Quantum-based multi-frequency magnetic field simultaneous amplification measurement method

Abstract

The present invention discloses a quantum-based multi-frequency magnetic field simultaneous amplification measurement method, comprising the following steps: building a measurement model, including a mixed atomic vapor chamber, a non-magnetic heating system, a laser pumping and detection system, a signal acquisition system, a magnetic shielding system, and four groups of Helmholtz coils; heating and polarizing alkali metal atoms in the mixed atomic vapor chamber; applying a known oscillating AC magnetic field on the z-axis, and applying the oscillating AC magnetic field to be measured to the x-axis or y-axis; applying a bias magnetic field on the z-axis and adjusting the magnetic field frequency until an amplified magnetic field signal appears on the spectrum; removing the z-axis oscillating AC magnetic field, adjusting the bias magnetic field size to the multi-frequency amplification frequency, and finding the frequency corresponding to the highest peak of the spectrum, which is the frequency to be measured. By applying an oscillating AC magnetic field on the z-axis, the energy level of the inert gas nuclei is Zeeman split, and the external magnetic field signals of multiple frequencies are amplified at the same time, the retrieval efficiency is improved at the femto-tesla level, and the experimental cycle is effectively shortened.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic field detection, and in particular relates to a quantum-based multi-frequency magnetic field simultaneous amplification measurement method. Background Art

[0002] Weak magnetic field measurements are widely used in basic physics testing, cutting-edge physics research, diagnosis of major diseases such as brain magnetism / heart magnetism, structural analysis of chemical substances, national defense security and other important fields. Therefore, the detection of weak magnetic fields is particularly important.

[0003] In the prior art, an atomic magnetometer is generally used to detect magnetic fields. Its basic principle is to measure the magnetic field by utilizing the rotation in of the spin polarization vector of the outermost electron of an alkali metal atom in an external magnetic field. It uses a weak detection light beam to directly detect the size of the electron spin polarization to determine the rotation precession frequency, thereby measuring the external magnetic field. However, the atomic magnetometer has a low sensitivity for detecting extremely weak magnetic fields at low or very low frequencies. Some scholars have also used spin amplifiers to quantum-amplify the magnetic field to improve its measurement sensitivity. However, the existing quantum spin amplifiers use the magnetic measurement method of inert gas nuclei and can only amplify magnetic fields of a single inherent frequency. During measurement, it is necessary to scan the frequencies one by one to retrieve weak signals and amplify them, resulting in low retrieval efficiency. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a quantum-based multi-frequency magnetic field simultaneous amplification measurement method, which can simultaneously amplify multiple frequency magnetic field signals, effectively improve the efficiency of initial retrieval of weak magnetic field signals at the femtotesla level, and shorten the experimental cycle.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a quantum-based multi-frequency magnetic field simultaneous amplification measurement method, characterized in that it includes the following steps:

[0006] S1: Build the measurement model, including the hybrid atomic vapor chamber, non-magnetic heating system, laser pumping and detection system, signal acquisition system, magnetic shielding system and four sets of Helmholtz coils;

[0007] S2: heating and polarizing the alkali metal atoms in the mixed atomic vapor chamber to obtain the spin signals of the alkali metal atomic electrons;

[0008] S3: applying a known oscillating AC magnetic field in the z-axis direction, and applying the oscillating AC magnetic field to be measured in the x-axis or y-axis direction;

[0009] S4: applying a bias magnetic field in the z-axis direction and adjusting the frequency of the magnetic field until an amplified magnetic field signal appears on the spectrum, and obtaining an nth magnetic signal amplitude value A2n away from the center frequency;

[0010] S5: Remove the oscillating AC magnetic field in the z-axis direction, adjust the bias magnetic field frequency in the z-axis direction to the frequency position of the multi-frequency amplification in step S4 in turn, and find the Larmor precession frequency of the inert gas nuclei corresponding to the highest peak in the spectrum. This frequency is the oscillating AC magnetic field frequency to be measured.

[0011] Furthermore, step S2' is added before step S3: a bias magnetic field and an oscillating AC magnetic field are applied in the z-axis direction respectively, and an oscillating AC magnetic field of 1 pT and 220 Hz is applied in the x-axis or y-axis direction, and a signal of T time is collected, and a magnetic signal amplitude value A1 of the 220 Hz magnetic field on the spectrum is obtained through Fourier transform.

[0012] Furthermore, in step S1, the mixed atomic vapor chamber is arranged above the non-magnetic heating system, and the mixed atomic vapor chamber and the non-magnetic heating system are both arranged inside the magnetic shielding system; the laser pumping and detection system and the signal acquisition system are arranged outside the magnetic shielding system for detecting magnetic field signals.

