Free precession atom magnetometer modulation method and device based on optomagnetic double resonance pulses

Abstract

The invention discloses a free precession atom magnetometer modulation method and a free precession atom magnetometer modulation device based on optomagnetic double resonance pulse, and relates to the technical field of magnetic field precision measurement. Firstly, pumping light passes through a light intensity modulator to generate light pulse with pulse frequency being about Larmor precession frequency and duty ratio being 50% so as to generate macroscopic polarization, then the pumping light is turned off, and the light intensity modulator generates light pulse with pulse frequency being about Larmor precession frequency and duty ratio being 50%; the method comprises the following steps: instantly applying a radio frequency pulse corresponding to the frequency of an optical pulse, controlling a spin polarization vector to a plane vertical to the direction of a magnetic field, removing the radio frequency pulse, generating a free precession signal, and extracting a Larmor precession frequency by processing the free precession signal to obtain magnetic field information. According to the free precession atom magnetometer, enhancement of free precession signals can be achieved, the dead zone of the magnetometer is reduced to be a single axis in the direction of detection light, and a new scheme is provided for application of the free precession atom magnetometer.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic field precision measurement, and in particular to a modulation method and device of a free precession atomic magnetometer based on optical-magnetic double resonance pulse. Background Art

[0002] With the development of laser technology and micro-electro-mechanical system (MEMS) technology, optically pumped magnetometer (OPM) has gradually shown great potential for chip-based manufacturing. At the same time, it has the characteristics of high sensitivity, wide bandwidth, and high dynamic range, and can be applied to geomagnetic navigation, magnetic anomaly detection, mineral exploration and other fields, and has received extensive research and attention at home and abroad. Free-induction-decay (FID) atomic magnetometer, also known as free precession atomic magnetometer, is a new working mode of optically pumped atomic magnetometer. It has the characteristics of high accuracy, simple circuit, and strong robustness, and has gradually become one of the mainstream choices for scientific research and industrialization of optically pumped atomic magnetometer.

[0003] However, the free precession atomic magnetometer extracts magnetic field information by directly processing the free precession signal in the time domain. Therefore, the strength of the free precession signal directly determines the signal-to-noise ratio of the magnetometer, which in turn affects the sensitivity of the magnetometer.

[0004] Therefore, it is necessary to provide a modulation method and device of a free precession atomic magnetometer based on optical-magnetic double resonance pulse to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a free precession atomic magnetometer modulation method and device based on optical-magnetic double resonance pulses. Based on the optical-magnetic modulation technology, a free precession signal is generated by applying an optical-magnetic double resonance pulse for modulation, which can effectively enhance the intensity of the free precession signal and suppress the dead zone of the magnetometer, thereby improving the working performance of the magnetometer and facilitating the precise measurement of the magnetic field.

[0006] To achieve the above object, the present invention provides a modulation method of a free precession atomic magnetometer based on optical-magnetic double resonance pulse, comprising the following steps:

[0007] S1: Turn on the pump laser and the detection laser, adjust the emission frequencies of the pump laser and the detection laser, and make the pump light and the detection light pass through the alkali metal atom gas chamber respectively;

[0008] S2: Control the signal generator to input a square wave pulse with a duty cycle of 50% and a pulse frequency of approximately the Larmor precession frequency corresponding to the magnetic field to the optical intensity modulator to perform optical pumping operation, and remove the modulated optical signal after a period of time;

[0009] S3: At the moment when the input signal from the signal generator to the light intensity modulator is removed, a radio frequency pulse with the same frequency as the square wave pulse frequency of the light intensity modulator is applied, the spin polarization vector is manipulated to a plane perpendicular to the magnetic field direction, and then the radio frequency pulse is removed;

[0010] S4: After removing the input signal from the signal generator to the radio frequency coil, the detection light outputs a free precession signal, and the generated free precession signal is collected by a data acquisition device and processed to obtain magnetic field information.

[0011] Preferably, the adjustment of the pump laser and the detection laser in step S1 specifically includes the following steps:

[0012] S11: Adjust the frequency of the pumping light emitted by the pumping laser to the center of the alkali metal atomic spectrum line D1;

[0013] S12: adjusting the polarization device to generate circularly polarized light, and the circularly polarized light passes through the alkali metal atom gas chamber;

[0014] S13: adjusting the frequency detuning of the detection light emitted by the detection laser to maximize the optical rotation angle of the detection light;

[0015] S14: Generate linearly polarized light through a polarizer, and allow the linearly polarized light to pass through the alkali metal atom gas chamber.

