CN116879813A - Signal detection method and system based on in-situ magnetic compensation very low frequency atomic magnetometer - Google Patents
Signal detection method and system based on in-situ magnetic compensation very low frequency atomic magnetometer Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
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Abstract
The invention provides a signal detection method and a system based on an in-situ magnetic compensation very low frequency atomic magnetometer, comprising the following steps: the data acquisition and control system scans the main magnetic field from 0 in the z direction by controlling the triaxial magnetic field coils according to real-time triaxial magnetic field information obtained by measuring the first alkali metal atoms so that the magnetic fields of the atomic air chamber along the horizontal polarization x direction and the vertical polarization y direction are 0; the main magnetic field size corresponding to the maximum output amplitude of the balanced homodyne detector is found out and used as the optimal main magnetic field; the data acquisition and control system is used for fixing the main magnetic field generated by the triaxial magnetic field coil into a preferable main magnetic field, and the data acquisition and control system is used for detecting the very low frequency signal according to the output signal of the balanced homodyne detector. By applying the technical scheme of the invention, the technical problems that the very low frequency receiving antenna is difficult to apply due to large size, the polarization efficiency of the atomic ensemble is low and the external magnetic field interference suppression capability is poor in the prior art are solved.
Description
Technical Field
The invention relates to the technical field of quantum navigation and quantum sensing, in particular to a signal detection method and system based on an in-situ magnetic compensation very low frequency atomic magnetometer.
Background
Very Low Frequency (VLF) radio waves refer to radio waves having frequencies of 3kHz to 30kHz (wavelengths of 100km to 10 km), which are very characteristic bands of the radio spectrum. In the frequency band, the wave length is longer, the propagation loss of signals is small, the amplitude and the phase are stable, the anti-interference capability is extremely strong, the signals can be transmitted along the 'earth surface-ionized layer' waveguide for being received by remote equipment, and meanwhile, the signals can penetrate soil and seawater with a certain depth for being received by underground or underwater equipment, so that the device has great application value in the aspects of ultra-remote navigation, time service, communication, submarine communication, navigation and the like. Currently, the method is widely applied to aircrafts, submarines and other equipment, and is mainly used for remote communication and navigation.
The reception and detection of very low frequency radio signals is one of the core problems of very low frequency radio technology in applications. The conventional very low frequency radio detection and reception are realized by antennas, and there are mainly two types: one type is a very low frequency electric antenna that detects an electric field component of a very low frequency radio wave based on a capacitive coupling manner; the other is a very low frequency magnetic antenna that detects a magnetic field component of a very low frequency radio wave by means of inductive coupling. These two types of conventional very low frequency receiving antennas need to be designed to be physically large in order to ensure sufficient detection sensitivity. For electrical antennas, the length is often on the order of hundreds to thousands of meters, and for magnetic antennas, the volume is on the order of tens of thousands to hundreds of thousands of cubic centimeters. This size constraint has led to the adoption of conventional very low frequency receive antennas in many applications. Therefore, how to implement a high-sensitivity, microminiature receiving technique for very low frequency radio signals is a great difficulty in this field. And the detection and the reception of the very low frequency signals by utilizing the atomic magnetometer principle and theory to construct the very low frequency atomic magnetometer are novel technical approaches hopeful to solve the problem.
Disclosure of Invention
The invention provides a signal detection method and a system based on an in-situ magnetic compensation very low frequency atomic magnetometer, which can solve the technical problems that a very low frequency receiving antenna is difficult to apply due to large size, the polarization efficiency of an atomic ensemble is low and the external magnetic field interference suppression capability is poor in the prior art.
According to an aspect of the present invention, there is provided a signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer, the signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer comprising: the pumping light laser, the first gram-Taylor prism, the quarter wave plate, the detection light laser, the first half wave plate, the second gram-Taylor prism, the first reflecting mirror, the second half wave plate, the Wollaston prism, the balanced homodyne detector, the three-axis magnetic field coil, the third photoelectric detector and the data acquisition and control system are arranged, the balanced homodyne detector comprises the first photoelectric detector and the second photoelectric detector, the three-axis magnetic field coil is used for counteracting the interference of an environment magnetic field under the control of the data acquisition and control system and generating a precession main magnetic field at the same time, the data acquisition and control system is used for carrying out feedback control on the three-axis magnetic field coil according to signals acquired by the first photoelectric detector and the second photoelectric detector, and the atomic gas chamber is filled with first alkali metal atoms and second alkali metal atoms; tuning a pumping light laser to resonance of a first alkali metal atom transition frequency, enabling pumping laser generated by the pumping light laser to enter an atomic gas chamber to polarize first alkali metal atoms through a first gram-Taylor prism and a quarter wave plate in sequence, enabling second alkali metal atoms to be polarized through collision with the first alkali metal atoms, and enabling pumping laser transmitted from the atomic gas chamber to enter a data acquisition and control system through a third photoelectric detector; the detection laser device generates detection laser, the detection laser is used for detecting precession of a first alkali metal atom and a second alkali metal atom at the same time, the detection laser generated by the detection laser device sequentially enters an atomic gas chamber through a first half-wave plate, a second gram-Taylor prism and a first reflecting mirror, and the detection laser transmitted from the atomic gas chamber enters a first photoelectric detector and a second photoelectric detector through a second reflecting mirror, a second half-wave plate and a Wollaston prism; the data acquisition and control system scans the main magnetic field from 0 in the z direction by controlling the triaxial magnetic field coils according to real-time triaxial magnetic field information obtained by measuring the first alkali metal atoms so that the magnetic fields of the atomic air chamber along the horizontal polarization x direction and the vertical polarization y direction are 0; by scanning the size of the main magnetic field, observing the output amplitude change of the balanced homodyne detector in real time, finding out the main magnetic field size corresponding to the maximum output amplitude of the balanced homodyne detector as a preferable main magnetic field, and under the preferable main magnetic field, the precession frequency of the second alkali metal atoms resonates with a very low frequency signal to be detected; the data acquisition and control system is used for fixing the main magnetic field generated by the triaxial magnetic field coil into a preferable main magnetic field, and the data acquisition and control system is used for detecting the very low frequency signal according to the output signal of the balanced homodyne detector.
Further, the data acquisition and control system specifically comprises the following steps of: detecting the transmitted pumping laser signal through a third photoelectric detector, and performing phase-locking amplification algorithm processing on the transmitted pumping laser signal and an alternating-current magnetic field signal by a data acquisition and control system to obtain an X signal and a Y signal which are output by phase-locking amplification, wherein the X signal is in direct proportion to the size of a magnetic field in the X direction, and the Y signal is in direct proportion to the size of a magnetic field in the Y direction; when the calibration means determines that the magnetic fields in the X direction and the y direction are 0, the phase-locked amplification outputs a corresponding X signal calibration value X 0 And Y signal calibration value Y 0 The method comprises the steps of carrying out a first treatment on the surface of the Calculating and obtaining X-direction actual signal and X-signal calibration value X 0 Difference between X signal and Y signal, and calibration value Y of Y direction actual signal and Y signal 0 Y signal difference between; and respectively feeding back the X signal difference value and the Y signal difference value as error signals to the X-direction magnetic field coil and the Y-direction magnetic field coil by the data acquisition and control system so as to enable the magnetic fields of the atomic gas chamber along the horizontal polarization X-direction and the vertical polarization Y-direction to be 0.
Further, the method for fixing the magnitude of the main magnetic field generated by the triaxial magnetic field coil to be the preferable main magnetic field by using the data acquisition and control system specifically comprises the following steps: applying an alternating current magnetic field which enables first alkali metal atoms to precess and resonate with a main magnetic field through a triaxial magnetic field coil in the x direction by a data acquisition and control system; the data acquisition and control system performs phase-locking amplification processing on the first alkali metal atom precession signal detected by the detection laser and the alternating-current magnetic field signal to obtain a dispersion curve, and locks the main magnetic field at the phase zero position of the dispersion curve through feedback control of the triaxial magnetic coil, so that the main magnetic field is stabilized at the optimal main magnetic field.
Further, a reflecting film is plated on the pumping laser emergent surface of the atomic gas chamber, and the reflecting film is used for reflecting pumping laser back into the atomic gas chamber.
