SERF atom magnetometer based on pi pulse pumping detection and magnetic field detection method

Abstract

The invention relates to the field of quantum sensing, and provides an SERF atom magnetometer based on pi pulse pumping detection and a magnetic field detection method. According to the method, 770nm pumping light and 795nm detection light are modulated into an alternating pulse sequence through an acousto-optic modulator, optical frequency shift interference is avoided by adopting a time division multiplexing technology, and pumping pulses are configured to have a pi rotation effect so as to enhance atomic spin polarization. The device comprises an alkali metal gas chamber with multiple layers of magnetic shielding, a graphene heat conduction non-magnetic heating system based on infrared laser, a time division control light path module and a synchronous signal processing unit. Electric heating is replaced by laser heating to eliminate magnetic noise, a pulse interval tau adjustable mechanism is utilized to balance sensitivity and measuring range, and common-mode noise is suppressed in combination with differential photoelectric detection and phase-locked amplification technologies. The alternating current stark effect caused by continuous illumination and magnetic field interference of traditional heating are overcome, the magnetic field measurement precision, the system stability and the signal-to-noise ratio are improved, and a high-precision weak magnetic field detection scheme is provided for biomedical detection and quantum navigation.

Description

Technical Field

[0001] The present invention relates to the field of quantum sensing, and provides a SERF atomic magnetometer and a magnetic field detection method based on π-pulse pumping detection. Background Art

[0002] The spin-exchange relaxation-free (SERF) atomic magnetometer based on spin-exchange relaxation-free is an ultra-high-sensitivity quantum sensor for extremely weak magnetic fields, with the advantages of extremely high measurement accuracy and miniaturization. Its theoretical accuracy is only related to quantum noise and is not affected by other interferences. Its characteristics of high precision, miniaturization, and low cost have shown important application values in the fields of magnetocardiogram and magnetoencephalogram measurement, geomagnetic exploration, and precision navigation.

[0003] To achieve the ultra-high sensitivity of the SERF atomic magnetometer, it is necessary to strictly control the atomic density and the external magnetic field. On the one hand, it is necessary to increase the temperature by heating the atomic gas chamber, so as to increase the alkali metal atomic density to a sufficiently high level, increase the rate of atomic spin-exchange collisions, and enhance the response of the device to weak magnetic fields. On the other hand, it is necessary to ensure that the atomic spin works in the SERF state through multi-layer magnetic shielding and three-axis magnetic field compensation, maximally suppress the magnetic noise around the atomic gas chamber, reduce the Larmor precession frequency of the atoms, and thus eliminate the relaxation loss caused by spin-exchange collisions. In addition, extremely high requirements are also put forward for the stability and noise suppression of the pumping light and the detection light.

[0004] At present, continuous light illumination is generally adopted for the pumping light and the detection light in the SERF atomic magnetometer, that is, circularly polarized laser is continuously irradiated on alkali metal atoms to achieve spin polarization, and the angular rate signal can be read out by measuring the optical rotation angle generated by atomic spin precession. However, continuous light illumination will cause the atomic energy level to shift due to the AC-Stark effect, generating an optical frequency shift effect, which is equivalent to the existence of a false bias magnetic field, resulting in measurement errors and additional noise.

[0005] This limits the measurement accuracy and long-term stability of the SERF atomic magnetometer. At the same time, most SERF atomic magnetometers use electric heating to maintain the high temperature of the gas chamber to obtain a high atomic density, but the heating current will generate stray magnetic field noise, interfering with the zero magnetic field working environment of the atoms. Even if additional magnetic shielding and magnetic field compensation devices are used to reduce this interference, the environmental magnetic noise introduced by the heating current is still a prominent problem affecting the performance of the magnetometer.

