阅读说明：本技术 一种磁场梯度测量方法以及原子磁力梯度仪系统 (Magnetic field gradient measuring method and atomic magnetic gradiometer system ) 是由 徐晓天 杨胜军 范靖云 于 2021-07-23 设计创作，主要内容包括：本发明公开了一种磁场梯度测量方法以及原子磁力梯度仪系统,包括控制光调制器对激光进行处理,得到泵浦光以及探测光；控制光调制器对泵浦光进行周期性调制,得到带调制信号的调制泵浦光；控制信号探测器接收由探测光依次经过第一极化态原子的拉莫尔进动作用、第二极化态原子的拉莫尔进动作用后得到的第二变化探测光,获取第二变化探测光的偏振旋转角度信号；对第一变化探测光的偏振旋转角信号进行解调,并根据所述调制信号的频率计算获取第一待测外磁场的值,可同时获得第一极化态原子处的磁场强度。本发明实现了一种灵敏紧凑的磁场强度和磁场梯度的同时测量方法,并且能够抑制磁场梯度测量中的共模噪声,提升磁场梯度测量的灵敏度和精度。(The invention discloses a magnetic field gradient measuring method and an atomic magnetic gradiometer system, which comprises the steps of controlling an optical modulator to process laser to obtain pump light and probe light; controlling the optical modulator to periodically modulate the pump light to obtain modulated pump light with a modulation signal; the control signal detector receives second change detection light obtained by the detection light after the Larmor precession action of the first polarization state atoms and the Larmor precession action of the second polarization state atoms in sequence, and obtains a polarization rotation angle signal of the second change detection light; and demodulating the polarization rotation angle signal of the first change detection light, calculating and acquiring the value of the first external magnetic field to be detected according to the frequency of the modulation signal, and simultaneously acquiring the magnetic field intensity of the first polarization state atom. The invention realizes a sensitive and compact method for simultaneously measuring the magnetic field intensity and the magnetic field gradient, can inhibit common-mode noise in the magnetic field gradient measurement, and improves the sensitivity and the precision of the magnetic field gradient measurement.)

1. A method of magnetic field gradient measurement, comprising the steps of:

controlling the optical modulator to process the laser to obtain pump light and probe light;

controlling an optical modulator to periodically modulate the pump light to obtain modulated pump light with a modulation signal;

the control signal detector receives first change detection light obtained after the detection light passes through the Larmor precession action of first polarization state atoms, and obtains a polarization rotation angle signal of the first change detection light, wherein the first polarization state atoms are generated on the atom probe by the action of the modulation pump light, and the Larmor precession of the first polarization state atoms is generated under a first external magnetic field to be detected;

demodulating the polarization rotation angle signal of the first change detection light, and calculating according to the frequency of the modulation signal to obtain a value of a first external magnetic field to be detected;

the control signal detector receives second change detection light obtained by sequentially passing detection light through the Larmor precession action of first polarization atoms and the Larmor precession action of second polarization atoms to obtain polarization rotation angle signals of the second change detection light, wherein the second polarization atoms are generated on the atom probe by the action of the modulated pump light, the polarization directions of the second polarization atoms and the first polarization atoms are mutually vertical, and the Larmor precession of the second polarization atoms is generated under a second external magnetic field to be detected; and demodulating the polarization rotation angle signal of the second change detection light, and calculating and acquiring the difference value of the first external magnetic field to be detected and the second external magnetic field to be detected according to the frequency of the modulation signal.

2. The method according to claim 1, wherein the step of controlling the optical modulator to process the laser light to obtain the pump light and the probe light comprises: the optical modulator respectively carries out frequency shift on the two beams of laser to obtain resonant pump light and far detuned detection light, wherein the detuning amount of the detection light is 400 MHz.

3. The method according to claim 2, wherein the step of receiving the second varying probe light by the control signal detector after the probe light sequentially passes through the larmor precession of the first polarization atom and the larmor precession of the second polarization atom, and acquiring the polarization rotation angle signal of the second varying probe light further comprises the steps of:

and controlling the pump light and the detection light to act on the atomic probe after being combined by the polarization beam splitter.

4. The method according to claim 1, wherein the step of controlling the optical modulator to process the laser light to obtain the pump light and the probe light comprises:

and controlling the optical modulator to perform time-sharing control on a laser beam to obtain pump light and detection light, wherein the light intensity of the pump light is greater than that of the detection light.

5. The method according to claim 1, wherein the step of controlling the optical modulator to periodically modulate the pump light to obtain the modulated pump light with the modulation signal comprises:

the light modulator periodically modulates the frequency, intensity, or polarization of the pump light.

6. The magnetic field gradient measurement method according to claim 1, wherein the step of demodulating the polarization rotation angle signal of the second variation detection light and obtaining the difference between the first external magnetic field to be measured and the second external magnetic field to be measured by calculating the frequency of the modulation signal comprises:

demodulating the polarization rotation angle signal of the second variation detection light to obtain an extreme point of a demodulation signal and a frequency of the modulation signal corresponding to the extreme point;

acquiring a difference value of Larmor precession frequencies of first polarized atoms and second polarized atoms according to the frequency of the modulation signal corresponding to the extreme point;

and calculating the difference value of the first external magnetic field to be detected and the second external magnetic field to be detected according to the difference value of the Larmor precession frequencies of the first polarized atoms and the second polarized atoms.

7. The method according to claim 1, wherein the step of controlling the optical modulator to process the laser light to obtain the pump light and the probe light further comprises:

controlling a laser light source to emit laser and collect laser after being electrified, obtaining a frequency error signal of the laser light source, and performing feedback control on a driving current of the laser light source according to the frequency error signal of the laser light source to obtain stable laser, wherein the laser wavelength is 795nm, and the laser frequency is stabilized at⁸⁷F2 → F' 1 of Rb.