Further, the output amplitude of the balanced homodyne detector is proportional to the Faraday rotation angle, which is θWherein I is 0 ＝I 1 +I 2 ，I 1 For the output light intensity of the first photodetector, I 2 For the output light intensity of the second photodetector, I 0 Is the sum of the light intensities of the two laser beams output from the Wollaston prism.
Further, faraday rotation angle θ is proportional to polarization projection size S of spin ensemble in horizontal polarization x-direction x (t) polarization projection size S x (t) is S x (t)＝M x cos (ωt), where M x For the polarization projection amplitude, ω is the vibration frequency, and the polarization projection amplitude M x Proportional toWherein Γ is resonance line width, B is main magnetic field, and γ is gyromagnetic ratio.
Further, the main magnetic field B is preferred 0 Is B 0 ω/γ, where ω is the vibration frequency and γ is the gyromagnetic ratio.
According to still another aspect of the present invention, there is provided a signal detection system based on an in-situ magnetic compensation very low frequency atomic magnetometer, which performs very low frequency signal detection using the signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer as described above.
Further, the signal detection system based on the in-situ magnetic compensation very low frequency atomic magnetometer comprises a pumping light laser, a first gram-Taylor prism, a quarter wave plate, a detection light laser, a first half wave plate, a second gram-Taylor prism, a first reflecting mirror, a second half wave plate, a Wollaston prism, a balanced homodyne detector, a triaxial magnetic field coil, a third photoelectric detector and a data acquisition and control system, wherein the balanced homodyne detector comprises a first photoelectric detector and a second photoelectric detector, the pumping light laser is used for generating pumping laser, the pumping laser sequentially passes through the first gram-Taylor prism and the quarter wave plate to enter an atomic air chamber, the pumping laser transmitted from the atomic air chamber sequentially passes through the third photoelectric detector to enter the data acquisition and control system, the detection laser sequentially passes through the first half wave plate, the second gram-Taylor prism and the first reflecting mirror to enter the atomic air chamber, the third photoelectric detector, the balanced homodyne detector comprises a first photoelectric detector and a third photoelectric detector and a data acquisition and control system, the pumping laser sequentially passes through the second half wave plate, the second half wave plate and the first photoelectric detector enters the first photoelectric detector and the third photoelectric detector to enter the atomic air chamber, the data acquisition and control system is used for simultaneously, the data acquisition and the data and the control system are fed back to the data and the data acquisition and the magnetic field are controlled.
Further, the signal detection system based on the in-situ magnetic compensation very low frequency atomic magnetometer also comprises a reflecting film, wherein the reflecting film is arranged on the pumping laser emergent surface of the atomic gas chamber and is used for reflecting pumping laser back to the atomic gas chamber.
By applying the technical scheme of the invention, the invention provides a signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer, which adopts an atomic air chamber containing two alkali metal atoms a and b as a core sensitive component and carries out polarization by a mixed pumping method; polarizing the first alkali metal atom a along the driving laser direction (z direction) by using the driving laser to the atomic spin ensemble, and polarizing the second alkali metal atom b by colliding with the first alkali metal atom a; and applying a precession main magnetic field B in the z direction, so that polarization projections in the x and y directions precess along the z axis, the very low frequency electromagnetic wave signals of the external polarization direction in the xOy plane interact with spin ensembles of polarized second alkali metal atoms B to enable the polarized atoms in the z direction to deviate from the z direction, the projections are generated in the xOy plane, the projected precession frequency of the spins of the second alkali metal atoms B in the xOy direction resonates with the frequency of the very low frequency signals by tuning the magnitude of the precession main magnetic field B, and the precession of spin projection signals of the spins of the second alkali metal atoms B in the x direction is detected by using detection laser in the x direction, so that the detection of the very low frequency signals is realized. Compared with the prior art, the signal detection method based on the in-situ magnetic compensation very low frequency atomic magnetometer can realize high-sensitivity detection of the very low frequency signal, and the system is about 1000 times of the sensitivity of the traditional coil method under the same sensing volume; the method has high detection efficiency, and can greatly reduce the volume of the sensor on the premise of ensuring the sensitivity; in addition, the scheme for constructing the very low frequency atomic magnetometer to detect the very low frequency signal not only can cover a very low frequency band (3 kHz-30 kHz), but also can realize ultra-high sensitive signal reception in the low frequency and very low frequency bands; the very low frequency receiving method is unlike the traditional electromagnetic antenna, and has inductive (magnetic antenna) or capacitive (electric antenna) coupling, so that the difficulty is brought to the array integration, and the receiving antenna array can be better constructed, and better signal-to-noise ratio and anti-interference capability are realized. In addition, an atomic gas chamber containing two alkali metal atoms is adopted as a core sensitive component, polarization is carried out by a mixed pumping method, a second alkali metal atom b is polarized through spin exchange collision with a first alkali metal atom a, the types of the first alkali metal atom a and the second alkali metal atom b are selected, the spin exchange efficiency rate between the second alkali metal atom b and the first alkali metal atom a is ensured to be more than 1, and a large amount of second alkali metal atoms b can be polarized by a small amount of atoms, so that the second alkali metal atom b with high polarization rate is obtained. The high-sensitivity detection of the very low frequency signal can be realized by utilizing the second alkali metal atom b with high polarizability, so that the requirement of the very low frequency atomic magnetometer on polarized light power can be effectively reduced, and the polarization efficiency of the atomic ensemble under low power is improved; the polarization gradient of the atomic ensemble can be effectively reduced, and the detection sensitivity of the very low frequency signal of the very low frequency atomic magnetometer is improved; the detection sensitivity of the atomic magnetometer can be improved under low polarized light power, and the high-sensitivity detection of the very low frequency signal can be realized; the scheme of the very low frequency atomic magnetometer for detecting the very low frequency signal has a simple structure and is easy to realize miniaturized integration. In addition, the first alkali metal atom a is directly polarized by driving light, a triaxial vector atomic magnetometer is constructed by using the first alkali metal atom a to monitor the static magnetic field of the atomic air chamber in real time, the magnetic field information monitored by the first alkali metal atom a is fed back to the triaxial magnetic compensation coil through control to dynamically compensate and control the magnetic field of the atomic air chamber, so that in-situ magnetic compensation is realized, a quasi-shielding environment is constructed, the very low frequency atomic magnetometer is ensured to normally work in an unshielded environment, high-precision environment magnetic interference suppression is realized, and therefore, the high-sensitivity detection of the very low frequency signal can be realized based on the very low frequency atomic magnetometer in the unshielded environment.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. It is evident that the drawings in the following description are only some embodiments of the present invention and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a schematic diagram of a signal detection system based on an in-situ magnetic compensation very low frequency atomic magnetometer according to one embodiment of the invention;
fig. 2 shows a schematic diagram of a system output amplitude variation curve during scanning of the main magnetic field B according to an embodiment of the present invention.
Wherein the above figures include the following reference numerals:
10. pumping light laser; 20. a first gram-taylor prism; 30. a quarter wave plate; 40. a probe light laser; 50. a first half-wave plate; 60. a second gram-taylor prism; 70. a first mirror; 80. a second mirror; 90. a second half wave plate; 100. wollaston prism; 110. a balanced homodyne detector; 111. a first photodetector; 112. a second photodetector; 120. a triaxial magnetic field coil; 130. a third photodetector; 140. a data acquisition and control system; 150. an atomic gas chamber.
Detailed Description
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective parts shown in the drawings are not drawn in actual scale for convenience of description. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further discussion thereof is necessary in subsequent figures.