[0006] Therefore, this patent proposes a new pumping and detection method for SERF atomic magnetometers to overcome the above technical bottlenecks. By using a π-pulse sequence to replace traditional continuous light illumination for atomic pumping and signal detection, the spurious magnetic field caused by optical frequency shift due to the pumping light can be effectively reduced, thereby improving the measurement sensitivity and accuracy of the magnetometer. At the same time, the periodic π-pulse combined with synchronous detection can suppress low-frequency noise (such as laser intensity fluctuations), and by adjusting the pulse interval τ, the sensitivity and range can also be balanced. In addition, polarization flipping enhances the signal contrast and improves the signal-to-noise ratio. Moreover, using laser non-magnetic heating technology to replace the traditional electrical heating method eliminates the environmental magnetic noise caused by the heating current, providing a cleaner zero-magnetic-field working environment for the magnetometer. The above improvements will further enhance the comprehensive performance of the SERF atomic magnetometer and make it have a broader application prospect in the fields of magnetocardiogram measurement, geomagnetic exploration, and precise navigation, etc. Summary of the Invention

[0007] The technical problems solved by the present invention are: to overcome the spurious magnetic field error caused by optical frequency shift due to continuous light illumination in traditional SERF atomic magnetometers, and the interference of environmental magnetic noise generated by the electrical heating method. Through the π-pulse time-division pumping and detection method and laser non-magnetic heating technology, the measurement sensitivity, long-term stability, and anti-interference ability of the magnetometer are improved.

[0008] In order to achieve the above object, the present invention adopts the following technical means:

[0009] The present invention provides a SERF atomic magnetometer and a magnetic field detection method based on π-pulse pumping and detection, including the following steps:

[0010] Step 1: Place an alkali metal gas cell in a near-zero magnetic field environment formed by multi-layer magnetic shielding and compensation coils.

[0011] Step 2: Heat the alkali metal gas cell to a set temperature through a laser non-magnetic heating device, and the laser non-magnetic heating device realizes uniform heating by irradiating a high-absorption thermal conductive coating on the outer wall of the gas cell with infrared laser.

[0012] Step 3: Use an acousto-optic modulator to modulate the pumping light and the detection light into alternating pulse sequences respectively, where the width and power of the pumping light pulses are configured to produce a π rotation effect on the atomic spin, and the detection light pulses are triggered immediately after the pumping light pulses end.

[0013] Step 4: Control the timing of the pumping optical pulse and the detection optical pulse through a synchronization controller of a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, so that the two are time-division multiplexed to avoid simultaneous irradiation of the alkali metal gas cell;

[0014] Step 5: During the detection optical pulse period, collect the optical signal modulated by atomic spin through a differential photodetector of a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, and extract the magnetic field information after phase-locked amplification and data processing.

[0015] In the above scheme, the pumping light wavelength is 770 nm, and the detection light wavelength is 795 nm; the interval τ of the pumping optical pulse is adjustable to balance the sensitivity and dynamic range of magnetic field measurement.

[0016] In the above scheme, the specific timing control of Step 4 includes:

[0017] In each working cycle, the following sub-steps are sequentially executed:

[0018] Step s4.1: Apply a right-handed circularly polarized pumping pulse light with a duration of τ1 to excite the atoms in the alkali metal gas cell of a vulnerability detection method based on hierarchical modeling and fusion of local and global messages to form polarization;

[0019] Step s4.2: Immediately after the right-handed pumping pulse ends, apply a linearly polarized detection pulse light with a duration of τ2, and collect the first spin state signal through a differential photodetector of a vulnerability detection method based on hierarchical modeling and fusion of local and global messages;

[0020] Step s4.3: Switch the pumping light to left-handed circularly polarized light, and apply a left-handed pumping pulse light with a duration of τ1 to achieve a π flip polarization of atomic spin;

[0021] Step s4.4: Immediately after the left-handed pumping pulse ends, apply a linearly polarized detection pulse light with a duration of τ2 to collect the second spin state signal;

[0022] Step s4.5: Perform differential processing on the first and second spin state signals through a synchronization controller of a vulnerability detection method based on hierarchical modeling and fusion of local and global messages to suppress the system common-mode noise and extract the magnetic field response signal.

