from the atomic gas chamber is reflected by a first reflector, then passes through a first half-wave plate and a Wollaston prism before entering the balanced null detector. The signal acquired by the balanced null detector is output to the data acquisition and control system. A three-axis magnetic field coil, a three-axis fluxgate, and a main magnetic field B are installed outside the atomic gas chamber. e Coil and Main Magnetic Field - B e Coil, main magnetic field B e The coil is used to generate the main magnetic field B in the positive z-direction. e Main magnetic field -B e The coil is used to generate B e The main magnetic field -B in the opposite negative z-direction e .

[0006] Furthermore, since the Faraday rotation angle θ of light is proportional to the magnitude P of the polarization projection of the spin ensemble in the x-direction... x That is: θ∝P x The detection laser passes sequentially through two atomic ensembles with opposite main magnetic fields. The signal output by the balanced zero-beat detector is proportional to the polarization projection P of the spin ensemble in the x-direction. x P x = M1cos(ωt) - M2cos(ωt), where the amplitude M1 is the B of the atom under the action of a very low frequency signal. e The amplitude of the atomic precession signal in the main magnetic field region, M2 is the -B of the atom under the influence of the very low frequency signal. e The amplitude of the atomic precession signal in the main magnetic field region; for linearly polarized very low frequency signals, amplitudes M1 and M2 are equal, therefore the system does not respond to linearly polarized very low frequency signals; for σ + Circularly polarized very low frequency signals have only a main magnetic field of B. e The regional response, with a principal magnetic field of -B. e The region that does not respond, i.e., M2 = 0, is therefore the final detected signal is proportional to M1cos(ωt); for σ - Circularly polarized very low frequency signals have only a main magnetic field of -B. e Since there is a precession signal in the atomic region, M1 = 0. Therefore, the final output is proportional to -M2cos(ωt), thereby achieving selective reception of circularly polarized signals.

[0007] Furthermore, for circularly polarized signals, the signals received by the system are 180° out of phase. Therefore, the polarization of the detected signal can be determined by the phase information, thereby further realizing the resolution of circular polarization. By polarization-selective reception, environmental linear polarization noise interference can be effectively suppressed, and a stronger anti-interference communication technology can be achieved based on a specific polarization.

[0008] Furthermore, the Faraday rotation angle θ can be determined according to... The calculation yields the following: I1 is the light intensity of the first laser output from the Wollaston prism, I2 is the light intensity of the second laser output from the Wollaston prism, and I0 = I1 + I2, where I0 is the sum of the light intensities of the two laser beams.

[0009] According to another aspect of the present invention, a very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception is provided. This system uses the very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception described above to suppress very low frequency atomic magnetometer environmental interference.

[0010] Furthermore, the environmental interference suppression system for a very low frequency atomic magnetometer based on polarization-selective reception includes a pump laser, a first Glan Taylor prism, a quarter-wave plate, an atomic gas cell, a first reflector, a first half-wave plate, a Wollaston prism, a balanced null detector, a data acquisition and control system, a probe laser, a second half-wave plate, a second Glan Taylor prism, a second reflector, a triaxial magnetic field coil, a triaxial fluxgate, and a main magnetic field B. e Coil and Main Magnetic Field - B e The coil contains a pump laser generated by a pump laser, which passes sequentially through a first Glan-Taylor prism and a quarter-wave plate before entering the atomic gas cell. The pump laser interacts with the alkali metal atoms in the atomic gas cell, achieving polarization of the alkali metal atoms. A probe laser generated by a probe laser passes sequentially through a second half-wave plate, a second Glan-Taylor prism, and a second mirror before entering the atomic gas cell. The probe laser emitted from the atomic gas cell is reflected by a first mirror, then passes through a first half-wave plate and a Wollaston prism before entering a balanced null detector. The signal acquired by the balanced null detector is output to the data acquisition and control system. The system also includes a three-axis magnetic field coil, a three-axis fluxgate, and a main magnetic field B. e Coil and Main Magnetic Field - B e The coil is positioned outside the atomic gas chamber, with the main magnetic field B. e The coil is used to generate the main magnetic field B in the positive z-direction. e Main magnetic field -B e The coil is used to generate B e The main magnetic field -B in the opposite negative z-direction e .