8. An atomic magnetic gradiometer system, comprising: the device comprises a laser light source, an optical modulator, an atom probe, a signal detector and a controller;

the controller is electrically connected with the laser light source, the optical modulator and the signal detector respectively, and realizes the magnetic field gradient measuring method according to any one of claims 1 to 7.

9. The atomic magnetic gradiometer system of claim 8, wherein the atomic probe comprises:

a polarizing plate located at incident light;

the beam splitter is arranged on the light emitting side of the polaroid;

the first right-angle reflecting prism is positioned on one side, away from the polaroid, of the beam splitter;

a first atomic gas cell located between the beam splitter and the first right angle reflecting prism;

a light shield positioned between the beam splitter and the first atomic gas chamber;

the phase shifter is positioned on the light emergent side of the reflected light of the beam splitter;

a plane mirror obliquely placed on a side of the phase shifter facing away from the second beam splitter;

the second right-angle reflecting prism is positioned on the light-emitting side of the reflected light of the plane mirror; and

a second atomic gas cell located between the planar mirror and the second right angle reflecting prism;

the signal detector comprises a first signal detector, and the first signal detector is used for receiving detection light reflected by Larmor precession action of first polarization state atoms in the first atomic gas chamber;

the signal detector also comprises a second signal detector, and the second signal detector is used for receiving the detection light reflected by the Larmor precession action of the first polarized atom in the first atomic gas chamber and the Larmor precession action of the second polarized atom in the second atomic gas chamber in sequence.

10. The atomic magnetic gradiometer system of claim 8, wherein the atomic probe comprises:

a polarizing plate disposed at incident light;

a beam splitter disposed on a light exit side of the polarizer;

a first atomic gas cell located between the polarizer and the beam splitter;

the signal detector comprises a first signal detector, the first signal detector is positioned on the light-emitting side of the reflected light of the beam splitter and is used for receiving the detection light reflected by Larmor precession action of the first polarization state atoms in the first atomic gas chamber;

the phase shifter is arranged on the light emitting side of the transmitted light of the beam splitter; and

a second atomic gas chamber located on a side of the phase shifter facing away from the polarizer;

the signal detector comprises a second signal detector, and the second signal detector is positioned on the light-emitting side of the second atomic gas chamber and is used for receiving the detection light reflected after the Larmor precession action of the first polarized atoms in the first atomic gas chamber and the Larmor precession action of the second polarized atoms in the second atomic gas chamber in sequence.

Technical Field

The invention relates to the field of magnetic field measurement, in particular to a magnetic field gradient measurement method and an atomic magnetic gradiometer system.

Background

Magnetic field detection has wide requirements in the fields of resource exploration, geophysical, nondestructive testing, biomedical, national defense and military, basic science and the like, and a magnetic field gradiometer can provide richer and more accurate information of a measured object by measuring the magnetic field size difference values at different positions in space. Meanwhile, the magnetic field gradiometer can inhibit common-mode noise and improve the measurement sensitivity and precision of the magnetic field signal to be measured by distinguishing a measurement background magnetic field and a signal magnetic field. The atomic magnetometer and the atomic magnetic gradiometer as a novel magnetic field detection device have the advantages of high sensitivity, small volume, low power consumption and the like, and can play an important role in the field of magnetic field detection.

The existing atomic magnetic gradiometer respectively irradiates two atomic gases after splitting laser beams, respectively extracts magnetic field signals at the two atomic gases, and then acquires the information of the magnetic field gradient by processing the two signals, but the scheme can not effectively inhibit common-mode noise in the magnetic field gradient measurement and influences the sensitivity and the precision of the magnetic field gradient measurement.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a magnetic field gradient measurement method and an atomic magnetometer system, which solve the problems in the prior art that the influence of common mode noise is large, so that the atomic magnetometer cannot accurately measure the magnetic field, and is not favorable for the precise measurement of the magnetic field.

The technical scheme of the invention is as follows:

a magnetic field gradient measurement method comprising the steps of:

controlling the optical modulator to process the laser to obtain pump light and probe light;

controlling an optical modulator to periodically modulate the pump light to obtain modulated pump light with a modulation signal;

the control signal detector receives first change detection light obtained after the detection light passes through the Larmor precession action of first polarization state atoms, and obtains a polarization rotation angle signal of the first change detection light, wherein the first polarization state atoms are generated on the atom probe by the action of the modulation pump light, and the Larmor precession of the first polarization state atoms is generated under a first external magnetic field to be detected;

demodulating the polarization rotation angle signal of the first change detection light, and calculating according to the frequency of the modulation signal to obtain a value of a first external magnetic field to be detected;

the control signal detector receives second change detection light obtained by sequentially passing detection light through the Larmor precession action of first polarization atoms and the Larmor precession action of second polarization atoms to obtain polarization rotation angle signals of the second change detection light, wherein the second polarization atoms are generated on the atom probe by the action of the modulated pump light, the polarization directions of the second polarization atoms and the first polarization atoms are mutually vertical, and the Larmor precession of the second polarization atoms is generated under a second external magnetic field to be detected;

and demodulating the polarization rotation angle signal of the second change detection light, and calculating and acquiring the difference value of the first external magnetic field to be detected and the second external magnetic field to be detected according to the frequency of the modulation signal.

