Method and system for increasing the reception bandwidth of a very low frequency atomic magnetometer

Abstract

The application provides a method and system for improving the receiving bandwidth of a very low frequency atomic magnetometer, which polarizes alkali metal atoms in an atomic cell along the direction of a driving laser by using the driving laser; an external magnetic field at the cell is compensated by a three-axis magnetic coil and a three-axis magnetic sensor to provide a zero-field environment, and a main magnetic field B is applied to the coil in the direction of the driving light; the precession of the spin projection signal of the polarized atoms in the x direction is detected by using a detection laser in the x direction; an external very low frequency signal interacts with the atoms polarized in the z direction to make the atoms produce a precession signal in the xOy plane, so that the detection light is detected. After the detection light signal is collected, the control system feeds back a damping magnetic field to the atomic ensemble through the coil, and the bandwidth of the system is expanded by adjusting the feedback parameters while keeping the sensitivity unchanged. The technical scheme of the application solves the technical problem that high sensitivity and high bandwidth cannot be achieved simultaneously in the prior art.

Description

Technical Field

[0001] This invention relates to the field of quantum sensing technology, and in particular to a method and system for improving the receiving bandwidth of a very low frequency atomic magnetometer. Background Technology

[0002] In recent years, optically pumped alkali metal atomic magnetometers based on the Larmor precession effect of atomic spins under magnetic fields have been proven to be more sensitive to radio frequency magnetic fields than standard coil detection, especially in low-frequency radio waves such as the very low frequency band. The very low frequency atomic magnetometer technology based on the atomic magnetometer principle can achieve a sensitivity three orders of magnitude higher for the same effective sensing volume, providing a new approach to effectively solve the current bottleneck problem in the field of very low frequency communication.

[0003] The sensitivity of very low frequency (VLF) atomic magnetometers is related to the alkali metal spin relaxation time T². Achieving measurement sensitivity down to the ~fT level typically requires a relatively long alkali metal spin relaxation time T² (approximately ms). However, a longer relaxation time T² also means a longer time for the alkali metal atoms to recover to a standby state after one measurement and begin the next measurement. This implies a slower system response, or a narrower response bandwidth, characterized by the parameter Γ = 1 / T². Therefore, conventional VLF atomic magnetometers face the dilemma of not being able to simultaneously achieve high sensitivity and high bandwidth. For short-time signals or applications requiring good sensitivity over a high bandwidth, it is necessary to solve the problem of how to achieve high-bandwidth measurement capability without excessively sacrificing the sensitivity of the VLF atomic magnetometer. Summary of the Invention

[0004] This invention provides a method and system for improving the receiving bandwidth of a very low frequency atomic magnetometer, which can solve the technical problem that high sensitivity and high bandwidth cannot be achieved simultaneously in existing very low frequency atomic magnetometers.

[0005] According to one aspect of the present invention, a method for improving the receiving bandwidth of a very low frequency (VLF) atomic magnetometer is provided. The method includes: polarizing alkali metal atoms in an atomic chamber along the driving laser direction (z-direction) using a driving laser; providing a zero-field environment by compensating for an external magnetic field in the atomic chamber through a triaxial magnetic coil and a triaxial magnetic sensor; applying a main magnetic field B in the driving laser direction using the triaxial magnetic coil; detecting the precession of the spin projection signal of the polarized atoms in the x-direction using a detection laser, wherein the precession amplitude is proportional to the amplitude of the external VLF signal and the frequency is the same as the external VLF signal; and manipulating the atoms using the driving laser and the detection laser, wherein the driving laser is σ. + Circularly polarized light resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF = 1, the atoms will be pumped to m under the influence of the circularly polarized laser. FPolarization is achieved in the quantum state with the largest magnetic quantum number of F. The quantization axis of the system is along the direction of the driving light, and the spin of the polarized atoms points in the positive z direction. The main magnetic field is in the same direction as the driving laser, along the positive z direction, and has a magnitude of B. The very low frequency electromagnetic signal B0cos(ωt) propagating in the z direction and vibrating in the y direction will be absorbed by the polarized atoms, causing the polarization vector to deviate from the z direction and begin to precess around the z axis at a frequency γB, where γ is the gyromagnetic ratio of the alkali metal atom. The detection laser is linearly polarized, and its frequency is greatly detuned to the resonance frequency of the alkali metal atom. Therefore, the absorption of the detection laser by the atomic ensemble can be ignored, and the dichroism effect plays a dominant role. The detection light signal will change with the precession of the atomic spin. By adding a feedback magnetic field B in the x direction... fb =aP x Introducing the damping term aP x Where 'a' is the feedback parameter, a new dynamic equation for the system is constructed, and based on the new dynamic equation, the bandwidth parameter is transformed into Γ. eff =Γ+aγP z By adjusting the detection laser pump rate R pr This makes the detection laser pump rate R prr >>Γ, where Γ is the initial bandwidth parameter, to achieve bandwidth improvement without excessively sacrificing sensitivity.

