Method for suppressing common-mode noise of CPT magnetometer

Abstract

The invention discloses a method for suppressing common-mode noise of a CPT magnetometer, which can remarkably improve the performance of the CPT magnetometer by introducing a differential detection technology and an adaptive signal processing method. A beam of coherent laser is configured, two beams of light generated by a spectroscope respectively pass through different paths, one beam of light passes through an atomic gas chamber, the other beam of light does not pass through the atomic gas chamber, and a high-sensitivity photoelectric detector is used for collecting signals. A differential signal of two signals is generated by using a differential amplifier, so that the influence of common-mode noise is effectively eliminated. Then, the differential signal is subjected to adaptive filtering through a digital signal processor, and the signal quality is further improved. Experiments show that the method can significantly improve the measurement precision and stability of the CPT magnetometer, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the field of quantum precision measurement technology, and in particular to a method for suppressing common mode noise of a CPT magnetometer. Background Art

[0002] CPT magnetometer (CPT, coherent population trapping) is a high-precision measuring instrument based on coherent optical effect and cold atom technology, which is widely used in geophysical exploration, navigation, space science and other fields. However, in practical applications, the measurement signal of CPT magnetometer is often affected by various noises, especially common mode noise, which can significantly reduce its measurement accuracy and stability.

[0003] Common-mode noise usually comes from external environmental factors, such as electromagnetic interference, vibration, and temperature changes. These noises will affect multiple channels of the sensor at the same time. Traditional single-channel measurement technology has limited ability to suppress these noises, so an effective method is urgently needed to improve the anti-interference ability of the measurement system.

[0004] In recent years, differential detection technology has been gradually introduced into the application of coherent population trapping. This technology can effectively eliminate the influence of common mode noise by acquiring two signals at the same time and calculating their difference, thereby improving the accuracy and stability of the measurement. In addition, with the development of digital signal processing technology, combined with high-sensitivity photodetectors and advanced filtering algorithms, the performance of CPT magnetometers will be further improved.

[0005] Therefore, developing a method to suppress the common mode noise of CPT magnetometers using differential detection has important research significance and application value. This method can not only improve the anti-interference ability of the measurement system, but also maintain excellent performance in various complex environments, laying the foundation for the widespread application of CPT magnetometers. Summary of the invention

[0006] The purpose of the present invention is to provide a method for suppressing the common mode noise of a CPT magnetometer, which is conducive to significantly improving the measurement accuracy of a CPT magnetometer (CPT, coherent population trapping) in practical applications and reducing errors caused by common mode noise. The stability of the magnetometer under various environmental conditions is improved so that it can maintain reliable performance in complex or dynamic environments. The influence of external common mode noise on the signal is effectively suppressed, thereby improving the signal quality and ensuring the accuracy of the data. Technical support is provided for the wide application of CPT magnetometers, so that they can be applied to multiple fields with high-precision measurement requirements such as geophysical exploration, navigation, and space science. Adaptive filtering is performed by a digital signal processor to achieve real-time processing of the signal to meet the needs of fast and dynamic measurement. By configuring a beam of coherent laser, two beams of light generated by a spectroscope pass through different paths respectively, one beam of light passes through an atomic gas chamber, and the other beam of light does not pass through the atomic gas chamber, and a high-sensitivity photodetector is used to collect signals. A differential amplifier is used to generate a differential signal of the two signals, thereby effectively eliminating the influence of common mode noise. Subsequently, the differential signal is adaptively filtered through a digital signal processing module to further improve the signal quality.

[0007] The technical solution of the present invention is as follows:

[0008] A method for suppressing common mode noise of a CPT magnetometer, characterized by comprising the following steps:

[0009] Step 1, using a CPT magnetometer device based on feedback control and differential detection to generate multi-color lasers at the detection laser input side of the atomic gas chamber;

[0010] Step 2, using a polarization beam splitter to split the multicolor laser into two beams, one beam as a detection signal light entering the atomic gas chamber to interact with atoms, and the other beam as a reference signal light not entering the atomic gas chamber;

[0011] Step 3, the detection signal light emitted from the atomic gas chamber is connected to the first input end of the differential amplifier through the first reflector, the first beam splitter, the second 1 / 4 wave plate, the first analyzer and the first photodetector in sequence, the reference signal light is connected to the second input end of the differential amplifier through the second reflector, the first beam splitter, the second analyzer and the second photodetector, and the output end of the differential amplifier is connected to the digital signal processor;

[0012] Step 4, in the differential amplifier, the detection signal and the reference signal generate a differential signal, and the differential amplifier demodulates the phase difference between the detection signal and the reference signal, thereby eliminating the common mode noise component;

[0013] Step 5: Use a digital signal processor to adaptively filter the differential signal, thereby optimizing the signal quality in real time.

