Traceable multi-mode extremely low field magnetometer and method

Abstract

A traceable multi-mode extremely weak magnetic field measuring device and method, comprising helium-3 atoms and an atomic magnetometer in a spin-exchange relaxation-free state, the helium-3 atoms polarized by metastable exchange optical pumping under an extremely weak magnetic field provide a traceable magnetic field value for the atomic magnetometer, the value is compared with the output response of the atomic magnetometer to obtain a calibrated scale factor of the atomic magnetometer, so that the measurement values of the atomic magnetometer are traceable. The atomic magnetometer meter head comprises four independent detection channels, the four detection channels are obtained by beam splitting of two detection lasers with different frequency detuning amounts, and the channels have high consistency. The method proposed by the application is compatible with the cooperative use of multiple probes, and can realize single-meter-head multi-channel measurement, meter-head internal magnetic field gradient measurement and meter-head inter-magnetic field gradient measurement three measurement modes, each mode has high consistency and high sensitivity.

Description

Technical Field

[0001] This invention relates to a traceable multi-mode extremely weak magnetic field measurement device and method, belonging to the field of atomic magnetometer technology. Background Technology

[0002] SERF (Spin-Exchange-Relaxation-Free) atomic magnetometers are instruments for measuring extremely weak magnetic fields with ultra-high measurement sensitivity, and they have broad application prospects in medical research, paleogeological testing, cutting-edge physics research, industrial flaw detection, and diagnostics. Although SERF atomic magnetometers possess extremely sensitive relative measurement performance, they are limited by factors such as their own zero-point error and optical frequency shift error, typically requiring a complex calibration process before use. Furthermore, conventional SERF atomic magnetometers use a DC detection beam for detection, making the measurement results susceptible to low-frequency noise interference, and their limited number of channels restricts the amount of information that can be acquired. Helium-3 atoms are inert gas atoms with high traceability accuracy, and polarized helium-3 atoms are often used as high-precision measuring instruments to calibrate other magnetometers. However, due to limitations in readout methods, helium-based magnetic measurements are rarely used in extremely weak magnetic field environments. Summary of the Invention

[0003] This invention proposes a traceable multi-mode extremely weak magnetic field measurement device and method. The method utilizes an ultra-sensitive SERF atomic magnetometer placed near a helium-3 atom gas cell. Under an extremely weak magnetic field, the SERF atomic magnetometer measures the free precession signal of the polarized helium-3 atom magnetic moment. The frequency of this precession signal can be directly traced back to the international basic unit of physical quantity, thus accurately obtaining the magnitude of the current extremely weak magnetic field. The obtained magnitude of the extremely weak magnetic field can be used to calibrate the SERF atomic magnetometer online in situ, thereby obtaining the relationship between the SERF atomic magnetometer's output voltage and the scale of the extremely weak magnetic field, avoiding measurement inaccuracies caused by zero-point drift during long-term use of the SERF atomic magnetometer. The calibrated SERF atomic magnetometer's detection beam is designed with four channels: channel 1, channel 2, channel 3, and channel 4. These are obtained by splitting two lasers with different operating frequencies through a 2×2 high-speed optical switch and two 5:5 fiber beam splitters. The pump beam is designed to be pumped from both ends of the alkali metal atom gas cell in a counter-current mode, thus ensuring polarization uniformity. Channels 1 and 2 are split by the same fiber optic beam splitter and have the same optical parameters, as do channels 3 and 4. The high-speed optical switch operates in pulse mode, generating frequency-modulated detection beams in all four channels to obtain the optical rotation angle measurements for each channel. Different combinations of these measurements yield scalar and gradient information for the extremely weak magnetic field. Because the measurement process uses a frequency-modulated detection mode, low-frequency electrical noise interference is isolated, resulting in high sensitivity for all four channels. Furthermore, all measurement results are calibrated online using helium-3 atoms, ensuring transferability and traceability.

[0004] The technical solution of the present invention is as follows:

[0005] A traceable multi-mode extremely weak magnetic field measurement device, characterized in that it includes SERF atomic magnetometer heads A and B spaced apart along the x-axis, with a helium-3 atomic magnetic field measurement traceability standard system disposed within the interval. The helium-3 atomic magnetic field measurement traceability standard system includes a helium-3 atomic gas chamber, which is connected to a helium-3 atomic pump laser so that the helium-3 atomic pump light passes through the helium-3 atomic gas chamber along the z-axis. The pump laser in the SERF atomic magnetometer head A is decomposed into a first pump by a 5:5 fiber beam splitter C. The first pump light passes sequentially through a pump light collimator A, a circular polarization generator A, and a pump light reflector A before entering the alkali metal atom gas cell from the positive z-axis. The second pump light passes sequentially through a pump light collimator B, a circular polarization generator B, and a pump light reflector B before entering the alkali metal atom gas cell from the negative z-axis. The SERF atomic magnetometer head A is provided with four channels for matching four detection beams passing through the alkali metal atom gas cell from the positive y-axis. The detection beam output signals of the four channels are connected to the SERF atomic magnetometer controller A via a signal bus.

[0006] The helium-3 atom gas chamber is connected to the helium-3 atom pump laser via a laser beam expander. The laser beam expander, the helium-3 atom gas chamber, the SERF atomic magnetometer head A and the SERF atomic magnetometer head B are all located inside a magnetically shielded barrel. The SERF atomic magnetometer head B is connected to the SERF atomic magnetometer controller B.

[0007] Of the four channels, channel 1 is located in the second quadrant of the xz plane in the alkali metal atom gas cell, channel 2 is located in the third quadrant, channel 3 is located in the first quadrant, and channel 4 is located in the fourth quadrant. The detection light collimator of channel 1 and the detection light collimator of channel 2 are respectively connected to a 5:5 fiber beam splitter A. The detection light collimator of channel 3 and the detection light collimator of channel 4 are respectively connected to a 5:5 fiber beam splitter B. The 5:5 fiber beam splitter A is connected to the first output terminal of the high-speed optical switch, and the 5:5 fiber beam splitter B is connected to the second output terminal of the high-speed optical switch. The first input terminal of the high-speed optical switch is connected to the detection laser A, and the second input terminal of the high-speed optical switch is connected to the detection laser B. The laser frequency of the detection laser A is red detuned to the D1 line resonance frequency of the alkali metal atom, and the laser frequency of the detection laser B is blue detuned to the D1 line resonance frequency of the alkali metal atom.