[0011] This invention provides a method for suppressing environmental interference in a very low frequency (VLF) atomic magnetometer based on polarization-selective reception. This method can detect VLF magnetic field signals and, by cleverly utilizing the quantum mechanical law of conservation of angular momentum, enables the VLF atomic magnetometer to selectively receive the polarization state of radio frequency magnetic signals in a novel way. This achieves a novel VLF atomic magnetometer design that can suppress environmental noise, providing a new approach for suppressing environmental noise in unshielded environments and thus enabling efficient wireless communication technology. Therefore, compared with existing technologies, the VLF atomic magnetometer environmental interference suppression method based on polarization-selective reception provided by this invention can achieve polarization-selective reception of VLF signals, enabling the separation and detection of specific circularly polarized signals; it can effectively suppress interference from linearly polarized noise in the environment; and based on specific polarized electromagnetic waves, it can achieve efficient anti-interference communication. Furthermore, based on the selective reception of circularly polarized electromagnetic waves, this invention can further determine the polarity of circular polarization through phase information, realizing the detection of two types of circularly polarized signals; the method and system are simple and easy to integrate into the miniaturized sensor. Attached Figure Description

[0012] The accompanying drawings, which form part of this specification, are provided to further illustrate embodiments of the invention and, together with the textual description, explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0013] Figure 1 A schematic diagram of the structure of a very low frequency atomic magnetometer environmental interference suppression system based on polarization-selective reception according to a specific embodiment of the present invention is shown.

[0014] Figure 2a This illustrates a specific embodiment of the invention, showing how a received very low frequency signal, being linearly polarized, passes through a magnetic field B. e and -B e A schematic diagram of the precession signal generated during the process;

[0015] Figure 2b This illustrates a specific embodiment of the invention, provided when the received very low frequency signal is σ. - Circular polarization occurs when passing through magnetic field B e and -B e A schematic diagram of the precession signal generated during the process;

[0016] Figure 2c This illustrates a specific embodiment of the invention, provided when the received very low frequency signal is σ. + When a circularly polarized signal passes through a magnetic field B e and -Be A schematic diagram of the precession signal generated during the process.

[0017] The above figures include the following reference numerals:

[0018] 10. Pump laser; 20. First GlanTeller prism; 30. Quarter-wave plate; 40. Atomic gas cell; 50. First reflecting mirror; 60. First half-wave plate; 70. Wollaston prism; 80. Balanced null detector; 90. Data acquisition and control system; 100. Probe laser; 110. Second half-wave plate; 120. Second GlanTeller prism; 130. Second reflecting mirror; 140. Triaxial magnetic field coil; 150. Triaxial fluxgate; 160. Main magnetic field B e Coil; 170, Main Magnetic Field - B e Coil. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0022] like Figures 1 to 2c As shown, a specific embodiment of the present invention provides a method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception. This method includes: polarizing alkali metal atoms in the atomic gas chamber along the direction of the driving laser (z-direction) using a driving laser; providing a zero-field environment by compensating for the external magnetic field at the atomic gas chamber through a triaxial magnetic field coil and a triaxial magnetic sensor, and using the main magnetic field B... e Coil 160 and main magnetic field -B e Coil 170 applies precessing main magnetic fields B of equal magnitude and opposite direction in the z-direction and -z-direction, respectively, to two regions before and after the atomic gas cell. e and -B e The x-direction utilizes a detection laser to simultaneously measure B. e With -B e The precession of the spin projection signal of atoms in the x-direction is detected. The precession amplitude is proportional to the amplitude of the external very low frequency (VLF) signal, and the frequency is the same as the external VLF signal. Atoms are manipulated by pump and probe lasers. The pump laser is σ+ circularly polarized light, which resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF = +1, the atom will be pumped to m under the action of the circularly polarized pump laser. f =F max Polarization is achieved at the quantum state with the largest magnetic quantum number, with the system's quantization axis along the driving laser direction, and the polarized atom spin pointing in the positive z direction; for a main magnetic field of B e In the region where the polarized atomic spins point towards B... e Similarly, along the positive z-direction, for a principal magnetic field of -B e In the region where the polarized atomic spins point in the same direction as -B eConversely, also along the positive z-direction, very low frequency electromagnetic signals propagating in the xy-plane along the z-direction are absorbed by polarized atoms, causing the polarization vector to deviate from the z-direction and begin precessing around the z-axis at a frequency γBe, where γ is the gyromagnetic ratio of alkali metal atoms. The detection laser is linearly polarized, and its frequency is significantly detuned to the resonance frequency of the alkali metal atoms. Therefore, the absorption of the detection laser by the atomic ensemble is negligible, and dichroism plays a dominant role. The detection laser signal changes with the precession of atomic spin. When the received very low frequency signal is linearly polarized, according to the transition selection rule, polarized atoms in both magnetic field regions can absorb the electromagnetic signal, resulting in precession. Since the precession magnetic fields in the two regions are opposite, according to the right-hand rule, the precession directions of the atoms in the two regions are also opposite. Therefore, the precession of the detection light after passing through the two regions will cancel each other out, ultimately resulting in no signal. When the received signal is σ... - For circularly polarized signals, according to the transition selection rule, only B... e The atoms in the region will interact with the electromagnetic field under this polarization, thereby generating a precession signal, -B e There is no atomic precession signal in the region, and the detection laser passes through B. e With -B e B will be detected after the region. e The atomic precession of the region enables the detection of very low frequency signals; when the received signal is σ + For circularly polarized signals, according to the transition selection rule, only -B e The atoms in the region will interact with the electromagnetic field under this polarization, thereby generating a precession signal, B. e There is no atomic precession signal in the region, and the detection laser passes through B. e With -B e -B will be detected after the region. e The precession of atoms in the region enables the detection of very low frequency signals, thereby completing the environmental interference suppression of the very low frequency atomic magnetometer based on polarization-selective reception.

