An ellipsometric atomic magnetometer-based magnetic field in-situ monitoring and automatic compensation device and method

Abstract

An ellipsometric atomic magnetometer-based magnetic field in-situ monitoring and automatic compensation device and method enable the magnetometer to automatically trigger an online magnetic field compensation program in a timely manner according to the monitoring result of the environmental magnetic field, and then restore the environmental magnetic field to zero field, thereby improving the ability of the magnetometer to resist changes in the environmental interference magnetic field, enabling the magnetometer to work stably for a long time without the need for manual zeroing of the magnetic field. The present application additionally collects the previously unused second harmonic component on the basis of the original magnetometer collecting the first harmonic component for magnetic field measurement, and realizes real-time monitoring of the three-axis magnetic field by comparing the difference between the value of the current second harmonic component and the value of the second harmonic component in a zero-field environment; the intelligent optimization algorithm is combined with the second harmonic component to realize online high-precision magnetic field compensation of three axes simultaneously with a low sampling point number, improve the compensation efficiency, and ultimately improve the long-term stability and magnetic field interference resistance of the magnetometer without affecting the original measurement sensitivity.

Description

TECHNICAL FIELD

[0001] The application relates to a magnetic field in-situ monitoring and automatic compensation device and method based on an ellipsoidal light atomic magnetometer, and belongs to the technical field of atomic magnetometers. BACKGROUND

[0002] The SERF (Spin-Exchange-Relaxation-Free) atomic magnetometer is an ultra-high-sensitivity quantum precision magnetic field measuring instrument working in a near-zero field environment, and is widely applied in the fields of biomagnetic measurement, magnetic anomaly detection and frontier physics research. The ellipsoidal light SERF atomic magnetometer utilizes an ellipsoidal polarized light to simultaneously perform pumping and detection, and has the technical advantages of small volume, easy integration and high sensitivity. However, the performance of the ellipsoidal light SERF magnetometer is affected by the environmental magnetic field around the magnetometer. When the environmental magnetic field significantly drifts or is disturbed to cause a large change in the magnetic field, the SERF magnetometer works in a non-zero field environment, thereby causing the sensitivity to decrease, and even exceeding the linear working area and failing to continue normal work, thereby affecting the long-term stable use of the ellipsoidal light SERF magnetometer. SUMMARY

[0003] The application solves the problem of providing a magnetic field in-situ monitoring and automatic compensation device and method based on an ellipsoidal light atomic magnetometer, so that the magnetometer can monitor the changes of the three-axis environmental magnetic field in real time, and when the environmental magnetic field deviates from the zero field, the magnetometer automatically triggers a rapid online three-axis magnetic field compensation program to compensate the magnetic field sensed by the magnetometer to the zero field, so that the magnetometer can continue to perform high-sensitivity magnetic field measurement. The method is realized online based on the working mode of the magnetometer, and does not need to stop and reset the magnetometer, thereby enhancing the ability of the ellipsoidal light SERF magnetometer to resist the change of the environmental magnetic field, and ensuring that the magnetometer can be used stably for a long time.

[0004] The technical scheme of the application is as follows:

[0005] The application discloses a magnetic field in-situ monitoring and automatic compensation device based on an ellipsoidal light atomic magnetometer, and relates to the technical field of atomic magnetometers.

[0006] The polarization differential detection system comprises a half-wave plate located at a laser exit side of the atomic gas chamber, the half-wave plate is connected with an input side of a lateral displacement polarization beam splitter prism, a transmission side of the lateral displacement polarization beam splitter prism is connected with a first photoelectric detector, a reflection side of the lateral displacement polarization beam splitter prism is connected with a second photoelectric detector, the first photoelectric detector is connected with a first input end of a differential amplification circuit, the second photoelectric detector is connected with a second input end of the differential amplification circuit, an output end of the differential amplification circuit is connected with an input end of the lock-in amplifier, and a laser incident side of the atomic gas chamber is sequentially connected with a collimator through a quarter-wave plate and a linear polarizer.

[0007] The narrow-line-width semiconductor laser emits laser light with a frequency deviated from a D1 line resonance frequency of an alkali metal atom by 100 GHz, the laser light is converted into elliptical polarized light with an ellipticity of 22.5 degrees after passing through the linear polarizer and the quarter-wave plate, and the elliptical polarized light passes through the atomic gas chamber and then sequentially passes through the half-wave plate and the lateral displacement polarization beam splitter prism to reach the first photoelectric detector and the second photoelectric detector respectively.

[0008] The first harmonic component is θ ω , the second harmonic component is θ 2ω , and when the environmental magnetic field is a near-zero field, the following relationship is established:

[0009]

[0010] Where I0 is the optical power density of the pump laser, e is the natural constant, v is the frequency of the pump laser, v0 is the D1 line resonance frequency of the potassium atom, OD(v) is the optical depth, Γ is the pressure broadening of the atomic cell, J0, J1, and J2 are the 0th, 1st, and 2nd order Bessel functions, respectively, l is the length of the atomic cell, n is the atomic number density of potassium atoms, c is the speed of light, r is the classical electron radius, f is the D1 line resonance intensity of the potassium atom, and R... op R is the optical pump rate. rel γ is the transverse relaxation rate, s is the spin angular momentum of the pump light, and γ is the transverse relaxation rate. e Electron gyromagnetic ratio, u is the magnetic field modulation coefficient, and B0 is the magnetic field to be measured pointing in the positive z-axis direction.

[0011] The data acquisition and control system monitors the second harmonic component θ. 2ω Perform sampling and record θ 2ω Let the initial sampling result be Θ0, and let the i-th sampling result be Θ. i i is a positive integer, K0 is the amplification factor of the input signal by the data acquisition and control system, and Θ0 and Θ i Expressed as:

[0012]

[0013] Let ξ be the set threshold, when |Θ0–Θ i When |<ξ, the magnetometer operates normally without triggering any action; when |Θ0–Θ i When |≥ξ, it indicates that the magnetometer has detected an deviation of the ambient magnetic field from zero. At this point, the magnetometer stops measuring and triggers an online automatic magnetic field compensation program. After the automatic magnetic field compensation program ends, |Θ0–Θ i The condition |<ξ is satisfied again, and the magnetometer resumes normal operation.