[0008] The output of the signal bus is connected to the output display module in sequence through a data memory, a lock-in amplifier, and a data analyzer. The input of the signal bus is connected to the differential signals of channel 1, channel 2, channel 3, and channel 4, respectively.

[0009] The alkali metal atom gas chamber is located inside the ceramic oven.

[0010] The detection light emission side of the alkali metal atom gas cell is respectively provided with a first half-wave plate, a second half-wave plate, a third half-wave plate, and a fourth half-wave plate. The first half-wave plate is sequentially connected to a first lateral displacement polarization beam splitter, a channel 1 photodetector group, and a channel 1 subtractor. The channel 1 subtractor outputs a channel 1 differential signal. The second half-wave plate is sequentially connected to a second lateral displacement polarization beam splitter, a channel 3 photodetector group, and a channel 3 subtractor. The channel 3 subtractor outputs a channel 3 differential signal. The third half-wave plate is sequentially connected to a third lateral displacement polarization beam splitter, a channel 2 photodetector group, and a channel 2 subtractor. The channel 2 subtractor outputs a channel 2 differential signal. The fourth half-wave plate is sequentially connected to a fourth lateral displacement polarization beam splitter, a channel 4 photodetector group, and a channel 4 subtractor. The channel 4 subtractor outputs a channel 4 differential signal.

[0011] A traceable multi-mode extremely weak magnetic field measurement method, characterized in that it employs the aforementioned traceable multi-mode extremely weak magnetic field measurement device.

[0012] Includes the following steps:

[0013] Step 1: Set the laser frequency of detection laser A to the red detuned frequency of the D1 line resonance of alkali metal atoms, and the laser power to I. Set the laser frequency of detection laser B to the blue detuned frequency of the D1 line resonance of alkali metal atoms, and the laser power to I. Set the driving signal of the high-speed optical switch to a pulse signal with a duty cycle of 50% and a frequency of Ω. The lasers emitted by detection lasers A and B are transmitted to the high-speed optical switch through a polarization-maintaining fiber.

[0014] Step 2: Adjust the optical axis angle of the first half-wave plate so that the S-ray and P-ray obtained by the first lateral displacement polarization beam splitter have the same power. Adjust the optical axis angle of the second half-wave plate so that the S-ray and P-ray obtained by the second lateral displacement polarization beam splitter have the same power. Perform the same operation on the optical paths of the detection collimator in channel 2 and the detection collimator in channel 4.

[0015] Step 3: Turn on the helium-3 atom pump laser and set the laser frequency to 1083.3 nm. Use the metastable exchange light pumping method to polarize the helium-3 atoms in the helium-3 atom gas chamber, so that the polarizability of the helium-3 atoms reaches the set value P. At this time, turn off the helium-3 atom pump laser, stop the metastable exchange light pumping method, and let the helium-3 atoms precess freely in the magnetic field.

[0016] Step 4: Run SERF atomic magnetometer controller A and SERF atomic magnetometer controller B. Place SERF atomic magnetometer head A and SERF atomic magnetometer head B close to the helium-3 atom gas chamber to measure the free precession signal of the helium-3 atoms. For SERF atomic magnetometer head A, use frequency Ω in the lock-in amplifier to demodulate the differential signals of channel 1, channel 2, channel 3, and channel 4 respectively, obtaining the corresponding demodulation results V1(t), V2(t), V3(t), and V4(t). Fit V1(t), V2(t), V3(t), and V4(t) to obtain the precession frequency ω of the helium-3 atoms. Then, the magnetic field B0 in the environment is B0 = γω, where γ is the gyromagnetic ratio of the helium-3 atoms. Perform the same operation on SERF atomic magnetometer head B as on SERF atomic magnetometer head A.

[0017] Step 5: Obtain the calibration scale coefficients k1= B0 / V1(t), k2= B0 / V2(t), k3= B0 / V3(t), and k4= B0 / V4(t) for the measurement results of channels 1, 2, 3, and 4 in SERF atomic magnetometer head A. This completes the calibration of the scale coefficients for the four channels in SERF atomic magnetometer head A. Perform the same operation on SERF atomic magnetometer head B to obtain the scale coefficients for the four channels as g1, g2, g3, and g4, respectively.

[0018] Step 6, apply the magnetic field B to be measured. c The distance between SERF atomic magnetometer head A and SERF atomic magnetometer head B is measured as L. The measurement results of the four channels obtained by SERF atomic magnetometer head A are V1(t)', V2(t)', V3(t)', V4(t)', and the measurement results of the four channels obtained by SERF atomic magnetometer head B are G1(t)', G2(t)', G3(t)', G4(t)'. The magnetic field measurement values ​​of the four channels of SERF atomic magnetometer head A are calculated as follows: B 11 =k1V1(t)',B 12 =k2V2(t)',B 13 =k3V3(t)',B 14 =k4V4(t)', the magnetic field measurements of the four channels of the SERF atomic magnetometer head B are as follows: B 21 =g1G1(t)',B 22 =g2G2(t)',B 23 =g3G3(t)',B 24 =g4G4(t)';

[0019] Step 7, select the measurement mode. If high-sensitivity multi-channel measurement is required, the measurement result will be directly output as: B11 B 12 B 13 B 14 B 21 B 22 B 23 B 24 If it is necessary to output the magnetic field gradient information within the space of the magnetometer head, the calculated magnetic field gradient within the meter is as follows: , Where L1 is the distance between channels 1 and 2 of SERF atomic magnetometer head A along the x-axis, and L2 is the distance between channels 1 and 3 of SERF atomic magnetometer head A along the z-axis. If it is necessary to output the magnetic field gradient information between SERF atomic magnetometer head A and SERF atomic magnetometer head B, the spatial magnetic field gradient between the magnetometers is calculated as follows: .

