Conducting medium detection method and device

Abstract

The invention discloses a conductive medium detection method and device, the method is suitable for a transient magnetic field exciter, and the method comprises the steps: responding to a detection demand of a detected area, and applying a background field to an atomic gas chamber along a first direction parallel to a magnetic field coil; starting the first detection light and controlling the first detection light to pass through the atomic gas chamber along a second direction; synchronously starting the pump light and the magnetic field coil according to a preset detection frequency, controlling the pump light to penetrate through the magnetic field coil to enter the atomic gas chamber, and controlling the magnetic field coil to send a pulsed magnetic field to the detected area; and synchronously closing the pump light and the magnetic field coil in a preset time window to obtain second detection light generated after the first detection light passes through the atomic gas chamber, so as to obtain free induction attenuation signals of atoms in the atomic gas chamber and a detection result of a transient eddy current magnetic field, and determining a detection result of the conducting medium in the detected area according to the detection result. And the detection precision and the response rate are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive medium detection, and in particular to a conductive medium detection method and device. Background Art

[0002] Transient Electromagnetic Method (TEM) is one of the important technical means in the field of geophysical exploration. As a core branch of electromagnetic detection technology, TEM technology has the advantages of large detection depth, high resolution, and strong anti-interference ability. It plays an irreplaceable role in mineral resource exploration, environmental geological surveys, engineering geological evaluation, and military underground target detection.

[0003] In the 1950s, American scientist Dehmelt observed the free induction decay (FID) phenomenon in an alkali metal gas cell and proved that when there is an external magnetic field with a perpendicular polarization direction, the precession of the sodium atomic magnetic moment will modulate the absorption of circularly polarized probe light. As a result, people began to gradually use the FID phenomenon to measure external magnetic fields. In traditional FID magnetometer schemes, synchronous optical pumping is generally used to modulate the pump light, but this requires a prior judgment of the magnetic field size. When the actual magnetic field differs greatly from the estimated magnetic field, the sensitivity of the FID magnetometer will drop significantly. For this reason, the pump-enhanced FID magnetometer scheme came into being. In this magnetometer scheme, normal FID signal detection can be achieved by simply controlling the synchronous on and off of the pulsed magnetic field and the pump light without estimating the unknown magnetic field. This FID magnetometer scheme is particularly suitable for TEM systems, and no relevant research has been reported so far.

[0004] Traditional transient electromagnetic detection techniques often use pickup coils to receive magnetic field signals. However, these coils often suffer from insufficient sensitivity, resulting in low magnetic field measurement accuracy. Furthermore, conventional FID magnetometers for external magnetic field detection require real-time tracking of the Larmor frequency of the external magnetic field, making them difficult to use in environments with fluctuating magnetic fields. Furthermore, the closed-loop circuitry required to track the external magnetic field adds additional complexity to the FID magnetometer system. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention discloses a conductive medium detection method and system for improving the detection accuracy and the detection response rate.

[0006] To achieve the above-mentioned object, the present invention discloses a conductive medium detection method applicable to a transient magnetic field exciter; the transient magnetic field exciter comprises a magnetic shielding cylinder and an atomic gas chamber filled with atoms located inside the magnetic shielding cylinder; a group of magnetic field coils are symmetrically fixed at both axial ends of the atomic gas chamber; the method comprises:

[0007] In response to a detection requirement of a measured area, applying a background field to the atomic gas chamber along a first direction parallel to the magnetic field coil;

[0008] Starting a first detection light and controlling the first detection light to pass through the atomic gas chamber along a second direction parallel to the magnetic field coil and perpendicular to the first direction;

[0009] Synchronously starting the pump light and the magnetic field coil according to a preset detection frequency, controlling the pump light to pass through the magnetic field coil into the atomic gas chamber, and controlling the magnetic field coil to send a pulsed magnetic field to the measured area;

[0010] Synchronously turning off the pump light and the magnetic field coil within a preset time window to obtain a second detection light generated after the first detection light passes through the atomic gas chamber;

[0011] A free induction decay signal of atoms in the atomic gas chamber is obtained according to the second detection light to obtain a detection result of a transient eddy current magnetic field, and a detection result of the conductive medium in the measured area is determined according to the detection result.

[0012] The present invention discloses a method for detecting conductive media. This method utilizes the structural design of a magnetic shielding tube and symmetrical magnetic field coils, combined with the physical properties of an atomic gas chamber, to establish a highly sensitive magnetic field detection foundation. A background magnetic field is then applied in a specific direction to polarize the atomic magnetic moment, providing an initial state for subsequent magnetic field detection. Based on the detection requirements, a probe light is directly activated parallel to the magnetic field coil and perpendicular to the background field, ensuring that the probe light remains in the activated state. This not only utilizes the sensitivity of light-atom interactions to magnetic field changes to form a contactless measurement path, but also avoids detection re-response, thereby improving the detection response rate. The pump light and magnetic field coil are synchronously triggered. The pump light regulates the atomic energy state to enhance the magnetic moment precession response. Simultaneously, a pulsed magnetic field excites transient eddy currents in the measured area. The pump and magnetic field are then turned off within a preset time window, eliminating active excitation interference and capturing only the free induction decay signal. Transient magnetic field information is extracted by analyzing the phase changes of the probe light. The difference between the background field and the real-time magnetic field is used as the basis for eddy current magnetic field detection, directly determining the presence of the conductive medium. The entire process utilizes an open-loop detection method, avoiding the complexity of traditional closed-loop tracking systems while improving the accuracy of transient magnetic field detection through spatiotemporal synchronization.

[0013] As a preferred example, the step of starting the first detection light and controlling the first detection light to pass through the atomic gas chamber along a second direction parallel to the magnetic field coil and perpendicular to the first direction includes:

[0014] generating a first optical fiber light according to a wavelength corresponding to a first energy level transition line of atoms in the atomic gas chamber;

[0015] acquiring power jitter of the first optical fiber light, and performing power compensation on the first optical fiber light according to the power jitter to obtain second optical fiber light;

[0016] converting the second optical fiber light into a first spatial light and performing light intensity modulation on the first spatial light to obtain a first detection light;

[0017] acquiring a first angle between a propagation direction of the first detection light and the second direction, so as to determine a first reflection angle of the first detection light according to the first angle;

[0018] The first detection light is controlled to pass through the atomic gas chamber along the second direction according to the first reflection angle.

[0019] In the above scheme, multi-level regulation is used to achieve the stability and directional accuracy of the probe light. The pump light then pumps the atoms. A first fiber light of a specific wavelength is generated based on the atomic first-level transition line, ensuring that the probe light frequency matches the atomic absorption characteristics. This helps improve signal amplitude and, consequently, detection accuracy. Real-time monitoring of power jitter and dynamic compensation eliminate the impact of the light source's inherent fluctuations on measurement accuracy, resulting in a stable second fiber light. After converting the fiber light into spatial light, intensity regulation is performed to ensure that the probe light intensity meets the requirements for atomic gas cell interaction while avoiding signal distortion caused by intensity overload. By calculating the angle between the propagation direction and the target direction, the precise adjustment parameters of the reflector are determined, ensuring that the probe light strictly follows the predetermined path through the atomic gas cell, eliminating the degradation of spatial resolution caused by optical path deviation. These steps work together to form a closed-loop control loop, achieving high-precision optical path control while maintaining system simplicity.

[0020] As a preferred example, the synchronously starting the pump light and the magnetic field coil according to a preset detection frequency, controlling the pump light to pass through the magnetic field coil into the atomic gas chamber, and controlling the magnetic field coil to send a pulsed magnetic field to the measured area includes:

[0021] generating initial fiber light according to the wavelength corresponding to the second energy level transition line of the atom and synchronously applying a current signal to the magnetic field coil;

[0022] modulating the optical power of the initial fiber light to start the pump fiber light and convert the pump fiber light into pump spatial light;

[0023] obtaining a second angle between a propagation direction of the pump spatial light and a third direction perpendicular to the magnetic field coil;

[0024] determining a second reflection angle of the pumping space light according to the second included angle, so as to control the pumping space light to pass through the magnetic field coil and enter the atomic gas chamber according to the second reflection angle;

[0025] The magnetic field coil is controlled according to the current signal to send a pulsed magnetic field to the measured area along the third direction.

[0026] In this scheme, a coordinated control mechanism for the pump light and magnetic field coils is established to achieve temporal matching between magnetic field excitation and optical excitation, thereby controlling the synchronous activation and deactivation of the pump light and magnetic field, thereby improving detection accuracy. Initial fiber light is generated based on the atomic second-level transition line, ensuring that the pump light wavelength precisely matches the atomic energy level transition characteristics and avoiding energy loss caused by non-resonant excitation. The synchronous application of current signals synchronizes the magnetic field coil excitation with pump light generation, eliminating the time delay error associated with traditional step-by-step control. By modulating the optical power of the initial fiber light, the energy threshold of the pump light is precisely controlled, ensuring sufficient polarization of the atomic gas cell while avoiding optical power overload. The angle parameter between the propagation direction of the pump light in the spatial direction and the axial direction of the magnetic field coil is obtained. A dynamic reflection angle compensation mechanism is used to ensure precise alignment of the geometric axes of the pump beam and the magnetic field coil, ensuring that the pump light is perpendicular to the direction of the probe light, thereby enhancing atomic polarization and, consequently, detection accuracy. Finally, the magnetic field direction is controlled based on the current signal to ensure consistency between the pulsed magnetic field and the propagation direction of the pump light, achieving optimal detection results.

[0027] As a preferred example, the method of synchronously starting the pump light and the magnetic field coil according to a preset detection frequency, controlling the pump light to pass through the magnetic field coil into the atomic gas chamber, and controlling the magnetic field coil to send a pulsed magnetic field to the measured area further includes:

[0028] Expanding the beam spot of the pump spatial light and adjusting the intensity of the pump spatial light to obtain a first pump spatial light;

[0029] The first pump spatial light is converted into circularly polarized light, and the circularly polarized light is controlled to pass through the magnetic field coil along the third direction and enter the atomic gas chamber.

[0030] In the above scheme, the polarization efficiency of atoms is improved by optimizing the spatial distribution and polarization state of the pump light. First, expanding the beam spot of the pump space light can increase the interaction area between the pump light and the atoms in the atomic gas chamber, avoiding the saturation of atomic energy levels due to excessive local light intensity or the polarization unevenness caused by insufficient light intensity. Secondly, the intensity of the pump space light is regulated to ensure that the pump light power is in the optimal polarization efficiency range, avoiding both the inability to effectively polarize atoms due to too low power and the nonlinear effects caused by too high power. Finally, the regulated pump light is converted into circularly polarized light, and the angular momentum matching characteristics of circularly polarized light and atomic magnetic moment are used to enhance the optical pumping effect, so that the atoms form a macroscopic magnetic moment along a specific direction, thereby improving the response sensitivity to external transient magnetic fields. By precisely controlling the propagation path of the circularly polarized light along the third direction, it is ensured that the pump light and the pulsed magnetic field generated by the magnetic field coil act synergistically in space, further enhancing the excitation and detection capabilities of the transient eddy current magnetic field.

[0031] As a preferred example, obtaining a free induction decay signal of atoms in the atomic gas chamber according to the second detection light to obtain a detection result of a transient eddy current magnetic field, and determining a detection result of a conductive medium in the measured area according to the detection result, includes:

[0032] Extracting instantaneous phase information of the free induction decay signal to obtain the instantaneous precession frequency of the magnetic moment of the atom according to the instantaneous phase information;

[0033] obtaining the gyromagnetic ratio of the atoms, dividing the instantaneous precession frequency by the gyromagnetic ratio, and measuring the real-time magnetic field in the atomic gas chamber;

[0034] Obtaining comparison information between the real-time magnetic field and the background field, so as to obtain a detection result of the transient eddy current magnetic field according to the comparison information;

[0035] When the presence of the transient eddy current magnetic field is detected, it is determined that a conductive medium exists.