[0016] Preferably, in step S2, the specific steps of the optical pumping operation are as follows:

[0017] S21: inputting a square wave pulse with a frequency of about Larmor precession frequency and a duty cycle of 50% to the light intensity modulator through a signal generator, and removing the input signal after a period of time;

[0018] S22: The duty cycle in step S21 is controlled to remain unchanged, and the frequency of the square wave pulse is changed so that the detection light output signal is maximized when the light intensity modulator input signal is removed, thereby completing the optical pumping operation.

[0019] Preferably, in step S3, the specific steps of controlling the spin polarization vector to be perpendicular to the magnetic field direction are as follows:

[0020] S31: inputting a radio frequency pulse signal with the same frequency as the square wave frequency of the light intensity modulator to the radio frequency coil through a signal generator in a direction perpendicular to the plane of the pumping light and the detection light, and then withdrawing it after it lasts for less than 0.05ms;

[0021] S32: Control the RF field action time and frequency to remain unchanged, adjust the RF input signal amplitude so that the signal amplitude is maximum when the RF pulse is removed, and the spin polarization vector will be controlled to a plane perpendicular to the magnetic field direction.

[0022] Preferably, in step S4, the free precession signal collection and processing specifically includes the following steps:

[0023] S41: After the RF pulse is removed, the spin polarization vector undergoes a free precession process, and the detection light outputs a free precession signal;

[0024] S42: Collecting a free precession signal output by the detection light through a data acquisition device;

[0025] S43: Process the free precession signal, extract the Larmor precession frequency contained in the free precession signal, and obtain magnetic field information.

[0026] A free precession atomic magnetometer device based on optical-magnetic double resonance pulses, including a device for realizing a pumping optical path and a detection optical path of the free precession atomic magnetometer, and steps for realizing a modulation method of the free precession atomic magnetometer based on optical-magnetic double resonance pulses;

[0027] The pumping optical path of the free precession atomic magnetometer passes through the pumping laser, the light intensity modulator, the first half-wave plate, the first polarizer, the reflector, and the quarter-wave plate to reach the alkali metal gas chamber;

[0028] The detection optical path of the free precession atomic magnetometer passes through the detection laser, the second polarizer, the alkali metal gas chamber, the second half-wave plate and then reaches the spectroscopic system;

[0029] A polarization balance differential detection circuit is arranged on one side of the spectroscopic system, a first photodetector and a second photodetector are arranged in parallel on the polarization balance differential detection circuit, the reflection side of the spectroscopic system is connected to the first photodetector, the transmission side of the spectroscopic system is connected to the second photodetector, the output end of the polarization balance differential detection circuit is connected to the input end of the transimpedance amplifier, the output end of the transimpedance amplifier is connected to the input end of the data acquisition device, and the output end of the signal generator is respectively connected to the input end of the light intensity modulator and the input end of the radio frequency coil perpendicular to the direction of the pumping light and the detection light plane.

[0030] Preferably, a first polarizer is arranged between the first half wave plate and the reflector, a quarter wave plate is arranged between the first polarizer and the alkali metal gas chamber, the second polarizer and the second half wave plate are arranged on both sides of the alkali metal gas chamber respectively, a non-magnetic electric heating system is arranged on the outside of the alkali metal gas chamber, and a spectroscopic system is arranged between the second half wave plate and the polarization balance differential detection circuit. All of the above components are arranged in an area surrounded by a radio frequency coil, and the radio frequency coil is arranged in a magnetometer support shell.

[0031] Therefore, the present invention adopts the above-mentioned free precession atomic magnetometer modulation method based on optical and magnetic double resonance pulse, which has the following beneficial effects:

[0032] (1) The present invention is simple to operate and can enhance the free precession signal without increasing the system volume, cost, and complexity, thereby improving the signal-to-noise ratio of the free precession magnetometer and facilitating the improvement of the sensitivity of the magnetometer.