[0014] The control current of the triaxial magnetic field coil drives the triaxial magnetic field coil to generate the expected magnetic field determined by the particle swarm optimization algorithm run by the data acquisition and control system as the compensation magnetic field.

[0015] The particle swarm optimization algorithm includes C = (C x C y C z Let C be the initial point, where C is the initial compensation magnetic field. x C y C z These are the initial compensation magnetic fields along the x-axis, y-axis, and z-axis, respectively, in W. x =[C x –R x C x +R x ], W y =[C y –R yC y +R y ], W z =[C z –R z C z +R z Within the space, N particles B are generated. j = (B xj B yj B zj ), where j = 1, 2, 3, ..., N, where R x It is the remanent magnetization space in the x-direction set by the magnetic shielding system, R y It is the remanent magnetization space in the y-direction set by the magnetic shielding system, R z It is based on the remanent magnetization space in the z-direction set by the magnetic shielding system, B j It is the magnetic field of the j-th particle, B xj B yj B zj These are the x-axis, y-axis, and z-axis magnetic fields of the j-th particle, respectively. x W y W z The search domains are the x-axis, y-axis, and z-axis, respectively. The positions of these 30 particles in space are continuously updated until the compensating magnetic field B = –B is found. E = (B x B y B z ), where B x B y B z These are the x-axis, y-axis, and z-axis compensation magnetic fields, respectively, B E It is the environmental magnetic field deviating from zero field value, B x ∈W x B y ∈W y B z ∈W z This ensures that, under the condition of a compensating magnetic field of B, |Θ0–Θ i When |<ξ, the algorithm stops running and the magnetometer resumes normal operation; when |Θ0–Θ i When the condition |≥ξ occurs again, C=(B x B y B z The particle swarm optimization algorithm is iteratively run with 0 as the initial point.

[0016] A method for in-situ monitoring and automatic compensation of magnetic field based on ellipsometric atomic magnetometer, characterized in that it includes the above-mentioned in-situ monitoring and automatic compensation device for magnetic field based on ellipsometric atomic magnetometer.

[0017] Includes the following steps:

[0018] Step 1, adjust the emission frequency of the narrow linewidth semiconductor laser to be resonant with the D1 line of the alkali metal atom, and the light is linearly polarized, the light is transmitted to the collimator through the polarization maintaining fiber, and is converted into a collimated beam, the beam is converted into elliptically polarized light with an ellipticity of α after passing through a linear polarizer and a quarter-wave plate, the elliptically polarized light is used as a pumping laser to irradiate the atomic cell to realize the pumping of the alkali metal atom;

[0019] Step 2, the environmental magnetic field experienced by the atomic cell is compensated to zero by using in-situ three-dimensional magnetic compensation technology, and the sizes of the compensation magnetic fields of the three axes are recorded as C x , C y and C z respectively, then a high-frequency modulated magnetic field with a frequency of ω is applied in the y direction by controlling a three-channel high-precision current source, then a lock-in amplification technology is used in a lock-in amplifier to demodulate the differential amplified signal at a frequency of ω, 2ω respectively, to obtain a first harmonic component θ ω and a second harmonic component θ 2ω ;

[0020] Step 3, the first harmonic component θ ω is output as a magnetometer output signal, the second harmonic component θ 2ω is transmitted to a data acquisition and control system as an environmental magnetic field monitoring signal, and the initial value of the second harmonic component θ 2ω is recorded as Θ0 by the data acquisition and control system;

[0021] Step 4, the value of the second harmonic component θ 2ω is recorded by the data acquisition and control system once every interval T, and the value of the i-th sampling is recorded as Θ i , and the sampling data Θ i is judged in the data acquisition and control system, when |Θ0–Θ i |<ξ, the magnetometer works normally without triggering any action, when |Θ0–Θ i |≥ξ, it indicates that the environmental magnetic field deviates from zero field monitored by the magnetometer, at this time the magnetometer stops measuring and triggers the online automatic magnetic field compensation program, after the automatic magnetic field compensation program ends, the condition |Θ0–Θ i |<ξ is satisfied again, and the magnetometer resumes normal work, wherein ξ is a set threshold value;

[0022] Step 5, the calculation unit of the automatic magnetic field compensation program is the data acquisition and control system, the execution unit is the three-axis magnetic field coil, and the execution process is that three-dimensional control signals are generated in the data acquisition and control system and transmitted to the three-channel high-precision current source, so that the current source generates three-axis magnetic field coil control current, and the current drives the three-axis magnetic field coil to generate the expected magnetic field in the data acquisition and control system.

[0023] Step 6: The expected magnetic field is generated by running an intelligent optimization algorithm in the data acquisition and control system. The algorithm's goal is to achieve a magnetic field of C = (C x C y C z ( ) is the initial point, at W x =[C x –R x C x +R x ], W y =[C y –R y C y +R y ], W z =[C z –R z C z +R z Within the space, find the compensating magnetic field B = (B x B y B z ), where R x It is the remanent magnetization space in the x-direction set by the magnetic shielding system, R y It is the remanent magnetization space in the y-direction set by the magnetic shielding system, R z It is based on the remanent magnetization space in the z-direction set by the magnetic shielding system, B x ∈W x B y ∈W y B z ∈W z This ensures that |Θ0–Θ| is satisfied under the compensated magnetic field. i |<ξ, then set the initial point for the next trigger of the online automatic magnetic field compensation procedure to C=(B x B y B z ), searching for space as W x =[B x –R x B x +R x ], W y =[B y –R y B y +R y ], W z =[B z –R z B z +R z] the parameters of triggering the online magnetic field compensation program, and so on, and at this time, the automatic magnetic field compensation program is completed, at this time, the environmental magnetic field returns to zero field again, and the magnetometer starts to measure again, that is, enters the normal working state.