Further, the step of controlling the optical modulator to process the laser to obtain the pump light and the probe light comprises:

the optical modulator respectively carries out frequency shift on the two beams of laser to obtain resonant pump light and far detuned detection light, wherein the detuning amount of the detection light is 400 MHz.

Further, the step of receiving, by the control signal detector, second variation detection light obtained by sequentially passing the detection light through a larmor precession action of the first polarization state atom and a larmor precession action of the second polarization state atom, and obtaining a polarization rotation angle signal of the second variation detection light further includes, before the step of obtaining a polarization rotation angle signal of the second variation detection light, the steps of:

and controlling the pump light and the detection light to act on the atomic probe after being combined by the polarization beam splitter.

Further, the step of controlling the optical modulator to process the laser to obtain the pump light and the probe light comprises:

and controlling the optical modulator to perform time-sharing control on a laser beam to obtain pump light and detection light, wherein the light intensity of the pump light is greater than that of the detection light.

Further, the step of controlling the optical modulator to periodically modulate the pump light to obtain modulated pump light with a modulation signal includes:

the light modulator periodically modulates the frequency, intensity, or polarization of the pump light.

Further, the step of demodulating the polarization rotation angle signal of the second variation detection light and calculating and acquiring the difference value between the first external magnetic field to be detected and the second external magnetic field to be detected according to the frequency of the modulation signal includes:

demodulating the polarization rotation angle signal of the second variation detection light to obtain an extreme point of a demodulation signal and a frequency of the modulation signal corresponding to the extreme point;

acquiring a difference value of Larmor precession frequencies of first polarized atoms and second polarized atoms according to the frequency of the modulation signal corresponding to the extreme point;

and calculating the difference value of the first external magnetic field to be detected and the second external magnetic field to be detected according to the difference value of the Larmor precession frequencies of the first polarized atoms and the second polarized atoms.

Further, before the step of controlling the optical modulator to process the laser to obtain the pump light and the probe light, the method further includes:

controlling a laser light source to emit laser and collect laser after being electrified, obtaining a frequency error signal of the laser light source, and performing feedback control on a driving current of the laser light source according to the frequency error signal of the laser light source to obtain stable laser, wherein the laser wavelength is 795nm, and the laser frequency is stabilized at⁸⁷F2 → F' 1 of Rb.

Based on the same conception, the invention also discloses an atomic magnetic gradiometer system, comprising: the device comprises a laser light source, an optical modulator, an atom probe, a signal detector and a controller;

the controller is electrically connected with the laser light source, the optical modulator and the signal detector respectively, and the magnetic field gradient measuring method is realized.

Further, the atom probe includes:

a polarizing plate located at incident light;

the beam splitter is arranged on the light emitting side of the polaroid;

the first right-angle reflecting prism is positioned on one side, away from the polaroid, of the beam splitter;

a first atomic gas cell located between the beam splitter and the first right angle reflecting prism;

a light shield positioned between the beam splitter and the first atomic gas chamber;

the phase shifter is positioned on the light emergent side of the reflected light of the beam splitter;

a plane mirror obliquely placed on a side of the phase shifter facing away from the second beam splitter;

the second right-angle reflecting prism is positioned on the light-emitting side of the reflected light of the plane mirror; and

a second atomic gas cell located between the planar mirror and the second right angle reflecting prism;

the signal detector comprises a first signal detector, and the first signal detector is used for receiving detection light reflected by Larmor precession action of first polarization state atoms in the first atomic gas chamber;

the signal detector also comprises a second signal detector, and the second signal detector is used for receiving the detection light reflected by the Larmor precession action of the first polarized atom in the first atomic gas chamber and the Larmor precession action of the second polarized atom in the second atomic gas chamber in sequence.

Further, the atom probe includes:

a polarizing plate disposed at incident light;

a beam splitter disposed on a light exit side of the polarizer;

a first atomic gas cell located between the polarizer and the beam splitter;

the signal detector comprises a first signal detector, the first signal detector is positioned on the light-emitting side of the reflected light of the beam splitter and is used for receiving the detection light reflected by Larmor precession action of the first polarization state atoms in the first atomic gas chamber;

the phase shifter is arranged on the light emitting side of the transmitted light of the beam splitter; and

a second atomic gas chamber located on a side of the phase shifter facing away from the polarizer;

the signal detector comprises a second signal detector, and the second signal detector is positioned on the light-emitting side of the second atomic gas chamber and is used for receiving the detection light reflected after the Larmor precession action of the first polarized atoms in the first atomic gas chamber and the Larmor precession action of the second polarized atoms in the second atomic gas chamber in sequence.

