CPT magnetometer sensitivity improving method based on magnetic field modulation in geomagnetic prospecting

Abstract

A CPT magnetometer sensitivity improving method based on magnetic field modulation in geomagnetic prospecting comprises the following steps: performing half-wave modulation on laser generated by a laser by using an EOM to obtain multicolor laser, and weakening the light intensity and changing the polarization state of the laser through a light intensity adjusting device; meanwhile, sine wave modulation is applied to the magnetic field where the air chamber is located, a lock-in amplifier is used for demodulating optical signals through sine wave modulation signals to obtain corresponding dispersion signals, and the size of the magnetic field to be measured in geomagnetic prospecting is further obtained. The sensitivity of the magnetometer modulated by the magnetic field is close to the sensitivity obtained by the traditional laser light source modulation method, but the magnetic field modulation method gets rid of the difficulty of too high requirement on the laser light source, and the coil structure and principle are relatively simple and are more suitable for a complex working environment. In conclusion, the CPT atomic magnetometer based on the magnetic field modulation method can be widely applied to the fields of magnetic field drawing, mineral exploration and the like, has the characteristics of high precision, high resolution and the like, and also shows a wide market application prospect in the aspects of miniaturization, low power consumption and the like.

Description

Technical Field

[0001] The invention relates to the technical field of interaction between light and alkali metal atoms in geomagnetic prospecting, and in particular to a method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting. Background Art

[0002] CPT magnetometer 87 When the frequency difference of two colors of light in the polychromatic light is equal to the energy difference of the Zeeman sublevel (CPT, Coherent Population Trapping), the atom will be trapped in the ground state and no longer absorb light, thereby generating a transmission signal for magnetic field measurement. Usually, the Zeeman sublevel is modulated and demodulated to obtain accurate magnetic field information. At present, the mainstream method is to modulate the frequency of the laser light source. Common lasers generally have a modulation signal entrance, and the technical means of laser light source modulation are relatively mature. However, with the rise of micro-nano processing technology, atomic magnetometers are gradually developing in the direction of miniaturization. For the common micro atomic magnetometers, the large volume of the laser and the high requirements for laser frequency stability are gradually highlighted. In order to get rid of the dilemma of large volume, the existing micro lasers mostly adopt high integration and simplified components, resulting in many micro lasers not having a modulation signal entrance. For the problem of laser frequency stability, optical means are often used for frequency stabilization, but when the modulation signal is applied to the laser, the frequency stability will be significantly reduced, thus affecting the performance of the magnetometer. In order to further reduce the size of the magnetometer and reduce the impact of the system on the laser frequency stability, the use of magnetic field modulation technology can reasonably meet these two requirements. In addition, existing atomic magnetometers all contain excitation magnetic field modules, and the modulated magnetic field is just a weak modulation signal applied on the basis of the excitation magnetic field. There is no need to add additional modules or new equipment to the magnetometer itself, and it does not affect the laser frequency.

[0003] At present, this method is also used in spin-exchange relaxation-free magnetometers, but it is not commonly used because it will affect the magnetic field measurement results. SERF magnetometers are mainly used to measure weak magnetic signals. The weak noise of the modulation signal will directly affect the measurement performance of the magnetometer. However, compared with SERF magnetometers (SERF, Spin-Exchange Relaxation-Free, spin-exchange relaxation-free), CPT magnetometers have a large magnetic field measurement range and are less affected by weak changes in magnetic field modulation signals. Magnetic field modulation methods are more applicable. In addition, CPT magnetometers are mainly used in geomagnetic prospecting and magnetic field mapping. Highly integrated laser light sources that do not require modulation and larger measured magnetic fields are more suitable for the use of magnetic field modulation technology. Summary of the invention

[0004] The problem solved by the present invention is as follows: the present invention proposes a method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting, half-wave modulating the laser generated by a laser using an EOM to obtain a multicolor laser (EOM, Electro-Optic Modulator), weakening the light intensity and changing the laser polarization state through a light intensity modulator; at the same time, sinusoidal wave modulation is applied to the magnetic field in the gas chamber, a phase-locked amplifier is used to demodulate the optical signal using the sinusoidal wave modulation signal to obtain a corresponding dispersion signal, and further the magnitude of the magnetic field to be measured in geomagnetic prospecting is obtained.

