CN113466756A - Magnetic field measurement method and atomic magnetometer system - Google Patents
Magnetic field measurement method and atomic magnetometer system Download PDFInfo
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Abstract
The invention provides a magnetic field measurement method and an atomic magnetometer system, wherein the method comprises the following steps: controlling a light intensity modulator to periodically modulate laser to obtain pump light and detection light, wherein the light intensity of the pump light is greater than that of the detection light; controlling a light intensity modulator to modulate the pump light to obtain modulated pump light with a modulation signal; the control signal detector receives the changed detection light obtained by the detection light through the Larmor precession action of the polarized atoms, and obtains the polarization rotation angle signal of the changed detection light, wherein the polarized atoms are generated by the modulation pumping light acting on the atom probe, and the Larmor precession of the polarized atoms is generated under a magnetic field to be detected; and demodulating the polarization rotation angle signal, and calculating and acquiring the value of the magnetic field to be measured according to the frequency of the modulation signal. The invention solves the problem of low sensitivity of the atomic magnetometer in the prior art.
Description
Technical Field
The invention relates to the field of magnetic field measurement, in particular to a magnetic field measurement method and an atomic magnetometer system.
Background
Magnetic field detection has a wide demand in the fields of resource exploration, geophysical, nondestructive testing, biomedical and basic science, etc. Compared with the traditional magnetometer, the atomic magnetometer has the advantages of high sensitivity, small size, low power consumption and the like, and is suitable for numerous application scenes such as geomagnetic exploration, geomagnetic navigation, magnetic anomaly detection, biomagnetic detection and the like. The full-optical atomic magnetometer adopts full-optical state preparation and optical signal detection, does not need to introduce additional radio frequency magnetic field signals, and is beneficial to non-interference and integration of multiple probes; compared with a radio frequency atomic magnetometer, the high-frequency component magnetic noise introduced by radio frequency signals is reduced, and the stable or slowly varying magnetic field signals can be accurately measured.
However, in the atomic magnetometer in the prior art, the pump light and the detection light with the same light intensity are provided by the laser light source, that is, the pump light and the detection light adopt the same laser with the same light intensity, and since the pump light and the detection light have the same light intensity, the sensitivity is not high due to too strong light intensity of the detection light in the detection process.
Accordingly, the prior art is yet to be improved and developed.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention is directed to a magnetic field measurement method and an atomic magnetometer system, which solve the problem of low sensitivity of the atomic magnetometer in the prior art.
The invention provides a magnetic field measuring method, which comprises the following steps:
controlling a light intensity modulator to periodically modulate laser to obtain pump light and detection light, wherein the light intensity of the pump light is greater than that of the detection light;
controlling a light intensity modulator to modulate the pump light to obtain modulated pump light with a modulation signal;
the control signal detector receives the changed detection light obtained by the detection light through the Larmor precession action of the polarized atoms, and obtains the polarization rotation angle signal of the changed detection light, wherein the polarized atoms are generated by the modulation pumping light acting on the atom probe, and the Larmor precession of the polarized atoms is generated under a magnetic field to be detected;
and demodulating the polarization rotation angle signal, and calculating and acquiring the value of the magnetic field to be measured according to the frequency of the modulation signal.
Further, the step of controlling the light intensity modulator to periodically modulate the laser to obtain the pump light and the probe light includes:
and controlling the light intensity modulator to modulate the laser emission duration into a plurality of periods T, periodically modulating the laser in all the periods T, and acquiring the pump light with the period duration of T1 and the probe light with the period duration of T2, wherein T is T1+ T2.
Further, the laser wavelength is 795 nm;
the period duration T1 is 0.3ms, and the light intensity of the pump light is: 700 μ W;
the period duration T2 is 0.2ms, and the light intensity of the probe light is: 10 μ W.