[0023] This configuration provides a method for suppressing environmental interference in very low frequency atomic magnetometers based on polarization-selective reception. In wireless communication, polarization-selective reception can improve signal selectivity and anti-interference capabilities, effectively suppressing noise interference. For example, in wireless communication, signals may be subject to various interferences during propagation. Using a polarization-selective receiving antenna can effectively distinguish and select the desired signal while effectively filtering out signals with other polarization states, thereby improving the purity of the received signal and enhancing communication quality. For instance, in satellite communication, selecting a specific polarization state can reduce interference caused by atmospheric and ground reflections; in radar systems, polarization characteristics can be used to distinguish targets from clutter, improving target detection accuracy; and in wireless networks, polarization selection can reduce signal attenuation and interference in multipath propagation environments. Based on this, this invention addresses the noise suppression problem of very low frequency (VLF) atomic magnetometers in unshielded environments by designing a polarization-selective dual-channel VLF atomic magnetometer scheme. This scheme can detect VLF magnetic field signals and, by cleverly utilizing the quantum mechanical law of conservation of angular momentum, enables the VLF atomic magnetometer to selectively receive the polarization state of radio frequency magnetic signals in a novel way. This achieves a novel VLF atomic magnetometer design that can suppress environmental noise, providing a new approach for suppressing environmental noise in unshielded VLF atomic magnetometers and thus enabling efficient wireless communication technology. Therefore, compared with existing technologies, the VLF atomic magnetometer environmental interference suppression method based on polarization-selective reception provided by this invention can achieve polarization-selective reception of VLF signals, enabling the separation and detection of specific circularly polarized signals; it can effectively suppress interference from linearly polarized noise in the environment; and based on specific polarized electromagnetic waves, it can achieve efficient anti-interference communication. Furthermore, based on the selective reception of circularly polarized electromagnetic waves, this invention can further determine the polarity of circular polarization through phase information, realizing the detection of two types of circularly polarized signals; the method and system are simple and easy to integrate into the miniaturized sensor.

[0024] Furthermore, the pump laser generated by the pump laser 10 passes sequentially through the first Glan Taylor prism 20 and the quarter-wave plate 30 before entering the atomic gas chamber 40. Through interaction with the alkali metal atoms in the atomic gas chamber 40, polarization of the alkali metal atoms is achieved. The probe laser generated by the probe laser 100 passes sequentially through the second half-wave plate 110, the second Glan Taylor prism 120, and the second reflector 130 before entering the atomic gas chamber 40. The detection laser emitted from the atomic gas chamber 40 is reflected by the first reflector 50, then passes through the first half-wave plate 60 and the Wollaston prism 70 before entering the balanced null detector 80. The signal acquired by the balanced null detector 80 is output to the data acquisition and control system 90. A three-axis magnetic field coil 140, a three-axis fluxgate 150, and a main magnetic field B are installed outside the atomic gas chamber 40. e Coil 160 and main magnetic field -Be Coil 170, main magnetic field B e Coil 160 is used to generate the main magnetic field B in the positive z direction. e Main magnetic field -B e Coil 170 is used to generate B e The main magnetic field -B in the opposite negative z-direction e When detecting very low frequency signals, the data acquisition and control system first controls the ambient magnetic field of the gas chamber based on the real-time measurement information of the triaxial fluxgate, so that the magnetic fields in the x, y, and z directions are zero; on this basis, the main magnetic field B... e Coil and Main Magnetic Field - B e The coil applies a resonant main magnetic field B of equal magnitude and opposite direction along the z-direction in two different regions of the gas chamber. e and -B e .