[0006] Furthermore, the new kinetic equation of the system is: Among them, P x P represents the polarization projection intensity of alkali metal atoms in the x-direction. y Let γ be the y-axis polarization projection intensity of alkali metal atoms, γ be the gyromagnetic ratio of alkali metal atoms, B0 be the amplitude of the very low frequency electromagnetic signal, and P be the amplitude of the signal. z Γ represents the z-direction polarization projection intensity of alkali metal atoms, Γ is the initial bandwidth parameter, and a is the feedback parameter.

[0007] Furthermore, the pump laser generated by the pump laser passes sequentially through the first GlanTell prism and a quarter-wave plate before entering the atomic gas chamber. Through interaction with the alkali metal atoms in the atomic gas chamber, the alkali metal atoms are polarized. The probe laser generated by the probe laser passes sequentially through the second half-wave plate, the second GlanTell prism, and the second reflector before entering the atomic gas chamber. The detection laser emitted from the atomic gas chamber is reflected by the first reflector and then passes through the first half-wave plate and the Wollaston prism before entering the balanced null detector. The signal collected by the balanced null detector is output to the data acquisition and control system. A three-axis magnetic field coil and a three-axis fluxgate are set outside the atomic gas chamber.

[0008] Furthermore, regarding the very low frequency signal B... xWhen detecting cos(ωt), the data acquisition and control system first controls the magnetic field of the gas chamber environment based on the real-time measurement information of the three-axis fluxgate magnetometer, so that the magnetic fields in the x, y, and z directions are 0. On this basis, a main magnetic field of magnitude B is applied in the z direction by a three-dimensional magnetic field coil. 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 At this time, the signal output by the balanced zero-beat detector will be proportional to: P x =Mcos(ωt), where the amplitude M is the amplitude of the atomic precession signal under the action of a very low frequency signal; when the above signal is detected, the data acquisition and control system passes the signal through a triaxial magnetic field coil with a magnitude B fb =aP x Feedback is sent in the x-direction to extend the bandwidth of the very low frequency atomic magnetometer from Γ to Γ+aγP. z .

[0009] 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.

[0010] According to another aspect of the present invention, a very low frequency atomic magnetometer receiving bandwidth enhancement system is provided. This polarization-selective receiving system enhances the receiving bandwidth of a very low frequency atomic magnetometer using the very low frequency atomic magnetometer receiving bandwidth enhancement method described above.