Further, the step of demodulating the polarization rotation angle signal and obtaining the value of the magnetic field to be measured according to the frequency calculation of the modulation signal includes:
demodulating the polarization rotation angle signal to obtain an extreme point of a demodulation signal and a frequency of the modulation signal corresponding to the extreme point;
acquiring Larmor precession frequency of atoms in a polarization state according to the frequency of the modulation signal corresponding to the extreme point;
and calculating the value of the magnetic field to be measured according to the Larmor precession frequency of the atoms in the polarization state.
Further, the control signal detector receives the changed detection light obtained by the detection light through the larmor precession action of the polarized atoms, and obtains a polarization rotation angle signal of the changed detection light, wherein the polarized atoms are generated by the modulation pumping light acting on the atom probe, and the larmor precession of the polarized atoms is generated under a magnetic field to be detected:
the magnetic field to be detected comprises a target magnetic field and a uniform magnetic field, and the value of the magnetic field to be detected is the value of the uniform magnetic field plus the value of the target magnetic field; wherein the uniform magnetic field is generated in the atomic probe, the magnitude value of the uniform magnetic field is known, and the direction of the uniform magnetic field is the same as that of the target magnetic field;
the step of calculating the value of the magnetic field to be measured according to the larmor precession frequency of the atoms in the polarized state further comprises the following steps:
and subtracting the value of the uniform magnetic field from the value of the magnetic field to be measured to obtain the value of the target magnetic field.
Further, before the step of controlling the light intensity modulator to periodically modulate the laser to obtain the pump light and the probe light, the method further includes:
controlling a laser light source to be electrified, then emitting laser and collecting the laser to obtain a frequency error signal of the laser light source;
and according to the frequency error signal of the laser light source, feedback-controlling the driving current of the laser light source to obtain stable laser.
Further, the step of feedback-controlling the driving current of the laser light source according to the frequency error signal of the laser light source to obtain stable laser further comprises:
and controlling the acousto-optic modulator to shift the frequency of the stabilized laser to generate linearly polarized laser.
Based on the same inventive concept, the present scheme also provides an atomic magnetometer system, which comprises: the device comprises a laser light source, a light intensity modulator, an atom probe, a signal detector and a controller;
the controller is electrically connected with the laser light source, the light intensity modulator and the signal detector respectively, and the magnetic field measuring method is realized.
Further, the atom probe includes:
a polarizing plate,
the plane reflector is obliquely arranged on the light emergent side of the polaroid, the reflecting surface of the plane reflector faces back to the polaroid, and a first through hole and a second through hole are formed in the plane reflector at intervals;
the first right-angle reflecting prism is positioned on one side, away from the polaroid, of the plane reflector;
an atomic gas cell located between the planar mirror and the first right angle reflecting prism;
and
a second right-angle reflecting prism located on a reflected light path of the plane mirror;
the laser penetrates through the polaroid and enters the atomic gas chamber through the first through hole, is emitted from the second through hole after being reflected for multiple times by the first right-angle reflecting prism, the plane reflecting mirror and the second right-angle reflecting prism, and is received by the signal detector.
Further, the distance between the first through hole and the second through hole is L √ 2 · d · N, where d is a spot diameter and N is the total number of times the laser light is reflected on the first right-angle reflecting prism and the second reflecting prism.
Further, another atom probe includes:
a polarizing plate,
the beam splitter is positioned on the light-emitting side of the polaroid sheet;
an atomic gas chamber located on a side of the beam splitter facing away from the polarizer; and
a second planar mirror located on a side of the atomic gas chamber facing away from the beam splitter;
the signal detector is positioned on the light-emitting side of the beam splitter;
the laser passes through the polaroid and enters the atomic gas chamber through the beam splitter, is reflected into the atomic gas chamber through the second plane mirror, passes through the beam splitter and is received by the signal detector.
