CN113203965A - High-sensitivity pulse optical pumping type scalar magnetic field measuring device and method - Google Patents
High-sensitivity pulse optical pumping type scalar magnetic field measuring device and method Download PDFInfo
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Abstract
A high-sensitivity pulse optical pumping type scalar magnetic field measuring device comprises a first laser, a first isolator, a first lambda/2 wave plate, a first polarization beam splitter, a first optical fiber coupler, a first frequency spectrograph, a reflective mirror, an atom sensor probe, a third lambda/2 wave plate, a third polarization beam splitter, a first photoelectric converter, a second photoelectric converter, a data acquisition system, a second laser, a second isolator, an acousto-optic modulator, a second lambda/2 wave plate, a second polarization beam splitter, a second optical fiber coupler, a second frequency spectrograph, a lambda/4 wave plate and a beam expander; and planar reflectors facing the atom sensor probe are arranged on two sides of the atom sensor probe, and the planar reflectors are arranged in parallel with the pump light beam input into the atom sensor probe. The invention adopts the technology of combining the parallel plane reflector and the atomic sensor probe, realizes multi-light-path turning back, effectively increases the action distance and the angle of Faraday optical rotation, and improves the sensitivity of magnetic field measurement.
Description
Technical Field
The invention belongs to the technical field of weak magnetic detection, and particularly relates to a high-sensitivity pulse optical pumping type scalar magnetic field measuring device and method.
Background
The high-sensitivity weak magnetic detection technology has important application value in biomedicine, space detection, geophysical detection, ocean detection and the like. For example, the magnetic field generated by some organs of the human body or other organisms, such as the heart and brain, is extremely weak, but contains abundant information, and the data obtained by measuring the magnetic field has important reference value for medical research. The all-optical atomic magnetometer (or magnetometer) device and the related detection technology thereof are widely concerned by researchers because of the realization of relatively ideal sensitivity. The existing high-sensitivity weak magnetic detection technology based on all-optical mainly includes methods based on the principle of spin-exchange-relaxation (SERF), Optical Pumping (OP), nonlinear magneto-optical rotation (NMOR), and some improved technologies. The main basic principle of these techniques is to measure the oscillation signal or spin evolution signal of polarized atoms in a magnetic field by using a narrow line width laser, and obtain the magnitude and change of the magnetic field by analyzing the characteristics of the signal. In particular, several major process features are not identical.
The SERF is mainly a vector weak magnetic detection method, and the basic principle of the SERF is that atomic spins can keep longer-time coherence by using highly polarized high-density atoms under a near-zero magnetic field (extremely weak background magnetic field), and the decay relaxation of the atomic spins is related to the magnetic field. The SERF is more suitable for precise measurement under a near-zero magnetic field, has high sensitivity and needs a magnetic shielding cylinder. For relatively larger magnetic fields in the background, such as geomagnetic fields, it does not work properly unless active compensation is used. To achieve high density atomic numbers, high temperatures above 150 degrees celsius are typically operated. In addition, in order to improve the sensitivity and suppress noise during the measurement process, a lock-in amplifier (LIA) is often required, and the sensitivity performance is directly reduced by a high sampling frequency, so that the actual sampling frequency or bandwidth is generally 10-100Hz, and only a few of the sampling frequency or bandwidth can reach the kHz level (for example, CN 202011300255.1).
Optical Pumping Magnetometers (OPMs) can achieve scalar single axis and vector multi-axis measurements. According to the physical phenomenon that atomic energy level generates Zeeman splitting under the action of a magnetic field, a radio frequency field is used for matching the energy difference of the splitting energy level, so that atoms generate resonance absorption, and the magnetic field size is obtained according to an absorption signal and the frequency of the radio frequency field. Higher sensitivity can be achieved and can operate in larger magnetic fields such as the earth's magnetic field, but in order to increase sensitivity and reduce noise, LIA is also required, so the sampling frequency for magnetic fields is also not high, typically 10-100 Hz.