[0011] Furthermore, the very low frequency atomic magnetometer receiving bandwidth enhancement system 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, and a triaxial fluxgate. The pump laser generated by the pump laser passes sequentially through the first Glan Taylor prism and the quarter-wave plate before entering the atomic gas cell. Through interaction with the alkali metal atoms in the atomic gas cell, polarization of the alkali metal atoms is achieved. The probe laser generated by the probe laser passes sequentially through... The laser beam emitted from the atomic gas chamber is reflected by the second half-wave plate, the second GranTeller prism, and the second reflector. After reflection by the first reflector, the laser beam passes through the first half-wave plate and the Wollaston prism before entering the balanced null detector. The signal collected by the balanced null detector is output to the data acquisition and control system. The three-axis magnetic field coil and the three-axis fluxgate are located outside the atomic gas chamber. The three-axis magnetic field coil generates a magnetic field in three directions, which is controlled by the data acquisition and control system to counteract the interference of the ambient magnetic field and provide a feedback magnetic field. The three-axis fluxgate is used to detect the magnitude of the ambient magnetic field at the atomic gas chamber in real time, and the result is used as a feedback variable input to the data acquisition and control system.

[0012] The present invention provides a method for improving the receiving bandwidth of a very low frequency (VLF) atomic magnetometer. This method can effectively improve the bandwidth while maintaining the sensitivity of the VLF atomic magnetometer. Based on the high-bandwidth VLF atomic magnetometer, rapid short-time signal acquisition can be achieved. By changing the feedback parameters, the bandwidth can be further narrowed to achieve a longer coherence time. The system is simple and easy to miniaturize and integrate. Based on the optical Bloch equation of atomic spin precession, the system bandwidth is increased from Γ to the effective bandwidth Γ by adjusting the damping effect. eff Meanwhile, by adjusting the detection optical power parameter, the detection bandwidth can be broadened without significantly reducing the sensitivity of the very low frequency atomic magnetometer. Attached Figure Description

[0013] 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.

[0014] Figure 1 A schematic diagram of a very low frequency atomic magnetometer receiving bandwidth enhancement system according to a specific embodiment of the present invention is shown.

[0015] The above figures include the following reference numerals:

[0016] 10. Pump laser; 20. First Glan-Taylor prism; 30. Quarter-wave plate; 40. Atomic gas cell; 50. First 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 Glan-Taylor prism; 130. Second mirror; 140. Triaxial magnetic field coil; 150. Triaxial fluxgate. Detailed Implementation

[0017] 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.

[0018] 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.

[0019] 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.

[0020] like Figure 1As shown, a method for improving the receiving bandwidth of a very low frequency (VLF) atomic magnetometer is provided according to a specific embodiment of the present invention. This method includes: polarizing alkali metal atoms in an atomic chamber along the driving laser direction (z-direction) using a driving laser; providing a zero-field environment by compensating for the external magnetic field in the atomic chamber through a triaxial magnetic coil and a triaxial magnetic sensor; applying a main magnetic field B in the driving laser direction using the triaxial magnetic coil; detecting the precession of the spin projection signal of the polarized atoms in the x-direction using a detection laser, the precession amplitude being proportional to the amplitude of the external VLF signal and the frequency being the same as the external VLF signal; manipulating the atoms using the driving laser and the detection laser, the driving laser being σ... + Circularly polarized light resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF = 1, the atoms will be pumped to m under the influence of the circularly polarized laser. F Polarization is achieved in the quantum state with the largest magnetic quantum number of F. The quantization axis of the system is along the direction of the driving light, and the spin of the polarized atoms points in the positive z direction. The main magnetic field is in the same direction as the driving laser, along the positive z direction, and has a magnitude of B. The very low frequency electromagnetic signal B0cos(ωt) propagating in the z direction and vibrating in the y direction will be absorbed by the polarized atoms, causing the polarization vector to deviate from the z direction and begin to precess around the z axis at a frequency γB, where γ is the gyromagnetic ratio of the alkali metal atom. The detection laser is linearly polarized, and its frequency is greatly detuned to the resonance frequency of the alkali metal atom. Therefore, the absorption of the detection laser by the atomic ensemble can be ignored, and the dichroism effect plays a dominant role. The detection light signal will change with the precession of the atomic spin. By adding a feedback magnetic field B in the x direction... fb =aP x Introducing the damping term aP x Where 'a' is the feedback parameter, a new dynamic equation for the system is constructed, and based on the new dynamic equation, the bandwidth parameter is transformed into Γ. eff =Γ+aγP z By adjusting the detection laser pump rate R pr This makes the detection laser pump rate R prr >>Γ, where Γ is the initial bandwidth parameter, to achieve bandwidth improvement without excessively sacrificing sensitivity.

