Method for simultaneously improving sensitivity and absolute precision of CPT magnetometer

Abstract

A method for simultaneously improving sensitivity and absolute precision of a CPT magnetometer is characterized in that pumping radiation intensity is adjusted through a feedback loop to keep atomic vapor autofluorescence at a constant level, and contrast of CPT resonance is further improved. The experiment adopts a double-frequency laser field, and two hyperfine energy level states of 87Rb atoms are excited by modulating 795nm laser and dividing the 795nm laser into two beams of orthogonal polarized light. A fluorescence signal is detected, and the fixed intensity is kept through PID feedback control. The two groups of CPT signals are subjected to differential processing, interference factors such as common-mode noise are eliminated, and therefore the Larmor frequency under the simulated 5000nT magnetic field is accurately measured, and the Larmor frequency is about 350kHz. The invention provides a fluorescent feedback loop and differential detection method, the sensitivity and the precision of the magnetometer are remarkably improved, the problem of frequency deviation caused by common-mode noise and a nonlinear effect in a traditional method is solved, and the method is suitable for high-precision magnetic field measurement.

Description

Technical Field

[0001] The present invention relates to the field of quantum precision measurement technology, and in particular to a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer. Background Art

[0002] The CPT magnetometer is a precision instrument that uses the resonance effect between atomic energy levels to measure magnetic fields. It is widely used in high-precision magnetic field detection fields, such as geomagnetic measurement, space navigation, and medical imaging (CPT, Coherent Population Trapping). The key performance indicators of the CPT magnetometer include sensitivity and absolute accuracy, which directly affect the measurement stability and reliability of the magnetometer. Traditional CPT magnetometer measurement methods usually obtain CPT resonance signals by adjusting the frequency of the pump laser to match the hyperfine splitting frequency of the atomic energy level. However, due to the influence of noise interference, nonlinear Zeeman effect, and atomic collisions, conventional methods still have room for improvement in sensitivity and absolute accuracy.

[0003] Most of the existing improvement methods focus on improving the contrast and stability of CPT signals. For example, noise is reduced by optimizing the laser source, improving the optical path design, and adding external magnetic shielding. However, these methods usually rely on complex equipment and expensive hardware facilities, which not only increase the cost of the system, but also have the limitations of large size and complex operation. Especially in high-sensitivity measurements, common-mode noise, nonlinear frequency shift caused by the Zeeman effect, and collision effects between atoms can significantly affect the quality of the CPT signal, resulting in inaccurate measurement results.

[0004] Some current studies have proposed a method of adjusting the laser intensity through feedback control to improve the contrast of the CPT signal. This method adjusts the radiation intensity of the pump laser to keep the atomic fluorescence signal at a constant level, thereby enhancing the resonance contrast to a certain extent. However, relying solely on feedback control cannot completely solve the frequency offset problem caused by common-mode noise and nonlinear effects, which still limits the accuracy improvement of the magnetometer.

[0005] Therefore, there is an urgent need for an improved technical solution that can not only improve the sensitivity of the CPT magnetometer but also eliminate the influence of common-mode noise and nonlinear frequency shift, thereby achieving high-precision magnetic field measurement without increasing the complexity of the system. Summary of the invention

[0006] The purpose of the present invention is to design a method for simultaneously improving the sensitivity and absolute accuracy of CPT magnetometers in view of the shortcomings of existing CPT magnetometers in terms of sensitivity and absolute accuracy. The core of the method is to use a feedback loop to adjust the intensity of the pump laser so that the atomic fluorescence signal is maintained at a constant level. In this way, the contrast of the CPT resonance can be significantly improved, which is a key factor affecting the performance of the CPT magnetometer. In addition, the present invention also uses differential detection technology to perform differential processing on two groups of CPT signals, eliminating the frequency offset problem caused by common mode noise, nonlinear Zeeman effect and interatomic collision, thereby achieving accurate measurement of the Larmor frequency.