[0033] (2) The present invention reduces the dead zone of the free precession magnetometer to a single-axis dead zone in the detection light direction without changing the magnetometer structure or sacrificing the magnetometer sensitivity, further improving the application flexibility of the free precession atomic magnetometer.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of a modulation method of a free precession atomic magnetometer based on optical-magnetic double resonance pulse of the present invention;

[0036] Figure 2 It is a structural schematic diagram of a free precession atomic magnetometer device based on optical and magnetic double resonance pulses of the present invention;

[0037] Figure 3 It is a timing diagram of a signal waveform applied by a signal generator involved in a free precession atomic magnetometer modulation method based on optical-magnetic double resonance pulses in an embodiment of the present invention;

[0038] Figure Annotation

[0039] 1. Pumping laser; 2. Detection laser; 3. Light intensity modulator; 4. First half-wave plate; 5. First polarizer; 6. Reflector; 7. Quarter-wave plate; 8. Second polarizer; 9. Second half-wave plate; 10. Alkali metal gas chamber; 11. Non-magnetic electric heating system; 12. Spectral system; 13. Polarization balance differential detection circuit; 14. Transimpedance amplifier; 15. Data acquisition equipment; 16. Signal generator; 17. Radio frequency coil; 18. Magnetometer support shell. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0041] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0042] The words "include" or "comprises" and the like used in the present invention mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of also including other elements. The orientation or position relationship indicated by the terms "inside", "outside", "upper", "lower", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention. When the absolute position of the described object changes, the relative position relationship may also change accordingly. In the present invention, unless otherwise clearly specified and limited, the terms "attachment" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral body; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] Example

[0044] like Figure 2 As shown, xyz is the three axes (x-axis, y-axis, z-axis) of the Cartesian coordinate system established with the laboratory pumping light direction as the z-axis; x'y'z' is the three axes (x'-axis, y'-axis, z'-axis) of the Cartesian coordinate system established with the direction of the magnetic field to be measured as the z'-axis; B0 is the magnetic field to be measured; θ is the polar angle of the magnetic field to be measured in the z-axis direction; φ is the azimuth angle of the magnetic field to be measured in the xy plane.

[0045] The present invention provides a modulation method of a free precession atomic magnetometer based on optical-magnetic double resonance pulse, comprising the following steps:

[0046] S1: Turn on the pump laser and the detection laser, adjust the emission frequencies of the pump laser and the detection laser, and respectively make the pump light and the detection light pass through the alkali metal atom gas chamber; in step S1, the adjustment of the pump laser and the detection laser specifically includes the following steps:

[0047] S11: Adjust the frequency of the pumping light emitted by the pumping laser to the center of the alkali metal atomic spectrum line D1;

[0048] S12: adjusting the polarization device to generate circularly polarized light, and the circularly polarized light passes through the alkali metal atom gas chamber;

[0049] S13: adjusting the frequency detuning of the detection light emitted by the detection laser to maximize the optical rotation angle of the detection light;

[0050] S14: Generate linearly polarized light through a polarizer, and allow the linearly polarized light to pass through the alkali metal atom gas chamber.

[0051] S2: Control the signal generator to input a square wave pulse with a duty cycle of 50% and a pulse frequency of approximately the Larmor precession frequency corresponding to the magnetic field to the optical intensity modulator to perform optical pumping operation, and then remove the modulated optical signal after a period of time; Figure 3 As shown, the signal waveform timing is divided into three stages. In the pumping stage, the signal generator inputs a square wave pulse with a frequency of Larmor precession frequency and a duty cycle of 50% to the light intensity modulator; in the RF stage, the signal generator applies an RF pulse with a frequency of Larmor precession frequency to the y-axis of the RF coil; and no signal is input in the detection stage.

[0052] In step S2, the specific steps of the optical pumping operation are as follows:

[0053] S21: inputting a square wave pulse with a frequency of about Larmor precession frequency and a duty cycle of 50% to the light intensity modulator through a signal generator, and removing the input signal after a period of time;

[0054] S22: The duty cycle in step S21 is controlled to remain unchanged, and the frequency of the square wave pulse is changed so that the detection light output signal is maximized when the light intensity modulator input signal is removed, thereby completing the optical pumping operation.

