Compact atom magnetometer based on coaxial pumping-detection and measurement method

Abstract

The invention discloses a compact atom magnetometer based on coaxial pumping-detection and a measurement method, and the compact atom magnetometer comprises a light beam combination system which is used for coupling pumping laser and detection laser to the same polarization maintaining optical fiber, and obtaining combined light; the atom magnetometer header system is used for receiving the combined light and generating a differential detection signal through decoupling, shaping, beam combination and differential detection; and the signal processing system is used for amplifying, demodulating and collecting the differential detection signal to obtain the information of the magnetic field to be detected. The coaxial pumping-detection scheme penetrates through the whole optical path, the coaxial pumping-detection scheme is adopted in the optical path inside the atomic magnetometer header and the external light beam combining part, and compared with a traditional orthogonal pumping-detection scheme, the structure is more compact, and miniaturization development of the double-beam-configuration atomic magnetometer is promoted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of atomic magnetometer, and particularly relates to a compact atomic magnetometer based on coaxial pumping-detection and a measurement method. BACKGROUND

[0002] Quantum magnetometers have always attracted the attention of researchers. The Spin-Exchange Relaxation-Free (SERF) atomic magnetometer realizes full inhibition of spin exchange relaxation under the conditions of high atomic density and low environmental magnetic field. In this state, the electron spin of alkali metal atoms has a longer relaxation time, thereby greatly improving the sensitivity of magnetic field measurement. However, the traditional double-beam magnetometer has high sensitivity but large volume, and the single-beam magnetometer has a compact structure but limited sensitivity. In brain science research, the application of brain magnetic detection technology is increasingly widespread, providing people with a deeper understanding of the operation of healthy and disease-affected brains. Therefore, it is of great significance to realize the close fitting of the measurement probe and the cerebral cortex by studying a brain magnetic measurement system based on a miniaturized SERF atomic magnetometer, which has the advantages of low cost, light weight, and flexible installation in any light and soft helmet with a head shape. SUMMARY

[0003] To solve the above technical problems, the application provides a compact atomic magnetometer based on coaxial pumping-detection and a measurement method. The compact atomic magnetometer based on coaxial pumping-detection comprises:

[0004] A light combining system is configured to couple the pumping laser and the detection laser into the same polarization maintaining optical fiber to obtain combined light.

[0005] An atomic magnetometer head system is configured to receive the combined light and generate a differential detection signal through decoupling, shaping, combining, and differential detection.

[0006] A signal processing system is configured to amplify, demodulate, and collect the differential detection signal to obtain the to-be-measured magnetic field information.

[0007] Preferably, the light combining system comprises:

[0008] A linear polarizer is configured to perform linear polarization processing on the pumping laser and the detection laser to generate first linearly polarized light.

[0009] A first polarization beam splitter is configured to couple the first linearly polarized light into the polarization maintaining optical fiber to generate the combined light.

[0010] Preferably, the atomic magnetometer head system comprises:

[0011] a second polarization beam splitter, configured to receive the combined light and decouple the combined light to output the pump light and the probe light respectively;

[0012] a first optical shaping module, configured to perform circular polarization and hollowing processing on the pump light to generate a circularly polarized hollow pump light beam;

[0013] a second optical shaping module, configured to perform center region interception on the probe light to generate a center probe light beam;

[0014] a beam splitting prism, configured to coaxially combine the circularly polarized hollow pump light beam and the center probe light beam to generate a coaxial pump-probe light beam, and configured to keep the pump light component in the coaxial pump-probe light beam as circularly polarized light and the probe light component as linearly polarized light;

[0015] an alkali metal cell, configured to receive the coaxial pump-probe light beam and interact with alkali metal atoms inside the alkali metal cell to generate a polarized atomic medium;

[0016] a third optical shaping module, configured to perform spatial filtering and polarization processing on the light beam passing through the polarized atomic medium to generate a to-be-measured light beam;

[0017] a photodetector, configured to perform differential detection on the to-be-measured light beam to generate the differential detection signal.