The pulse optical pumping NMOR is mainly a scalar detection method, and its basic principle is that atoms polarized by pump light generate precession (larmor precession) in a magnetic field, and the magnetic field magnitude is obtained by measuring the precession frequency. The advantages are that: (1) can work in a large background magnetic field, such as a geomagnetic field environment; (2) compared with SERF, under the condition that the same atomic medium is adopted, the high temperature of the SERF is not needed, and the NMOR can achieve better performance at the temperature of below 100 ℃; (3) direct frequency measurement and a natural reference are adopted, and calibration is not needed in long-term operation; (4) the LIA is not needed, and the structure is simpler; (5) the sensitivity is high, and the SERF level can be achieved through optimization. The method has the following defects: (1) using a pulsed pump-probe mode in which the pump light is a periodic pulse t1The longer the pulse time, the higher the pumping efficiency, followed by a certain duration of the RF pulse t2Therefore, a certain total sampling time is consumed, and the sampling frequency of the magnetic field measurement is influencedf B(ii) a (2) Suitable repetition period T for each sample point0Signal to noise ratio with output signal, decay relaxation time T of atomic spin after polarization2Are concerned, e.g. for increasing the sampling frequency of magnetic field measurementsf BThe repetition period is shortened, which may reduce the signal-to-noise ratio and thus the sensitivity; (3) high sampling frequencyf BThe data volume is too large, and the technical difficulty of high-speed processing is obviously increased. Therefore, in general, it is difficult to increase the sampling frequency while maintaining high sensitivity.
Some important applications such as space detection, biological magnetic fieldDetection, etc., requiring higher magnetic field sampling frequenciesf BTo obtain richer measurement information. Therefore, there is a need for a magnetic field measuring method and apparatus that can effectively increase the sampling frequency and maintain high sensitivity, to solve the above problems.
Disclosure of Invention
In order to solve the above problems, the present invention provides a high-sensitivity pulse optical pumping type scalar magnetic field measurement apparatus and method capable of effectively increasing the sampling frequency and maintaining high sensitivity.
The technical scheme adopted by the invention is as follows:
a high-sensitivity pulse optical pumping type scalar magnetic field measuring device comprises a first laser for outputting detection light and a second laser for outputting pumping light, wherein the output end of the first laser is connected with the input end of a first isolator, the output end of the first isolator is connected with the input end of a first lambda/2 wave plate, the output end of the first lambda/2 wave plate is connected with the input end of a first polarization beam splitter for splitting a light beam into two beams, the first output end of the first polarization beam splitter is connected with the input end of a first optical fiber coupler, the output end of the first optical fiber coupler is connected with the input end of a first frequency spectrograph for dynamic detection, the light beam output by the second output end of the first polarization beam splitter is converted into the light beam by a reflector and then enters an atomic sensor probe, and the emergent light of the atomic sensor probe is input to a third lambda/2 wave plate, the output end of the third lambda/2 wave plate is connected with the input end of a third polarization beam splitter which divides the light beam into two beams, the first output end of the third polarization beam splitter is connected with the input end of the first photoelectric converter, the second output end of the third polarization beam splitter is connected with the input end of the second photoelectric converter, and the differential output ends of the first photoelectric converter and the second photoelectric converter are connected with a data acquisition system which acquires, stores, processes and displays the detection signal;
the output end of the second laser is connected with the input end of a second isolator, the output end of the second isolator is connected with the input end of an acousto-optic modulator for controlling the intensity of light beams, the output end of the acousto-optic modulator is connected with the input end of a second lambda/2 wave plate, the output end of the second lambda/2 wave plate is connected with the input end of a second polarization beam splitter for dividing the light beams into two beams, the first output end of the second polarization beam splitter is connected with the input end of a second optical fiber coupler, the output end of the second optical fiber coupler is connected with the input end of a second frequency spectrograph for dynamic detection, the second output end of the second polarization beam splitter is connected with a lambda/4 wave plate for converting the light beams into circularly polarized light beams, and the output light beams of the lambda/4 wave plate are irradiated into the atom sensor probe after being expanded by a beam expander;
the method is characterized in that: and planar reflectors facing the atom sensor probe are arranged on two sides of the atom sensor probe, and the planar reflectors are arranged in parallel with the pump light beam input into the atom sensor probe. The pumping light and the detection light adopt the technology of combining the parallel plane reflector and the atomic sensor probe, realize multi-light-path turning back, effectively increase the action distance and the angle of Faraday optical rotation, have more stable structure, improve the sensitivity of magnetic field measurement, and are easier to build and adjust.
Further, the atomic sensor probe comprises an atomic air chamber, a heat preservation chamber is arranged outside the atomic air chamber, a heater for heating the atomic air chamber is arranged in the heat preservation chamber, the heater is connected with a temperature controller for stabilizing the temperature, a three-dimensional magnetic field coil is arranged outside the atomic air chamber, and a precision current source of the three-dimensional magnetic field coil is electrically connected with a fourth controller for controlling the size of the magnetic field.