Has the advantages that: in the magnetic field measurement method and the atomic magnetometer system, in the atomic polarization state preparation stage, the light intensity modulator is used for periodically modulating laser to obtain pumping light and detection light, wherein the light intensity of the pumping light is greater than that of the detection light, and then the pumping light is modulated by the light intensity modulator to obtain the modulated pumping light with a modulation signal. During detection, the 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 change detection light with a polarization rotation angle change under the action of Larmor precession of atoms in a polarization state, the change detection light is received through the signal acquisition module to acquire a polarization rotation angle signal of the change detection light, the signal demodulation processing module demodulates the polarization rotation angle signal, and the value of the magnetic field to be detected is calculated and acquired according to the frequency of the modulation signal. Through this scheme, produce the pumping light and the detecting light of different light intensities through same laser, can the timesharing realize effective pumping and the high signal-to-noise ratio of atomic polarization state and survey, promoted the sensitivity of atomic magnetometer greatly. Meanwhile, the pump light and the detection light generated by the same laser have better consistency, and the coordination of the pumping process and the detection process between the two lights is improved.
Drawings
FIG. 1 is a flow chart of the main steps of a magnetic field measurement method of the present invention.
FIG. 2 is a flow chart of a preferred embodiment of a magnetic field measurement method of the present invention.
FIG. 3 is a schematic time-sharing period diagram of a magnetic field measurement method according to the present invention.
FIG. 4 is a graph comparing the effects of a magnetic field measurement method of the present invention.
FIG. 5 is a schematic block diagram of the electrical circuitry of an atomic magnetometer system of the present invention.
FIG. 6 is a schematic diagram of the operation of an atom probe of an atom magnetometer system of the present invention.
FIG. 7 is a schematic diagram of a plane mirror in an atom probe of an atom magnetometer system of the present invention.
FIG. 8 is a schematic diagram of the operation of another atom probe of an atom magnetometer system of the present invention.
In the figure: 10. a laser light source; 20. a light intensity modulator; 30. an atom probe; 31. a polarizing plate; 32. a plane mirror; 33. a first right-angle reflecting prism; 34. an atomic gas chamber; 35. a second right-angle reflecting prism; 36. a beam splitter; 37. a second planar mirror; 38. a first through hole; 39. a second through hole; 40. a signal detector; 50. and a controller.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying 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 measurement method for measuring a magnitude value of a magnetic field to be measured, wherein the magnetic field measurement method includes 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 an acousto-optic modulator to shift the frequency of the stable laser to generate linearly polarized laser.
In the specific process, an acousto-optic modulator is provided, and the acousto-optic modulator can be turned on or 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 acousto-optic modulator, linear polarization light with near resonance is generated, and the detuning amount of the laser is 90 MHz. 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.
And step S300, controlling the light intensity modulator to periodically modulate the laser to obtain pump light and detection light, wherein the light intensity of the pump light is greater than that of the detection light.
The light intensity modulator consists of an acousto-optic modulator, a radio frequency signal generator and a radio frequency amplifier. The light intensity modulator is used for periodically modulating the laser, and the process of acquiring the Pump light and the Probe light is a single-path Pump-Probe light pulse periodic modulation process. Specifically, as shown in fig. 3, the light intensity modulator implements periodic modulation of the intensity of the laser light under the control of the controller instruction, 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.
In the preparation stage of the atomic polarization state with the time length of T1 in this embodiment, the pump light with strong light intensity is selected because the strong pump light can increase the pumping rate of the atoms and increase the polarization degree of the atoms, thereby increasing the signal intensity, and the laser light intensity is recorded as P1 at this time; in the detection stage with the duration of T2, the detection light with weaker light intensity is selected because the weaker detection light can reduce the shot noise introduced by the detection light intensity, and the laser light intensity is recorded as P2. In the process of periodic modulation of the single-path Pump-Probe optical pulse, effective pumping of an atom polarization state and high signal-to-noise ratio detection are usually realized in a time-sharing mode, and the sensitivity of an atom magnetometer can be effectively improved. In this embodiment, the period duration T1 is 0.3ms, and the light intensity of the pump light is: 700 μ W; the period duration T2 is 0.2ms, and the light intensity of the probe light is: 10 μ W. By adopting the measurement process, as shown in fig. 4, the experimental result of the rotation angle response of the Probe light under the constant light intensity scheme of the Pump-Probe and the scheme of the periodic modulation of the light pulse of the Pump-Probe in the experiment is shown. As can be seen from the figure, the amplitude of the rotation angle response under the scheme of the periodic modulation of the Pump-Probe light pulse is improved by about 30 times than that of the constant light intensity scheme of the Pump-Probe, and the sensitivity is also improved by one order of magnitude.