[0013] Furthermore, in step S1, four groups of Helmholtz coils are arranged between the magnetic shielding system and the mixed atomic vapor chamber, and one group is arranged along the x-axis and the other along the y-axis, and two groups are arranged along the z-axis.

[0014] Furthermore, in step S2, the non-magnetic heating system is first turned on to heat the mixed atomic vapor chamber to increase the number density of alkali metal atoms in the mixed atomic vapor chamber; then the laser pumping and detection system is turned on to polarize the alkali metal atoms in the mixed atomic vapor chamber with the pump laser, and the polarized electrons of the alkali metal atoms polarize the inert gas nuclei through spin exchange collision; the detection laser detects the Faraday rotation angle of the alkali metal atomic cluster through the mixed atomic vapor chamber, obtains the spin signal of the alkali metal atomic electrons and transmits it to the signal acquisition system.

[0015] Furthermore, the mixed atomic vapor chamber is an atomic gas chamber filled with alkali metals, inert gases and nitrogen; the non-magnetic heating system uses non-magnetic materials to heat the mixed atomic vapor chamber; the laser pumping and detection system includes two vertically arranged pump lasers and detection lasers, which are respectively used to polarize potassium alkali metal atoms and detect alkali metal atoms; the magnetic shielding system is composed of five layers of cylindrical Permalloy and ferrite, and the innermost and outermost layers of the five layers of cylindrical Permalloy are provided with demagnetization coils; the signal acquisition system includes an acousto-optic modulator, a phase-locked amplifier, a photodetector, an optical element and an acquisition card, which are used to acquire the magnetic signal detected by the detection laser and perform Fourier transform on the acquired magnetic signal.

[0016] The beneficial effect of adopting the above technical scheme is as follows: the present invention applies an oscillating AC magnetic field and a bias magnetic field in the z-axis direction, and the oscillating AC magnetic field causes the energy levels of the inert gas nuclei in the mixed atomic vapor chamber 10 to form Zeeman splitting, and an amplification effect occurs at certain frequency intervals near the center frequency, while responding to and amplifying external magnetic signals at multiple frequencies, thereby forming a multi-frequency amplified signal with the Larmor precession frequency of the inert gas nuclei under the bias magnetic field as the center frequency. In this way, multiple frequencies can be formed at one time for frequency scanning, which greatly improves the retrieval efficiency compared with the existing single frequency scanning method and effectively shortens the laboratory test cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the measurement model of the present invention;

[0018] Numbers in the figure: 10, hybrid atomic vapor chamber, 20, non-magnetic heating system, 30, laser pumping and detection system, 40, signal acquisition system, 50 magnetic shielding system; DETAILED DESCRIPTION

[0019] The present invention is further described in detail below through a specific embodiment.

[0020] As shown in the figure, a measurement model is constructed, including a mixed atomic vapor chamber 10, a non-magnetic heating system 20, a laser pumping and detection system 30, a signal acquisition system 40 and a magnetic shielding system 50; the mixed atomic vapor chamber 10 is an atomic gas chamber filled with alkali metal, inert gas and nitrogen. Preferably, the alkali metal is potassium, the inert gas is helium, and the nitrogen can also be replaced by 4 He. The non-magnetic heating system 20 uses non-magnetic materials to avoid magnetic interference. The non-magnetic heating system 20 is arranged below the mixed atomic vapor chamber 10, and is mainly used to heat the potassium and helium in the mixed atomic vapor chamber 10. The laser pumping and detection system 30 includes two vertically arranged lasers, which are used to emit pump lasers and detection lasers respectively. The pump laser is used to polarize potassium alkali metal atoms, and the detection laser is used to detect alkali metal atoms. The signal acquisition system 40 includes an acousto-optic modulator, a phase-locked amplifier, a photodetector, an optical element and an acquisition card, which are used to collect the magnetic signal detected by the detection light and perform Fourier transform on the collected magnetic signal. The magnetic shielding system 50 is composed of five layers of cylindrical Permalloy and ferrite. The innermost and outermost layers of the five layers of cylindrical Permalloy are provided with demagnetization coils, which are mainly used to shield the interference of the external magnetic field on the entire measurement system.