[0025] Specifically, in this invention, since the Faraday rotation angle θ of light is proportional to the polarization projection P of the spin ensemble in the x-direction... x That is: θ∝P x The Faraday rotation angle θ can be determined according to The calculations are as follows: I1 is the intensity of the first laser beam output from the Wollaston prism 70; I2 is the intensity of the second laser beam output from the Wollaston prism 70; and I0 = I1 + I2, where I0 is the sum of the intensities of the two laser beams. The detection laser passes sequentially through two atomic ensembles with opposite main magnetic fields. The signal output by the balanced null detector 80 is proportional to the polarization projection P of the spin ensemble in the x-direction. x P x = M1cos(ωt) - M2cos(ωt), where the amplitude M1 is the B of the atom under the action of a very low frequency signal. e The amplitude of the atomic precession signal in the main magnetic field region, M2 is the -B of the atom under the influence of the very low frequency signal. e The amplitude of the atomic precession signal in the main magnetic field region; for linearly polarized very low frequency signals, amplitudes M1 and M2 are equal, therefore the system does not respond to linearly polarized very low frequency signals; for σ + Circularly polarized very low frequency signals have only a main magnetic field of B. e The regional response, with a principal magnetic field of -B. e The region that does not respond, i.e., M2 = 0, is therefore the final detected signal is proportional to M1cos(ωt); for σ - Circularly polarized very low frequency signals have only a main magnetic field of -B. e Since there is a precession signal in the atomic region, M1 = 0. Therefore, the final output is proportional to -M2cos(ωt), thereby achieving selective reception of circularly polarized signals.

[0026] In this invention, for circularly polarized signals, the signals received by the system are 180° out of phase. Therefore, the polarization of the detected signal can be determined by the phase information, thereby further realizing the resolution of circular polarization. By polarization-selective reception, environmental linear polarization noise interference can be effectively suppressed, and a stronger anti-interference communication technology can be achieved based on a specific polarization.

[0027] According to another aspect of the present invention, a very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception is provided. This system uses the very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception described above to suppress very low frequency atomic magnetometer environmental interference.

[0028] This configuration provides an environmental interference suppression system for a very low frequency atomic magnetometer based on polarization-selective reception. This system enables polarization-selective reception of very low frequency signals, achieving the separation and detection of specific circularly polarized signals. It effectively suppresses interference from linearly polarized noise in the environment and achieves efficient anti-interference communication based on specific polarized electromagnetic waves. Furthermore, based on the selective reception of circularly polarized electromagnetic waves, this invention can further determine the polarity of circular polarization through phase information, realizing the detection of two types of circularly polarized signals. The method and system are simple and easily integrated into the miniaturized sensor.

[0029] Specifically, such as Figure 1 As shown, the environmental interference suppression system for a very low frequency atomic magnetometer based on polarization-selective reception includes a pump laser 10, a first Glan Taylor prism 20, a quarter-wave plate 30, an atomic gas cell 40, a first reflector 50, a first half-wave plate 60, a Wollaston prism 70, a balanced null detector 80, a data acquisition and control system 90, a probe laser 100, a second half-wave plate 110, a second Glan Taylor prism 120, a second reflector 130, a triaxial magnetic field coil 140, a triaxial fluxgate 150, and a main magnetic field B. e Coil 160 and main magnetic field -B e The pump laser generated by the pump laser 10 passes sequentially through the first Glan-Taylor prism 20 and the quarter-wave plate 30 before entering the atomic gas chamber 40. It interacts with the alkali metal atoms in the atomic gas chamber 40 to achieve polarization. The probe laser generated by the probe laser 100 passes sequentially through the second half-wave plate 110, the second Glan-Taylor prism 120, and the second reflector 130 before entering the atomic gas chamber 40. The detection laser emitted from the atomic gas chamber 40 is reflected by the first reflector 50, then passes through the first half-wave plate 60 and the Wollaston prism 70 before entering the balanced null detector 80. The signal acquired by the balanced null detector 80 is output to the data acquisition and control system 90. The system includes a three-axis magnetic field coil 140, a three-axis fluxgate 150, and a main magnetic field B.e Coil 160 and main magnetic field -B e Coil 170 is positioned outside atomic gas chamber 40, with main magnetic field B. e Coil 160 is used to generate the main magnetic field B in the positive z direction. e The main magnetic field - Be coil 170 is used to generate a magnetic field with B. e The main magnetic field -B in the opposite negative z-direction e .

[0030] To gain a further understanding of the present invention, the following description is provided in conjunction with... Figure 1 Figure 2 and the present invention provide a detailed description of the method and system for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization-selective reception.

[0031] like Figure 1 As shown in Figure 2, in order to solve the problem of environmental magnetic noise interference caused by very low frequency atomic magnetometers in practical application scenarios, this invention designs a dual-channel destructive very low frequency atomic magnetometer method and system based on the transition selection rule caused by the conservation of angular momentum. This enables polarization-selective reception of very low frequency radio signals, and based on this, specific radio polarization states can be used for transmission and reception, effectively suppressing environmental noise interference.