As shown in fig. 1 and 2, according to an embodiment of the present invention, there is provided a signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer, the signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer comprising: a pumping light laser 10, a first gram-taylor prism 20, a quarter wave plate 30, a detection light laser 40, a first half wave plate 50, a second gram-taylor prism 60, a first reflecting mirror 70, a second reflecting mirror 80, a second half wave plate 90, a Wollaston prism 100, a balanced homodyne detector 110, a triaxial magnetic field coil 120, a third photodetector 130 and a data acquisition and control system 140 are arranged, the balanced homodyne detector 110 comprises a first photodetector 111 and a second photodetector 112, the triaxial magnetic field coil 120 is used for generating a precession main magnetic field while canceling interference of an environmental magnetic field under the control of the data acquisition and control system 140, the data acquisition and control system 140 is used for performing feedback control on the triaxial magnetic field coil 120 according to signals acquired by the first photodetector 111 and the second photodetector 112, and an atom 150 is filled with a first alkali atom and a second alkali atom; tuning the pump light laser 10 to resonance at a first alkali metal atom transition frequency, the pump light laser 10 generating pump laser light that enters the atomic gas chamber sequentially through the first gram-taylor prism 20 and the quarter wave plate 30 to polarize the first alkali metal atom, the second alkali metal atom being polarized by collision with the first alkali metal atom, the pump laser light transmitted from the atomic gas chamber entering the data acquisition and control system 140 through the third photodetector 130; the detection light laser 40 generates detection laser light, and detects precession of the first alkali metal atom and the second alkali metal atom simultaneously by using the detection laser light, the detection laser light generated by the detection light laser 40 sequentially enters the atomic gas chamber 150 through the first half-wave plate 50, the second gram-taylor prism 60 and the first reflecting mirror 70, and the detection laser light transmitted from the atomic gas chamber 150 enters the first photodetector 111 and the second photodetector 112 through the second reflecting mirror 80, the second half-wave plate 90 and the Wollaston prism 100; the data acquisition and control system 140 scans the main magnetic field from 0 in the z direction by controlling the triaxial magnetic field coil 120 so that the magnetic fields of the atomic gas chamber 150 along the horizontal polarization x direction and the vertical polarization y direction are both 0 according to the real-time triaxial magnetic field information obtained by measuring the first alkali metal atom; by scanning the main magnetic field, observing the output amplitude change of the balanced homodyne detector 110 in real time, and finding out the main magnetic field size corresponding to the maximum output amplitude of the balanced homodyne detector 110 as a preferable main magnetic field, wherein under the preferable main magnetic field, the precession frequency of the second alkali metal atoms resonates with the very low frequency signal to be detected; the data acquisition and control system 140 is utilized to fix the main magnetic field generated by the triaxial magnetic field coil 120 into a preferable main magnetic field, and the data acquisition and control system 140 completes the detection of the very low frequency signal according to the output signal of the balanced homodyne detector 110.
By applying the configuration mode, the signal detection method based on the in-situ magnetic compensation very low frequency atomic magnetometer is provided, and the method adopts an atomic air chamber containing two alkali metal atoms a and b as a core sensitive component, and is polarized by a mixed pumping method; polarizing the first alkali metal atom a along the driving laser direction (z direction) by using the driving laser to the atomic spin ensemble, and polarizing the second alkali metal atom b by colliding with the first alkali metal atom a; and applying a precession main magnetic field B in the z direction, so that polarization projections in the x and y directions precess along the z axis, the very low frequency electromagnetic wave signals of the external polarization direction in the xOy plane interact with spin ensembles of polarized second alkali metal atoms B to enable the polarized atoms in the z direction to deviate from the z direction, the projections are generated in the xOy plane, the projected precession frequency of the spins of the second alkali metal atoms B in the xOy direction resonates with the frequency of the very low frequency signals by tuning the magnitude of the precession main magnetic field B, and the precession of spin projection signals of the spins of the second alkali metal atoms B in the x direction is detected by using detection laser in the x direction, so that the detection of the very low frequency signals is realized. Compared with the prior art, the signal detection method based on the in-situ magnetic compensation very low frequency atomic magnetometer can realize high-sensitivity detection of the very low frequency signal, and the system is about 1000 times of the sensitivity of the traditional coil method under the same sensing volume; the method has high detection efficiency, and can greatly reduce the volume of the sensor on the premise of ensuring the sensitivity; in addition, the scheme for constructing the very low frequency atomic magnetometer to detect the very low frequency signal not only can cover a very low frequency band (3 kHz-30 kHz), but also can realize ultra-high sensitive signal reception in the low frequency and very low frequency bands; the very low frequency receiving method is unlike the traditional electromagnetic antenna, and has inductive (magnetic antenna) or capacitive (electric antenna) coupling, so that the difficulty is brought to the array integration, and the receiving antenna array can be better constructed, and better signal-to-noise ratio and anti-interference capability are realized. In addition, an atomic gas chamber containing two alkali metal atoms is adopted as a core sensitive component, polarization is carried out by a mixed pumping method, a second alkali metal atom b is polarized through spin exchange collision with a first alkali metal atom a, the types of the first alkali metal atom a and the second alkali metal atom b are selected, the spin exchange efficiency rate between the second alkali metal atom b and the first alkali metal atom a is ensured to be more than 1, and a large amount of second alkali metal atoms b can be polarized by a small amount of atoms, so that the second alkali metal atom b with high polarization rate is obtained. The high-sensitivity detection of the very low frequency signal can be realized by utilizing the second alkali metal atom b with high polarizability, so that the requirement of the very low frequency atomic magnetometer on polarized light power can be effectively reduced, and the polarization efficiency of the atomic ensemble under low power is improved; the polarization gradient of the atomic ensemble can be effectively reduced, and the detection sensitivity of the very low frequency signal of the very low frequency atomic magnetometer is improved; the detection sensitivity of the atomic magnetometer can be improved under low polarized light power, and the high-sensitivity detection of the very low frequency signal can be realized; the scheme of the very low frequency atomic magnetometer for detecting the very low frequency signal has a simple structure and is easy to realize miniaturized integration. In addition, the first alkali metal atom a is directly polarized by driving light, a triaxial vector atomic magnetometer is constructed by using the first alkali metal atom a to monitor the static magnetic field of the atomic air chamber in real time, the magnetic field information monitored by the first alkali metal atom a is fed back to the triaxial magnetic compensation coil through control to dynamically compensate and control the magnetic field of the atomic air chamber, so that in-situ magnetic compensation is realized, a quasi-shielding environment is constructed, the very low frequency atomic magnetometer is ensured to normally work in an unshielded environment, high-precision environment magnetic interference suppression is realized, and therefore, the high-sensitivity detection of the very low frequency signal can be realized based on the very low frequency atomic magnetometer in the unshielded environment.
In the invention, in order to further improve the polarization efficiency of the spin ensemble, a reflection film is plated on the pumping laser emitting surface of the atomic gas chamber, and the reflection film is used for reflecting the pumping laser back into the atomic gas chamber.
Specifically, in the invention, the atomic magnetometer is a magnetic sensor for measuring a magnetic field by utilizing larmor precession of electron spin or nuclear spin under the magnetic field, is a magnetic field sensor with highest detection sensitivity at present, and has the advantages of normal temperature operation, small volume, low power consumption and low cost. The magnetic field detection technology has wide application in the fields of basic research, medicine, military, space and the like. The very low frequency signal detection method for constructing the very low frequency atomic magnetometer based on the atomic magnetometer principle is expected to be applied to the underwater technology such as submarine communication, very low frequency communication and navigation, and the bottleneck problem that the volume and the sensitivity of the very low frequency antenna in the technical fields are difficult to be compatible is solved.
The atomic spin precession frequency and the frequency of the detected very low frequency signal reach resonance by tuning the main magnetic field of the very low frequency atomic magnetometer so as to realize the detection of the very low frequency signal. The main magnetic field is usually less than 10000nT and much smaller than the geomagnetic field (-50000 nT), so that the interference of external magnetic fields such as geomagnetic field must be overcome, and the very low frequency atomic magnetometer can work in an unshielded environment. The very low frequency atomic magnetometer is used as a receiving antenna in the application of the very low frequency communication and navigation technology, and the application of the very low frequency atomic magnetometer in an unshielded environment (such as geomagnetic environment) is needed, namely, the technology of the unshielded very low frequency atomic magnetometer is needed. The technology of the unshielded atomic magnetometer in the research at the present stage mainly has two ideas, namely, the technology of the unshielded atomic magnetometer based on multi-channel difference is characterized in that a magnetic field gradiometer is constructed by utilizing a plurality of atomic magnetometers through differential detection, so that the suppression of common mode magnetic noise in the environment is realized, the interference of an environmental magnetic field is eliminated, and the high-sensitivity detection of very low frequency signals is realized. The dynamic magnetic field feedback compensation method is to utilize a fluxgate/magnetic resistance to monitor the change of the environmental magnetic field of the atomic air chamber in real time, and the change of the environmental magnetic field is dynamically compensated by the triaxial magnetic coil through feedback, so that a static quasi-shielding magnetic environment is provided, and the normal operation of the atomic magnetometer is ensured. However, the two methods have insufficient external magnetic field interference suppression capability, limit the further improvement of the detection sensitivity of the non-shielding atomic magnetometer, and simultaneously additionally increase the magnetic sensor, greatly increase the complexity of the non-shielding atomic magnetometer and bring difficulty to the miniaturization integration of the non-shielding atomic magnetometer. Therefore, how to realize high-precision suppression of external magnetic fields and easy microminiature integration of the unshielded very low frequency atomic magnetometer technology for high-sensitivity detection of very low frequency signals is still a problem to be solved, and a new thought and a new method to be developed for solving the problem are still needed.