[0021] Using this configuration, a method for improving the receiving bandwidth of a very low frequency atomic magnetometer is provided. This method uses a driving laser to polarize alkali metal atoms in the atomic gas chamber along the driving laser direction (z direction); 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. Then, the coil applies a main magnetic field B in the driving light direction; the detection laser is used in the x direction to detect the precession of the spin projection signal of the polarized atom in the x direction. The precession amplitude is proportional to the amplitude of the external very low frequency signal, and the frequency is the same as 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 atom polarized in the z direction to generate a precession signal in the xOy plane, which is then detected by the detection light. After the detection light signal is collected, the control system feeds it back to the atomic ensemble in the form of a damped magnetic field through the coil. The system bandwidth is expanded by adjusting the feedback parameters while keeping the sensitivity unchanged. Compared with existing technologies, the method for improving the receiving bandwidth of a very low frequency atomic magnetometer provided by this invention can effectively improve its bandwidth while maintaining the sensitivity of the very low frequency atomic magnetometer. Based on the high-bandwidth very low frequency atomic magnetometer, rapid short-time signal acquisition can be achieved. By changing the feedback parameters, the bandwidth can be further narrowed to achieve a longer coherence time. The system is simple and easy to miniaturize and integrate. Based on the optical Bloch equation of atomic spin precession, the system bandwidth is increased from Γ to the effective bandwidth Γ by adjusting the damping effect. eff Meanwhile, by adjusting the detection optical power parameter, the detection bandwidth can be broadened without significantly reducing the sensitivity of the very low frequency atomic magnetometer.

[0022] Furthermore, in this invention, the new kinetic equation of the system is: Among them, P x P represents the polarization projection intensity of alkali metal atoms in the x-direction. y Let γ be the y-axis polarization projection intensity of alkali metal atoms, γ be the gyromagnetic ratio of alkali metal atoms, B0 be the amplitude of the very low frequency electromagnetic signal, and P be the amplitude of the signal. z Γ represents the z-direction polarization projection intensity of alkali metal atoms, Γ is the initial bandwidth parameter, and a is the feedback parameter.

[0023] As a specific embodiment of the present invention, such as Figure 1As shown, 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, the alkali metal atoms are polarized. 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 and then passes through 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. A three-axis magnetic field coil 140 and a three-axis fluxgate 150 are set outside the atomic gas chamber 40.

[0024] Furthermore, in this invention, regarding the very low frequency signal B... x When detecting cos(ωt), the data acquisition and control system first controls the magnetic field of the gas chamber environment based on the real-time measurement information of the three-axis fluxgate magnetometer, so that the magnetic fields in the x, y, and z directions are 0. On this basis, a main magnetic field of magnitude B is applied in the z direction by a three-dimensional magnetic field coil. 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 At this time, the signal output by the balanced zero-beat detector will be proportional to: P x =Mcos(ωt), where the amplitude M is the amplitude of the atomic precession signal under the action of a very low frequency signal; when the above signal is detected, the data acquisition and control system passes the signal through a triaxial magnetic field coil with a magnitude B fb =aP x Feedback is sent in the x-direction to extend the bandwidth of the very low frequency atomic magnetometer from Γ to Γ+aγP. z .

[0025] Wherein, 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 70, I2 is the light intensity of the second laser output from the Wollaston prism 70, and I0 = I1 + I2, where I0 is the sum of the light intensities of the two laser beams.

[0026] According to another aspect of the present invention, a very low frequency atomic magnetometer receiving bandwidth enhancement system is provided. This polarization-selective receiving system enhances the receiving bandwidth of a very low frequency atomic magnetometer using the very low frequency atomic magnetometer receiving bandwidth enhancement method described above.