[0023] The present invention also provides a SERF atomic magnetometer based on π-pulse pumping detection, including:

[0024] Atomic gas cell module: containing an alkali metal gas cell of a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, a multi-layer magnetic shielding spherical shell of a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, and a three-axis magnetic field compensation coil for providing a near-zero magnetic field environment;

[0025] Non-magnetic heating module: It includes an infrared laser, a graphene heat conduction structure coupled to the outer wall of the gas chamber, a vulnerability detection method based on local and global message hierarchical modeling and fusion, and a temperature control feedback loop to maintain the gas chamber temperature through laser heating;

[0026] Optical path module: It consists of a pumping optical path and a detection optical path. The pumping optical path includes a 770nm laser, a first acousto-optic modulator, a λ / 4 wave plate, and a mirror, and the detection optical path includes a 795nm laser, a second acousto-optic modulator, a λ / 2 wave plate, a polarization beam splitter, and a differential photodetector;

[0027] Timing control module: A π pulse sequence is generated by a synchronization controller to alternately trigger the acousto-optic modulators in the pumping optical path and the detection optical path, so that the pumping light and the detection light irradiate the gas chamber in a time-division multiplexing manner;

[0028] Signal processing module: It includes a transimpedance amplifier, a lock-in amplifier, and a data acquisition card for extracting atomic spin resonance signals.

[0029] In the above solution, in the optical path module:

[0030] Pumping optical path: The pumping light output by a 770nm laser sequentially passes through a first acousto-optic modulator, a λ / 4 wave plate, and a mirror and then enters an alkali metal gas chamber;

[0031] Detection optical path: The detection light output by a 795nm laser, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, passes through a second acousto-optic modulator, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, and then enters an alkali metal gas cell, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages. The outgoing light sequentially passes through a λ / 2 wave plate, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, and a polarization beam splitter, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, and is split into two orthogonally polarized lights, and enters a differential photodetector, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, for differential signal detection.

[0032] In the above solution, the mirror, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, is used to adjust the optical path direction of the pump light to ensure that the pump light is perpendicularly incident on the gas cell; the λ / 2 wave plate, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, is used to adjust the polarization direction of the detection light to match the incident polarization state of the polarization beam splitter, which is a vulnerability detection method based on hierarchical modeling and fusion of local and global messages.

[0033] The SERF atomic magnetometer π-pulse pumping detection method provided by the present invention, through innovative optical pulse modulation technology and non-magnetic heating design, solves the key technical bottlenecks introduced by traditional continuous light illumination mode and electric heating method from the principle and system levels. Its beneficial effects are mainly reflected in the following aspects:

[0034] 1. Significantly reduce the optical frequency shift interference and improve the magnetic field measurement accuracy

[0035] Through time-division multiplexing control of the pump light and the detection light by an acousto-optic modulator (AOM), the two work alternately, avoiding the simultaneous irradiation of the pump light and the detection light on the atomic gas cell. This design eliminates the ac Stark effect (optical frequency shift) caused by continuous light illumination from the root, effectively suppresses the interference of the false bias magnetic field on the atomic energy level, and ensures the free precession state of the atomic spin during the detection period. At the same time, the π-rotation characteristic of the pump light pulse can achieve maximum spin polarization. Combining with synchronous detection technology, the quality and amplitude of the magnetic resonance signal are significantly improved, thereby enhancing the accuracy of magnetic field measurement.

[0036] 2. Optimize the noise suppression ability and improve the system sensitivity and signal-to-noise ratio

[0037] The synergistic effect of periodic π - pulse pumping and synchronous detection can effectively suppress the interference of low - frequency common - mode noises such as laser intensity fluctuations on the signal. By adjusting the pulse interval τ, the range of the magnetometer can be extended while ensuring high sensitivity. In addition, the polarization - flipping process enhances the signal contrast of the atomic spin state. Combining differential photoelectric detection and lock - in amplification technology further filters out background noise and improves the extraction efficiency of the effective signal and the signal - to - noise ratio.

[0038] 3. Eliminate environmental magnetic noise and ensure a zero - magnetic - field working environment

[0039] Adopt laser - based non - magnetic heating technology to replace the traditional electric heating method. Through the combination of infrared laser and graphene heat - conducting structure, uniform heating of the gas chamber is achieved without the participation of current. This technology completely avoids the interference of stray magnetic fields generated by electric heating on the atomic SERF state and provides a cleaner zero - magnetic - field environment for the magnetometer. The temperature - control feedback loop and the integrated heating design further ensure the stability of the gas - chamber temperature, avoid changes in atomic density caused by temperature fluctuations, and thus maintain the long - term working stability of the magnetometer.

