Dead-zone-free atomic magnetometer device and method based on pump-probe information fusion

Abstract

The application discloses a dead-zone-free atomic magnetometer device and method based on pumping-detection information fusion and relates to the technical field of atomic magnetometers. Through optical-magnetic double-resonance pulse modulation, atoms can generate free precession signals in each magnetic field direction. In the spin polarization free precession stage, the output signals of pumping light and detection light are collected and detected, the dead zones of the output signals of the two light beams are complementary, one signal with a high signal-to-noise ratio is selected as an output through signal processing, and then a dead-zone-free high-sensitivity optical pumping atomic magnetometer is realized. The application realizes the full-range dead-zone-free atomic magnetometer without reducing the sensitivity of the magnetometer, and is helpful to the further application of the optical pumping atomic magnetometer in the field of space magnetic field measurement in the future.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of atomic magnetometer, and particularly to a dead-zone-free atomic magnetometer device and method based on pump-probe information fusion. BACKGROUND

[0002] In the prior art, as a quantum precision magnetic field measurement instrument, the optical pumping atomic magnetometer gradually becomes an important development direction of high-sensitivity magnetic field measurement research and application, with the advantages of small sensor size, high sensitivity, large dynamic range, etc. The optical pumping atomic magnetometer based on the free precession mechanism has the characteristics of high measurement accuracy, simple circuit structure and strong robustness, and has made important progress in scientific research and industrialization. The optical pumping atomic magnetometer has a dead zone in magnetic field measurement. When the direction of the measured magnetic field is in the dead zone, the magnetometer will not have signal output, which leads to the failure of magnetic field measurement and affects the use of the optical pumping atomic magnetometer. Therefore, the suppression of the dead zone of the magnetometer becomes an important problem in the research and application of the optical pumping atomic magnetometer. SUMMARY

[0003] The purpose of the present application is to provide a dead-zone-free atomic magnetometer device and method based on pump-probe information fusion, which can realize full-range dead-zone-free magnetometer without reducing the sensitivity of the magnetometer, and is helpful for the further application of the optical pumping atomic magnetometer in the field of space magnetic field measurement in the future.

[0004] To achieve the above purpose, the present application provides a dead-zone-free atomic magnetometer device based on pump-probe information fusion, comprising a pump light path and a detection light path; the pump light path comprises a pump laser, an optical intensity modulator, a first polarization maintaining optical fiber, a first collimator, a first half-wave plate, a first polarizer, a first mirror, a quarter-wave plate, an alkali metal cell and a first photodetector connected in sequence; the output of the first photodetector is input to the input end of a data acquisition and processing system through a first transimpedance amplifier and a first band-pass filter;

[0005] The detection light path comprises a detection laser, a second polarization maintaining optical fiber, a second collimator, a second polarizer, the alkali metal cell, a second half-wave plate, a light splitting module and a polarization balance differential detection circuit connected in sequence; the output of the polarization balance differential detection circuit is input to the input end of the data acquisition and processing system through a second transimpedance amplifier and a second band-pass filter; the frequency range of the first band-pass filter and the second band-pass filter is centered on the Larmor precession frequency corresponding to the measured magnetic field; the output end of the data acquisition and processing system is connected to the first band-pass filter, the second band-pass filter and a signal generator respectively, and the acquired Larmor precession frequency is fed back.

[0006] Preferably, the pumping laser generates laser light whose frequency is tuned to the D1 line of the alkali metal atom; the first half-wave plate in the pumping light path maximizes the optical power of the pumping light after the pumping light passes through the first polarizer, and the first polarizer, the first mirror and the quarter-wave plate form circularly polarized light from the pumping light and the pumping light passes through the alkali metal cell.

[0007] Preferably, the input end of the light intensity modulator is connected to the output end of the signal generator.

[0008] Preferably, the detection laser generates laser light whose frequency is tuned to the maximum free precession signal; the second polarizer in the detection light path forms linearly polarized light from the detection light and the detection light passes through the alkali metal cell.