And S400, controlling a light intensity modulator to modulate the pump light to obtain modulated pump light with a modulation signal.
In the specific process, the Pump-Probe optical pulse period modulation is adopted in the magnetic field measurement process, and effective pumping and high signal-to-noise ratio detection of the atom polarization state on the atom Probe are realized in a time-sharing mode. In the atomic polarization state preparation stage (pumping light acting atomic stage), 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 and superposed on the light intensity of the pumping light after being clearer, and the pumping light has clear performance parameters through the signal.
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.
Step S500, a signal detector is controlled to receive the changed detection light obtained after the detection light is subjected to Larmor precession action of polarized atoms, and a polarization rotation angle signal of the changed detection light is obtained, wherein the polarized atoms are generated on an atom probe under the action of the modulated pump light, and the Larmor precession of the polarized atoms is generated under a magnetic field to be detected.
In this embodiment, an atomic probe is provided for receiving pump light, and polarized atoms are obtained in the atomic probe under the action of modulating the pump light, at this time, the atomic probe is placed in a magnetic field to be measured, the polarized atoms perform larmor precession under the action of the magnetic field to be measured, and after probe light irradiates the polarized atoms performing larmor precession, a polarization rotation angle of the probe light changes, so as to form changed probe light. And providing a signal detector to receive the 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 change detection light.
And S600, demodulating the polarization rotation angle signal, and calculating and acquiring the value of the magnetic field to be measured according to the frequency of the modulation signal.
In the specific process, a beam of near-resonance laser irradiates on the alkali metal atomic gas to carry out a pumping process on atoms, so that the atoms are distributed on a magneton energy level and redistributed, macroscopically, the atoms have a certain polarization orientation, and the process is a polarization state preparation process 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.
Based on the principle, the controller can demodulate the polarization rotation angle signal and calculate and acquire the value of the magnetic field to be measured according to the frequency of the modulation signal.
As shown in fig. 1 and 2, step S600 specifically includes:
step S610, demodulating the polarization rotation angle signal to obtain an extreme point of the demodulated signal and a frequency of the modulated signal corresponding to the extreme point.
And S620, acquiring Larmor precession frequency of the polarized atoms according to the frequency of the modulation signal corresponding to the extreme point.
Step S630, calculating the value of the magnetic field to be measured according to the Larmor precession frequency of the atoms in the polarization state.
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 is T ', the frequency of the modulation signal is the reciprocal 1/T ' of the period, so that the Larmor frequency value of the atoms in the polarization state, namely, the half 1/T ', can be obtained. The Larmor frequency value is in direct proportion to the size of the external magnetic field, and the controller calculates the value of the magnetic field to be measured according to the direct proportion relation between the Larmor precession frequency of the atoms in the polarized state and the magnetic field to be measured.
In another embodiment, when the frequency of the modulation signal is less than or approximately equal to the frequency of the Pump-Probe time-division pulse, that is, the larmor precession frequency of the atom is small, and the external magnetic field is weak, the larmor precession process of the atom is not obvious, and the effect on the Probe light is not obvious, so that the magnetic field needs to be increased to enhance the whole magnetic field to be measured. And providing a uniform magnetic field with a known magnitude in the atomic probe, wherein the direction of the uniform magnetic field is the same as that of the target magnetic field, and the value of the magnetic field to be measured is the sum of the value of the uniform magnetic field and the value of the target magnetic field. Thus, the magnetic field to be measured is the uniform magnetic field plus the target magnetic field, and the value of the target magnetic field in the embodiment is the magnetic field value to be calculated.