Further, the atom gas chamber is transparent and is filled with saturated rubidium atom steam.
Further, the first laser is electrically connected with a first controller which provides high-precision temperature and current control for the first laser.
Further, the second laser is electrically connected with a second controller which provides high-precision temperature and current control for the second laser.
Furthermore, the acousto-optic modulator is electrically connected with a third controller for controlling the acousto-optic modulator.
A high-sensitivity pulse optical pumping type scalar magnetic field measurement method comprises the following specific steps:
(1) adjusting the positions of the two plane reflectors and the atom sensor, placing an atom sensor probe in a magnetic shielding cylinder, heating to a set temperature, and generating a static magnetic field and superposing an alternating test magnetic field in the z direction of the three-dimensional magnetic field coil;
(2) starting from the initial time t =0, the pumping light emitted by the second laser is periodically turned off and turned on by the acousto-optic modulator in combination with a third controller, wherein the pumping light is turned on for a time period t1Each switching cycle having a duration of T0；
(3) Starting from t =0, the y-direction of the three-dimensional magnetic field coil is loaded with a radio frequency pulse with the duration t2The pulse waveform is sinusoidal, the frequency of the pulse waveform is the same as the atomic spin oscillation frequency, and the amplitude and the duration are optimized according to the optical measurement signal;
(4) starting from t =0, the detection light emitted by the first laser is continuously turned on, and signals of the detection light passing through the atom sensor probe are received by the first photoelectric converter and the second photoelectric converter;
(5) starting from T =0, the data acquisition system acquires and analyzes signals received by the first photoelectric converter and the second photoelectric converter, wherein the acquired effective data has a duration of T0-t2；
(6) In a continuous mode or an intermittent mode, starting from t =0, corresponding magnetic field data acquisition is carried out;
(7) and carrying out spectrum analysis on the collected magnetic field data and fitting according to the requirement to obtain the measurement sensitivity and the magnetic field change frequency.
Further, in the continuous mode, the magnetic field data acquisition is periodically and continuously sampled, and the sampling frequency of the original data pointsf sDetermined by a data acquisition system; in each pulse period T0And analyzing the signal to obtain a magnetic field data point B with a time stampnThen magnetic field data B1,B2,B3…BnHas a sampling frequency of 1/T0 。
Further, in the intermittent mode, the magnetic field data acquisition is: a certain number of times NThe periodic continuous sampling is carried out, then the sampling is not carried out in the intermittent period, and the periodic continuous sampling is carried out for a certain number of times N, so that the sampling is repeated; raw data point sampling frequencyf sDetermined by a data acquisition system; in each pulse period T0And analyzing the signal to obtain a magnetic field data point B with a time stampnEvery N magnetic field data points are grouped into one group, and the sampling frequency of each group is 1/T0And each group of data has a pause of a certain time length, and no magnetic field data measuring action exists in the pause.
The invention has the advantages that:
1. the pumping light and the detection light adopt the technology of combining the parallel plane reflector and the atomic sensor probe, realize multi-light-path turning back, effectively increase the action distance and the angle of Faraday optical rotation, have more stable structure, improve the sensitivity of magnetic field measurement, and are easier to build and adjust.
2. The invention adopts the pulse control technology of the continuous mode or the intermittent mode, can carry out other interrupt operations in the measuring process, can still effectively sample data when the data volume is larger, and improves the sampling frequency of magnetic field measurementf B。
3. The invention maintains the high sensitivity of weak magnetic field measurement and improves the sampling frequency in the pulse pumping type high sensitivity scalar magnetic field measurement.
Drawings
FIG. 1 is a schematic structural diagram of the present invention.
Fig. 2 is a schematic structural diagram of an atom sensor probe of the present invention.
FIG. 3 is a schematic diagram of the sequential mode measurement pulse timing control of the present invention.
FIG. 4 is a schematic diagram of the intermittent mode measurement pulse timing control according to the present invention.
FIG. 5 is a diagram illustrating the continuous mode pulse timing control and magnetic field measurement results of the present invention.
FIG. 6 is a schematic diagram of the continuous measurement data and signal recovery of the magnetic field according to the present invention.
FIG. 7 is a graph showing the results of the burst mode of the present invention.
FIG. 8 is a diagram illustrating the sensitivity spectrum of the magnetic field measurement according to the present invention.
Detailed Description
The present invention is further illustrated by the following examples, which are not intended to limit the invention to these embodiments. It will be appreciated by those skilled in the art that the present invention encompasses all alternatives, modifications and equivalents as may be included within the scope of the claims.