[0009] Preferably, the light splitting module is composed of a polarization splitting prism and a second mirror, and the polarization balance differential detection circuit is provided with a second photodetector and a third photodetector in parallel; the second mirror of the light splitting module is connected to the second photodetector, and the polarization splitting prism is connected to the third photodetector; the second half-wave plate and the light splitting module make the polarization balance differential detection circuit output zero when the magnetometer does not work.

[0010] Preferably, the alkali metal cell is surrounded by an oven, a non-magnetic electric heating coil, a radio frequency coil and a magnetometer support shell from the inside to the outside; the non-magnetic electric heating coil is driven by high-frequency alternating current far away from the Larmor precession frequency; the radio frequency coil is connected to another output end of the signal generator perpendicular to an axis of the pumping light direction.

[0011] The application also provides a control method of the dead-zone-free atomic magnetometer device based on pumping-detection information fusion.

[0012] S1, controlling the signal generator to input a square wave pulse sequence with a period of 1-10 ms and a duty cycle of 30%-50% to the light intensity modulator, wherein the duty cycle of the square wave pulse in the sequence is 50%, and the pulse repetition frequency is the Larmor precession frequency corresponding to the magnetic field, so that the pumping light is synchronously optically pumped to prepare atomic spin polarization, and after completion, the modulation pulse signal is removed, and a low-amplitude direct current signal is input to the light intensity modulator to ensure a certain light intensity of the pumping light for subsequent detection.

[0013] S2, at the moment when the square wave pulse sequence input by the signal generator to the light intensity modulator is removed every period, the signal generator is used to apply a radio frequency magnetic field pulse with the same frequency as the square wave pulse frequency of the light intensity modulator to the radio frequency coil perpendicular to the pumping light direction, and the duration is less than 0.05 ms, and the spin polarization vector is controlled to the plane perpendicular to the magnetic field direction by adjusting the amplitude and duration of the radio frequency magnetic field pulse, so that the free precession signal amplitude is maximized, and then the radio frequency magnetic field pulse is removed.

[0014] S3, after removing the input signal of the signal generator to the radio frequency coil in each cycle, the atomic spin polarization undergoes free precession, and the output signals of the pumping light and the detection light are collected by the data acquisition and processing system to realize the collection of the free precession signals;

[0015] S4, the output signals of the pumping light and the detection light are collected by the data acquisition and processing system, and the free precession signals with high signal-to-noise ratio are selected for processing to obtain the information of the measured magnetic field.

[0016] Preferably, in S3, the spin polarization vector undergoes free precession, and the evolution expression of the spin polarization in the pumping light direction is:

[0017]

[0018] The evolution expression of the spin polarization in the detection light direction is:

[0019]

[0020] Wherein, t is time, R pr is the pumping rate in the free precession stage, R r1 is the longitudinal relaxation rate in the free precession stage, R r2 is the transverse relaxation rate in the free precession stage, θ is the angle between the measured magnetic field and the z direction, φ is the angle between the measured magnetic field and the y direction, P is the size of the spin polarization participating in the free precession, γ is the gyromagnetic ratio, B0 is the size of the measured magnetic field, is the signal phase;

[0021] The first term of the two formulas is a slow varying direct current term caused by light pumping, and the second term is the free precession expression of the spin polarization.

[0022] Preferably, after the detection light signal passes through the first transimpedance amplifier and the first band-pass filter, the slow varying direct current term is filtered out, and the signal collected by the data acquisition and processing system is represented as:

[0023]

[0024] After the detection light signal passes through the second transimpedance amplifier and the second band-pass filter, the slow varying direct current term is filtered out, and the signal collected by the data acquisition and processing system is represented as:

[0025]

[0026] Wherein, V1 and V2 are the voltage signal amplitudes output by the first band-pass filter and the second band-pass filter respectively.

[0027] Therefore, the application adopts the above-mentioned pumping-detection information fusion based dead-zone-free atomic magnetometer device and method based on a double-beam free-precession optical pumping atomic magnetometer configuration, realizes double light measurement dead-zone complementation, realizes full-range dead-zone-free magnetometer without reducing the sensitivity of the magnetometer, does not cause the magnetic field measurement problem caused by the dead zone of the magnetometer, and further improves the application flexibility of the optical pumping atomic magnetometer.