[0055] S3: At the moment when the input signal from the signal generator to the light intensity modulator is removed, a radio frequency pulse with the same frequency as the square wave pulse frequency of the light intensity modulator is applied, and the spin polarization vector is manipulated to a plane perpendicular to the direction of the magnetic field, and then the radio frequency pulse is removed; in step S3, the specific steps of manipulating the spin polarization vector to a plane perpendicular to the direction of the magnetic field are as follows:

[0056] S31: inputting a radio frequency pulse signal with the same frequency as the square wave frequency of the light intensity modulator to the radio frequency coil through a signal generator in a direction perpendicular to the plane of the pumping light and the detection light, and then withdrawing it after it lasts for less than 0.05ms;

[0057] S32: Control the RF field action time and frequency to remain unchanged, adjust the RF input signal amplitude so that the signal amplitude is maximum when the RF pulse is removed, and the spin polarization vector will be controlled to a plane perpendicular to the magnetic field direction.

[0058] S4: After removing the input signal from the signal generator to the RF coil, the detection light outputs a free precession signal, and the generated free precession signal is collected by a data acquisition device and processed to obtain magnetic field information. In step S4, the free precession signal collection and processing specifically includes the following steps:

[0059] S41: After the RF pulse is removed, the spin polarization vector undergoes a free precession process, and the detection light outputs a free precession signal;

[0060] S42: collecting a free precession signal output by the detection light through a data acquisition device;

[0061] S43: Process the free precession signal, extract the Larmor precession frequency contained in the free precession signal, and obtain magnetic field information.

[0062] The laboratory coordinate system is established with the Cartesian coordinate system of the free precession atomic magnetometer, where the x direction is the detection direction, the z direction is the pumping direction, and the y direction is the RF field direction. A pulsed RF field is applied. The main magnetic field direction is at an angle of θ with the z axis, and the projection on the xy plane is at an angle of φ with the y axis.

[0063] In this state, the relationship between the spin polarization vector and the pumping time t1 in step S2 can be described by the following formula:

[0064]

[0065] in, is the pumping rate, R1 is the longitudinal relaxation rate, R2 is the transverse relaxation rate, S x2 , S y2 , S z2 They are respectively the changes of the spin polarization vector in the rotating coordinate system established with the direction of the main magnetic field to be measured as the z” axis.

[0066] In step S3, the pumping is turned off after the pumping is completed, and a radio frequency pulse 2B1cos(ωt2) is applied instantaneously. The time is very short and the relaxation can be ignored. A rotating coordinate system is established with the radio frequency pulse as the y" axis. The change of the spin polarization vector with the radio frequency pulse application time t2 can be described by the following formula:

[0067]

[0068] Where γ is the gyromagnetic ratio, B1 is the RF pulse amplitude, ω is the Larmor precession frequency, δ is the angle between the spin polarization vector in the x”y” plane and the x” axis of the rotating coordinate system at the start of applying the RF pulse,

[0069]

[0070] By controlling the amplitude and time of the RF pulse, the spin polarization vector can be manipulated to the x"y" plane, making the polarization in the z" direction 0. At this time, the spin polarization vector in the x"y" plane is

[0071]

[0072] In step S4, the radio frequency pulse is removed, and the spin polarization vector precesses freely. At this time, in the magnetic field coordinate system established with the magnetic field direction as z', the following is obtained:

[0073]

[0074] Among them, t3 is the free precession time, B0 is the amplitude of the main magnetic field to be measured, is the angle between the spin polarization vector and the x' axis of the magnetic field coordinate system, is the transverse relaxation rate after pumping is turned off, S x1 , S y1 , S z1 They are respectively the changes of the spin polarization vector in the magnetic field coordinate system established with the direction of the main magnetic field to be measured as the z' axis.

[0075] Convert the magnetic field coordinate system to the laboratory coordinate system and we get:

[0076]

[0077] Among them, S x , S y , S z They are respectively the changes of the spin polarization vector in the laboratory coordinate system established with the direction of the laboratory pump light as the z-axis.

[0078] During free precession, after the detection light passes through the polarization balanced differential detection circuit and the transimpedance amplifier, the signal collected by the data acquisition device is

[0079] V signal =AS x

[0080] Among them, V signal is the free precession voltage signal collected by the data acquisition device, and A is the photoelectric amplification factor of the polarization balance differential detection circuit and the transimpedance amplifier.