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, unless otherwise specified, "a plurality" means two or more unless explicitly defined otherwise.
In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. The first feature being "under," "below," and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or merely means that the first feature is less than the second feature at a horizontal height.
Example one
Referring to fig. 1 and 2, the present embodiment provides a high-sensitivity pulse optical pumping scalar magnetic field measurement apparatus, which includes a first laser 2 outputting probe light, and a second laser 18 outputting pump light.
The output of the second laser 18 is connected to the input of a second isolator 19 in this embodiment, the output of the second isolator 19 is connected to the input of an acousto-optic modulator 20 which controls the intensity of the beam, the output of the acousto-optic modulator 20 is connected to the input of a second lambda/2 plate 22, the output of said second lambda/2-plate 22 is connected to the input of a second polarizing beam splitter 23 which splits the light beam into two beams, the output end of the second polarization beam splitter 23 is connected with the input end of the second fiber coupler 24, the output end of the second optical fiber coupler 24 is connected with the input end of a second frequency spectrograph 25 for dynamic detection, the second output of said second polarization beam splitter 23 is connected to a lambda/4 plate 26 which transforms the beam into a circularly polarized beam, the output light beam of the lambda/4 wave plate 26 is expanded by the beam expander 27 and then is irradiated into the atom sensor probe 11. The second laser 18 is electrically connected to a second controller 17 which provides high precision temperature and current control thereto. The acousto-optic modulator 20 is electrically connected to a third controller 21 for controlling the same. The second controller 17 of the present invention provides high precision temperature and current control to the second laser 18. the second laser 18 outputs laser as pump light, and after passing through the second isolator 19, the intensity of the light beam is controlled by the acousto-optic modulator 20 in combination with the third controller 21. And then the two beams of light are divided into two beams by a second lambda/2 wave plate 22 and a second polarization beam splitter 23, one beam of light enters a second optical fiber coupler 24 and is input to a second frequency spectrograph 25 for dynamic detection, and the other beam of light is converted into circularly polarized light by a lambda/4 wave plate 26, is expanded by a beam expander 27 and irradiates the atom sensor probe 11.
In this embodiment, an output end of the first laser 2 is connected to an input end of a first isolator 3, an output end of the first isolator 3 is connected to an input end of a first λ/2 wave plate 4, an output end of the first λ/2 wave plate 4 is connected to an input end of a first polarization beam splitter 5 that splits a light beam into two beams, a first output end of the first polarization beam splitter 5 is connected to an input end of a first optical fiber coupler 6, an output end of the first optical fiber coupler 6 is connected to an input end of a first spectrometer 7 that performs dynamic detection, a second output end of the first polarization beam splitter 5 transforms the light beam by a reflector 8 and then enters an atom sensor probe 11, an emergent light of the atom sensor probe 11 is input to a third λ/2 wave plate 12, an output end of the third λ/2 wave plate 12 is connected to an input end of a third polarization beam splitter 13 that splits the light beam into two beams, the first output end of the third polarization beam splitter 13 is connected with the input end of the first photoelectric converter 14, the second output end of the third polarization beam splitter 13 is connected with the input end of the second photoelectric converter 15, and the differential output ends of the first photoelectric converter 14 and the second photoelectric converter 15 are both connected with a data acquisition system 16 for acquiring, storing, processing and displaying detection signals; the first laser 2 is electrically connected to a first controller 1 which provides high precision temperature and current control thereto. Planar reflectors facing the atom sensor probe 11 are arranged on two sides of the atom sensor probe, one planar reflector is a front planar reflector 10, the other planar reflector is a rear planar reflector 9, and the planar reflectors are arranged in parallel with the pump light beams input into the atom sensor probe 11. The first controller 1 of the invention provides high-precision temperature and current control for the first laser 2, the first laser 2 outputs laser as probe light, the laser passes through the first isolator 3 and the first lambda/2 wave plate 4 and then is divided into two beams by the first polarization beam splitter 5, one beam enters the first optical fiber coupler 6 and is input to the first frequency spectrograph 7 for dynamic detection, and the other beam passes through the reflector 8 and is converted into a beam and then enters the atom sensor probe 11. The device is designed so that the light can be reflected back and forth for multiple times in the combination of the rear plane reflector 9, the front plane reflector 10 and the atom sensor probe 11, the effective optical action distance is increased, the Faraday optical rotation angle is increased, the emergent light passes through the third lambda/2 wave plate 12 and is divided into two beams by the third polarization beam splitter 13, differential detection is carried out by the first photoelectric converter 14 and the second photoelectric converter 15 respectively, and the detected signals are collected, stored, processed and displayed by the data collection system 16.