[0020] The technical effects of this invention are as follows: This invention provides a traceable multi-mode extremely weak magnetic field measurement device and method, comprising helium-3 atoms and an atomic magnetometer in a spin-free exchange relaxation state. Under extremely weak magnetic fields, the metastable exchange-pumped polarized helium-3 atoms provide a traceable magnetic field value to the atomic magnetometer. This value is compared with the output response of the atomic magnetometer to obtain the calibrated scale coefficient of the atomic magnetometer, thus ensuring the traceability of all measurements. The proposed atomic magnetometer head includes four independent detection channels. These four channels are obtained by splitting the beam through two detection lasers with different frequency detuning values ​​via a high-speed optical switch (e.g., a 2×2 optical switch) and two 5:5 fiber beam splitters. From a time-domain perspective, each channel operates in frequency modulation mode. Demodulation using lock-in amplification technology isolates low-frequency electrical noise in each channel, achieving high-sensitivity measurement, and ensuring high consistency between channels. The method proposed in this invention is compatible with the collaborative use of multiple probes and can realize three measurement modes: single probe multi-channel measurement, internal magnetic field gradient measurement, and inter-probe magnetic field gradient measurement. Each mode has high consistency and high sensitivity.

[0021] The present invention provides a traceable multi-mode extremely weak magnetic field measurement device and method, which has the following advantages compared with the prior art:

[0022] (1) Conventional SERF atomic magnetometers require offline, non-operational calibration, and prolonged use can lead to measurement inaccuracies due to the zero-point drift of the SERF magnetometer itself. This invention places helium-3 atoms near the SERF atomic magnetometer and utilizes the high-precision traceability of the free precession frequency of helium-3 atoms during the measurement process to perform high-precision online, in-situ calibration of the SERF atomic magnetometer, thereby enabling the SERF atomic magnetometer to have high sensitivity, long-term stability, and high-precision traceability.

[0023] (2) The measurement signal of a conventional SERF atomic magnetometer is easily affected by low-frequency noise. This invention uses a high-speed optical switch to modulate all channels of the SERF atomic magnetometer into frequency modulation mode, thereby using lock-in amplification technology to isolate low-frequency electrical noise during the measurement process and improving the low-frequency performance of the SERF atomic magnetometer.

[0024] (3) Conventional SERF atomic magnetometers typically have only one channel or can only measure the magnitude of the magnetic field. The SERF atomic magnetometer proposed in this invention has four measurement channels, each with its own independent optical and measurement characteristics. By using all four channels simultaneously for measurement, the gradient of extremely weak magnetic fields and multi-channel measurement information can be obtained, as well as the magnitude information that conventional SERF atomic magnetometers can obtain. The measurement values ​​obtained by the measurement method proposed in this invention are all calibrated with helium-3 atoms, ensuring traceability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a traceable multi-mode extremely weak magnetic field measuring device for implementing the present invention.

[0026] Figure 2 This is a schematic diagram of the spatial positions of the four channels in the SERF atomic magnetometer head A.

[0027] Figure 3 This is a schematic diagram of the spatial location of the traceability standard system for the magnetic field value of helium-3 atoms.

[0028] The reference numerals in the attached figures are explained as follows: 1- SERF atomic magnetometer head A (SERF, Spin-Exchange-Relaxation-Free); 2- Pump collimator A; 3- Circular polarization generator A; 4- Pump reflector A; 5- Ceramic oven; 6- Alkali metal atom gas cell; 7- Pump reflector B; 8- Circular polarization generator B; 9- Pump collimator B; 101- Channel 1 detection collimator; 102- Channel 2 detection collimator; 11- First half-wave plate; 12- First lateral displacement polarization beam splitter prism; 13- Channel 1 photodetector group; 14- Channel 1 subtractor; 15- Channel 1 differential signal; 16- Channel 2 differential signal. Signal; 171-Channel 3 detection collimator; 172-Channel 4 detection collimator; 18-Second half-wave plate; 19-Second lateral displacement polarization beam splitter; 20-Channel 3 photodetector group; 21-Channel 3 subtractor; 22-Channel 3 differential signal; 23-Channel 4 differential signal; 24-Signal bus; 25-Data memory; 26-Lock-in amplifier; 27-Data analyzer; 28-Output display module; 29-Detection laser A; 30-Detection laser B; 31-High-speed optical switch; 32-5:5 fiber beam splitter A; 33-5:5 fiber beam splitter B; 341-Pump laser; 342-5:5 fiber beam splitter C; 35- SERF Atomic Magnetometer Controller A; 36- SERF Atomic Magnetometer Head B; 37- SERF Atomic Magnetometer Controller B; 38- Helium-3 Atom Pump Laser (Helium-3 atoms are isotopes of helium gas); 39- Laser Beam Expander; 40- Helium-3 Atom Gas Chamber; 41- Magnetic Shielding Barrel; xyz- Cartesian coordinate system three axes (i.e., x-axis, y-axis, and z-axis). Detailed Implementation

[0029] The following is in conjunction with the attached diagram ( Figures 1-3 The present invention will be described in conjunction with the embodiments.

[0030] Figure 1 This is a schematic diagram of the structure of a traceable multi-mode extremely weak magnetic field measuring device for implementing the present invention. Figure 2 This is a schematic diagram of the spatial positions of the four channels in the SERF atomic magnetometer head A. Figure 3 This is a schematic diagram of the spatial location of the standard system for tracing the magnetic field values ​​of helium-3 atoms. (Reference) Figures 1 to 3As shown, a traceable multi-mode extremely weak magnetic field measurement device includes SERF atomic magnetometer heads A1 and B36 spaced along the x-axis. A helium-3 atomic magnetic field measurement traceability standard system is installed within the spaced intervals. The helium-3 atomic magnetic field measurement traceability standard system includes a helium-3 atomic gas chamber 40. The helium-3 atomic gas chamber 40 is connected to a helium-3 atomic pump laser 38 so that the helium-3 atomic pump light passes through the helium-3 atomic gas chamber 40 along the z-axis. The pump laser 341 in the SERF atomic magnetometer head A1 is decomposed into a first pump laser by a 5:5 fiber beam splitter C342. The first pump light passes sequentially through a pump light collimator A2, a circular polarization generator A3, and a pump light reflector A4 before being incident on the alkali metal atom gas cell 6 from the positive z-axis. The second pump light passes sequentially through a pump light collimator B9, a circular polarization generator B8, and a pump light reflector B7 before being incident on the alkali metal atom gas cell 6 from the negative z-axis. The SERF atomic magnetometer head A1 is provided with four channels for matching four detection beams passing through the alkali metal atom gas cell 6 from the positive y-axis. The detection beam output signals of the four channels are connected to the SERF atomic magnetometer controller A35 via a signal bus 24.