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

[0006] The method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting is characterized in that it includes: using EOM to perform half-wave modulation on the laser generated by a laser to obtain a multi-color laser, and then irradiating the atomic gas chamber in the CPT magnetometer system after weakening the light intensity and changing the laser polarization state through a light intensity regulator; at the same time, applying sinusoidal wave modulation to the magnetic field in which the atomic gas chamber is located, using a phase-locked amplifier to demodulate the EIT optical signal output from the atomic gas chamber using the sinusoidal wave modulation signal to obtain a corresponding dispersion signal, and further obtaining the size of the magnetic field to be measured in geomagnetic prospecting.

[0007] The following steps are involved:

[0008] Step 1, prepare light and atoms to realize CPT effect;

[0009] Step 2: A Helmholtz coil is installed on the outer layer of the oven to generate an excitation magnetic field. This magnetic field receives a sinusoidal modulation signal with the help of a signal generator. At the same time, the photovoltage signal provided by the PD and the sinusoidal modulation signal of the signal generator are transmitted to the phase-locked amplifier for demodulation. During this demodulation process, a CPT dispersion signal is generated. The dispersion signal is sent to the data acquisition system for a series of analyses, and the dispersion signal optimization is implemented according to the analysis results.

[0010] Step 3: The optimized dispersion signal is sent to the data acquisition system to analyze the magnetic field measurement data. After preliminary data preprocessing, including removing possible DC offsets and filtering operations, the data will be further processed. In order to use it in noise power spectrum analysis, the processed time domain magnetic field data is converted into frequency domain data by Fourier transform. After obtaining the frequency domain data, the power spectrum density estimation method is used to calculate the power value of each frequency point to obtain the noise power spectrum density diagram, so as to identify and evaluate the noise level and characteristics in different frequency ranges.

[0011] Step 1 includes: adjusting the laser to 87The linear polarized light is adjusted to reduce the power to 50 microwatts after the D1 line resonance frequency of the Rb atom, and the output light is circularly polarized after passing through a quarter-wave plate. After the spatial light is converted into fiber light, it is transmitted to the EOM through the optical fiber to achieve half-wave modulation of the laser into multi-color light, and its first-order sideband light domain frequency is equal to the frequency difference of the hyperfine structure energy level; then the laser passes through the 87 The atomic gas chamber of Rb and 30Torr buffer gas is heated to 50°C; then the photodiode receives the transmitted light and outputs a photovoltage signal, which is then modulated into a 3.417 GHz radio frequency signal to observe the EIT signal.

[0012] Step 2 includes: analyzing the intensity, signal-to-noise ratio and linewidth characteristics of the dispersion signal, adjusting the output of the signal generator according to these characteristics, and adjusting the amplitude, frequency and phase of the sinusoidal modulation signal, so that the subsequently generated dispersion signal has greater intensity, higher signal-to-noise ratio and narrower linewidth, so as to improve the performance of the entire system.

[0013] Step 3 includes: using a signal generator to generate a sinusoidal modulated signal and applying it to the Helmholtz coil for magnetic field modulation, feeding back the sinusoidal modulated signal after outputting the dispersion signal, optimizing the intensity, signal-to-noise ratio and line width of the dispersion signal, and after optimization, realizing magnetic field detection by measuring the frequency difference of the dispersion signal, and then applying time-frequency conversion technology to obtain the noise power spectrum result.

[0014] The atomic gas chamber is placed in a magnetic field to be measured in geomagnetic prospecting. The laser input side of the atomic gas chamber is connected to the laser through an optical component. The coil outside the atomic gas chamber for providing an excitation magnetic field is connected to a signal generator. The signal generator transmits a triangular wave scanning signal to a radio frequency signal generator, which is connected to the laser. The laser output side of the atomic gas chamber is connected to a phase-locked amplifier through a photodiode. The phase-locked amplifier is connected to the signal generator through a signal processing system, and the phase-locked amplifier receives a sinusoidal modulation signal.