[0024] The technical effects of the present application are as follows: the magnetic field in-situ monitoring and automatic compensation device and method based on the ellipsometric atomic magnetometer provides a scheme for real-time monitoring of the environmental magnetic field and online fast compensation of the environmental magnetic field for the ellipsometric SERF atomic magnetometer, so that the magnetometer can automatically trigger the online magnetic field compensation program in time according to the monitoring result of the environmental magnetic field, and then restore the environmental magnetic field to zero field, thereby improving the ability of the magnetometer to resist the change of the environmental interference magnetic field, and enabling the magnetometer to work stably for a long time without human zeroing of the magnetic field. On the basis of the original magnetometer collecting the first harmonic component for magnetic field measurement, the present application additionally collects the previously unused second harmonic component, realizes real-time monitoring of the three-axis magnetic field by comparing the difference between the value of the current second harmonic component and the value of the second harmonic component under zero field environment; combines the intelligent optimization algorithm with the second harmonic component, realizes online high-precision magnetic field compensation of three axes at the same time with low sampling point number, improves the compensation efficiency and speed compared with the previous magnetic field compensation method, and finally improves the long-term stability and magnetic field interference resistance of the magnetometer without affecting the original measurement sensitivity of the magnetometer.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] (1) The conventional ellipsometric SERF atomic magnetometer has poor ability to resist the change of the environmental magnetic field, and when the environmental magnetic field changes significantly, the magnetometer is easily out of the linear region and invalid or the sensitivity is reduced. On the basis of the original magnetometer using a frequency doubler for magnetic field measurement, the present application additionally introduces the previously unused second harmonic component as a monitoring signal, realizes real-time three-axis monitoring of the environmental magnetic field, so that the magnetometer can monitor the state of the environmental magnetic field while normally measuring the magnetic field, and when the environmental magnetic field deviates from zero field, the automatic magnetic field compensation program can be triggered in time to restore the zero field environment, so that the magnetometer can work in the zero field environment for a long time without human zeroing of the magnetic field, improving the ability of the magnetometer to resist the change of the environmental magnetic field, and improving the long-term stability and practicality of the magnetometer;

[0027] (2) The prior art three-dimensional magnetic compensation technology is three-axis time-sharing, and when the magnetic field of each axis is compensated, high-density sampling of the output signal is required to achieve high-precision magnetic field compensation. The online automatic magnetic field compensation program provided by the application uses a particle swarm optimization algorithm to simultaneously compensate the three axes of the environmental magnetic field, fully utilizes the characteristics of automatic optimization and high numerical precision of the algorithm, and only needs to sample a small number of sample points of the three-dimensional compensation magnetic field to achieve simultaneous and high-precision compensation of the three-axis magnetic field, thereby saving the time and efficiency of magnetic field compensation.

[0028] (3) The application does not change the original ellipsometric SERF atomic magnetometer probe structure, and realizes the monitoring and compensation of the environmental magnetic field by extracting the second harmonic component, without affecting the measurement process of the first harmonic component, so that the technical advantages of compact structure and high sensitivity of the ellipsometric SERF magnetometer are retained. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a structure schematic diagram of a magnetic field in-situ monitoring and automatic compensation device based on an ellipsometric atomic magnetometer.

[0030] The reference signs are explained as follows: 1 - narrow line width semiconductor laser; 2 - polarization maintaining optical fiber; 3 - collimator; 4 - linear polarizer; 5 - quarter wave plate; 6 - atomic gas chamber; 7 - side displacement polarization beam splitting prism; 9 - photodetector (including first photodetector and second photodetector); 10 - differential amplification circuit; 11 - polarization difference detection system; 12 - ceramic oven; 13 - three-axis magnetic field coil; 14 - differential amplification signal; 15 - lock-in amplifier; 16 - second harmonic component (which is an environmental magnetic field monitoring signal); 17 - first harmonic component (which is a magnetometer output signal); 18 - data acquisition and control system; 19 - three-dimensional control signal; 20 - three-channel high-precision current source; 21 - three-axis magnetic field coil control current; 22 - magnetometer probe shell; 23 - photoelectric integrated system; 24 - atomic magnetometer probe; 25 - magnetic shielding system. DETAILED DESCRIPTION

[0031] The application will be described below in conjunction with the drawings Figure 1 ) and examples.

[0032] Figure 1 is a structure schematic diagram of a magnetic field in-situ monitoring and automatic compensation device based on an ellipsometric atomic magnetometer. Reference Figure 1As shown, a magnetic field in-situ monitoring and automatic compensation device based on ellipsoidal light atomic magnetometer, comprising a magnetic shielding system 25 and a photoelectric integrated system 23, the atomic magnetometer probe 24 is placed in the magnetic shielding system 25, the atomic magnetometer probe 24 comprises a polarization differential detection system 11 and an atomic cell 6 surrounded by a three-axis magnetic field coil 13, which are all located in the magnetometer probe shell 22, the polarization differential detection system 11 outputs the differential amplification signal 14 obtained from the outgoing laser of the atomic cell 6 to the phase-locked amplifier 15 in the photoelectric integrated system 23, the phase-locked amplifier 15 resolves the first harmonic component 17 as the magnetometer output signal and the second harmonic component 16 as the environmental magnetic field monitoring signal from the differential amplification signal 14, the second harmonic component 16 generates a three-dimensional control signal 19 through the data acquisition and control system 18 and transmits to the three-channel high-precision current source 20, the three-channel high-precision current source 20 generates three-axis magnetic field coil control current 21 and transmits to the three-axis magnetic field coil 13 to automatically realize online three-axis magnetic compensation for the atomic cell 6.