[0081] like Figure 1 As shown, a free precession atomic magnetometer device based on optical-magnetic double resonance pulses includes a device for realizing a pumping optical path and a detection optical path of the free precession atomic magnetometer, and steps for realizing a modulation method of the free precession atomic magnetometer based on optical-magnetic double resonance pulses;

[0082] The pumping optical path of the free precession atomic magnetometer passes through the pumping laser, the light intensity modulator, the first half-wave plate, the first polarizer, the reflector, and the quarter-wave plate to reach the alkali metal gas chamber;

[0083] The detection optical path of the free precession atomic magnetometer passes through the detection laser, the second polarizer, the alkali metal gas chamber, the second half-wave plate and then reaches the spectroscopic system;

[0084] A polarization balance differential detection circuit is arranged on one side of the spectroscopic system, a first photodetector and a second photodetector are arranged in parallel on the polarization balance differential detection circuit, the reflection side of the spectroscopic system is connected to the first photodetector, the transmission side of the spectroscopic system is connected to the second photodetector, the output end of the polarization balance differential detection circuit is connected to the input end of the transimpedance amplifier, the output end of the transimpedance amplifier is connected to the input end of the data acquisition device, and the output end of the signal generator is respectively connected to the input end of the light intensity modulator and the input end of the radio frequency coil perpendicular to the direction of the pumping light and the detection light plane.

[0085] A first polarizer is arranged between the first half wave plate and the reflector, a quarter wave plate is arranged between the first polarizer and the alkali metal gas chamber, the second polarizer and the second half wave plate are arranged on both sides of the alkali metal gas chamber respectively, a non-magnetic electric heating system is arranged on the outside of the alkali metal gas chamber, and a spectroscopic system is arranged between the second half wave plate and the polarization balance differential detection circuit. All of the above components are arranged in an area surrounded by a radio frequency coil, and the radio frequency coil is arranged in a magnetometer support shell.

[0086] Comparative Example

[0087] In the prior art, under the condition of ensuring the consistency of the average pumping rate of the pumping light, the amplitude of the free precession signal of the free precession atomic magnetometer modulation method using only optical resonance pulses is smaller than that of the present solution. The dead zone of the free precession atomic magnetometer modulation method using only optical resonance pulses is the pumping light direction (z-axis) and the detection light direction (x-axis). The dead zone of the free precession atomic magnetometer modulation method based on optical and magnetic double resonance pulses of the present invention is the detection light direction (x-axis).

[0088] In the prior art, while ensuring the consistency of the average pumping rate of the pumping light, the free precession signal amplitude of the free precession atomic magnetometer modulation method using only magnetic resonance pulses is smaller than that of the present scheme, and the dead zone of the free precession atomic magnetometer modulation method using only optical resonance pulses is the xy plane. The dead zone of the free precession atomic magnetometer modulation method based on optical and magnetic double resonance pulses of the present invention is the detection light direction (x-axis).

[0089] Therefore, the present invention adopts the above-mentioned free precession atomic magnetometer modulation method based on optical and magnetic double resonance pulses, and performs optical pumping and spin polarization vector manipulation by successively applying resonant optical pulses and radio frequency magnetic field pulses to the alkali metal atomic gas chamber, and realizes the free precession signal after the pulse is removed; ultimately, the free precession signal is enhanced without increasing the complexity of the system, the signal-to-noise ratio of the magnetometer is improved, and then the sensitivity of the free precession atomic magnetometer is improved, and in addition, the dead zone suppression of the magnetometer is realized, and the dead zone of the magnetometer is reduced to a single axis in the detection light direction, providing a new solution for the application of the free precession atomic magnetometer.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A modulation method for a free precession atomic magnetometer based on optical-magnetic double resonance pulse, characterized in that: The following steps are involved: S1: Turn on the pump laser and the detection laser, adjust the emission frequencies of the pump laser and the detection laser, and make the pump light and the detection light pass through the alkali metal atom gas chamber respectively; S2: Control the signal generator to input a square wave pulse with a duty cycle of 50% and a pulse frequency of approximately the Larmor precession frequency corresponding to the magnetic field to the optical intensity modulator to perform optical pumping operation, and remove the modulated optical signal after a period of time; S3: At the moment when the input signal from the signal generator to the light intensity modulator is removed, a radio frequency pulse with the same frequency as the square wave pulse frequency of the light intensity modulator is applied, the spin polarization vector is manipulated to a plane perpendicular to the magnetic field direction, and then the radio frequency pulse is removed; S4: After removing the input signal from the signal generator to the radio frequency coil, the detection light outputs a free precession signal, and the generated free precession signal is collected by a data acquisition device and processed to obtain magnetic field information.

