A dual-axis serf atomic magnetometer measurement device and method without magnetic field modulation

Abstract

A kind of SERF biaxial magnetic field measuring device and method without magnetic field modulation, for the problem that modulation magnetic field needs to be applied in traditional biaxial measurement, leading to spin exchange relaxation increase and magnetic field crosstalk, it is proposed to replace the traditional magnetic field modulation by modulating the pumping light in SERF atomic magnetometer, then measure biaxial atomic spin polarizability information, realize biaxial magnetic field measurement.This method can realize higher sensitivity biaxial magnetic field measurement without introducing modulation magnetic field by abandoning the external modulation magnetic field in traditional biaxial measurement, and can completely suppress magnetic field crosstalk.Provide a new scheme for future new generation of ultra-high sensitivity array atomic magnetometer technology and application.

Description

Technical Field

[0001] This invention relates to the field of extremely weak magnetic field measurement technology based on atomic magnetometers, and in particular to a dual-axis SERF atomic magnetometer measurement device and method without magnetic field modulation, belonging to an all-optical dual-axis vector SERF atomic magnetometer technology that eliminates the need for a modulation magnetic field. Background Technology

[0002] Atomic magnetometers based on the SERF (Spin-exchange relaxation-free) effect can achieve ultra-high sensitivity measurements of extremely weak magnetic fields, with the potential for measurement sensitivity at the aT level. A classic SERF atomic magnetometer is a single-axis vector magnetometer; to achieve multi-axis real-time measurements, an additional modulation magnetic field is required. However, the modulation magnetic field increases atomic spin exchange relaxation, leading to a decrease in measurement sensitivity. Furthermore, when SERF atomic magnetometers are used in array-type measurement systems, the modulation magnetic fields generated by different magnetometers can interfere with each other, affecting measurement accuracy.

[0003] To address the aforementioned challenges, a magnetic field-modulated dual-axis SERF atomic magnetometer measurement device and method are proposed. This method modulates the pump light within the SERF atomic magnetometer to replace traditional magnetic field modulation, thereby measuring the dual-axis atomic spin polarization information and achieving dual-axis magnetic field measurement. Because this method does not introduce a modulating magnetic field, it enables higher sensitivity dual-axis magnetic field measurement and completely suppresses magnetic field crosstalk. This provides a novel solution for future next-generation ultra-high sensitivity array-type atomic magnetometer technology and applications. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a dual-axis SERF atomic magnetometer measurement device and method without magnetic field modulation, thus solving the problems of increased relaxation and crosstalk introduced by the modulation magnetic field in traditional methods.

[0005] The technical solution of the present invention is as follows:

[0006] A magnetic field-free, dual-axis SERF atomic magnetometer measuring device includes a pump optical path passing through an alkali metal gas cell 21 along the z-axis and a detection optical path passing through the alkali metal gas cell 21 along the x-axis. The pump laser in the pump optical path is emitted by a pump laser 8 and passes sequentially through an acousto-optic modulator 9, an aperture 10, a second polarizer 11, a beam expander 12, a first reflector 13, and a second quarter-wave plate 14 before entering the alkali metal gas cell 21. After passing through the alkali metal gas cell 21, the pump laser passes through a second reflector 15 and a second photodetector 16 and is connected to the detection signal input terminal of a second lock-in amplifier 17. The reference signal input terminal of the second lock-in amplifier 17 is connected to the acousto-optic modulator 9. The detection light in the detection optical path is emitted by the detection laser 1, and passes sequentially through the first polarizer 2, the photoelastic modulator 3, and the first quarter-wave plate 4 before entering the alkali metal gas chamber 21. After passing through the alkali metal gas chamber 21, the detection light passes sequentially through the analyzer 5 and the first photodetector 6, and is connected to the detection signal input terminal of the first lock-in amplifier 7. The reference signal input terminal of the first lock-in amplifier 7 is connected to the photoelastic modulator 3. The first lock-in amplifier 7 demodulates the detection light, and the second lock-in amplifier 17 demodulates the pump laser. A triaxial magnetic compensation coil 20, a ferrite magnetic shielding cylinder 19, and a permalloy magnetic shielding cylinder 18 are sequentially arranged outwards from the periphery of the alkali metal gas chamber 21.