[0033] The polarization differential detection system 11 comprises a half-wave plate 7 located on the laser outgoing side of the atomic cell, the half-wave plate 7 is connected to the input side of the lateral displacement polarization beam splitter prism 8, the transmission side of the lateral displacement polarization beam splitter prism 8 is connected to the first photoelectric detector (photoelectric detector 9), the reflection side of the lateral displacement polarization beam splitter prism 8 is connected to the second photoelectric detector (photoelectric detector 9), the first photoelectric detector is connected to the first input end of the differential amplification circuit 10, the second photoelectric detector is connected to the second input end of the differential amplification circuit 10, the output end of the differential amplification circuit 10 is connected to the input end of the phase-locked amplifier 15, the laser incident side of the atomic cell 6 is connected to the collimator 3 through the quarter-wave plate 5 and the linear polarizer 4 in turn, and the collimator 3 is connected to the narrow linewidth semiconductor laser 1 in the photoelectric integrated system 23 through the polarization maintaining optical fiber 2. The laser emitted by the narrow linewidth semiconductor laser 1 is frequency detuned from the D1 line resonance frequency of 100 GHz of the alkali metal atom, and the laser is converted into elliptical polarized light with an ellipticity of 22.5° after passing through the linear polarizer 4 and the quarter-wave plate 5, and the elliptical polarized light passes through the half-wave plate 7 and the lateral displacement polarization beam splitter prism 8 in turn to reach the first photoelectric detector and the second photoelectric detector respectively. The atomic cell 6 is located in the ceramic oven 12.

[0034] Let the first harmonic component be θ ω , and the second harmonic component be θ 2ω , then

[0035]

[0036] Where I0 is the optical power density of the pump laser, e is the natural constant, v is the frequency of the pump laser, v0 is the D1 line resonance frequency of the potassium atom, OD(v) is the optical depth, Γ is the pressure broadening of the atomic cell, J0, J1, and J2 are the 0th, 1st, and 2nd order Bessel functions, respectively, l is the length of the atomic cell, n is the atomic number density of potassium atoms, c is the speed of light, r is the classical electron radius, f is the D1 line resonance intensity of the potassium atom, and R... op R is the optical pump rate. rel γ is the transverse relaxation rate, s is the spin angular momentum of the pump light, and γ is the transverse relaxation rate. e The electron gyromagnetic ratio, u is the magnetic field modulation coefficient, and B0 is the magnetic field to be measured pointing in the positive z-axis direction. The data acquisition and control system monitors the second harmonic component θ. 2ω Perform sampling and record θ 2ω Let the initial sampling result be Θ0, and let the i-th sampling result be Θ. i i is a positive integer, ξ is a set threshold, when |Θ0–Θ i When |<ξ, the magnetometer operates normally without triggering any action; when |Θ0–Θ i When |≥ξ, it indicates that the magnetometer has detected an deviation of the ambient magnetic field from zero. At this point, the magnetometer stops measuring and triggers an online automatic magnetic field compensation program. After the automatic magnetic field compensation program ends, |Θ0–Θ i The condition |<ξ is satisfied again, and the magnetometer resumes normal operation.

[0037] The triaxial magnetic field coil is controlled by a current that drives it to generate a desired magnetic field determined by a particle swarm optimization algorithm run by the data acquisition and control system, serving as a compensation magnetic field. The particle swarm optimization algorithm includes a formula C = (C... x C y C z Let C be the initial point, where C is the initial compensation magnetic field. x C y C z These are the initial compensation magnetic fields along the x-axis, y-axis, and z-axis, respectively, in W. x =[C x –R x C x +R x ], W y =[C y –R y C y +R y ], W z =[C z –R z C z +R z Within the space, N particles B are generated. j = (B xj Byj , B zj ), where j = 1, 2, 3,..., N, where R x is the remanent space in x direction set according to the magnetic shielding system, R y is the remanent space in y direction set according to the magnetic shielding system, R z is the remanent space in z direction set according to the magnetic shielding system, B j is the jth particle magnetic field, B xj , B yj , B zj are the x axis, y axis, z axis magnetic field of the jth particle magnetic field, respectively, W x , W y , W z are the x axis, y axis, z axis space search domain, the positions of the 30 particles in space are constantly updated until the compensation magnetic field B = -B E = (B x , B y , B z ) is found, where B x , B y , B z are the x axis, y axis, z axis compensation magnetic field, respectively, B E is the environmental magnetic field deviating from the zero field value, B x ∈ W x , B y ∈ W y , B z ∈ W z , so that under the condition of the compensation magnetic field B, |Θ0-Θ i | < ξ is satisfied, at which time the algorithm stops running and the magnetometer resumes normal operation; when |Θ0-Θ i | ≥ ξ occurs again, the particle swarm optimization algorithm is iteratively run with C = (B x , B y , B z ) as the initial point

[0038] An in-situ monitoring and automatic compensation device and method of magnetic field based on ellipsoidal light atomic magnetometer, comprising narrow line width semiconductor laser (1), polarization maintaining optical fiber (2), collimator (3), linear polarizer (4), quarter wave plate (5), atomic gas chamber (6), half wave plate (7), lateral displacement polarization beam splitter prism (8), photodetector (9), differential amplifier circuit (10), polarization difference detection system (11), ceramic oven (12), three-axis magnetic field coil (13), differential amplification signal (14), lock-in amplifier (15), second harmonic component (16), first harmonic component (17), data acquisition and control system (18), three-dimensional control signal (19), three-channel high-precision current source (20), three-axis magnetic field coil control current (21), magnetometer probe shell (22), photoelectric integrated system (23), atomic magnetometer probe (24), magnetic shielding system (25).

[0039] The narrow line width semiconductor laser (1) emits linearly polarized incident laser with frequency mismatched to the D1 line resonance frequency of alkali metal atoms, which is transmitted to the collimator (3) through the polarization maintaining optical fiber (2); the collimator (3) adopts cylindrical barrel packaging to convert the incident laser into a collimated beam with a determined spot diameter, and aligns the beam to the center of the linear polarizer (4); the optical axis angle between the linear polarizer (4) and the half wave plate (5) is α, which converts the linearly polarized incident laser into elliptically polarized light with an ellipticity of α, which is then incident into the atomic gas chamber (6) as the pumping laser of the SERF magnetometer; the polarization difference detection module (11) includes a half wave plate (7), a lateral displacement polarization beam splitter prism (8), a photodetector (9), and a differential amplifier circuit (10), wherein the optical axis direction of the half wave plate (7) and the optical axis direction of the lateral displacement polarization beam splitter prism (8) are at an angle of 45°, the lateral displacement polarization beam splitter prism (8) decomposes the laser emitted from the half wave plate (7) into two beams with orthogonal polarization directions and parallel propagation directions, and then the beams are incident into the photodetector (9), and the differential amplifier circuit (10) differentially amplifies the output signal of the photodetector (9) to obtain the differential amplification signal (14).