In order to realize the technology of high-precision suppression of an external magnetic field and easy microminiature integration of receiving a very low frequency signal by an unshielded very low frequency atomic magnetometer, the invention provides a very low frequency detection scheme based on an in-situ magnetic compensation very low frequency atomic magnetometer. The scheme adopts a diatomic ensemble as a sensing core component. On the one hand, the very low frequency signal is received by mixing one of the atomic spins in the diatomic source; on the other hand, an in-situ triaxial atomic magnetometer is built based on the spin of another atom in the mixed diatomic source, high-precision feedback control is carried out on the environmental magnetic field of the atomic ensemble by matching with the magnetic field coil, in-situ magnetic compensation is carried out, high-efficiency inhibition on the external magnetic field is realized, a quasi-shielding environment is provided for the work of the very low frequency atomic magnetometer, the normal work of the very low frequency atomic magnetometer in an unshielded environment is ensured, and the technology for high-sensitivity detection of the very low frequency signal in the unshielded environment is realized based on the quasi-shielding environment.
The specific implementation principle of the invention is as follows: an atomic air chamber filled with two alkali metal atoms a and b is used as a core sensing component, the first alkali metal atom a is directly polarized by circularly polarized driving light which is in transition resonance with the first alkali metal atom a by utilizing the principle of mixed pumping, and the second alkali metal atom b is indirectly polarized by collision between the second alkali metal atom b and the first alkali metal atom a. The precession of the first alkali metal atom a and the second alkali metal atom b is detected simultaneously by the detection light. The detection of the very low frequency signal is achieved by tuning the magnitude of the main magnetic field parallel to the driving light such that the second alkali metal atom b precesses and the detected very low frequency signal reaches resonance. Constructing a triaxial vector atomic magnetometer by using a first alkali metal atom a: polarization M in z-direction of first alkali metal atom a obtained by using transmitted driving light information z And signals are used for realizing magnetic field measurement in the x and y directions and carrying out feedback control on the magnetic fields in the x and y directions through the triaxial magnetic field coils. The triaxial vector atomic magnetometer constructed by the first alkali metal atom a is used for in-situ measurement of the magnetic field of the atomic air chamber, and the magnetic compensation coil is combined for in-situ compensation of the environmental magnetic field of the atomic air chamber, so that a quasi-shielding environment is provided for the work of the very low frequency atomic magnetometer, the normal work of the very low frequency atomic magnetometer is ensured, and the non-shielding very low frequency atomic magnetometer technology is realized. Polarization M of first alkali metal atom a in x-direction obtained by using precession signal of first alkali metal atom a detected by detection light x The dispersion relation of the information along with the change of the main magnetic field realizes the monitoring of the main magnetic field B, and the main magnetic field is stably controlled through the triaxial magnetic field coil.
Specifically, in order to realize the detection of the non-shielding very low frequency signal, the triaxial magnetic field coil 120 is controlled to make the magnetic field of the atomic gas chamber along the horizontal polarization x direction and the vertical polarization y direction be 0 according to the real-time triaxial magnetic field information obtained by measuring the first alkali metal atom a. In the present invention, the data acquisition and control system 140 specifically includes: at the position of The first alkali metal atom precession is applied by the data acquisition and control system through the triaxial magnetic field coil to resonate (omega) with the main magnetic field in the x direction a ＝γ a B 0 ) Ac magnetic field B of (2) a cos(ω a t) such that the first alkali metal atom constitutes an M x Atomic magnetometer. Detecting the transmitted pumping laser signal by the third photodetector 130, and performing phase-locked amplification algorithm processing on the transmitted pumping laser signal and the alternating-current magnetic field signal by the data acquisition and control system 140 to obtain an X signal and a Y signal which are output by phase-locked amplification, wherein the X signal is in direct proportion to the magnitude of the magnetic field in the X direction, and the Y signal is in direct proportion to the magnitude of the magnetic field in the Y direction; when the calibration means determines that the magnetic fields in the X direction and the y direction are 0, the phase-locked amplification outputs a corresponding X signal calibration value X 0 And Y signal calibration value Y 0 The method comprises the steps of carrying out a first treatment on the surface of the Calculating and obtaining X-direction actual signal and X-signal calibration value X 0 Difference between X signal and Y signal, and calibration value Y of Y direction actual signal and Y signal 0 Y signal difference between; the X-signal difference and the Y-signal difference are fed back as error signals to the X-direction magnetic field coil and the Y-direction magnetic field coil by the data acquisition and control system 140 respectively to set the magnetic fields of the atomic gas chamber along the horizontal polarization X-direction and the vertical polarization Y-direction to be 0.
Further, after the magnetic fields of the atomic air chamber along the horizontal polarization x direction and the vertical polarization y direction are controlled to be 0, the main magnetic field can be scanned from 0 in the z direction, the output amplitude change of the balanced homodyne detector 110 is observed in real time through the scanning of the main magnetic field, the main magnetic field corresponding to the maximum output amplitude of the balanced homodyne detector 110 is found out to be the preferable main magnetic field, and under the preferable main magnetic field, the precession frequency of the second alkali metal atoms resonates with the very low frequency signal to be detected. The data acquisition and control system 140 is utilized to fix the main magnetic field generated by the triaxial magnetic field coil 120 into a preferable main magnetic field, and the data acquisition and control system 140 completes the detection of the very low frequency signal according to the output signal of the balanced homodyne detector 110.
Specifically, in the present invention, the pump laser light generated by the pump light laser 10 is tuned to resonate with the transition frequency of the first alkali metal atom a, and after the pump laser light is polarized and purified by the first gram-taylor prism 20, the transmitted light becomes circularly polarized positive laser light required by the very low frequency atomic magnetometer system through the first quarter wave plate 30, and is injected into the atomic gas cell 150 located in the center of the coil, and polarization of the first alkali metal atom a is achieved by interaction with the first alkali metal atom a in the atomic gas cell 150. Polarized light transmitted through the atomic cell 150 is reflected by the cell surface reflective film to re-enter the cell, so that the optical field in the cell is more uniform, and the polarization of the first alkali metal atom a is more uniform. In the process, the second alkali metal atom b is already polarized in the atom gas chamber by collision with the first alkali metal atom a.
After the detection laser beam emitted from the detection laser 40 is polarized and purified by the second gram-taylor prism 60, the detection laser beam enters the atomic gas chamber 150 through a reflecting mirror in a linear polarization state, the precession of the first alkali metal atom a and the second alkali metal atom b is detected by the detection laser beam at the same time, the transmitted light passing through the atomic gas chamber 150 passes through the second half wave plate 90 and then is generated by the wollaston prism 100 into two laser beams with orthogonal polarization directions, the light intensity of the two laser beams is related to the faraday rotation angle after passing through the gas chamber, and the specific light intensity can be expressed as follows:
Wherein I is 0 ＝I 1 +I 2 The sum of the light intensities of the two laser beams is that theta is the Faraday rotation angle of the laser beams after the laser beams pass through the air chamber, and the Faraday rotation angle is related to the polarization intensity of the air chamber atoms in the laser propagation direction. The light intensity of the two laser beams is respectively received by two photoelectric detectors of the balance homodyne detector behind the two laser beams, and the Faraday rotation angle can be obtained by the signals of the two photoelectric detectors:
so that the difference result (I 2 -I 1 ) Directly proportional to the faraday rotation angle theta.