2. The modulation method of a free precession atomic magnetometer based on optical-magnetic double resonance pulse according to claim 1, characterized in that: The adjustment of the pump laser and the detection laser in step S1 specifically includes the following steps: S11: Adjust the frequency of the pumping light emitted by the pumping laser to the center of the alkali metal atomic spectrum line D1; S12: adjusting the polarization device to generate circularly polarized light, and the circularly polarized light passes through the alkali metal atom gas chamber; S13: adjusting the frequency detuning of the detection light emitted by the detection laser to maximize the optical rotation angle of the detection light; S14: Generate linearly polarized light through a polarizer, and allow the linearly polarized light to pass through the alkali metal atom gas chamber.

3. The modulation method of a free precession atomic magnetometer based on optical-magnetic double resonance pulse according to claim 1, characterized in that: In step S2, the specific steps of the optical pumping operation are as follows: S21: inputting a square wave pulse with a frequency of about Larmor precession frequency and a duty cycle of 50% to the light intensity modulator through a signal generator, and removing the input signal after a period of time; S22: The duty cycle in step S21 is controlled to remain unchanged, and the frequency of the square wave pulse is changed so that the detection light output signal is maximized when the light intensity modulator input signal is removed, thereby completing the optical pumping operation.

4. The modulation method of a free precession atomic magnetometer based on optical-magnetic double resonance pulse according to claim 1, characterized in that: In step S3, the specific steps of controlling the spin polarization vector to be perpendicular to the magnetic field direction are as follows: S31: inputting a radio frequency pulse signal with the same frequency as the square wave frequency of the light intensity modulator to the radio frequency coil through a signal generator in a direction perpendicular to the plane of the pumping light and the detection light, and then withdrawing it after it lasts for less than 0.05ms; S32: Control the RF field action time and frequency to remain unchanged, adjust the RF input signal amplitude so that the signal amplitude is maximum when the RF pulse is removed, and the spin polarization vector will be controlled to a plane perpendicular to the magnetic field direction.

5. The modulation method of a free precession atomic magnetometer based on optical-magnetic double resonance pulse according to claim 1, characterized in that: In step S4, the free precession signal collection and processing specifically includes the following steps: S41: After the RF pulse is removed, the spin polarization vector undergoes a free precession process, and the detection light outputs a free precession signal; S42: collecting a free precession signal output by the detection light through a data acquisition device; S43: Process the free precession signal, extract the Larmor precession frequency contained in the free precession signal, and obtain magnetic field information.

6. A free-precession atomic magnetometer device based on optical-magnetic double resonance pulse, characterized in that: The device comprises a pumping optical path and a detection optical path of a free precession atomic magnetometer, and implements the steps of a modulation method of a free precession atomic magnetometer based on a photomagnetic double resonance pulse as described in any one of claims 1 to 5; The pumping optical path of the free precession atomic magnetometer passes through the pumping laser, the light intensity modulator, the first half-wave plate, the first polarizer, the reflector, and the quarter-wave plate to reach the alkali metal gas chamber; The detection optical path of the free precession atomic magnetometer passes through the detection laser, the second polarizer, the alkali metal gas chamber, the second half-wave plate and then reaches the spectroscopic system; A polarization balance differential detection circuit is arranged on one side of the spectroscopic system, a first photodetector and a second photodetector are arranged in parallel on the polarization balance differential detection circuit, the reflection side of the spectroscopic system is connected to the first photodetector, the transmission side of the spectroscopic system is connected to the second photodetector, the output end of the polarization balance differential detection circuit is connected to the input end of the transimpedance amplifier, the output end of the transimpedance amplifier is connected to the input end of the data acquisition device, and the output end of the signal generator is respectively connected to the input end of the light intensity modulator and the input end of the radio frequency coil perpendicular to the direction of the pumping light and the detection light plane.

7. The free precession atomic magnetometer device based on optical and magnetic double resonance pulses according to claim 6, characterized in that: A first polarizer is arranged between the first half wave plate and the reflector, a quarter wave plate is arranged between the first polarizer and the alkali metal gas chamber, the second polarizer and the second half wave plate are arranged on both sides of the alkali metal gas chamber respectively, a non-magnetic electric heating system is arranged on the outside of the alkali metal gas chamber, and a spectroscopic system is arranged between the second half wave plate and the polarization balance differential detection circuit. All of the above components are arranged in an area surrounded by a radio frequency coil, and the radio frequency coil is arranged in a magnetometer support shell.

Images