[0018] Preferably, the first optical shaping module comprises:

[0019] a quarter-wave plate, configured to convert the pump light from linearly polarized light to circularly polarized light;

[0020] a first customized diaphragm, configured to block a center region of the circularly polarized light to obtain the circularly polarized hollow pump light beam.

[0021] Preferably, the second optical shaping module comprises:

[0022] a mirror group, configured to reflect and collimate the probe light;

[0023] a second customized diaphragm, configured to block an edge region of the probe light to obtain the center probe light beam;

[0024] wherein a light passing aperture of the second customized diaphragm matches a size of an intercepted region of the first customized diaphragm.

[0025] Preferably, the alkali metal atoms in the alkali metal cell are potassium, rubidium or cesium atoms;

[0026] The alkali metal cell is placed in a ceramic oven, and the ceramic oven is driven by a power amplifier to heat the alkali metal cell to a SERF working state.

[0027] Preferably, the third optical shaping module comprises:

[0028] a third custom diaphragm for spatially filtering the light beam after passing through the polarized atomic medium, blocking the pump light after passing through the polarized atomic medium;

[0029] a half-wave plate for rotating the polarization of the filtered light beam;

[0030] a third polarization beam splitter for splitting the light beam after polarization rotation into two beams of orthogonal polarized light and outputting them to the photodetector respectively.

[0031] Preferably, the signal processing system comprises:

[0032] a transimpedance amplifier for current-voltage conversion and amplification of the differential detection signal, generating an amplified signal;

[0033] a lock-in amplifier for harmonic demodulation of the amplified signal, extracting in-phase and quadrature components;

[0034] a data acquisition device for acquiring the in-phase and quadrature components, outputting the measured magnetic field information.

[0035] The application also provides a measurement method of a compact atomic magnetometer based on coaxial pump-probe, comprising:

[0036] coupling the pump laser and the probe laser into the same polarization maintaining optical fiber through the light beam combining system, obtaining a combined light beam;

[0037] receiving the combined light beam by the atomic magnetometer head system and generating a differential detection signal through decoupling, shaping, combining and differential detection;

[0038] amplifying, demodulating and acquiring the differential detection signal through the signal processing system, obtaining the measured magnetic field information.

[0039] Preferably, the process of amplifying, demodulating and acquiring the differential detection signal through the signal processing system to obtain the measured magnetic field information comprises:

[0040] heating the alkali metal cell in the atomic magnetometer head system to make the atomic magnetometer in normal working state, and applying a modulation magnetic field B mod cos(ωt) along the x-axis; wherein B mod is the amplitude of the modulation magnetic field, ω is the angular frequency, and t is the time;

[0041] demodulating the first harmonic component of the differential detection signal through the lock-in amplifier in the signal processing system, obtaining the in-phase and quadrature components;

[0042] Collect in-phase and quadrature components to obtain the measurement results of the magnetic field to be measured along the x-axis.

[0043] Compared with the prior art, the present invention has the following advantages and technical effects:

[0044] This invention employs a coaxial optical path design, shaping the pump laser into a hollow beam and coaxially transmitting the probe beam along its central axis. This coaxial design retains the high sensitivity advantages of a dual-beam system without requiring orthogonal optical structures, while achieving a compact sensor structure. The resulting compactness makes this device particularly suitable for constructing high-density sensor arrays, and it can be widely used in biomedical imaging fields such as magnetoencephalography (MEG) and magnetocardiography (MCG), where spatial resolution is critical.

[0045] This invention incorporates a coaxial pump-probe scheme throughout the entire optical path. The coaxial pump-probe scheme is used in both the internal optical path of the atomic magnetometer head and the external optical beam combining section. Compared with the traditional orthogonal pump-probe scheme, the structure is more compact, which promotes the miniaturization of the dual-beam configuration atomic magnetometer.