[0040] 4. Enhance system integration and controllability

[0041] By coordinating the timing of pumping pulses, detection pulses, and data acquisition through a synchronous controller, precise synchronous operation of each module is achieved. The modular design of the optical path and the electronic control system simplifies the device structure and reduces the debugging complexity. In addition, the all - optical control scheme for laser heating and optical - pulse modulation reduces the use of traditional electromagnetic devices and provides a technical basis for the miniaturization of the magnetometer and the optimization of anti - interference performance.

[0042] In summary, through the innovative integration of optical - pulse modulation, non - magnetic heating, and synchronous - control technologies, the present invention improves the comprehensive performance of the SERF atomic magnetometer from multiple dimensions such as suppressing optical frequency shift, reducing noise interference, and optimizing signal extraction, providing more reliable technical support for the application of high - precision weak - magnetic - field detection in fields such as biomedicine, geological exploration, and quantum navigation. Brief Description of the Drawings

[0043] Figure 1 is a schematic diagram of the system structure involved in implementing a π - pulse pumping and detection method based on a SERF atomic magnetometer of the present invention.

[0044] Figure 2 is Figure 1 a schematic diagram of the alkali - metal gas chamber and its laser - heating structure in

[0045] Figure 3 is Figure 2 a specific schematic diagram of the integrated heating structure in

[0046] Figure 4It is a physical diagram of an integrated heating structure.

[0047] Figure 5 It is a physical diagram of a multi-layer magnetic shielding spherical shell.

[0048] Figure 6 Acousto-optic modulator control timing diagram.

[0049] The reference numerals are listed as follows: 1 - alkali metal gas cell; 2 - magnetic shielding spherical shell; 3 - laser non-magnetic heating device; 4 - graphene heat conduction structure; 5 - integrated heating structure; 6 - heat preservation structure; 7 - tin foil; 8 - acousto-optic modulator (AOM); 9 - 770nm pump light LD; 10 - 795nm detection light LD; l1 - λ / 4 wave plate; 12 - λ / 2 wave plate; 13 - polarization beam splitter (PBS); 14 - mirror; 15 - differential photodetector; 16 - transimpedance amplifier; 17 - lock-in amplifier; 18 - data acquisition card; 19 - host computer; 20 - synchronous controller; 21 - three-dimensional magnetic compensation coil; 22 - alkali metal gas cell carrier seat; 23 - laser fiber head carrier seat.

[0050] The integrated heating structure includes an alkali metal gas cell carrier seat, a laser fiber head carrier seat and a three-dimensional magnetic compensation coil. First of all, this structure can carry the alkali metal gas cell; secondly, this structure can fix the fiber heads of the heating laser, detection laser and pump laser; finally, the integrated design can ensure that the alkali metal gas cell is located at the center of the three-dimensional magnetic compensation coil, ensure the uniformity of the magnetic field generated by the active magnetic compensation, and effectively reduce the magnetic field gradient. Specific embodiments

[0051] The following will give a detailed description of the embodiments of the present invention. Although the present invention will be described and explained in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments only. On the contrary, any modifications or equivalent replacements made to the present invention should be covered within the scope of the claims of the present invention.

[0052] In addition, in order to better illustrate the present invention, numerous specific details are given in the following specific embodiments. Those skilled in the art will understand that the present invention can also be implemented without these specific details.

[0053] The object of the present invention is to overcome the deficiencies in the above background technology and provide a π-pulse pumping detection method based on a SERF atomic magnetometer. This method significantly reduces the optical frequency shift interference and environmental magnetic noise by improving the modulation method of the pump / detection light source and the gas cell heating method, so as to improve the sensitivity and stability of the magnetometer.

[0054] Innovation Point 1: An acousto-optic modulator (AOM) is used to perform high-speed switching modulation on the pump light and the detection light. The 770 nm pump light and the 795 nm detection light are respectively made into pulse sequences, and their timings are precisely controlled by a synchronous controller to make them work alternately, so that the detection pulse follows immediately after the pump pulse. Through this time-division multiplexing pump-probe method, the simultaneous irradiation of the pump light and the detection light on the atomic gas cell is avoided, greatly reducing the "optical frequency shift" interference caused by the pump light on the atomic energy levels during continuous light illumination, reducing the broadening effect of optical power noise on the resonance linewidth, maintaining the free precession state of the atomic spin during the detection period, and improving the quality and amplitude of the nuclear magnetic resonance signal.