[0014] In step 2, the input side of the polarization beam splitter is connected to the detection laser through the electro-optic phase modulator, the 1 / 2 wave plate and the second linear polarizer in sequence, the transmission side of the polarization beam splitter is connected to the first reflector through the atomic gas chamber, the reflection side of the polarization beam splitter is connected to the second reflector, the pump laser input side of the atomic gas chamber is connected to the saturated absorption frequency stabilization module through the first 1 / 4 wave plate, the first linear polarizer, the laser power stabilization system, the lens group and the pump laser in sequence, the atomic gas chamber is located in the oven, the oven is located in the magnetic field coil, and the magnetic field coil is located in the magnetic shielding device.

[0015] The pump laser generates laser light with a central wavelength of 770 nm, which is the D1 resonance line of K. The wavelength of the laser light emitted by the detection laser is shifted by 0.2 nm relative to 795 nm, which is the D1 resonance line of Rb.

[0016] In step 3, the detection signal light meets the reference signal light at the first beam splitter and interferes with each other.

[0017] Step 3 includes the following expressions:

[0018] E t =E pt +E sr ,

[0019] E r =E pr +E st ,

[0020] Where E t is the resultant vibration, E pt is the p-polarized light vibration of the detection signal light, E sr is the s-polarized light vibration of the reference signal light, E r is the resulting vibration, E pr is the p-polarized light vibration of the reference signal light, E st is the s-polarized light vibration of the detection signal light.

[0021] Step 4 includes the following expressions:

[0022] V diff =V1-V2,

[0023]

[0024] a=tanβ1tanβ2(1+tan(φ BS / 2)tanφ),

[0025] b=tanβ1(1-tan(φ BS / 2)tanφ)+tanβ2(tan(φ BS / 2)-tanφ),

[0026] c=tan(φ BS / 2)+tanφ,

[0027] Where V diff is the differential signal, V1 is the detection signal, V2 is the reference signal, Δψ is the phase difference, ψ t is the total phase of the detection signal light, ψ r is the total phase of the reference signal light, φ t is the intrinsic phase of the detection signal light, φ r is the intrinsic phase of the reference signal light, φ Bs is the phase delay involving the first beam splitter, φ is the phase delay involving the first reflector and the first beam splitter, θ is the optical rotation angle, a, b, c are all intermediate quantities, β1 is the angle between the transmission axis of the first analyzer and the y-axis, and β2 is the angle between the transmission axis of the second analyzer and the y-axis.

[0028] The adaptive filtering in step 5 is a Kalman filter or a minimum mean square error filter.

[0029] The technical effects of the present invention are as follows: Compared with the prior art, the method for suppressing the common mode noise of a CPT magnetometer of the present invention can form the following advantages:

[0030] (1) Effectively eliminate common mode noise: improve the accuracy and reliability of measurement results.

[0031] (2) Enhanced measurement sensitivity: suitable for high-precision detection of weak magnetic fields.

[0032] (3) Real-time signal processing: Rapid response capability meets the needs in dynamic environments.

[0033] (4) Adaptive adjustment capability: Automatically optimize parameters according to environmental changes to enhance system adaptability.

[0034] (5) Simplify system structure: reduce system complexity and cost, and improve integration.

[0035] (6) Broad application prospects: Applicable to many fields such as geophysical exploration and navigation.

[0036] (7) The present invention provides an innovative and effective solution for achieving high-precision magnetic field measurement, and has significant practical value and application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1The present invention is a schematic flow chart of a method for suppressing common mode noise of a CPT magnetometer. CPT is coherent population trapping. Figure 1 The method comprises step 1, generating multicolor laser; step 2, modulating the laser by a linear polarizer, a half-wave plate and an electro-optic phase modulator; step 3, using a polarization beam splitter to split the laser beam into two beams, one beam is used to interact with atoms and is the signal light, and the other beam is used as a reference signal; step 4, after the signal light is reflected by a mirror, it meets and interferes with the reference light at the beam splitter, and the interference signal is detected by a photodetector after passing through a polarization element; step 5, inputting the signal passing through the gas chamber and the reference signal into a differential amplifier to generate a differential signal and eliminate the common-mode noise component; step 6, adaptively filtering the differential signal, using an algorithm to automatically adjust the filtering parameters to optimize the signal quality in real time, and using algorithms such as fast Fourier transform to analyze the signal spectrum to further extract useful information.