[0027] This configuration provides a system for enhancing the receiving bandwidth of a very low frequency atomic magnetometer. This system can effectively increase the bandwidth of the very low frequency atomic magnetometer while maintaining its sensitivity. Based on the high-bandwidth very low frequency atomic magnetometer, it can achieve rapid short-time signal acquisition. By changing the feedback parameters, the bandwidth can be further narrowed to achieve a longer coherence time. The system is simple and easy to miniaturize and integrate.

[0028] Specifically, in this invention, the very low frequency atomic magnetometer receiving bandwidth enhancement system 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, and a triaxial fluxgate 150. 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 cell 40. Through interaction with the alkali metal atoms in the atomic gas cell 40, polarization of the alkali metal atoms is achieved. The probe laser generated by the probe laser 100... The laser beam sequentially passes through 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 beam 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 collected by the balanced null detector 80 is output to the data acquisition and control system 90. The triaxial magnetic field coil 140 and the triaxial fluxgate 150 are located outside the atomic gas chamber 40. The triaxial magnetic field coil 140 is used to generate a magnetic field in three directions, which is controlled by the data acquisition and control system 90 to cancel the interference of the ambient magnetic field and provide a feedback magnetic field. The triaxial fluxgate 150 is used to detect the magnitude of the ambient magnetic field at the atomic gas chamber in real time, and the result is input into the data acquisition and control system 90 as a feedback variable.

[0029] To gain a further understanding of the present invention, the following description is provided in conjunction with... Figure 1 The present invention provides a detailed description of the method for improving the receiving bandwidth of a very low frequency atomic magnetometer.

[0030] like Figure 1 As shown, this invention proposes a method using feedback damping based on the optical Bloch equation for atomic spin precession. By adjusting the damping effect, the system bandwidth is increased from Γ to the effective bandwidth Γ. eff Meanwhile, by adjusting the detection optical power parameter, the detection bandwidth can be broadened without significantly reducing the sensitivity of the very low frequency atomic magnetometer.

[0031] Very low frequency (VLF) atomic magnetometers utilize the Larmor precession resonance principle of atomic spins to receive and detect VLF signals. Compared to traditional VLF magnetic field receiving antennas, they offer significant potential advantages in sensitivity and compact integration. However, as mentioned earlier, since VLF atomic magnetometers detect VLF signals through resonance, their effective bandwidth is limited by the resonant bandwidth, posing a challenge to the design and implementation of high-bandwidth VLF atomic magnetometers. To address these issues, this invention proposes a method and system for implementing a high-bandwidth VLF atomic magnetometer, which can effectively improve its receiving bandwidth while maintaining the same receiving sensitivity.

[0032] The technical solution adopted to achieve the above objectives is as follows: (1) The alkali metal atoms in the atomic gas chamber are polarized along the direction of the driving laser (z direction) using a driving laser; (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. Then, the coil applies a main magnetic field B in the direction of the driving light; (3) The precession of the spin projection signal of the polarized atom in the x direction is detected by a detection laser in the x direction. 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 atom polarized in the z direction, causing it to generate a precession signal in the xOy plane, which is then detected by the detection light. After the detection light signal is acquired, the control system feeds it back to the atomic ensemble in the form of a damped magnetic field through the coil. The system bandwidth is expanded by adjusting the feedback parameters, while the sensitivity remains unchanged.

[0033] The beneficial effects of this invention are: it can effectively improve the bandwidth of the very low frequency atomic magnetometer while keeping the sensitivity unchanged; based on the high bandwidth very low frequency atomic magnetometer, it can achieve rapid short-time signal acquisition.

[0034] Additional benefits: By changing the feedback parameters, the bandwidth can be further narrowed to achieve a longer coherence time; the system is simple and easy to miniaturize and integrate.