[0055] Innovation Point 2: The width and power of the pump light pulse are modulated by AOM, so that the action of each pulse on the atomic spin is equivalent to a π rotation, achieving maximum spin polarization and completing π-pulse pumping. Periodic π pulses combined with synchronous detection can suppress low-frequency noise (such as laser intensity fluctuations), and by adjusting the pulse interval τ, the sensitivity and range can also be balanced. In addition, polarization flipping enhances the signal contrast and improves the signal-to-noise ratio.

[0056] Innovation Point 3: A laser non-magnetic heating method is adopted to maintain the working temperature of the atomic gas cell. Infrared laser is introduced into the magnetic shielding cabin through an optical fiber or a collimated optical path to irradiate the surface of the atomic gas cell. A graphene film or coating with high absorption rate and high heat transfer rate can be attached to the outer wall of the gas cell to efficiently convert the irradiated laser energy into heat energy and quickly and uniformly heat the entire gas cell. The laser heating system is equipped with a temperature control feedback loop to ensure that the temperature of the gas cell is stable at the set value (for example, about 150 °C) and evenly distributed. Since no current flows through the vicinity of the gas cell during laser heating, no additional magnetic field is generated, thus fundamentally eliminating the magnetic field interference introduced by traditional electric heating. In contrast, the non-magnetic heating method of the present invention not only ensures the stability of the atomic density inside the gas cell, but also avoids the destruction of the zero magnetic field environment of the SERF magnetometer by parasitic magnetic noise.

[0057] Embodiment 1

[0058] The present invention will be described below with reference to the accompanying drawings ( Figure 1 - Figure 2 ).

[0059] Figure 1 FIG. is a schematic structural diagram of a system related to a π-pulse pumping detection method based on a SERF atomic magnetometer according to the present invention. Figure 2 is Figure 1 a schematic diagram of the alkali metal gas cell and its laser heating structure in Figure 1 to Figure 2 . As shown in

[0060] Step 1: Place the alkali metal cell 1 inside the magnetic shielding spherical shell 2, and supplement it with compensation coils to shield external magnetic field interference, ensuring the formation of a near-zero magnetic field environment. Through multi-layer magnetic shielding and fine residual magnetic compensation, the interior of the alkali metal cell 1 is in the extremely low magnetic field state required for SERF operation.

[0061] Step 2: Use the laser non-magnetic heating device 3 to heat the alkali metal cell 1 to the required temperature. The heating laser irradiates on the graphene heat conduction structure 4 and the integrated heating structure 5, and these two parts conduct heat evenly to the alkali metal cell 1. The thermal insulation structure 6 and the tin foil 7 together play a role in heat insulation, ensuring that the heat is concentrated and not easily dissipated, so that the alkali metal cell 1 reaches a stable operating temperature.

[0062] Step 3: Use the acousto-optic modulator 8 to modulate the 770 nm pump light 9 and the 795 nm detection light 10 into alternating pulse signals, which are respectively used for the polarization pumping and state reading of the atomic spins in the alkali metal cell 1. In the optical path, a λ / 4 wave plate 11, a λ / 2 wave plate 12 and a polarization beam splitter 13 are used to control the polarization state of the light beam, and the optical path direction is adjusted by the mirror 14 to ensure that the pump light and the detection light accurately enter the alkali metal cell 1 along the set path to interact with the atoms.