[0038] Figure 2 The present invention is a schematic diagram of the structure of a CPT magnetometer device based on feedback control and differential detection involved in a method for suppressing common mode noise of a CPT magnetometer.

[0039] The reference numerals are as follows: 1-saturated absorption frequency stabilization module; 2-pump laser; 3-lens group; 4-first linear polarizer; 5-first 1 / 4 wave plate; 6-magnetic shielding device; 7-oven; 8-atomic gas chamber; 9-magnetic field coil; 10-first reflector; 11-first beam splitter; 12-second 1 / 4 wave plate; 13-first analyzer; 14-first photodetector; 15-second analyzer; 16-second photodetector; 17-differential amplifier; 18-digital signal processor; 19-second reflector; 20-polarization beam splitter; 21-electro-optic phase modulator; 22-1 / 2 wave plate; 23-second linear polarizer; 24-detection laser; 25-laser power stabilization system. DETAILED DESCRIPTION

[0040] Below is the attached figure ( Figure 1-Figure 2 ) and Examples illustrate the present invention.

[0041] Figure 1 The present invention is a schematic flow chart of a method for suppressing common mode noise of a CPT magnetometer. Figure 2 The present invention is a method for suppressing the common mode noise of a CPT magnetometer, and a schematic diagram of the structure of a CPT magnetometer device based on feedback control and differential detection. Figure 1 to Figure 2 As shown, a method for suppressing common mode noise of a CPT magnetometer comprises the following steps: Step 1, using a CPT magnetometer device based on feedback control and differential detection ( Figure 2) generates a multi-color laser at the detection laser input side of the atomic gas chamber 8; step 2, using a polarization beam splitter 20 to split the multi-color laser into two beams, one beam as a detection signal light enters the atomic gas chamber 8 to interact with atoms, and the other beam is used as a reference signal light and does not enter the atomic gas chamber; step 3, the detection signal light emitted from the atomic gas chamber 8 passes through the first reflector 10, the first beam splitter 11, the second 1 / 4 wave plate 12, the first analyzer 13 and the first photodetector 14 in sequence to connect to the first input end of the differential amplifier 17, and the reference signal light passes through the second reflector The mirror 19, the first beam splitter 11, the second analyzer 15 and the second photodetector 16 are connected to the second input end of the differential amplifier 17, and the output end of the differential amplifier 17 is connected to the digital signal processor 18; step 4, in the differential amplifier 17, the detection signal and the reference signal generate a differential signal, and the differential amplifier 17 demodulates the phase difference between the detection signal and the reference signal, thereby eliminating the common mode noise component; step 5, using the digital signal processor 18 to adaptively filter the differential signal, thereby optimizing the signal quality in real time.

[0042] In step 2, the input side of the polarization beam splitter 20 is connected to the detection laser 24 through the electro-optic phase modulator 21, the 1 / 2 wave plate 22 and the second linear polarizer 23 in sequence, the transmission side of the polarization beam splitter 20 is connected to the first reflector 10 through the atomic gas chamber 8, the reflection side of the polarization beam splitter 20 is connected to the second reflector 19, the pump laser input side of the atomic gas chamber 8 is connected to the saturated absorption frequency stabilization module 1 through the first 1 / 4 wave plate 5, the first linear polarizer 4, the laser power stabilization system 25, the lens group 3 and the pump laser 2 in sequence, the atomic gas chamber 8 is located in the oven 7, the oven 7 is located in the magnetic field coil 9, and the magnetic field coil 9 is located in the magnetic shielding device 6. The pump laser 2 generates a laser with a central wavelength of 770nm, which is the D1 resonance line of K, and the laser wavelength emitted by the detection laser 24 is offset by 0.2nm relative to 795nm, which is the D1 resonance line of Rb. In step 3, the detection signal light meets the reference signal light at the first beam splitter 11 and interferes with each other.