[0015] Includes the following formulas:

[0016] Δv=γ|B|

[0017] Where Δv is the optical frequency difference, γ is the gyromagnetic ratio of the rubidium atom, and |B| is the magnetic field to be measured in geomagnetic prospecting.

[0018] Compared with the prior art, the advantages of the present invention are: the use of magnetic field modulation technology when conducting mineral exploration in a geomagnetic environment can effectively solve the problems of large laser volume and unstable frequency, and no additional equipment or modules are required. This modulation technology can effectively reduce the size of the magnetometer, reduce the impact of the system on the stability of the laser frequency, and make the magnetic field measurement more accurate and reliable. Since the CPT magnetometer has a large magnetic field measurement range and is less affected by slight changes in the magnetic field modulation signal. This invention relies on the principle of the CPT magnetometer and uses87 The mutual interference effect of the energy levels of Rb atoms realizes high-precision magnetic field measurement. The laser generates multi-color laser, frequency modulation, and optical device adjustment to convert the laser into circular polarization and enter the atomic gas chamber. The magnetic shielding barrel is equipped with a magnetic field coil and PD for optical signal reception (PD, Photodiode), and the phase-locked amplifier demodulates the CPT signal to analyze the magnetic field intensity. While the Helmholtz coil provides the excitation magnetic field, frequency modulation is performed, and then the phase-locked amplifier processes the dispersion signal, analyzes the intensity line width of the dispersion signal and feeds back to the modulation signal to continuously optimize the dispersion signal, so as to realize high-sensitivity measurement and analysis of the magnetic field. The sensitivity of the system is obtained by precise calculation, and after data acquisition and analysis, it is compared with the results obtained by the traditional laser light source modulation method to verify the system performance and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic flow chart of a method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting according to the present invention. Figure 1 The method includes step 1, preparing light and atoms to realize CPT effect (CPT, Coherent Population Trapping), and measuring EIT signal (EIT, Electromagnetically induced transparency); step 2, modulating the signal of the magnetic field coil, and inputting the modulation signal of the magnetic field and the EIT signal into the phase-locked amplifier; step 3, demodulating to obtain the dispersion signal of the EIT signal and determining the magnetic field using the distance of the dispersion signal, and feeding back the dispersion signal intensity to the magnetic field modulation signal source so that the dispersion signal reaches a higher intensity; step 4, calculating the system sensitivity.

[0020] Figure 2 It is a schematic diagram of the structure of a CPT magnetometer system involved in the method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting of the present invention.

[0021] Figure 3 This is a sensitivity comparison chart of the CPT magnetometer based on magnetic field modulation and the CPT magnetometer based on laser light source modulation in geomagnetic prospecting.

[0022] The description of the accompanying drawings is as follows: 1-laser; 2-optical component (adjusting the polarization and power of light); 3-atomic gas chamber; 4-photodiode (receiving transmitted light and outputting photovoltage signal / EIT signal); 5-phase-locked amplifier (demodulating the CPT signal to obtain the CPT dispersion signal); 6-data processing system or signal processing system; 7-feedback modulation signal; 8-signal generator; 9-triangle wave scanning signal; 10-RF signal generator (generating a RF signal with a frequency of 3.417 GHz); 11-coil (providing an excitation magnetic field); 12-magnetic field to be measured; 13-optimizing the amplitude, frequency and phase of the modulation signal; 14-sinusoidal modulation signal. DETAILED DESCRIPTION

[0023] Below is the attached figure ( Figure 1-Figure 3 ) and Examples illustrate the present invention.

[0024] Figure 1 It is a schematic flow chart of a method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting according to the present invention. Figure 2 It is a schematic diagram of the structure of a CPT magnetometer system involved in the method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting of the present invention. Figure 3 This is a comparison chart of the sensitivity of CPT magnetometers based on magnetic field modulation and CPT magnetometers based on laser light source modulation in geomagnetic prospecting. Figures 1 to 3 As shown, a method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting includes: using EOM to perform half-wave modulation on the laser generated by a laser to obtain a multi-color laser, and then irradiating the atomic gas chamber in the CPT magnetometer system after weakening the light intensity and changing the laser polarization state through a light intensity modulator; at the same time, applying sinusoidal wave modulation to the magnetic field in which the atomic gas chamber is located, and using a phase-locked amplifier to demodulate the EIT optical signal output from the atomic gas chamber with the sinusoidal wave modulation signal to obtain a corresponding dispersion signal, and further obtaining the size of the magnetic field to be measured in geomagnetic prospecting.