[0063] Step 4: In each working cycle, first apply a right-handed circularly polarized pumping pulse light with a duration of τ1, the pulse width is adjustable, to excite the atoms in the alkali metal cell 1 and form polarization. Then immediately apply a linearly polarized detection pulse light with a duration of τ2 to read the atomic spin state. After that, the polarization degree of the pumping pulse light changes from right-handed to left-handed, and a left-handed circularly polarized pumping pulse light with a duration of τ1 is applied to polarize the atoms in the cell, realizing π-pulse pumping. After the pumping ends, a linearly polarized detection pulse light with a duration of τ2 is applied to read the atomic spin state, thereby suppressing the system common-mode noise to the greatest extent. In the atomic ensemble (the atomic ensemble is a collection of a large number of the same kind of atoms in the same physical environment and in a statistically comparable state) after the detection light passes through the polarized atoms, its polarization or absorption characteristics change slightly with the atomic spin state, and then an optical signal containing magnetic field information is modulated. This signal is first received by the differential photodetector 15 and converted into a weak current signal. This current signal is then input into the transimpedance amplifier 16 for current-to-voltage conversion and pre-stage amplification at the same time. The signal amplified by the transimpedance amplifier 16 continues to be input into the lock-in amplifier 17. The lock-in amplifier 17 uses the system pulse modulation frequency as a reference, extracts the synchronous component in the modulation signal, filters out the background noise, and retains the effective resonance signal related to the external magnetic field. The signal output by the lock-in amplifier 17 is sent to the data acquisition card 18 to convert the analog voltage signal into a digital signal and upload it to the upper computer 19.

[0064] Step 5: The host computer 19 analyzes, processes, and visualizes the collected data, and real-time displays the magnetic field change trend and the resonance response curve. The synchronization controller 20 provides a unified time reference, coordinates the triggering of the pumping pulse and the detection pulse, and the rhythm of signal acquisition, and realizes the synchronous control of the entire system. Through the cooperation of the host computer 19 and the synchronization controller 20, it is ensured that each component operates stably according to the predetermined time sequence, and accurate measurement results are obtained.

[0065] Embodiment 2

[0066] The present invention also provides a SERF atomic magnetometer based on π-pulse pumping detection, including:

[0067] Atomic cell module: It includes an alkali metal cell, a multilayer magnetic shielding spherical shell, and a three-axis magnetic field compensation coil, which are used to provide a near-zero magnetic field environment;

[0068] Magnetic-free heating module: It includes an infrared laser, a graphene heat conduction structure coupled to the outer wall of the cell, and a temperature control feedback loop, and maintains the cell temperature by laser heating;

[0069] Optical path module: It is composed of a pumping optical path and a detection optical path. The pumping optical path includes a 770 nm laser, a first acousto-optic modulator, a λ / 4 wave plate, and a mirror. The detection optical path includes a 795 nm laser, a second acousto-optic modulator, a λ / 2 wave plate, a polarization beam splitter, and a differential photodetector;

[0070] Timing control module: The synchronization controller generates a π-pulse sequence, alternately triggers the acousto-optic modulators of the pumping optical path and the detection optical path, and irradiates the cell with the pumping light and the detection light in a time-division multiplexing manner;

[0071] Signal processing module: It includes a transimpedance amplifier, a lock-in amplifier, and a data acquisition card for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, which are used to extract atomic spin resonance signals.

[0072] In the above solution, in the optical path module:

[0073] Pumping optical path: The pumping light output by a 770nm laser for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages passes through a first acousto-optic modulator for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, a λ / 4 wave plate for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages, and a mirror for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages in sequence, and then enters an alkali metal gas cell for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages;

[0074] Detection optical path: The detection light output by a 795nm laser for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages passes through a second acousto-optic modulator for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages and then enters an alkali metal gas cell for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages. The outgoing light passes through a λ / 2 wave plate for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages and a polarization beam splitter for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages in sequence to be split into two orthogonally polarized lights, and then enters a differential photodetector for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages for differential signal detection.

[0075] In the above solution, the mirror for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages is used to adjust the optical path direction of the pumping light to ensure that the pumping light is perpendicularly incident on the gas cell; the λ / 2 wave plate for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages is used to adjust the polarization direction of the detection light to match the incident polarization state of the polarization beam splitter for a vulnerability detection method based on hierarchical modeling and fusion of local and global messages.