[0007] The first lock-in amplifier demodulates the detection light, and the second lock-in amplifier demodulates the pump light.

[0008] The alkali metal gas chamber is surrounded by a triaxial magnetic compensation coil, a ferrite magnetic shielding cylinder, and a permalloy magnetic shielding cylinder arranged sequentially from the outside.

[0009] A method for measuring atomic magnetometers without magnetic field modulation, characterized by comprising the above-mentioned measuring device for biaxial SERF atomic magnetometers without magnetic field modulation and the following steps:

[0010] Step 1: Start the SERF dual-axis magnetic field measurement device without magnetic field modulation. Adjust the frequency of the pump light emitted from the pump laser to the center of the alkali metal atom spectral line D1 to minimize the frequency shift of the alkali metal atom light caused by the pump light. Adjust the frequency detuning of the detection light emitted from the detection laser to maximize the optical rotation angle of the detection light, that is, to maximize the response signal of the alkali metal atoms to the detection light.

[0011] Step 2: Apply a slowly varying sawtooth wave calibration magnetic field in the x-axis or y-axis direction, and adjust the duty cycle of the square wave loaded on the acousto-optic modulator so that the peak-to-peak value of the first harmonic signal of the pump light entering the photodetector is maximized.

[0012] Step 3: Apply a slowly varying sawtooth wave calibration magnetic field in the y direction, and record the first harmonic signal of the voltage signal received by the photodetector in the detection light direction and the first harmonic signal of the voltage signal received by the photodetector in the pump light direction.

[0013] Step 4: Measure the first harmonic signal in the direction of the detection light and the first harmonic signal in the direction of the pump light, and determine the electronic polarizability P in the sensitive detection direction of the demodulated signal of the detection optical path. x When the magnetic field B in the z-axis direction z When it approaches 0, the electronic polarizability P x Sensitive to magnetic field B y The expression is as follows:

[0014]

[0015] Where R op R is the average pumping rate of the pumped light. tot It is the total relaxation rate, γ e It is the electron gyromagnetic ratio, B x It is the magnetic field along the x-axis, B y It is the magnetic field along the y-axis; B can be measured by detecting the demodulated signal in the optical path. y The demodulated signal of the pump optical path is sensitive to the electronic polarization P in the pump direction. z , where B z When P approaches 0, z Sensitive to the magnitude of the transverse magnetic field in the xy plane, Among them B ⊥ It is a transverse magnetic field;

[0016]

[0017] Where d is the duty cycle of the square wave periodic signal, π is pi, q is the nuclear spin slowing factor, ω is the pump light modulation angular frequency, and i is the imaginary unit; B is obtained by acquiring the demodulated signal from the pump light path. ⊥ ;

[0018] Step 5: Utilize Find the magnetic field B along the x-axis x Thus achieving B x and B y Biaxial measurement.

[0019] Step 2 includes applying a 0-5V square wave periodic signal through an external signal generator to control the acousto-optic modulator, thereby modulating the intensity of the pump light.

[0020] Step 2 includes applying a slowly varying sawtooth wave calibration magnetic field of -5nT to 5nT and 0.2Hz in a direction perpendicular to the pump light.

[0021] Step 3 includes applying a slowly varying sawtooth wave calibration magnetic field of -5nT to 5nT and 0.2Hz in the y direction.

[0022] Step 4 includes the following relationship between polarizability and triaxial magnetic field:

[0023]

[0024] The technical effects of the present invention are as follows: The present invention provides a SERF dual-axis magnetic field measurement device and method without magnetic field modulation, which eliminates the external modulation magnetic field in traditional dual-axis measurement, can achieve higher sensitivity dual-axis magnetic field measurement, and can completely suppress magnetic field crosstalk. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a SERF biaxial magnetic field measurement device without magnetic field modulation.