Has the advantages that: compared with the prior art, the magnetic field gradient measuring method and the atomic magnetic gradiometer system provided by the invention have the advantages that in the atomic polarization state preparation stage, the laser is processed through the optical modulator to obtain the pumping light and the detection light, wherein the light intensity of the pumping light is greater than that of the detection light, the pumping light is modulated through the optical modulator to obtain the modulated pumping light with a modulation signal, and thus the pumping light with stronger light intensity is selected, because the stronger pumping light can improve the pumping rate of atoms and increase the polarization degree of the atoms, the atoms in the polarization state perform Larmor precession under the action of a magnetic field to be detected, and the atoms with higher polarization degree are more beneficial to the detection of the system, so that the signal intensity is improved. During detection, detection light with weak light intensity is selected, because the weak detection light can reduce shot noise introduced by the detection light intensity, the detection light with weak light intensity forms second change detection light with a polarization rotation angle change under the action of Larmor precession of first polarization atoms and the action of Larmor precession of second polarization atoms in sequence, the polarization directions of the first polarization atoms and the second polarization atoms are mutually vertical, the second change detection light is received by the signal acquisition module to acquire a polarization rotation angle signal of the second change detection light, the polarization rotation angle signal is demodulated by the signal demodulation processing module, and a difference value of external magnetic fields to be detected at two positions is calculated and acquired according to the frequency of the modulation signal. Through this scheme, not only have advantages such as atom magnetometer sensitivity height, small, low power dissipation. Meanwhile, one beam of detection light continuously passes through two polarized atoms with mutually perpendicular polarization directions to carry out Larmor precession, so that common-mode noise can be inhibited, the atomic magnetic gradiometer can measure a magnetic field more accurately, the precise measurement of the magnetic field is facilitated, and the atomic magnetic gradiometer can be better used in practical application requirements of geomagnetic navigation, biomedical treatment, magnetic anomaly detection, anti-latency and the like. In addition, the detection light passing through the first polarization state atom is subjected to beam splitting detection, a polarization rotation angle signal of the first change detection light forming polarization rotation angle change under the action of Larmor precession of the first polarization state atom can be independently obtained, the signal demodulation processing module demodulates the polarization rotation angle signal of the first change detection light, and a value of a first external magnetic field to be detected is obtained through calculation according to the frequency of the modulation signal.

Drawings

FIG. 1 is a flow chart of the main steps of a magnetic field gradient measurement method of the present invention.

FIG. 2 is a flow chart of a preferred embodiment of a magnetic field gradient measurement method of the present invention.

FIG. 3 is a schematic block diagram of an atomic magnetic gradiometer system of the invention.

FIG. 4 is a schematic diagram of the operation of an atom probe of an atom magnetic gradiometer system of the present invention.

FIG. 5 is a schematic diagram of the operation of another atom probe of an atom magnetic gradiometer system of the invention;

FIG. 6 is a diagram of the working principle of the polarization beam splitter in the atomic magnetic gradiometer method of the present invention.

The reference numbers in the figures: 10. a laser light source; 20. an optical modulator; 30. an atom probe; 31. a polarizing plate; 32. a beam splitter; 331. a first atomic gas chamber; 332. a second atomic gas chamber; 34. a phase shifter; 351. a first right-angle reflecting prism; 352. a second right-angle reflecting prism; 36. light blocking; 37. a plane mirror; 38. a polarizing beam splitter; 40. a signal detector; 401. a first signal detector; 402. a second signal detector; 50. and a controller.

Detailed Description

The invention provides a magnetic field gradient measuring method and an atomic magnetic gradiometer system, and in order to make the purpose, technical scheme and effect of the invention clearer and clearer, the invention is further described in detail by referring to the attached drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The basic working principle of the full-light type atomic magnetometer is as follows: firstly, a beam of laser irradiates on alkali metal atomic gas, and a pumping process is carried out on atoms, so that the atoms are distributed on a magnetic energy level and redistributed, macroscopically, the atoms have certain polarization orientation, and the process is a polarization state preparation process of the atoms; then the polarized atoms carry out Larmor precession around the direction of the external magnetic field, and the precession frequency (namely the Larmor frequency) of the polarized atoms is in direct proportion to the size of the external magnetic field; the linearly polarized probe light impinges on the precessing polarized atoms and its plane of polarization is rotated, the rotation angle being proportional to the magnitude of the external magnetic field. The whole process is the open-loop structure of the full-light type atomic magnetometer.

The basic principle of the closed-loop measurement of the magnetic field of the full-light type atomic magnetometer is as follows: firstly, preparing the polarization state of atoms; then, the polarization rotation angle of the laser after atomic larmor precession action is changed, the polarization rotation angle signal of the laser is received for demodulation, and when the frequency of the modulation signal is equal to twice larmor frequency, the demodulation signal reaches an extreme value. The extreme point of the demodulation signal can be obtained by scanning the frequency of the modulation signal, the larmor frequency is obtained, and the size of the magnetic field is further obtained.

As shown in fig. 1 and fig. 2, the present invention is improved based on the above basic principle, and provides a magnetic field gradient measuring method, wherein the magnetic field gradient measuring method comprises the steps of:

and S100, controlling the laser light source to emit laser and collect the laser after being electrified, and acquiring a frequency error signal of the laser light source.

Specifically, after the laser light source is powered on, the controller can control the laser light source to start to emit laser light, the laser light source is composed of a laser tube, a laser driving power supply and a laser frequency detection device, the laser driving power supply drives the laser tube to generate laser light after being powered on, and the laser frequency detection device detects the frequency of the laser light, so that the frequency of the laser light can be controlled conveniently.

And step S120, controlling the driving current of the laser light source in a feedback manner according to the frequency error signal of the laser light source to obtain stable laser.

Specifically, the laser frequency detection device collects and detects laser emitted by the laser light source, obtains the frequency of the emitted laser, and obtains a frequency error signal by comparing the frequency with a set frequency. And the controller calculates a difference value between the laser being emitted and the preset laser frequency according to the frequency error signal, and then sends a control command to the laser driving power supply, and the laser driving power supply adjusts the current according to different control commands to ensure that the frequency of the emitted laser is stabilized on the set laser frequency value.

For example, the process of implementing feedback control is: the laser tube of the laser light source emits laser, the emitted laser is detected by the laser frequency detection device to obtain the actual frequency of the emitted laser, the controller calculates, when the actual frequency is greater than the preset laser frequency, the controller emits a control signal to the laser driving power supply, the laser driving power supply reduces the current of the control laser, so that the frequency of the laser is reduced, and the frequency of the emitted laser is adjusted to be equal to the preset frequency; when the actual frequency is smaller than the preset laser frequency, the controller sends a control signal to the laser driving power supply, and the laser driving power supply increases the current of the control laser, so that the frequency of the laser is increased, and the frequency of the laser is adjusted to be equal to the preset frequency. Through the above process, the stable laser with the wavelength of 795nm generated by the laser light source in this embodiment stabilizes the laser frequency in a saturated absorption locking manner⁸⁷F2 → F' 1 of Rb.