[0028] The technical solutions of the application will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a structural schematic diagram of the pumping-detection information fusion based dead-zone-free atomic magnetometer device embodiment of the application;

[0030] Figure 2 is a flowchart of the pumping-detection information fusion based dead-zone-free atomic magnetometer device control method of the application.

[0031] REFERENCE NUMERALS

[0032] 1, pumping laser; 2, light intensity modulator; 3, first polarization maintaining optical fiber; 4, first collimator; 5, first half-wave plate; 6, first polarizer; 7, first reflector; 8, quarter-wave plate; 9, alkali metal cell; 10, first photodetector; 11, first transimpedance amplifier; 12, first band-pass filter; 13, data acquisition and processing system; 14, detection laser; 15, second polarization maintaining optical fiber; 16, second collimator; 17, second polarizer; 18, second half-wave plate; 19, light splitting module; 20, polarization balance differential detection circuit; 201, second photodetector; 202, third photodetector; 21, second transimpedance amplifier; 22, second band-pass filter; 23, signal generator; 24, oven; 25, non-magnetic electric heating coil; 26, radio frequency coil; 27, magnetometer support shell. DETAILED DESCRIPTION

[0033] The technical solutions of the application will be further described in detail below with reference to the drawings and embodiments.

[0034] Unless otherwise defined, technical terms or scientific terms used in the present application shall have the meanings as commonly understood by one of ordinary skill in the art to which this application belongs. The terms "first", "second", and similar terms do not denote any order, quantity, or importance, but are used to distinguish one element from another, and the terms "comprises", "comprising", "includes", "including" and the like can be used synonymously. The terms "connected", "coupled", and "pathway" are not limited to direct or physical connections, but can include indirect connections or indirect physical connections such as through a wired or wireless interface, through the movement of air or other medium for sound waves, through the capacitance or induction between or among conductors, or the like. The terms "upper", "lower", "left", "right", and the like are used only to indicate relative positions, and when the absolute positions of the described objects are changed, the relative positions can also be changed accordingly.

[0035] xyz is a three-axis (x-axis, y-axis, z-axis) Cartesian coordinate system established with the laboratory pumping light direction as the z-axis and the detection light direction as the x-axis.

[0036] Embodiment one

[0037] As shown in Figure 1 The present application provides a dead-zone-free atomic magnetometer device based on pumping-detection information fusion, which comprises a pumping light path and a detection light path. The pumping light path comprises a pumping laser 1, an optical intensity modulator 2, a first polarization maintaining optical fiber 3, a first collimator 4, a first half-wave plate 5, a first polarizer 6, a first mirror 7, a quarter-wave plate 8, an alkali metal cell 9, and a first photodetector 10, which are connected in sequence. The output of the first photodetector 10 is input to the input end of a data acquisition and processing system 13 through a first transimpedance amplifier 11 and a first band-pass filter 12.

[0038] The detection light path comprises a detection laser 14, a second polarization maintaining optical fiber 15, a second collimator 16, a second polarizer 17, the alkali metal cell 9, a second half-wave plate 18, a light splitting module 19, and a polarization balance differential detection circuit 20, which are connected in sequence. The output of the polarization balance differential detection circuit 20 is input to the input end of the data acquisition and processing system 13 through a second transimpedance amplifier 21 and a second band-pass filter 22.

[0039] The frequency range of the first band-pass filter 12 and the second band-pass filter 22 is centered on the Larmor precession frequency corresponding to the magnetic field to be measured. The output end of the data acquisition and processing system 13 is connected to the first band-pass filter 12, the second band-pass filter 22, and a signal generator 23, respectively, to feed back the acquired Larmor precession frequency for real-time tracking of the magnetic field changes.