[0036] In the above scheme, the dynamic changes of the magnetic field are directly correlated through the phase characteristics of the free induction decay signal, so as to achieve high-precision detection of transient eddy current magnetic fields. Specifically, the instantaneous phase information of the free induction decay signal is extracted, and the phase change is used to directly reflect the instantaneous precession frequency of the atomic magnetic moment, avoiding the complex closed-loop control required for traditional frequency tracking. By dividing the instantaneous precession frequency by the known gyromagnetic ratio, the quantum mechanical behavior of the atomic magnetic moment can be directly converted into a macroscopic magnetic field intensity measurement value, thereby accurately obtaining the real-time magnetic field in the atomic gas chamber. By comparing the difference between the real-time magnetic field and the preset background field, the transient eddy current magnetic field component generated by the conductive medium in the measured area can be directly separated. When the transient eddy current magnetic field is detected, it can be determined that there is a conductive medium in the measured area. The entire process does not require the additional setting of a magnetic field feedback adjustment device. The complete characterization of the dynamic changes of the magnetic field can be completed through a single measurement, thereby reducing the difficulty of measurement.

[0037] On the other hand, the present invention also discloses a conductive medium detection device, comprising a background field coil, a detection light component, a pump light component, a transient magnetic field exciter, a signal converter, and a controller; wherein the transient magnetic field exciter comprises a magnetic shielding tube and an atomic gas chamber filled with atoms located inside the magnetic shielding tube; a group of magnetic field coils are symmetrically fixed at both axial ends of the atomic gas chamber; the background field coil is arranged inside the magnetic shielding tube along a first direction parallel to the magnetic field coil;

[0038] The background field coil is electrically connected to the controller, so that the controller controls the background field coil to apply a background field to the atomic gas chamber along the first direction in response to a detection requirement of the measured area;

[0039] The detection light assembly is connected to the controller by signal, so that the controller controls the detection light assembly to generate a first detection light and controls the detection light assembly to control the first detection light so that the first detection light passes through the atomic gas chamber along a second direction parallel to the magnetic field coil and perpendicular to the first direction;

[0040] The pump light assembly and the magnetic field coil are respectively connected to the controller signal so that the controller performs the following steps:

[0041] Synchronously controlling the pump light component to start pump light and synchronously controlling the magnetic field coil to send a pulsed magnetic field to the measured area according to a preset detection frequency;

[0042] controlling the pump light component to control the pump light so that the pump light passes through the magnetic field coil and enters the atomic gas chamber;

[0043] Controlling the pump light component to turn off the pump light and synchronously controlling the magnetic field coil to turn off the pulsed magnetic field within a preset time window;

[0044] The signal converter is connected to the controller signal, and is used to obtain a second detection light generated after the first detection light passes through the atomic gas chamber after the pump light and the magnetic field coil are turned off, and obtain a free induction decay signal of the atoms in the atomic gas chamber based on the second detection light, so as to send the free induction decay signal to the controller;

[0045] The controller receives the free induction decay signal and obtains a detection result of a transient eddy current magnetic field according to the free induction decay signal, so as to determine a detection result of the conductive medium in the measured area according to the detection result.

[0046] The present invention discloses a conductive medium detection device, which includes a transient magnetic field exciter comprising a magnetic shielding tube and an atomic gas chamber filled with atoms located within the magnetic shielding tube. A set of magnetic field coils are symmetrically fixed at both axial ends of the atomic gas chamber, and a background field coil is disposed within the magnetic shielding tube along a first direction parallel to the magnetic field coil. The background field coil is electrically connected to a controller to apply a background field. A detection light component generates and controls a first detection light to pass through the atomic gas chamber along a second direction. The pump light component and the magnetic field coil are synchronously controlled to transmit a pulsed magnetic field. A signal converter acquires the second detection light and extracts a free induction decay signal. The controller analyzes the transient eddy current magnetic field based on the signal and determines the presence of a conductive medium. A stable polarization reference is established by the background field coil, eliminating the need for dynamic tracking. An orthogonal optical path design is used to separate the pump and detection optical paths to prevent interference with the detection signal during the optical pumping process. Through the synergistic effect of pulsed magnetic field excitation and optical pumping with precisely controlled timing, the free precession signal is directly measured after the external excitation is turned off, retaining the high sensitivity characteristics of free induction decay while avoiding the system complexity brought about by closed-loop control.

[0047] As a preferred example, the detection light assembly includes a first laser, an optical power stabilization circuit, a first optical conversion assembly, and a first reflector arranged in sequence; wherein the first laser is signal-connected to the controller; the output end of the first laser is optically connected to the first input end of the optical power stabilization circuit via an optical fiber; the output end of the optical power stabilization circuit is optically connected to the input end of the first optical conversion assembly; the output end of the first optical conversion assembly is optically connected to the second input end of the optical power stabilization circuit; the output end of the first optical conversion assembly is optically connected to the input end of the first reflector; and the output end of the first reflector is optically connected to the input end of the atomic gas chamber;

[0048] The first laser is used to generate and emit first fiber light to the optical power stabilization circuit according to the wavelength corresponding to the first energy level transition line of the atom;

[0049] The optical power stabilization circuit obtains the power jitter of the first optical fiber light, performs power compensation on the first optical fiber light according to the power jitter, and outputs the second optical fiber light to the first optical conversion component;

[0050] The first optical conversion component is used to convert the second optical fiber light into a first spatial light and perform light intensity adjustment on the first spatial light, and output a first detection light to the first reflector;

[0051] The first reflector is used to reflect the first detection light so that the first detection light passes through the atomic gas chamber along the second direction;

[0052] The first reflector is connected to the controller signal so that the controller performs the following steps:

[0053] acquiring a first angle between a propagation direction of the first detection light and the second direction, so as to determine a first reflection angle of the first detection light according to the first angle;

[0054] Calculating a first reflector pitch angle and a first reflector reflection angle of the first reflector according to the first reflection angle;

[0055] The first reflector is controlled to be adjusted according to the pitch angle of the first reflector and the reflection angle of the first reflector, so that the light beam propagation direction of the first reflector coincides with the second direction.

[0056] In the above scheme, the first laser emits fiber light of a specific wavelength, which matches the atomic energy level transition line to ensure resonant detection. The optical power stabilization circuit monitors optical power fluctuations in real time via a photodetector. The PID circuit calculates compensation based on the fluctuation signal and controls the acousto-optic modulator to adjust the light intensity, eliminating the impact of light source jitter on the measurement. After the first collimator converts the fiber light into spatial light, the polarization direction is adjusted using a polarizer and a half-wave plate. The polarization beam splitter further adjusts the output light intensity to form stable linearly polarized detection light. The angle of the first reflector is adjusted by a controller that calculates the beam direction deviation in real time and drives the reflector to rotate to a predetermined angle, ensuring that the detection light propagates strictly perpendicular to the background magnetic field, avoiding measurement errors caused by optical path deviation. Precise control of the beam propagation direction ensures spatial alignment of the detection light with the atomic gas chamber, improving the accuracy of free induction decay signal extraction. The synergistic effect of the power stabilization circuit and the reflector adjustment mechanism enables the device to maintain stable detection performance even under complex environmental conditions.

[0057] As a preferred example, the first optical conversion component includes a first collimator, a first polarizer, a first half-wave plate and a first polarization beam splitter prism arranged in sequence along the propagation direction of the first optical fiber light;

[0058] The first optical conversion assembly includes a first collimator, a first polarizer, a first half-wave plate, and a first polarization beam splitter arranged in sequence along the propagation direction of the first optical fiber light beam; the input end of the first collimator is optically connected to the output end of the optical power stabilization circuit through an optical fiber; the input end of the first polarizer is optically connected to the output end of the first collimator; the input end of the first half-wave plate is optically connected to the output end of the first polarizer; the input end of the first polarization beam splitter is optically connected to the output end of the first half-wave plate; and the output end of the first polarization beam splitter is optically connected to the input end of the first reflector;

[0059] The first collimator is used to convert the second fiber light into first spatial light and send the first spatial light to the first polarization;

[0060] The first polarizer is used to convert the polarization dither of the first spatial light into power dither, and output the second spatial light to the first half-wave plate;

[0061] The first half-wave plate and the first polarization beam splitter prism are used to adjust the light intensity of the second spatial light and output the detection light to the first reflector.

[0062] In the above scheme, the first fiber light enters the first collimator after being compensated by the optical power stabilization circuit, where it is converted into a first spatial light with a defined propagation direction. The first polarizer converts the polarization jitter of the first spatial light into power jitter, forming a second spatial light. At this point, polarization noise is converted into a quantifiable power signal. When the second spatial light passes through the first half-wave plate, the polarization direction is changed by mechanically rotating the half-wave plate, thereby adjusting the transmitted light intensity and generating a third spatial light. After the third spatial light enters the first polarization beam splitter, one polarization component is reflected while the other is transmitted. By adjusting the incident angle, the direction of the transmitted beam is perpendicular to the detection path, ultimately forming a first detection light with stable light intensity and controlled propagation direction. These components work together to eliminate polarization noise through the polarization-power conversion mechanism, adjust the light intensity in stages, and avoid optical path interference through spatial direction control.

[0063] As a preferred example, the optical power stabilization circuit includes a first acousto-optic modulator, a PID circuit, and a photodetector; wherein the input end of the first acousto-optic modulator is optically connected to the first laser via an optical fiber; the output end of the first acousto-optic modulator is optically connected to the input end of the first collimator via an optical fiber; the photosensitive surface of the photodetector is disposed on the splitting optical path of the first polarization splitter prism; the input end of the PID circuit is electrically connected to the photodetector; and the output end of the PID circuit is electrically connected to the control end of the first acousto-optic modulator;

[0064] The input end of the first acousto-optic modulator is connected to the first laser light via an optical fiber, so as to obtain the first optical fiber light;

[0065] The photodetector is used to obtain the power jitter of the first detection light and input the power jitter into the PID circuit;

[0066] The PID circuit calculates a compensation power of the first fiber light according to the power jitter, and sends the compensation power to the first acousto-optic modulator, so that the first acousto-optic modulator performs power compensation on the first fiber light and outputs a second fiber light value to the first collimator.

[0067] In the above scheme, the photodetector collects the spectroscopic power signal of the detection light before entering the atomic gas chamber in real time, converts the optical power fluctuation into an electrical signal and transmits it to the PID circuit. The PID circuit calculates the RF drive power adjustment required for compensation based on the deviation between the preset power value and the actual detection value, and outputs a control signal to the RF driver of the first acousto-optic modulator. The first acousto-optic modulator dynamically adjusts the diffraction efficiency based on the compensation signal, performs power correction on the original optical fiber light, and forms a closed-loop negative feedback regulation. This process directly compensates for the actual detection light power entering the atomic gas chamber, eliminating the polarization-related loss introduced by components such as polarizers and wave plates in the optical path. The PID algorithm achieves a millisecond-level response speed, effectively suppresses high-frequency power jitter, and avoids the deviation problem between the laser output monitoring and the actual optical power of the gas chamber in traditional open-loop control.

[0068] As a preferred example, the pump light component includes a second laser, a second light conversion component and a second reflector arranged in sequence;

[0069] Wherein, the second laser is connected to the controller signal and is used to generate and emit initial fiber light according to the wavelength corresponding to the second energy level transition line of the atom;

[0070] The input end of the second optical conversion component is optically connected to the second laser, and is used to receive the initial fiber light and modulate the optical power of the initial fiber light to generate pump fiber light and convert the pump fiber light into pump spatial light;

[0071] The input end of the second reflector is optically connected to the output end of the second optical conversion component, and is used to adjust the propagation direction of the pumping space light so that the pumping space light passes through the magnetic field coil and enters the atomic gas chamber;

[0072] The second reflector is connected to the controller signal so that the controller performs the following steps:

[0073] obtaining a second angle between a propagation direction of the pump spatial light and a third direction perpendicular to the magnetic field coil;

[0074] determining a second reflection angle of the pump spatial light according to the second included angle, so as to calculate a second reflector pitch angle and a second reflector reflection angle of the second reflector according to the second reflection angle;

[0075] The second reflector is controlled to be adjusted according to the pitch angle of the second reflector and the reflection angle of the second reflector, so that the light beam propagation direction of the second reflector coincides with the third direction.