And S200, controlling the optical modulator to process the laser to obtain pump light and probe light.

The light intensity modulator consists of a light modulator, a radio frequency signal generator and a radio frequency amplifier. The pump light and the probe light in this step are obtained in two ways.

The first mode is as follows: the light intensity modulator periodically modulates a laser beam to obtain pump light and probe light. Specifically, the optical modulator is controlled to shift the frequency of the stabilized laser to generate linearly polarized laser. In a specific process, an optical modulator is provided, and the optical modulator can be turned on or turned off through a controller, for example, after stable laser with the wavelength of 795nm is generated by the laser light source, frequency shift is performed on the laser through the optical modulator, and linearly polarized light with near resonance is generated. The near-resonant linearly polarized laser light is a linearly polarized laser light having a frequency close to the resonant frequency, and is confirmed mainly by the interaction intensity and the atomic characteristics used in the experimental system. The light intensity modulator realizes the periodic modulation of the intensity of the laser light under the control of the instruction of the controller, and modulates the laser emission duration into a plurality of periods T; all the periods T are divided into an atomic polarization state preparation stage with the duration of T1 and a detection stage with the duration of T2, namely T1+ T2; the laser is modulated to emit stronger light as pumping light within T1 time, and the weaker light is emitted as detection light within T2 time, so that the pumping light and the detection light are emitted by the same laser, the stability of the two lights is kept consistent, the consistency is better, and the coordination of the pumping process and the detection process between the two lights is improved. In the time-sharing process, atomic polarization with the time length of T1 is firstly carried out in one period, and then the time length of T2 is detected, so that the polarization preparation process and the detection process can be separately carried out, the interference among lights is avoided, the measurement process is more sensitive, and the measurement is more accurate.

The second way is: the optical modulator respectively carries out frequency shift on the two beams of laser to obtain resonant pump light and far detuned detection light, wherein the detuning amount of the detection light is 400 MHz.

And step S300, controlling the optical modulator to periodically modulate the pump light to obtain modulated pump light with a modulation signal.

In the specific process, in the atomic polarization state preparation stage (pumping light action atomic stage) of the magnetic field measurement process, the controller controls the radio frequency signal generator of the light intensity modulator to generate a modulation signal with a period of T', the modulation signal is amplified by the radio frequency amplifier, the signal is superposed on the pumping light after being clearer, and the pumping light has definite performance parameters through the signal, for example, the modulation process of the modulation signal on the pumping light is to perform periodic modulation on one optical parameter of the pumping light. In this embodiment, the light intensity of the pump light is periodically modulated, and the modulated pump light with a modulation signal generated after modulation acts on an atom to polarize the atomic state, thereby realizing the atomic polarization state. The frequency of the modulation signal in the embodiment is a multiple of the polarization state atomic larmor precession frequency, and the detection and real-time tracking of the detected magnetic field signal are realized by superposing the periodic modulation signal with the polarization state atomic larmor precession frequency multiple.

After the pump light and the probe light are obtained in the second way, as shown in fig. 6, the pump light and the probe light need to be controlled to be combined by the polarization beam splitter 38 and act on the atomic probe, so as to realize atomic polarization. The polarization beam splitter 38 combines the beams so that the region where the probe light acts is covered with the region where the pump light performs atomic polarization. This improves the accuracy of the measurement.

Step S400, a signal detector is controlled to receive first change detection light obtained after the detection light is subjected to Larmor precession action of first polarization state atoms, and a polarization rotation angle signal of the first change detection light is obtained, wherein the first polarization state atoms are generated on an atom probe under the action of the modulation pump light, and the Larmor precession of the first polarization state atoms is generated under a first external magnetic field to be detected.

In this embodiment, an atom probe is provided for receiving pump light, a first atom in a polarization state is obtained by modulating the pump light in the atom probe, the atom probe is placed in a first external magnetic field to be detected, the first atom in the polarization state performs larmor precession under the action of the first magnetic field to be detected, and when a probe light irradiates on the first atom in the polarization state performing the larmor precession, a polarization rotation angle of the probe light changes to form a first changed probe light. And providing a signal detector to receive the first change detection light, wherein the signal detector can be controlled by a controller, and the controller controls the polarization rotation angle signal of the first change detection light to be obtained by analyzing after the signal detector receives the first change detection light.

Step S500, demodulating the polarization rotation angle signal of the first change detection light, and calculating and acquiring a value of the first external magnetic field to be detected according to the frequency of the modulation signal.

After the signal detector receives the first change detection light, the polarization rotation angle signal of the first change detection light is obtained through analysis of the controller. The controller demodulates a polarization rotation angle signal of the first variation detection light, and the demodulated signal reaches an extreme value when the frequency of the modulated signal is equal to twice the larmor frequency. Thus, the extreme point of the demodulation signal is obtained by scanning the frequency of the modulation signal, the Larmor frequency is obtained, and the size of the first external magnetic field to be detected is further obtained.

Step S600, the control signal detector receives second variation detection light obtained by sequentially passing the detection light through a larmor precession action of a first polarized atom and a larmor precession action of a second polarized atom, and obtains a polarization rotation angle signal of the second variation detection light, wherein the second polarized atom is generated by the modulated pump light acting on the atomic probe, polarization directions of the second polarized atom and the first polarized atom are perpendicular to each other, and the larmor precession of the second polarized atom is generated in a second external magnetic field to be detected.