[0040] The atomic gas chamber (6) is filled with alkali metal atoms and is in a weak magnetic environment, and is surrounded by a ceramic oven (12), wherein the number density of alkali metal atoms reaches 10 13 ~10 14 / cm 3 , and both are placed at the center of the three-axis magnetic field coil (13), and the three-axis magnetic field coil (13) can generate uniform magnetic fields along the x, y and z directions.

[0041] The differential amplification signal (14) is demodulated by a phase-locked amplifier (15) to obtain a second harmonic component (16) and a first harmonic component (17) in the zero-order resonance signal of the SERF atomic magnetometer, wherein the first harmonic component (17) is the output signal of the magnetometer, which is the measurement result of the magnetic field in the sensitive axis direction of the magnetometer, and the second harmonic component (16) is a monitoring signal, which is transmitted to a data acquisition and control system (18); the data acquisition and control system (18) processes the input monitoring signal and automatically triggers a fast online three-axis magnetic compensation program under specific monitoring conditions to generate a three-dimensional control signal (19) and realize online three-axis magnetic compensation; the three-dimensional control signal (19) drives a three-channel high-precision current source (20) to generate a three-axis magnetic field coil control current (21), which drives the three-axis magnetic field coil (13) to generate a three-axis magnetic field; the collimator (3), the linear polarizer (4), the half-wave plate (5), the atomic gas chamber (6), the polarization differential detection system (11), the ceramic oven (12), and the three-axis magnetic field coil (13) are packaged in a magnetometer probe shell (22) to form an atomic magnetometer probe together with the magnetometer probe shell (22); the narrow linewidth semiconductor laser (1), the phase-locked amplifier (15), the data acquisition and control system (18), and the three-channel high-precision current source (20) form an optoelectronic integrated system (23) together; the optoelectronic integrated system (23) and the atomic magnetometer probe (24) form an atomic magnetometer together, and the atomic magnetometer probe (24) is placed in a magnetic shielding system (25), and the optoelectronic integrated system (23) is placed outside the magnetic shielding system (25) to fully shield the geomagnetic field and the electromagnetic field of the optoelectronic integrated system.

[0042] A magnetic field in-situ monitoring and automatic compensation device and method based on an elliptically polarized atomic magnetometer, comprising the following steps:

[0043] Step 1, adjust the narrow linewidth semiconductor laser to be misaligned with the D1 line resonance frequency of the alkali metal atom, and to be linearly polarized light, transmit the laser to the collimator through the polarization maintaining light, convert it into a collimated light beam, and convert it into elliptically polarized light with an ellipticity of α after passing through a linear polarizer and a quarter wave, use the elliptically polarized light as a pumping laser to irradiate the atomic gas to realize the pumping of the alkali metal atom;

[0044] Step 2, use the in-situ three-dimensional magnetic compensation technology to compensate the environmental magnetic field sensed by the atomic gas chamber to zero, and record the compensation magnetic field of the three axes at this time as C x , C y and C z , then control the three-channel high-precision current source to apply a high-frequency modulated magnetic field with a frequency of ω in the y direction, then use the phase-locked amplification technology in the phase-locked amplifier to demodulate the differential amplification signal at the frequency of ω and 2ω respectively, and obtain the first harmonic component θω Second harmonic component θ 2ω ;

[0045] Step 3, convert the first harmonic component (17)θ ω As the output signal of the magnetometer, the second harmonic component (16)θ 2ω As an environmental magnetic field monitoring signal, it is transmitted to the data acquisition and control system (18) to record the second harmonic component (16)θ. 2ω The initial value is processed by the data to be Θ0;

[0046] Step 4: Record the second harmonic component θ every time interval T using data processing. 2ω The value of the i-th sample is denoted as Θ. i In the data acquisition and control system, the sampled data Θ i Make a judgment when |Θ0–Θ i When |<ξ, the magnetometer operates normally without triggering any action; when |Θ0–Θ i When |≥ξ, it indicates that the magnetometer has detected an deviation of the ambient magnetic field from zero. At this point, the magnetometer stops measuring and triggers an online automatic magnetic field compensation program. After the automatic magnetic field compensation program ends, |Θ0–Θ i The condition |<ξ is satisfied again, and the magnetometer resumes normal operation. Here, ξ is the difference between the sampled value of the data processing and Θ0 when the ambient magnetic field is at the critical value of zero field and non-zero field. The calculation unit of the automatic magnetic field compensation program is data processing, and the execution unit is the three-axis magnetic field line. The execution process is to generate a three-dimensional control signal in the data processing and transmit it to the three-channel high-precision current, so that the current source generates the control current of the three-axis magnetic field coil. This current drives the three-axis magnetic field line to generate the magnetic field expected in the data processing.

[0047] Step 5: The desired magnetic field is generated by running an intelligent optimization algorithm during data processing. The algorithm's goal is to achieve a magnetic field of C = (C x C y C z ( ) is the initial point, at W x =[C x –R x C x +R x ], W y =[C y –R y C y +R y ], W z =[C z –R z C z +R z Within the space, find the compensating magnetic field B = (B x B y, B z ), wherein R x is the remanence space in x direction set according to the magnetic shielding system, R y is the remanence space in y direction set according to the magnetic shielding system, R z is the remanence space in z direction set according to the magnetic shielding system, B x ∈ W x , B y ∈ W y , B z ∈ W z , so that under the compensation magnetic field, |Θ0-Θ i |<ξ is satisfied, and then the initial point when the next trigger of the online automatic magnetic field compensation program is C=(B x , B y , B z ), the search space is W x =[B x -R x , B x +R x ], W y =[B y -R y , B y +R y ], W z =[B z -R z , B z +R z ], and the parameters when the following trigger of the online magnetic field compensation program are in this way, and at this time, the automatic magnetic field compensation program is completed, the environmental magnetic field returns to zero field, and the magnetometer starts to measure again, i.e., enters the normal working state.