[0076] In the above scheme, the initial fiber optic light emitted by the second laser is processed for optical power stabilization by the second optical conversion component, and is converted into pump space light after real-time compensation for power fluctuations through the acousto-optic modulator. The propagation direction of the pump space light is determined by the reflection angle of the second reflector. The controller detects the deviation angle between the beam propagation direction and the axial direction of the magnetic field coil in real time, decomposes it into two independent parameters, the pitch angle and the reflection angle, and drives the reflector to perform precise angle adjustment in three-dimensional space. This closed-loop control mechanism does not rely on external optical tracking devices. It directly adjusts the pitch angle and reflection angle parameters of the reflector to achieve automatic calibration of the beam propagation path, ensuring that the pump light always propagates along the axial direction of the magnetic field coil. Precise control of the beam propagation direction enables the pump light to effectively cover the atoms in the atomic gas chamber, improve the atomic polarization efficiency, and avoid magnetic field excitation position errors caused by beam offset.

[0077] As a preferred example, the second light conversion component includes a second acousto-optic modulator and a second collimator arranged in sequence;

[0078] The input end of the second acousto-optic modulator is connected to the second laser via an optical fiber, and is used to modulate the optical power of the initial optical fiber light and output pump optical fiber light;

[0079] The output end of the second collimator is optically connected to the input end of the second reflector; the input end of the second collimator is connected to the output end of the second acousto-optic modulator through an optical fiber, and is used to receive the pump fiber light and convert the pump fiber light into pump spatial light, so as to send the pump spatial light to the second reflector.

[0080] In this solution, the pump fiber light is converted by a first collimator into a first spatial light with a defined propagation direction. This first spatial light is then transformed by a reflector into a pump light with stable intensity and controlled propagation direction. By controlling the propagation direction of the pump light, the atomic gas cell is affected, thereby improving detection accuracy.

[0081] As a preferred example, the conductive medium detection device further includes a third optical conversion component; wherein the third optical conversion component includes a beam expander, a second half-wave plate, a second polarization beam splitter prism and a quarter-wave plate arranged in sequence along the third direction; wherein the input end of the beam expander is optically connected to the output end of the second reflector; the input end of the second half-wave plate is optically connected to the output end of the beam expander; the input end of the second polarization beam splitter prism is optically connected to the output end of the second half-wave plate; the input end of the quarter-wave plate is optically connected to the output end of the second polarization beam splitter prism;

[0082] The beam expander is used to receive the pump spatial light and expand the beam spot of the pump spatial light, and send the pump spatial light with the expanded beam spot to the second half-wave plate;

[0083] The second half-wave plate and the second polarization beam splitter sequentially adjust the intensity of the pump spatial light with the expanded beam spot to obtain a first pump spatial light, and send the first pump spatial light to the quarter-wave plate;

[0084] The quarter-wave plate is used to convert the first pump spatial light into circularly polarized light, and control the circularly polarized light to pass through the magnetic field coil along the third direction and enter the atomic gas chamber.

[0085] In the above scheme, the collimated light beam is expanded through a beam expander to expand the beam spot size, thereby increasing the area of ​​interaction between light and atoms. This is beneficial to increasing the signal amplitude of the free induction decay signal and thus improving detection accuracy. The pump light intensity is then regulated by adjusting the optical axis angle of the half-wave plate through a combination of a half-wave plate and a polarization beam splitter. At the same time, the light polarization is purified and the beam is converted into linearly polarized light. The optical axis angle of the quarter-wave plate is adjusted to 45° with the polarization direction of the linearly polarized light to convert the linearly polarized light into circularly polarized light. Using circularly polarized light to achieve orientational polarization, so that the polarization direction is consistent with the propagation direction of the pump light, the macroscopic magnetic moment generated during Larmor precession has a projection in the direction of the probe light, thereby achieving optical rotation modulation of the probe light. The higher the circular polarization degree of the pump light, the larger the free induction decay signal, which improves the detection accuracy.

[0086] As a preferred example, the signal converter includes a third half-wave plate, a third polarization beam splitter prism, and a third reflector-balanced detector arranged in sequence; wherein the first photosensitive surface of the third reflector-balanced detector is arranged on the splitting optical path of the third polarization beam splitter prism;

[0087] The second photosensitive surface of the third reflector balance detector is arranged in the light beam propagation direction of the third reflector;

[0088] The three half-wave plates and the third polarization beam splitter prism are arranged in the extension direction of the second direction, and are used to receive the second detection light generated after the first detection light passes through the atomic gas chamber, and send the second detection light to the third reflector balance detector;

[0089] The third reflector is arranged in the light beam projection direction of the third polarization beam splitter prism, and is used to receive the second detection light projected by the third polarization beam splitter prism, and reflect the second detection light to the third reflector balance detector;

[0090] The third reflector balance detector is connected to the controller signal, and is used to obtain a free induction decay signal of atoms in the atomic gas chamber according to the second detection light, and send the free induction decay signal to the controller.

[0091] In the above scheme, when the probe light passes through the atomic gas chamber, its polarization direction rotates under the influence of the background field and eddy current magnetic field. It then passes through the optical rotation detection device composed of a half-wave plate and a polarization splitter prism. The corresponding optical rotation angle information is received by a balanced photodetector. A third reflector is provided to ensure that the projected probe light is also received by the balanced photodetector, thereby improving the accuracy of signal acquisition.

[0092] As a preferred example, the controller receives the free induction decay signal to perform the following steps:

[0093] Extracting instantaneous phase information of the free induction decay signal to obtain the instantaneous precession frequency of the magnetic moment of the atom according to the instantaneous phase information;

[0094] obtaining the gyromagnetic ratio of the atoms, dividing the instantaneous precession frequency by the gyromagnetic ratio, and measuring the real-time magnetic field in the atomic gas chamber;

[0095] Obtaining comparison information between the real-time magnetic field and the background field, so as to obtain a detection result of the transient eddy current magnetic field according to the comparison information;

[0096] When the presence of the transient eddy current magnetic field is detected, it is determined that a conductive medium exists.

[0097] In the above scheme, the controller directly associates the dynamic changes of the magnetic field with the phase characteristics of the free induction decay signal, thereby realizing high-precision detection of transient eddy current magnetic fields. Specifically, the instantaneous phase information of the free induction decay signal is extracted, and the phase change is used to directly reflect the instantaneous precession frequency of the atomic magnetic moment, thereby avoiding the complex closed-loop control required for traditional frequency tracking. By dividing the instantaneous precession frequency by the known gyromagnetic ratio, the quantum mechanical behavior of the atomic magnetic moment can be directly converted into a macroscopic magnetic field intensity measurement value, thereby accurately obtaining the real-time magnetic field in the atomic gas chamber. By comparing the difference between the real-time magnetic field and the preset background field, the transient eddy current magnetic field component generated by the conductive medium in the measured area can be directly separated. When the transient eddy current magnetic field is detected, it can be determined that there is a conductive medium in the measured area. The entire process does not require the additional setting of a magnetic field feedback adjustment device. The complete characterization of the dynamic changes of the magnetic field can be completed through a single measurement, thereby reducing the difficulty of measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the implementation. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0099] Figure 1 This is a flow chart of a conductive medium detection method provided by an embodiment of the present invention;

[0100] Figure 2 1 is a schematic structural diagram of a conductive medium detection device provided by an embodiment of the present invention;

[0101] Figure 3 1 is a schematic structural diagram of a conductive medium detection device provided by another embodiment of the present invention;

[0102] Figure 4 1 is a flow chart of a conductive medium detection method provided by another embodiment of the present invention;

[0103] Among them, 1. first laser; 2. first optical fiber; 3. first acousto-optic modulator; 4. second optical fiber; 5. first collimator; 6. first polarizer; 7. first half-wave plate; 8. first polarization beam splitter; 9. first photodetector; 10. second half-wave plate; 11. first reflector; 12. second polarizer; 13. second laser; 14. third optical fiber; 15. second acousto-optic modulator; 16. fourth optical fiber; 17. second collimator; 18. second reflector; 19. beam expander; 20. third half-wave plate; 21. second polarization beam splitter; 22. quarter-wave plate; 23. magnetic field coil; 24. atomic gas chamber; 25. aluminum block; 26. background field; 27. fourth half-wave plate; 28. third polarization beam splitter; 29. ​​third reflector; 30. balanced photodetector; 31. data processing module; 32. magnetic shielding tube; 33. PID. DETAILED DESCRIPTION

[0104] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0105] Example 1

[0106] In order to solve the technical problems of low detection accuracy and low detection response rate in the existing technology, Figure 1 This embodiment provides a conductive medium detection method applicable to a transient magnetic field exciter; the transient magnetic field exciter includes a magnetic shielding tube and an atomic gas chamber filled with atoms located inside the magnetic shielding tube; a group of magnetic field coils are symmetrically fixed at both axial ends of the atomic gas chamber; the method includes:

[0107] Step 101: In response to a detection requirement of a measured area, a background field is applied to the atomic gas cell along a first direction parallel to the magnetic field coil.

[0108] Step 102: Start a first detection light and control the first detection light to pass through the atomic gas cell along a second direction parallel to the magnetic field coil and perpendicular to the first direction.

[0109] In this embodiment, this step mainly includes: generating a first fiber light according to the wavelength corresponding to the first energy level transition line of the atoms in the atomic gas chamber; obtaining the power jitter of the first fiber light, and performing power compensation on the first fiber light according to the power jitter to obtain a second fiber light; converting the second fiber light into a first spatial light and performing light intensity adjustment on the first spatial light to obtain a first detection light; obtaining a first angle between the propagation direction of the first detection light and the second direction, and determining a first reflection angle of the first detection light according to the first angle; and controlling the first detection light to pass through the atomic gas chamber along the second direction according to the first reflection angle.

[0110] In this embodiment, the above steps achieve the stability and directional accuracy of the detection light through multi-level regulation. Then, due to the pumping effect of the pump light on the atoms, a first fiber light of a specific wavelength is generated based on the atomic first energy level transition line, ensuring that the detection light frequency matches the atomic absorption characteristics, which is conducive to improving the signal amplitude and thus the detection accuracy. By real-time monitoring of power jitter and dynamic compensation, the influence of the light source's own fluctuations on measurement accuracy is eliminated, and a stable second fiber light is obtained. After converting the fiber light into spatial light, light intensity regulation is performed to ensure that the detection light intensity meets the requirements of atomic gas chamber interaction and avoid signal distortion caused by light intensity overload. By calculating the angle between the propagation direction and the target direction, the precise adjustment parameters of the reflector are determined to ensure that the detection light strictly passes through the atomic gas chamber along the predetermined path, eliminating the problem of reduced spatial resolution caused by optical path deviation. Each step works together to form a closed-loop control, achieving high-precision optical path control while maintaining system simplicity.

[0111] Step 103: synchronously start the pump light and the magnetic field coil according to a preset detection frequency, control the pump light to pass through the magnetic field coil into the atomic gas chamber, and control the magnetic field coil to send a pulsed magnetic field to the measured area.

[0112] In this embodiment, this step mainly includes: generating initial fiber light according to the wavelength corresponding to the second energy level transition line of the atom and synchronously applying a current signal to the magnetic field coil; modulating the optical power of the initial fiber light to start pump fiber light and convert the pump fiber light into pump space light; obtaining a second angle between the propagation direction of the pump space light and a third direction perpendicular to the magnetic field coil; determining a second reflection angle of the pump space light according to the second angle, and controlling the pump space light to pass through the magnetic field coil and enter the atomic gas chamber according to the second reflection angle; and controlling the magnetic field coil to send a pulsed magnetic field to the measured area along the third direction according to the current signal.

[0113] In one implementation of this embodiment, the beam spot of the pump space light can be expanded and the intensity of the pump space light can be adjusted to obtain a first pump space light; the first pump space light is converted into circularly polarized light, and the circularly polarized light is controlled to pass through the magnetic field coil along the third direction and enter the atomic gas chamber.