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

[0008] A method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer, characterized in that it comprises the following steps:

[0009] Step 1, generating multi-color laser using a CPT magnetometer device based on feedback control and differential detection;

[0010] Step 2, using a microwave source to perform frequency modulation of the multi-color laser at 3.417 GHz, wherein the 3.417 GHz corresponds to the fine structure frequency difference of 6.835 GHz of the D1 energy level of the 87Rb atom, to generate a dual-frequency laser field;

[0011] Step 3, using a polarization beam splitter to separate the dual-frequency laser field to form two beams of light with equal intensity and orthogonal polarization, so as to excite different magnon state systems in the 87Rb atoms and generate two Λ-type CPT resonance systems;

[0012] Step 4, introducing the two light beams into a vapor chamber containing 87Rb atoms, the two light beams interact with the 87Rb atoms, excite atoms in different magnetic states and generate CPT signals, monitor the autofluorescence intensity of the vapor chamber through a first photodetector, and detect the intensity of the pump light after passing through the vapor chamber through a second photodetector;

[0013] Step 5, using a CPT fluorescence intensity feedback control loop to enable the electro-optic modulator on the pump light path to adjust the pump light intensity in real time according to the spontaneous fluorescence intensity, to ensure that the fluorescence signal is constant, thereby improving the contrast of the CPT resonance;

[0014] Step 6: Improve the magnetic field measurement accuracy and sensitivity of the CPT magnetometer by eliminating common mode noise through differential detection processing.

[0015] The CPT magnetometer device based on feedback control and differential detection in step 1 includes a laser, a lens, an electro-optic modulator, a 1 / 2 wave plate, a polarization beam splitter, a steam chamber and a second photodetector connected in sequence, the second photodetector is connected to a data acquisition processor, the steam chamber is connected to the electro-optic modulator through a first photodetector and a PID controller in sequence, the laser is connected to a DDS signal generator through a microwave source, the steam chamber is located in an oven, the oven is located in a magnetic field coil, the magnetic field coil is located in a ferrite shielding layer, and the ferrite shielding layer is located in a permalloy shielding layer.

[0016] The laser generates laser light with a wavelength of 795 nm.

[0017] The 87Rb atoms in step 4 include |F g =1,m F =1〉and|F g =2,m F =1〉, and |F g =1,m F =-1〉 and |F g =2,m F =-1〉, the two sets of CPT signals generated by these two different magnetic state systems have different frequency shifts.

[0018] Step 5 includes the following expression:

[0019]

[0020] I(α,δ R )∝Ω 2 (α,δ R ),

[0021] Where S sp is the autofluorescence intensity, N e is the total number of atoms, ρ 33 is the monatomic population number, n at is the atomic density, r 0 is the beam radius, L is the length of the vapor chamber, const is a constant, I(α,δ R ) is the light intensity adjustment, α is the feedback control parameter, δ R is the detuning amount and Ω is the contrast.

[0022] Step 6 includes performing differential processing on two groups of CPT signals with different frequency shifts, so that the frequency shift caused by noise and nonlinear Zeeman effect is eliminated, thereby accurately extracting the Larmor frequency. When the intensity of the differential signal is zero, the frequency output by the system is the Larmor frequency. Since the differential processing eliminates the influence of common-mode noise, the measurement of the Larmor frequency is more accurate, thereby achieving high-precision magnetic field measurement.

[0023] Step 6 includes the following expression:

[0024]

[0025] Y diff =Y 1 -Y 2 ,

[0026]

[0027] where Y 1 is the first group of CPT signals, k is the proportionality coefficient, v is half of the magnetic resonance line width, w is the frequency output by the DDS signal generator, and v Larmor is the Larmor frequency, Δv is the magnon energy level offset, N c (w) is the common mode noise, Y 2 is the second group of CPT signals, Y diff is the signal difference component, δB is the sensitivity of the CPT magnetometer, Δx is the CPT resonance linewidth, γ is the gyro ratio, S is the resonance signal amplitude, and N is the noise.