[0048] The three-dimensional magnetic compensation technology in the step 2 is a technology for making the environmental magnetic field sensed by the atomic gas chamber return to zero by controlling the three-axis magnetic field coils around the atomic gas to generate a magnetic field with the same size and opposite direction as the environmental magnetic field.

[0049] The application provides a magnetic field in-situ monitoring and automatic compensation device and method based on ellipsoidal light atomic magnetometer, which uses the first harmonic component to measure the magnetic field and uses the second harmonic component to monitor the environmental magnetic field in real time, triggers the automatic magnetic field compensation program when the environmental magnetic field deviates from zero field, and makes the environmental magnetic field sensed by the magnetometer return to zero field, so that the magnetometer can work stably for a long time. The application is described in detail below in combination with the drawings and specific embodiments, and it should be understood that the embodiments are only used for illustrating the application and are not used for limiting the scope of the application, and after reading the application, the modifications of various equivalent forms of the application made by those skilled in the art all fall within the scope defined by the appended claims.

[0050] As Figure 1 shown, the specific implementation steps of the present application are as follows:

[0051] (1) Adjust the emission frequency of the narrow line width semiconductor laser 1 to be 100 GHz, which is the D1 line resonance frequency of the alkali metal potassium atom, and the light is linearly polarized. The laser is transmitted to the collimator 3 through the polarization maintaining fiber 2, and is converted into a collimated light beam with a beam diameter of 4 mm. After passing through the linear polarizer 4 and the quarter-wave plate 5, the light is converted into elliptically polarized light with an ellipticity of 22.5°. The elliptically polarized light is used as the pumping laser to irradiate the potassium atom-filled atomic cell 6 with a size of 4 mm, thereby realizing the pumping of the alkali metal atom;

[0052] (2) After completing step (1), the environmental magnetic field experienced by the atomic cell 6 is compensated to zero using the in-situ three-dimensional magnetic compensation technology, and the sizes of the compensation magnetic fields of the three axes at this time are recorded as C x , C y and C z . Subsequently, the three-channel high-precision current source 20 is controlled to apply a high-frequency modulated magnetic field with a frequency of 1000 Hz and an amplitude of 100 nT in the y direction. Subsequently, the lock-in amplification technology is used in the lock-in amplifier 15 to demodulate the differential amplified signal 14 at a frequency of one frequency 1000 Hz and two frequencies 2000 Hz, respectively, to obtain a first harmonic component 17, denoted as θ ω , and a second harmonic component 16, denoted as θ 2ω , and their expressions are:

[0053]

[0054] θ ω is the first harmonic component, θ 2ω is the second harmonic component, I0 is the optical power density of the pumping laser, v is the frequency of the pumping laser, v0 is the D1 line resonance frequency of the potassium atom, OD(v) is the optical depth, Г is the pressure broadening of the atomic cell 6, J0, J1 and J2 are the 0th, 1st and 2nd Bessel functions, respectively, l is the length of the atomic cell 6, n is the atomic number density of the potassium atom, c is the speed of light, r is the classical electron radius, f is the D1 line resonance intensity of the potassium atom, R op is the optical pumping rate, R rel is the transverse relaxation rate, s is the spin angular momentum of the pumping light, γ e is the electron gyromagnetic ratio, u is the magnetic field modulation coefficient, and B0 refers to the magnetic field to be measured pointing to the positive direction of the z axis.

[0055] (3) The first harmonic component 17 θ ω obtained in step (2) is output as a magnetometer output signal for user use, and the second harmonic component 16 θ 2ωAs the environmental magnetic field monitoring signal is transmitted to the data acquisition and control system 18, the initial value of the second harmonic component 16θ 2ω is recorded as Θ0, whose expression is:

[0056]

[0057] where K0 is the amplification coefficient of the phase-locked amplifier to the differential amplified signal 14;

[0058] (4) After completing step (3), the value of the second harmonic component 16θ 2ω is recorded by the data acquisition and control system 18 once every 0.1 s, and the value of the i-th sampling is recorded as Θ i The sampling data Θ i is judged in the data acquisition and control system 18, and when the environmental magnetic field deviates from the zero field to B E = (–B x , –B y , –B z ), the expression of Θ i is:

[0059]

[0060] Obviously, under the condition of non-zero field, Θ i is always smaller than Θ0, so when it is observed that the two are close to each other, it means that the environmental magnetic field reaches the zero field. When |Θ0– Θ i | < ξ, the magnetometer works normally without triggering any action, and when |Θ0– Θ i | ≥ ξ, it indicates that the magnetometer monitors that the environmental magnetic field deviates from the zero field, at which time the magnetometer stops measuring and triggers the online automatic magnetic field compensation program, where ξ is the difference between the sampling value of the data acquisition and control system 18 and Θ0 when the environmental magnetic field is the critical value of the zero field and the non-zero field;

[0061] (5) The calculation unit of the automatic magnetic field compensation program in step (4) is the data acquisition and control system 18, the execution unit is the three-axis magnetic field coil 13, and the execution process is to generate a three-dimensional control signal 19 in the data acquisition and control system 18 and transmit it to the three-channel high-precision current source 20, so that the current source generates a three-axis magnetic field coil control current 21, which drives the three-axis magnetic field coil 13 to generate the expected magnetic field in the data acquisition and control system 18;

[0062] (6) The expected magnetic field in step (5) is generated by running a particle swarm optimization algorithm in the data acquisition and control system 18, and the goal of the algorithm is to take C = (C x , C y , C z ) as the initial point, and W x = [Cx - 50nT, C x + 50nT], W y = [C y - 50nT, C y + 50nT], W z = [C z - 50nT, C z + 50nT], W j = (B xj , B yj , B zj ), where j = (1, 2, 3…, 30), constantly update the position of the 30 particles in the space under the driving of the PSO algorithm (PSO, Particle Swarm optimization algorithm), until the compensation magnetic field B = -B E = (B x , B y , B z ), where B x ∈ W x , B y ∈ W y , B z ∈ W z , so that under the condition of compensation magnetic field B, |Θ0-Θ i | < ξ, at this time the algorithm stops running, and the magnetometer resumes normal work;

[0063] (7) When |Θ0-Θ i | ≥ ξ occurs again, the online automatic magnetic field compensation program is triggered again, the initial point at this time becomes C = (B x , B y , B z ), and the search space becomes W x = [B x - 50nT, B x + 50nT], W y = [B y - 50nT, B y + 50nT], W z = [B z - 50nT, B z + 50nT], and other execution processes are the same as described in step (6), and the subsequent automatic magnetic field compensation program is the same, that is, the initial point and search space of each running algorithm need to be updated according to the last compensation magnetic field.