[0035] Implementation principle

[0036] The specific implementation principle of this scheme is as follows:

[0037] Very low frequency (VLF) atomic magnetometers utilize Larmor precession of atomic spins in resonance with the main magnetic field to detect the magnetic field component of VLF radio signals, thereby achieving the reception of VLF radio signals. The basic principle is as follows: Figure 1 As shown, atoms are manipulated by pump light 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 under the influence of the circularly polarized pump light. FPolarization is achieved in the quantum state with the largest magnetic quantum number of F. The quantization axis of the system is along the direction of the driving light, and the spin of the polarized atoms points in the positive z direction. The main magnetic field is in the same direction as the driving light, along the positive z direction, and has a magnitude of B. The very low frequency electromagnetic signal B0cos(ωt) propagating in the z direction and vibrating in the y direction is absorbed by the polarized atoms, causing the polarization vector to deviate from the z direction and begin to precess around the z axis at a frequency γB, where γ is the gyromagnetic ratio of the alkali metal atom. The detection laser is linearly polarized, and its frequency is greatly detuned to the resonance frequency of the alkali metal atom. Therefore, the absorption of the detection laser by the atomic ensemble is negligible, and the dichroism effect plays a dominant role. The detection light signal changes with the precession of the atomic spin. Its dynamic evolution is determined by the Bloch equation:

[0038]

[0039] Its bandwidth is the parameter Γ in the equation, while P x P represents the polarization projection intensity of alkali metal atoms in the x-direction. y P represents the y-direction polarization projection intensity of alkali metal atoms. z γ is the z-direction polarization projection intensity of alkali metal atoms, γ is the gyromagnetic ratio of alkali metal atoms, and B0 is the amplitude of the very low frequency electromagnetic signal.

[0040] In the above-mentioned ordinary Bloch equations, this invention adds a feedback magnetic field B in the x-direction. fb =aP x Introducing the damping term aP x Where 'a' is the feedback parameter, the new dynamic equations of the system are constructed as follows:

[0041]

[0042] Rewrite the above equation as follows:

[0043]

[0044] Comparing the above equation with the original equation, it can be seen that by using a negative feedback mechanism and adding a damping field, the bandwidth parameter P in this equation... x The coefficient before changed from Γ to Γ eff =Γ+aγP z This increases bandwidth.

[0045] The expression for sensitivity is:

[0046] Where n is the density of alkali metal atoms, V is the volume of atomic vapor, and R... pr To detect the laser pump rate (proportional to the detected optical power), OD is the optical thickness, and η is the detector quantum efficiency. This is achieved by adjusting parameter R. pr That is, to detect the laser power, so that R pr>>Γ, thus the sensitivity expression can be approximately simplified to: This is independent of Γ, thus achieving an increase in bandwidth without excessively sacrificing sensitivity.

[0047] Physical implementation

[0048] A typical physical implementation structure is as follows Figure 1 As shown, the system mainly consists of 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, an atomic gas cell, a mirror, a balanced null detector, and a data acquisition and control system.

[0049] Functions of each component

[0050] Pump laser: generates pump laser light; Detector laser: generates detection laser light; Quarter-wave plate: changes laser polarization, mainly used here to convert linearly polarized light into circularly polarized light; Half-wave plate: changes laser polarization, mainly used here to change the polarization direction of linearly polarized light; Glan-Taylor prism: polarizes and splits the beam, used here to purify the polarization of the transmitted laser, ensuring it is horizontally polarized (x-direction polarized); 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, and also provides a feedback magnetic field; Three-axis fluxgate: Used to detect the magnitude of the ambient magnetic field at the gas chamber in real time, and the result is input as a feedback variable into the acquisition and control system; Atomic gas chamber: The core working device, used to detect the atomic ensemble of 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.

[0051] Specific working methods

[0052] The pump laser generated by the pump laser is polarized and purified by a Glan Taylor prism. The transmitted light, polarized in the x-direction, is then converted into circularly polarized laser light required by the very low frequency atomic magnetometer system by a quarter-wave plate and enters the gas cell. Through interaction with the alkali metal atoms in the gas cell, the laser polarizes them.