[0046] This invention relates to an atomic magnetometer based on a coaxial pump-probe scheme, which effectively avoids the optical frequency shift noise introduced by the dual-beam configuration scheme based on elliptical polarized light, thus ensuring a higher signal-to-noise ratio and measurement stability. Attached Figure Description

[0047] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0048] Figure 1 This is a schematic diagram of the structure of a compact atomic magnetometer based on coaxial pump-probe according to an embodiment of the present invention;

[0049] Among them, 1. Atomic magnetometer meter head system; 2. Optical beam combining system; 3. Signal processing system; 101. First fiber collimator; 102. Beam combining beam; 103. Second polarization beam splitter; 104. Quarter-wave plate; 105. First custom-made aperture; 106. Alkali metal gas chamber; 107. Ceramic oven; 108. Second custom-made aperture; 109. Half-wave plate; 110. Photodetector; 111. Differential amplifier; 112. 113. Mirror assembly; 114. Beam splitter; 115. Third custom aperture; 116. Third polarization beam splitter; 201. Pump laser; 202. Probe laser; 203. Polarization-maintaining fiber; 204. Second fiber collimator; 205. Linear polarizer; 206. First polarization beam splitter; 207. Fiber coupling head; 301. Transimpedance amplifier; 302. Lock-in amplifier; 303. Data acquisition unit; 304. Power amplifier. Detailed Implementation

[0050] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0051] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0052] like Figure 1 As shown, this embodiment provides a compact atomic magnetometer based on coaxial pump-probe, comprising:

[0053] The optical beam combining system 2 is used to couple the pump laser and the probe laser to the same polarization-maintaining fiber to obtain combined light;

[0054] The atomic magnetometer head system 1 is used to receive the combined beam light and generate a differential detection signal through decoupling, shaping, beam combining and differential detection;

[0055] Signal processing system 3 is used to amplify, demodulate and acquire the differential detection signal to obtain the magnetic field information to be measured.

[0056] Furthermore, the optical beam combining system 2 includes: a pump laser 201, a probe laser 202, a polarization-maintaining fiber 203, a second fiber collimator 204, a linear polarizer 205, a first polarization beam splitter 206, and a fiber coupler 207.

[0057] Among them, the linear polarizer 205 is used to perform linear polarization processing on the pump laser and the probe laser to generate the first linearly polarized light;

[0058] The first polarization beam splitter 206 is used to couple the first linearly polarized light to the polarization-maintaining fiber to generate a combined beam.

[0059] Furthermore, in the optical beam combining system 2, the pump laser 201 and the probe laser 202 are coupled to a single polarization-maintaining fiber 203 in sequence through a linear polarizer 205 and a first polarization beam splitter 206.

[0060] The optical beam combining system 2 couples the pump laser and the probe laser into the same polarization-maintaining fiber 203, and then uses the polarization-maintaining fiber 203 as the input light source of the atomic magnetometer meter head system 1, saving space and avoiding the additional noise introduced by multiple optical fibers.

[0061] In the optical beam combining system 2, the pump laser 201 emits a laser at the D1 line resonance frequency of alkali metal atoms, and the probe laser 202 emits a laser that is approximately 100 GHz detuned to the D2 line resonance frequency of alkali metal atoms. The two laser beams are coupled to a single polarization-maintaining fiber 203 in sequence through a linear polarizer 205 and a first polarization beam splitter 206.

[0062] Furthermore, the atomic magnetometer meter head system 1 includes: a first fiber collimator 101, a beam combiner 102, a second polarization beam splitter 103, a quarter-wave plate 104, a first custom-made aperture 105, an alkali metal gas chamber 106, a ceramic oven 107, a second custom-made aperture 108, a half-wave plate 109, a photodetector 110, a differential amplifier 111, a mirror assembly 112, a beam splitter prism 113, a third custom-made aperture 114, and a third polarization beam splitter 115;

[0063] The second polarization beam splitter 103 is used to receive the combined beam and decouple it, and output pump light and probe light respectively.

[0064] The first optical shaping module is used to perform circular polarization and hollowing processing on the pump light to generate a circularly polarized hollow pump beam.

[0065] The second optical shaping module is used to extract the central region of the probe light to generate a central probe beam.

[0066] Beam splitter 113 is used to coaxially combine a circularly polarized hollow pump beam and a central probe beam to generate a coaxial pump-probe beam. Simultaneously, the beam splitter maintains that the pump light component of the coaxial pump-probe beam is circularly polarized and the probe light component is linearly polarized.