[0026] Figure 2 This is a flowchart illustrating the implementation of a non-magnetic field modulated SERF biaxial magnetic field measurement method according to the present invention. SERF (Spin-Exchange Relaxation-Free) is a method without spin-exchange relaxation. Figure 2 The process includes the following steps: Step 1, activating the non-magnetic field modulated SERF dual-axis magnetic field measurement device, adjusting the frequency of the pump light emitted from the pump laser to the center of the alkali metal atom spectral line D1, minimizing the frequency shift of the alkali metal atom light caused by the pump light; adjusting the frequency detuning of the detection light emitted from the detection laser to maximize the optical rotation angle of the detection light, i.e., maximizing the response signal of the alkali metal atoms to the detection light; Step 2, applying a slowly varying sawtooth wave calibration magnetic field in the x-axis or y-axis direction, adjusting the square wave duty cycle loaded on the acousto-optic modulator to maximize the peak-to-peak value of the first harmonic signal of the pump light entering the photodetector; Step 3, applying a slowly varying sawtooth wave magnetic field in the y-axis direction, recording the first harmonic signal of the voltage signal received by the photodetector in the direction of the detection light and the first harmonic signal of the voltage signal received by the photodetector in the direction of the pump light; Step 4, measuring the first harmonic signal in the direction of the detection light and the first harmonic signal in the direction of the pump light, and detecting the electronic polarizability P in the demodulated signal sensitive detection direction of the detection optical path. x When the magnetic field B in the z-axis direction z When it approaches 0, the electronic polarizability P x Sensitive to magnetic field B y P z Sensitive to the magnitude of the transverse magnetic field in the xy plane, Among them B ⊥ It is a transverse magnetic field; Step 5, using Find the magnetic field B along the x-axis x Thus achieving B x and B y Biaxial measurement.

[0027] The reference numerals in the attached figures are listed below: 1-Detection laser; 2-First polarizer; 3-Photoelastic modulator (PEM); 4-First quarter-wave plate; 5-Analyzer; 6-First photodetector; 7-First lock-in amplifier (with a photodetector signal input and a reference signal input from the photoelastic modulator); 8-Pump laser; 9-Acousto-optic modulator (AOM); 10-Aperture; 11-Second polarizer; 12-Beam expander; 13-First mirror; 14-Second quarter-wave plate; 15-Second mirror; 16-Second photodetector; 17-Second lock-in amplifier (with a photodetector signal input and a reference signal input from the acousto-optic modulator); 18-Permalloy magnetic shielding barrel; 19-Ferrite magnetic shielding barrel; 20-Triaxial magnetic compensation coil; 21-Alkali metal gas chamber. Detailed Implementation

[0028] The following is in conjunction with the attached diagram ( Figures 1-2 The invention will be described in the following sections and examples.

[0029] Figure 1 This is a schematic diagram of a SERF biaxial magnetic field measurement device without magnetic field modulation. Figure 2 This is a schematic flowchart illustrating the implementation of a non-magnetic field modulated SERF biaxial magnetic field measurement method according to the present invention. Figures 1 to 2 As shown, a dual-axis SERF atomic magnetometer measuring device without magnetic field modulation includes a pump optical path passing through an alkali metal gas cell 21 from the z-axis direction and a detection optical path passing through the alkali metal gas cell 21 from the x-axis direction. The pump laser in the pump optical path is emitted by a pump laser 8, and passes through an acousto-optic modulator 9, an aperture 10, a second polarizer 11, a beam expander 12, a first reflector 13, and a second quarter-wave plate 14 before entering the alkali metal gas cell 21. After passing through the alkali metal gas cell 21, the pump laser passes through a second reflector 15 and a second photodetector 16 and is connected to the detection signal input terminal of a second lock-in amplifier 17. The reference signal input terminal of the second lock-in amplifier 17 is connected to the acousto-optic modulator 9. The detection light in the detection optical path is emitted by the detection laser 1, and passes sequentially through the first polarizer 2, the photoelastic modulator 3, and the first quarter-wave plate 4 before entering the alkali metal gas chamber 21. After passing through the alkali metal gas chamber 21, the detection light passes sequentially through the analyzer 5 and the first photodetector 6, and is connected to the detection signal input terminal of the first lock-in amplifier 7. The reference signal input terminal of the first lock-in amplifier 7 is connected to the photoelastic modulator 3. The first lock-in amplifier 7 demodulates the detection light, and the second lock-in amplifier 17 demodulates the pump laser. A triaxial magnetic compensation coil 20, a ferrite magnetic shielding cylinder 19, and a permalloy magnetic shielding cylinder 18 are sequentially arranged outwards from the periphery of the alkali metal gas chamber 21.