[0064] In summary, the magnetic field in-situ monitoring and automatic compensation device and method based on ellipsometric atomic magnetometer, by using the first harmonic component in the traditional magnetometer to measure the magnetic field, and collecting the second harmonic component, the monitoring and timely compensation of the environmental magnetic field in the working state are realized, so that the ability of the traditional magnetometer to resist the magnetic field change is improved, and the long-term stability of the magnetometer is enhanced. In the automatic magnetic field compensation process, by using the particle swarm optimization algorithm, the in-situ and high-precision three-axis magnetic field compensation based on a small number of sampling points is realized, so that the speed and efficiency of the automatic magnetic field compensation are improved.

[0065] The contents not described in detail in the specification of the present application belong to the prior art known to the person skilled in the art. It is indicated herein that the above description is helpful for the person skilled in the art to understand the present application, but is not limited to the protection scope of the present application. Any implementation of equivalent replacement, modification, improvement and / or deletion of the above description without departing from the essential content of the present application falls within the protection scope of the present application.

Claims

1. An ellipsometric atomic magnetometer-based magnetic field in-situ monitoring and automatic compensation device, characterized in that, The system includes a magnetic shielding system and an optoelectronic integrated system. The magnetic shielding system houses an atomic magnetometer probe. The atomic magnetometer probe includes a polarization differential detection system and an atomic gas chamber surrounded by a triaxial magnetic field coil, both located within the probe's housing. The polarization differential detection system outputs a differentially amplified signal from the emitted laser from the atomic gas chamber to a lock-in amplifier in the optoelectronic integrated system. The lock-in amplifier extracts the first harmonic component (as the magnetometer output signal) and the second harmonic component (as the environmental magnetic field monitoring signal) from the differentially amplified signal. The second harmonic component generates a three-dimensional control signal through a data acquisition and control system, which is transmitted to a three-channel high-precision current source. The three-channel high-precision current source generates a control current for the triaxial magnetic field coil, which is transmitted to the triaxial magnetic field coil to automatically achieve online triaxial magnetic compensation for the atomic gas chamber. The data acquisition and control system samples the second harmonic component θ 2ω The initial sampling result is θ 2ω The i-th sampling result is θ i , i is a positive integer, K0 is the amplification multiple of the data acquisition and control system to the input signal, and θ i is expressed as: where I0 is the light power density of the pumping laser, e is the natural constant, OD(v) is the optical depth, v is the frequency of the pumping laser, v0 is the potassium atom D1 line resonance frequency, Г is the pressure broadening of the atomic cell, J0 and J1 and J2 are the 0th, 1st and 2nd order Bessel functions respectively, u is the magnetic field modulation coefficient, l is the length of the atomic cell, n is the atomic number density of the potassium atom, r is the classical electron radius, c is the light speed, f is the potassium atom D1 line resonance strength, s is the spin angular momentum of the pumping light, R op is the optical pumping rate, R rel is the transverse relaxation rate, γ e is the electron gyromagnetic ratio, B0 is the magnetic field to be measured pointing to the positive direction of the z axis; Let ξ be a set threshold, when |Θ0-Θ i |<ξ, the magnetometer works normally without triggering any action, when |Θ0-Θ i |≥ξ, it indicates that the magnetometer monitors that the ambient magnetic field deviates from the zero field, at this time the magnetometer stops measuring, and triggers the online automatic magnetic field compensation program, after the automatic magnetic field compensation program ends, the condition of |Θ0-Θ i |<ξ is re-satisfied, the magnetometer resumes normal work.

2. The in-situ magnetic field monitoring and automatic compensation device based on ellipsometric atomic magnetometer according to claim 1, characterized in that, The polarization differential detection system includes a half-wave plate located on the laser emission side of the atomic gas cell. The half-wave plate is connected to the input side of a lateral displacement polarization beam splitter. The transmission side of the lateral displacement polarization beam splitter is connected to a first photodetector, and the reflection side of the lateral displacement polarization beam splitter is connected to a second photodetector. The first photodetector is connected to the first input terminal of a differential amplifier circuit, and the second photodetector is connected to the second input terminal of the differential amplifier circuit. The output terminal of the differential amplifier circuit is connected to the input terminal of a lock-in amplifier. The laser incident side of the atomic gas cell is connected to a collimator in sequence via a quarter-wave plate and a linear polarizer. The collimator is connected to a narrow-linewidth semiconductor laser in the optoelectronic integrated system via a polarization-maintaining fiber.

3. The magnetic field in-situ monitoring and automatic compensation device based on ellipsometric atomic magnetometer according to claim 2, characterized in that, The laser emitted by the narrow linewidth semiconductor laser is detuned to the D1 line resonance frequency of the alkali metal atom. After passing through a linear polarizer and a quarter-wave plate, the laser is converted into elliptically polarized light with an ellipticity of 22.5°. After passing through the atomic gas cell, the elliptically polarized light passes sequentially through a half-wave plate and a lateral displacement polarization beam splitter to reach the first photodetector and the second photodetector, respectively.