[0028] The technical effects of the present invention are as follows: The present invention provides a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer, and adopts feedback control technology to significantly improve the contrast of the CPT resonance signal, thereby improving the sensitivity of the magnetometer; the application of differential detection technology eliminates the frequency offset problem caused by common mode noise, nonlinear effects and atomic collisions, and greatly improves the absolute measurement accuracy. In addition, the present invention also simplifies the structure of the CPT magnetometer, reduces the complexity and operation difficulty of the system, and makes the device easier to operate and maintain in practical applications. The device can not only meet the needs of high-precision magnetic field measurement, but also provide a strong guarantee for the wide application of CPT magnetometers in industry, scientific research, medical treatment and other fields.

[0029] The CPT magnetometer device and method based on feedback control and differential detection of the present invention have important theoretical significance and broad application prospects. It not only provides a new idea for improving the performance of the magnetometer, but also lays a foundation for further research and development of high-sensitivity and high-precision quantum measurement equipment. Through the technical solution proposed by the present invention, it is possible to better realize the detection of weak magnetic fields and promote the development and innovation of related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a schematic flow chart of a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer. Figure 1The method comprises the following steps: 1, generating multicolor laser; 2, modulating the laser with a 3.417 GHz microwave signal, and dividing the laser into two beams using a polarization beam splitter PBS, and adjusting the polarization direction thereof to ensure signal stability; 3, passing the laser through a vapor cavity filled with 87Rb atoms, and collecting the spontaneous fluorescence signal using a photodetector; 4, controlling the laser intensity in a feedback loop to keep the fluorescence signal in the vapor cavity constant, thereby improving the signal contrast; 5, collecting and differentially processing two groups of CPT signals (CPT, Coherent Population Trapping, coherent population trapping or coherent population trapping) to eliminate common mode noise and ensure signal accuracy; and 6, determining the Larmor frequency by the frequency zero point of the differential signal, thereby accurately measuring the magnetic field and calculating its magnetic field sensitivity.

[0031] Figure 2 The present invention is a schematic structural diagram of a CPT magnetometer device based on feedback control and differential detection, which is involved in a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer.

[0032] Figure 3 The diagram is a schematic diagram of the distribution of the D1 energy level of 87Rb atoms in a magnetic field and the formation of a double Λ configuration for a CPT state involved in a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer according to the present invention. Figure 3 where Δv is the frequency shift, v Larmor is the Larmor frequency, 5 2 represents the spin multiplicity of principal quantum number 5, P 1 / 2 represents the P orbital involving magnetic quantum number 1 / 2, S 1 / 2 represents the S orbital involving the magnetic quantum number 1 / 2, Fg represents the total angular momentum quantum number of the atom, and m F It represents the projected quantum number of the total angular momentum in the direction of the magnetic field, and Fe represents the projected quantum number of the total angular momentum in the direction of the magnetic field. 2 P 1 / 2 The total angular momentum in this excited state, 6.835GHz is the frequency of light emitted by energy level transition.

[0033] The reference numerals in the accompanying drawings are as follows: 1-laser; 2-lens; 3-electro-optic modulator (EOM); 4-1 / 2 wave plate; 5-polarization beam splitter (PBS); 6-Permalloy shielding layer; 7-ferrite shielding layer; 8-oven; 9-steam chamber (atomic gas chamber); 10-first photodetector (PD1); 11-magnetic field coil; 12-second photodetector (PD2); 13-PID controller (PID, proportional-integral-derivative control, proportional-integral-derivative control of deviation); 14-microwave source (3.417GHz or 3.4GHz); 15-DDS signal generator (DDS, Direct Digital Frequency Synthesis); 16-data acquisition processor. DETAILED DESCRIPTION

[0034] Below is the attached figure ( Figure 1-Figure 3 ) and Examples illustrate the present invention.