[0021] A bobbin for carrying Helmholtz coils is arranged between the non-magnetic heating system 20 and the magnetic shielding system 50. A group of Helmholtz coils are arranged on the bobbin along the x-axis and y-axis directions, respectively, and two groups of Helmholtz coils are arranged along the z-axis direction. The Helmholtz coils in the x-axis, y-axis and z-axis directions are all used to generate an applied magnetic field during the measurement process.

[0022] During specific measurements, the non-magnetic heating system 20 is first turned on to heat the mixed atomic vapor chamber 10 to increase the number density of alkali metal atoms in the mixed atomic vapor chamber 10; then the laser pumping and detection system 30 is turned on to polarize the alkali metal atoms in the mixed atomic vapor chamber 10 with the pump laser, and the polarized electrons of the alkali metal atoms polarize the inert gas nuclei through spin exchange collision; the detection laser detects the Faraday rotation angle of the alkali metal atomic cluster through the mixed atomic vapor chamber 10, obtains the spin signal of the alkali metal atomic electrons and transmits it to the signal acquisition system 40.

[0023] First, a bias magnetic field and an oscillating AC magnetic field are applied to two groups of Helmholtz coils in the z-axis direction, respectively. The bias magnetic field is a static magnetic field, and the Larmor precession frequency of the inert gas nuclei under the bias magnetic field is the center frequency of multi-frequency simultaneous amplification; the oscillating AC magnetic field can cause the energy levels of the inert gas nuclei to form Zeeman splitting, and an amplification effect appears at certain intervals near the center frequency, while responding to and amplifying external magnetic signals at multiple frequencies. That is, under the joint action of the bias magnetic field and the oscillating AC magnetic field, a multi-frequency amplified magnetic signal is formed with the Larmor precession frequency of the inert gas nuclei under the bias magnetic field as the center and the integer multiples of the oscillating AC magnetic field frequency as the interval. A 1pT, 220Hz oscillating AC magnetic field is applied in the x-axis or y-axis direction, and the signal of T time is collected. Through Fourier transform, the 220Hz magnetic signal amplitude value on the spectrum is obtained, and the magnetic signal amplitude value is the unamplified magnetic signal amplitude value A1.

[0024] Next, the oscillating AC magnetic field in the z-axis direction is kept unchanged, and an oscillating AC magnetic field of 1pT and the frequency to be measured is applied along the x-axis or y-axis direction. The size of the bias magnetic field in the z-axis direction is continuously adjusted, and the Larmor precession frequency of the inert gas nuclei and the center frequency of the multi-frequency amplification are changed by the size of the bias magnetic field, thereby changing the frequency values ​​of each point of the multi-frequency amplification until an amplified magnetic field signal appears on the spectrum, indicating that there is a frequency value in the multi-frequency amplification that is consistent with the frequency of the oscillating AC magnetic field to be measured, and the amplitude value A2n of the nth magnetic signal away from the center frequency is obtained.

[0025] Finally, remove the oscillating AC magnetic field in the z-axis direction, and adjust the bias magnetic field in the z-axis direction according to the frequency values ​​of each point in the last multi-frequency amplification in the previous step so that the Larmor precession frequency of the inert gas nuclei is the above frequencies in sequence, and find the Larmor precession frequency of the inert gas nuclei corresponding to the highest peak in the spectrum, which is the frequency of the oscillating AC magnetic field to be measured. The above method can not only quickly and accurately measure the frequency of the oscillating AC magnetic field to be measured, but also calculate the amplification factor of the multi-frequency amplification, that is, ampn=A2n / A1, so as to know the sensitivity of the measurement method.

[0026] The principle of the present invention is: by applying an oscillating AC magnetic field and a bias magnetic field in the z-axis direction, the oscillating AC magnetic field causes the energy level of the inert gas nuclei in the mixed atomic vapor chamber 10 to form Zeeman splitting, and an amplification effect appears at a certain frequency interval near the center frequency, and simultaneously responds to and amplifies external magnetic signals at multiple frequencies, thereby forming a multi-frequency amplified signal with the Larmor precession frequency of the inert gas nuclei under the action of the bias magnetic field as the center frequency, that is, the bias magnetic field determines the center frequency of the multi-frequency amplification; the oscillating AC magnetic field determines the frequency interval of the multi-frequency amplification, and forms a magnetic signal corresponding to multiple frequency values ​​and amplified at the same time. The oscillating AC magnetic field to be measured is applied to the measurement model through the Helmholtz line in the x-axis or y-axis direction, the bias magnetic field size is changed to adjust the frequency values ​​in the multi-frequency amplification, and the multi-frequency values ​​corresponding to the frequency of the oscillating AC magnetic field to be measured are quickly obtained by multi-frequency sweeping, and then the oscillating AC magnetic field in the z-axis direction is removed, the bias magnetic field size is changed to change the Larmor precession frequency of the inert gas nuclei, and a single frequency sweep is performed to determine the frequency of the oscillating AC magnetic field to be measured. Through the above steps, the frequency range of the oscillating AC magnetic field to be measured can be quickly determined at the femtotesla level by using multi-frequency simultaneous amplification and sweeping, and then accurately measured by single-frequency sweeping, which greatly saves the sweeping time, improves the retrieval efficiency, and effectively shortens the laboratory test cycle.