[0114] In this embodiment, the above steps achieve temporal matching of magnetic field excitation and optical excitation by establishing a coordinated control mechanism for the pump light and magnetic field coil, thereby controlling the synchronous activation and deactivation of the pump light and magnetic field to improve detection accuracy. Initial fiber light is generated based on the atomic second-level transition line, ensuring that the wavelength of the pump light precisely matches the atomic energy-level transition characteristics and avoiding energy loss caused by non-resonant excitation. The synchronous application of the current signal synchronizes the timing of magnetic field coil excitation and pump light generation, eliminating the time delay error associated with traditional step-by-step control. By modulating the optical power of the initial fiber light, the energy threshold of the pump light is precisely controlled, ensuring sufficient polarization of the atomic gas cell while avoiding optical power overload. The angle parameter between the propagation direction of the pump light in the space and the axial direction of the magnetic field coil is obtained. A dynamic reflection angle compensation mechanism is used to ensure precise alignment of the geometric axes of the pump beam and the magnetic field coil, ensuring that the pump light is perpendicular to the direction of the probe light, thereby enhancing atomic polarization and, consequently, detection accuracy. Finally, the magnetic field direction is controlled based on the current signal to ensure consistency between the pulsed magnetic field and the propagation direction of the pump light, achieving optimal detection results. By optimizing the spatial distribution and polarization state of the pump light, the polarization efficiency of the atoms can be improved. First, expanding the beam spot of the pump space light can increase the interaction area between the pump light and the atoms in the atomic gas chamber, avoiding local excessive light intensity causing atomic energy level saturation or insufficient light intensity causing polarization unevenness. Secondly, the intensity of the pump space light is regulated to ensure that the pump light power is in the optimal polarization efficiency range, avoiding both the inability to effectively polarize the atoms due to too low power and the nonlinear effects caused by too high power. Finally, the regulated pump light is converted into circularly polarized light, and the angular momentum matching characteristics of circularly polarized light and atomic magnetic moment are used to enhance the optical pumping effect, causing the atoms to form a macroscopic magnetic moment along a specific direction, thereby improving the response sensitivity to external transient magnetic fields. By precisely controlling the propagation path of the circularly polarized light along the third direction, it is ensured that the pump light and the pulsed magnetic field generated by the magnetic field coil act synergistically in space, further enhancing the excitation and detection capabilities of the transient eddy current magnetic field.

[0115] Step 104: Synchronously turning off the pump light and the magnetic field coil within a preset time window to obtain a second detection light generated after the first detection light passes through the atomic gas chamber.

[0116] Step 105: obtaining a free induction decay signal of atoms in the atomic gas chamber according to the second detection light to obtain a detection result of a transient eddy current magnetic field, and determining a detection result of the conductive medium in the detected area according to the detection result.

[0117] In this embodiment, this step mainly includes: extracting the instantaneous phase information of the free induction decay signal to obtain the instantaneous precession frequency of the magnetic moment of the atom according to the instantaneous phase information; obtaining the gyromagnetic ratio of the atom to divide the instantaneous precession frequency by the gyromagnetic ratio to measure the real-time magnetic field in the atomic gas chamber; obtaining comparison information between the real-time magnetic field and the background field to obtain the detection result of the transient eddy current magnetic field according to the comparison information; when the presence of the transient eddy current magnetic field is detected, it is determined that a conductive medium exists.

[0118] In this embodiment, the above steps are directly associated with the dynamic changes of the magnetic field through the phase characteristics of the free induction decay signal, thereby realizing high-precision detection of the transient eddy current magnetic field. Specifically, the instantaneous phase information of the free induction decay signal is extracted, and the phase change is used to directly reflect the instantaneous precession frequency of the atomic magnetic moment, thereby avoiding the complex closed-loop control required for traditional frequency tracking. By dividing the instantaneous precession frequency by the known gyromagnetic ratio, the quantum mechanical behavior of the atomic magnetic moment can be directly converted into a macroscopic magnetic field intensity measurement value, thereby accurately obtaining the real-time magnetic field in the atomic gas chamber. By comparing the difference between the real-time magnetic field and the preset background field, the transient eddy current magnetic field component generated by the conductive medium in the measured area can be directly separated. When the transient eddy current magnetic field is detected, it can be determined that there is a conductive medium in the measured area. The entire process does not require the additional setting of a magnetic field feedback adjustment device. The complete characterization of the dynamic changes of the magnetic field can be completed through a single measurement, thereby reducing the difficulty of measurement.

[0119] On the other hand, refer to Figure 2 This embodiment also discloses a conductive medium detection device, which mainly includes a background field coil 201, a detection light component 202, a pump light component 203, a transient magnetic field exciter 204, a signal converter 205 and a controller 206; wherein the transient magnetic field exciter 204 includes a magnetic shielding tube and an atomic gas chamber filled with atoms located inside the magnetic shielding tube; a group of magnetic field coils are symmetrically fixed at both axial ends of the atomic gas chamber; the background field coil 201 is arranged inside the magnetic shielding tube along a first direction parallel to the magnetic field coil;

[0120] It should be noted that, from Figure 2 It can be seen that different modules have different connection methods. There are optical connections and signal connections between modules, and the different connection methods are displayed on the connection lines between modules.

[0121] The background field coil 201 is electrically connected to the controller 206, so that the controller 206 controls the background field coil 201 to apply a background field to the atomic gas chamber along the first direction in response to a detection requirement of the measured area;

[0122] The detection light assembly 202 is signal-connected to the controller 206, so that the controller 206 controls the detection light assembly 202 to generate a first detection light and controls the detection light assembly 202 to control the first detection light so that the first detection light passes through the atomic gas chamber along a second direction parallel to the magnetic field coil and perpendicular to the first direction;

[0123] The pump light assembly 203 and the magnetic field coil are respectively connected to the controller 206 for signal communication, so that the controller 206 performs the following steps:

[0124] Synchronously controlling the pump light component 203 to start pump light and synchronously controlling the magnetic field coil to send a pulsed magnetic field to the measured area according to a preset detection frequency;

[0125] controlling the pump light component 203 to control the pump light so that the pump light passes through the magnetic field coil and enters the atomic gas chamber;

[0126] Controlling the pump light component 203 to turn off the pump light and synchronously controlling the magnetic field coil to turn off the pulsed magnetic field within a preset time window;

[0127] The signal converter 205 is signal-connected to the controller 206, and is configured to obtain a second detection light generated after the first detection light passes through the atomic gas chamber after the pump light and the magnetic field coil are turned off, and obtain a free induction decay signal of the atoms in the atomic gas chamber based on the second detection light, so as to send the free induction decay signal to the controller 206;

[0128] The controller 206 receives the free induction decay signal and obtains a detection result of the transient eddy current magnetic field according to the free induction decay signal, so as to determine a detection result of the conductive medium in the detected area according to the detection result.

[0129] In one implementation of the present embodiment, in order to improve the accuracy of the detection light component, the detection light component 202 is provided to include a first laser, an optical power stabilization circuit, a first optical conversion component and a first reflector arranged in sequence; wherein, the first laser is signal-connected to the controller 206; the output end of the first laser is optically connected to the first input end of the optical power stabilization circuit through an optical fiber; the output end of the optical power stabilization circuit is optically connected to the input end of the first optical conversion component; the output end of the first optical conversion component is optically connected to the second input end of the optical power stabilization circuit; the output end of the first optical conversion component is optically connected to the input end of the first reflector; the output end of the first reflector is optically connected to the second input end of the optical power stabilization circuit; the output end of the first optical conversion component is optically connected to the input end of the first reflector; The output end is optically connected to the input end of the atomic gas chamber; the first laser is used to generate and emit a first fiber light to the optical power stabilization circuit according to the wavelength corresponding to the first energy level transition line of the atom; the optical power stabilization circuit obtains the power jitter of the first fiber light, and performs power compensation on the first fiber light according to the power jitter, and outputs a second fiber light to the first optical conversion component; the first optical conversion component is used to convert the second fiber light into a first spatial light and perform optical intensity adjustment on the first spatial light, and output a first detection light to the first reflector; the first reflector is used to reflect the first detection light so that the first detection light passes through the atomic gas chamber along the second direction;

[0130] The first reflector is connected to the controller 206 by signal so that the controller 206 performs the following steps: obtaining a first angle between the propagation direction of the first detection light and the second direction to determine a first reflection angle of the first detection light based on the first angle; calculating a first reflector pitch angle and a first reflector reflection angle of the first reflector based on the first reflection angle; and controlling the first reflector to adjust according to the first reflector pitch angle and the first reflector reflection angle so that the light beam propagation direction of the first reflector coincides with the second direction.

[0131] In the implementation scheme provided in this embodiment, the first laser emits fiber light of a specific wavelength, which matches the atomic energy level transition line to ensure the resonance detection effect. The optical power stabilization circuit monitors the optical power fluctuation in real time through a photodetector. The PID circuit calculates the compensation amount based on the fluctuation signal and controls the acousto-optic modulator to adjust the light intensity, eliminating the influence of light source jitter on the measurement. After the first collimator converts the fiber light into spatial light, the polarization direction is adjusted by a polarizer and a half-wave plate. The polarization splitter prism further adjusts the output light intensity to form a stable linear polarized detection light. The angle adjustment of the first reflector is achieved by calculating the beam direction deviation in real time through the controller, driving the reflector to rotate to a predetermined angle, ensuring that the detection light strictly propagates in a direction perpendicular to the background magnetic field, avoiding measurement errors caused by optical path deviation. Among them, the precise control of the beam propagation direction ensures the spatial alignment of the detection light and the atomic gas chamber, improving the extraction accuracy of the free induction decay signal. The synergistic effect of the power stabilization circuit and the reflector adjustment mechanism enables the device to maintain stable detection performance under complex environmental conditions.

[0132] In one implementation of this embodiment, in order to improve the accuracy of detection based on the detection light, the first optical conversion component is provided, including a first collimator, a first polarizer, a first half-wave plate and a first polarization beam splitter arranged in sequence along the propagation direction of the light beam of the first optical fiber light; wherein the input end of the first collimator is optically connected to the output end of the optical power stabilization circuit through an optical fiber; the input end of the first polarizer is optically connected to the output end of the first collimator; the input end of the first half-wave plate is optically connected to the output end of the first polarizer; the input end of the first polarization beam splitter is optically connected to the output end of the first polarizer; the input end of the first polarization beam splitter is optically connected to the output end of the first half-wave plate; the output end of the first polarization beam splitter is optically connected to the input end of the first reflector; the first collimator is used to convert the second optical fiber light into first spatial light and send the first spatial light to the first polarization; the first polarizer is used to convert the polarization jitter of the first spatial light into power jitter and output the second spatial light to the first half-wave plate; the first half-wave plate and the first polarization beam splitter are used to perform light intensity adjustment on the second spatial light and output the detection light to the first reflector.

[0133] In the implementation scheme provided in this embodiment, the first optical fiber light enters the first collimator after being compensated by the optical power stabilization loop and is converted into a first spatial light with a determined propagation direction. The first polarizer converts the polarization jitter of the first spatial light into power jitter to form a second spatial light. At this time, the polarization noise is converted into a quantifiable power signal. When the second spatial light passes through the first half-wave plate, the polarization direction is changed by mechanically rotating the half-wave plate, thereby adjusting the transmitted light intensity to generate a third spatial light. After the third spatial light enters the first polarization beam splitter prism, one polarization component is reflected and the other polarization component is transmitted. By adjusting the incident angle, the direction of the transmitted light beam is perpendicular to the detection path, ultimately forming a first detection light with stable light intensity and controlled propagation direction. The various components work together to eliminate polarization noise through the polarization-power conversion mechanism, adjust the light intensity in stages, and avoid optical path interference through spatial direction control.

[0134] In one embodiment of the present invention, to reduce instability of light during transmission, an optical power stabilization circuit is provided, including a first acousto-optic modulator, a PID circuit, and a photodetector. The input end of the first acousto-optic modulator is optically connected to a first laser via an optical fiber. The output end of the first acousto-optic modulator is optically connected to an input end of a first collimator via an optical fiber. The photosensitive surface of the photodetector is disposed on the splitting optical path of the first polarization beam splitter. The input end of the PID circuit is electrically connected to the photodetector. The output end of the PID circuit is electrically connected to a control end of the first acousto-optic modulator. The input end of the first acousto-optic modulator is optically connected to a first laser via an optical fiber for acquiring the first fiber light. The photodetector is configured to acquire power jitter of the first detection light and input the power jitter into the PID circuit. The PID circuit calculates a compensation power of the first fiber light based on the power jitter and transmits the compensation power to the first acousto-optic modulator, so that the first acousto-optic modulator performs power compensation on the first fiber light and outputs a second fiber light value to the first collimator.

