A method for measuring characteristic parameters of an atomic magnetometer based on magneto-optical modulation

Abstract

A method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation is disclosed. This method involves magneto-optical integrated modulation of an alkali metal atom ensemble to obtain the system response, and then using a parameter identification algorithm to obtain multiple characteristic parameters of the magnetometer. First, an acousto-optic modulator is added to the pump optical path to switch the light intensity. A constant magnetic field is applied along the pump light direction. Simultaneously, when the pump light is turned off, an alternating magnetic field of a certain frequency and amplitude is applied in the transverse direction, obtaining the output response signal of the atomic ensemble. The Prony algorithm is used to identify the parameters of the signal, ultimately enabling the measurement of the electron relaxation rate, spin exchange time, alkali metal number density, transverse ambient magnetic field, and longitudinal ambient magnetic field of the atomic magnetometer. This invention can rapidly and accurately measure the system characteristic parameters of an atomic magnetometer, which is of great significance for optimizing the overall performance of the magnetometer.

Description

Technical Field

[0001] This invention relates to the field of atomic magnetometer measurement technology, and specifically to a method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation. Background Technology

[0002] Atomic magnetometers, developed based on the fundamental principles of magnetic field, light field and atomic interaction, have made great strides in the theory and methods of magnetic field measurement. With their ultra-high sensitivity, they have been widely used in physical science research, measurement of extremely weak magnetocardiograms and magnetoencephalograms, as well as high-resolution imaging and analysis of magnetic fields of matter.

[0003] To optimize the overall parameters and improve the performance of atomic magnetometers, it is necessary to analyze their system characteristics. For atomic magnetometers, parameters such as electron relaxation rate, spin exchange time, alkali metal number density, and ambient magnetic field are important indicators of system characteristics. These parameters are crucial for analyzing the magnetometer's operating state and improving its performance. Therefore, how to measure the characteristic parameters of atomic magnetometers has become an urgent problem to be solved in magnetometer research. Summary of the Invention

[0004] The purpose of this invention is to address the problem of measuring the characteristic parameters of atomic magnetometers in the field of atomic magnetometer measurement technology, and to propose a method for measuring the characteristic parameters of atomic magnetometers based on magneto-optical modulation.

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

[0006] A method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation, characterized by comprising the following steps:

[0007] Step 1: Turn on the atomic magnetometer device, heat the atomic magnetometer to the working temperature, turn on the pump light to polarize the atoms in the alkali metal gas chamber to a steady state, and use a triaxial coil to compensate for the residual magnetism.

[0008] Step 2: Apply a constant DC magnetic field B0 in the pump light direction, i.e., the z-axis direction, and turn off the pump light. At the same time as turning off the pump light, apply an AC magnetic field B1cos(ωt) along the x-axis direction, where B1 is the amplitude of the AC magnetic field, ω is the frequency of the AC magnetic field, and t is the time.

[0009] Step 3: Apply linearly polarized light along the y-axis as the detection light to detect the output response signal of the alkali metal atom ensemble under magneto-optical control, i.e., the electron spin polarizability Py in the y-direction.

[0010] Step 4: Obtain the atomic magnetometer characteristic parameters from Py using the Prony parameter identification algorithm. These atomic magnetometer characteristic parameters include the electronic relaxation rate R. rel Spin exchange time TSE Alkali metal number density n, transverse environmental magnetic field B1, and longitudinal environmental magnetic field B0.

[0011] The atomic magnetometer device in step 1 includes a pump optical path and a detection optical path. The pump optical path includes a pump laser, an acousto-optic modulator, a linear polarizer, a λ / 4 waveplate, and an alkali metal gas cell connected in sequence. The acousto-optic modulator is connected to an acousto-optic modulator driver. The detection optical path includes a detection laser, an alkali metal gas cell, and a photodetector connected in sequence. The alkali metal gas cell is located inside a heating and temperature measuring device. The heating and temperature measuring device, the photodetector, the linear polarizer, and the λ / 4 waveplate are all located inside a three-dimensional coil. The three-dimensional coil is located inside a magnetically shielded container. The heating and temperature measuring device, the photodetector, and the three-dimensional coil are connected to an electronic measurement and control system via signal cables. The electronic measurement and control system includes a signal conversion module, which is connected to a temperature control module, a magnetic field control module, and a photoelectric signal processing module, respectively.