After the step of step S630, calculating the value of the magnetic field to be measured according to the larmor precession frequency of the atom in the polarized state, the method further includes:
and subtracting the value of the uniform magnetic field from the value of the magnetic field to be measured to obtain the value of the target magnetic field.
In the specific process, because the size of the target standard magnetic field is small, the method for directly carrying out closed-loop measurement by using single-path light Pump-Probe light pulse periodic modulation cannot modulate and demodulate the size of the magnetic field under the independent action of the target magnetic field. At the moment, a uniform magnetic field with known magnitude in the target magnetic field direction is provided by using a magnetic field coil in the atom probe, namely, a uniform magnetic field with determined magnitude in the direction is superposed on the target magnetic field, so that the total magnetic field magnitude of the detection is improved, and the Larmor precession frequency of the polarized atoms is correspondingly improved. And then, the total size of the magnetic field to be measured is modulated and demodulated by utilizing the closed loop of the atomic magnetometer system, and finally, the value of the magnetic field to be measured is subtracted by the introduced uniform magnetic field with known size, so that the size of the target magnetic field is obtained. By setting the uniform magnetic field, the device can be used for compensation of the geomagnetic environment and translation of the size of a measured target magnetic field, measurement of high-frequency Larmor precession is achieved, and then precise measurement of a weak magnetic field is achieved.
As shown in fig. 5, based on the same inventive concept, the present invention further provides an atomic magnetometer system, comprising: the method comprises the following steps: a laser light source 10, a light intensity 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 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 light intensity 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 light intensity 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 controls the signal detector 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.
As shown in fig. 6 and 8, 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: a polarizer 31, a plane mirror 32, a first right-angle reflecting prism 33, an atomic gas chamber 34, and a second right-angle reflecting prism 35. The atom probe 30 implements a multi-reflection configuration of the optical path.
In a specific structure, the plane mirror 32 is obliquely arranged on the light-emitting side of the polarizer 31, the plane mirror 32 is obliquely arranged at 45 degrees, the reflecting surface of the plane mirror 32 faces away from the polarizer 31, and the plane mirror 32 is provided with a first through hole 38 and a second through hole 39 at intervals. The first right-angle reflecting prism 33 is located on a side of the plane mirror 32 facing away from the polarizing plate 31. The atomic gas chamber 34 is located between the plane mirror 32 and the first right-angle reflecting prism 33. The second right-angle reflecting prism 35 is located on the reflected light path of the plane mirror 32. Taking the example of the laser horizontal direction emitting as an example, the laser passes through the polarizer 31 in the horizontal direction and enters the atomic gas chamber 34 through the first through hole 38, the laser is reflected by the first right-angle reflecting prism 33 and then returns to the atomic gas chamber 34 in the horizontal direction, the laser passing through the atomic gas chamber 34 is reflected by the plane mirror 32 and makes the laser go along the vertical direction, then the laser in the vertical direction is reflected by the second right-angle reflecting prism 35 and then goes onto the plane mirror 32, and then is emitted toward the first right-angle reflecting prism 33 in the horizontal direction, and thus is reflected from the first right-angle prism to the plane mirror 32 and then goes to the second right-angle reflecting prism 35, and after passing through a plurality of times, the laser is emitted from the second through hole 39. The emitted laser light is received by a signal detector 40.
As shown in fig. 6 and 7, the distance between the first through hole 38 and the second through hole 39 is L √ 2 · d · N, where d is the spot diameter and N is the total number of times the laser beam is reflected by the first right-angle reflecting prism and the second reflecting prism. The spot size of the laser light selected in this embodiment is 2 mm. This reflection light path structure not only can increase effective atomicity through shining atomic gas many times to promote atomic magnetometer's measurement sensitivity, this structure is simple and convenient moreover, and effective detection area can be close to more by survey target object, does benefit to the miniaturization.