Claims

1. A quantum-based multi-frequency magnetic field simultaneous amplification measurement method, characterized in that: The following steps are involved: S1: Build the measurement model, including the hybrid atomic vapor chamber, non-magnetic heating system, laser pumping and detection system, signal acquisition system, magnetic shielding system and four sets of Helmholtz coils; S2: heating and polarizing the alkali metal atoms in the mixed atomic vapor chamber to obtain the spin signals of the alkali metal atomic electrons; S2': apply a bias magnetic field and an oscillating AC magnetic field in the z-axis direction, apply a 1pT, 220Hz oscillating AC magnetic field in the x-axis or y-axis direction, collect the signal for T time, and obtain the magnetic signal amplitude value A1 of the 220Hz magnetic field on the spectrum through Fourier transform; S3: applying a known oscillating AC magnetic field in the z-axis direction, and applying the oscillating AC magnetic field to be measured in the x-axis or y-axis direction; S4: Apply a bias magnetic field in the z-axis direction and adjust the frequency of the magnetic field until an amplified magnetic field signal appears on the spectrum, and obtain the amplitude value A2n of the nth magnetic signal away from the center frequency. The amplification factor of the nth magnetic signal by multi-frequency amplification is ampn=A2n / A1; S5: Remove the oscillating AC magnetic field in the z-axis direction, adjust the bias magnetic field frequency in the z-axis direction to the frequency position of the multi-frequency amplification in step S4 in turn, and find the Larmor precession frequency of the inert gas nuclei corresponding to the highest peak in the spectrum. This frequency is the oscillating AC magnetic field frequency to be measured.

2. The quantum-based multi-frequency magnetic field simultaneous amplification measurement method according to claim 1 is characterized in that: In step S1, the mixed atomic vapor chamber is arranged above the non-magnetic heating system, and the mixed atomic vapor chamber and the non-magnetic heating system are both arranged inside the magnetic shielding system; the laser pumping and detection system and the signal acquisition system are arranged outside the magnetic shielding system for detecting magnetic field signals.

3. The quantum-based multi-frequency magnetic field simultaneous amplification measurement method according to claim 1, characterized in that: In the step S1, four groups of Helmholtz coils are arranged between the magnetic shielding system and the mixed atomic vapor chamber, and one group is arranged along the x-axis and the other along the y-axis, and two groups are arranged along the z-axis.

4. The quantum-based multi-frequency magnetic field simultaneous amplification measurement method according to claim 1 is characterized in that: In step S2, the non-magnetic heating system is first turned on to heat the mixed atomic vapor chamber to increase the number density of alkali metal atoms in the mixed atomic vapor chamber; then the laser pumping and detection system is turned on to polarize the alkali metal atoms in the mixed atomic vapor chamber with the pump laser, and the polarized electrons of the alkali metal atoms polarize the inert gas nuclei through spin exchange collision; the detection laser detects the Faraday rotation angle of the alkali metal atomic cluster through the mixed atomic vapor chamber, obtains the spin signal of the alkali metal atomic electrons and transmits it to the signal acquisition system.

5. The quantum-based multi-frequency magnetic field simultaneous amplification measurement method according to claim 1, characterized in that: The mixed atomic vapor chamber is an atomic gas chamber filled with alkali metals, inert gases and nitrogen; the non-magnetic heating system uses non-magnetic materials to heat the mixed atomic vapor chamber; the laser pumping and detection system includes two vertically arranged pump lasers and detection lasers, which are respectively used to polarize potassium alkali metal atoms and detect alkali metal atoms; the magnetic shielding system is composed of five layers of cylindrical Permalloy and ferrite, and the innermost and outermost layers of the five layers of cylindrical Permalloy are provided with demagnetization coils; the signal acquisition system includes an acousto-optic modulator, a phase-locked amplifier, a photodetector, an optical element and an acquisition card, which are used to acquire magnetic signals detected by the detection laser and perform Fourier transform on the acquired magnetic signals.

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