[0012] Step 1 includes adding an acousto-optic modulator to the pump optical path to switch and modulate the pump light intensity, using a linear polarizer to convert the laser emitted by the pump laser into linearly polarized light, converting the linearly polarized light into circularly polarized light through a λ / 4 waveplate, heating the alkali metal gas cell with high-frequency alternating current, and using a weak-intensity resonant pump laser to polarize the atoms to a steady state.

[0013] Step 2 includes applying a DC current to the z-axis coil of the triaxial coil to achieve B0, and applying an AC current to the x-axis coil of the triaxial coil to achieve B1cos(ωt).

[0014] Step 2 includes:

[0015] ω=g s μ B B0 / q

[0016]

[0017] Where q is the nuclear spin slowing factor, and g s μ is the electronic Landé factor. B Let τ be the Bohr magneton, τ be the time when the alternating magnetic field is applied, and ω be the frequency of the alternating magnetic field, which is the Larmor precession frequency.

[0018] Step 3 includes:

[0019]

[0020] Where P0 is the initial electronic spin polarizability, e is the natural constant, q is the nuclear spin slowing factor, and g s μ is the electronic Landé factor. B It is the Bohr magneton.

[0021] Step 3 includes: Let ω′=g s μ B B1 / 2q, then

[0022]

[0023] Where ω′ is the oscillation envelope frequency.

[0024] Step 3 includes:

[0025] Step 4 includes:

[0026] When the alkali metal atom ensemble is in the SERF mechanism, the spin exchange time T SE From the following formula, we get:

[0027]

[0028] Where R SD For spin-destructive collision relaxation, For spin-exchange collision relaxation, R SE I is the spin exchange rate, and I is the nuclear spin angular momentum;

[0029] When the alkali metal atom ensemble is in a non-SERF mechanism, the spin exchange time T SE From the following formula, we get:

[0030]

[0031] Where q SE It is the electron spin slowing factor.

[0032] Step 4 includes the alkali metal number density n, which can be obtained from the following formula:

[0033]

[0034] in This represents the cross-sectional area of ​​spin-exchange collisions between alkali metal atoms. It represents the relative thermal velocity between alkali metal atoms.

[0035] The technical effects of this invention are as follows: This invention provides a method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation. It involves magneto-optical integrated modulation of an alkali metal atom ensemble to obtain the system response, and then using a parameter identification algorithm to obtain multiple characteristic parameters of the magnetometer. First, an acousto-optic modulator is added to the pump optical path to switch the light intensity. A constant magnetic field is applied along the pump light direction. Simultaneously, when the pump light is turned off, an alternating magnetic field of a certain frequency and amplitude is applied in the transverse direction, obtaining the output response signal of the atomic ensemble. The Prony algorithm is used to identify the parameters of the signal, ultimately achieving the measurement of the electron relaxation rate, spin exchange time, alkali metal number density, transverse ambient magnetic field, and longitudinal ambient magnetic field of the atomic magnetometer. This invention can quickly and accurately measure the system characteristic parameters of an atomic magnetometer, which is of great significance for optimizing the overall performance of the magnetometer. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to the present invention. Figure 1 The process includes: Step 1, turning on the atomic magnetometer, heating the atomic magnetometer to its operating temperature, using pump light to polarize the atoms to a steady state, and using a triaxial coil to compensate for the remanence; Step 2, applying a constant DC magnetic field in the direction of the pump light, turning off the pump light, and simultaneously applying an AC magnetic field of a certain frequency and amplitude in a selected transverse direction; Step 3, applying linearly polarized light in a transverse direction other than the direction of the AC magnetic field, and detecting the output response signal of the alkali metal atom ensemble under magneto-optical modulation; Step 4, using the Prony algorithm to identify the parameters of the output response signal, obtaining the electronic relaxation rate of the magnetometer and the ambient magnetic field, and further calculating the spin exchange time and the number density of alkali metals.