[0031] The helium-3 atom gas chamber 40 is connected to the helium-3 atom pump laser 38 via a laser beam expander 39. The laser beam expander 39, the helium-3 atom gas chamber 40, the SERF atomic magnetometer head A1 and the SERF atomic magnetometer head B36 are all located inside the magnetic shielding barrel 41. The SERF atomic magnetometer head B36 is connected to the SERF atomic magnetometer controller B37.

[0032] Of the four channels, channel 1 is located in the second quadrant of the xz plane in the alkali metal atom gas cell 6, channel 2 is located in the third quadrant, channel 3 is located in the first quadrant, and channel 4 is located in the fourth quadrant. The detection optical collimator 101 in channel 1 and the detection optical collimator 102 in channel 2 are respectively connected to a 5:5 fiber optic beam splitter A32. The detection optical collimator 171 in channel 3 and the detection optical collimator 172 in channel 4 are respectively connected to a 5:5 fiber optic beam splitter B33. Beam splitter A32 is connected to the first output terminal of high-speed optical switch 31, and 5:5 fiber beam splitter B33 is connected to the second output terminal of high-speed optical switch 31. The first input terminal of high-speed optical switch 31 is connected to detection laser A29, and the second input terminal of high-speed optical switch 31 is connected to detection laser B30. The laser frequency of detection laser A29 is red detuned to the D1 line resonance frequency of alkali metal atoms, and the laser frequency of detection laser B30 is blue detuned to the D1 line resonance frequency of alkali metal atoms.

[0033] The output of the signal bus 24 is connected to the output display module 28 in sequence through the data memory 25, the lock-in amplifier 26 and the data analyzer 27. The input of the signal bus 24 is connected to the differential signal 15 of channel 1, the differential signal 16 of channel 2, the differential signal 22 of channel 3 and the differential signal 23 of channel 4, respectively.

[0034] The alkali metal atom gas chamber 6 is located inside the ceramic oven 5.

[0035] The detection light emission side of the alkali metal atom gas cell 6 is respectively provided with a first half-wave plate 11, a second half-wave plate 18, a third half-wave plate, and a fourth half-wave plate. The first half-wave plate 11 is sequentially connected to a first lateral displacement polarization beam splitter 12, a channel 1 photodetector group 13, and a channel 1 subtractor 14. The channel 1 subtractor 14 outputs a channel 1 differential signal 15. The second half-wave plate 18 is sequentially connected to a second lateral displacement polarization beam splitter 19, a channel 1 subtractor 14, and a channel 1 differential signal 15. The system includes a photodetector group 20 and a channel 3 subtractor 21, with the channel 3 subtractor 21 outputting a channel 3 differential signal 22. A third half-wave plate is sequentially connected to a third lateral displacement polarization beam splitter, a channel 2 photodetector group, and a channel 2 subtractor, with the channel 2 subtractor outputting a channel 2 differential signal 16. A fourth half-wave plate is sequentially connected to a fourth lateral displacement polarization beam splitter, a channel 4 photodetector group, and a channel 4 subtractor, with the channel 4 subtractor outputting a channel 4 differential signal 23.

[0036] A traceable multi-mode extremely weak magnetic field measurement method, employing the aforementioned traceable multi-mode extremely weak magnetic field measurement device.

[0037] This invention proposes a traceable multi-mode extremely weak magnetic field measurement device and method. The proposed device comprises helium-3 atoms and an atomic magnetometer in a spin-free exchange-relaxed state. Under extremely weak magnetic fields, the metastable exchange-pumped polarized helium-3 atoms provide a traceable magnetic field value to the atomic magnetometer. This value is compared with the output response of the atomic magnetometer to obtain the calibrated scale coefficient of the atomic magnetometer, thus ensuring the traceability of all measurements. The proposed atomic magnetometer head includes four independent detection channels. These four channels are obtained by splitting the beams through a 2×2 optical switch and two 5:5 fiber beam splitters using two detection lasers with different frequency detuning. From a time-domain perspective, each channel operates in frequency modulation mode. Demodulation using lock-in amplification technology isolates low-frequency electrical noise in each channel, achieving high-sensitivity measurement, and ensuring high consistency between channels. The method proposed in this invention is compatible with the collaborative use of multiple probes and can realize three measurement modes: single probe multi-channel measurement, internal magnetic field gradient measurement, and inter-probe magnetic field gradient measurement. Each mode has high consistency and high sensitivity.

[0038] This invention comprises helium-3 atoms and an atomic magnetometer in a spin-free exchange-relaxed state. Under extremely weak magnetic fields, metastable exchange-pumped polarized helium-3 atoms provide a traceable magnetic field value for the atomic magnetometer. This value is compared with the output response of the atomic magnetometer to obtain the calibration coefficient of the atomic magnetometer. In other words, helium-3 atoms serve as the traceability standard, enabling measurements in multiple modes across multiple channels with high consistency and sensitivity between channels. The output measurement results are calibrated using helium-3 atoms.

[0039] The present invention can measure three magnetic field modes: dual-head multi-channel measurement, magnetic field gradient within each of the two heads, and magnetic field gradient between the two heads. These three magnetic field measurement modes can be output simultaneously or individually. The dual-head multi-channel measurement mode can output four independent channels with high consistency and high sensitivity from each head. The magnetic field gradient within each of the two heads can output the magnetic field gradient in the other two directions that are not parallel to the detection light direction. The magnetic field gradient between the two heads outputs the magnetic field gradient in the direction of the sensitive axis of the head. The scope of the present invention is not limited to two heads and can be extended to a larger number of heads.

[0040] This invention provides a traceable, multi-mode extremely weak magnetic field measurement device and method. Helium-3 atoms with extremely high traceability accuracy are placed around a SERF atomic magnetometer, enabling the SERF atomic magnetometer to be calibrated in situ, yielding calibrated scale coefficients. The SERF atomic magnetometer used in this invention has four independent channels with high consistency and operates in modulation mode, isolating low-frequency noise. Multiple high-performance measurement channels allow the magnetometer to operate in multiple modes: multi-channel mode and gradient measurement mode. The invention is described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and not for limiting the scope of the invention. After reading this invention, any modifications of the invention by those skilled in the art in various equivalent forms fall within the scope defined by the appended claims.