In the detection of the very low frequency signal Bcos (ωt), the precession frequency of the second alkali metal atom B is made to resonate with the very low frequency signal to be detected by tuning the magnitude of the main magnetic field B. The specific method comprises the following steps: the data acquisition and control system 140 controls the ambient magnetic field of the air chamber according to the real-time triaxial magnetic field information measured by the first alkali metal atom a, so that the magnetic fields in the x and y directions are 0, and the main magnetic field B is scanned from 0 in the z direction. Since the Faraday rotation angle θ of the light is proportional to the polarization projection size S of the spin ensemble in the x-direction x (t), namely: theta ≡S x (t) the signal magnitude output by the balanced homodyne detector will now be proportional to: s is S x (t)＝M x cos (ωt), where the polarization projection amplitude M of the spin ensemble in the x-direction x The relationship with the change of the main magnetic field size B is as follows:
wherein Γ is the resonance linewidth, here a constant term, B is the main magnetic field, ω is the vibration frequency, and γ is the gyromagnetic ratio. By scanning the size of the main magnetic field B, the change of the output amplitude of the balanced homodyne detector is shown in figure 2, and the optimal main magnetic field B with the maximum output amplitude is found out 0 =ω/γ, locking the main magnetic field magnitude to the preferred main magnetic field. At this time, the system and the very low frequency signal are in a resonance state, and the signal which is output by the balanced homodyne detector and is analyzed and processed by the data acquisition and control system is the received very low frequency signal, so that the detection of the very low frequency signal by the very low frequency atomic magnetometer is realized.
In the present invention, the fixing the magnitude of the main magnetic field generated by the triaxial magnetic field coil 120 to the preferred main magnetic field by using the data acquisition and control system 140 specifically includes: an alternating magnetic field that causes the first alkali metal atom precession to resonate with the main magnetic field is applied by the data acquisition and control system 140 in the x-direction through the triaxial magnetic field coil 120; the data acquisition and control system 140 performs phase-locking amplification processing on the first alkali metal atom precession signal detected by the detection laser and the alternating-current magnetic field signal to obtain a dispersion curve, and locks the main magnetic field at the phase zero position of the dispersion curve through feedback control of the triaxial magnetic coil, so that the main magnetic field is stabilized at the preferable main magnetic field.
According to another aspect of the present invention, there is provided a signal detection system based on an in-situ magnetic compensation very low frequency atomic magnetometer, which performs very low frequency signal detection using the signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer as described above.
By applying the configuration mode, a signal detection system based on an in-situ magnetic compensation very low frequency atomic magnetometer is provided, and the system adopts an atomic air chamber containing two alkali metal atoms a and b as a core sensitive component and is polarized by a mixed pumping method; polarizing the first alkali metal atom a along the driving laser direction (z direction) by using the driving laser to the atomic spin ensemble, and polarizing the second alkali metal atom b by colliding with the first alkali metal atom a; and applying a precession main magnetic field B in the z direction, so that polarization projections in the x and y directions precess along the z axis, the very low frequency electromagnetic wave signals of the external polarization direction in the xOy plane interact with spin ensembles of polarized second alkali metal atoms B to enable the polarized atoms in the z direction to deviate from the z direction, the projections are generated in the xOy plane, the projected precession frequency of the spins of the second alkali metal atoms B in the xOy direction resonates with the frequency of the very low frequency signals by tuning the magnitude of the precession main magnetic field B, and the precession of spin projection signals of the spins of the second alkali metal atoms B in the x direction is detected by using detection laser in the x direction, so that the detection of the very low frequency signals is realized. Compared with the prior art, the signal detection system based on the in-situ magnetic compensation very low frequency atomic magnetometer can realize high-sensitivity detection of very low frequency signals, and the system is about 1000 times of the sensitivity of the traditional coil method under the same sensing volume; the system has high detection efficiency, and can greatly reduce the volume of the sensor on the premise of ensuring the sensitivity; in addition, the scheme for detecting the very low frequency signal by the very low frequency atomic magnetometer can cover a very low frequency band (3 kHz-30 kHz) and can realize ultra-high sensitive signal reception in the low frequency and very low frequency bands; the very low frequency receiving method is unlike the traditional electromagnetic antenna, and has inductive (magnetic antenna) or capacitive (electric antenna) coupling, so that the difficulty is brought to the array integration, and the receiving antenna array can be better constructed, and better signal-to-noise ratio and anti-interference capability are realized. In addition, an atomic gas chamber containing two alkali metal atoms is adopted as a core sensitive component, polarization is carried out by a mixed pumping method, a second alkali metal atom b is polarized through spin exchange collision with a first alkali metal atom a, the types of the first alkali metal atom a and the second alkali metal atom b are selected, the spin exchange efficiency rate between the second alkali metal atom b and the first alkali metal atom a is ensured to be more than 1, and a large amount of second alkali metal atoms b can be polarized by a small amount of atoms, so that the second alkali metal atom b with high polarization rate is obtained. The high-sensitivity detection of the very low frequency signal can be realized by utilizing the second alkali metal atom b with high polarizability, so that the requirement of the very low frequency atomic magnetometer on polarized light power can be effectively reduced, and the polarization efficiency of the atomic ensemble under low power is improved; the polarization gradient of the atomic ensemble can be effectively reduced, and the detection sensitivity of the very low frequency signal of the very low frequency atomic magnetometer is improved; the detection sensitivity of the atomic magnetometer can be improved under low polarized light power, and the high-sensitivity detection of the very low frequency signal can be realized; the scheme of the very low frequency atomic magnetometer for detecting the very low frequency signal has a simple structure and is easy to realize miniaturized integration. In addition, the first alkali metal atom a is directly polarized by driving light, a triaxial vector atomic magnetometer is constructed by using the first alkali metal atom a to monitor the static magnetic field of the atomic air chamber in real time, the magnetic field information monitored by the first alkali metal atom a is fed back to the triaxial magnetic compensation coil through control to dynamically compensate and control the magnetic field of the atomic air chamber, so that in-situ magnetic compensation is realized, a quasi-shielding environment is constructed, the very low frequency atomic magnetometer is ensured to normally work in an unshielded environment, high-precision environment magnetic interference suppression is realized, and therefore, the high-sensitivity detection of the very low frequency signal can be realized based on the very low frequency atomic magnetometer in the unshielded environment.
Specifically, in the present invention, in order to achieve efficient polarization very low frequency signal detection, the signal detection system based on the in-situ magnetic compensation very low frequency atomic magnetometer includes a pumping light laser 10, a first gram-taylor prism 20, a quarter wave plate 30, a detection light laser 40, a first half wave plate 50, a second gram-taylor prism 60, a first mirror 70, a second mirror 80, a second half wave plate 90, a Wollaston prism 100, a balanced homodyne detector 110, a triaxial magnetic field coil 120, a third photodetector 130 and a data acquisition and control system 140, the balanced homodyne detector 110 includes a first photodetector 111 and a second photodetector 112, the pumping light laser 10 is used to generate pumping laser light, the pumping laser light enters the atomic gas cell sequentially through the first gram-taylor prism 20 and the quarter wave plate 30, the pumping laser transmitted from the atomic gas chamber enters the data acquisition and control system 140 through the third photodetector 130, the detection laser 40 is used for generating detection laser, the detection laser sequentially enters the atomic gas chamber through the first half-wave plate 50, the second gram-taylor prism 60 and the first reflecting mirror 70, the detection laser transmitted from the atomic gas chamber enters the first photodetector 111 and the second photodetector 112 through the second reflecting mirror 80, the second half-wave plate 90 and the Wollaston prism 100, the triaxial magnetic field coil 120 is used for counteracting the interference of the environmental magnetic field under the control of the data acquisition and control system 140 and generating a precession main magnetic field at the same time, and the data acquisition and control system 140 is used for performing feedback control on the triaxial magnetic field coil 120 according to signals acquired by the first photodetector 111 and the second photodetector 112.
In order to further improve the polarization efficiency of the atomic ensemble, the signal detection system based on the in-situ magnetic compensation very low frequency atomic magnetometer further comprises a reflecting film, wherein the reflecting film is arranged on the pumping laser emergent surface of the atomic air chamber and is used for reflecting pumping laser back to the atomic air chamber.
For further understanding of the present invention, the following describes in detail the signal detection method and system based on the in-situ magnetic compensation very low frequency atomic magnetometer provided by the present invention with reference to fig. 1 to 2.