[0037] Figure 2 This is a schematic diagram of the atomic magnetometer device involved in implementing the method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to the present invention.

[0038] The reference numerals in the attached figures are explained as follows: 1-Pump laser; 2-Acousto-optic modulator; 3-Linear polarizer; 4-λ / 4 waveplate; 5-Alkali metal gas cell; 6-Detection laser; 7-Three-dimensional coil; 8-Heating and temperature measuring device; 9-Signal cable; 10-Electronic measurement and control system; 11-Signal conversion module; 12-Temperature control module; 13-Magnetic field control module; 14-Photoelectric signal processing module; 15-Photodetector; 16-Magnetic shielding barrel; 17-Acousto-optic modulator driver. Detailed Implementation

[0039] The following is in conjunction with the attached diagram ( Figures 1-2 The invention will be described in the following sections and examples.

[0040] Figure 1This is a flowchart illustrating the method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to the present invention. Figure 2 This is a schematic diagram of the atomic magnetometer device involved in implementing the method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to the present invention. (Reference) Figures 1 to 2 As shown, a method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical control includes the following steps: Step 1, turning on the atomic magnetometer device, heating the atomic magnetometer to its operating temperature, turning on the pump light to polarize the atoms in the alkali metal gas chamber to a steady state, and using a triaxial coil to compensate for the remanence; Step 2, applying a constant DC magnetic field B0 in the direction of the pump light, i.e., the z-axis direction, turning off the pump light, and simultaneously applying an AC magnetic field B1cos(ωt) along the x-axis direction, where B1 is the amplitude of the AC magnetic field, ω is the frequency of the AC magnetic field, and t is time; Step 3, applying linearly polarized light as detection light along the y-axis direction to detect the output response signal of the alkali metal atom ensemble under magneto-optical control, i.e., the electron spin polarizability Py in the y-direction; Step 4, obtaining the characteristic parameters of the atomic magnetometer from Py using the Prony parameter identification algorithm, wherein the characteristic parameters of the atomic magnetometer include the electron relaxation rate R. rel Spin exchange time T SE Alkali metal number density n, transverse environmental magnetic field B1, and longitudinal environmental magnetic field B0.

[0041] The atomic magnetometer device in step 1 includes a pump optical path and a detection optical path. The pump optical path includes a pump laser 1, an acousto-optic modulator 2, a linear polarizer 3, a λ / 4 waveplate 4, and an alkali metal gas cell 5 connected in sequence. The acousto-optic modulator 2 is connected to an acousto-optic modulator driver 17. The detection optical path includes a detection laser 6, an alkali metal gas cell 5, and a photodetector 15 connected in sequence. The alkali metal gas cell 5 is located inside a heating and temperature measuring device 8. The heating and temperature measuring device 8, the photodetector 15, the linear polarizer 3, and the λ / 4 waveplate 4 are all located inside a three-dimensional coil 7. The three-dimensional coil 7 is located inside a magnetic shielding barrel 16. The heating and temperature measuring device 8, the photodetector 15, and the three-dimensional coil 7 are connected to an electronic measurement and control system 10 via a signal cable 9. The electronic measurement and control system 10 includes a signal conversion module 11, which is connected to a temperature control module 12, a magnetic field control module 13, and a photoelectric signal processing module 14.