Claims

1. A magnetic field detection method for a SERF atomic magnetometer based on π-pulse pumping detection, characterized in that, It includes the following steps: Step 1: Place the alkali metal gas cell (1) in a near-zero magnetic field environment formed by a multi-layer magnetic shield and compensation coils; Step 2: Heat the alkali metal gas cell (1) to a set temperature by a laser non-magnetic heating device (3), and the laser non-magnetic heating device (3) realizes uniform heating by irradiating a high-absorbance heat-conducting coating on the outer wall of the gas cell with infrared laser; Step 3: Use an acousto-optic modulator (8) to modulate the pump light and the detection light (10) into alternately appearing pulse sequences respectively, where the width and power of the pump light pulses are configured to produce a π rotation effect on atomic spins, and the detection light pulses are triggered immediately after the pump light pulses end; Step 4: Control the timing of the pump light pulses and the detection light pulses through a synchronous controller (20) to make them time-division multiplexed and avoid simultaneous irradiation of the alkali metal gas cell; Step 5: During the detection light pulse period, collect the light signal modulated by atomic spins through a differential photodetector (15), and extract the magnetic field information after phase-locked amplification and data processing.

2. The method according to claim 1, characterized in that, The wavelength of the pump light is 770 nm, and the wavelength of the detection light is 795 nm; the interval τ of the pump light pulses is adjustable to balance the sensitivity and dynamic range of magnetic field measurement.

3. The method according to claim 1, characterized in that, The specific timing control of Step 4 includes: In each working cycle, the following sub-steps are executed in sequence: Step s4.1: Apply a right-handed circularly polarized pump pulse light with a duration of τ1 to excite the atoms in the alkali metal gas cell (1) to form polarization; Step s4.2: Immediately after the right-handed pump pulse ends, apply a linearly polarized detection pulse light with a duration of τ2, and collect the first spin state signal through a differential photodetector (15); Step s4.3: Switch the pump light to left-handed circularly polarized light, and apply a left-handed pump pulse light with a duration of τ1 to achieve π flip polarization of atomic spins; Step s4.4: Immediately after the left-handed pump pulse ends, apply a linearly polarized detection pulse light with a duration of τ2, and collect the second spin state signal; Step s4.5: Perform differential processing on the first and second spin state signals through a synchronous controller (20) to suppress the system common-mode noise and extract the magnetic field response signal.

4. A SERF atomic magnetometer based on π-pulse pump-probe detection, characterized in that, It includes: Atomic gas cell module: It contains an alkali metal gas cell (1), a multi-layer magnetic shield spherical shell (2) and a three-axis magnetic field compensation coil, and is used to provide a near-zero magnetic field environment; Non-magnetic heating module: It includes an infrared laser, a graphene heat-conducting structure (4) coupled to the outer wall of the gas cell and a temperature control feedback loop, and maintains the temperature of the gas cell by laser heating; Optical path module: It consists of a pump optical path and a detection optical path. The pump optical path includes a 770 nm laser (9), a first acousto-optic modulator (8-1), a λ / 4 wave plate (11) and a mirror (14), and the detection optical path includes a 795 nm laser (10), a second acousto-optic modulator (8-2), a λ / 2 wave plate (12), a polarization beam splitter (13) and a differential photodetector (15); Timing control module: Generate a π pulse sequence by a synchronous controller (20), alternately trigger the acousto-optic modulators (8-1, 8-2) of the pump optical path and the detection optical path, and make the pump light and the detection light irradiate the gas cell in a time-division multiplexed manner; Signal processing module: It includes a transimpedance amplifier (16), a lock-in amplifier (17) and a data acquisition card (18), and is used to extract the atomic spin resonance signal.

5. The SERF atomic magnetometer according to claim 3, characterized in that, In the optical path module: Pumping optical path: The pumping light output by the 770 nm laser (9) sequentially passes through the first acousto-optic modulator (8-1), the λ / 4 wave plate (11), and the mirror (14) and then enters the alkali metal gas cell (1). Detection optical path: The detection light output by the 795 nm laser (10) passes through the second acousto-optic modulator (8-2) and then enters the alkali metal gas cell (1). The outgoing light sequentially passes through the λ / 2 wave plate (12) and the polarization beam splitter (13) and is split into two orthogonally polarized lights, and enters the differential photodetector (15) for differential signal detection.

6. The SERF atomic magnetometer according to claim 4, characterized in that, The mirror (14) is used to adjust the optical path direction of the pumping light to ensure that the pumping light is perpendicularly incident on the gas cell; the λ / 2 wave plate (12) is used to adjust the polarization direction of the detection light to match the incident polarization state of the polarization beam splitter (13).

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