In order to solve the defects that the traditional very low frequency signal receiving antenna is difficult to achieve both small volume and high sensitivity, and the very low frequency atomic magnetometer is low in polarization rate and detection sensitivity caused by low-power laser polarization under the constraint of small volume, and the problems that the existing unshielded atomic magnetometer technology is poor in external magnetic field interference suppression capability and difficult to realize microminiature integration, the invention designs a very low frequency detection scheme based on the in-situ magnetic compensation very low frequency atomic magnetometer, which can realize efficient polarization of an atomic ensemble under the low-power laser polarization and in-situ high-precision compensation of an environmental magnetic field where an atomic air chamber is located, thereby ensuring that the very low frequency atomic magnetometer works in a highly sensitive environment under the unshielded environment, and simultaneously, no additional sensor is needed, so that the method is easy to realize microminiature integration. Therefore, the invention can realize the microminiature non-shielding very low frequency atomic magnetometer with high sensitivity and the very low frequency signal high sensitivity and small volume receiving method and system based on the microminiature non-shielding very low frequency atomic magnetometer.
The technical scheme adopted by the design is as follows: (1) An atomic gas chamber containing two alkali metal atoms a and b is used as a core sensitive component; (2) Polarizing and detecting the atomic ensemble in the atomic gas chamber by using the driving light and the detecting light; (3) The second alkali metal atom b is polarized in a mixed pumping mode, and the resonance effect of the Larmor precession of the second alkali metal atom b and the very low frequency signal under the main magnetic field is utilized to realize the detection of the very low frequency signal; (4) The first alkali metal atom a is directly polarized by driving light, and a triaxial vector atomic magnetometer is constructed by using the first alkali metal atom a to monitor the static magnetic field of the atomic air chamber in real time; (5) And feeding back the magnetic field information monitored by the first alkali metal atom a to the triaxial magnetic field coil through control, dynamically compensating and controlling the magnetic field of the atomic air chamber, realizing in-situ magnetic compensation, constructing a quasi-shielding environment, ensuring the normal operation of the very low frequency atomic magnetometer in an unshielded environment, and realizing the detection of a very low frequency signal in the unshielded environment. In this embodiment, the first alkali metal atom a is potassium K and the second alkali metal atom b is rubidium Rb.
The beneficial effects of the invention are as follows: the detection of the very low frequency signal and the dynamic in-situ compensation of the environmental magnetic field can be simultaneously realized based on one atomic air chamber; the in-situ magnetic compensation scheme constructed based on the atomic air chamber can realize high-precision environment magnetic interference suppression; the high-sensitivity detection of the very low frequency signal can be realized based on the very low frequency atomic magnetometer in an unshielded environment; the scheme for receiving the very low frequency signal by the unshielded atomic magnetometer has a simple structure and is easy to realize miniaturized integration.
The additional beneficial effects are that: the polarization is carried out by adopting a mixed pumping method, so that the polarization efficiency and the detection sensitivity of the very low frequency atomic magnetometer can be improved; the sensing component is an air chamber, has a simple structure, and is easy to realize sensor array integration, so that interference is further suppressed, and sensitivity is improved.
As shown in fig. 1, the signal detection system based on the in-situ magnetic compensation very low frequency atomic magnetometer includes a pumping light laser 10, a first gram-taylor prism 20, a quarter wave plate 30, a detection light laser 40, a first half wave plate 50, a second gram-taylor prism 60, a first mirror 70, a second mirror 80, a second half wave plate 90, a wollaston prism 100, a balanced homodyne detector 110, a triaxial magnetic field coil 120, a third photodetector 130 and a data acquisition and control system 140.
Pumping light laser 10: for generating a pump laser; detection light laser 40: for generating a detection laser; quarter waveplate 30: changing the polarization of the laser, here mainly for changing linearly polarized light into circularly polarized light; half wave plates (i.e., first half wave plate 50 and second half wave plate 90): changing the polarization of the laser, which is mainly used for changing the polarization direction of linearly polarized light; gram taylor prisms (i.e., first gram taylor prism 20 and second gram taylor prism 60): polarization splitting is performed on the beam, here to purify the polarization of the transmitted laser, ensuring that it is horizontally polarized (x-direction polarization); wollaston prism 100: polarization splitting the beam such that light polarized vertically (y-direction) and horizontally (x-direction) is spatially separated; triaxial magnetic field coil 120: generating a magnetic field in three dimensions, the acquisition and control system controlling the drying for counteracting the ambient magnetic field Disturbing the simultaneous generation of a precessional main magnetic field B 0 The method comprises the steps of carrying out a first treatment on the surface of the Mixed atomic gas cell 150 of single sided reflective coating: the core working device is used for providing an atomic ensemble for mixing pumping and detecting very low frequency signals and simultaneously realizing closed-loop control by measuring the surrounding environment magnetic field of the air chamber and matching with the triaxial magnetic field coil; mirrors (i.e., first mirror 70 and second mirror 80): changing the direction of the light path; balanced homodyne detector 110: converting the detected optical precession information into a differential electric signal and outputting the differential electric signal; data acquisition and control system 140: and collecting and processing the data, and simultaneously carrying out feedback control on the system.
The specific working mode is as follows.
(1) Polarization and detection
The pump laser light generated by the pump light laser 10 is tuned to resonate with the first alkali metal atom a transition frequency, and after the pump laser light is polarized and purified by the first gram-taylor prism 20, the transmitted light is changed into circular polarized forward laser light required by the very low frequency atomic magnetometer system by the first quarter wave plate 30, and enters the atomic gas chamber 150 positioned at the center of the coil, and the polarization of the first alkali metal atom a is realized by interaction with the first alkali metal atom a in the atomic gas chamber 150. Polarized light transmitted through the atomic cell 150 is reflected by the cell surface reflective film to re-enter the cell, so that the optical field in the cell is more uniform, and the polarization of the first alkali metal atom a is more uniform. In the process, the second alkali metal atom b is already polarized in the atom gas chamber by collision with the first alkali metal atom a.
After the detection laser beam emitted from the detection laser 40 is polarized and purified by the second gram-taylor prism 60, the detection laser beam enters the atomic gas chamber 150 through a reflecting mirror in a linear polarization state, the precession of the first alkali metal atom a and the second alkali metal atom b is detected by the detection laser beam at the same time, the transmitted light passing through the atomic gas chamber 150 passes through the second half wave plate 90 and then is generated by the wollaston prism 100 into two laser beams with orthogonal polarization directions, the light intensity of the two laser beams is related to the faraday rotation angle after passing through the gas chamber, and the specific light intensity can be expressed as follows:
wherein I is 0 ＝I 1 +I 2 The sum of the light intensities of the two laser beams is that theta is the Faraday rotation angle of the laser beams after the laser beams pass through the air chamber, and the Faraday rotation angle is related to the polarization intensity of the air chamber atoms in the laser propagation direction. The light intensity of the two laser beams is respectively received by two photoelectric detectors of the balance homodyne detector behind the two laser beams, and the Faraday rotation angle can be obtained by the signals of the two photoelectric detectors:
so that the difference result (I 2 -I 1 ) Directly proportional to the faraday rotation angle theta.
(2) Triaxial magnetic field closed-loop control-non-shielding implementation
In detecting a triaxial magnetic field using a first alkali metal atom a, a data acquisition and control system applies a triaxial magnetic field coil in the x-direction to cause the first alkali metal atom to precess and resonate with the main magnetic field (ω) a ＝γ a B 0 ) Ac magnetic field B of (2) a cos(ω a t) such that the first alkali metal atom constitutes an M x Atomic magnetometer, wherein ω a Is the vibration frequency of the first alkali metal atom a, gamma a B is the gyromagnetic ratio of the first alkali metal atom a a Is the magnetic field of the first alkali metal atom a. The third photodetector 130 detects the transmitted pumping laser signal, and the data acquisition and control system 140 transmits the transmitted pumping laser signal and the alternating magnetic field signal B a cos(ω a t) performing phase-locked amplification algorithm to obtain X signal and Y signal, wherein the X signal is proportional to the X direction due to the fact that the pumping laser reflects the polarization vector in z direction, and the magnetic fields in X and Y directions project the vector to corresponding directions to influence the output signal of driving lightThe Y signal is proportional to the magnitude of the magnetic field in the Y direction; in practical application, firstly, when the magnetic fields in the X direction and the y direction are both 0, the calibration means is used for determining that the corresponding X signal calibration value X is output by phase-locked amplification 0 And Y signal calibration value Y 0 The method comprises the steps of carrying out a first treatment on the surface of the At a time of knowing X 0 And Y 0 Then, calculating and obtaining the actual X-direction signal and the X-signal calibration value X 0 Difference between X signal and Y signal, and calibration value Y of Y direction actual signal and Y signal 0 Y signal difference between; the X-signal difference and the Y-signal difference are fed back as error signals to the X-direction magnetic field coil and the Y-direction magnetic field coil by the data acquisition and control system 140 respectively to set the magnetic fields of the atomic gas chamber along the horizontal polarization X-direction and the vertical polarization Y-direction to be 0.