The atomic sensor probe 11 of this embodiment includes an atomic gas chamber 28, a heat preservation chamber 30 is provided outside the atomic gas chamber 28, a heater 29 for heating the atomic gas chamber is provided in the heat preservation chamber 30, the heater 29 is connected to a temperature controller 32 for stabilizing the temperature, a three-dimensional magnetic field coil 31 is provided outside the atomic gas chamber 28, and a precision current source 34 of the three-dimensional magnetic field coil 31 is electrically connected to a fourth controller 33 for controlling the magnitude of the magnetic field. The atomic gas cell 28 is transparent and filled with saturated rubidium atomic vapor. The invention uses a transparent atom gas chamber 28 filled with saturated rubidium atom steam as a medium for the action of atoms and a magnetic field, the atom gas chamber 28 is heated by a heater 29, the temperature is stabilized by a temperature controller 32, and an outer heat preservation chamber 30 is used for reducing heat loss. The three-dimensional magnetic field coil 31 is combined with a precision current source 34 to generate magnetic fields with variable directions x, y and z, respectively, and the magnitude of the magnetic fields is controlled by a fourth controller 33.
The pumping light and the detection light adopt the technology of combining the parallel plane reflector and the atomic sensor probe, realize multi-light-path turning back, effectively increase the action distance and the angle of Faraday optical rotation, have more stable structure, improve the sensitivity of magnetic field measurement, and are easier to build and adjust.
Example two
The embodiment provides a high-sensitivity pulse optical pumping type scalar magnetic field measuring method, which adopts a pulse pumping type NMOR scalar detection method and has the basic principle that precession (Larmor precession) can be generated in a magnetic field according to atom spin polarized by pumping light, the precession frequency of the atom spin is measured by the detecting light, and information such as the size of the magnetic field can be accurately obtained.
Firstly, the measuring device described in the first embodiment needs to be built, and the combination of the rear plane mirror 9, the front plane mirror 10 and the atom sensor probe 11 is adjusted to realize multiple back-and-forth reflection. The working timing of each device is precisely controlled by a control signal synchronized by a clock signal, such as the first controller 1, the second controller 17, the third controller 21, the fourth controller 33, the data acquisition system 16, the temperature controller 32, and the like, so as to precisely measure the optical signal change caused by the atomic spin change in the atomic gas chamber 28. The information of the magnetic field to be measured is inverted by recording and analyzing the changes through the data acquisition system 16. The corresponding pulse timing control is in both continuous and intermittent modes. The continuous mode is suitable for general cases, and the intermittent mode is suitable for cases where other interrupt-type operations need to be performed intermittently, or where a large amount of data needs to be processed in a short time. The control scheme has strong flexibility and adaptability in actual measurement.
In the continuous mode, the specific steps of measurement include:
(1) adjusting the positions of the two plane reflectors and the atom sensor, placing the atom sensor probe 11 in a magnetic shielding cylinder, heating to a set temperature, and generating a static magnetic field and superposing an alternating test magnetic field in the z direction of the three-dimensional magnetic field coil;
(2) from the initial time t =0, the pump light emitted from the second laser 18 is periodically turned off and on by the acousto-optic modulator 20 in combination with the third controller 21, as shown in fig. 3 by the pulse control timing, wherein the pump light is turned on for a period t1Each switching cycle having a duration of T0；
(3) Starting from t =0, the y-direction of the three-dimensional magnetic field coil 31 is loaded with a radio frequency pulse by the fourth controller 33 for a duration t2The pulse waveform is sinusoidal, the frequency of the pulse waveform is the same as the atomic spin oscillation frequency, and the amplitude and the duration of the pulse waveform areOptimizing the optical measurement signal;
(4) starting from t =0, the probe light emitted by the first laser 2 is continuously turned on, and a signal thereof after passing through the atom sensor probe 11 is received by the first photoelectric converter 14 and the second photoelectric converter 15;
(5) starting from T =0, the data acquisition system 16 acquires and analyzes signals received by the first and second photoelectric converters 14 and 15, wherein the acquired valid data has a duration T0-t2The pulse control timing shown in fig. 3;
(6) in continuous mode, as shown in the pulse control timing of fig. 3, starting from t =0, the magnetic field data is collected as a periodic continuous sample, with the original data point sampling frequencyf s(generally, the frequency of analog-to-digital conversion, sampling atomic spin oscillation signals) is determined by a data acquisition system; in each pulse period T0And analyzing the signal to obtain a magnetic field data point B with a time stampnThen magnetic field data B1,B2,B3…BnHas a sampling frequency of 1/T0. Data acquisition time stamps, individual pulses are precisely clock synchronized.