[0035] Figure 1 The present invention is a schematic flow chart of a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer. Figure 2 The present invention is a schematic structural diagram of a CPT magnetometer device based on feedback control and differential detection, which is involved in a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer. Figure 3 The diagram is a schematic diagram of the distribution of the D1 energy level of 87Rb atoms in a magnetic field and the formation of a double Λ configuration for a CPT state involved in a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer according to the present invention. Figures 1 to 3 As shown, a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer comprises the following steps:

[0036] Step 1, using a CPT magnetometer device based on feedback control and differential detection to generate a multi-color laser; Step 2, using a microwave source to perform frequency modulation of the multi-color laser at 3.417 GHz, wherein the 3.417 GHz corresponds to the fine structure frequency difference of 6.835 GHz of the D1 energy level of the 87Rb atom, thereby generating a dual-frequency laser field; Step 3, using a polarization beam splitter to separate the dual-frequency laser field to form two beams of light with equal intensity and orthogonal polarization, so as to excite different magnon state systems in the 87Rb atom and generate two Λ-type CPT resonance systems; Step 4, introducing the two beams into a 87 In the vapor chamber of Rb atoms, the two beams of light interact with the 87Rb atoms, excite atoms in different magnon states and generate CPT signals, the spontaneous fluorescence intensity of the vapor chamber is monitored by the first photodetector, and the intensity of the pump light after passing through the vapor chamber is detected by the second photodetector; step 5, through the CPT fluorescence intensity feedback control loop, the electro-optical modulator on the pump light path adjusts the pump light intensity in real time according to the spontaneous fluorescence intensity to ensure that the fluorescence signal is constant, thereby improving the contrast of the CPT resonance; step 6, through differential detection processing to eliminate common mode noise to improve the magnetic field measurement accuracy and sensitivity of the CPT magnetometer.

[0037] The CPT magnetometer device based on feedback control and differential detection in step 1 includes a laser 1, a lens 2, an electro-optic modulator 3, a 1 / 2 wave plate 4, a polarization beam splitter 5, a steam chamber 9 and a second photodetector 12 connected in sequence, the second photodetector 12 is connected to a data acquisition processor 16, the steam chamber 9 is connected to the electro-optic modulator 3 through a first photodetector 10 and a PID controller 13 in sequence, the laser 1 is connected to a DDS signal generator 15 through a microwave source 14, the steam chamber 9 is located in an oven 8, the oven 8 is located in a magnetic field coil 11, the magnetic field coil 11 is located in a ferrite shielding layer 7, and the ferrite shielding layer 7 is located in a permalloy shielding layer 6.

[0038] The laser generates a laser with a wavelength of 795 nm. The 87Rb atoms in step 4 include |F g =1,m F =1〉and|F g =2,m F =1〉, and |F g =1,m F =-1〉 and |F g =2,m F =-1〉, the two sets of CPT signals generated by these two different magnetic state systems have different frequency shifts.

[0039] Step 5 includes the following expression:

[0040]

[0041] I(α,δ R )∝Ω 2 (α,δ R ),

[0042] Where S sp is the autofluorescence intensity, N e is the total number of atoms, ρ 33 is the monatomic population number, n at is the atomic density, r 0 is the beam radius, L is the length of the vapor chamber, const is a constant, I(α,δ R ) is the light intensity adjustment, α is the feedback control parameter, δ R is the detuning amount and Ω is the contrast.

[0043] Step 6 includes performing differential processing on two groups of CPT signals with different frequency shifts, so that the frequency shift caused by noise and nonlinear Zeeman effect is eliminated, thereby accurately extracting the Larmor frequency. When the intensity of the differential signal is zero, the frequency output by the system is the Larmor frequency. Since the differential processing eliminates the influence of common-mode noise, the measurement of the Larmor frequency is more accurate, thereby achieving high-precision magnetic field measurement.