[0040] The laser frequency generated by the pumping laser 1 is tuned to the D1 line of the alkali metal atom, the first half-wave plate 5 in the pumping light path makes the light power of the pumping light maximum after the pumping light transmits through the first polarizer 6, the first polarizer 6, the first mirror 7 and the quarter-wave plate 8 make the pumping light form circularly polarized light and pass through the alkali metal cell 9, and the input end of the light intensity modulator 2 is connected with the output end of the signal generator 23.

[0041] The laser frequency generated by the detection laser 14 is tuned to the maximum of the free precession signal, the second polarizer 17 in the detection light path makes the detection light form linearly polarized light and pass through the alkali metal cell 9, the light splitting module 19 is composed of a polarization splitting prism and a second mirror, the polarization balance differential detection circuit 20 is provided with the second photoelectric detector 201 and the third photoelectric detector 202 in parallel, the second mirror of the light splitting module 19 is connected with the second photoelectric detector 201, the polarization splitting prism is connected with the third photoelectric detector 202, and the second half-wave plate 18 and the light splitting module 19 make the polarization balance differential detection circuit 20 output zero when the magnetometer does not work.

[0042] The alkali metal cell 9 is sequentially provided with an oven 24, a non-magnetic electric heating coil 25, an RF coil 26 and a magnetometer support shell 27 from inside to outside, the non-magnetic electric heating coil 25 is driven by high-frequency alternating current far away from the Larmor precession frequency, the alkali metal cell 9 is heated through the oven 24 to achieve high atomic density, and the RF coil 26 is connected with another output end of the signal generator 23 and perpendicular to an axis of the pumping light direction.

[0043] As shown in Figure 2 The application also provides a control method of the dead-zone-free atomic magnetometer device based on pumping-detection information fusion, which comprises the following steps:

[0044] S1, the signal generator 23 inputs a square wave pulse sequence with a period of 1-10 ms and a duty cycle of 30%-50% into the light intensity modulator 2, wherein the duty cycle of the square wave pulse in the sequence is 50%, and the pulse repetition frequency is the Larmor precession frequency corresponding to the magnetic field, so that the pumping light is synchronously pumped to prepare atomic spin polarization, and after completion, the modulation pulse signal is removed, and a low-amplitude direct current signal is input into the light intensity modulator 2 to ensure a certain light intensity of the pumping light for subsequent detection.

[0045] S2, at the moment when the square wave pulse sequence input by the signal generator 23 into the light intensity modulator 2 is removed every period, the signal generator 23 applies a radio frequency magnetic field pulse with the same frequency as the square wave pulse frequency of the light intensity modulator 2 to the RF coil 26 perpendicular to the pumping light direction, and the duration is less than 0.05 ms, the spin polarization vector is controlled to the plane perpendicular to the magnetic field direction by adjusting the amplitude and duration of the radio frequency magnetic field pulse, the free precession signal amplitude is maximized, and then the radio frequency magnetic field pulse is removed.

[0046] S3, after the signal generator 23 removes the input signal to the radio frequency coil 26 in each cycle, the atomic spin polarization undergoes free precession, and the output signals of the pumping light and the detection light are collected by the data acquisition and processing system 13 to realize the collection of the free precession signals.

[0047] The spin polarization vector undergoes free precession, and the evolution expression of the spin polarization in the pumping light direction is:

[0048]

[0049] The evolution expression of the spin polarization in the detection light direction is:

[0050]

[0051] where t is time, R pr is the pumping rate in the free precession stage, R r1 is the longitudinal relaxation rate in the free precession stage, R r2 is the transverse relaxation rate in the free precession stage, θ is the angle between the measured magnetic field and the z direction, φ is the angle between the measured magnetic field and the y direction, P is the size of the spin polarization participating in the free precession, γ is the gyromagnetic ratio, B0 is the size of the measured magnetic field, is the signal phase;

[0052] The first term of the two formulas is a slow direct current term caused by light pumping, and the second term is a free precession expression of the spin polarization.

[0053] From the free precession expressions of the pumping light and the detection light directions, it can be seen that when the measured magnetic field is along the pumping light direction, the pumping light has no free precession signal output, and at this time the direction is the dead zone of the pumping light output, and at this time the detection light direction has a free precession signal output. When the measured magnetic field is along the detection light direction, the detection light has no free precession signal output, and at this time the direction is the dead zone of the detection light output, and at this time the pumping light direction has a free precession signal output.