[0135] In the implementation scheme provided in this embodiment, the photodetector collects the split power signal of the detection light before entering the atomic gas chamber in real time, converts the optical power fluctuation into an electrical signal and transmits it to the PID circuit. The PID circuit calculates the RF drive power adjustment required for compensation based on the deviation between the preset power value and the actual detection value, and outputs a control signal to the RF driver of the first acousto-optic modulator. The first acousto-optic modulator dynamically adjusts the diffraction efficiency based on the compensation signal, performs power correction on the original optical fiber light, and forms a closed-loop negative feedback regulation. This process directly compensates for the actual detection light power entering the atomic gas chamber, eliminating the polarization-related loss introduced by components such as polarizers and wave plates in the optical path. The PID algorithm is used to achieve a millisecond-level response speed, effectively suppress high-frequency power jitter, and avoid the deviation problem between the laser output monitoring and the actual optical power of the gas chamber in traditional open-loop control.

[0136] In one implementation of this embodiment, the pump light component 203 is configured to include a second laser, a second optical conversion component, and a second reflector arranged in sequence; wherein the second laser is signal-connected to the controller 206 and is configured to generate and emit initial fiber light according to the wavelength corresponding to the second energy level transition line of the atom; an input end of the second optical conversion component is optically connected to the second laser and is configured to receive the initial fiber light and modulate the optical power of the initial fiber light to generate pump fiber light and convert the pump fiber light into pump space light; an input end of the second reflector is optically connected to an output end of the second optical conversion component and is configured to adjust a propagation direction of the pump space light so that the pump space light passes through the magnetic field coil and enters the atomic gas chamber; and the second reflector is signal-connected to the controller 206 so that the controller 206 performs the following steps:

[0137] Obtain a second angle between the propagation direction of the pump spatial light and a third direction perpendicular to the magnetic field coil; determine a second reflection angle of the pump spatial light according to the second angle, and calculate a second reflector pitch angle and a second reflector reflection angle of the second reflector according to the second reflection angle; and control the second reflector to adjust according to the second reflector pitch angle and the second reflector reflection angle so that the beam propagation direction of the second reflector coincides with the third direction.

[0138] In the implementation scheme provided in this embodiment, the initial fiber optic light emitted by the second laser is subjected to optical power stabilization processing by the second optical conversion component, and is converted into pump space light after real-time compensation of power fluctuations by the acousto-optic modulator. The propagation direction of the pump space light is determined by the reflection angle of the second reflector. The controller detects the deviation angle between the propagation direction of the light beam and the axial direction of the magnetic field coil in real time, decomposes it into two independent parameters, the pitch angle and the reflection angle, and drives the reflector to perform precise angle adjustment in three-dimensional space. This closed-loop control mechanism does not rely on an external optical tracking device, and directly adjusts the pitch angle and reflection angle parameters of the reflector to achieve automatic calibration of the light beam propagation path, ensuring that the pump light always propagates along the axial direction of the magnetic field coil. The precise control of the light beam propagation direction enables the pump light to effectively cover the atoms in the atomic gas chamber, improve the atomic polarization efficiency, and avoid the magnetic field excitation position error caused by beam offset.

[0139] In one implementation of this embodiment, the second optical conversion component includes a second acousto-optic modulator and a second collimator arranged in sequence; wherein the input end of the second acousto-optic modulator is connected to the second laser via an optical fiber, and is used to modulate the optical power of the initial optical fiber light and output pump optical fiber light; the output end of the second collimator is optically connected to the input end of the second reflector; and the input end of the second collimator is connected to the output end of the second acousto-optic modulator via an optical fiber, and is used to receive the pump optical fiber light and convert the pump optical fiber light into pump spatial light, so as to transmit the pump spatial light to the second reflector.

[0140] In the implementation scheme provided in this embodiment, pump fiber light is converted by a first collimator into first spatial light with a defined propagation direction. This first spatial light is then transformed by a reflector into pump light with stable intensity and controlled propagation direction. By controlling the propagation direction of the pump light, the atomic gas cell is affected, thereby improving detection accuracy.

[0141] In one embodiment of the present invention, a third optical conversion component is provided in the conductive medium detection; wherein the third optical conversion component includes a beam expander, a second half-wave plate, a second polarization beam splitter prism, and a quarter-wave plate arranged in sequence along the third direction; wherein the input end of the beam expander is optically connected to the output end of the second reflector; the input end of the second half-wave plate is optically connected to the output end of the beam expander; the input end of the second polarization beam splitter prism is optically connected to the output end of the second half-wave plate; and the input end of the quarter-wave plate is optically connected to the output end of the second polarization beam splitter prism. The beam expander is used to receive the pump spatial light and expand the beam spot of the pump spatial light, and send the pump spatial light with the expanded beam spot to the second half-wave plate; the second half-wave plate and the second polarization beam splitter sequentially adjust the light intensity of the pump spatial light with the expanded beam spot to obtain the first pump spatial light, and send the first pump spatial light to the quarter-wave plate; the quarter-wave plate is used to convert the first pump spatial light into circularly polarized light, and control the circularly polarized light to pass through the magnetic field coil along the third direction and enter the atomic gas chamber.

[0142] In the implementation scheme provided in this embodiment, the collimated light beam is expanded by a beam expander to expand the beam spot size, thereby increasing the area of ​​interaction between light and atoms, which is beneficial to increasing the signal amplitude of the free induction decay signal, thereby improving the detection accuracy. Afterwards, the pump light intensity is regulated by adjusting the optical axis angle of the half-wave plate through a combination of a half-wave plate and a polarization beam splitter. At the same time, the light polarization is purified and the light beam is converted into linearly polarized light. The angle of the optical axis of the quarter-wave plate is adjusted to 45° with the polarization direction of the linearly polarized light, and the linearly polarized light is converted into circularly polarized light. Orientational polarization is achieved using circularly polarized light, so that the polarization direction is consistent with the propagation direction of the pump light. The macroscopic magnetic moment generated during Larmor precession has a projection in the direction of the detection light, thereby achieving optical rotation modulation of the detection light, and the higher the circular polarization degree of the pump light, the larger the free induction decay signal, thereby improving the detection accuracy.

[0143] In one implementation of this embodiment, the signal converter 205 includes a third half-wave plate, a third polarization beam splitter prism, and a third reflector balanced detector, which are arranged in sequence; wherein the first photosensitive surface of the third reflector balanced detector is arranged on the splitting light path of the third polarization beam splitter prism; the second photosensitive surface of the third reflector balanced detector is arranged in the light beam propagation direction of the third reflector; the three half-wave plates and the third polarization beam splitter prism are arranged in the extension direction of the second direction, and are used to receive the second detection light generated after the first detection light passes through the atomic gas chamber, and send the second detection light to the third reflector balanced detector; the third reflector is arranged in the light beam projection direction of the third polarization beam splitter prism, and is used to receive the second detection light projected by the third polarization beam splitter prism, and reflect the second detection light to the third reflector balanced detector; the third reflector balanced detector is connected to the controller 206 by signal, and is used to obtain the free induction decay signal of the atoms in the atomic gas chamber according to the second detection light, and send the free induction decay signal to the controller 206.

[0144] In the implementation scheme provided in this embodiment, when the probe light passes through the atomic gas chamber, its polarization direction rotates under the influence of the background field and the eddy current magnetic field. The polarization direction is then rotated by the optical rotation detection device composed of a half-wave plate and a polarization beam splitter prism. The corresponding optical rotation angle information is received by a balanced photodetector. A third reflector is provided so that the projected probe light is also received by the balanced photodetector, thereby improving the accuracy of signal acquisition.

[0145] In one implementation of this embodiment, the controller 206 receives the free induction decay signal to perform the following steps: extracting instantaneous phase information of the free induction decay signal to obtain the instantaneous precession frequency of the magnetic moment of the atom based on the instantaneous phase information; obtaining the gyromagnetic ratio of the atom to divide the instantaneous precession frequency by the gyromagnetic ratio to measure the real-time magnetic field in the atomic gas chamber; obtaining comparison information between the real-time magnetic field and the background field to obtain a detection result of a transient eddy current magnetic field based on the comparison information; and determining the presence of a conductive medium when the presence of the transient eddy current magnetic field is detected.

[0146] In the implementation scheme provided by this embodiment, the controller 206 directly associates the dynamic changes of the magnetic field with the phase characteristics of the free induction decay signal, thereby realizing high-precision detection of the transient eddy current magnetic field. Specifically, the instantaneous phase information of the free induction decay signal is extracted, and the phase change is used to directly reflect the instantaneous precession frequency of the atomic magnetic moment, thereby avoiding the complex closed-loop control required for traditional frequency tracking. By dividing the instantaneous precession frequency by the known gyromagnetic ratio, the quantum mechanical behavior of the atomic magnetic moment can be directly converted into a macroscopic magnetic field intensity measurement value, thereby accurately obtaining the real-time magnetic field in the atomic gas chamber. By comparing the difference between the real-time magnetic field and the preset background field, the transient eddy current magnetic field component generated by the conductive medium in the measured area can be directly separated. When the transient eddy current magnetic field is detected, it can be determined that there is a conductive medium in the measured area. The entire process does not require the additional setting of a magnetic field feedback adjustment device. The complete characterization of the dynamic changes of the magnetic field can be completed through a single measurement, thereby reducing the difficulty of measurement.

[0147] The present embodiment provides a conductive medium detection method and device. Through the structural design of the magnetic shielding tube and the symmetrical magnetic field coil, combined with the physical properties of the atomic gas chamber, a high-sensitivity magnetic field detection foundation is constructed. Then, a background magnetic field is applied in a specific direction to polarize the atomic magnetic moment, providing an initial state for subsequent magnetic field detection. According to the detection requirements, the detection light is directly started parallel to the magnetic field coil and perpendicular to the background field direction, so that the detection light is always in the starting state. It not only utilizes the sensitivity of the interaction between light and atoms to the magnetic field change to form a non-contact measurement path, but also avoids the re-response of the detection and improves the response rate of the detection. The pump light and the magnetic field coil are triggered synchronously, and the atomic energy state is regulated by the pump light to enhance the precession response of the magnetic moment. At the same time, the pulsed magnetic field excites the measured area to generate transient eddy currents. The pump and magnetic field are turned off in the preset time window to eliminate active excitation interference and capture only the free induction decay signal. By analyzing the phase change of the detection light, the instantaneous magnetic field information is extracted, and the difference between the background field and the real-time magnetic field is used as the basis for eddy current magnetic field detection to directly determine the presence of the conductive medium. The entire process adopts an open-loop detection method to avoid the complexity of traditional closed-loop tracking systems, while improving the accuracy of transient magnetic field detection through spatiotemporal synchronous control.

[0148] Example 2

[0149] The transient electromagnetic method (TEM) is a key technique in geophysical exploration. As a core branch of electromagnetic exploration technology, TEM boasts advantages such as deep detection, high resolution, and strong anti-interference capabilities. It plays an irreplaceable role in mineral resource exploration, environmental geological surveys, engineering geological assessments, and military underground target detection. Based on Faraday's principle of electromagnetic induction, TEM detects minerals by observing the transient electromagnetic response of underground media. This system typically consists of a pulse transmission system, an electromagnetic field receiving system, and a signal acquisition and processing module. The pulse transmission system consists of a high-power pulsed current source and a transmitting coil. The transmitting coil is deployed on the surface or in mid-air. By injecting a transient current pulse of a specific waveform (such as a square wave or trapezoidal wave) into the coil, a transient electromagnetic field is generated in the surrounding space. When the pulsed current is suddenly turned off, the primary field rapidly decays. According to Faraday's law of electromagnetic induction, this transient process induces eddy current fields in the underground conductive medium. The intensity and diffusion characteristics of the eddy current fields are affected by the conductivity distribution of the medium. The induced eddy current magnetic field is sensed by a receiving system. This receiving system typically consists of a multi-turn toroidal induction coil to extract the time-varying eddy current magnetic field signal. The data acquisition module, equipped with a preamplifier and analog-to-digital conversion circuit, performs gain adjustment and digital sampling of the induced electromotive force. The sampling rate must meet the requirements for capturing transient signals. The signal processing module performs multi-dimensional processing on the acquired transient voltage data. This process first suppresses random noise through time-domain filtering and superposition averaging techniques to extract valid information from the attenuation curve. A forward model is then established based on Maxwell's equations. The measured attenuation curve is compared with the theoretical responses of different geoelectric structures. The resistivity-depth parameter is iteratively optimized using algorithms such as least-squares inversion and neural networks. Finally, a three-dimensional subsurface electrical distribution model is constructed, combining geological prior information to reveal the spatial location and scale of conductive anomalies. In recent years, researchers have observed the free induction decay (FID) phenomenon in alkali metal gas chambers and demonstrated that, in the presence of a perpendicularly polarized external magnetic field, the precession of the sodium atomic magnetic moment modulates the absorption of circularly polarized probe light. Atomic magnetometers based on the free induction decay phenomenon are called FID magnetometers. FID magnetometers have two phases: pumping and detection. During the pumping phase, commonly used optical pumping methods include synchronous optical pumping and direct current (DC) optical pumping. Synchronous optical pumping requires the pump light to be modulated at the Larmor frequency of the background field. Since the magnetic moment precesses in the direction of the pump light each time the pump light is turned on, a larger polarization degree can be achieved. In contrast, during DC optical pumping, since different atoms are polarized at different times, the precession phases between the atoms are incoherent, ultimately resulting in a smaller polarization degree for the atomic system.However, if a large magnetic field is applied along the direction of the pump light, and its amplitude is much greater than the background field, the total field direction can be considered to be approximately the same as the pump light direction. As a result, the magnetic moment almost no longer precesses but remains in the polarization direction, ultimately achieving a larger polarization degree. A magnetometer based on this scheme is called a pump-enhanced FID magnetometer. During the detection phase, the pump light and large magnetic field are turned off. The magnetic moment precesses at the Larmor frequency under the background field, and the absorption or polarization rotation angle of the probe beam oscillates and decays at the Larmor frequency. The signal is ultimately collected by a photodetector. In subsequent data processing, there are various ways to recover magnetic field information from the FID signal. Common signal processing methods include nonlinear curve fitting, Hilbert transform, center of gravity peak search, and zero-crossing frequency extraction. Different algorithms have their own advantages and disadvantages, and specific algorithms can be used for data processing according to actual needs to obtain magnetic field information.