[0025] The method comprises the following steps: step 1, preparing light and atoms to realize CPT effect; step 2, a Helmholtz coil is arranged on the outer layer of the oven to generate an excitation magnetic field, the magnetic field receives a sinusoidal modulation signal with the aid of a signal generator, and the photovoltage signal provided by the PD and the sinusoidal modulation signal of the signal generator are transmitted to a phase-locked amplifier for demodulation, during which a CPT dispersion signal is generated, the dispersion signal is sent to a data acquisition system for a series of analyses, and dispersion signal optimization is implemented according to the analysis results; step 3, the optimized dispersion signal is sent to a data acquisition system to analyze magnetic field measurement data, and preliminary data preprocessing is completed, including removing possible DC offset and filtering operations, and then further processing the data, in order to be used in noise power spectrum analysis, the processed time domain magnetic field data is converted into frequency domain data by means of Fourier transform, after obtaining the frequency domain data, the power spectrum density estimation method is used to calculate the power value of each frequency point to obtain a noise power spectrum density diagram, so as to identify and evaluate the noise level and characteristics in different frequency ranges.

[0026] Step 1 includes: adjusting the laser to 87 The linear polarized light is adjusted to reduce the power to 50 microwatts after the D1 line resonance frequency of the Rb atom, and the output light is circularly polarized after passing through a quarter-wave plate. After the spatial light is converted into fiber light, it is transmitted to the EOM through the optical fiber to achieve half-wave modulation of the laser into multi-color light, and its first-order sideband light domain frequency is equal to the frequency difference of the hyperfine structure energy level; then the laser passes through the 87 The atomic gas chamber of Rb and 30Torr buffer gas is heated to 50°C; then the photodiode receives the transmitted light and outputs a photovoltage signal, which is then modulated into a 3.417 GHz radio frequency signal to observe the EIT signal.

[0027] Step 2 includes: analyzing the intensity, signal-to-noise ratio and line width characteristics of the dispersion signal, adjusting the output of the signal generator according to these characteristics, adjusting the amplitude, frequency and phase of the sinusoidal modulation signal, so that the dispersion signal generated subsequently has greater intensity, higher signal-to-noise ratio and narrower line width, so as to improve the performance of the entire system. Step 3 includes: using a signal generator to generate a sinusoidal modulation signal and applying it to the Helmholtz coil for magnetic field modulation, feeding back the sinusoidal modulation signal after outputting the dispersion signal, optimizing the intensity, signal-to-noise ratio and line width of the dispersion signal, realizing magnetic field detection by measuring the frequency difference of the dispersion signal after optimization, and then applying the time-frequency conversion technology to obtain the noise power spectrum result.

[0028] The atomic gas chamber 3 is placed in the magnetic field 12 to be measured in geomagnetic prospecting. The laser input side of the atomic gas chamber 3 is connected to the laser 1 through the optical component 2. The coil 11 outside the atomic gas chamber 3 for providing an excitation magnetic field is connected to the signal generator 8. The signal generator 8 transmits the triangular wave scanning signal 9 to the radio frequency signal generator 10. The radio frequency signal generator 10 is connected to the laser 1. The laser output side of the atomic gas chamber 3 is connected to the phase-locked amplifier 5 through the photodiode 4. The phase-locked amplifier 5 is connected to the signal generator 8 through the signal processing system 6. The phase-locked amplifier 5 receives the sinusoidal modulation signal 14.