[0032] The technical solution adopted to achieve the above objectives is as follows: (1) Using a driving laser to polarize the alkali metal atoms in the atomic gas chamber along the driving laser direction (z direction); (2) The external magnetic field in the gas chamber is compensated by a triaxial magnetic coil and a triaxial magnetic sensor to provide a zero-field environment, and the precessing main magnetic field B is applied by the main magnetic field coil in the two regions before and after the gas chamber along the z direction and the -z direction, respectively. e and -B e (3) The x-direction uses a detection laser to simultaneously measure B. e With -B e The precession of the spin projection signal of the atoms in the region in the x direction is detected. The precession amplitude is proportional to the amplitude of the external very low frequency signal, and the frequency is the same as that of the external very low frequency signal, thereby realizing the detection of the very low frequency signal; (4) The external very low frequency signal interacts with the atoms polarized in the z direction, causing them to generate a precession signal in the xOy plane, which is then detected by the optical detector. When the external signal is linearly polarized, according to the selection rule of conservation of angular momentum, B e and -B e The atomic precession signals in the region cancel each other out, therefore the system does not respond to linearly polarized signals. For circularly polarized signals, only B... e Or -B e The atoms in the region will have precession signals, thus enabling the detection of circularly polarized signals.

[0033] The beneficial effects of this invention are: it can achieve polarization-selective reception of very low frequency signals and separation and detection of specific circularly polarized signals; it can effectively suppress interference from linearly polarized noise in the environment; and it can achieve efficient anti-interference communication based on specific polarized electromagnetic waves.

[0034] Additional beneficial effects: Based on the selection of receiving circularly polarized electromagnetic waves, this invention can further determine the polarity of circular polarization through phase information, realizing the two types of circularly polarized signals; the method and system are simple and easy to realize the miniaturization and integration of sensors.

[0035] The specific implementation principle of this scheme is as follows:

[0036] Very low frequency (VLF) atomic magnetometers utilize Larmor precession of atomic spins under resonance with the main magnetic field to detect the magnetic field component of VLF radio signals, thereby achieving VLF radio signal reception. This invention utilizes the superposition of precession signals from atomic spin ensembles with opposite main magnetic fields to achieve polarization-selective reception. The basic principle is shown in the figure. Atoms are manipulated by pump and probe light, with the pump light being σ... + Circularly polarized light resonates with the D1 line of an alkali metal atom. Due to the transition selection rule ΔF = +1, the atom will be pumped to m by the circularly polarized pump light. f =F max Polarization is achieved at the quantum state with the largest magnetic quantum number, with the system's quantization axis pointing along the driving light direction, and the polarized atom's spin pointing in the positive z direction. For the main magnetic field B... e In the region where the polarized atomic spins point towards B... e Same, along the positive z-direction. For, the principal magnetic field is -B. e In the region where the polarized atomic spins point in the same direction as -B e Conversely, it also occurs along the positive z-direction. Very low frequency electromagnetic signals propagating in the xy-plane along the z-direction are absorbed by polarized atoms, causing the polarization vector to deviate from the z-direction and begin to revolve around the z-axis at a frequency γB. e Precession, where γ is the gyromagnetic ratio of alkali metal atoms. The detection laser is linearly polarized, with a frequency significantly detuned to the resonance frequency of the alkali metal atoms. Therefore, the absorption of the detection laser by the atomic ensemble is negligible, and dichroism plays a dominant role. The detection light signal changes with the precession of atomic spin. When the received very low frequency signal is linearly polarized (as shown in Case 1 in the figure), according to the transition selection rule, polarized atoms in both magnetic field regions can absorb the electromagnetic signal, thus generating precession. Since the precession magnetic fields in the two regions are in opposite directions, according to the right-hand rule, the precession directions of the atoms in the two regions are also opposite. Therefore, the precession of the detection light after passing through the two regions will cancel each other out, ultimately resulting in no signal. When the received signal is σ... - In circular polarization (as shown in case 2 in the figure), by the transition selection rule, only B... eThe atoms in the region will interact with the electromagnetic field under this polarization, thereby generating a precession signal from -B. e There is no atomic precession signal in the region, and the detection light passes through B. e With -B e B will be detected after the region. e The atomic precession of the region enables the detection of very low frequency signals. And for σ... + Similarly, for circularly polarized signals (as shown in scenario three in the figure), only -B... e The region atoms interact with it, thereby enabling the detection of the polarization signal.