In this embodiment, an atom probe is provided for receiving pump light, two atom gas chambers are provided in the atom probe, and the pump light is modulated to pass through the two atom gas chambers in sequence, so that the first polarization atom and the second polarization atom are obtained in the two atom gas chambers, respectively, and polarization directions of the second polarization atom and the first polarization atom are perpendicular to each other. And when the detection light sequentially irradiates the first polarization state atom and the second polarization state atom which are subjected to Larmor precession, the polarization rotation angle of the detection light is changed to form second change detection light. And providing a signal detector to receive the second change detection light, wherein the signal detector can be controlled by a controller, and the controller controls the polarization rotation angle signal of the change detection light to be obtained by analyzing after the signal detector receives the second change detection light.

Step S700, demodulating the polarization rotation angle signal of the second change detection light, and calculating and acquiring the difference value of the first external magnetic field to be detected and the second external magnetic field to be detected according to the frequency of the modulation signal.

In the specific process, laser irradiates on alkali metal atomic gas, and a pumping process is carried out on atoms, so that the atom population is redistributed on a magnetic energy level, macroscopically, the atoms have certain polarization orientation, and the process is the preparation process of the polarization state of the atoms. And modulating the polarization state preparation of the atoms, wherein the modulation process can be frequency modulation, intensity modulation or polarization modulation of pump light to obtain the modulated pump light, the modulated pump light irradiates an atom probe to carry out an atom polarization process, Larmor precession is carried out under the action of a magnetic field to be detected, when the probe light irradiates polarized atoms which are in Larmor precession, the probe light is changed to generate changed probe light, and after the signal detector receives the changed probe light, a polarization rotation angle signal is obtained through analysis of a controller. The controller demodulates the polarization rotation angle signal of the probe light, and the demodulated signal reaches an extreme value when the frequency of the modulated signal is equal to twice the larmor frequency. Thus, the extreme point of the demodulation signal is obtained by scanning the frequency of the modulation signal, the larmor frequency is obtained, and the size of the magnetic field is further obtained. On the basis of the above theory, the linear polarization probe light continuously passes through two atomic gases, and the polarization directions of the pump light to the two atomic gases are adjusted, so that the polarization rotation angles of the probe light under the action of larmor precession of the second polarization state atoms and the second polarization state atoms are opposite, and finally the total polarization rotation angle is proportional to the difference value of the external magnetic fields at the two positions. The whole process is the open-loop structure of the all-optical atomic magnetic gradiometer.

Based on the principle, the controller can demodulate the polarization rotation angle signal of the second change detection light, and calculate and obtain the difference value of the two external magnetic fields to be measured according to the frequency of the modulation signal.

As shown in fig. 1 and 2, step S700 specifically includes:

step S710 of demodulating the polarization rotation angle signal of the second variation detection light to obtain an extreme point of the demodulated signal and a frequency of the modulated signal corresponding to the extreme point.

Step S720, acquiring a difference value of Larmor precession frequencies of the first polarized atoms and the second polarized atoms according to the frequency of the modulation signal corresponding to the extreme point.

Step S730, calculating a difference between the first external magnetic field to be measured and the second external magnetic field to be measured according to the difference between the larmor precession frequencies of the first polarized atoms and the second polarized atoms.

The controller obtains an extreme point of a demodulation signal through demodulation, the frequency value of the modulation signal corresponding to the extreme point is two times of the larmor frequency value, the frequency value of the modulation signal can be obtained through scanning and is a known value, and when the period of the modulation signal (the change of light intensity) is T ', the frequency of the modulation signal is 1/T ' which is the reciprocal of the period, so that the larmor frequency value of atoms in a polarization state, namely 1/T ' which is half of the period, can be obtained. The larmor frequency value is in direct proportion to the magnitude of the external magnetic field, and the controller obtains the difference value of the magnitudes of the two external magnetic fields according to the direct proportion relation between the larmor precession frequency of the polarized atoms and the external magnetic fields to be measured at the two positions.

In a specific process, a polarization rotation angle signal of light is detectedProportional to polarization of atomsIntensity P and magnitude B of external magnetic field, and polarization intensity P of atoms and pumping speed gamma of pumping light_opAnd relaxation rate of atoms Γ_relCorrelation (which may be expressed as) Pumping rate of pump light gamma_opProportional to the intensity I of the pump light, and thus detecting the polarization rotation angle signal of the lightThe relationship between the intensity I of the pump light and the magnitude B of the external magnetic field can be expressed as:when the light intensity I of the pump light is large enough, the polarization rotation angle signal of the probe lightDependent only on the magnitude B of the external magnetic field, i.e.In this embodiment, the light intensity of the pump light is 1mW, and the light intensity of the probe light is 10 μ W. Therefore, the difference value of the sizes of the two external magnetic fields (the first external magnetic field to be detected and the second external magnetic field to be detected) can be calculated more conveniently, and an optimized result is obtained.

In the scheme, the magnetic field gradient is measured by only one beam of detection light, because the polarization directions of the first polarization state atom and the second polarization state atom are mutually vertical, the rotation angle directions generated when the detection light passes through the first polarization state atom and the second polarization state atom respectively are opposite, and the final rotation angle signal is the difference value of the two rotation angle signals, so that the common magnetic noise at the first polarization state atom and the second polarization state atom and the optical noise related to optical polarization are effectively suppressed.