[0054] After the detection light signal passes through the first transimpedance amplifier 11 and the first band-pass filter 22, the slow direct current term is filtered out, and the signal collected by the data acquisition and processing system is represented as:

[0055]

[0056] After the detection light signal passes through the second transimpedance amplifier 21 and the second band-pass filter 22, the slow direct current term is filtered out, and the signal collected by the data acquisition and processing system 13 is represented as:

[0057]

[0058] where V1 and V2 are the voltage signal amplitudes output by the first band-pass filter and the second band-pass filter, respectively.

[0059] S4, the data acquisition and processing system 13 collects the output signals of the pumping light and the detection light, analyzes the output signals, selects a free precession signal with high signal-to-noise ratio for processing to obtain the information of the magnetic field to be measured.

[0060] The selection of the signal with high signal-to-noise ratio ensures that the sensitivity of the magnetometer will not be lower than the sensitivity of any one signal, and the acquisition of the two signals makes the dead zones complementary, so that the detection of the free precession signal of one direction can be realized while the dead zone of the signal of another direction, and the magnetometer will not be in a state of being unable to work due to the dead zone of a certain signal, and the all-directional and dead-zone-free magnetometer is realized.

[0061] Therefore, the application adopts the above-mentioned dead-zone-free atomic magnetometer device and method based on pumping-detection information fusion, first prepares atomic spin polarization through synchronous light pumping, then applies a transverse resonance radio frequency magnetic field pulse to control the spin polarization to a plane perpendicular to the magnetic field to realize the maximum free precession signal amplitude. The light-magnetic double resonance pulse modulation enables the atoms to generate free precession signals in each magnetic field direction, then the output signals of the pumping light and the detection light are collected in the spin polarization free precession stage, and one signal with high signal-to-noise ratio is selected as the output, the dead zones of the two light path output signals are complementary, and then the dead-zone-free high-sensitivity optical pumping atomic magnetometer is realized. Without reducing the sensitivity of the magnetometer, the all-directional and dead-zone-free magnetometer is realized, which is convenient for the further development and application of the optical pumping atomic magnetometer in the field of quantum precise magnetic field measurement.