[0030] The first lock-in amplifier demodulates the detection light, and the second lock-in amplifier demodulates the pump light. A triaxial magnetic compensation coil, a ferrite magnetic shielding cylinder, and a permalloy magnetic shielding cylinder are sequentially arranged outwards from the periphery of the alkali metal gas chamber.

[0031] A method for measuring the biaxial magnetic field of a SERF without magnetic field modulation includes the following steps: Step 1, starting the biaxial magnetic field measurement device of the SERF without magnetic field modulation, adjusting the frequency of the pump light emitted from the pump laser to the center of the alkali metal atom spectral line D1, so as to minimize the frequency shift of the alkali metal atom light caused by the pump light; adjusting the frequency detuning of the detection light emitted from the detection laser to maximize the optical rotation angle of the detection light, i.e., the strongest response signal of the alkali metal atoms to the detection light; Step 2, applying a slowly varying sawtooth wave calibration magnetic field in the x-axis or y-axis direction, adjusting the duty cycle of the square wave loaded on the acousto-optic modulator to maximize the peak-to-peak value of the first harmonic signal of the pump light entering the photodetector; Step 3, applying a slowly varying sawtooth wave magnetic field in the y-direction, recording the first harmonic signal of the voltage signal received by the photodetector in the direction of the detection light and the first harmonic signal of the voltage signal received by the photodetector in the direction of the pump light; Step 4, measuring the first harmonic signal in the direction of the detection light and the first harmonic signal in the direction of the pump light, and detecting the electronic polarizability P in the demodulation signal sensitive detection direction of the detection optical path. x When the magnetic field B in the z-axis direction z When it approaches 0, the electronic polarizability P x Sensitive to magnetic field B y P z Sensitive to the magnitude of the transverse magnetic field in the xy plane, Among them B ⊥ It is a transverse magnetic field; Step 5, using Find the magnetic field B along the x-axis x Thus achieving B x and B y Biaxial measurement.

[0032] Step 4 includes the following formula: Under this working state, the relationship between polarizability and triaxial magnetic field is as shown in the following formula.

[0033]

[0034]

[0035] Where R op It is the light pumping rate, R tot γ is the total relaxation rate, d is the duty cycle of the square wave periodic signal, and γ is the total relaxation rate. e It is the electron gyromagnetic ratio, q is the nuclear spin slowing factor, ω is the pump light modulation angular frequency, and B is the electron gyromagnetic ratio. x B y B zIt is a three-axis magnetic field, and i is the imaginary unit.

[0036] Step 2 includes applying a slowly varying sawtooth wave calibration magnetic field of -5nT to 5nT and 0.2Hz in the transverse direction. Step 3 includes applying a slowly varying sawtooth wave calibration magnetic field of -5nT to 5nT and 0.2Hz in the y-direction.

[0037] The first lock-in amplifier 7 demodulates the detection light, wherein the demodulated reference signal comes from the photoelastic modulator 3, the input signal comes from the first photodetector 6 in the detection optical path, the modulation frequency is approximately 50kHz, and the first harmonic signal is demodulated. The second lock-in amplifier 17 demodulates the pump light, wherein the demodulated reference signal comes from the outer square wave input of the acousto-optic modulator 9, the input signal comes from the second photodetector 16 in the pump optical path, the modulation frequency is 1kHz, and the first harmonic signal is demodulated.

[0038] The acousto-optic modulator 9 is connected to an external signal generator, which applies a 0-5V square wave periodic signal, allowing the pump light to pass through the acousto-optic modulator 9 periodically.

[0039] The demodulated signal in the detection optical path is sensitive to the x-axis electronic polarizability P. x , where B z When P approaches 0, x Sensitive y-axis magnetic field B y .

[0040] The demodulation signal sensitive z-axis electronic polarizability P of the pump optical path z , where B z When it approaches 0, where P z Sensitive transverse (in the xy plane) magnetic field B ⊥ Then B can be calculated separately. x and B y This enables biaxial measurement.