As shown in fig. 3, based on the same inventive concept, the present invention further provides an atomic magnetometer system, which includes: the method comprises the following steps: a laser light source 10, an optical modulator 20, an atom probe 30, a signal detector 40, and a controller 50; the controller 50 is electrically connected to the laser light source 10, the light intensity modulator 20, and the signal detector 40, respectively, and implements the magnetic field gradient measurement method as described above.

The method specifically comprises the following steps: the laser light source comprises a laser tube, a laser driving power supply and a laser frequency detection device. The optical modulator comprises an acousto-optic modulator, a radio frequency signal generator and a radio frequency amplifier. The controller comprises a CPU, an analog/digital signal input/output module, a signal processing module (software) and a data memory. In the working process, the laser light source emits laser, the laser is modulated by the acousto-optic modulator and then acts on the atomic probe, the controller realizes the stabilization of the laser frequency and the control of the periodic modulation of the intensity of the laser light, and the signal detector is controlled to collect the signal of the change detection light emitted by the atomic probe. In addition, the signal detector and the controller can be integrated into a whole, for example, integrated into a computer, and the signal control and acquisition are carried out by the computer.

In addition, it should be noted that: in order to make the measuring result more reasonable and accurate. The difference value of the first external magnetic field to be detected and the second external magnetic field to be detected cannot be larger than the magnetic line width of the atomic gas chamber used for generating polarized atoms in the atomic probe. And when the difference value between the first external magnetic field to be measured and the second external magnetic field to be measured is larger than the magnetic line width of the atomic gas chamber, the difference value between the two magnetic fields cannot be measured.

As shown in fig. 3 and 4, the optical path structure of the atom probe 30 in the present embodiment has two modes, and as shown in fig. 6, one of the atom probes 30 includes: polarizer 31, beam splitter 32, first right-angle reflecting prism 351, first atomic gas chamber 331, light shield 36, phase shifter 34, plane mirror 37, second right-angle reflecting prism 352, and second atomic gas chamber 332. The atom probe 30 implements a multi-reflection configuration of the optical path. The polarizing plate 31 is located on the light incident side of the laser light, the beam splitter 32 is disposed on the light emitting side of the polarizing plate 31, the first rectangular reflecting prism 351 is located on the side of the beam splitter 32 away from the polarizing plate 31, and the first atomic gas chamber 331 is located between the beam splitter 32 and the first rectangular reflecting prism 351. The light shield 36 is located between the beam splitter 32 and the first atomic gas chamber 331. The phase shifter 34 is located on the light exit side of the beam splitter 32 from which light is reflected. The plane mirror 37 is placed obliquely on the side of the phase shifter 34 facing away from the second beam splitter 32. The second rectangular reflecting prism 352 is located on the light exit side of the light reflected by the plane mirror 37, and the second atomic gas chamber 332 is located between the plane mirror 37 and the second rectangular reflecting prism 352. The signal detector 40 includes a first signal detector 401, and the first signal detector 401 is configured to receive the detection light reflected by the larmor precession of the first polarization state atom in the first atomic gas chamber 331. The signal detector 40 further includes a second signal detector 402, and the second signal detector 402 is configured to receive the detection light reflected by the larmor precession action of the first polarized atom in the first atomic gas chamber 331 and the larmor precession action of the second polarized atom in the second atomic gas chamber 332 in sequence.

Modulated pump light in laser passes through a polarizing plate 31 to be polarized, is transmitted and enters a first atomic gas chamber 331 after passing through a beam splitter 32, atoms in the first atomic gas chamber 331 are polarized, so that polarized atoms in the first atomic gas chamber 331 generate larmor precession under the action of an external magnetic field, the modulated pump light is reflected by a first right-angle reflecting prism 351, the returned modulated pump light is reflected by the beam splitter 32 and enters a phase shifter 34, the modulated pump light is adjusted by the phase shifter 34, the polarization directions of the modulated pump light to two atomic gases are opposite, and therefore when probe light passes through two polarized atomic gases which are subjected to larmor precession, the directions of two polarization rotation angles are opposite.

In the structure of the atomic probe 30, the probe light has two optical paths, wherein the first optical path is: the detection light in the laser passes through the polarizing plate 31 for polarization, is transmitted and enters the first atomic gas chamber 331 after passing through the beam splitter 32, the polarization rotation angle is changed once under the action of larmor precession of polarization atoms in the first atomic gas chamber 331, the detection light is reflected by the first right-angle reflecting prism 351, and the returned detection light is received by the first signal detector 401 after being transmitted by the beam splitter 32. At this time, the polarization rotation angle signal received by the first signal detector 401 is proportional to the magnitude of the magnetic field at the first atomic gas chamber 331, and the magnitude of the magnetic field at the first atomic gas chamber 331 can be obtained by demodulating the signal received by the first signal detector 401.

In the second optical path, the detection light in the laser passes through the polarizer 31 for polarization, is transmitted, passes through the beam splitter 32, and then enters the first atomic gas chamber 331, undergoes a first polarization rotation angle change under the action of larmor precession of polarized atoms in the first atomic gas chamber 331, is reflected by the first right-angle reflecting prism 351, and the return detection light is reflected by the beam splitter 32, passes through the transmission phase shifter 34, then enters the second atomic gas chamber 332 after being reflected by the plane mirror 37, undergoes a second polarization rotation angle change under the action of larmor precession of polarized atoms, is finally reflected by the second right-angle reflecting prism 352, is reflected by the plane mirror, then passes through the beam splitter 32 for transmission, and is received by the second signal detector 402. At this time, the polarization rotation angle signal received by the second signal detector 402 is proportional to the difference between the magnitudes of the magnetic fields in the first atomic gas chamber 331 and the second atomic gas chamber 332, and the difference between the magnitudes of the magnetic fields in the two atomic gas chambers can be obtained by demodulating the signal received by the second signal detector 402.