[0044] Step 6 includes the following expression:

[0045]

[0046] Y diff =Y 1 -Y 2 ,

[0047]

[0048] where Y 1 is the first group of CPT signals, k is the proportionality coefficient, v is half of the magnetic resonance line width, w is the frequency output by the DDS signal generator, and v Larmor is the Larmor frequency, Δv is the magnon energy level offset, N c (w) is the common mode noise, Y 2 is the second group of CPT signals, Y diff is the signal difference component, δB is the sensitivity of the CPT magnetometer, Δx is the CPT resonance linewidth, γ is the gyro ratio, S is the resonance signal amplitude, and N is the noise.

[0049] The present invention discloses a method for improving the sensitivity and absolute accuracy of a coherent population trapping (CPT) magnetometer based on feedback control and differential detection. The invention adjusts the intensity of pump radiation through a feedback loop to keep the atomic vapor autofluorescence at a constant level, thereby improving the contrast of the CPT resonance. The experiment uses a dual-frequency laser field to excite two hyperfine energy levels of 87Rb atoms by modulating a 795nm laser and dividing it into two beams of orthogonal polarized light. The fluorescence signal is detected and maintained at a fixed intensity through PID feedback control. By differentially processing two groups of CPT signals, interference factors such as common mode noise are eliminated, thereby accurately determining the Larmor frequency under a simulated 5000nT magnetic field, which is about 350kHz. The present invention proposes a method through a fluorescence feedback loop and differential detection, which significantly improves the sensitivity and accuracy of the magnetometer, while solving the frequency offset problem caused by common mode noise and nonlinear effects in traditional methods, and is suitable for high-precision magnetic field measurement.

[0050] A method for improving the sensitivity and absolute accuracy of a CPT magnetometer based on feedback control and differential detection comprises the following steps:

[0051] (1) Generation and modulation of multicolor lasers

[0052] The laser was used to generate a laser with a wavelength of 795 nm, and a microwave source was used to modulate the laser at a frequency of 3.417 GHz. This frequency corresponds to the fine structure frequency difference of the D1 energy level of the 87Rb atom, generating a dual-frequency laser field, which provides suitable excitation conditions for the subsequent CPT resonance.

[0053] (2) Beam separation and polarization processing

[0054] The generated dual-frequency laser field is separated by a polarization beam splitter (PBS) to form two beams of equal intensity and orthogonal polarization. The polarized beams are used to excite different magnon states in 87Rb atoms, thereby generating two Λ-type CPT resonance systems.

[0055] (3) Steam chamber and signal detection

[0056] Two beams of light are introduced into the vapor chamber containing 87Rb atoms, so that they interact with the atoms in the chamber, excite atoms in different magnon states and generate CPT signals. The spontaneous fluorescence intensity of the vapor chamber is monitored by photodetector PD1, and another photodetector PD2 is used to detect the intensity of the pump light after passing through the vapor chamber.

[0057] (4) CPT fluorescence intensity feedback control

[0058] In order to ensure the contrast and stability of the CPT signal, a feedback control loop is designed in the system. Through the PID controller and electro-optic modulator (EOM), the pump light intensity is adjusted in real time according to the spontaneous fluorescence intensity measured by the photodetector PD1 to ensure the constant fluorescence signal, thereby improving the contrast of the CPT resonance.

[0059] (5) Differential detection processing determines the magnetic field measurement accuracy of the CPT magnetometer

[0060] In order to eliminate common mode noise and improve measurement accuracy, a differential detection method is used. g =1,m F =1〉、|F g =2,m F =1〉 and |F g =1,m F =-1〉, |F g =2,m F =-1〉combination) have different frequency shifts. After differential processing of the two sets of signals, the frequency shift caused by noise and nonlinear Zeeman effect can be eliminated, so that the Larmor frequency can be accurately extracted. When the intensity of the differential signal is zero, the frequency output by the system is the Larmor frequency. Since differential processing eliminates the influence of common mode noise, the measurement of Larmor frequency is more accurate, thus achieving high-precision magnetic field measurement.