[0067] Furthermore, in the atomic magnetometer head system 1, the combined beam 102 emitted from the single polarization-maintaining fiber 203 is decoupled by the second polarization beam splitter 103. The decoupled pump beam is sequentially connected to a quarter-wave plate 104 and a first custom-designed aperture 105, shaping the pump beam into a circularly polarized hollow beam. The decoupled probe beam is sequentially connected to the second custom-designed aperture 108 of the mirror assembly 112. The mirror assembly 112 includes a first mirror and a second mirror; the hollow pump beam and the probe beam are combined by a beam splitter prism 113, and the probe laser is guided through the central space of the hollow pump beam, allowing the two beams to propagate coaxially. The coaxially propagating pump-probe laser is sequentially connected to an alkali metal gas cell 106, a third custom-designed aperture 114, a half-wave plate 109, and a third polarization beam splitter 115, and is finally differentially detected by a photodetector 110. The photodetector 110 includes a first photodetector and a second photodetector.

[0068] The beam splitter prism 113 keeps the polarization state of the incident pump and probe lasers unchanged, meaning that the pump laser after emission is still circularly polarized light and the probe laser is still linearly polarized light.

[0069] The coaxially propagating pump-probe laser passes through the alkali metal gas chamber 106. The outer pump laser polarizes the alkali metal atoms, which then diffuse to the central region. The probe laser in the central region interacts with the polarized atoms, thus reflecting information about the magnetic field to be measured. A third custom aperture blocks the pump laser, allowing only the probe laser to pass through. The probe laser then passes sequentially through a half-wave plate 109 and a third polarization beam splitter 115, and is finally differentially detected by a photodetector 110.

[0070] Furthermore, the first optical shaping module includes:

[0071] A quarter-wave plate 104 is used to convert pump light from linearly polarized to circularly polarized light.

[0072] The first custom aperture 105 is used to block the central region of circularly polarized light to obtain a circularly polarized hollow pump beam.

[0073] Furthermore, the second optical shaping module includes:

[0074] The reflector group 112 is used to reflect and collimate the probe light.

[0075] The second custom aperture 108 is used to block the edge region of the detection light to obtain the central detection beam;

[0076] The aperture of the second custom aperture 108 is matched with the size of the interception area of ​​the first custom aperture 105.

[0077] Furthermore, the first custom aperture 105 intercepts light from the central region of the pump laser, thus forming a hollow beam. The second custom aperture 108 intercepts light from the edge region of the probe laser, allowing only light from the central region to pass through. The aperture size of the second custom aperture 108 is matched to the size of the light intercepted by the first custom aperture 105. The third custom aperture 114 is identical to the second custom aperture 108.

[0078] Furthermore, the atomic magnetometer meter head system 1 also includes:

[0079] Alkali metal gas chamber 106 is used to receive the coaxial pump-probe beam and interact with the alkali metal atoms inside to generate a polarized atomic medium;

[0080] The third optical shaping module is used to perform spatial filtering and polarization processing on the beam after it passes through the polarized atomic medium to generate the beam to be measured.

[0081] The photodetector 110 is used to perform differential detection on the beam under test and generate a differential detection signal.

[0082] Furthermore, the alkali metal atoms in the alkali metal gas chamber 106 are potassium, rubidium, or cesium atoms;

[0083] The alkali metal chamber 106 is placed inside the ceramic oven 107, which is driven by the power amplifier 304 to heat the alkali metal chamber 106 to the SERF operating state.

[0084] Furthermore, the third optical shaping module includes:

[0085] The third custom aperture 114 is used to spatially filter the beam after it passes through the polarized atomic medium and block the pump light after it passes through the polarized atomic medium.

[0086] Half-wave plate 109 is used to perform polarization rotation on the filtered beam;

[0087] The third polarization beam splitter 115 is used to split the polarization-rotated beam into two orthogonally polarized beams and output them to the photodetector respectively.