[0043] Step 3 includes the following expressions:

[0044] E t =E pt +E sr ,

[0045] E r =E pr +E st ,

[0046] Where E t is the resultant vibration, E ptis the p-polarized light vibration of the detection signal light, E sr is the s-polarized light vibration of the reference signal light, E r is the resulting vibration, E pr is the p-polarized light vibration of the reference signal light, E st is the s-polarized light vibration of the detection signal light.

[0047] Step 4 includes the following expressions:

[0048] V diff =V1-V2,

[0049]

[0050] a=tanβ1tanβ2(1+tan(φ BS / 2)tanφ),

[0051] b=tanβ1(1-tan(φ BS / 2)tanφ)+tanβ2(tan(φ BS / 2)-tanφ),

[0052] c=tan(φ BS / 2)+tanφ,

[0053] Where V diff is the differential signal, V1 is the detection signal, V2 is the reference signal, Δψ is the phase difference, ψ t is the total phase of the detection signal light, ψ r is the total phase of the reference signal light, φ t is the intrinsic phase of the detection signal light, φ r is the intrinsic phase of the reference signal light, φ BS is the phase delay involving the first beam splitter, φ is the phase delay involving the first reflector and the first beam splitter, θ is the optical rotation angle, a, b, c are all intermediate quantities, β1 is the angle between the transmission axis of the first analyzer and the y-axis, and β2 is the angle between the transmission axis of the second analyzer and the y-axis.

[0054] The adaptive filtering in step 5 is a Kalman filter or a minimum mean square error filter.

[0055] The present invention discloses a method for suppressing common-mode noise of a coherent population trapping (CPT) magnetometer by differential detection. By introducing differential detection technology and adaptive signal processing methods, the performance of the CPT magnetometer can be significantly improved. The invention configures a coherent laser beam, and uses two beams of light generated by a spectroscope to pass through different paths, one of which passes through an atomic gas chamber and the other does not pass through the atomic gas chamber, and uses a high-sensitivity photodetector to collect signals. A differential amplifier is used to generate a differential signal of the two signals, thereby effectively eliminating the influence of common-mode noise. Subsequently, the differential signal is adaptively filtered by a digital signal processor to further improve the signal quality. Experiments show that this method can significantly improve the measurement accuracy and stability of the CPT magnetometer, and has broad application prospects.

[0056] A method for suppressing common mode noise of a CPT magnetometer, the method being used to suppress common mode noise of a CPT atomic magnetometer, comprising the following steps:

[0057] (1) An additional coherent laser beam is configured, and two beams of light generated by a beam splitter are respectively passed through different paths, one of which passes through the gas cell, and the other does not pass through the atomic gas cell;

[0058] (2) Use high-sensitivity photodetectors to collect signals;

[0059] (3) Using a differential amplifier to generate a differential signal of two signals, thereby effectively eliminating the influence of common-mode noise;

[0060] (4) The differential signal is adaptively filtered through a digital signal processor to further improve signal quality.

[0061] (5) Output the processed signal as the measurement result of the CPT magnetometer.

[0062] The calculation formula of the differential signal is V diff =V1-V2, where V diff is a differential signal, V1 is a signal passing through the air chamber, and V2 is a reference signal. The adaptive filtering algorithm is a Kalman filter, a minimum mean square error (MMSE) filter, or other adaptive filtering techniques. The high-sensitivity photodetector used is a photodiode, a photomultiplier tube, or other suitable photoelectric detection equipment. The present invention processes the differential signal in real time to ensure the accuracy and stability of the measurement result. The present invention can significantly improve the measurement accuracy and stability of the CPT magnetometer, and can be widely used in various optical sensors.

[0063] The structure diagram and coordinate setting of the CPT magnetometer device based on feedback control and differential detection are as follows: Figure 2 shown.

[0064] According to the experimental design, a laser with high stability and coherence is selected as the light source to ensure the coherence and wavelength consistency of the light beam. The pump laser generates a laser with a central wavelength of 770nm (D1 resonance line of K), which is emitted through a distributed Bragg reflection laser. After passing through a saturated absorption frequency stabilization module, a laser power stabilization system, and lens beam expansion, the linear polarizer and a quarter-wave plate convert the pump laser into a circularly polarized laser. The circularly polarized laser is incident on the atomic gas chamber to spin-polarize the atoms along the z-axis. The detection laser is emitted through a distributed feedback laser, and the laser wavelength is offset by 0.2nm relative to 795nm (D1 resonance line of Rb). The beam emitted by the detection laser is modulated and irradiated into the atomic gas. The probe laser passing through the linear polarizer p and the 1 / 2 wave plate has a Jones vector E in , Jones vector is a mathematical tool used to describe polarized light. It represents the complex amplitude of the electric field of light in two orthogonal directions. The polarization state of light can be represented by this vector. Here, its formula is:

[0065]

[0066] Where α indicates that the fast axis of the 1 / 2 wave plate is at an angle of α / 2 with the x-axis, cosα is the amplitude of the electric field component of the incident light in the x-direction, and sinα is the amplitude of the electric field component of the incident light in the y-direction. The electro-optic phase modulator is driven by a sinusoidal signal, and the modulation phase it produces can be expressed as φ(t)=φ0sin(ωt), where φ0 is the modulation depth and ω is the modulation angular frequency. The electro-optic phase modulator is used to generate phase modulation with a frequency of 500KHz. After passing through the electro-optic phase modulator, the Jones vector of the incident light becomes:

[0067]

[0068] Among them J EOM is the Jones matrix of the electro-optic phase modulator, which describes the different phase changes of the electro-optic modulator to the two orthogonal polarization components. The complex term e -iφ(t) / 2 and e iφ(t) / 2 represents the phase change of light, e -iφ(t) / 2 represents the phase modulation of the x-axis component, e iφ(t) / 2 represents the phase modulation of the y-axis component. The light transmitted through the polarization beam splitter is called p-polarized light, and the reflected light is called s-polarized light. The p-polarized light is used to interact with atoms and is the signal light, while the s-polarized light is used as the reference light.

[0069] The gas chamber is designed to accommodate atomic gas and provide a good environment for the interaction between light and atoms. The gas chamber is composed of a spherical aluminosilicate glass with an outer diameter of 10 mm, and is filled with a small amount of alkali metal potassium (K) and rubidium (Rb) mixture, 1atm (standard atmospheric pressure) of rare gas Ne (neon), and 50Torr (Tor, pressure unit) of N2 (nitrogen). The gas chamber is fixed in a boron nitride furnace, and its temperature is stabilized at 185°C by a non-magnetic high-frequency AC current heating coil and a PID (proportional-integral-differential) controller. On this basis, the optical path is optimized to ensure that the incident and outgoing beams can effectively pass through the gas chamber and maximize the signal strength.

[0070] The p-polarized light undergoes coherent population capture with atoms, producing specific signal changes.

[0071] The s-polarized light is reflected by the reflector and finally meets the p-polarized light in the beam splitter. t is the composite vibration of the transmitted p-polarized light and the reflected s-polarized light. According to the principle of light wave superposition, its formula is:

[0072]

[0073] Among them, E pt is the transmitted light component of p-polarized light, E sr is the reflected light component of s-polarized light.

[0074] is the mirror M p The Jones matrix of Indicates M p Produce an additional phase delay to the phase of light. cell represents the Jones matrix of the atomic vapor unit, and θ represents the optical rotation angle introduced by the atomic vapor unit, corresponding to the polarization change caused by the precession of atomic spins. PBS_p represents the Jones matrix of the polarization beam splitter (PBS) for selecting p-polarized light. E' in is the incident optical field vector after passing through the electro-optic phase modulator (EOM), which has been derived by the formula in the above text. BS is the Jones matrix of the beam splitter (BS), φ BS represents the phase delay it produces, is the mirror M s The Jones matrix of It produces an additional phase delay for the phase of light. PBS_s is the Jones matrix of the polarization beam splitter (PBS), which is used to select s-polarized light, k is the wave vector of the light, and d is the optical path difference between the two light paths.

[0075] Similarly, the composite vibration E after the reflected p-polarized light and the transmitted s-polarized light are superimposed r It can be expressed as:

[0076]

[0077] The subscripts p and s represent p-polarization and s-polarization, respectively, and r and t represent the reflection and transmission of the beam splitter, respectively. J cell , J PBS-p , J PBS-s and J BS They represent the reflector, atomic gas cell, polarization beam splitter and Jones matrix of beam splitter respectively. , E pr is the reflected light component of p-polarized light, E st is the transmitted light component of s-polarized light. The remaining quantities are the same as those in formula (3).

[0078] The specific representation forms of each intermediate quantity are explained below.