[0042] Step 1 includes adding an acousto-optic modulator 2 to the pump optical path to switch and modulate the pump light intensity; using a linear polarizer 3 to convert the laser emitted by the pump laser 1 into linearly polarized light; converting the linearly polarized light into circularly polarized light through a λ / 4 waveplate 4; heating the alkali metal gas cell 5 with high-frequency alternating current; and using a weak-intensity resonant pump laser to polarize the atoms to a steady state. Step 2 includes achieving B0 by applying a DC current to the z-axis coil of the triaxial coil 7, and achieving B1cos(ωt) by applying an AC current to the x-axis coil of the triaxial coil 7.

[0043] Step 2 includes:

[0044] ω=g s μ B B0 / q

[0045]

[0046] Where q is the nuclear spin slowing factor, and g s μ is the electronic Landé factor. B Let τ be the Bohr magneton, τ be the time when the alternating magnetic field is applied, and ω be the frequency of the alternating magnetic field, which is the Larmor precession frequency.

[0047] Step 3 includes:

[0048]

[0049] Where P0 is the initial electronic spin polarizability, e is the natural constant, q is the nuclear spin slowing factor, and g s μ is the electronic Landé factor. B It is the Bohr magneton.

[0050] Step 3 includes: Let ω′=g s μ B B1 / 2q, then

[0051]

[0052] Where ω′ is the oscillation envelope frequency.

[0053] Step 3 includes:

[0054] Step 4 includes:

[0055] When the alkali metal atom ensemble is in a SERF (Spin-Exchange Relaxation-Free) mechanism, the spin exchange time T SE From the following formula, we get:

[0056]

[0057] Where R SD For spin-destructive collision relaxation, For spin-exchange collision relaxation, R SE I is the spin exchange rate, and I is the nuclear spin angular momentum;

[0058] When the alkali metal atom ensemble is in a non-SERF mechanism, the spin exchange time T SE From the following formula, we get:

[0059]

[0060] Where q SE It is an electron spin slowing factor.

[0061] Step 4 includes the alkali metal number density n, which can be obtained from the following formula:

[0062]

[0063] in This represents the cross-sectional area of ​​spin-exchange collisions between alkali metal atoms. It represents the relative thermal velocity between alkali metal atoms.

[0064] A method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation is proposed. This method involves magneto-optical integrated modulation of an alkali metal atom ensemble to obtain the system response, and then using a parameter identification algorithm to obtain multiple characteristic parameters of the magnetometer. First, an acousto-optic modulator is added to the pump optical path to switch the light intensity. A constant magnetic field is applied along the pump light direction. Simultaneously, when the pump light is turned off, an alternating magnetic field of a certain frequency and amplitude is applied in the transverse direction, obtaining the output response signal of the atomic ensemble. The Prony algorithm (also known as the Prony algorithm) is used to identify the parameters of the signal, ultimately enabling the measurement of the electron relaxation rate, spin exchange time, alkali metal number density, transverse ambient magnetic field, and longitudinal ambient magnetic field of the atomic magnetometer.

[0065] Specifically, the following steps are included:

[0066] Step 1: Add an acousto-optic modulator to the pump optical path to switch and modulate the pump light intensity, heat the atomic magnetometer to the working temperature, use a weak-intensity resonant pump laser to polarize the atoms to a steady state, and use a triaxial coil to compensate for the remanence.

[0067] Step 2: Apply a constant DC magnetic field in the direction of the pump light, turn off the pump light, and at the same time as the light is turned off, apply an AC magnetic field of a certain frequency and amplitude in a certain transverse direction.

[0068] Step 3: Apply a beam of linearly polarized light in the transverse direction outside the direction of the alternating magnetic field to detect the output response signal of the alkali metal atom ensemble under magneto-optical modulation;

[0069] Step 4: The output response signal is parameter identified using the Prony algorithm to obtain the electronic relaxation rate of the magnetometer and the ambient magnetic field. At the same time, the spin exchange time and alkali metal number density are further calculated.