(7) And carrying out spectrum analysis on the collected magnetic field data and fitting according to requirements to obtain parameters such as measurement sensitivity, magnetic field change frequency and the like.
In the intermittent mode, the specific steps of measurement include:
(1) adjusting the positions of the two plane reflectors and the atom sensor, placing the atom sensor probe 11 in a magnetic shielding cylinder, heating to a set temperature, and generating a static magnetic field and superposing an alternating test magnetic field in the z direction of the three-dimensional magnetic field coil;
(2) from the initial time t =0, the pump light emitted from the second laser 18 is periodically turned off and on by the acousto-optic modulator 20 in combination with the third controller 21, as shown in fig. 3 by the pulse control timing, wherein the pump light is turned on for a period t1Each switching cycle having a duration of T0；
(3) Starting from t =0, the y-direction of the three-dimensional magnetic field coil 31 is loaded by one by the fourth controller 33Radio frequency pulse with duration t2The pulse waveform is sinusoidal, the frequency of the pulse waveform is the same as the atomic spin oscillation frequency, and the amplitude and the duration are optimized according to the optical measurement signal;
(4) starting from t =0, the probe light emitted by the first laser 2 is continuously turned on, and a signal thereof after passing through the atom sensor probe 11 is received by the first photoelectric converter 14 and the second photoelectric converter 15;
(5) starting from T =0, the data acquisition system 16 acquires and analyzes signals received by the first and second photoelectric converters 14 and 15, wherein the acquired valid data has a duration T0-t2The pulse control timing shown in fig. 3;
(6) in the intermittent mode, as shown in the pulse control timing shown in fig. 4, starting from t =0, the magnetic field data is acquired as: a certain number of times of N periodic continuous sampling is carried out, then no sampling is carried out in the intermittent period, and a certain number of times of N periodic continuous sampling is carried out again and again; raw data point sampling frequencyf s(generally, the frequency of analog-to-digital conversion, sampling atomic spin oscillation signals) is determined by a data acquisition system; in each pulse period T0And analyzing the signal to obtain a magnetic field data point B with a time stampnEvery N magnetic field data points are grouped into one group, and the sampling frequency of each group is 1/T0There is a pause of a certain duration between each set of data, during which there is no magnetic field data measurement action, so that the system performs other operations. Data acquisition time stamps, individual pulses are precisely clock synchronized.
(7) And carrying out spectrum analysis on the collected magnetic field data and fitting according to requirements to obtain parameters such as measurement sensitivity, magnetic field change frequency and the like.
The invention optimizes the measuring means and the data processing method, adopts the pulse control technology of a continuous mode or an intermittent mode, can carry out other interrupt operations in the measuring process, realizes effective data sampling when the data volume is larger, and improves the sampling frequency of magnetic field measurementf B(ii) a In the pulse pumping type high-sensitivity scalar magnetic field measurement, the high sensitivity of the weak magnetic field measurement is maintained, and the improvement of the sensitivity of the weak magnetic field measurement is realizedIts sampling frequency.
One specific implementation is as follows:
【1】 The first laser 2 is controlled by the first controller 1 to achieve an output wavelength of 795.01nm and a power of 7 mW. The power of the detection light entering the atom sensor probe 11 is 0.2mW through the first λ/2 wave plate 4 and the first polarization beam splitter 5.
【2】 The angle of the incident detection light is set to be 4 degrees, and the distance between the parallel rear plane reflector 9 and the parallel front plane reflector 10 is 20cm, so that the detection light is reflected back and forth to form a 4-time turn-back light path and is emitted from the atom sensor probe 11.
【3】 The atom gas cell 28 of the atom sensor probe 11 was filled with rubidium 87 atom vapor, and heated to 90 degrees celsius by controlling the heater 29 via the temperature controller 32.
【4】 The atom sensor probe 11 is placed inside a magnetic shielding cylinder to shield the ambient electromagnetic field interference.
【5】 In the atom sensor probe 11, the precision current source 34 is controlled by the fourth controller 33 so that the three-dimensional magnetic field coil 31 generates a static magnetic field of 13.7 μ T in the z direction and superimposes an alternating test magnetic field of 11.6nT at a frequency of 500 Hz.