[0029] The present invention relates to a method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting. By modulating the Zeeman sub-energy level through an alternating magnetic field, a phase-sensitive detection scheme suitable for a micro coherent population trapping (CPT) magnetometer is realized, providing a new method for detecting magnetic field intensity. 87 Rb) atoms are used as research objects, light and atoms are prepared to realize CPT effect, electromagnetically induced transparency (EIT) signals are measured to modulate signals of magnetic field coils, microwave frequency scans EIT signals and inputs the modulation signals of magnetic field and EIT signals into phase-locked amplifiers to demodulate and obtain dispersion signals of EIT signals and use the distance of dispersion signals to determine magnetic fields; and the dispersion signal intensity is fed back to the magnetic field modulation signal source to make the dispersion signal reach a higher intensity. The sensitivity of the magnetometer after magnetic field modulation is similar to that obtained by the traditional laser light source modulation method, but the magnetic field modulation method gets rid of the dilemma of excessively high requirements for laser light sources in the existing technology, and the coil structure and principle are relatively simple and more suitable for complex working environments. In general, this method can be widely used in magnetic field mapping, mineral exploration and other fields. This CPT atomic magnetometer based on magnetic field modulation method not only has the characteristics of high precision and high resolution, but also shows a broad market application prospect in terms of miniaturization and low power consumption.

[0030] The method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting includes the following steps:

[0031] (1) Preparation of light and atoms to achieve CPT effect

[0032] The laser output frequency is tuned by its laser controller to 87The resonant frequency of the Rb atomic D1 line (the first spectral line of the D series). The laser outputs linearly polarized light, and the optical power is attenuated to 50 microwatts through the optical power adjustment structure. The laser converts spatial light into fiber light through a fiber coupling head, and is transmitted to the electro-optic modulator (EOM) through a polarization-maintaining fiber. The laser and RF output signals are coupled into the optical path by the EOM to achieve half-wave modulation of the laser frequency. The laser is modulated and transformed from monochromatic light to polychromatic light. The frequency difference of the first-order sideband light field generated is exactly equal to the frequency difference between the ground state energy level and the excited state energy level of the hyperfine structure. The fiber optic light output by the EOM is transmitted to the laser collimator to adjust the laser spot diameter. Adjust the quarter glass slide to convert the laser into circular polarization, and then pass it through a 87 The atomic gas cell is filled with Rb and 30Torr buffer gas, and the atomic gas cell is uniformly heated to 50°C by an oven. The transmitted light is received by a photodiode (PD) and a photovoltage signal is output. A triangular wave signal generator is used to generate a scanning signal, which is modulated by a 3.417 GHz RF signal generated by a RF signal generator to observe the EIT signal.

[0033] (2) A Helmholtz coil is wound around the outside of the oven to provide an excitation magnetic field. A sinusoidal modulation signal is applied to the Helmholtz coil by a signal generator. The photovoltage signal output by the PD and the sinusoidal modulation signal of the signal generator are sent to the phase-locked amplifier for demodulation. The CPT dispersion signal is output and sent to the data acquisition system for analysis of the intensity, signal-to-noise ratio and line width of the dispersion signal. The signal is fed back to the signal generator to continuously adjust the amplitude, frequency and phase of the sinusoidal modulation signal to ensure that the dispersion signal has a large intensity, a high signal-to-noise ratio and a narrow line width.

[0034] (3) The optimized dispersion signal is sent to the data acquisition system for magnetic field measurement and analysis. The collected magnetic field data is preprocessed, including removing possible DC offsets and filtering operations to prepare for noise power spectrum analysis. The preprocessed time domain magnetic field data is converted into frequency domain data, and spectrum analysis can be performed using methods such as Fourier transform. The power spectrum density estimation method is applied to the frequency domain data to calculate the power value of each frequency point, and the noise power spectrum density diagram is obtained by analysis to identify and evaluate the noise level and characteristics in different frequency ranges.

[0035] A signal generator is used to generate a sinusoidal modulation signal and apply it to the Helmholtz coil for magnetic field modulation. After the dispersion signal is output, the sinusoidal modulation signal is fed back to optimize the intensity, signal-to-noise ratio and line width of the dispersion signal. After optimization, the magnetic field detection is achieved by measuring the frequency difference of the dispersion signal, and then the noise power spectrum result is obtained by applying the time-frequency conversion technology. Compared with traditional laser light source modulation, the application of magnetic field modulation is more stable and convenient, and can better adapt to the complex working environment of mineral exploration under the geomagnetic environment, and is more suitable for micro lasers.