[0070] Step 1 includes: converting the laser output from the pump laser into circularly polarized light by sequentially passing it through a linear polarizer and a λ / 4 waveplate; then using an acousto-optic modulator to switch the intensity of the pump light; injecting the first-order diffracted light through the acousto-optic modulator into the alkali metal gas cell for pumping; and heating the alkali metal gas cell using high-frequency alternating current.

[0071] The theoretical analysis of the atomic ensemble spin evolution process in the atomic magnetometer under the magneto-optical modulation in step 2 is as follows:

[0072] First, the Z direction is defined as the pump light direction, the X direction as the applied AC magnetic field direction, and the Y direction as the detection linearly polarized light direction. The spin evolution process of alkali metal atoms can be approximately described by the Bloch equation in classical mechanics:

[0073]

[0074] Where P is the electron spin polarizability, t is time, B is the external magnetic field, and × is the cross product of vectors; g s μ is the electronic Landé factor. B For the Bohr magneton, both the electron Landé factor and the Bohr magneton are constants; R op Let be the pump rate, and s be the circular polarization vector of the photon. For direction, R rel is the electron spin relaxation rate; q is the nuclear spin slowing factor, which can be considered a constant under low light intensity.

[0075] After the external magnetic field is compensated to zero, a constant DC magnetic field B0 is applied in the Z direction. When the atomic ensemble is polarized to a steady state by the pump light, the pump light is turned off and an AC magnetic field B1cos(ωt) is applied simultaneously, with the frequency of the applied AC magnetic field ω = g. s μ B B0 / q, so that the amplitude B1 of the alternating magnetic field satisfies Where τ is the time during which the alternating magnetic field is applied.

[0076] Under these conditions, the electronic spin polarizability Py in the Y direction can be further derived as follows:

[0077]

[0078] Where P0 is the initial electron spin polarization. It is easy to see that Py directly contains information on the electron relaxation rate, the transverse ambient magnetic field, and the longitudinal ambient magnetic field.

[0079] Let ω′=g s μ B B1 / 2q, combined with the above ω=g s μ B B0 / q, can be used to write Py as:

[0080]

[0081] Where ω′ is the oscillation envelope frequency and ω is the Larmor precession frequency.

[0082] In step 2, a magnetic field is applied by applying current to the triaxial coil outside the air chamber. After applying a fixed current (DC magnetic field) in the pump light direction, an alternating current is applied in a certain transverse direction to apply an alternating magnetic field. The scanning frequency is selected to determine a specific frequency value based on theoretical analysis, and a fixed amplitude of the alternating current is set according to theoretical analysis.

[0083] In step 3, the linearly polarized detection light passes through the alkali metal gas cell and reaches the photodetector. The optical signal is converted into an electrical signal and then input into the electronic measurement and control system to obtain the atomic ensemble output response signal.

[0084] The Prony algorithm described in step 4 is a parameter identification algorithm for time-domain signals. Its typical application model is a combination of exponential functions with arbitrary amplitude, phase, frequency, and attenuation factor, i.e., a set of exponentially decaying sinusoidal components. The output signal Py can be further written as:

[0085]

[0086] The signal is now in the form of the sum of two sinusoidally decaying signals, and the parameters of the output signal can be identified using the Prony algorithm.

[0087] In step 4, the output signal Py is identified by the Prony algorithm, and the electronic relaxation rate R can be directly obtained. rel Horizontal environmental magnetic field B1 and longitudinal environmental magnetic field B0.