[0061] (6) Determine the sensitivity of the CPT magnetometer

[0062] The sensitivity of the CPT magnetometer can be calculated by the following formula:

[0063]

[0064] Where: δB is the magnetometer sensitivity, γ is the gyro ratio, Δx is the CPT resonance linewidth, S is the resonance signal amplitude, and N is the noise.

[0065] The pump radiation intensity is adjusted via a feedback loop to maintain a constant level of atomic vapor autofluorescence, thereby improving the CPT resonance contrast, and differential detection is used to eliminate common-mode noise, nonlinear Zeeman effects, and atomic collision effects to accurately determine the Larmor frequency. The constructed device includes: a laser 1 for generating a 795nm dual-frequency laser field; an electro-optic modulator 3 for modulating a 3.417GHz microwave signal onto the output beam of the laser; a polarization beam splitter prism (i.e., a polarization beam splitter 5) and a λ / 2 wave plate 4 for splitting the laser beam into two beams with orthogonal polarization directions and equal light intensities; a vapor pool (i.e., a vapor chamber 9 or an atomic gas chamber) filled with 87Rb atoms and a buffer gas for realizing CPT resonance; a first photodetector 10 for detecting the intensity of atomic spontaneous fluorescence in the vapor pool; a second photodetector 12 for detecting the intensity of pump light after passing through the vapor pool; a PID feedback control system (i.e., a PID controller 13) connected to the first photodetector 10 and the electro-optic modulator 3 for adjusting the intensity of the pump light to keep the spontaneous fluorescence at a constant level; and a differential detection module (i.e., a PID controller 13) for performing differential processing on two CPT signals to eliminate common-mode noise and frequency offset problems.

[0066] The principle of CPT magnetometer feedback control and differential detection system is as follows Figure 2 In order to generate CPT resonance in 87Rb atoms, this experimental scheme uses a laser to generate a laser with a wavelength of 795nm and performs dual-frequency modulation of the laser through a 3.417GHz microwave source. This frequency modulation matches the fine structure of the D1 energy level of the 87Rb atom, allowing the dual-frequency laser field to excite a specific magnetic quantum state, thereby generating CPT resonance.

[0067] The generated dual-frequency laser field is split by a polarization beam splitter (PBS) to obtain two beams with equal intensity and orthogonal polarization directions. The two beams are used to excite different magnetic sub-state systems of 87Rb atoms, forming two Λ-type system configurations. This beam processing method ensures accurate excitation and detection of CPT signals.

[0068] After beam splitting and polarization treatment, the light beam is introduced into the vapor cavity filled with 87Rb atoms and interacts with the atoms in the cavity. The atoms are stimulated to emit spontaneous fluorescence signals under the action of the dual-frequency laser field. The photodetector PD1 detects the fluorescence intensity in the cavity, while the photodetector PD2 detects the intensity of the pump light after passing through the vapor cavity. The fluorescence signal is used as the key input of feedback control to achieve dynamic adjustment of the laser pump intensity.

[0069] To maintain the contrast and stability of the CPT signal, a feedback control loop was designed for the system. The loop includes a PID controller and an electro-optical modulator (EOM) to adjust the laser pump light intensity through the fluorescence signal measured by PD1. By adjusting the pump light intensity to keep the fluorescence signal constant, the contrast of the CPT signal is maximized and the sensitivity of the CPT magnetometer is significantly improved.

[0070] The method of the present invention needs to realize a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer based on feedback control and differential detection through 6 steps.

[0071] Step 1: Multicolor laser generation

[0072] See attached Figure 2 The experimental setup includes a 795nm laser (1), the beam emitted by the laser is collimated by a lens. A 3.417GHz microwave source is mixed with the current supply of the laser to achieve laser modulation. The signal generator uses direct digital synthesis (DDS) technology to modulate the microwave source, so that the modulation sidebands of the dual-frequency laser field generated by the laser can be coupled to the different magnetic energy states of the two hyperfine energy levels of the 87Rb atom.