[0088] Furthermore, the signal processing system 3 includes:

[0089] Transimpedance amplifier 301 is used to perform current-to-voltage conversion and amplification on differential detection signals to generate amplified signals;

[0090] The lock-in amplifier 302 is used to perform harmonic demodulation on the amplified signal and extract the in-phase and quadrature components.

[0091] The data acquisition unit 303 is used to acquire in-phase and quadrature components and output the magnetic field information to be measured.

[0092] Furthermore, the frequency of the pump laser 201 is set to the D1 resonance frequency of the alkali metal atom;

[0093] The frequency of the probe laser 202 is set to be 100 GHz detuned relative to the D2 resonance frequency of the alkali metal atom.

[0094] Furthermore, in the signal processing system 3, the differential detection signal is amplified by the transimpedance amplifier 301 and demodulated by the lock-in amplifier 302 to obtain the first harmonic component as the detection result of the magnetometer on the magnitude of the magnetic field, which is finally acquired by the data acquisition unit 303.

[0095] Based on the same inventive concept, this embodiment also provides a measurement method for a compact atomic magnetometer based on coaxial pump-probe, including the following steps:

[0096] A combined beam is obtained by coupling the pump laser and the probe laser to the same polarization-maintaining fiber using an optical beam combining system.

[0097] The atomic magnetometer meter head system receives the combined beam light and generates a differential detection signal through decoupling, shaping, beam combining, and differential detection.

[0098] The differential detection signal is amplified, demodulated, and acquired by the signal processing system to obtain the magnetic field information to be measured.

[0099] Furthermore, the process of amplifying, demodulating, and acquiring the differential detection signal through a signal processing system, and measuring the magnetic field to obtain the information of the magnetic field to be measured, includes:

[0100] Step 1: Heat the alkali metal gas chamber 106 in the atomic magnetometer head system 1 to bring the atomic magnetometer into normal working condition, and apply a modulation magnetic field B along the x-axis. mod cos(ωt), where B mod ω is the amplitude of the modulating magnetic field, ω is the angular frequency, and t is the time.

[0101] Step 2: The first harmonic component of the differential detection signal is demodulated by the lock-in amplifier 302 in the signal processing system 3 to obtain the in-phase and quadrature components.

[0102] Step 3: Collect in-phase and quadrature components to achieve the measurement of the magnetic field to be measured along the x-axis and obtain the measurement results of the magnetic field to be measured along the x-axis.

[0103] Specifically, the measurement method for a compact atomic magnetometer based on coaxial pump-probe includes the following expressions:

[0104]

[0105] ΔV=KP z(1st) +C

[0106] Where n is the magnetic resonance order, ω is the angular frequency of the modulated magnetic field applied along the x-axis, and P z(1st) It is the first harmonic component of electron spin polarization along the z-direction obtained by demodulation using a lock-in amplifier. It is the in-phase component of the first harmonic. It is the orthogonal component of the first harmonic, R op Γ is the optical pump rate, Γ is the spin relaxation rate, and J is the optical pump rate. n (m) is the nth-order Bessel function of the first kind, m is the modulation index, γ is the gyromagnetic ratio of the electron, and B x ΔV is the magnetic field to be measured in the x-direction, K is the differential detection signal, and C is the linear fitting coefficient.

[0107] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A compact atomic magnetometer based on coaxial pump-probe, characterized in that, include: An optical beam combining system is used to couple pump lasers and probe lasers to the same polarization-maintaining fiber to obtain combined light. An atomic magnetometer head system is used to receive the combined beam and generate a differential detection signal through decoupling, shaping, beam combining, and differential detection. The signal processing system is used to amplify, demodulate, and acquire the differential detection signal to obtain the magnetic field information to be measured.

2. The compact atomic magnetometer based on coaxial pump-probe according to claim 1, characterized in that, The optical beam combining system includes: A linear polarizer is used to linearly polarize the pump laser and the probe laser to generate first linearly polarized light. A first polarization beam splitter is used to couple the first linearly polarized light to the polarization-maintaining fiber to generate the combined beam.