[0150] However, in traditional TEM systems, the pickup coils in the receiving system often suffer from insufficient sensitivity, resulting in low magnetic field measurement accuracy. Furthermore, FID magnetometers using synchronous optical pumping require real-time tracking of the Larmor frequency of the external magnetic field, making them difficult to use in environments with fluctuating magnetic fields. Furthermore, the closed-loop circuitry required to track the external magnetic field adds additional complexity to the FID magnetometer system.

[0151] In view of the technical problems existing in the above-mentioned prior art, this embodiment provides a conductive medium detection device for detecting whether a conductive medium exists in a detected area. Figure 3 .

[0152] like Figure 3 As shown, the conductive medium detection device can be functionally divided into a detection light excitation component for generating detection light, a pump light excitation component for generating pump light, a transient magnetic field excitation component for magnetic field induction, and a signal processing excitation component for performing signal processing to obtain conductive medium detection results.

[0153] like Figure 3 As shown, the detection light excitation component includes a first laser 1, a first optical fiber 2, a first acousto-optic modulator 3, a second optical fiber 4, a first collimator 5, a first polarizer 6, a first half-wave plate 7, a first polarization splitter prism 8, a first photodetector 9, a second half-wave plate 10, a first reflector 11, a second polarizer 12 and a PID33.

[0154] The pump light excitation components include a second laser 13, a third optical fiber 14, a second acousto-optic modulator 14, a fourth optical fiber 16, a second collimator 17, a second reflector 18, a beam expander 19, a third half-wave plate 20, a second polarization beam splitter prism 21, and a quarter-wave plate 22.

[0155] The transient magnetic field excitation component includes a magnetic shielding tube 32 and an atomic gas chamber 24 filled with atoms located inside the magnetic shielding tube 32. A set of magnetic field coils 23 are symmetrically fixed at both ends of the axial direction of the atomic gas chamber 24. A background field 26 is provided along a first direction parallel to the magnetic field coils. Figure 3 The conductive medium shown is a transient eddy current magnetic field generated by the aluminum block 25. It should be noted that the conductive medium that can be detected is not only the aluminum block 25, but also other conductive media such as iron and copper.

[0156] The signal processing and excitation components include a fourth half-wave plate 27 , a third polarization beam splitter prism 28 , a third reflector 29 , a balanced photodetector 30 and a data processing module 31 .

[0157] Reference Figure 3 The output end of the laser 1 is optically connected to the input end of the first acousto-optic modulator 3 through the first optical fiber 2; the output end of the first acousto-optic modulator 3 is optically connected to the input end of the first collimator 5 through the second optical fiber 4; the output end of the first collimator 5 is optically connected to the input end of the first polarizer 6; the output end of the first polarizer 6 is optically connected to the input end of the first half-wave plate 7; the output end of the first half-wave plate 7 is optically connected to the input end of the first polarization beam splitter prism 8; the first output end of the first polarization beam splitter prism 8 is optically connected to the input end of the second half-wave plate 10; the second output end of the first polarization beam splitter prism 8 is optically connected to the input end of the second half-wave plate 10; the output end of the second half-wave plate 10 is optically connected to the input end of the first photodetector 9; the output end of the first reflector 11 is optically connected to the input end of the second polarizer 12; the output end of the first photodetector 9 is electrically connected to the input end of the PID33; and the output end of the PID33 is electrically connected to the control end of the first acousto-optic modulator 3.

[0158] Reference Figure 3 The output end of the second laser 13 is optically connected to the input end of the second acousto-optic modulator 14 through the third optical fiber 14; the output end of the second acousto-optic modulator 14 is optically connected to the input end of the second collimator 17 through the fourth optical fiber 16; the output end of the second collimator 17 is optically connected to the input end of the second reflector 18; the output end of the second reflector 18 is optically connected to the input end of the beam expander 19; the output end of the beam expander 19 is optically connected to the input end of the third half-wave plate 20; the output end of the third half-wave plate 20 is optically connected to the input end of the second polarization beam splitter prism 21; the output end of the second polarization beam splitter prism 21 is optically connected to the input end of the quarter-wave plate 22;

[0159] Reference Figure 3 The light propagation direction of the second polarizer 12 is perpendicular to the axial direction of the atomic gas chamber 24 and parallel to the magnetic field coil 23; the light propagation direction of the quarter-wave plate 22 is parallel to the axial direction of the atomic gas chamber 24 and passes through the magnetic field coil 23.

[0160] Reference Figure 3 The fourth half-wave plate 27 is disposed perpendicularly below the magnetic shield tube 32 and perpendicular to the light propagation direction of the second polarizer 12. The output end of the fourth half-wave plate 27 is optically connected to the input end of the third polarization beam splitter prism 28. The input end of the balanced photodetector 30 is disposed on the beam splitting path of the third polarization beam splitter prism 28. The input end of the third reflector 29 is optically connected to the output end of the third polarization beam splitter prism 28. The output end of the third reflector 29 is optically connected to the input end of the balanced photodetector 30. The output end of the balanced photodetector 30 is electrically connected to the data processing module 31.

[0161] like Figure 3 The conductive medium detection device based on transient magnetic field measurement shown further includes a controller, wherein the controller is signal-connected to the first laser 1, the first reflector 11, the second laser 13, the second reflector 18, and the magnetic field coil 23 respectively.

[0162] It should be noted that the first AOM 3 and the second AOM 14 modulate optical power to generate optical pulses. It should be noted that in addition to the AOM scheme, other instruments for generating optical pulses can also be considered. For example, an optical attenuator can be used to control optical power to output optical pulses, or an optical switch can be used to directly control the on and off of the light beam to generate optical pulses. This diversity of instrument solutions helps improve the environmental adaptability of the detection device.

[0163] In one embodiment of this embodiment, refer to Figure 3 The conductive medium detection device shown and the controller connected to the conductive medium detection device detect the conductive medium in the detected area. The specific detection method is as follows: Figure 4 The detection method includes:

[0164] Step 401: The controller activates the detection light excitation component in response to a detection demand of the detected area to apply a first detection light perpendicular to the axis of the atomic gas cell to the transient magnetic field excitation component;

[0165] In this embodiment, the first laser 1 is controlled to emit light having a specific wavelength in response to detection requirements of the measured area and based on the atoms filling the atomic gas chamber 24. In one embodiment of this embodiment, the atomic gas chamber 24 can be filled with alkali metal atoms such as cesium atoms or various types of atoms belonging to the helium atomic system. In order to utilize the magnetic moment generated by atomic polarization to detect transient magnetic fields and thereby obtain detection results of conductive media, the wavelength of light emitted by the first laser 1 is determined based on the corresponding characteristics of the atoms in the atomic gas chamber 24.

[0166] In one embodiment, when the atoms filling the atomic gas chamber 24 are cesium atoms, due to the pumping effect of the pump light, most of the atoms will be in the ground state of the D2 line. The D2 line corresponds to the transition of atoms from the ground state to a higher excited state. In this case, the first laser 1 can be configured to emit fiber light with a wavelength close to or identical to the D2 line. For example, if the wavelength of D2 is 852 nanometers, the first laser 1 can be configured as an 852 nanometer laser. The 852 nanometer laser is used to detect the cesium atom D2 line and outputs fiber light that enters the first acousto-optic modulator 3.

[0167] In this embodiment, the first acousto-optic modulator 3 acts as a control device for power-stabilizing closed-loop feedback, stabilizing the power of the fiber light emitted by the first laser 1. The output fiber light is converted into spatial light by the first collimator 5. This spatial light first passes through the first polarizer 6, converting polarization jitter into power jitter. This power jitter is then compensated by the power-stabilizing loop consisting of the first photodetector 9, PID 33, and the first acousto-optic modulator 3, further improving the stability of the detection beam. The light intensity is then adjusted by the combination of the first half-wave plate 7 and the first polarization beam splitter prism 8. A portion of the light reflected by the first polarization beam splitter prism 8 is received by the first photodetector 9. The first photodetector 9 serves as the sensing device of the power-stabilizing closed-loop circuit to detect jitter in the spatial light power, which is then fed back and compensated by the subsequent PID 33 (integral operation circuit).

[0168] The light passing through the first polarization beam splitter 8 passes through the second half-wave plate 10. The second half-wave plate 10 is rotated to adjust the polarization direction of the light passing through the first polarization beam splitter 8 so that the polarization direction of the light is aligned with the polarization direction of the second polarizer 12, ensuring that most of the light can pass through the polarizer. The light is then reflected by the first reflector 11 and prepared to enter the magnetic shielding tube 32.

[0169] In this embodiment, the controller is connected to the first reflector 11 by signal, and is used to control the first reflector 11 to adjust the pitch angle and reflection angle of the first reflector 11, so that the propagation direction of the detection light reflected by the first reflector 11 is perpendicular to the pump light generated by the pump light excitation component and the background field 26, so that the magnetic moment has a larger projection in the direction of the detection light during Larmor precession, thereby increasing the FID signal amplitude and improving the detection accuracy.

[0170] In this embodiment, the probe light reflected by the first reflector 11 passes through the second polarizer 12 before entering the magnetic shield 32, thereby purifying the polarization state of the probe light. Purifying the polarization state helps reduce external interference with subsequent optical rotation detection. As the probe light passes through the atomic gas chamber 24, its polarization direction rotates under the influence of the background field 26 and the eddy current magnetic field. The probe light then passes through the optical rotation detection device, which is composed of a fourth half-wave plate 27, a third polarization beam splitter prism 28, and a third reflector 29. The corresponding optical rotation angle information is received by a balanced photodetector 30.

[0171] Step 402: The controller starts the background field.

[0172] In this embodiment, the background field is generated by a three-axis Helmholtz coil, and its direction is perpendicular to the propagation direction of the pump light and the propagation direction of the detection light.

[0173] Step 403: According to the preset detection frequency, the controller synchronously starts the pump light excitation component and the magnetic field coil to generate pump light that passes through the magnetic field coil and enters the atomic gas chamber and a pulsed magnetic field applied to the measured area along the direction of the pump light.

[0174] In this embodiment, the pump light and pulsed magnetic field coil are synchronously turned on and off by a controller at a repetitive detection frequency, which is adjusted based on the actual eddy current field signal. To simplify the experimental setup, the detection light excitation component remains on throughout the entire detection process when detecting conductive media. To minimize the impact of the initial state of the detection light on detection accuracy, the quarter-wave plate 22 is adjusted to ensure that the differential output signal of the balanced photodetector 30 is zero when only the detection light is on.