[0079] Let d be the optical path difference between the two paths. According to the Fresnel formula, the transmitted wave does not change phase. The phase change of the reflected wave depends on the refractive index of the medium and the angle of incidence. The reflector and beam splitter can be equivalent to a wave plate with a phase delay of φ. Its Jones matrix can be written as:

[0080]

[0081] The transmission direction and reflection direction of the polarization beam splitter are equivalent to two polarizers, and the corresponding Jones matrix can be written as:

[0082]

[0083] The Jones matrix of an atomic gas cell with an optical rotation angle θ can be written as:

[0084]

[0085] The transmitted light of the beam splitter (BS) passes through a quarter wave plate (with the fast axis located on the y-axis) and an analyzer (A t ) and then detected by the photodetector (PD t ) is detected. In terms of detector selection, a high-sensitivity photodetector, such as an avalanche photodiode, is used to receive the signal passing through the gas chamber and the reference signal respectively. At this time, its Jones vector E′ t It can be expressed as:

[0086]

[0087] in, Analyzer A t Jones matrix, β1 is the angle between its transmission axis and the y-axis. If β1 = 0°, the analyzer only transmits polarized light in the y direction. If β1 = 90°, the analyzer only transmits polarized light in the x direction. 1 / 4(0°) is the Jones matrix of the quarter wave plate, which introduces a 90° phase delay into one polarization component. A1 and A2 are intermediate variables introduced for the convenience of expression. t is the composite vibration of the transmitted p-polarized light and the reflected s-polarized light, and its expression is shown in formula (3), which is directly substituted here.

[0088] The photodetector (PD t ) The detected light intensity I t for:

[0089]

[0090] in

[0091]

[0092] E′ t is the Jones vector of the transmitted light from the beam splitter (BS) after passing through the quarter wave plate and the analyzer, E′ t H is its conjugate transpose, ψ t , A′1, A′2 are intermediate variables introduced for convenience of expression, and the other quantities have been explained in the previous text and will not be repeated here.

[0093] On the other hand, the reflected light from the beam splitter (BS) passes through the analyzer (A r ) and then detected by the photodetector (PD r ) detected, β2 is the analyzer (A r ) is the angle between the transmission axis and the y-axis. At this time, the Jones vector E′ r It can be expressed as:

[0094]

[0095] in, Analyzer A r The Jones matrix of E, β2 is the angle between the transmission axis and the y axis. B1 and B2 are intermediate variables introduced for the convenience of expression. r is the composite vibration of the reflected p-polarized light and the transmitted s-polarized light, and its expression is shown in formula (4), which is directly substituted here.

[0096] The photodetector (PD t ) The detected light intensity I t for:

[0097] I r =E′ r H ·E′ r =B′1 2 +B′2 2 +2B′1B′2cos(φ(t)+ψ r ) (11)

[0098] in

[0099]

[0100] S′2=B2sinα=sinαsinβ2

[0101] E′ r is the Jones vector of the reflected light from the beam splitter (BS) after passing through the analyzer, E′ r H is its conjugate transpose, ψ r , B′1, B′2 are intermediate variables introduced for convenience of expression.

[0102] The signal captured by the detector is processed by a differential amplifier to eliminate common-mode noise.

[0103] The phase difference Δψ demodulated by the differential amplifier is:

[0104]

[0105] where ψ t is the total phase of the transmitted light, ψ r is the total phase of the reflected light, φ t is the intrinsic phase of the transmitted light, φ r is the intrinsic phase of the reflected light.

[0106] The phase difference φ between the signal light and the reference light caused by the optical rotation of the atomic gas cell can be obtained as:

[0107]

[0108] The relationship between the phase difference φ and the optical rotation θ is:

[0109]

[0110] The optical rotation θ of the atomic gas cell can be solved as:

[0111]

[0112] in

[0113]

[0114] Among them, a, b, and c are intermediate variables introduced for convenience of expression.

[0115] The differential signal is adaptively filtered by a digital signal processor, and the filtering parameters are automatically adjusted by an algorithm to optimize the signal quality in real time. The Fast Fourier Transform (FFT) and other algorithms are used to analyze the signal spectrum and further extract useful information.

[0116] Finally, the processed signal is converted into visual data and output to a display screen or data recording device. At the same time, a user-friendly interface is designed to facilitate operators to conduct real-time monitoring and data analysis.