3. The compact atomic magnetometer based on coaxial pump-probe according to claim 1, characterized in that, The atomic magnetometer head system includes: The second polarization beam splitter is used to receive the combined beam and decouple it, and output pump light and probe light respectively. The first optical shaping module is used to perform circular polarization and hollowing processing on the pump light to generate a circularly polarized hollow pump beam. The second optical shaping module is used to extract the central region of the probe light to generate a central probe beam. A beam splitter is used to coaxially combine the circularly polarized hollow pump beam and the central probe beam to generate a coaxial pump-probe beam; it is also used to maintain the pump light component of the coaxial pump-probe beam as circularly polarized light and the probe light component as linearly polarized light. An alkali metal gas chamber is used to receive a coaxial pump-probe beam and interact with the alkali metal atoms inside to generate a polarized atomic medium. The third optical shaping module is used to perform spatial filtering and polarization processing on the beam after it passes through the polarized atomic medium to generate the beam to be tested. A photodetector is used to perform differential detection on the beam to be measured and generate the differential detection signal.

4. The compact atomic magnetometer based on coaxial pump-probe according to claim 3, characterized in that, The first optical shaping module includes: A quarter-wave plate is used to convert the pump light from linearly polarized to circularly polarized light. A first custom aperture is used to block the central region of the circularly polarized light to obtain the circularly polarized hollow pump beam.

5. The compact atomic magnetometer based on coaxial pump-probe according to claim 3, characterized in that, The second optical shaping module includes: A set of reflectors is used to reflect and collimate the probe light; A second custom aperture is used to block the edge region of the detection light to obtain the central detection beam; The aperture of the second custom aperture matches the size of the interception area of ​​the first custom aperture.

6. The compact atomic magnetometer based on coaxial pump-probe according to claim 3, characterized in that, The alkali metal atoms in the alkali metal chamber are potassium, rubidium, or cesium atoms; The alkali metal chamber is placed inside a ceramic oven, which is driven by a power amplifier to heat the alkali metal chamber to a state of spin-free exchange relaxation.

7. The compact atomic magnetometer based on coaxial pump-probe according to claim 3, characterized in that, The third optical shaping module includes: A third custom aperture is used to spatially filter the light beam after it passes through the polarized atomic medium and block the pump light after it passes through the polarized atomic medium. A half-wave plate is used to polarize and rotate the filtered beam. The third polarization beam splitter is used to split the polarization-rotated beam into two orthogonally polarized beams and output them to the photodetector respectively.

8. The compact atomic magnetometer based on coaxial pump-probe according to claim 1, characterized in that, The signal processing system includes: A transimpedance amplifier is used to perform current-to-voltage conversion and amplification on the differential detection signal to generate an amplified signal; A lock-in amplifier is used to perform harmonic demodulation on the amplified signal and extract the in-phase and quadrature components. A data acquisition unit is used to acquire the in-phase component and the quadrature component, and output the magnetic field information to be measured.

9. A measurement method for a compact atomic magnetometer based on coaxial pump-probe, characterized in that, include: A combined beam is obtained by coupling the pump laser and the probe laser to the same polarization-maintaining fiber using an optical beam combining system. The atomic magnetometer meter head system receives the combined beam and generates a differential detection signal through decoupling, shaping, beam combining, and differential detection. The differential detection signal is amplified, demodulated, and acquired by a signal processing system to obtain the magnetic field information to be measured.

10. The measurement method of the compact atomic magnetometer based on coaxial pump-probe according to claim 9, characterized in that, The process of amplifying, demodulating, and acquiring the differential detection signal through a signal processing system to obtain the magnetic field information to be measured includes: The alkali metal gas chamber in the atomic magnetometer's meter head system is heated to bring the atomic magnetometer into normal operating condition, and a modulating magnetic field B is applied along the x-axis. mod cos(ωt); where B mod ω is the amplitude of the modulating magnetic field, ω is the angular frequency, and t is time; The first harmonic component of the differential detection signal is demodulated by the lock-in amplifier in the signal processing system to obtain the in-phase and quadrature components; Collect in-phase and quadrature components to obtain the measurement results of the magnetic field to be measured along the x-axis.

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