[0037] Physical implementation

[0038] A typical physical implementation structure is as follows Figure 1 As shown, the system mainly includes a pump laser, a probe laser, a quarter-wave plate, a half-wave plate, a Glan Taylor prism, a Wollaston prism, a triaxial magnetic compensation coil, a triaxial fluxgate, and a B-type magnetic flux gate. e Main magnetic field coil, -B e It consists of a main magnetic field coil, an atomic gas chamber, a reflector, a balanced zero-beat detector, and a data acquisition and control system.

[0039] Functions of each component

[0040] Pump laser: generates pump laser; Detection laser: generates detection laser; Quarter-wave plate: changes laser polarization, mainly used to convert linearly polarized light into circularly polarized light; Half-wave plate: changes laser polarization, mainly used to change the polarization direction of linearly polarized light; GranTeller prism: polarizes and splits the beam, used to purify the polarization of the transmitted laser, ensuring it is horizontally polarized (x-direction polarization); Wollaston prism: polarizes and splits the beam, separating vertically (y-direction) and horizontally (x-direction) polarized light in spatial propagation; Triaxial magnetic field coil: generates a three-axis magnetic field, controlled by the acquisition and control system to counteract interference from the ambient magnetic field; Triaxial fluxgate: used to detect the magnitude of the ambient magnetic field at the gas chamber in real time, with the result used as a feedback variable input to the acquisition and control system; Main magnetic field B e Coil: Used to generate the main magnetic field B in the positive z-direction. e Main magnetic field - B e Coil: Used to generate a connection with B e The main magnetic field -B in the opposite negative z-direction e Atomic gas cell: The core working device, providing an atomic ensemble for detecting very low frequency signals; Reflector: Changes the direction of the light beam; Balanced zero-beat detector: Converts the precession information detected by the detection light into a differential electrical signal for output; Data acquisition and control system: Acquires and processes data, and provides feedback control for the system.

[0041] Specific working methods

[0042] The pump laser generated by the pump laser is polarized and purified by a GranTeller prism. The transmitted light polarized in the x-direction is then converted into circularly polarized laser required by the very low frequency atomic magnetometer system by a quarter-wave plate and enters the gas cell. It is then polarized by interacting with the alkali metal atoms in the gas cell.

[0043] The laser beam emitted from the probe laser is purified by a GranTaylor mirror for polarization. It then enters the gas cell with linear polarization in the x-direction through a mirror. The transmitted light through the gas cell is modulated by a half-wave plate and then split into two orthogonally polarized laser beams by a Wollaston prism. The intensity of the two laser beams is related to the Faraday turn after passing through the gas cell, which can be specifically expressed as:

[0044]

[0045] Where I0 = I1 + I2 is the sum of the light intensities of the two laser beams, I1 is the light intensity of laser 1, and I2 is the light intensity of laser 2. θ is the Faraday rotation angle of the laser beam after passing through the gas cell, which is related to the polarization intensity of the gas cells atoms in the laser propagation direction. The light intensities of these two laser beams are received by two photodetectors of the subsequent balanced zero-beat detector. From the signals of these two photodetectors, the Faraday rotation angle can be obtained:

[0046]

[0047] Therefore, the differential result (I2-I1) output by the balanced zero-beat detector is directly proportional to the Faraday rotation angle θ. When detecting very low frequency signals, the data acquisition and control system first controls the ambient magnetic field of the gas chamber based on the real-time measurement information of the three-axis fluxgate, ensuring that the magnetic fields in the x, y, and z directions are zero. Based on this, the main magnetic field B... e Coil and Main Magnetic Field - B e The coil applies a resonant main magnetic field B of equal magnitude and opposite direction along the z-direction in two different regions of the gas chamber. e and -B e Since the Faraday rotation angle θ of light is proportional to the magnitude P of the polarization projection of the spin ensemble in the x-direction. x That is: θ∝P x Since the detection light passes through two atomic ensembles with opposite main magnetic fields sequentially, the signal output by the balanced zero-beat detector will be proportional to: P x = M1cos(ωt) - M2cos(ωt), where the amplitudes M1 and M2 are the B values ​​of the atom under the influence of a very low frequency signal. e Main magnetic field region and -B eThe amplitude of the atomic precession signal in the main magnetic field region. For linearly polarized very low frequency signals, according to the aforementioned principle, M1 = M2, therefore the system does not respond to linearly polarized very low frequency signals. For circularly polarized very low frequency signals, according to the aforementioned principle, for σ... + Polarization, only when the main magnetic field is B e The regional response, with a principal magnetic field of -B. e The region that does not respond, i.e., M2 = 0, is therefore the final detected signal is proportional to M1cos(ωt). Similarly, for σ... - Circular polarization occurs only when the main magnetic field is -B. e Since the atomic regions exhibit precession signals, M1 = 0. Therefore, the final output is proportional to -M2cos(ωt), thus achieving selective reception of circularly polarized signals. Furthermore, for circularly polarized signals, the signals received by this system are 180° out of phase. Therefore, the polarization of the detected signal can be determined through phase information, thereby further achieving circular polarization resolution. Through polarization-selective reception, environmental linear polarization noise interference can be effectively suppressed, and a more interference-resistant communication technology can be achieved based on specific polarization.