[0036] The CPT magnetometer utilizes 87 The mutual interference effect of Rb atomic energy levels. In order to produce multi-color light to meet the frequency difference of ultrafine energy levels, we use lasers to emit 87 The laser of the Rb atomic D1 line is input into the electro-optic modulator. The laser frequency is half-wave modulated by the 3.417GHz electrical signal generated by the radio frequency signal to generate two sideband light with a frequency difference of 6.834GHz. When the laser passes through the gas chamber, the CPT phenomenon caused by atomic interference can be observed.

[0037] A sine wave modulation is applied to the magnetic field coil in the shielding barrel. Since the change of the magnetic field will cause the frequency difference of the atomic Zeeman energy level to change, the modulation will also be reflected in the intensity of the optical signal. The CPT signal is demodulated with the help of a phase-locked amplifier to obtain a dispersion signal. The changes in the dispersion signal intensity, signal-to-noise ratio, and line width are observed by adjusting the frequency amplitude and phase of the sinusoidal modulation signal and fed back to the signal generator to continue to optimize the sinusoidal modulation signal until the dispersion signal reaches the optimal intensity, signal-to-noise ratio, and line width. Finally, by measuring the optical signal frequency difference between the zero crossing points of adjacent dispersion signals, the magnitude of the magnetic field at this time can be measured using Δv (optical frequency difference) = γ (gyromagnetic ratio of rubidium atoms) | B | (measured magnetic field).

[0038] This method requires three steps to achieve the means of improving the sensitivity of the CPT magnetometer based on magnetic field modulation in geomagnetic prospecting.

[0039] Step 1: Prepare light and atoms to achieve the CPT effect

[0040] The laser is adjusted to 87 The linear polarized light is adjusted to 50 microwatts after adjusting the resonance frequency of the Rb atom D1 line. After passing through a quarter glass plate, the output light is circularly polarized. After the spatial light is converted into fiber light, it is transmitted to the EOM through the optical fiber to achieve half-wave modulation of the laser into polychromatic light. The frequency of the first-order sideband light domain is equal to the frequency difference of the hyperfine structure energy level. The laser then passes through the 87 The atomic gas chamber of Rb and 30Torr buffer gas is heated to 50°C. Then the photodiode receives the transmitted light and outputs a photovoltage signal, which is then modulated to a 3.417 GHz radio frequency signal to observe the EIT signal.

[0041] Step 2: There is a Helmholtz coil on the outer layer of the oven to generate an excitation magnetic field, which receives a sinusoidal modulated signal with the help of a signal generator. At the same time, the photovoltage signal provided by the PD and the sinusoidal modulated signal of the signal generator are transmitted to the phase-locked amplifier for demodulation. In this demodulation process, a CPT dispersion signal is generated. The dispersion signal is sent to the data acquisition system for a series of analyses. These analyses cover various characteristics of the dispersion signal, such as intensity, signal-to-noise ratio, and line width. According to these characteristics, the output of the signal generator is adjusted, and the amplitude, frequency, and phase of the sinusoidal modulated signal are adjusted, so that the subsequent dispersion signal has greater intensity, higher signal-to-noise ratio, and narrower line width, so as to improve the performance of the entire system.

[0042] Step 3: The optimized dispersion signal is sent to the data acquisition system to analyze the magnetic field measurement data. After completing the preliminary data preprocessing, including removing possible DC offsets and filtering operations, the data will be further processed. In order to use it in noise power spectrum analysis, the processed time domain magnetic field data is converted into frequency domain data by means of Fourier transform and other means. After obtaining the frequency domain data, the power spectrum density estimation method is used to calculate the power value of each frequency point to obtain the noise power spectrum density diagram, so that the noise level and characteristics in different frequency ranges can be identified and evaluated.

[0043] 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 improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting, characterized in that: include: The laser generated by the laser is half-wave modulated by EOM to obtain multi-color laser. The light intensity is weakened by the light intensity modulator and the laser polarization state is changed to irradiate the atomic gas chamber in the CPT magnetometer system. At the same time, sinusoidal wave modulation is applied to the magnetic field of the atomic gas chamber, and a phase-locked amplifier is used to demodulate the EIT optical signal output from the atomic gas chamber with the sinusoidal wave modulation signal to obtain the corresponding dispersion signal, and further the size of the magnetic field to be measured in geomagnetic prospecting is obtained.