[0073] Step 2: Beam separation and polarization processing

[0074] In the experimental setup, a cylindrical vapor chamber is filled with an appropriate amount of 87Rb atoms and buffer gas. The laser enters the vapor chamber through an amplitude electro-optic modulator (EOM), which is used to adjust the incoming laser intensity. The laser beam passes through a lens, EOM, λ / 2 wave plate, and polarization beam splitter (PBS) in sequence. The PBS splits the linearly polarized light into two beams with orthogonal polarizations and equal intensities.

[0075] Step 3: Steam Chamber and Signal Detection

[0076] The PBS and λ / 2 wave plate can purify the laser polarization. The laser passes through the vapor chamber containing 87Rb atoms, and the photodetector is used to collect the autofluorescence signal. One beam of light passes through the vapor chamber. Photodetector PD1 is used to measure the autofluorescence intensity, and photodetector PD2 is used to measure the intensity of the pump light after passing through the vapor chamber.

[0077] Step 4: CPT fluorescence intensity feedback control

[0078] The PID feedback control loop is connected to the EOM to maintain the autofluorescence S sp The design of this feedback control mechanism can be expressed by the following formula: sp Relationship with feedback parameters:

[0079]

[0080] Where: 33 is the monatomic population of the upper state atom, n at is the atomic density, r 0 is the beam radius, and L is the length of the steam chamber.

[0081] By adjusting the light intensity I(α,δ R ) and the feedback control parameter α and the detuning amount δ R The signal contrast can be further optimized by:

[0082] I(α,δ R )∝Ω 2 (α,δ R )

[0083] The above experiments show that feedback control can maintain S by adjusting the light intensity. sp constant, thus significantly improving the contrast of the CPT resonance signal.

[0084] Step 5: Differential detection processing to determine the accuracy of the CPT magnetometer

[0085] See attached Figure 3 The dual-frequency laser field excites two sets of energy levels of the ground state of 87Rb atoms, namely |F g =1,m F =1〉、|F g =2,m F =1〉 and |F g =1,m F =-1〉, |F g =2,m F =-1〉 respectively generate CPT states in Λ-type configuration. The first modulation is performed by a microwave source at 3.417 GHz, which is half the frequency difference of the 87Rb D1 line hyperfine structure. The second modulation is performed by DDS, whose frequency v mod is variable. When only the linear Zeeman effect is considered, v mod Equal to the Larmor frequency when the CPT signal appears.

[0086] In fact, the energy level of the magnon will move due to factors such as atomic collisions and nonlinear Zeeman effect. This movement can be expressed as a frequency shift Δv, and the Larmor frequency can be expressed as v Larmor Therefore, the center frequency of the CPT resonance is v Larmor +Δv, and the center frequency of the second one is v Larmor -Δv.

[0087] Considering the differential processing of these two sets of signals, in this step, the differential detection process can be described by the following formula:

[0088] For CPT signal 1:

[0089]

[0090] For CPT signal 2:

[0091]

[0092] The differential signal is:

[0093] Y diff =Y 1 -Y 2

[0094] This differential signal eliminates the interference of common mode noise and nonlinear effects on the signal. When the light intensity of the differential signal is zero, the Larmor frequency can be determined, ensuring high-precision magnetic field measurement.

[0095] Step 6: Determine the CPT magnetometer sensitivity

[0096] The sensitivity of the CPT magnetometer can be calculated by the following formula:

[0097]

[0098] Where: δB is the magnetometer sensitivity, γ is the gyro ratio, Δx is the CPT resonance linewidth, S is the resonance signal amplitude, and N is the noise.

[0099] Through the experimental device of the present invention, the system common mode noise N c (w) is eliminated, and the system noise N is weakened. The present invention can improve the sensitivity and absolute accuracy of the CPT magnetometer at the same time.