In this embodiment, an optical stop 36 is disposed between the beam splitter 32 and the first atomic gas chamber 331, and is used to prevent multiple reflections of the pump light and the probe light in the two atomic gas chambers from affecting the detection result.

This reflection light path structure not only can shine atomic gas and increase effective atomicity to promote atomic magnetometer's measurement sensitivity, this structure is simple and convenient moreover, and effective detection area can be close to the target object of being surveyed more, does benefit to the miniaturization.

As shown in fig. 3 and 5, another atom probe 30 includes: a polarizing plate 31, a beam splitter 32, a first atomic gas chamber 331, a phase shifter 34, and a second atomic gas chamber 332. The signal detector 40 includes a first signal detector 401, and a second signal detector 402. The polarizer 31 is disposed at the incident light, and the beam splitter 32 is disposed at the light exit side of the polarizer 31. The first atomic gas chamber 331 is located between the polarizer 31 and the beam splitter 32, and the first signal detector 401 is located on the light-emitting side of the reflected light of the beam splitter 32 and is configured to receive the probe light reflected by the larmor precession of the first polarization state atom in the first atomic gas chamber 331. The phase shifter 34 is disposed on the light outgoing side of the transmitted light of the beam splitter 32, and the second atomic gas chamber 332 is disposed on the side of the phase shifter 34 facing away from the polarizing plate 31. The second signal detector 402 is located on the light-emitting side of the second atomic gas chamber 332, and is configured to receive the detection light reflected by the larmor precession action of the first polarized atom in the first atomic gas chamber 331 and the larmor precession action of the second polarized atom in the second atomic gas chamber 332 in sequence.

In order to make the measuring result more reasonable and accurate. The magnetic line width of the first atomic gas chamber 331 and the magnetic line width of the second atomic gas chamber 332 are greater than or equal to the difference value between the first external magnetic field to be measured and the second external magnetic field to be measured.

There are also two types of optical paths in the structure of the atomic probe 30, and the following description will be made by taking the path of the probe light as an example, and these are the first type of optical path: the first optical path is that the detection light passes through the polarizing plate 31 to be polarized, then enters the first atomic gas chamber 331, undergoes a first polarization rotation angle change under the action of larmor precession of polarized atoms in the first atomic gas chamber 331, passes through the first atomic gas chamber 331, then passes through the beam splitter 32, and is reflected by the beam splitter 32 and then received by the first signal detector 401. At this time, the polarization rotation angle signal received by the first signal detector 401 is proportional to the magnitude of the magnetic field at the first atomic gas chamber 331, and the magnitude of the magnetic field at the first atomic gas chamber 331 can be obtained by demodulating the signal received by the first signal detector 401.

In the second optical path, the detection light passes through the polarizer 31 for polarization, then enters the first atomic gas chamber 331, undergoes a first polarization rotation angle change under the action of larmor precession of polarized atoms in the first atomic gas chamber 331, passes through the first atomic gas chamber 331, then passes through the beam splitter 32, is transmitted by the beam splitter 32, then enters the phase shifter 34, passes through the second atomic gas chamber 332, undergoes a second polarization rotation angle change under the action of larmor precession of polarized atoms, and is received by the second signal detector 402 after penetrating through the second atomic gas chamber 332. At this time, the polarization rotation angle signal received by the second signal detector 402 is proportional to the difference between the magnitudes of the magnetic fields in the first atomic gas chamber 331 and the second atomic gas chamber 332, and the difference between the magnitudes of the magnetic fields in the two atomic gas chambers can be obtained by demodulating the signal received by the second signal detector 402.

In summary, in the magnetic field measurement method and the atomic magnetometer system of the present invention, in the atomic polarization state preparation stage, the optical modulator is used to process the laser to obtain the pump light and the probe light, wherein the light intensity of the pump light is greater than the light intensity of the probe light, and then the optical modulator is used to modulate the pump light to obtain the modulated pump light with the modulation signal. During detection, detection light with weak light intensity is selected, because the weak detection light can reduce shot noise introduced by the detection light intensity, the detection light with weak light intensity forms second change detection light with a polarization rotation angle change under the action of Larmor precession of first polarization atoms and the action of Larmor precession of second polarization atoms in sequence, the polarization directions of the first polarization atoms and the second polarization atoms are mutually vertical, the second change detection light is received by the signal acquisition module to acquire a polarization rotation angle signal of the second change detection light, the polarization rotation angle signal is demodulated by the signal demodulation processing module, and a difference value of external magnetic fields to be detected at two positions is calculated and acquired according to the frequency of the modulation signal. Through this scheme, not only have advantages such as atom magnetometer sensitivity height, small, low power dissipation. Meanwhile, one beam of detection light continuously passes through two polarized atoms with mutually perpendicular polarization directions to carry out Larmor precession, so that common-mode noise can be inhibited, the atomic magnetic gradiometer can measure a magnetic field more accurately, the precise measurement of the magnetic field is facilitated, and the atomic magnetic gradiometer can be better used in practical application requirements of geomagnetic navigation, biomedical treatment, magnetic anomaly detection, anti-latency and the like. In addition, the polarization rotation angle signal of the first change detection light which forms the change of the polarization rotation angle only under the action of Larmor precession of the first polarization state atom can be acquired independently, the signal demodulation processing module demodulates the polarization rotation angle signal of the first change detection light, and the value of the first external magnetic field to be detected is acquired through calculation according to the frequency of the modulation signal.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.