[0175] In this embodiment, while synchronously activating the pump light and pulsed magnetic field according to the detection frequency, the controller first activates the second laser 13 to generate light having a specific wavelength based on the atoms in the atomic gas chamber 24. In one embodiment of this embodiment, the atomic gas chamber 24 is filled with cesium atoms. In this case, pumping based on the D1 line of the cesium atoms is beneficial for increasing the polarizability of the atomic system, thereby increasing the FID signal amplitude and further improving detection accuracy. The wavelength of the D1 line of the cesium atoms is 894.6 nanometers, which is one of the wavelengths of light emitted or absorbed by cesium atoms when they transition from an excited state to a ground state. Therefore, in this embodiment, the second laser 13 is set to an 894 nanometer laser to output light with a wavelength of 894 nanometers.

[0176] In this embodiment, the light output by the second laser 13 is modulated in optical power by a second acousto-optic modulator 14, thereby controlling the on-off switching of the pump light and achieving timing control of the FID magnetometer. The output fiber light is then connected to a second collimator 17, which converts the fiber light into spatial light, generating pump light. The pump light is reflected by a second reflector 18; this second reflector 18 is connected to a controller signal. The controller controls the second reflector 18 to adjust its own pitch and reflection angles to collimate the optical path of the pump light, ensuring that the pump light passes perpendicularly through the magnetic field coil 23, parallel to the direction of the pulsed magnetic field generated by the magnetic field coil 23.

[0177] In this embodiment, the controller simultaneously applies a current to the magnetic field coil 23 while activating the second laser 13, causing the magnetic field coil 23 to generate a pulsed magnetic field parallel to the direction of the pump light. In this embodiment, controlling the optical path of the pump light and the magnetic field direction of the magnetic field coil 23 facilitates increasing the FID signal amplitude during the polarization phase, thereby improving detection accuracy.

[0178] In this embodiment, the pump light beam reflected by the second reflector 18 passes through a beam expander 19 to expand the beam spot size, thereby increasing the area of ​​interaction between the light and the atoms. This helps to increase the FID signal amplitude and, in turn, improve detection accuracy. The pump light intensity is then regulated by adjusting the optical axis angle of the third half-wave plate 20 and the second polarization beam splitter prism 21. While increasing the optical power, the transverse relaxation time of the FID signal output by the balanced photodetector 30 is observed. When the transverse relaxation time increases significantly, the optical power is stopped to increase the FID signal while avoiding photobroadening. Simultaneously, the light polarization is purified, converting the beam into linearly polarized light. The optical axis angle of the quarter-wave plate 22 is adjusted to 45° with respect to the polarization direction of the linearly polarized light, converting the linearly polarized light into circularly polarized light. Using circularly polarized light achieves orientational polarization, so that the polarization direction aligns with the propagation direction of the pump light.

[0179] This embodiment utilizes the projection of the macroscopic magnetic moment generated during Larmor precession in the direction of the probe light, thereby achieving optical rotation modulation of the probe light. The higher the circular polarization degree of the pump light, the larger the FID signal. The circularly polarized light passes through a magnetic field coil 23 of a certain diameter, placed parallel to the atomic gas chamber 24, and enters the atomic gas chamber 24. The pulsed magnetic field and the pump light are synchronously controlled on and off by a signal generator. When a large magnetic field is applied in the direction of the pump light, and its amplitude is much greater than the background field, the total field direction can be considered to be approximately the direction of the pump light. As a result, the magnetic moment almost no longer precesses, but remains in the polarization direction. Ultimately, a larger polarization degree can be achieved, thereby improving detection accuracy. During this stage, due to the sudden shutdown of the pulsed magnetic field, if a conductive medium is present in the measured area, an eddy current magnetic field will be generated according to Faraday's law of electromagnetic induction. After the pump light and magnetic field are turned off, the macroscopic magnetic moment generated by the atomic polarization will precess under the combined action of the background field and the eddy current magnetic field, thereby modulating the polarization rotation angle of the probe light. In one embodiment of the present invention, the diameter of the magnetic field coil 23 is 10 mm. The large magnetic field generated by the magnetic field coil 23 increases the atomic polarization degree in the pumping stage, thereby increasing the signal amplitude of the FID magnetometer and improving the FID magnetometer's response to the external magnetic field. At the same time, after the large magnetic field is generated by the coil, the moment it is turned off will induce the metal conductor to generate an eddy current magnetic field. The presence of the metal conductor is determined by detecting the eddy current magnetic field, thereby achieving active magnetic detection.

[0180] Step 404: The controller synchronously turns off the pump light excitation component and the magnetic field coil to collect the second detection light passing through the atomic gas chamber through the signal processing excitation component, and obtains the detection result of the conductive medium based on the second detection light.

[0181] In this embodiment, when the probe light passes through the atomic gas chamber 24, its polarization direction rotates under the influence of the background field and the eddy current magnetic field generated by the conductive medium. The probe light then passes through the optical rotation detection device composed of a fourth half-wave plate 27, a third polarization beam splitter prism 28, and a third reflector 29. The corresponding optical rotation angle information is received by a balanced photodetector 30.

[0182] In this embodiment, since the amplitude of the large magnetic field generated by the magnetic field coil 23 is much greater than that of the background field 26, the total field direction can be considered to be approximately the direction of the pump light. Therefore, the magnetic moment almost no longer precesses, but remains in the polarization direction, ultimately achieving a larger polarization degree. During the detection phase, when the pump light and the magnetic field coil 23 are simultaneously and instantaneously shut off, if a conductive medium exists in the measured area, that is, if a conductive medium exists in the measured area near the magnetic field coil 23, the sudden shutdown of the magnetic field coil 23 will generate an eddy current field. According to Faraday's law of electromagnetic induction, the eddy current field will generate an eddy current magnetic field with the same direction as the original pulsed magnetic field generated by the magnetic field coil 23, but with a reduced amplitude. At this time, the macroscopic magnetic moment of the atoms will precess under the combined influence of the background field and the eddy current magnetic field. Under the influence of the precessing atomic magnetic moment, the polarization direction of the probe light is continuously modulated by the precessing magnetic moment, thereby carrying information about the background field and the eddy current magnetic field, which is detected in the subsequent optical rotation detection.

[0183] Therefore, this embodiment only collects the probe light signal during the pump light-off period. Because the polarization rotation angle of the probe light is continuously modulated, the voltage signal at the differential output of the balanced photodetector 30 in the optical rotation analyzer system continuously oscillates and decays. The signal output from the differential output of the balanced photodetector 30 is collected and analyzed by the data processing module 31.

[0184] In this embodiment, after receiving the detection light sent by the optical rotation and polarization analyzer system, the balanced photodetector 30 extracts the free decay signal of the atoms in the atomic gas cell 24 from the detection light, and sends the free decay signal to the data processing module 31;

[0185] The data processing module 31 extracts the instantaneous phase information of the free induction decay signal to obtain the instantaneous precession frequency of the magnetic moment of the atom based on the instantaneous phase information; obtains the gyromagnetic ratio of the atom to divide the instantaneous precession frequency by the gyromagnetic ratio to measure the real-time magnetic field in the atomic gas chamber; obtains comparison information between the real-time magnetic field and the background field to obtain the detection result of the transient eddy current magnetic field based on the comparison information; and determines that a conductive medium exists when the presence of the transient eddy current magnetic field is detected.

[0186] In one implementation of this embodiment, taking the atom as a cesium atom as an example, the gyromagnetic ratio of the cesium atom is calculated through the hyperfine structure in atomic physics and the interaction between electron spin and orbital angular momentum.

[0187] In one embodiment of this invention, the data processing module 31 is configured to acquire signals using a USB-6361 board. The data processing module 31 can extract and process the instantaneous phase information of the signal using a Hilbert transform algorithm to derive the instantaneous precession frequency of the magnetic moment. Dividing the instantaneous precession frequency by the gyromagnetic ratio yields the magnetic field magnitudes of the background field and the eddy current magnetic field.

[0188] In a time-varying magnetic field diagram, when an eddy current magnetic field is present, an eddy current magnetic field that oscillates over time is superimposed on the background field. The magnitude of the instantaneous magnetic field is the sum of the eddy current and background magnetic fields, and the oscillation frequency of the instantaneous magnetic field is the oscillation frequency of the eddy current magnetic field. Therefore, simply by comparing the instantaneous magnetic field diagram with the measured instantaneous magnetic field diagram when only the background field is present, it is possible to determine whether a metal conductor has generated an eddy current magnetic field.

[0189] It should be noted that in order to ensure smooth transmission of light through the detection light excitation component, pump light excitation component, transient magnetic field excitation component, and signal processing excitation component, the material parameters of each component in the detection light excitation component, pump light excitation component, transient magnetic field excitation component, and signal processing excitation component must be determined based on the light generated by the laser. For example, when the first laser 1 is determined to be an 852-nanometer semiconductor laser and the second laser 13 is determined to be an 895-nanometer semiconductor laser using cesium atoms as an example, the first polarizer 6, first half-wave plate 7, first polarization beam splitter prism 8, second half-wave plate 10, first reflector 11, and second polarizer 12 are all wave plates with a center wavelength of 852 nanometers. The first photodetector 9 can detect a wavelength range of 600-1000 nanometers, the balanced photodetector 30 can detect a wavelength range of 320-1060 nanometers, and the first acousto-optic modulator 3 has a center wavelength of 852 nanometers. The third half-wave plate 20 and quarter-wave plate 22 are both wave plates with a center wavelength of 895 nanometers. The background field is a magnetic field B of 5000nT z The atomic gas chamber 24 is a cylindrical cesium atomic gas chamber with a bottom diameter of 25 mm and a height of 16 mm, and is filled with 250 Torr N2 buffer gas.

[0190] It should be noted that the parameter settings of each component in the above-mentioned detection light excitation component, pump light excitation component, transient magnetic field excitation component and signal processing excitation component are not unique and can be set according to actual needs.

[0191] This embodiment discloses a conductive medium detection device and method. By synchronously turning on and off pump light and a large magnetic field, the large magnetic field is turned off to induce an eddy current magnetic field in a metal conductor. This eddy current magnetic field is then detected during the detection phase to determine the presence of the metal conductor, thereby achieving active magnetic detection. Compared to traditional measurement schemes, this invention improves the measurement system's ability to extract and identify eddy current magnetic field signals. Furthermore, an FID magnetometer operating in this mode does not need to track and lock the Larmor frequency, eliminating structures such as closed-loop feedback circuits. This effectively reduces system complexity and facilitates the design of miniaturized systems.

[0192] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that 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 for those skilled in the art.

Claims

1. A conductive medium detection method, characterized in that: Applicable to a transient magnetic field exciter; the transient magnetic field exciter includes a magnetic shielding tube and an atomic gas chamber filled with atoms located inside the magnetic shielding tube; a group of magnetic field coils are symmetrically fixed at both axial ends of the atomic gas chamber; the method includes: In response to a detection requirement of a measured area, applying a background field to the atomic gas chamber along a first direction parallel to the magnetic field coil; Starting a first detection light and controlling the first detection light to pass through the atomic gas chamber along a second direction parallel to the magnetic field coil and perpendicular to the first direction; Synchronously starting the pump light and the magnetic field coil according to a preset detection frequency, controlling the pump light to pass through the magnetic field coil into the atomic gas chamber, and controlling the magnetic field coil to send a pulsed magnetic field to the measured area; Synchronously turning off the pump light and the magnetic field coil within a preset time window to obtain a second detection light generated after the first detection light passes through the atomic gas chamber; A free induction decay signal of atoms in the atomic gas chamber is obtained according to the second detection light to obtain a detection result of a transient eddy current magnetic field, and a detection result of the conductive medium in the measured area is determined according to the detection result.

2. A conductive medium detection method according to claim 1, characterized in that: The starting of the first detection light and controlling the first detection light to pass through the atomic gas chamber along a second direction parallel to the magnetic field coil and perpendicular to the first direction includes: generating a first optical fiber light according to a wavelength corresponding to a first energy level transition line of atoms in the atomic gas chamber; acquiring power jitter of the first optical fiber light, and performing power compensation on the first optical fiber light according to the power jitter to obtain second optical fiber light; converting the second optical fiber light into a first spatial light and performing light intensity modulation on the first spatial light to obtain a first detection light; acquiring a first angle between a propagation direction of the first detection light and the second direction, so as to determine a first reflection angle of the first detection light according to the first angle; The first detection light is controlled to pass through the atomic gas chamber along the second direction according to the first reflection angle.