(3) Very low frequency signal detection
In the detection of the very low frequency signal Bcos (ωt), the precession frequency of the second alkali metal atom B is made to resonate with the very low frequency signal to be detected by tuning the magnitude of the main magnetic field B. The specific method comprises the following steps: the data acquisition and control system 140 controls the ambient magnetic field of the air chamber according to the real-time triaxial magnetic field information measured by the first alkali metal atom a, so that the magnetic fields in the x and y directions are 0, and the main magnetic field B is scanned from 0 in the z direction. Since the Faraday rotation angle θ of the light is proportional to the polarization projection size S of the spin ensemble in the x-direction x (t), namely: theta ≡S x (t) the signal magnitude output by the balanced homodyne detector will now be proportional to: s is S x (t)＝M x cos (ωt), where the polarization projection amplitude M of the spin ensemble in the x-direction x The relationship with the change of the main magnetic field size B is as follows:
wherein Γ is the resonance linewidth, here a constant term, B is the main magnetic field, ω is the vibration frequency, and γ is the gyromagnetic ratio. By scanning the size of the main magnetic field B, the change of the output amplitude of the balanced homodyne detector is shown in figure 2, and the optimal main magnetic field B with the maximum output amplitude is found out 0 The data acquisition and control system 140 detects for the detection laser light =ω/γThe first alkali metal atom precession signal and the alternating magnetic field signal are subjected to phase-locking amplification treatment to obtain a dispersion curve, and the main magnetic field is locked at the phase zero position of the dispersion curve by controlling the triaxial magnetic coil through feedback, so that the main magnetic field is stabilized at the preferable main magnetic field B 0 Thereby realizing magnetic field control and locking of the main magnetic field direction. At this time, the system and the very low frequency signal are in a resonance state, and the signal which is output by the balanced homodyne detector and is analyzed and processed by the data acquisition and control system is the received very low frequency signal, so that the detection of the very low frequency signal by the very low frequency atomic magnetometer is realized. The data acquisition and control system 140 ensures the stability of the environmental magnetic field where the atomic gas chamber is located by means of the feedback closed-loop control of the magnetic fields in three directions, thereby realizing the work of the very low frequency atomic magnetometer in an unshielded environment.
In summary, the invention provides a signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer, which adopts an atomic air chamber containing two alkali metal atoms a and b as a core sensitive component, and performs polarization by a mixed pumping method; polarizing the first alkali metal atom a along the driving laser direction (z direction) by using the driving laser to the atomic spin ensemble, and polarizing the second alkali metal atom b by colliding with the first alkali metal atom a; and applying a precession main magnetic field B in the z direction, so that polarization projections in the x and y directions precess along the z axis, the very low frequency electromagnetic wave signals of the external polarization direction in the xOy plane interact with spin ensembles of polarized second alkali metal atoms B to enable the polarized atoms in the z direction to deviate from the z direction, the projections are generated in the xOy plane, the projected precession frequency of the spins of the second alkali metal atoms B in the xOy direction resonates with the frequency of the very low frequency signals by tuning the magnitude of the precession main magnetic field B, and the precession of spin projection signals of the spins of the second alkali metal atoms B in the x direction is detected by using detection laser in the x direction, so that the detection of the very low frequency signals is realized. Compared with the prior art, the signal detection method based on the in-situ magnetic compensation very low frequency atomic magnetometer can realize high-sensitivity detection of the very low frequency signal, and the system is about 1000 times of the sensitivity of the traditional coil method under the same sensing volume; the method has high detection efficiency, and can greatly reduce the volume of the sensor on the premise of ensuring the sensitivity; in addition, the scheme for detecting the very low frequency signal by the very low frequency atomic magnetometer can cover a very low frequency band (3 kHz-30 kHz) and can realize ultra-high sensitive signal reception in the low frequency and very low frequency bands; the very low frequency receiving method is unlike the traditional electromagnetic antenna, and has inductive (magnetic antenna) or capacitive (electric antenna) coupling, so that the difficulty is brought to the array integration, and the receiving antenna array can be better constructed, and better signal-to-noise ratio and anti-interference capability are realized. In addition, an atomic gas chamber containing two alkali metal atoms is adopted as a core sensitive component, polarization is carried out by a mixed pumping method, a second alkali metal atom b is polarized through spin exchange collision with a first alkali metal atom a, the types of the first alkali metal atom a and the second alkali metal atom b are selected, the spin exchange efficiency rate between the second alkali metal atom b and the first alkali metal atom a is ensured to be more than 1, and a large amount of second alkali metal atoms b can be polarized by a small amount of atoms, so that the second alkali metal atom b with high polarization rate is obtained. The high-sensitivity detection of the very low frequency signal can be realized by utilizing the second alkali metal atom b with high polarizability, so that the requirement of the very low frequency atomic magnetometer on polarized light power can be effectively reduced, and the polarization efficiency of the atomic ensemble under low power is improved; the polarization gradient of the atomic ensemble can be effectively reduced, and the detection sensitivity of the very low frequency signal of the very low frequency atomic magnetometer is improved; the detection sensitivity of the atomic magnetometer can be improved under low polarized light power, and the high-sensitivity detection of the very low frequency signal can be realized; the scheme of the very low frequency atomic magnetometer for detecting the very low frequency signal has a simple structure and is easy to realize miniaturized integration. In addition, the first alkali metal atom a is directly polarized by driving light, a triaxial vector atomic magnetometer is constructed by using the first alkali metal atom a to monitor the static magnetic field of the atomic air chamber in real time, the magnetic field information monitored by the first alkali metal atom a is fed back to the triaxial magnetic compensation coil through control to dynamically compensate and control the magnetic field of the atomic air chamber, so that in-situ magnetic compensation is realized, a quasi-shielding environment is constructed, the very low frequency atomic magnetometer is ensured to normally work in an unshielded environment, high-precision environment magnetic interference suppression is realized, and therefore, the high-sensitivity detection of the very low frequency signal can be realized based on the very low frequency atomic magnetometer in the unshielded environment.