[0117] Through the above technical scheme, the present invention provides an effective common-mode noise suppression method, which significantly improves the measurement accuracy and stability of the CPT magnetometer and provides reliable technical support for high-precision magnetic field measurement. In the differential detection part, by differentially processing the two groups of CPT signals, the influence of common-mode noise on the measurement results can be effectively eliminated. Specifically, the two groups of signals measured will be subject to the same external interference. By subtracting each other, these interference signals can cancel each other out, thereby obtaining a clearer resonance signal. This method not only improves the quality of the signal, but also maintains good measurement performance in a high-noise environment, ensuring the accurate calculation of the Larmor frequency. Through the above measures, the present invention achieves a dual improvement in sensitivity and absolute accuracy, solving the key technical problems faced by traditional CPT magnetometers.

[0118] The present invention realizes the suppression of the common mode noise of the CPT magnetometer through five steps.

[0119] Step 1: Generation of multicolor laser

[0120] According to the experimental design, a laser with high stability and coherence is selected as the light source to ensure the coherence and wavelength consistency of the beam. The pump laser generates a laser with a central wavelength of 770nm (D1 resonance line of K), and the detection laser is emitted via a distributed feedback laser, and the laser wavelength is offset by 0.2nm relative to 795nm (D1 resonance line of Rb).

[0121] Step 2: Modulation and generation of signal light and reference light

[0122] After the pump laser passes through the saturated absorption frequency stabilization module, laser power stabilization system and lens beam expansion, the linear polarizer and quarter wave plate convert the pump laser into circularly polarized laser. The circularly polarized laser is incident on the atomic gas chamber and spin-polarizes the atoms along the z-axis. The detection laser generates a phase modulation with a frequency of 500KHz through the electro-optic phase modulator. sThe vector becomes the above formula (2).

[0123] A polarization beam splitter is used to split the probe laser beam into two beams, one for interacting with atoms as signal light and the other as a reference signal.

[0124] Step 3: Signal Reception

[0125] After the signal light is reflected by the mirror, it meets the reference light at the beam splitter and interferes with it. The composite vibration E after the transmitted p-polarized light and the reflected s-polarized light are superimposed t It can be expressed as the above formula (3).

[0126] The resulting vibration E after the reflected p-polarized light and the transmitted s-polarized light are superimposed r It can be expressed as the above formula (4).

[0127] The transmitted light of the beam splitter passes through a quarter wave plate and an analyzer (A t ) and is detected by the photodetector. Jones vector E′ t It can be expressed as the above formula (8).

[0128] The photodetector (PD t ) The detected light intensity I t is the above formula (9).

[0129] The reflected light from the beam splitter (BS) passes through the analyzer (A r ) and then detected by the photodetector (PD r ) detected, its Jones vector E′ r It can be expressed as the above formula (10).

[0130] Its light intensity is given by the above formula (11).

[0131] In terms of detector selection, a high-sensitivity photodetector, such as an avalanche photodiode, is used to receive the signal passing through the gas chamber and the reference signal respectively.

[0132] Step 4: Differential processing of signals

[0133] The signal passing through the gas cell and the reference signal are input to the differential amplifier to generate a differential signal and eliminate the common mode noise component.

[0134] The phase difference Δψ demodulated by the differential amplifier is

[0135]

[0136] The phase difference φ between the signal light and the reference light caused by the optical rotation of the atomic gas cell can be obtained as:

[0137]

[0138] The relationship between the phase difference φ and the optical rotation θ is:

[0139]

[0140] The optical rotation θ can be expressed as

[0141]

[0142] in

[0143] a=tanβ1tanβ2(1+tan(φ BS / 2)tanφ),

[0144] b=tanβ1(1-tan(φ BS / 2)tanφ)+tanβ2(tan(φ BS / 2)-tanφ),

[0145] c=tan(φ BS / 2)+tanφ.

[0146] Step 5: Data collection and analysis

[0147] The differential signal is adaptively filtered by a digital signal processor, and the filtering parameters are automatically adjusted by an algorithm to optimize the signal quality in real time. The Fast Fourier Transform (FFT) and other algorithms are used to analyze the signal spectrum and further extract useful information. Finally, the processed signal is converted into visual data and output to a display screen or data recording device. At the same time, a user-friendly interface is designed to facilitate real-time monitoring and data analysis by operators.

[0148] Key Component Description

[0149] Laser: Select a laser with high stability and low drift characteristics to ensure the quality of the light source.

[0150] Optical modulator: Used to modulate the laser signal so that it interacts with the atomic gas at a specific frequency.