[0041]

[0042]

[0043] P z Sensitive B ⊥ Where P x P represents the x-axis electronic polarizability. z R represents the z-axis polarizability. op It is the light pumping rate, R tot γ is the total relaxation rate, d is the duty cycle of the square wave periodic signal, and γ is the total relaxation rate. e It is the electron gyromagnetic ratio, q is the nuclear spin slowing factor, ω is the pump light modulation angular frequency, and B is the electron gyromagnetic ratio. x B y B zIt is a three-axis magnetic field, and i is the imaginary unit.

[0044] The measurement includes the following steps:

[0045] Step 1: Under specific atomic gas cell parameters and heating temperature, by adjusting the frequency of the pump light emitted from the pump laser to the center of the alkali metal atomic spectral line D1, the frequency shift of the alkali metal atomic light caused by the pump light is minimized; by adjusting the frequency detuning of the detection light emitted from the detection laser, the optical rotation angle of the detection light is maximized, that is, the response signal of the alkali metal atoms to the detection light is strongest.

[0046] Step 2: Apply a slowly varying sawtooth wave calibration magnetic field in the x-axis or y-axis direction, and adjust the duty cycle of the square wave loaded on the acousto-optic modulator so that the peak-to-peak value of the first harmonic signal of the pump light entering the photodetector is maximized.

[0047] Step 3: Apply a slowly varying sawtooth wave calibration magnetic field in the y direction, and record the first harmonic signal of the voltage signal received by the photodetector in the detection light direction and the first harmonic signal of the voltage signal received by the photodetector in the pump light direction.

[0048] Step 4: Measure the first harmonic signal in the direction of the detection light and the first harmonic signal in the direction of the pump light, and determine the electronic polarizability P in the sensitive detection direction of the demodulated signal of the detection optical path. x When magnetic field B z When it approaches 0, the electronic polarizability P x Sensitive to magnetic field B y As shown in the following formula:

[0049]

[0050] B can be measured by detecting the demodulated signal in the optical path. y The demodulated signal of the pump optical path is sensitive to the electronic polarizability P in the pump direction. z , where B z When P approaches 0, z Magnitude of the transverse magnetic field in the sensitive xy plane

[0051]

[0052] B is obtained by acquiring the demodulated signal from the pump optical path. ⊥ ;

[0053] Step 5: Utilize Find the magnetic field B along the x-axis x Thus achieving B x and B y Biaxial measurement.

[0054] Step 2 includes applying a 0-5V square wave periodic signal through an external signal generator to control the acousto-optic modulator, thereby modulating the intensity of the pump light.

[0055] Step 2 includes applying a slowly varying sawtooth wave calibration magnetic field of 5nT to 5nT and 0.2Hz in a direction perpendicular to the pump light.

[0056] Step 3 includes applying a slowly varying sawtooth wave calibration magnetic field of -5nT to 5nT and 0.2Hz in the y direction.

[0057] In step 4, R op It is the light pumping rate, R tot γ is the total relaxation rate, d is the duty cycle of the square wave periodic signal, and γ is the total relaxation rate. e It is the electron gyromagnetic ratio, q is the nuclear spin slowing factor, ω is the pump light modulation angular frequency, and B is the electron gyromagnetic ratio. x B y B z These are magnetic fields in three orthogonal directions, and i is the imaginary unit.