3. A conductive medium detection method according to claim 2, characterized in that: The step of synchronously starting the pump light and the magnetic field coil according to a preset detection frequency, controlling the pump light to pass through the magnetic field coil into the atomic gas chamber, and controlling the magnetic field coil to send a pulsed magnetic field to the measured area includes: generating initial fiber light according to the wavelength corresponding to the second energy level transition line of the atom and synchronously applying a current signal to the magnetic field coil; modulating the optical power of the initial fiber light to start the pump fiber light and convert the pump fiber light into pump spatial light; obtaining a second angle between a propagation direction of the pump spatial light and a third direction perpendicular to the magnetic field coil; determining a second reflection angle of the pumping space light according to the second included angle, so as to control the pumping space light to pass through the magnetic field coil and enter the atomic gas chamber according to the second reflection angle; The magnetic field coil is controlled according to the current signal to send a pulsed magnetic field to the measured area along the third direction.

4. A conductive medium detection method according to claim 3, characterized in that: The method further comprises: synchronously starting the pump light and the magnetic field coil according to a preset detection frequency, controlling the pump light to pass through the magnetic field coil into the atomic gas chamber, and controlling the magnetic field coil to send a pulsed magnetic field to the measured area. Expanding the beam spot of the pump spatial light and adjusting the intensity of the pump spatial light to obtain a first pump spatial light; The first pump spatial light is converted into circularly polarized light, and the circularly polarized light is controlled to pass through the magnetic field coil along the third direction and enter the atomic gas chamber.

5. The conductive medium detection method according to claim 1, characterized in that: The step of acquiring a free induction decay signal of atoms in the atomic gas chamber according to the second detection light to obtain a detection result of a transient eddy current magnetic field, and determining a detection result of a conductive medium in the measured area according to the detection result, includes: Extracting instantaneous phase information of the free induction decay signal to obtain the instantaneous precession frequency of the magnetic moment of the atom according to the instantaneous phase information; obtaining the gyromagnetic ratio of the atoms, dividing the instantaneous precession frequency by the gyromagnetic ratio, and measuring the real-time magnetic field in the atomic gas chamber; Obtaining comparison information between the real-time magnetic field and the background field, so as to obtain a detection result of the transient eddy current magnetic field according to the comparison information; When the presence of the transient eddy current magnetic field is detected, it is determined that a conductive medium exists.

6. A conductive medium detection device, characterized in that: It includes a background field coil, a detection light component, a pump light component, a transient magnetic field exciter, a signal converter and a controller; wherein the transient magnetic field exciter includes a magnetic shielding tube and an atomic gas chamber filled with atoms located inside the magnetic shielding tube; a group of magnetic field coils are symmetrically fixed at both axial ends of the atomic gas chamber; the background field coil is arranged inside the magnetic shielding tube along a first direction parallel to the magnetic field coil; The background field coil is electrically connected to the controller, so that the controller controls the background field coil to apply a background field to the atomic gas chamber along the first direction in response to a detection requirement of the measured area; The detection light assembly is connected to the controller by signal, so that the controller controls the detection light assembly to generate a first detection light and controls the detection light assembly to control the first detection light so that the first detection light passes through the atomic gas chamber along a second direction parallel to the magnetic field coil and perpendicular to the first direction; The pump light assembly and the magnetic field coil are respectively connected to the controller signal so that the controller performs the following steps: Synchronously controlling the pump light component to start pump light and synchronously controlling the magnetic field coil to send a pulsed magnetic field to the measured area according to a preset detection frequency; controlling the pump light component to control the pump light so that the pump light passes through the magnetic field coil and enters the atomic gas chamber; Controlling the pump light component to turn off the pump light and synchronously controlling the magnetic field coil to turn off the pulsed magnetic field within a preset time window; The signal converter is connected to the controller signal, and is used to obtain a second detection light generated after the first detection light passes through the atomic gas chamber after the pump light and the magnetic field coil are turned off, and obtain a free induction decay signal of the atoms in the atomic gas chamber based on the second detection light, so as to send the free induction decay signal to the controller; The controller receives the free induction decay signal and obtains a detection result of a transient eddy current magnetic field according to the free induction decay signal, so as to determine a detection result of the conductive medium in the measured area according to the detection result.

7. The conductive medium detection device according to claim 6, characterized in that: The detection light assembly includes a first laser, an optical power stabilization circuit, a first optical conversion assembly, and a first reflector arranged in sequence; wherein the first laser is signal-connected to the controller; the output end of the first laser is optically connected to the first input end of the optical power stabilization circuit via an optical fiber; the output end of the optical power stabilization circuit is optically connected to the input end of the first optical conversion assembly; the output end of the first optical conversion assembly is optically connected to the second input end of the optical power stabilization circuit; the output end of the first optical conversion assembly is optically connected to the input end of the first reflector; and the output end of the first reflector is optically connected to the input end of the atomic gas chamber; The first laser is used to generate and emit first fiber light to the optical power stabilization circuit according to the wavelength corresponding to the first energy level transition line of the atom; The optical power stabilization circuit obtains the power jitter of the first optical fiber light, performs power compensation on the first optical fiber light according to the power jitter, and outputs the second optical fiber light to the first optical conversion component; The first optical conversion component is used to convert the second optical fiber light into a first spatial light and perform light intensity adjustment on the first spatial light, and output a first detection light to the first reflector; The first reflector is used to reflect the first detection light so that the first detection light passes through the atomic gas chamber along the second direction; The first reflector is connected to the controller signal so that the controller performs the following steps: acquiring a first angle between a propagation direction of the first detection light and the second direction, so as to determine a first reflection angle of the first detection light according to the first angle; Calculating a first reflector pitch angle and a first reflector reflection angle of the first reflector according to the first reflection angle; The first reflector is controlled to be adjusted according to the pitch angle of the first reflector and the reflection angle of the first reflector, so that the light beam propagation direction of the first reflector coincides with the second direction.

8. The conductive medium detection device according to claim 7, characterized in that: The first optical conversion assembly includes a first collimator, a first polarizer, a first half-wave plate, and a first polarization beam splitter prism arranged in sequence along the propagation direction of the first optical fiber light beam; wherein the input end of the first collimator is optically connected to the output end of the optical power stabilization circuit through an optical fiber; the input end of the first polarizer is optically connected to the output end of the first collimator; the input end of the first half-wave plate is optically connected to the output end of the first polarizer; the input end of the first polarization beam splitter prism is optically connected to the output end of the first half-wave plate; and the output end of the first polarization beam splitter prism is optically connected to the input end of the first reflector; The first collimator is used to convert the second fiber light into first spatial light and send the first spatial light to the first polarization; The first polarizer is used to convert the polarization dither of the first spatial light into power dither, and output the second spatial light to the first half-wave plate; The first half-wave plate and the first polarization beam splitter prism are used to adjust the light intensity of the second spatial light and output the detection light to the first reflector.

9. The conductive medium detection device according to claim 8, characterized in that: The optical power stabilization circuit includes a first acousto-optic modulator, a PID circuit, and a photodetector; wherein the input end of the first acousto-optic modulator is optically connected to the first laser via an optical fiber; the output end of the first acousto-optic modulator is optically connected to the input end of the first collimator via an optical fiber; the photosensitive surface of the photodetector is arranged on the splitting optical path of the first polarization splitter prism; the input end of the PID circuit is electrically connected to the photodetector; and the output end of the PID circuit is electrically connected to the control end of the first acousto-optic modulator; The input end of the first acousto-optic modulator is connected to the first laser light via an optical fiber, so as to obtain the first optical fiber light; The photodetector is used to obtain the power jitter of the first detection light and input the power jitter into the PID circuit; The PID circuit calculates a compensation power of the first fiber light according to the power jitter, and sends the compensation power to the first acousto-optic modulator, so that the first acousto-optic modulator performs power compensation on the first fiber light and outputs a second fiber light value to the first collimator.

10. The conductive medium detection device according to claim 6, characterized in that: The pump light assembly includes a second laser, a second light conversion assembly and a second reflector arranged in sequence; Wherein, the second laser is connected to the controller signal and is used to generate and emit initial fiber light according to the wavelength corresponding to the second energy level transition line of the atom; The input end of the second optical conversion component is optically connected to the second laser, and is used to receive the initial fiber light and modulate the optical power of the initial fiber light to generate pump fiber light and convert the pump fiber light into pump spatial light; The input end of the second reflector is optically connected to the output end of the second optical conversion component, and is used to adjust the propagation direction of the pumping space light so that the pumping space light passes through the magnetic field coil and enters the atomic gas chamber; The second reflector is connected to the controller signal so that the controller performs the following steps: obtaining a second angle between a propagation direction of the pump spatial light and a third direction perpendicular to the magnetic field coil; determining a second reflection angle of the pump spatial light according to the second included angle, so as to calculate a second reflector pitch angle and a second reflector reflection angle of the second reflector according to the second reflection angle; The second reflector is controlled to be adjusted according to the pitch angle of the second reflector and the reflection angle of the second reflector, so that the light beam propagation direction of the second reflector coincides with the third direction.

11. The conductive medium detection device according to claim 10, characterized in that: The second light conversion assembly includes a second acousto-optic modulator and a second collimator arranged in sequence; The input end of the second acousto-optic modulator is connected to the second laser via an optical fiber, and is used to modulate the optical power of the initial optical fiber light and output pump optical fiber light; The output end of the second collimator is optically connected to the input end of the second reflector; the input end of the second collimator is connected to the output end of the second acousto-optic modulator through an optical fiber, and is used to receive the pump fiber light and convert the pump fiber light into pump spatial light, so as to send the pump spatial light to the second reflector.

12. The conductive medium detection device according to claim 10, characterized in that: The optical fiber transmission system further comprises a third optical conversion component; wherein the third optical conversion component comprises a beam expander, a second half-wave plate, a second polarization beam splitter prism, and a quarter-wave plate arranged in sequence along the third direction; wherein the input end of the beam expander is optically connected to the output end of the second reflector; the input end of the second half-wave plate is optically connected to the output end of the beam expander; the input end of the second polarization beam splitter prism is optically connected to the output end of the second half-wave plate; and the input end of the quarter-wave plate is optically connected to the output end of the second polarization beam splitter prism. The beam expander is used to receive the pump spatial light and expand the beam spot of the pump spatial light, and send the pump spatial light with the expanded beam spot to the second half-wave plate; The second half-wave plate and the second polarization beam splitter sequentially adjust the intensity of the pump spatial light with the expanded beam spot to obtain a first pump spatial light, and send the first pump spatial light to the quarter-wave plate; The quarter-wave plate is used to convert the first pump spatial light into circularly polarized light, and control the circularly polarized light to pass through the magnetic field coil along the third direction and enter the atomic gas chamber.

13. The conductive medium detection device according to claim 6, characterized in that: The signal converter includes a third half-wave plate, a third polarization beam splitter prism, and a third reflector-balanced detector, which are arranged in sequence; wherein the first photosensitive surface of the third reflector-balanced detector is arranged on the splitting optical path of the third polarization beam splitter prism; The second photosensitive surface of the third reflector balance detector is arranged in the light beam propagation direction of the third reflector; The three half-wave plates and the third polarization beam splitter prism are arranged in the extension direction of the second direction, and are used to receive the second detection light generated after the first detection light passes through the atomic gas chamber, and send the second detection light to the third reflector balance detector; The third reflector is arranged in the light beam projection direction of the third polarization beam splitter prism, and is used to receive the second detection light projected by the third polarization beam splitter prism, and reflect the second detection light to the third reflector balance detector; The third reflector balance detector is connected to the controller signal, and is used to obtain a free induction decay signal of atoms in the atomic gas chamber according to the second detection light, and send the free induction decay signal to the controller.

14. The conductive medium detection device according to claim 13, characterized in that: The controller receives the free induction decay signal to perform the following steps: Extracting instantaneous phase information of the free induction decay signal to obtain the instantaneous precession frequency of the magnetic moment of the atom according to the instantaneous phase information; obtaining the gyromagnetic ratio of the atoms, dividing the instantaneous precession frequency by the gyromagnetic ratio, and measuring the real-time magnetic field in the atomic gas chamber; Obtaining comparison information between the real-time magnetic field and the background field, so as to obtain a detection result of the transient eddy current magnetic field according to the comparison information; When the presence of the transient eddy current magnetic field is detected, it is determined that a conductive medium exists.

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