A method for simultaneously improving sensitivity and absolute accuracy of CPT magnetometer

Abstract

The application discloses a method for simultaneously improving sensitivity and absolute accuracy of a CPT magnetometer, and the method adjusts the intensity of pumping radiation through a feedback loop to keep the spontaneous fluorescence of atomic vapor at a constant level, thereby improving the contrast of CPT resonance. In the experiment, a double-frequency laser field is adopted, the 795nm laser is modulated and divided into two beams of orthogonal polarized light to excite two hyperfine level states of 87Rb atoms. The fluorescence signal is detected and kept at a fixed intensity through PID feedback control. The common-mode noise and other interference factors are eliminated through differential processing of two groups of CPT signals, so that the Larmor frequency under a simulated 5000nT magnetic field is accurately determined, and the Larmor frequency is about 350kHz. The application proposes a method for improving the sensitivity and accuracy of the magnetometer through a fluorescence feedback loop and differential detection, and simultaneously solves the frequency offset problem caused by common-mode noise and nonlinear effects in the traditional method, and 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] Existing improvement methods mostly focus on improving the contrast and stability of CPT signals. For example, methods such as optimizing the laser source, improving optical path design, and adding external magnetic shielding are used to reduce noise. However, these methods often rely on complex equipment and expensive hardware, which not only increases system costs but also has limitations such as bulk and complex operation. Especially in high-sensitivity measurements, common-mode noise, nonlinear frequency shifts caused by the Zeeman effect, and interatomic collision effects can significantly affect the quality of the CPT signal, leading to inaccurate measurement results.

[0004] Some current research has proposed improving the contrast of CPT signals by regulating laser intensity through feedback control. This approach, by adjusting the intensity of the pump laser radiation to maintain a constant atomic fluorescence signal, enhances the resonance contrast to a certain extent. However, relying solely on feedback control cannot completely eliminate the frequency offset caused by common-mode noise and nonlinear effects, which still limits the accuracy of magnetometers.

[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 present invention addresses the shortcomings of existing CPT magnetometers in terms of sensitivity and absolute accuracy by designing a method to simultaneously improve both sensitivity and absolute accuracy. The core of this method is the use of a feedback loop to regulate the intensity of the pump laser, thereby maintaining the atomic fluorescence signal at a constant level. This significantly improves the contrast of the CPT resonance, a key factor affecting CPT magnetometer performance. Furthermore, the present invention utilizes differential detection technology to perform differential processing on two sets of CPT signals, eliminating frequency offsets caused by common-mode noise, the nonlinear Zeeman effect, and interatomic collisions, thereby achieving precise measurement of the Larmor frequency.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer, comprising the following steps:

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

[0010] Step 2: Using a microwave source to perform frequency modulation on the multi-color laser at 3.417 GHz, where 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: Separating the dual-frequency laser field using a polarization beam splitter to form two beams of equal intensity and orthogonal polarization to excite different magnon states 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, wherein the two light beams interact with the 87Rb atoms, exciting atoms in different magnon states and generating CPT signals, monitoring the autofluorescence intensity of the vapor chamber by a first photodetector, and detecting the intensity of the pump light after passing through the vapor chamber by a second photodetector;

[0013] Step 5: Using a CPT fluorescence intensity feedback control loop, an electro-optical modulator on the pump light path adjusts the pump light intensity in real time according to the spontaneous fluorescence intensity to ensure a constant fluorescence signal, 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-optical 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-optical 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〉magnetic state system, and |F g =1,m F =-1〉and|F g =2,m F =-1〉magnon state system, the two sets of CPT signals generated by these two different magneton 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] Among them S sp is the autofluorescence intensity, N e is the total number of atoms, ρ 33 is the monatomic population, 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.

[0022] Step 6 includes differential processing of two sets 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 =Y1-Y2,

[0026]

[0027] Where Y1 is the first set 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 set 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. Feedback control technology is used to significantly increase the contrast of the CPT resonance signal, thereby enhancing the sensitivity of the magnetometer. The application of differential detection technology eliminates frequency offset problems caused by common-mode noise, nonlinear effects, and atomic collisions, significantly improving absolute measurement accuracy. Furthermore, the present invention simplifies the structure of the CPT magnetometer, reducing the complexity and operational difficulty of the system, making the device easier to operate and maintain in practical applications. This device not only meets the demand for high-precision magnetic field measurements, but also provides a strong guarantee for the widespread application of CPT magnetometers in industrial, scientific research, and medical fields.