[0041] See Figure 1 , Figure 2 This invention provides a traceable multi-mode extremely weak magnetic field measurement device and method. For example... Figure 1 , Figure 2As shown, a traceable multi-mode extremely weak magnetic field measurement device and method includes: a SERF atomic magnetometer head A1, a pump optical collimator A2, a circular polarization generator A3, a pump optical reflector A4, a ceramic oven 5, an alkali metal atomic gas cell 6, a pump optical reflector B7, a circular polarization generator B8, a pump optical collimator B9, a channel 1 detection optical collimator 101, a channel 2 detection optical collimator 102, a first half-wave plate 11, a first lateral displacement polarization beam splitter 12, a channel 1 photodetector group 13, a channel 1 subtractor 14, a channel 1 differential signal 15, a channel 2 differential signal 16, and a channel 3 detection optical collimator 17. 71. Channel 4 detection collimator; 172. Second half-wave plate; 18. Second lateral displacement polarization beam splitter; 19. Channel 3 photodetector group; 20. Channel 3 subtractor; 21. Channel 3 differential signal; 22. Channel 4 differential signal; 23. Signal bus; 24. Data memory; 25. Lock-in amplifier; 26. Data analyzer; 27. Output display module; 28. Detection laser A; 29. ​​Detection laser B; 30. High-speed optical switch; 31. 5:5 fiber beam splitter A; 32. 5:5 fiber beam splitter B; 33. Pump laser; 341. 5:5 fiber beam splitter C; 342. SERF atomic magnetometer controller A; 35.

[0042] See Figure 2 This invention provides a traceable multi-mode extremely weak magnetic field measurement device and method. For example... Figure 2 The four channels of the SERF atomic magnetometer head A1 shown are symmetrically distributed within the alkali metal atom gas chamber 6.

[0043] See Figure 3 This invention provides a traceable multi-mode extremely weak magnetic field measurement device and method. For example... Figure 3 As shown, a traceable multi-mode extremely weak magnetic field measurement device and method includes: SERF atomic magnetometer head B36, SERF atomic magnetometer controller B37, helium-3 atomic pump laser 38, laser beam expander 39, helium-3 atomic gas chamber 40, and magnetic shielding barrel 41.

[0044] like Figure 1 , Figure 2 , Figure 3 As shown, the specific implementation steps of the present invention are as follows:

[0045] (1) Set the laser frequency of the detection laser A (29) to be red detuned to the D1 line resonance frequency of the alkali metal atom at 100 GHz and the laser power to be 3 mW. Set the laser frequency of the detection laser B (30) to be blue detuned to the D1 line resonance frequency of the alkali metal atom at 100 GHz and the laser power to be 3 mW. Apply a pulse drive signal with a frequency of 10 kHz and a duty cycle of 50% to the high-speed optical switch (31). The detection laser A (29) and the detection laser B (30) are transmitted to the high-speed optical switch (31) through the polarization-maintaining fiber. Thus, the two input ends of the optical switch are red detuned and blue detuned lasers, respectively. The laser frequencies output by the two output ends change periodically with time and the frequencies of the output light from the two output channels are always opposite.

[0046] (2) After completing step (1), adjust the optical axis angle of the first half-wave plate (11) so that the s-light and p-light obtained by the first lateral displacement polarization beam splitter (12) have the same power. At this time, the optical axis angle of the first half-wave plate (11) and the optical axis angle of the first lateral displacement polarization beam splitter (12) are 45°. Adjust the optical axis angle of the second half-wave plate (18) so that the s-light and p-light obtained by the second lateral displacement polarization beam splitter (19) have the same power. Perform the same operation on the optical paths of the detection collimator (102) in channel 2 and the detection collimator (172) in channel 4.

[0047] (3) After completing step (2), turn on the helium-3 atom pump laser (38), set the laser frequency to 1083.33nm, use the metastable exchange light pump method to polarize the helium-3 atoms in the helium-3 atom gas chamber (40), and turn off the helium-3 atom pump laser (38) when the polarization rate of the helium-3 atoms reaches 70%, stop the metastable exchange light pump method, and let the helium-3 atoms precess freely in the magnetic field;

[0048] (4) After completing step (3), turn on SERF atomic magnetometer controller A (35) and SERF atomic magnetometer controller B (37), place SERF atomic magnetometer head A (1) and SERF atomic magnetometer head B (36) on the upper and lower surfaces of the helium-3 atom gas chamber (40), and measure the free precession signal of helium-3 atoms. For SERF atomic magnetometer head A (1), use a frequency of 10kHz in the lock-in amplifier (26) to demodulate the differential signal of channel 1 (15) and the differential signal of channel 2 respectively. The demodulation results obtained from the sub-signal (16), channel 3 differential signal (22), and channel 4 differential signal (23) are: V1(t), V2(t), V3(t), V4(t). The precession frequency ω of the helium-3 atom is obtained by fitting V1(t), V2(t), V3(t), and V4(t). Then the magnetic field in the environment is B0=γω, where γ is the gyromagnetic ratio of the helium-3 atom. The same operation as that of the SERF atomic magnetometer head A(1) is performed on the SERF atomic magnetometer head B(36).

[0049] (5) After completing step (4), calculate the calibration coefficients of channels 1, 2, 3 and 4 of the SERF atomic magnetometer head A (1) as k1= B0 / V1(t), k2= B0 / V2(t), k3= B0 / V3(t) and k4= B0 / V4(t). Then calculate the calibration coefficients of the four channels of the SERF atomic magnetometer head B (36) as g1, g2, g3 and g4 respectively.

[0050] (6) After completing step (5), apply the magnetic field B to be measured. c Record the measurement results V1(t)', V2(t)', V3(t)', V4(t)' of the four channels of SERF atomic magnetometer head A (1), and the measurement results G1(t)', G2(t)', G3(t)', G4(t)' of the four channels of SERF atomic magnetometer head B (36). The distance between SERF atomic magnetometer head A (1) and SERF atomic magnetometer head B (36) is 10mm. Calculate the magnetic field measurement values ​​of the four channels of SERF atomic magnetometer head A (1) as follows: B 11 =k1V1(t)',B 12 =k2V2(t)',B 13 =k3V3(t)',B 14 =k4V4(t)', since the calibration coefficients of each channel have been calibrated, the four channels are for B c The measurements are traceable, and the same calculations are performed on the four channels of the SERF atomic magnetometer head B(36) for B. c The measured values ​​are as follows: B 21 =g1G1(t)',B22 =g2G2(t)',B 23 =g3G3(t)',B 24 =g4G4(t)';

[0051] (7) After completing step (6), select one of the following measurement modes: multi-channel measurement, magnetic field gradient inside the meter head, or magnetic field gradient between meter heads. If high-sensitivity multi-channel measurement is required, the measurement result will be output directly as: B 11 B 12 B 13 B 14 B 21 B 22 B 23 B 24 If it is necessary to output the magnetic field gradient information within the space of the magnetometer head, the output magnetic field gradient within the meter's space is as follows: , Where L1=2mm is the distance between channels 1 and 2 of SERF atomic magnetometer head A(1) along the x-axis, and L2=2mm is the distance between channels 1 and 3 of SERF atomic magnetometer head A(1) along the z-axis. If the magnetic field gradient information between SERF atomic magnetometer head A(1) and SERF atomic magnetometer head B(36) is output, the spatial magnetic field gradient between the magnetometers is: .