Spatially relative terms, such as "above … …," "above … …," "upper surface at … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial location relative to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or structures would then be oriented "below" or "beneath" the other devices or structures. Thus, the exemplary term "above … …" may include both orientations of "above … …" and "below … …". The device may also be positioned in other different ways (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
In addition, the terms "first", "second", etc. are used to define the components, and are only for convenience of distinguishing the corresponding components, and the terms have no special meaning unless otherwise stated, and therefore should not be construed as limiting the scope of the present invention.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The signal detection method based on the in-situ magnetic compensation very low frequency atomic magnetometer is characterized by comprising the following steps of:
providing a pumping light laser (10), a first gram-taylor prism (20), a quarter wave plate (30), a detection light laser (40), a first half wave plate (50), a second gram-taylor prism (60), a first reflecting mirror (70), a second reflecting mirror (80), a second half wave plate (90), a Wollaston prism (100), a balanced homodyne detector (110), a triaxial magnetic field coil (120), a third photodetector (130) and a data acquisition and control system (140), wherein the balanced homodyne detector (110) comprises a first photodetector (111) and a second photodetector (112), the triaxial magnetic field coil (120) is used for generating a precession main magnetic field at the same time of counteracting the interference of an ambient magnetic field under the control of the data acquisition and control system (140), and the data acquisition and control system (140) is used for performing feedback control on the triaxial magnetic field coil (120) according to signals acquired by the first photodetector (111) and the second photodetector (112), and the first atomic filling room is filled with alkali atoms and second atomic alkali metal atoms;
Tuning a pump light laser (10) to a first alkali metal atom transition frequency resonance, the pump light laser (10) generating pump laser light which enters an atomic gas chamber through the first gram-taylor prism (20) and the quarter wave plate (30) in sequence to polarize the first alkali metal atom, a second alkali metal atom being polarized through collision with the first alkali metal atom, and the pump laser light transmitted from the atomic gas chamber entering the data acquisition and control system (140) through the third photodetector (130);
the detection light laser (40) generates detection laser light, the detection laser light is utilized to detect the precession of the first alkali metal atom and the second alkali metal atom at the same time, the detection light laser (40) generates detection laser light which sequentially passes through the first half-wave plate (50), the second gram-taylor prism (60) and the first reflecting mirror (70) to enter the atomic gas chamber, and the detection laser light transmitted from the atomic gas chamber passes through the second reflecting mirror (80), the second half-wave plate (90) and the Wollaston prism (100) to enter the first photoelectric detector (111) and the second photoelectric detector (112);
the data acquisition and control system (140) scans the main magnetic field from 0 in the z direction by controlling the triaxial magnetic field coil (120) according to real-time triaxial magnetic field information obtained by measuring the first alkali metal atom so that the magnetic fields of the atomic air chamber along the horizontal polarization x direction and the vertical polarization y direction are 0;
By scanning the main magnetic field, observing the output amplitude change of the balanced homodyne detector (110) in real time, and finding out the main magnetic field size corresponding to the maximum output amplitude of the balanced homodyne detector (110) as a preferable main magnetic field, wherein under the preferable main magnetic field, the precession frequency of the second alkali metal atoms resonates with a very low frequency signal to be detected;
the data acquisition and control system (140) is utilized to fix the main magnetic field generated by the triaxial magnetic field coil (120) into a preferable main magnetic field, and the data acquisition and control system (140) completes detection of the very low frequency signal according to the output signal of the balanced homodyne detector (110).
2. The signal detection method based on the in-situ magnetic compensation very low frequency atomic magnetometer according to claim 1, wherein the data acquisition and control system (140) specifically comprises, according to the real-time triaxial magnetic field information obtained by the first alkali metal atom measurement, controlling the triaxial magnetic field coil (120) so that the magnetic fields of the atomic gas cell along the horizontal polarization x-direction and the vertical polarization y-direction are both 0:
detecting the transmitted pumping laser signal through a third photoelectric detector (130), and performing phase-locked amplification algorithm processing on the transmitted pumping laser signal and an alternating-current magnetic field signal by a data acquisition and control system (140) to obtain an X signal and a Y signal which are phase-locked amplified and output, wherein the X signal is in direct proportion to the size of a magnetic field in the X direction, and the Y signal is in direct proportion to the size of a magnetic field in the Y direction;
When the calibration means determines that the magnetic fields in the X direction and the y direction are 0, the phase-locked amplification outputs a corresponding X signal calibration value X 0 And Y signal calibration value Y 0 ；
Calculation and acquisitionTaking X-direction actual signal and X-signal calibration value X 0 Difference between X signal and Y signal, and calibration value Y of Y direction actual signal and Y signal 0 Y signal difference between;
and respectively feeding back the X signal difference value and the Y signal difference value as error signals to an X-direction magnetic field coil and a Y-direction magnetic field coil by the data acquisition and control system (140) so as to enable the magnetic fields of the atomic gas chamber along the horizontal polarization X-direction and the vertical polarization Y-direction to be 0.
3. The method of in-situ magnetic compensation very low frequency atomic magnetometer based signal detection according to claim 2, wherein using the data acquisition and control system (140) to fix the magnitude of the main magnetic field generated by the tri-axial magnetic field coil (120) to a preferred main magnetic field comprises:
applying an alternating magnetic field in the x-direction by the data acquisition and control system (140) through a triaxial magnetic field coil (120) to cause precession of the first alkali metal atom to resonate with the main magnetic field;
the data acquisition and control system (140) performs phase-locking amplification processing on the first alkali metal atom precession signal detected by the detection laser and the alternating-current magnetic field signal to obtain a dispersion curve, and locks the main magnetic field at the phase zero position of the dispersion curve through feedback control of the triaxial magnetic coil, so that the main magnetic field is stabilized at the preferable main magnetic field.
4. A signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer according to any one of claims 1 to 3, characterized in that a reflective film is coated on the pumping laser exit face of the atomic gas chamber, said reflective film being used to reflect the pumping laser back into the interior of the atomic gas chamber.
5. The method for signal detection based on an in-situ magnetic compensation very low frequency atomic magnetometer according to claim 4, characterized in that the output amplitude of the balanced homodyne detector (110) is proportional to the faraday rotation angle θ, which isWherein I is 0 ＝I 1 +I 2 ，I 1 For the output light intensity of the first photodetector (111), I 2 For the output light intensity of the second photodetector (112), I 0 Is the sum of the light intensities of the two laser beams output from the Wollaston prism (100).
6. The method for signal detection based on an in-situ magnetic compensation very low frequency atomic magnetometer according to claim 5, wherein said Faraday rotation angle θ is proportional to the polarization projection size S of the spin ensemble in the horizontal polarization x-direction x (t) the polarization projection size S x (t) is S x (t)＝M x cos (ωt), where M x For the polarization projection amplitude, ω is the vibration frequency, the polarization projection amplitude M x Proportional to Wherein Γ is resonance line width, B is main magnetic field, and γ is gyromagnetic ratio.
7. The method for signal detection based on an in situ magnetic compensation very low frequency atomic magnetometer according to claim 6, characterized in that said preferred main magnetic field B 0 Is B 0 ω/γ, where ω is the vibration frequency and γ is the gyromagnetic ratio.
8. A signal detection system based on an in-situ magnetic compensation very low frequency atomic magnetometer, wherein the signal detection system based on an in-situ magnetic compensation very low frequency atomic magnetometer performs very low frequency signal detection using the signal detection method based on an in-situ magnetic compensation very low frequency atomic magnetometer according to any one of claims 1 to 7.
9. The in-situ magnetic compensated vlf-atv-based signal detection system of claim 8, comprising a pump light laser (10), a first gran-taylor prism (20), a quarter-wave plate (30), a detection light laser (40), a first half-wave plate (50), a second gran-taylor prism (60), a first mirror (70), a second mirror (80), a second half-wave plate (90), a wollaston prism (100), a balanced homodyne detector (110), a triaxial magnetic field coil (120), a third photo detector (130) and a data acquisition and control system (140), the balanced homodyne detector (110) comprising a first photo detector (111) and a second photo detector (112), the pump light laser (10) for generating pump lasers, the pump lasers sequentially passing through the first gran-taylor prism (20) and the quarter-wave plate (80), the wollaston prism (100), the balanced homodyne detector (110), the triaxial magnetic field coil (120), the third photo detector (130) and the data acquisition and control system (140), the balanced homodyne detector (110) comprising a first photo detector (111) and a second photo detector (112), the pump laser light laser (10) for generating pump lasers, the transmission lasers sequentially passing through the first graniser-prism (20) and the quarter-wave plate (30) and the light detector (30) and the laser light detector (40) and the system (40) The second gram-taylor prism (60) and the first reflecting mirror (70) enter the atomic gas chamber, detection laser transmitted from the atomic gas chamber passes through the second reflecting mirror (80), the second half-wave plate (90) and the Wollaston prism (100) to enter the first photoelectric detector (111) and the second photoelectric detector (112), the triaxial magnetic field coil (120) is used for counteracting interference of an ambient magnetic field under the control of the data acquisition and control system (140) and generating a precession main magnetic field at the same time, and the data acquisition and control system (140) is used for performing feedback control on the triaxial magnetic field coil (120) according to signals acquired by the first photoelectric detector (111) and the second photoelectric detector (112).
10. The in-situ magnetic compensation very low frequency atomic magnetometer based signal detection system of claim 9, further comprising a reflective film disposed on a pumping laser exit face of the atomic gas cell, the reflective film being configured to reflect pumping laser light back to the atomic gas cell.
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