[0029] The CPT magnetometer device and method based on feedback control and differential detection presented in this invention have significant theoretical significance and broad application prospects. They not only provide new insights into improving magnetometer performance but also lay the foundation for further research and development of highly sensitive and precise quantum measurement devices. The technical solutions proposed in this invention can better detect weak magnetic fields, promoting development and innovation in related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a flow chart of a method for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer. Figure 1The method includes step 1, generating multicolor laser light; step 2, modulating the laser light with a 3.417 GHz microwave signal, and splitting the laser light into two beams using a polarization beam splitter (PBS), adjusting the polarization direction to ensure signal stability; step 3, passing the laser light through a vapor cavity filled with 87Rb atoms, and collecting the spontaneous fluorescence signal using a photodetector; step 4, controlling the laser intensity in a feedback loop to maintain a constant fluorescence signal in the vapor cavity, thereby improving signal contrast; step 5, collecting and differentially processing two sets of CPT (Coherent Population Trapping) signals to eliminate common-mode noise and ensure signal accuracy; and step 6, determining the Larmor frequency by using 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 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 the CPT state involved in a method of the present invention for simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer. 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 figures 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); 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 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 This 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 the CPT state involved in a method of simultaneously improving the sensitivity and absolute accuracy of a CPT magnetometer in 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: Generate multi-color laser using a CPT magnetometer device based on feedback control and differential detection; Step 2: Use a microwave source to perform frequency modulation on the multi-color laser at 3.417 GHz, where 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: Use a polarization beam splitter to separate the dual-frequency laser field into two beams of equal intensity and orthogonal polarization, so as to excite different magnetic substate systems in the 87Rb atom and generate two Λ-type CPT resonance systems; Step 4: Introduce the two beams into a 87Rb atom equipped with a laser. In the vapor chamber of Rb atoms, the two beams of light interact with the 87Rb atoms, exciting atoms in different magnon states and generating a CPT signal. The spontaneous fluorescence intensity of the vapor chamber is monitored by a first photodetector, and the intensity of the pump light after passing through the vapor chamber is detected by a second photodetector. In step 5, an electro-optical modulator on the pump light path adjusts the pump light intensity in real time according to the spontaneous fluorescence intensity through a CPT fluorescence intensity feedback control loop to ensure a constant fluorescence signal, thereby improving the contrast of the CPT resonance. In step 6, common-mode noise is eliminated through differential detection processing 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-optical 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-optical 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〉magnetic state system, and |F g =1,m F =-1〉and|F g =2,m F =-1〉magnon state system, the two sets of CPT signals generated by these two different magneton 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] Among them S sp is the autofluorescence intensity, N e is the total number of atoms, ρ 33 is the monatomic population, 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.

[0043] Step 6 includes differential processing of two sets 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 =Y1-Y2,

[0047]

[0048] Where Y1 is the first set 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 set 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 simultaneously improving the sensitivity and absolute accuracy of a coherent population trapping (CPT) magnetometer based on feedback control and differential detection. The invention adjusts the pump radiation intensity 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 polarization. The fluorescence signal is detected and maintained at a fixed intensity through PID feedback control. By differentially processing the two groups of CPT signals, interference factors such as common mode noise are eliminated, thereby accurately measuring 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 simultaneously 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 team used a laser to generate a 795nm wavelength laser and used a microwave source to modulate the laser at a frequency of 3.417GHz. This frequency corresponds to the fine structure frequency difference of the D1 energy level of the 87Rb atom, generating a dual-frequency laser field that provides the appropriate 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), forming two beams of equal intensity and orthogonal polarization. These polarized beams are then used to excite different magnon states in the 87Rb atoms, generating two Λ-type CPT resonance systems.

[0055] (3) Steam chamber and signal detection

[0056] Two beams of light are introduced into a vapor chamber filled with 87Rb atoms, interacting with the atoms within the chamber, exciting atoms in different magnon states and generating CPT signals. Photodetector PD1 monitors the autofluorescence intensity of the vapor chamber, while another photodetector, PD2, detects the intensity of the pump light after it passes through the chamber.

[0057] (4) CPT fluorescence intensity feedback control

[0058] To ensure the contrast and stability of the CPT signal, a feedback control loop was designed. Using a PID controller and an electro-optical modulator (EOM), the pump light intensity is adjusted in real time based on the autofluorescence intensity measured by photodetector PD1, ensuring a constant fluorescence signal and thus 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. Two different magnetic sub-state systems in 87Rb atoms (for example, |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〉 combination) have different frequency shifts. By performing differential processing on these two signals, the frequency shift caused by noise and the nonlinear Zeeman effect can be eliminated, allowing for precise extraction of the Larmor frequency. When the intensity of the differential signal reaches zero, the frequency output by the system is the Larmor frequency. Because differential processing eliminates the influence of common-mode noise, the Larmor frequency measurement is more accurate, enabling high-precision magnetic field measurements.