[0052] The present invention can measure three magnetic field modes: dual-head multi-channel measurement, magnetic field gradient within each of the two heads, and magnetic field gradient between the two heads. These three magnetic field measurement modes can be output simultaneously or individually. The dual-head multi-channel measurement mode can output four independent channels with high consistency and high sensitivity from each head. The magnetic field gradient within each of the two heads can output the magnetic field gradient in the other two directions that are not parallel to the detection light direction. The magnetic field gradient between the two heads outputs the magnetic field gradient in the direction of the sensitive axis of the head. The scope of the present invention is not limited to two heads and can be extended to a larger number of heads.

[0053] A traceable multi-mode extremely weak magnetic field measurement device and method, the main components of which include: SERF atomic magnetometer head A (1), pump optical collimator A (2), circular polarization generator A (3), pump optical reflector A (4), ceramic oven (5), alkali metal atomic gas cell (6), pump optical reflector B (7), circular polarization generator B (8), pump optical collimator B (9), channel 1 detection optical collimator (101), channel 2 detection optical collimator (102), first half-wave plate (11), first lateral displacement polarization beam splitter (12), channel 1 photodetector group (13), channel 1 subtractor (14), channel 1 differential signal (15), channel 2 differential signal (16), channel 3 detection optical collimator (171), channel 4 detection optical collimator (172), second half-wave plate (18), second lateral displacement polarization beam splitter Light prism (19), Channel 3 photodetector group (20), Channel 3 subtractor (21), Channel 3 differential signal (22), Channel 4 differential signal (23), signal bus (24), data memory (25), lock-in amplifier (26), data analyzer (27), output display module (28), detection laser A (29), detection laser B (30), high-speed optical switch (31), 5:5 fiber beam splitter A (32), 5:5 fiber beam splitter B (33), pump laser (341), 5:5 fiber beam splitter C (342), SERF atomic magnetometer controller A (35), SERF atomic magnetometer meter head B (36), SERF atomic magnetometer controller B (37), helium-3 atom pump laser (38), laser beam expander (39), helium-3 atom gas chamber (40), magnetic shielding barrel (41);

[0054] The SERF atomic magnetometer head A (1) includes a pump collimator A (2), a circular polarization generator A (3), a pump reflector A (4), a ceramic oven (5), an alkali metal atom gas cell (6), a pump reflector B (7), a circular polarization generator B (8), a pump collimator B (9), a channel 1 detection collimator (101), a channel 2 detection collimator (102), a first half-wave plate (11), a first lateral displacement polarization beam splitter (12), a channel 1 photodetector group (13), and a channel... The subtractor (14), channel 1 differential signal (15), channel 2 differential signal (16), channel 3 detection light collimator (171), channel 4 detection light collimator (172), second half-wave plate (18), second lateral displacement polarization beam splitter (19), channel 3 photodetector group (20), channel 3 subtractor (21), channel 3 differential signal (22), channel 4 differential signal (23), and signal bus (24) are components that perform measurement tasks in the SERF atomic magnetometer and are made of non-magnetic materials.

[0055] The SERF atomic magnetometer controller A (35) includes a data storage device (25), a lock-in amplifier (26), a data analyzer (27), an output display module (28), a detection laser A (29), a detection laser B (30), a high-speed optical switch (31), a 5:5 fiber beam splitter A (32), a 5:5 fiber beam splitter B (33), a pump laser (341), and a 5:5 fiber beam splitter C (342). It performs the task of processing measurement signals and integrates the light source required for the operation of the SERF atomic magnetometer.

[0056] The SERF atomic magnetometer controller A (35) and SERF atomic magnetometer meter head B (36) have the same working principle and composition structure, and the SERF atomic magnetometer controller A (35) and SERF atomic magnetometer controller B (37) have the same working principle and composition structure.

[0057] The pump collimator A (2) and pump collimator B (9) are respectively connected to the two output ends of the 5:5 fiber beam splitter C (342) through polarization-maintaining fiber. The input end of the 5:5 fiber beam splitter C (342) is connected to the pump laser (341). The pump laser (341) outputs a linearly polarized laser with a radio frequency of the alkali metal atom D1 line resonance frequency. The 5:5 fiber beam splitter C (342) does not change the polarization state of the laser, but only transmits the optical power to the pump collimator A (2) and pump collimator B (9) in a 5:5 ratio. The collimated spot diameters of the pump collimator A (2) and pump collimator B (9) are the same.

[0058] The pump laser emitted from the pump collimator A (2) is converted into a circularly polarized laser by the circular polarization generator A (3), and after being reflected by the pump reflector A (4), it irradiates the alkali metal atom gas cell (6) along the positive z-axis. The pump laser emitted from the pump collimator B (9) is converted into a circularly polarized laser by the circular polarization generator B (8), and after being reflected by the pump reflector B (7), it irradiates the alkali metal atom gas cell (6) along the negative z-axis, thereby achieving uniform polarization of alkali metal atoms.

[0059] The linearly polarized lasers emitted by the detection laser A (29) and the detection laser B (30) have the same power and polarization direction, but the frequency detuning is opposite to that of the alkali metal atom D1 line. The two emitted laser beams pass through a high-speed optical switch (31) with two input ports and two output ports. The high-speed optical switch (31) is driven by a pulse signal and periodically changes the on / off state of the two input ports and the output ports. The two outputs of the high-speed optical switch (31) are respectively connected to 5:5 fiber beam splitter A (32) and 5:5 fiber beam splitter B (33). A (32) transmits the incoming laser to the detection collimator (101) of channel 1 and the detection collimator (102) of channel 2 in a 5:5 ratio. The collimated lasers emitted from the detection collimator (101) of channel 1 and the detection collimator (102) of channel 2 have the same radius. The 5:5 fiber beam splitter B (33) transmits the incoming laser to the detection collimator (171) of channel 3 and the detection collimator (172) of channel 4 in a 5:5 ratio. The collimated lasers emitted from the detection collimator (171) of channel 3 and the detection collimator (172) of channel 4 have the same radius.