[0100] 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 simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer, characterized in that: The following steps are involved: Step 1, generating multi-color laser using a CPT magnetometer device based on feedback control and differential detection; Step 2, using a microwave source to perform frequency modulation of the multi-color laser at 3.417 GHz, wherein the 3.417 GHz corresponds to the fine structure frequency difference of 6.835 GHz of the D1 energy level of the 87Rb atom, to generate a dual-frequency laser field; Step 3, using a polarization beam splitter to separate the dual-frequency laser field to form two beams of light with equal intensity and orthogonal polarization, so as to excite different magnon state systems in the 87Rb atoms and generate two Λ-type CPT resonance systems; Step 4, introducing the two light beams into a vapor chamber containing 87Rb atoms, the two light beams interact with the 87Rb atoms, excite atoms in different magnetic states and generate CPT signals, monitor the autofluorescence intensity of the vapor chamber through a first photodetector, and detect the intensity of the pump light after passing through the vapor chamber through a second photodetector; Step 5, using a CPT fluorescence intensity feedback control loop to enable the electro-optic modulator on the pump light path to adjust the pump light intensity in real time according to the spontaneous fluorescence intensity, to ensure that the fluorescence signal is constant, thereby improving the contrast of the CPT resonance; Step 6: Improve the magnetic field measurement accuracy and sensitivity of the CPT magnetometer by eliminating common mode noise through differential detection processing.

2. The method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer according to claim 1, characterized in that: The CPT magnetometer device based on feedback control and differential detection in step 1 includes a laser, a lens, an electro-optic modulator, a 1 / 2 wave plate, a polarization beam splitter, a steam chamber and a second photodetector connected in sequence, the second photodetector is connected to a data acquisition processor, the steam chamber is connected to the electro-optic modulator through a first photodetector and a PID controller in sequence, the laser is connected to a DDS signal generator through a microwave source, the steam chamber is located in an oven, the oven is located in a magnetic field coil, the magnetic field coil is located in a ferrite shielding layer, and the ferrite shielding layer is located in a permalloy shielding layer.

3. The method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer according to claim 2, characterized in that: The laser generates laser light with a wavelength of 795 nm.

4. The method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer according to claim 1, characterized in that: The 87Rb atoms in step 4 include |F g =1,m F =1〉and|F g =2,m F =1〉, and |F g =1,m F =-1〉 and |F g =2,m F =-1〉, the two sets of CPT signals generated by these two different magnetic state systems have different frequency shifts.

5. The method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer according to claim 1, characterized in that: Step 5 includes the following expression: I(a,d R )∝Ω 2 (a,d R ), Where S sp is the autofluorescence intensity, N e is the total number of atoms, ρ 33 is the monatomic population number, n at is the atomic density, r0 is the beam radius, L is the vapor chamber length, const is a constant, I(α,δ R ) is the light intensity adjustment, α is the feedback control parameter, δ R is the detuning amount and Ω is the contrast.

6. The method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer according to claim 1, characterized in that: Step 6 includes performing differential processing on two groups of CPT signals with different frequency shifts, so that the frequency shift caused by noise and nonlinear Zeeman effect is eliminated, thereby accurately extracting the Larmor frequency. When the intensity of the differential signal is zero, the frequency output by the system is the Larmor frequency. Since the differential processing eliminates the influence of common-mode noise, the measurement of the Larmor frequency is more accurate, thereby achieving high-precision magnetic field measurement.

7. The method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer according to claim 1, characterized in that: Step 6 includes the following expression: Y diff =Y1-Y2, Where Y1 is the first group of CPT signals, k is the proportional coefficient, v is half of the magnetic resonance line width, w is the frequency output by the DDS signal generator, and v Larmor is the Larmor frequency, Δv is the magnon energy level offset, N c (w) is the common mode noise, Y2 is the second group of CPT signals, Y diff is the signal difference component, δB is the sensitivity of the CPT magnetometer, Δx is the CPT resonance linewidth, γ is the gyro ratio, S is the resonance signal amplitude, and N is the noise.

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