[0151] Detector: Choose a detector with high sensitivity and fast response time to capture the modulated light signal.

[0152] Differential signal processing circuit: Use differential amplifier to amplify the signal and eliminate the influence of environmental noise.

[0153] Through this experimental device, the present invention can realize a method for suppressing common mode noise of a CPT magnetometer.

[0154] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A method for suppressing common mode noise of a CPT magnetometer, characterized in that: The following steps are involved: Step 1, using a CPT magnetometer device based on feedback control and differential detection to generate multi-color lasers at the detection laser input side of the atomic gas chamber; Step 2, using a polarization beam splitter to split the multicolor laser into two beams, one beam as a detection signal light entering the atomic gas chamber to interact with atoms, and the other beam as a reference signal light not entering the atomic gas chamber; Step 3, the detection signal light emitted from the atomic gas chamber is connected to the first input end of the differential amplifier through the first reflector, the first beam splitter, the second 1 / 4 wave plate, the first analyzer and the first photodetector in sequence, the reference signal light is connected to the second input end of the differential amplifier through the second reflector, the first beam splitter, the second analyzer and the second photodetector, and the output end of the differential amplifier is connected to the digital signal processor; Step 4, in the differential amplifier, the detection signal and the reference signal generate a differential signal, and the differential amplifier demodulates the phase difference between the detection signal and the reference signal, thereby eliminating the common mode noise component; Step 5: Use a digital signal processor to adaptively filter the differential signal, thereby optimizing the signal quality in real time.

2. The method for suppressing common mode noise of a CPT magnetometer according to claim 1, characterized in that: In step 2, the input side of the polarization beam splitter is connected to the detection laser through the electro-optic phase modulator, the 1 / 2 wave plate and the second linear polarizer in sequence, the transmission side of the polarization beam splitter is connected to the first reflector through the atomic gas chamber, the reflection side of the polarization beam splitter is connected to the second reflector, the pump laser input side of the atomic gas chamber is connected to the saturated absorption frequency stabilization module through the first 1 / 4 wave plate, the first linear polarizer, the laser power stabilization system, the lens group and the pump laser in sequence, the atomic gas chamber is located in the oven, the oven is located in the magnetic field coil, and the magnetic field coil is located in the magnetic shielding device.

3. The method for suppressing common mode noise of a CPT magnetometer according to claim 2, characterized in that: The pump laser generates laser light with a central wavelength of 770 nm, which is the D1 resonance line of K. The wavelength of the laser light emitted by the detection laser is shifted by 0.2 nm relative to 795 nm, which is the D1 resonance line of Rb.

4. The method for suppressing common mode noise of a CPT magnetometer according to claim 1, characterized in that: In step 3, the detection signal light meets the reference signal light at the first beam splitter and interferes with each other.

5. The method for suppressing common mode noise of a CPT magnetometer according to claim 1, characterized in that: Step 3 includes the following expressions: AND t =And pt +E sr , AND r =And pr +E st , Where E t is the resultant vibration, E pt is the p-polarized light vibration of the detection signal light, E sr is the s-polarized light vibration of the reference signal light, E r is the resulting vibration, E pr is the p-polarized light vibration of the reference signal light, E st is the s-polarized light vibration of the detection signal light.

6. The method for suppressing common mode noise of a CPT magnetometer according to claim 1, characterized in that: Step 4 includes the following expressions: V diff =V1-V2, a=tanβ1tanβ2(1+tan(φ BS / 2)tanφ), b=tanβ1(1-tan(φ BS / 2)tanφ)+tanβ2(tan(φ BS / 2)-tanφ), c=tan(φ BS / 2)+tanφ, Where V diff is the differential signal, V1 is the detection signal, V2 is the reference signal, Δψ is the phase difference, ψ t is the total phase of the detection signal light, ψ r is the total phase of the reference signal light, φ t is the intrinsic phase of the detection signal light, φ r is the intrinsic phase of the reference signal light, φ BS is the phase delay involving the first beam splitter, φ is the phase delay involving the first reflector and the first beam splitter, θ is the optical rotation angle, a, b, c are all intermediate quantities, β1 is the angle between the transmission axis of the first analyzer and the y-axis, and β2 is the angle between the transmission axis of the second analyzer and the y-axis.

7. The method for suppressing common mode noise of a CPT magnetometer according to claim 1, characterized in that: The adaptive filtering in step 5 is a Kalman filter or a minimum mean square error filter.

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