【6】 The detection light emitted from the atom sensor probe 11 passes through the third lambda/2 wave plate 12 and the third polarization beam splitter 13, is converted into an electric signal by the first photoelectric converter 14 and the second photoelectric converter 15, and is collected by the data collection system 16, and the sampling frequency of the original data pointf s=10MHz。
【7】 The second laser 18 is set by the second controller 17 to achieve an output wavelength of 794.98nm and a power of 40 mW.
【8】 The acousto-optic modulator 20 is controlled by a third controller 21 to be on for a time t1=0.25ms, repetition period T0=0.5ms。
【9】 When the acousto-optic modulator 20 is in an open state, the power of the pump light entering the atom sensor probe 11 is 39mW through the second λ/2 wave plate 22 and the second polarization beam splitter 23, and through the λ/4 wave plate 26 and the beam expander 27.
【10】 By means of a fourth controlThe controller 33 controls the precision current source 34 so that the three-dimensional magnetic field coil 31 generates a radio frequency pulse in the y direction for a time period t2=0.03ms。
【11】 The probe light remains on.
【12】 In continuous mode, the data acquisition system 16 is off for the RF pulse time t2After 0.03ms, the measuring signal is periodically and continuously acquired, and the sampling frequency is measured by the magnetic fieldf B=2kHz。
【13】 In the intermittent mode, the data acquisition system 16 performs periodic continuous sampling with a frequency N =10, and the magnetic field measurement sampling frequencyf B=2 kHz. Then, the intermittent period is not sampled for 7ms, and periodic continuous sampling is performed again for N =10 times.
【14】 FIG. 5 shows the corresponding pulse sequence control scheme in continuous mode, and 10 magnetic field data B1-B10Measuring the raw signal and analyzing the calculation result.
【15】 FIG. 6 shows the results of the measurements in FIG. 5, which were fit calculated to the continuous mode measured periodic magnetic field data to recover the original 11.6nT alternating test magnetic field signal at 500 Hz.
【16】 Fig. 7 shows N =10 magnetic field data points grouped in an intermittent mode, e.g., B1, B2, B3… B10Group B11, BN+2, BN+3… B20A set of the raw data and the corresponding magnetic field numerical analysis calculation result. The original 11.6nT alternating test magnetic field signal with a frequency of 500Hz was also recovered.
【17】 Fig. 8 shows the FFT-transformed spectral distribution of the magnetic field measurement values over a period of 20s, and the noise level. Shows that the magnetic field measurement sensitivity is better than 700fT/Hz within the range of 10-1000Hz1/2。
In summary, the embodiment realizes the magnetic field sampling rate of 2kHz, and the magnetic field measurement sensitivity is better than 700fT/Hz within the range of 10-1000Hz1/2。
Claims (9)
1. A high-sensitivity pulse optical pumping type scalar magnetic field measuring device comprises a first laser for outputting detection light and a second laser for outputting pumping light, wherein the output end of the first laser is connected with the input end of a first isolator, the output end of the first isolator is connected with the input end of a first lambda/2 wave plate, the output end of the first lambda/2 wave plate is connected with the input end of a first polarization beam splitter for splitting a light beam into two beams, the first output end of the first polarization beam splitter is connected with the input end of a first optical fiber coupler, the output end of the first optical fiber coupler is connected with the input end of a first frequency spectrograph for dynamic detection, the light beam output by the second output end of the first polarization beam splitter is converted into the light beam by a reflector and then enters an atomic sensor probe, and the emergent light of the atomic sensor probe is input to a third lambda/2 wave plate, the output end of the third lambda/2 wave plate is connected with the input end of a third polarization beam splitter which divides the light beam into two beams, the first output end of the third polarization beam splitter is connected with the input end of the first photoelectric converter, the second output end of the third polarization beam splitter is connected with the input end of the second photoelectric converter, and the differential output ends of the first photoelectric converter and the second photoelectric converter are connected with a data acquisition system which acquires, stores, processes and displays the detection signal;
the output end of the second laser is connected with the input end of a second isolator, the output end of the second isolator is connected with the input end of an acousto-optic modulator for controlling the intensity of light beams, the output end of the acousto-optic modulator is connected with the input end of a second lambda/2 wave plate, the output end of the second lambda/2 wave plate is connected with the input end of a second polarization beam splitter for dividing the light beams into two beams, the first output end of the second polarization beam splitter is connected with the input end of a second optical fiber coupler, the output end of the second optical fiber coupler is connected with the input end of a second frequency spectrograph for dynamic detection, the second output end of the second polarization beam splitter is connected with a lambda/4 wave plate for converting the light beams into circularly polarized light beams, and the output light beams of the lambda/4 wave plate are irradiated into the atom sensor probe after being expanded by a beam expander;
the method is characterized in that: and planar reflectors facing the atom sensor probe are arranged on two sides of the atom sensor probe, and the planar reflectors are arranged in parallel with the pump light beam input into the atom sensor probe.