[0053] 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:

[0054]

[0055] Where I0 = I1 + I2 is the sum of the light intensities of the two laser beams, I1 is the light intensity of laser 1, I2 is the light intensity of laser 2, and θ is the Faraday rotation angle of the laser 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:

[0056]

[0057] Therefore, the differential result (I2-I1) output by the balanced zero-beat detector is directly proportional to the Faraday rotation angle θ. I0 needs to be adjusted to be strong enough to ensure R pr >>When the condition is met, according to the aforementioned principle, under this condition the sensitivity of the very low frequency atomic magnetometer is independent of the bandwidth.

[0058] In the case of very low frequency signal B x When detecting cos(ωt), the data acquisition and control system first controls the magnetic field of the gas chamber environment based on the real-time measurement information of the three-axis fluxgate, so that the magnetic fields in the x, y, and z directions are zero. Based on this, a main magnetic field of magnitude B is applied in the z direction by three-dimensional magnetic field lines. 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 At this time, the signal output by the balanced zero-beat detector will be proportional to: P x =Mcos(ωt), where the amplitude M is the amplitude of the atomic precession signal under the influence of a very low frequency signal. Once the above signal is detected, the data acquisition and control system transmits the signal through a triaxial magnetic field coil with a magnitude B. fb =aP x Feedback in the x-direction, as described by the aforementioned principle, successfully extends the bandwidth of the very low frequency atomic magnetometer from Γ to Γ+aγP. z .

[0059] This invention, based on the optical Bloch equation for atomic spin precession, proposes a method for enhancing the receiving bandwidth of a very low frequency atomic magnetometer using feedback damping. By adjusting the damping effect, the system bandwidth is increased from Γ to the effective bandwidth Γ. eff Meanwhile, by adjusting the detection optical power parameter, the detection bandwidth can be broadened without significantly reducing the sensitivity of the very low frequency atomic magnetometer.

[0060] 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.

[0061] 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.

[0062] 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 improving the receiving bandwidth of a very low frequency atomic magnetometer, characterized in that, The method for improving the receiving bandwidth of the very low frequency atomic magnetometer includes: Alkali metal atoms in the atomic gas chamber are polarized along the direction of the driving laser, which is the z-direction, using a driving laser. The external magnetic field at the atomic gas chamber is compensated by a triaxial magnetic coil and a triaxial magnetic sensor to provide a zero-field environment; then the triaxial magnetic coil applies the main magnetic field B in the direction of driving the laser. The precession of the spin projection signal of polarized atoms in the x-direction is detected by a detection laser. 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 driving laser and a detection laser, with the driving laser being σ. + Circularly polarized light resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF=1, the atoms will be pumped to m under the influence of the circularly polarized laser. F Polarization is achieved in the quantum state with the largest magnetic quantum number of F. The quantization axis of the system is along the direction of the driving laser, and the spin of the polarized atoms points in the positive z direction. The main magnetic field is in the same direction as the driving laser, along the positive z direction, and has a magnitude of B. The very low frequency electromagnetic signal B0cos(ωt) propagating in the z direction and vibrating in the y direction will be absorbed by the polarized atoms, causing the polarization vector to deviate from the z direction and begin to revolve around the z axis at a frequency of γ B precession, γ The gyromagnetic ratio of alkali metal atoms; the detection laser is linearly polarized and its 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 light signal will change with the precession of atomic spin. By adding a feedback magnetic field B in the x-direction fb = aP x Introducing a damping term aP x ,in a For feedback parameters, P x To determine the polarization projection intensity of alkali metal atoms in the x-direction, a new kinetic equation for the system is constructed. Based on this new kinetic equation, the bandwidth parameter is transformed into... Γ eff =Γ+aγP z By adjusting the pumping rate of the detection laser R pr This enables the detection of laser pump rate R prr >>Γ, where Γ is the initial bandwidth parameter, to achieve bandwidth improvement without excessively sacrificing sensitivity.