[0060] The laser emitted from the collimator (101) of channel 1 passes through the alkali metal atom gas cell (6) and is then incident on the first half-wave plate (11), and subsequently on the first lateral displacement polarization beam splitter (12). The first lateral displacement polarization beam splitter (12) splits the beam into s-beams and p-beams. The s-beams and p-beams are received by the photodetector group (13) of channel 1 and converted into current signals. The current signals are converted into differential voltage signals by the subtractor (14) of channel 1, i.e., the differential signal of channel 1 (15). The collimator (102) of channel 2 has the same propagation mechanism and process as the collimator (101) of channel 1, and the differential signal of channel 2 (16) is obtained. Since the laser emitted from the collimator (102) of channel 2 and the collimator (101) of channel 1 both come from the 5:5 fiber beam splitter A (32), the optical properties of the two channels are exactly the same.

[0061] The laser emitted from the collimator (171) of channel 3 passes through the alkali metal atom gas cell (6) and is then incident on the second half-wave plate (18), and subsequently on the second lateral displacement polarization beam splitter (19). The second lateral displacement polarization beam splitter (19) splits the beam into s-beams and p-beams. The s-beams and p-beams are received by the photodetector group (20) of channel 3 and converted into current signals. The current signals are converted into differential voltage signals by the subtractor (21) of channel 3, namely the differential signal (22) of channel 3. The collimator (171) of channel 3 and the collimator (172) of channel 4 have the same propagation mechanism and process, resulting in the differential signal (23) of channel 4. Since the lasers emitted from the collimator (171) of channel 3 and the collimator (172) of channel 4 both come from the 5:5 fiber beam splitter B (33), the optical properties of the two channels are exactly the same.

[0062] The laser frequencies emitted by the detection collimator (101) of channel 1 and the detection collimator (171) of channel 3 are modulated by a high-speed optical switch (31). At the same time, the frequency detuning of the emitted laser frequencies of channel 1 and channel 3 are opposite. The detection collimator (101) of channel 1 and the detection collimator (102) of channel 2 are arranged along the x-axis direction of the alkali metal atom gas cell (6). The detection collimator (101) of channel 1 and the detection collimator (171) of channel 3 are arranged along the z-axis direction. The detection collimator (171) of channel 3 and the detection collimator (172) of channel 4 are arranged along the x-axis direction.

[0063] The differential signals of channel 1 (15), channel 2 (16), channel 3 (22), and channel 4 (23) are transmitted to the data memory (25) via the signal bus (24). The lock-in amplifier (26) calls the data memory (25) and demodulates it. The demodulated signal is transmitted to the data analyzer (27), and the analysis result is displayed to the user in the output display module (28).

[0064] The alkali metal atom gas chamber (6) is enclosed in a ceramic oven (5) and heated to an atomic number density of 10. 13 ~10 14 pcs / cm 3 ;

[0065] The helium-3 atom pump laser (38) emits a linearly polarized laser with a radio frequency of around 1083 nm. Its function is to excite the transition of helium-3 atoms to achieve the helium atom pumping function. The emitted laser is expanded by a laser beam expander (39) into a beam with a spot diameter that is comparable to the diameter of a spherical helium-3 atom gas chamber (40). The helium-3 atom gas chamber (40) is filled only with helium-3 atoms. The helium-3 atoms are polarized through metastable exchange light pumping technology.

[0066] The sensitive axes of the SERF atomic magnetometer head A (1) and SERF atomic magnetometer head B (36) point to the x-axis and are symmetrically distributed on both sides of the spherical helium-3 atom gas chamber (40) along the x-axis. The SERF atomic magnetometer head A (1), SERF atomic magnetometer head B (36), helium-3 atom gas chamber (40), and laser beam expander (39) are placed in a magnetic shielding barrel (41) to shield against interference from the Earth's magnetic field.

[0067] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A traceable multi-mode extremely weak magnetic field measuring device, characterized in that, The system includes SERF atomic magnetometer heads A and B, spaced apart along the x-axis. A helium-3 atomic magnetic field traceability standard system is installed within each interval. This system includes a helium-3 atom gas chamber connected to a helium-3 atom pump laser, allowing the helium-3 atom pump light to pass through the chamber along the z-axis. The pump laser in SERF atomic magnetometer head A is split into a first pump light and a second pump light by a 5:5 fiber optic beam splitter C. The pump light sequentially passes through pump light collimator A, circular polarization generator A, and pump light reflector A before entering the alkali metal atom gas cell from the positive z-axis. The second pump light sequentially passes through pump light collimator B, circular polarization generator B, and pump light reflector B before entering the alkali metal atom gas cell from the negative z-axis. The SERF atomic magnetometer head A is provided with four channels for matching four detection beams passing through the alkali metal atom gas cell from the positive y-axis. The detection beam output signals of the four channels are connected to the SERF atomic magnetometer controller A via a signal bus.

2. The traceable multi-mode extremely weak magnetic field measuring device according to claim 1, characterized in that, The helium-3 atom gas chamber is connected to the helium-3 atom pump laser via a laser beam expander. The laser beam expander, the helium-3 atom gas chamber, the SERF atomic magnetometer head A and the SERF atomic magnetometer head B are all located inside a magnetically shielded barrel. The SERF atomic magnetometer head B is connected to the SERF atomic magnetometer controller B.

3. The traceable multi-mode extremely weak magnetic field measuring device according to claim 1, characterized in that, Of the four channels, channel 1 is located in the second quadrant of the xz plane in the alkali metal atom gas cell, channel 2 is located in the third quadrant, channel 3 is located in the first quadrant, and channel 4 is located in the fourth quadrant. The detection light collimator of channel 1 and the detection light collimator of channel 2 are respectively connected to a 5:5 fiber beam splitter A. The detection light collimator of channel 3 and the detection light collimator of channel 4 are respectively connected to a 5:5 fiber beam splitter B. The 5:5 fiber beam splitter A is connected to the first output terminal of the high-speed optical switch, and the 5:5 fiber beam splitter B is connected to the second output terminal of the high-speed optical switch. The first input terminal of the high-speed optical switch is connected to the detection laser A, and the second input terminal of the high-speed optical switch is connected to the detection laser B. The laser frequency of the detection laser A is red detuned to the D1 line resonance frequency of the alkali metal atom, and the laser frequency of the detection laser B is blue detuned to the D1 line resonance frequency of the alkali metal atom.