As shown in fig. 8, another atom probe 30 includes: a polarizer 31, a beam splitter 36, an atomic gas chamber 34, and a second plane mirror 37. The beam splitter 36 is located on the light-emitting side of the polarizer 31, the atomic gas chamber 34 is located on the side of the beam splitter 36 away from the polarizer 31, the second plane mirror 37 is located on the side of the atomic gas chamber 34 away from the beam splitter 36, and the signal detector 40 is located on the light-emitting side of the beam splitter 36. The light-emitting side of the beam splitter 36 is the side which finally emits light, and the second plane mirror 37 is arranged along the vertical direction. Taking the example of laser light emitted in the horizontal direction as an example to illustrate the optical path, the laser light in the horizontal direction passes through the polarizer 31, enters the atomic gas chamber 34 through the beam splitter 36, is reflected by the second plane mirror 37, enters the atomic gas chamber 34, changes the direction into the laser light emitted in the vertical direction after passing through the beam splitter 36, and is received by the signal detector 40. The atom probe 30 has a simple structure, can be closer to a target object to be detected in an effective detection area, and is beneficial to miniaturization.
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 light intensity modulator periodically modulates 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 pump light is modulated by the light intensity modulator to obtain the modulated pump light with the modulation signal, so that the pump light with stronger light intensity is selected, because the stronger pump light can increase the pumping rate of the atom and increase the polarization degree of the atom, the atom in the polarization state performs larmor precession under the action of the magnetic field to be detected, and the atom with higher polarization degree is more favorable for the detection of the system, thereby increasing the signal intensity. During detection, the 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 change detection light with a polarization rotation angle change under the action of Larmor precession of atoms in a polarization state, the change detection light is received through the signal acquisition module to acquire a polarization rotation angle signal of the change detection light, the signal demodulation processing module demodulates the polarization rotation angle signal, and the value of the magnetic field to be detected is calculated and acquired according to the frequency of the modulation signal. Through this scheme, adopt the pumping light and the detecting light of different light intensities, can the timesharing realize effective pumping and the high SNR of atom polarization state and survey, promoted atom magnetometer's sensitivity greatly. The reflection-type optical path structure not only can increase the effective atomic number by irradiating atomic gas for multiple times, thereby improving the measurement sensitivity of the atomic magnetometer, but also has simple structure, and the effective detection area can be closer to a measured target object, thereby being beneficial to miniaturization.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; 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.
Claims (10)
1. A magnetic field measurement method, comprising the steps of:
controlling a light intensity modulator to periodically modulate laser to obtain pump light and detection light, wherein the light intensity of the pump light is greater than that of the detection light;
controlling a light intensity modulator to modulate the pump light to obtain modulated pump light with a modulation signal;
the control signal detector receives the changed detection light obtained by the detection light through the Larmor precession action of the polarized atoms, and obtains the polarization rotation angle signal of the changed detection light, wherein the polarized atoms are generated by the modulation pumping light acting on the atom probe, and the Larmor precession of the polarized atoms is generated under a magnetic field to be detected;
and demodulating the polarization rotation angle signal, and calculating and acquiring the value of the magnetic field to be measured according to the frequency of the modulation signal.
2. The method according to claim 1, wherein the step of controlling the light intensity modulator to periodically modulate the laser light to obtain the pump light and the probe light comprises:
and controlling the light intensity modulator to modulate the laser emission duration into a plurality of periods T, periodically modulating the laser in all the periods T, and acquiring the pump light with the period duration of T1 and the probe light with the period duration of T2, wherein T is T1+ T2.
3. The magnetic field measuring method according to claim 2, wherein the step of controlling the light intensity modulator to modulate the laser emission time period to a plurality of periods T, and periodically modulating the laser light in all the periods T to obtain the pump light having a period time period T1 and the probe light having a period time period T2:
the laser wavelength is 795 nm;
the period duration T1 is 0.3ms, and the light intensity of the pump light is: 700 μ W;
the period duration T2 is 0.2ms, and the light intensity of the probe light is: 10 μ W.