[0048] In summary, to address the environmental magnetic noise interference problem caused by very low frequency atomic magnetometers in practical applications, this invention designs a dual-channel destructive very low frequency atomic magnetometer method and system based on the transition selection rule caused by the conservation of angular momentum. This enables polarization-selective reception of very low frequency radio signals, and based on this, specific radio polarization states can be used for transmission and reception, effectively suppressing environmental noise interference.

[0049] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0050] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception, characterized in that, The method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception includes: The alkali metal atoms in the atomic gas chamber are polarized along the z-direction of the driving laser using a driving laser; the external magnetic field in the atomic gas chamber is compensated by a triaxial magnetic field coil and a triaxial magnetic sensor to provide a zero-field environment, which is provided by the main magnetic field B. e Coil (160) and main magnetic field -B e Coil (170) applies precessing main magnetic fields B of equal magnitude and opposite direction along the z-direction and -z-direction in two regions before and after the atomic gas cell, respectively. e and -B e The x-direction utilizes a detection laser to simultaneously measure B. e With -B e The precession of the spin projection signal of the atoms in the region in the x-direction is detected. The precession amplitude is proportional to the amplitude of the external very low frequency signal, and the frequency is the same as that of the external very low frequency signal. Atoms are manipulated by a pump laser and a probe laser. The pump laser is σ+ circularly polarized light, which resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF = +1, the atom will be pumped to m under the influence of the circularly polarized pump laser. f =F max Polarization is achieved at the quantum state with the largest magnetic quantum number, with the system's quantization axis along the driving laser direction, and the polarized atom spin pointing in the positive z direction; for a main magnetic field of B e In the region where the polarized atomic spins point towards B... e Similarly, along the positive z-direction, for a principal magnetic field of -B e In the region where the polarized atomic spins point in the same direction as -B e Conversely, also along the positive z-direction, very low frequency electromagnetic signals propagating in the xy-plane along the z-direction are absorbed by polarized atoms, causing the polarization vector to deviate from the z-direction and begin to revolve around the z-axis at a frequency γB. e Precession, γ is the gyromagnetic ratio of alkali metal atoms, the detection laser is linearly polarized, and the frequency is greatly detuned to the resonance frequency of alkali metal atoms. Therefore, the absorption of the detection laser by the atomic ensemble can be ignored, and the dichroic effect plays a dominant role. The detection laser signal will change with the precession of atomic spin. When the received very low frequency signal is linearly polarized, according to the transition selection rule, polarized atoms in both magnetic field regions can absorb the electromagnetic signal, thus generating precession. Since the precession magnetic fields in the two regions are in opposite directions, according to the right-hand rule, the precession directions of the atoms in the two regions are also opposite. Therefore, the precession of the detection light after passing through the two regions will cancel each other out, ultimately resulting in no signal. When the received signal is σ-circularly polarized, according to the transition selection rule, only B... e The atoms in the region will interact with the electromagnetic field under this polarization, thereby generating a precession signal, -B e There is no atomic precession signal in the region, and the detection laser passes through B. e With -B e B will be detected after the region. e The atomic precession in the region enables the detection of very low frequency signals; when the received signal is a σ+ circularly polarized signal, according to the transition selection rule, only -B... e The atoms in the region will interact with the electromagnetic field under this polarization, thereby generating a precession signal, B. e There is no atomic precession signal in the region, and the detection laser passes through B. e With -B e -B will be detected after the region. e The precession of atoms in the region enables the detection of very low frequency signals, thereby completing the environmental interference suppression of the very low frequency atomic magnetometer based on polarization-selective reception.

2. The method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception according to claim 1, characterized in that, The pump laser generated by the pump laser (10) passes through the first GranTeller prism (20) and the quarter-wave plate (30) in sequence before entering the atomic gas chamber (40). It achieves polarization of the alkali metal atoms by interacting with them. The probe laser generated by the probe laser (100) passes through the second half-wave plate (110), the second GranTeller prism (120), and the second reflector (130) in sequence before entering the atomic gas chamber (40). The detection laser emitted from the atomic gas chamber (40) is reflected by the first reflector (50), then passes through the first half-wave plate (60) and the Wollaston prism (70) before entering the balance null detector (80). The signal collected by the balance null detector (80) is output to the data acquisition and control system (90). A three-axis magnetic field coil (140), a three-axis fluxgate (150), and a main magnetic field B are set outside the atomic gas chamber (40). e Coil (160) and main magnetic field -B e Coil (170), the main magnetic field B e The coil (160) is used to generate the main magnetic field B in the positive z direction. e The main magnetic field -B e Coil (170) is used to generate B e The main magnetic field -B in the opposite negative z-direction e .