4. The traceable multi-mode extremely weak magnetic field measuring device according to claim 1, characterized in that, The output of the signal bus is connected to the output display module in sequence through a data memory, a lock-in amplifier, and a data analyzer. The input of the signal bus is connected to the differential signals of channel 1, channel 2, channel 3, and channel 4, respectively.

5. The traceable multi-mode extremely weak magnetic field measuring device according to claim 1, characterized in that, The alkali metal atom gas chamber is located inside the ceramic oven.

6. The traceable multi-mode extremely weak magnetic field measuring device according to claim 1, characterized in that, The detection light emission side of the alkali metal atom gas cell is respectively provided with a first half-wave plate, a second half-wave plate, a third half-wave plate, and a fourth half-wave plate. The first half-wave plate is sequentially connected to a first lateral displacement polarization beam splitter, a channel 1 photodetector group, and a channel 1 subtractor. The channel 1 subtractor outputs a channel 1 differential signal. The second half-wave plate is sequentially connected to a second lateral displacement polarization beam splitter, a channel 3 photodetector group, and a channel 3 subtractor. The channel 3 subtractor outputs a channel 3 differential signal. The third half-wave plate is sequentially connected to a third lateral displacement polarization beam splitter, a channel 2 photodetector group, and a channel 2 subtractor. The channel 2 subtractor outputs a channel 2 differential signal. The fourth half-wave plate is sequentially connected to a fourth lateral displacement polarization beam splitter, a channel 4 photodetector group, and a channel 4 subtractor. The channel 4 subtractor outputs a channel 4 differential signal.

7. A traceable multi-mode method for measuring extremely weak magnetic fields, characterized in that, The traceable multi-mode extremely weak magnetic field measuring device according to any one of claims 1-6 is adopted.

8. The traceable multi-mode extremely weak magnetic field measurement method according to claim 7, characterized in that, Includes the following steps: Step 1: Set the laser frequency of detection laser A to the red detuned frequency of the D1 line resonance of alkali metal atoms, and the laser power to I. Set the laser frequency of detection laser B to the blue detuned frequency of the D1 line resonance of alkali metal atoms, and the laser power to I. Set the driving signal of the high-speed optical switch to a pulse signal with a duty cycle of 50% and a frequency of Ω. The lasers emitted by detection lasers A and B are transmitted to the high-speed optical switch through a polarization-maintaining fiber. Step 2: Adjust the optical axis angle of the first half-wave plate so that the S-ray and P-ray obtained by the first lateral displacement polarization beam splitter have the same power. Adjust the optical axis angle of the second half-wave plate so that the S-ray and P-ray obtained by the second lateral displacement polarization beam splitter have the same power. Perform the same operation on the optical paths of the detection collimator in channel 2 and the detection collimator in channel 4. Step 3: Turn on the helium-3 atom pump laser and set the laser frequency to 1083.3 nm. Use the metastable exchange light pumping method to polarize the helium-3 atoms in the helium-3 atom gas chamber, so that the polarizability of the helium-3 atoms reaches the set value P. At this time, turn off the helium-3 atom pump laser, stop the metastable exchange light pumping method, and let the helium-3 atoms precess freely in the magnetic field. Step 4: Run SERF atomic magnetometer controller A and SERF atomic magnetometer controller B. Place SERF atomic magnetometer head A and SERF atomic magnetometer head B close to the helium-3 atom gas chamber to measure the free precession signal of the helium-3 atoms. For SERF atomic magnetometer head A, use frequency Ω in the lock-in amplifier to demodulate the differential signals of channel 1, channel 2, channel 3, and channel 4 respectively, obtaining the corresponding demodulation results V1(t), V2(t), V3(t), and V4(t). Fit V1(t), V2(t), V3(t), and V4(t) to obtain the precession frequency ω of the helium-3 atoms. Then, the magnetic field B0 in the environment is B0 = γω, where γ is the gyromagnetic ratio of the helium-3 atoms. Perform the same operation on SERF atomic magnetometer head B as on SERF atomic magnetometer head A. Step 5: Obtain the calibration scale coefficients k1= B0 / V1(t), k2= B0 / V2(t), k3= B0 / V3(t), and k4= B0 / V4(t) for the measurement results of channels 1, 2, 3, and 4 in SERF atomic magnetometer head A. This completes the calibration of the scale coefficients for the four channels in SERF atomic magnetometer head A. Perform the same operation on SERF atomic magnetometer head B to obtain the scale coefficients for the four channels as g1, g2, g3, and g4, respectively. Step 6, apply the magnetic field B to be measured. c The distance between SERF atomic magnetometer head A and SERF atomic magnetometer head B is measured as L. The measurement results of the four channels obtained by SERF atomic magnetometer head A are V1(t)', V2(t)', V3(t)', V4(t)', and the measurement results of the four channels obtained by SERF atomic magnetometer head B are G1(t)', G2(t)', G3(t)', G4(t)'. The magnetic field measurement values ​​of the four channels of SERF atomic magnetometer head A are calculated as follows: B 11 =k1V1(t)',B 12 =k2V2(t)',B 13 =k3V3(t)',B 14 =k4V4(t)', the magnetic field measurements of the four channels of the SERF atomic magnetometer head B are as follows: B 21 =g1G1(t)',B 22 =g2G2(t)',B 23 =g3G3(t)',B 24 =g4G4(t)'; Step 7, select the measurement mode. If high-sensitivity multi-channel measurement is required, the measurement result will be directly output as: B 11 B 12 B 13 B 14 B 21 B 22 B 23 B 24 If it is necessary to output the magnetic field gradient information within the space of the magnetometer head, the calculated magnetic field gradient within the meter is as follows: , Where L1 is the distance between channels 1 and 2 of SERF atomic magnetometer head A along the x-axis, and L2 is the distance between channels 1 and 3 of SERF atomic magnetometer head A along the z-axis. If it is necessary to output the magnetic field gradient information between SERF atomic magnetometer head A and SERF atomic magnetometer head B, the spatial magnetic field gradient between the magnetometers is calculated as follows: .

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