4. The in-situ magnetic field monitoring and automatic compensation device based on ellipsometric atomic magnetometer according to claim 1, characterized in that, Let the first harmonic component be θ ω and the second harmonic component be θ 2ω then 5. The in-situ magnetic field monitoring and automatic compensation device based on ellipsometric atomic magnetometer according to claim 1, characterized in that, The control current of the triaxial magnetic field coil drives the triaxial magnetic field coil to generate the expected magnetic field determined by the particle swarm optimization algorithm run by the data acquisition and control system as the compensation magnetic field.

6. The in-situ magnetic field monitoring and automatic compensation device based on ellipsometric atomic magnetometer according to claim 5, characterized in that, The particle swarm optimization algorithm includes taking C=(C x , C y , C z ) as an initial point, wherein C is an initial compensation magnetic field, C x , C y , C z are x-axis, y-axis, and z-axis initial compensation magnetic fields, respectively, W x =[C x –R x , C x +R x ], W y =[C y –R y , C y +R y ], and W z =[C z –R z , C z +R z ] are spaces, N particles B j =(B xj , B yj , B zj ) are generated, wherein j=1, 2, 3, …, N, wherein R x is a residual magnetic space in the x direction according to the magnetic shielding system, R y is a residual magnetic space in the y direction according to the magnetic shielding system, R z is a residual magnetic space in the z direction according to the magnetic shielding system, B j is the jth particle magnetic field, B xj , B yj , B zj are x-axis, y-axis, and z-axis magnetic fields of the jth particle magnetic field, respectively, W x , W y , W z are x-axis, y-axis, and z-axis space search domains, respectively, the positions of the 30 particles in the space are constantly updated until the compensation magnetic field B=-B E =(B x , B y , B z ) is found, wherein B x , B y , B z are x-axis, y-axis, and z-axis compensation magnetic fields, respectively, B E is an environmental magnetic field offset from zero, B x ∈W x , B y ∈W y , and B z ∈W z , so that under the condition that the compensation magnetic field is B, |Θ0–Θ i When |<ξ, the algorithm stops running and the magnetometer resumes normal operation; when |Θ0–Θ i When the condition |≥ξ occurs again, C=(B x B y B z The particle swarm optimization algorithm is iteratively run with 0 as the initial point.

7. An in-situ magnetic field monitoring and automatic compensation method based on ellipsometric atomic magnetometer, characterized in that, This includes the in-situ magnetic field monitoring and automatic compensation device based on an ellipsoidal atomic magnetometer as described in any one of claims 1-6.

8. The method of claim 7, wherein the method is based on an ellipsometric atomic magnetometer. Includes the following steps: Step 1: Adjust the output frequency of the narrow linewidth semiconductor laser to be detuned to the D1 line resonance frequency of the alkali metal atoms and to be linearly polarized. Transmit the laser through a polarization-maintaining fiber to a collimator and convert it into a collimated beam. After passing through a linear polarizer and a quarter-wave plate, the beam is converted into elliptically polarized light with an ellipticity of α. Use the elliptically polarized light as a pump laser to irradiate the atomic gas cell, thereby realizing the pumping of alkali metal atoms. Step 2, the ambient magnetic field sensed by the atomic cell is compensated to zero by using in-situ three-dimensional magnetic compensation technology, and the sizes of the compensation magnetic fields of the three axes at this time are C x , C y and C z , respectively. Then, a high-frequency modulated magnetic field with a frequency of ω is applied in the y direction by controlling a three-channel high-precision current source. Then, a lock-in amplification technology is used in a lock-in amplifier to demodulate the differential amplified signals at a frequency of one frequency ω and two frequencies 2ω, respectively, to obtain a first harmonic component θ ω and a second harmonic component θ 2ω ; Step 3, the first harmonic component θ ω as a magnetometer output signal, the second harmonic component θ 2ω as an ambient magnetic field monitoring signal to the data acquisition and control system, the second harmonic component θ 2ω the initial value of which is recorded by the data acquisition and control system as Θ0; Step 4, second harmonic component Θ 2ω The value of Θ is recorded by the data acquisition and control system every interval T, and the value of the i-th sample is denoted as Θ i The sampled data Θ i is judged in the data acquisition and control system, when |Θ i 0 - Θ i | < ξ, the magnetometer works normally without triggering any action, when |Θ i 0 - Θ i | ≥ ξ, it indicates that the magnetometer monitors the environmental magnetic field deviates from the zero field, at this time the magnetometer stops measuring and triggers the online automatic magnetic field compensation program, after the automatic magnetic field compensation program ends, the condition |Θ i 0 - Θ i | < ξ is re-satisfied, the magnetometer resumes normal work, wherein ξ is a set threshold value; Step 5, the calculation unit of the automatic magnetic field compensation program is the data acquisition and control system, the execution unit is the three-axis magnetic field coil, and the execution process is to generate three-dimensional control signals in the data acquisition and control system and transmit them to the three-channel high-precision current source, so that the current source generates three-axis magnetic field coil control current, and the current drives the three-axis magnetic field coil to generate the expected magnetic field in the data acquisition and control system; Step 6: The expected magnetic field is generated by running an intelligent optimization algorithm in the data acquisition and control system. The algorithm's goal is to achieve a magnetic field of C = (C x C y C z ( ) is the initial point, at W x =[C x –R x C x +R x ], W y =[C y –R y C y +R y ], W z =[C z –R z C z +R z Within the space, find the compensating magnetic field B = (B x B y B z ), where R x It is the remanent magnetization space in the x-direction set by the magnetic shielding system, R y It is the remanent magnetization space in the y-direction set by the magnetic shielding system, R z It is based on the remanent magnetization space in the z-direction set by the magnetic shielding system, B x ∈W x B y ∈W y B z ∈W z This ensures that |Θ0–Θ| is satisfied under the compensated magnetic field. i |<ξ, then set the initial point for the next trigger of the online automatic magnetic field compensation procedure to C=(B x B y B z ), searching for space as W x =[B x –R x B x +R x ], W y =[B y –R y B y +R y ], W z =[B z –R z B z +R z The parameters for triggering the online magnetic field compensation program are similar. At this point, the automatic magnetic field compensation program is completed, the ambient magnetic field returns to zero, and the magnetometer starts measuring again, thus entering normal working condition.

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