2. The method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting according to claim 1, characterized in that: The following steps are involved: Step 1, prepare light and atoms to realize CPT effect; Step 2: A Helmholtz coil is installed on the outer layer of the oven to generate an excitation magnetic field. This magnetic field receives a sinusoidal modulation signal with the help of a signal generator. At the same time, the photovoltage signal provided by the PD and the sinusoidal modulation signal of the signal generator are transmitted to the phase-locked amplifier for demodulation. During this demodulation process, a CPT dispersion signal is generated. The dispersion signal is sent to the data acquisition system for a series of analyses, and the dispersion signal optimization is implemented according to the analysis results. Step 3: The optimized dispersion signal is sent to the data acquisition system to analyze the magnetic field measurement data. After preliminary data preprocessing, including removing possible DC offsets and filtering operations, the data will be further processed. In order to use it in noise power spectrum analysis, the processed time domain magnetic field data is converted into frequency domain data by Fourier transform. After obtaining the frequency domain data, the power spectrum density estimation method is used to calculate the power value of each frequency point to obtain the noise power spectrum density diagram, so as to identify and evaluate the noise level and characteristics in different frequency ranges.

3. The method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting according to claim 2, characterized in that: Step 1 includes: adjusting the laser to 87 The linear polarized light is adjusted to reduce the power to 50 microwatts after the D1 line resonance frequency of the Rb atom, and the output light is circularly polarized after passing through a quarter-wave plate. After the spatial light is converted into fiber light, it is transmitted to the EOM through the optical fiber to achieve half-wave modulation of the laser into multi-color light, and its first-order sideband light domain frequency is equal to the frequency difference of the hyperfine structure energy level; then the laser passes through the 87 The atomic gas chamber of Rb and 30Torr buffer gas is heated to 50°C; then the photodiode receives the transmitted light and outputs a photovoltage signal, which is then modulated into a 3.417 GHz radio frequency signal to observe the EIT signal.

4. The method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting according to claim 2, characterized in that: Step 2 includes: analyzing the intensity, signal-to-noise ratio and linewidth characteristics of the dispersion signal, adjusting the output of the signal generator according to these characteristics, and adjusting the amplitude, frequency and phase of the sinusoidal modulation signal, so that the subsequently generated dispersion signal has greater intensity, higher signal-to-noise ratio and narrower linewidth, so as to improve the performance of the entire system.

5. The method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting according to claim 2, characterized in that: Step 3 includes: using a signal generator to generate a sinusoidal modulated signal and applying it to the Helmholtz coil for magnetic field modulation, feeding back the sinusoidal modulated signal after outputting the dispersion signal, optimizing the intensity, signal-to-noise ratio and line width of the dispersion signal, and after optimization, realizing magnetic field detection by measuring the frequency difference of the dispersion signal, and then applying time-frequency conversion technology to obtain the noise power spectrum result.

6. The method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting according to claim 1, characterized in that: The atomic gas chamber is placed in a magnetic field to be measured in geomagnetic prospecting. The laser input side of the atomic gas chamber is connected to the laser through an optical component. The coil outside the atomic gas chamber for providing an excitation magnetic field is connected to a signal generator. The signal generator transmits a triangular wave scanning signal to a radio frequency signal generator, which is connected to the laser. The laser output side of the atomic gas chamber is connected to a phase-locked amplifier through a photodiode. The phase-locked amplifier is connected to the signal generator through a signal processing system, and the phase-locked amplifier receives a sinusoidal modulation signal.

7. The method for improving the sensitivity of a CPT magnetometer based on magnetic field modulation in geomagnetic prospecting according to claim 1, characterized in that: Includes the following formulas: Δv=γ|B| Where Δv is the optical frequency difference, γ is the gyromagnetic ratio of the rubidium atom, and |B| is the magnetic field to be measured in geomagnetic prospecting.

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