[0058] 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 method for measuring atomic magnetometers with a dual-axis SERF system without magnetic field modulation, characterized in that, Includes the following steps: Step 1: Start the SERF dual-axis magnetic field measurement device without magnetic field modulation. Adjust the frequency of the pump light emitted from the pump laser to the center of the alkali metal atom spectral line D1 to minimize the frequency shift of the alkali metal atom light caused by the pump light. Adjust the frequency detuning of the detection light emitted from the detection laser to maximize the optical rotation angle of the detection light, that is, to maximize the response signal of the alkali metal atoms to the detection light. Step 2: Apply a slowly varying sawtooth wave calibration magnetic field in the x-axis or y-axis direction, and adjust the duty cycle of the square wave loaded on the acousto-optic modulator so that the peak-to-peak value of the first harmonic signal of the pump light entering the second photodetector is maximized. Step 3: Apply a slowly varying sawtooth wave magnetic field in the y direction and record the first harmonic signal of the voltage signal received by the first photodetector in the detection light direction and the first harmonic signal of the voltage signal received by the second photodetector in the pump light direction. Step 4: Measure the first harmonic signal in the direction of the detection light and the first harmonic signal in the direction of the pump light, and determine the electronic polarizability P in the sensitive detection direction of the demodulated signal of the detection optical path. x When the magnetic field in the z-axis direction When it approaches 0, the electronic polarizability P x Sensitive to magnetic field B y The expression is as follows: ， in It is the average pumping rate of the pumped light. It is the total relaxation rate. It is the electron gyromagnetic ratio. It is the magnetic field along the x-axis. It is the magnetic field along the y-axis; B can be measured by detecting the demodulated signal in the optical path. y The demodulated signal of the pump optical path is sensitive to the electronic polarization P in the pump direction. z , among which when When P approaches 0, z Sensitive to the magnitude of the transverse magnetic field in the xy plane, ,in It is a transverse magnetic field; ， in It is the duty cycle of a square wave periodic signal, and π is the mathematical constant pi. It is a nuclear spin slowing factor. It is the pump light modulation angular frequency, and i is the imaginary unit; B is obtained by acquiring the demodulated signal from the pump optical path. ⊥ ; Step 5: Utilize Find the magnetic field B along the x-axis x Thus achieving B x and B y Biaxial measurement.

2. The method for measuring atomic magnetometers with non-magnetic field modulation according to claim 1, characterized in that: The SERF dual-axis magnetic field measurement device without magnetic field modulation in step 1 includes a pump optical path passing through the alkali metal gas cell (21) from the z-axis direction and a detection optical path passing through the alkali metal gas cell (21) from the x-axis direction. The pump laser in the pump optical path is emitted by the pump laser (8), and passes through the acousto-optic modulator (9), aperture (10), second polarizer (11), beam expander (12), first reflector (13), and second 1 / 4 wave plate (14) in sequence before entering the alkali metal gas cell (21). After passing through the alkali metal gas cell (21), the pump laser passes through the second reflector (15) and the second photodetector (16) and is connected to the detection signal input terminal of the second lock-in amplifier (17). The reference signal input terminal of the second lock-in amplifier (17) is connected to the acousto-optic modulator (9). The detection light in the detection optical path is emitted by the detection laser (1), passes through the first polarizer (2), the photoelastic modulator (3), and the first quarter wave plate (4) in sequence, and then enters the alkali metal gas cell (21). After passing through the alkali metal gas cell (21), the detection light passes through the analyzer (5) and the first photodetector (6) in sequence and is connected to the detection signal input terminal of the first lock-in amplifier (7). The reference signal input terminal of the first lock-in amplifier (7) is connected to the photoelastic modulator (3). The first lock-in amplifier (7) demodulates the detection light, and the second lock-in amplifier (17) demodulates the pump laser. A triaxial magnetic compensation coil (20), a ferrite magnetic shielding cylinder (19), and a permalloy magnetic shielding cylinder (18) are arranged outward from the periphery of the alkali metal gas cell (21).

3. The SERF biaxial magnetic field measurement method without magnetic field modulation according to claim 1, characterized in that, Step 2 includes applying a slowly varying sawtooth wave calibration magnetic field of -5nT to 5nT and 0.2Hz in a direction perpendicular to the pump light.

4. The SERF biaxial magnetic field measurement method without magnetic field modulation according to claim 1, characterized in that, Step 3 includes applying a slowly varying sawtooth wave calibration magnetic field of -5nT to 5nT and 0.2Hz in the y direction.

5. The SERF biaxial magnetic field measurement method without magnetic field modulation according to claim 1, characterized in that, Step 2 includes applying a 0-5V square wave periodic signal to the acousto-optic modulator through an external signal generator, so that the pump light passes through the acousto-optic modulator periodically.

6. The SERF biaxial magnetic field measurement method without magnetic field modulation according to claim 1, characterized in that, Step 4 includes the following relationship between polarizability and triaxial magnetic field: ， 。

Images