2. A high sensitivity pulsed optically pumped scalar magnetic field measurement device as claimed in claim 1, wherein: the atomic sensor probe comprises an atomic air chamber, a heat preservation chamber is arranged outside the atomic air chamber, a heater for heating the atomic air chamber is arranged in the heat preservation chamber, the heater is connected with a temperature controller for stabilizing the temperature, a three-dimensional magnetic field coil is arranged outside the atomic air chamber, and a precise current source of the three-dimensional magnetic field coil is electrically connected with a fourth controller for controlling the size of the magnetic field.
3. A high-sensitivity pulsed optically pumped scalar magnetic field measurement device as claimed in claim 2, wherein: the atomic gas chamber is transparent and is filled with saturated rubidium atomic vapor.
4. A high sensitivity pulsed optically pumped scalar magnetic field measurement device as claimed in claim 1, wherein: the first laser is electrically connected to a first controller that provides high precision temperature and current control thereto.
5. A high sensitivity pulsed optically pumped scalar magnetic field measurement device as claimed in claim 1, wherein: the second laser is electrically connected to a second controller that provides high precision temperature and current control thereto.
6. A high sensitivity pulsed optically pumped scalar magnetic field measurement device as claimed in claim 1, wherein: the acousto-optic modulator is electrically connected with a third controller for controlling the acousto-optic modulator.
7. The magnetic field measurement method of a high-sensitivity pulsed optical pumped scalar magnetic field measurement device according to claim 1, wherein: the method comprises the following specific steps:
(1) adjusting the positions of the two plane reflectors and the atom sensor, placing an atom sensor probe in a magnetic shielding cylinder, heating to a set temperature, and generating a static magnetic field and superposing an alternating test magnetic field in the z direction of the three-dimensional magnetic field coil;
(2) starting from the initial time t =0, the pumping light emitted by the second laser is periodically turned off and turned on by the acousto-optic modulator in combination with a third controller, wherein the pumping light is turned on for a time period t1Each switching cycle having a duration of T0；
(3) Starting from t =0, the y-direction of the three-dimensional magnetic field coil is loaded with a radio frequency pulse with the duration t2The pulse waveform is sinusoidal, the frequency of the pulse waveform is the same as the atomic spin oscillation frequency, and the amplitude and the duration are optimized according to the optical measurement signal;
(4) starting from t =0, the detection light emitted by the first laser is continuously turned on, and signals of the detection light passing through the atom sensor probe are received by the first photoelectric converter and the second photoelectric converter;
(5) starting from T =0, the data acquisition system acquires and analyzes signals received by the first photoelectric converter and the second photoelectric converter, wherein the acquired effective data has a duration of T0-t2；
(6) In a continuous mode or an intermittent mode, starting from t =0, corresponding magnetic field data acquisition is carried out;
(7) and carrying out spectrum analysis on the collected magnetic field data and fitting according to the requirement to obtain the measurement sensitivity and the magnetic field change frequency.
8. The magnetic field measurement method according to claim 7, characterized in that: in continuous mode, the magnetic field data acquisition is periodically and continuously sampled, and the sampling frequency of the original data pointsf sDetermined by a data acquisition system; in each pulse period T0And analyzing the signal to obtain a magnetic field data point B with a time stampnThen magnetic field data B1,B2,B3…BnHas a sampling frequency of 1/T0 。
9. The magnetic field measurement method according to claim 7, characterized in that: in the intermittent mode, the magnetic field data acquisition is: a certain number of times of N periodic continuous sampling is carried out, then no sampling is carried out in the intermittent period, and a certain number of times of N periodic continuous sampling is carried out again and again; raw data point sampling frequencyf sDetermined by a data acquisition system; in each pulse period T0And analyzing the signal to obtain a magnetic field data point B with a time stampnEvery N magnetic field data points are grouped into one group, and the sampling frequency of each group is 1/T0And each group of data has a pause of a certain time length, and no magnetic field data measuring action exists in the pause.
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