4. The magnetic field measurement method according to claim 1, wherein the step of demodulating the polarization rotation angle signal and obtaining the value of the magnetic field to be measured from the frequency calculation of the modulation signal comprises:
demodulating the polarization rotation angle signal to obtain an extreme point of a demodulation signal and a frequency of the modulation signal corresponding to the extreme point;
acquiring Larmor precession frequency of atoms in a polarization state according to the frequency of the modulation signal corresponding to the extreme point;
and calculating the value of the magnetic field to be measured according to the Larmor precession frequency of the atoms in the polarization state.
5. The magnetic field measurement method according to claim 4, wherein the control signal detector receives the varying probe light obtained by subjecting the probe light to a larmor precession action of atoms in polarization state generated by the modulated pump light acting on the atomic probe, and obtains a polarization rotation angle signal of the varying probe light, wherein the larmor precession of the atoms in polarization state is generated under the magnetic field to be measured in the step of:
the magnetic field to be detected comprises a target magnetic field and a uniform magnetic field, and the value of the magnetic field to be detected is the value of the uniform magnetic field plus the value of the target magnetic field; wherein the uniform magnetic field is generated in the atomic probe, the magnitude value of the uniform magnetic field is known, and the direction of the uniform magnetic field is the same as that of the target magnetic field;
the step of calculating the value of the magnetic field to be measured according to the larmor precession frequency of the atoms in the polarized state further comprises the following steps:
and subtracting the value of the uniform magnetic field from the value of the magnetic field to be measured to obtain the value of the target magnetic field.
6. The method according to claim 1, wherein before the step of controlling the light intensity modulator to periodically modulate the laser light to obtain the pump light and the probe light, the method further comprises:
controlling a laser light source to be electrified, then emitting laser and collecting the laser to obtain a frequency error signal of the laser light source;
and according to the frequency error signal of the laser light source, feedback-controlling the driving current of the laser light source to obtain stable laser.
7. The magnetic field measurement method according to claim 6, wherein the step of feedback-controlling the driving current of the laser light source according to the frequency error signal of the laser light source to obtain the stable laser further comprises:
and controlling the acousto-optic modulator to shift the frequency of the stabilized laser to generate linearly polarized laser.
8. An atomic magnetometer system, comprising: the device comprises a laser light source, a light intensity modulator, an atom probe, a signal detector and a controller;
the controller is electrically connected with the laser light source, the light intensity modulator and the signal detector respectively, and realizes the magnetic field measuring method as claimed in any one of claims 1 to 7.
9. The atomic magnetometer system of claim 8, wherein the atom probe comprises:
a polarizing plate;
the plane reflector is obliquely arranged on the light emergent side of the polaroid, the reflecting surface of the plane reflector faces back to the polaroid, and a first through hole and a second through hole are formed in the plane reflector at intervals;
the first right-angle reflecting prism is positioned on one side, away from the polaroid, of the plane reflector;
an atomic gas cell located between the planar mirror and the first right angle reflecting prism; and
a second right-angle reflecting prism located on a reflected light path of the plane mirror;
the laser penetrates through the polaroid and enters the atomic gas chamber through the first through hole, is emitted out of the second through hole after being reflected for multiple times by the first right-angle reflecting prism, the plane reflecting mirror and the second right-angle reflecting prism, and is received by the signal detector;
the distance between the first through hole and the second through hole is
Wherein d isAnd N is the total times of reflection of the laser on the first right-angle reflecting prism and the second reflecting prism.
10. The atomic magnetometer system of claim 8, wherein the atom probe comprises:
a polarizing plate;
the beam splitter is positioned on the light-emitting side of the polaroid sheet;
an atomic gas chamber located on a side of the beam splitter facing away from the polarizer; and
a second planar mirror located on a side of the atomic gas chamber facing away from the beam splitter;
the signal detector is positioned on the light-emitting side of the beam splitter;
the laser passes through the polaroid and enters the atomic gas chamber through the beam splitter, is reflected into the atomic gas chamber through the second plane mirror, passes through the beam splitter and is received by the signal detector.
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