2. The method for improving the receiving bandwidth of a very low frequency atomic magnetometer according to claim 1, characterized in that, The new kinetic equation of the system is: Among them, P x P represents the polarization projection intensity of alkali metal atoms in the x-direction. y Let γ be the y-axis polarization projection intensity of alkali metal atoms, γ be the gyromagnetic ratio of alkali metal atoms, B0 be the amplitude of the very low frequency electromagnetic signal, and P be the amplitude of the signal. z Γ represents the z-direction polarization projection intensity of alkali metal atoms, Γ is the initial bandwidth parameter, and a is the feedback parameter.

3. The method for improving the receiving bandwidth of a very low frequency atomic magnetometer according to claim 2, 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 mirror (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 mirror (50) and 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) and a three-axis fluxgate (150) are set outside the atomic gas chamber (40).

4. The method for improving the receiving bandwidth of a very low frequency atomic magnetometer according to claim 3, characterized in that, In the case of very low frequency signal B x cos( ωt During testing, the data acquisition and control system first controls the magnetic field of the air chamber environment based on the real-time measurement information of the three-axis fluxgate magnetometer, ensuring that the magnetic fields in the x, y, and z directions are zero. Then, a three-dimensional magnetic field coil applies a main magnetic field of magnitude B in the z direction. Due to the Faraday rotation angle of light... θ Proportional to the size of the polarization projection of the spin ensemble in the x-direction P x ,Right now: At this point, the signal output by the balanced zero-beat detector will be proportional to: P x =Mcos( ω t ), where the amplitude M is the amplitude of the atomic precession signal under the action of the very low frequency signal; when the above signal is detected, the data acquisition and control system passes the signal through a triaxial magnetic field coil with a magnitude B fb = aP x Feedback is sent in the x-direction to reduce the bandwidth of the very low frequency atomic magnetometer from Γ Expand to Γ+aγP z .

5. The method for improving the receiving bandwidth of a very low frequency atomic magnetometer according to claim 4, characterized in that, The Faraday rotation angle θ can be determined according to... The calculation yields I1, which is the intensity of the first laser output by the Wollaston prism (70), and I2, which is the intensity of the second laser output by the Wollaston prism (70). I0 is the sum of the light intensities of the two laser beams.

6. A system for enhancing the receiving bandwidth of a very low frequency atomic magnetometer, characterized in that, The polarization-selective reception-based very low frequency atomic magnetometer receiving bandwidth enhancement system uses the very low frequency atomic magnetometer receiving bandwidth enhancement method as described in any one of claims 1 to 5 to enhance the very low frequency atomic magnetometer receiving bandwidth.

7. The very low frequency atomic magnetometer receiving bandwidth enhancement system according to claim 6, characterized in that, The very low frequency atomic magnetometer receiving bandwidth enhancement system 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 three-axis magnetic field coil (140), and a three-axis fluxgate (150). 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 cell (40). Through interaction with the alkali metal atoms in the atomic gas cell (40), the alkali metal atoms are polarized. The probe laser generated by the probe laser (100) passes sequentially through the second half-wave plate (60) and the quarter-wave plate (70). After being reflected by the waveplate (110), the second GranTeller prism (120) and the second reflector (130), the laser emitted from the atomic gas chamber (40) is reflected by the first reflector (50), and then enters the balanced null detector (80) after passing through the first half-waveplate (60) and the Wollaston prism (70). The signal collected by the balanced null detector (80) is output to the data acquisition and control system (90). The triaxial magnetic field coil (140) and the triaxial fluxgate (150) are set outside the atomic gas chamber (40). The triaxial magnetic field coil (140) is used to generate a magnetic field in three directions, which is controlled by the data acquisition and control system (90) to cancel the interference of the ambient magnetic field and provide a feedback magnetic field. The triaxial fluxgate (150) is used to detect the magnitude of the ambient magnetic field at the atomic gas chamber in real time, and the result is input into the data acquisition and control system (90) as a feedback variable.

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