[0062] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A dead-zone-free atomic magnetometer device based on pump-detection information fusion, characterized by: It includes a pumping optical path and a detection optical path; the pumping optical path includes a pumping laser, a light intensity modulator, a first polarization-maintaining optical fiber, a first collimator, a first half-wave plate, a first polarizer, a first reflector, a quarter-wave plate, an alkali metal gas chamber, and a first photodetector connected in sequence; The output of the first photodetector is input to the input end of the data acquisition and processing system after passing through a first transimpedance amplifier and a first bandpass filter; The detection optical path includes a detection laser, a second polarization-maintaining optical fiber, a second collimator, a second polarizer, the alkali metal gas chamber, a second half-wave plate, a spectrometer module, and a polarization balance differential detection circuit, which are connected in sequence; the output of the polarization balance differential detection circuit is input to the input end of the data acquisition and processing system after passing through a second transimpedance amplifier and a second band-pass filter; the frequency range of the first band-pass filter and the second band-pass filter is centered on the Larmor precession frequency corresponding to the magnetic field to be measured; the output end of the data acquisition and processing system is respectively connected to the first band-pass filter, the second band-pass filter and the signal generator, and the acquired Larmor precession frequency is fed back; The method for controlling the device comprises the following steps: S1. Control the signal generator to input a square wave pulse sequence with a period of 1-10ms and a duty cycle of 30%-50% to the optical intensity modulator, wherein the duty cycle of the square wave pulse in the sequence is 50% and the pulse repetition frequency is the Larmor precession frequency corresponding to the magnetic field, so that the pumping light performs synchronous optical pumping to prepare atomic spin polarization. After completion, the modulated pulse signal is removed, and a DC signal with a low amplitude is input to the optical intensity modulator to ensure a certain intensity of the pumping light for subsequent detection; S2. At the moment of removing the square wave pulse sequence input from the signal generator to the optical intensity modulator in each cycle, a radio frequency magnetic field pulse having the same frequency as the square wave pulse frequency of the optical intensity modulator is applied to the radio frequency coil perpendicular to the pumping light direction through the signal generator, with a duration of less than 0.05 ms. The spin polarization vector is manipulated to a plane perpendicular to the magnetic field direction by adjusting the amplitude and duration of the radio frequency magnetic field pulse to achieve the maximum amplitude of the free precession signal, and then the radio frequency magnetic field pulse is removed; S3. After the input signal from the signal generator to the RF coil is removed in each cycle, the atomic spin polarization undergoes free precession, and the output signals of the pumping light and the detection light are collected by the data acquisition and processing system to realize the collection of the free precession signal; S4. The output signals of the pumping light and the detection light are collected and analyzed by the data acquisition and processing system, and the free precession signal with a high signal-to-noise ratio is selected for processing to obtain the magnetic field information to be measured; In S3, the spin polarization vector undergoes free precession, and the evolution expression of the spin polarization in the pumping light direction is: ； The evolution expression of the spin polarization in the detection light direction is: ； in, For time, is the pumping rate during the free precession phase, is the longitudinal relaxation rate during the free precession phase, is the transverse relaxation rate during the free precession phase, is the angle between the magnetic field to be measured and the z direction, is the angle between the magnetic field to be measured and the y direction, P is the spin polarization size participating in free precession, is the gyromagnetic ratio, is the magnitude of the magnetic field to be measured, is the signal phase; The first term of the two formulas is the slowly varying DC term caused by optical pumping, and the second term is the free precession expression of spin polarization; After the detection optical signal passes through the first transimpedance amplifier and the first bandpass filter, the slowly varying DC term is filtered out. The signal collected by the data acquisition and processing system is expressed as: ； After the detection optical signal passes through the second transimpedance amplifier and the second bandpass filter, the slowly varying DC term is filtered out. The signal collected by the data acquisition and processing system is expressed as: ； in, 、 are the voltage signal amplitudes output by the first band-pass filter and the second band-pass filter respectively.

2. The dead-zone-free atomic magnetometer device based on pump-detection information fusion according to claim 1, characterized in that: The laser frequency generated by the pumping laser is tuned to the D1 line of the alkali metal atom; the first half-wave plate in the pumping light path maximizes the optical power of the pumping light after passing through the first polarizer; the first polarizer, the first reflector, and the quarter-wave plate enable the pumping light to form circularly polarized light and pass through the alkali metal gas chamber.

3. The dead-zone-free atomic magnetometer device based on pump-detection information fusion according to claim 1, characterized in that: The input end of the light intensity modulator is connected to the output end of the signal generator.

4. The dead-zone-free atomic magnetometer device based on pump-detection information fusion according to claim 1, characterized in that: The laser frequency generated by the detection laser is tuned to a maximum free precession signal; the second polarizer in the detection light path causes the detection light to form linearly polarized light and pass through the alkali metal gas chamber.

5. The dead-zone-free atomic magnetometer device based on pump-detection information fusion according to claim 1, characterized in that: The spectrometer module is composed of a polarization beam splitter prism and a second reflector. A second photodetector and a third photodetector are arranged in parallel on the polarization balance differential detection circuit. The second reflector of the spectrometer module is connected to the second photodetector, and the polarization beam splitter prism is connected to the third photodetector. The second half-wave plate and the spectrometer module ensure that the output of the polarization balance differential detection circuit is zero when the magnetometer is not operating.

6. The dead-zone-free atomic magnetometer device based on pump-detection information fusion according to claim 1, characterized in that: An oven, a non-magnetic electric heating coil, a radio frequency coil, and a magnetometer support shell are sequentially arranged around the alkali metal gas chamber from the inside out; the non-magnetic electric heating coil is driven by a high-frequency alternating current far away from the Larmor precession frequency; the radio frequency coil is connected to the other output end of the signal generator with one axis perpendicular to the direction of the pumping light.

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