[0088] 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 the characteristic parameters of an atomic magnetometer based on magneto-optical modulation, characterized in that, Includes the following steps: Step 1: Turn on the atomic magnetometer device, heat the atomic magnetometer to the working temperature, turn on the pump light to polarize the atoms in the alkali metal gas chamber to a steady state, and use a triaxial coil to compensate for the residual magnetism. Step 2: Apply a constant DC magnetic field B0 in the pump light direction, i.e., the z-axis direction, and turn off the pump light. At the same time as turning off the pump light, apply an AC magnetic field B1cos(ωt) along the x-axis direction, where B1 is the amplitude of the AC magnetic field, ω is the frequency of the AC magnetic field, and t is the time. Step 3: Apply linearly polarized light along the y-axis as the detection light to detect the output response signal of the alkali metal atom ensemble under magneto-optical control, i.e., the electron spin polarizability Py in the y-direction. Step 4: Obtain the atomic magnetometer characteristic parameters from Py using the Prony parameter identification algorithm. These atomic magnetometer characteristic parameters include the electronic relaxation rate R. rel Spin exchange time T SE Alkali metal number density n, transverse environmental magnetic field B1, and longitudinal environmental magnetic field B0.

2. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 1, characterized in that, The atomic magnetometer device in step 1 includes a pump optical path and a detection optical path. The pump optical path includes a pump laser, an acousto-optic modulator, a linear polarizer, a λ / 4 waveplate, and an alkali metal gas cell connected in sequence. The acousto-optic modulator is connected to an acousto-optic modulator driver. The detection optical path includes a detection laser, an alkali metal gas cell, and a photodetector connected in sequence. The alkali metal gas cell is located inside a heating and temperature measuring device. The heating and temperature measuring device, the photodetector, the linear polarizer, and the λ / 4 waveplate are all located inside a triaxial coil. The triaxial coil is located inside a magnetically shielded container. The heating and temperature measuring device, the photodetector, and the triaxial coil are connected to an electronic measurement and control system via signal cables. The electronic measurement and control system includes a signal conversion module, which is connected to a temperature control module, a magnetic field control module, and a photoelectric signal processing module, respectively.

3. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 2, characterized in that, Step 1 includes adding an acousto-optic modulator to the pump optical path to switch and modulate the pump light intensity, using a linear polarizer to convert the laser emitted by the pump laser into linearly polarized light, converting the linearly polarized light into circularly polarized light through a λ / 4 waveplate, heating the alkali metal gas cell with high-frequency alternating current, and using a weak-intensity resonant pump laser to polarize the atoms to a steady state.

4. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 2, characterized in that, Step 2 includes applying a DC current to the z-axis coil of the triaxial coil to achieve B0, and applying an AC current to the x-axis coil of the triaxial coil to achieve B1cos(ωt).

5. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 1, characterized in that, Step 2 includes: ω=g s μ B B0 / q Where q is the nuclear spin slowing factor, and g s μ is the electronic Landé factor. B Let τ be the Bohr magneton, τ be the time when the alternating magnetic field is applied, and ω be the frequency of the alternating magnetic field, which is the Larmor precession frequency.

6. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 5, characterized in that, Step 3 includes: Where P0 is the initial electronic spin polarizability, e is the natural constant, q is the nuclear spin slowing factor, and g s μ is the electronic Landé factor. B It is the Bohr magneton.

7. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 5, characterized in that, Step 3 includes: Let ω′=g s μ B B1 / 2q, then Where ω′ is the oscillation envelope frequency.

8. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 7, characterized in that, Step 3 includes:

9. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 1, characterized in that, Step 4 includes: When the alkali metal atom ensemble is in the SERF mechanism, the spin exchange time T SE From the following formula, we get: Where R SD For spin-destructive collision relaxation, For spin-exchange collision relaxation, R SE I is the spin exchange rate, and I is the nuclear spin angular momentum; When the alkali metal atom ensemble is in a non-SERF mechanism, the spin exchange time T SE From the following formula, we get: Where q SE It is an electron spin slowing factor.

10. The method for measuring the characteristic parameters of an atomic magnetometer based on magneto-optical modulation according to claim 9, characterized in that, Step 4 includes the alkali metal number density n, which can be obtained from the following formula: in This represents the cross-sectional area of ​​spin-exchange collisions between alkali metal atoms. It represents the relative thermal velocity between alkali metal atoms.

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