[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 by a feedback loop to maintain a constant level of atomic vapor spontaneous fluorescence, thereby improving the CPT resonance contrast, eliminating common-mode noise, nonlinear Zeeman effect and atomic collision effects by differential detection to accurately determine the Larmor frequency. The constructed device includes: a laser 1 for generating a 795 nm dual-frequency laser field; an electro-optical modulator 3 for modulating a 3.417 GHz microwave signal onto the output beam of the laser; a polarization beam splitter (i.e. 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 intensity; a vapor cell (i.e. vapor chamber 9 or atomic gas chamber) filled with 87Rb atoms and buffer gas for realizing CPT resonance; a first photodetector 10 for detecting the intensity of atomic spontaneous fluorescence in the vapor cell; a second photodetector 12 for detecting the intensity of the pump light after passing through the vapor cell; a PID feedback control system (i.e. PID controller 13) connected with the first photodetector 10 and the electro-optical modulator 3 for adjusting the intensity of the pump light to maintain a constant level of spontaneous fluorescence; a differential detection module (i.e. PID controller 13) for differentially processing the 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 shown in Figure 2 To generate CPT resonance in 87Rb atoms, the experimental scheme uses a laser to generate a 795 nm laser, and a 3.417 GHz microwave source to modulate the laser into a dual-frequency laser. This frequency modulation matches the fine structure of the D1 level of 87Rb atoms, allowing the dual-frequency laser field to excite specific magnetic quantum states and produce 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 substate systems of 87Rb atoms to form two Λ-type system configurations. This beam processing method ensures accurate excitation and detection of CPT signals.

[0068] After beam splitting and polarization processing, the beams are introduced into a vapor chamber filled with 87Rb atoms and interact with the atoms in the chamber. The atoms are excited by the dual-frequency laser field to emit spontaneous fluorescence signals, which are detected by photodetector PD1. Photodetector PD2 detects the intensity of the pump light after passing through the vapor chamber. The fluorescence signal is used as the key input for feedback control to dynamically adjust the intensity of the laser pump.

[0069] To maintain the contrast and stability of the CPT signal, a feedback control loop was designed. This loop, consisting of a PID controller and an electro-optical modulator (EOM), adjusts the laser pump light intensity based on the fluorescence signal measured by PD1. By adjusting the pump light intensity to maintain a constant fluorescence signal, the CPT signal contrast is maximized, significantly improving the sensitivity of the CPT magnetometer.

[0070] The method of the present invention needs to realize a method of 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 consists of a 795 nm laser (1) whose beam is collimated by a lens. A 3.417 GHz microwave source is mixed with the laser's current supply 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 couple 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 a buffer gas. Laser light enters the vapor chamber through an amplitude electro-optical modulator (EOM), which regulates the incoming laser light intensity. The laser beam passes through a lens, the EOM, a λ / 2 wave plate, and a polarization beam splitter (PBS). The PBS splits the linearly polarized light into two beams of orthogonal polarization and equal intensity.

[0075] Step 3: Steam Chamber and Signal Detection

[0076] The PBS and λ / 2 wave plate purify the laser's polarization. The laser passes through a vapor chamber containing 87Rb atoms, and a photodetector collects the autofluorescence signal. One beam of light passes through the vapor chamber. Photodetector PD1 measures the autofluorescence intensity, while photodetector PD2 measures the pump light intensity 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: ρ 33 is the monatomic population of the upper state atom, n at is the atomic density, r0 is the beam radius, and L is the vapor chamber length.

[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 the relationship:

[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 the 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 =Y1-Y2

[0094] This differential signal eliminates interference from common-mode noise and nonlinear effects. 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 simultaneously improve the sensitivity and absolute accuracy of the CPT magnetometer.

[0100] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present 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, using a CPT magnetometer device based on feedback control and differential detection to generate multi-color lasers; Step 2: Using a microwave source to perform frequency modulation on the multi-color laser at 3.417 GHz, where 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: Separating the dual-frequency laser field using a polarization beam splitter to form two beams of equal intensity and orthogonal polarization to excite different magnon states 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, wherein the two light beams interact with the 87Rb atoms, exciting atoms in different magnon states and generating CPT signals, monitoring the autofluorescence intensity of the vapor chamber by a first photodetector, and detecting the intensity of the pump light after passing through the vapor chamber by a second photodetector; Step 5: Using a CPT fluorescence intensity feedback control loop, an electro-optical modulator on the pump light path adjusts the pump light intensity in real time according to the spontaneous fluorescence intensity to ensure a constant fluorescence signal, thereby improving the contrast of the CPT resonance; Step 6, improving the magnetic field measurement accuracy and sensitivity of the CPT magnetometer by eliminating common mode noise through differential detection processing; Step 5 includes the following expression: I(a,d R )∝Ω 2 (a, d) R ), Among them S sp is the autofluorescence intensity, N e is the total number of atoms, ρ 33 is the monatomic population, 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.

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-optical 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-optical 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〉magnetic state system, and |F g =1,m F =-1〉and|F g =2,m F =-1〉magnon state system, the two sets of CPT signals generated by these two different magneton 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 6 includes differential processing of two sets 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.

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 the following expression: Y diff =Y1-Y2, Where Y1 is the first set 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 set 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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