3. The method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception according to claim 2, characterized in that, Since the Faraday rotation angle θ of light is proportional to the magnitude P of the polarization projection of the spin ensemble in the x-direction. x That is: θ∝P x The detection laser passes sequentially through two atomic ensembles with opposite main magnetic fields. The signal output by the equilibrium zero-beat detector (80) is proportional to the polarization projection P of the spin ensemble in the x-direction. x P x = M1cos(ωt) - M2cos(ωt), where the amplitude M1 is the B of the atom under the action of a very low frequency signal. e The amplitude of the atomic precession signal in the main magnetic field region, M2 is the -B of the atom under the influence of the very low frequency signal. e The amplitude of the atomic precession signal in the main magnetic field region; for linearly polarized very low frequency signals, the amplitudes M1 and M2 are equal, therefore the system does not respond to linearly polarized very low frequency signals; for σ+ circularly polarized very low frequency signals, only when the main magnetic field is B... e The regional response, with a principal magnetic field of -B. e The region that does not respond, i.e., M2 = 0, is therefore the final detected signal is proportional to M1cos(ωt); for σ-circularly polarized very low frequency signals, only the main magnetic field is -B e Since there is a precession signal in the atomic region, M1 = 0. Therefore, the final output is proportional to -M2cos(ωt), thereby achieving selective reception of circularly polarized signals.

4. The method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception according to claim 3, characterized in that, For circularly polarized signals, the signals received by the system are 180° out of phase. Therefore, the polarization of the detected signal can be determined by the phase information, thereby further realizing the resolution of circular polarization. Polarization-selective reception can effectively suppress environmental linear polarization noise interference, while achieving stronger anti-interference communication technology based on specific polarization.

5. The method for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception according to claim 3, characterized in that, The Faraday rotation angle θ can be determined according to... The calculation yields I1, which is the light intensity of the first laser output by the Wollaston prism (70), I2, which is the light intensity of the second laser output by the Wollaston prism (70), and I0 = I1 + I2, where I0 is the sum of the light intensities of the two lasers.

6. A system for suppressing environmental interference in a very low frequency atomic magnetometer based on polarization-selective reception, characterized in that, The very low frequency atomic magnetometer environmental interference suppression system based on polarization-selective reception uses the very low frequency atomic magnetometer environmental interference suppression method based on polarization-selective reception as described in any one of claims 1 to 5 to suppress very low frequency atomic magnetometer environmental interference.

7. The environmental interference suppression system for a very low frequency atomic magnetometer based on polarization-selective reception according to claim 6, characterized in that, The very low frequency atomic magnetometer environmental interference suppression system based on polarization-selective reception includes a pump laser (10), a first Glan Taylor prism (20), a quarter-wave plate (30), an atomic gas cell (40), a first reflector (50), a first half-wave plate (60), a Wollaston prism (70), a balanced null detector (80), a data acquisition and control system (90), a probe laser (100), a second half-wave plate (110), a second Glan Taylor prism (120), a second reflector (130), a triaxial magnetic field coil (140), a triaxial fluxgate (150), and a main magnetic field B. e Coil (160) and main magnetic field -B e The coil (170) is pumped by the pump laser (10) and passes through the first Glan Taylor prism (20) and the quarter-wave plate (30) in sequence before entering the atomic gas cell (40). The pump laser interacts with the alkali metal atoms in the atomic gas cell (40) to achieve polarization of the alkali metal atoms. The detection laser generated by the detection laser (100) is reflected sequentially by the second half-wave plate (110), the second GranTeller prism (120), and the second reflector (130) before entering the atomic gas chamber (40). The detection laser emitted from the atomic gas chamber (40) is reflected by the first reflector (50), and then by the first half-wave plate (60) and the Wollaston prism (70) before entering the balanced null detector (80). The signal collected by the balanced null detector (80) is output to the data acquisition and control system (90). The three-axis magnetic field coil (140), the three-axis fluxgate (150), and the main magnetic field B e Coil (160) and the main magnetic field -B e The coil (170) is disposed outside the atomic gas chamber (40), and the main magnetic field B e The coil (160) is used to generate the main magnetic field B in the positive z direction. e The main magnetic field -B e Coil (170) is used to generate B e The main magnetic field -B in the opposite negative z-direction e .

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