Plasma detection method and device for magnetometer

Abstract

The invention relates to the field of quantum sensing, and discloses a plasma detection method and device for a magnetometer. According to the method, frequency modulation is carried out on detection laser emitted by a DBR laser through an acousto-optic modulator, laser-induced fluorescence signals in an alkali metal gas chamber are synchronously collected, and correlation analysis is carried out on the laser-induced fluorescence signals and magnetic field parameters. The device comprises a fluorescence detection module and a differential detection module, magnetic field parameters are obtained through light splitting of a polarization splitting prism, plasma characteristic fluorescence is captured through a lens, a filter and a spectrograph, and signal synchronous processing is achieved in combination with a trans-impedance amplifier and a lock-in amplifier. A laser-induced fluorescence technology is creatively adopted to noninvasively detect a plasma threshold value, and a correlation model of laser frequency and fluorescence intensity is established, so that the technical problem that sensitivity is reduced due to a plasma effect caused by high atomic density in a magnetometer miniaturization process is solved; and meanwhile, the measurement precision is improved by utilizing the plasma to enhance the atomic spin polarizability characteristic, and a technical support is provided for research and development of a chip magnetometer.

Description

Technical Field

[0001] The present invention relates to the field of quantum sensing, and provides a plasma detection method and device for a magnetometer. Background Art

[0002] Compared with traditional weak magnetic detection devices, the alkali metal atomic magnetometer based on Spin-Exchange Relaxation Free (SERF) can effectively solve problems such as complex systems, high costs, and low sensitivity, and has wide applications in frontier physics exploration, magnetocardiogram and magnetoencephalogram medical detection, military anti-submarine, and other fields. At present, the atomic magnetometer has high sensitivity, but in application fields such as magnetocardiogram and magnetoencephalogram medical detection, higher requirements are put forward for its sensitivity and chip integration. It is expected to obtain a magnetometer with both high sensitivity and chip integration to obtain high-resolution magnetocardiograms and magnetoencephalograms. To achieve high resolution, it is required that the volume of the probe be as small as possible, so the volume of the atomic gas chamber of the magnetometer needs to be reduced. To maintain sensitivity, it is necessary to increase the atomic number density to improve sensitivity. However, a high atomic density will inevitably be accompanied by the generation of plasma. Research shows that when the atomic number density exceeds 1×10 13 cm -3 the formation of plasma will be accelerated, and when the heating temperature of the alkali metal gas chamber reaches 180°C, the atomic number density has reached 1×10 14 cm -3 . In current research, high-energy state excitation is ignored, many-body collisions are simplified, and plasma effects are not considered. However, with the dual requirements of improving sensitivity and reducing volume, it is necessary to consider the positive and negative effects of plasma. On the one hand, it may lead to a decrease in sensitivity, but on the other hand, the collective effect of plasma can enhance the atomic spin polarization rate and improve the light-spin coupling efficiency. This characteristic can provide new ideas for improving the sensitivity of the magnetometer. Therefore, the detection of plasma in the magnetometer gas chamber and the research on plasma effects have become a hot topic.

[0003] Laser-Induced Fluorescence (LIF) detection technology emits a laser with a specific wavelength to selectively excite target particles to the excited state and detect the fluorescence signal of their spontaneous emission. If there is plasma in the gas chamber, the metastable particles in it will be excited by the laser and emit fluorescence with a specific wavelength. Using this technology, by monitoring the sudden change in the fluorescence intensity of a specific energy level in the gas chamber, it can be measured whether plasma appears and its generation threshold.

[0004] Based on this, the present invention innovatively uses the laser fluorescence detection method to measure the occurrence of plasma and its threshold value, and for the first time proposes to consider the plasma effect in the alkali metal atomic magnetometer, laying a solid theoretical foundation for improving the sensitivity and long-term stability of inertial and magnetic field measurements and realizing the next-generation chip-based magnetometer, which is of great significance in many fields such as national defense and biomedicine. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problem that in the process of miniaturizing the magnetometer, the high atomic density causes the plasma effect, resulting in a decrease in sensitivity. By using the laser-induced fluorescence technology, the non-invasive real-time detection of the plasma threshold is realized, and the sensitivity and stability of the magnetometer are improved by using the characteristic of the plasma-enhanced atomic spin polarization rate.

[0006] In order to achieve the above object, the present invention adopts the following technical means: The present invention provides a plasma detection method for a magnetometer, including: (a) Emitting a detection laser with adjustable frequency to a heated alkali metal atomic gas chamber, and the detection laser is frequency-modulated by an acousto-optic modulator; (b) Synchronously collecting the fluorescence signal induced by the laser in the gas chamber, and keeping time-domain synchronization with the acousto-optic modulator during collection; (c) Establishing a correspondence model between the detection laser frequency parameters and the fluorescence intensity characteristics; (d) Real-time monitoring the change of the gas chamber magnetic field parameters through a differential detection system; (e) Combining the relationship model and the change of the magnetic field parameters to determine the plasma generation state and threshold parameters.

[0007] Further, the method specifically includes: Step 1, the DBR laser emits a laser beam, and after being modulated by the acousto-optic modulator, the beam I enters the alkali metal atomic gas chamber. The laser beam is affected by a weak magnetic field and becomes a detection beam I' carrying the change information of the gas chamber parameters; Step 2, the detection beam I' passes through a half-wave plate and is split by a polarization beam splitter prism. After being affected by the external weak magnetic field and temperature, the precession direction of the atoms in the alkali metal gas chamber deflects, thereby changing the polarization direction of the light. At this time, the differential signal of the two beams of light split by the polarization beam splitter prism is no longer 0, and the photodetector PD1 and the photodetector PD2 will detect a differential signal. After extracting information from it, the detection of the internal information of the gas chamber can be realized; Step 3: Using the laser-induced fluorescence scattering detection technique, the frequency or on / off state of the laser beam can be changed into the detection beam I through the laser power driver and the acousto-optic modulator. After the lens focuses the fluorescence induced by the detection laser, the filter removes the light of the pump light and detection light wavelengths, and only allows the newly induced fluorescence to enter the CCD or spectrometer to obtain the fluorescence signal. After the signal is amplified and collected by the transimpedance amplifier, the lock-in amplifier, and the data acquisition card, it is transmitted to the computer, and the existing software tools are used to perform plasma characteristic spectral line matching and signal-to-noise ratio analysis on the collected fluorescence signal, so as to obtain whether the plasma exists and its appearance threshold. The CCD / spectrometer acquires the signal and is synchronized with the acousto-optic modulator in frequency or controls the time delay to reduce the background noise, and a relationship model between the laser frequency, the fluorescence intensity, and the plasma parameters is established. The plasma parameter detection system and the differential detection system operate simultaneously, and the relevant parameters of the plasma and its influence on the sensitivity and long-term stability index of the magnetometer can be detected in real time.

[0008] In the above solution, the heating structure heats the gas chamber, and the pump light pumps the alkali metal atoms in the alkali metal atom gas chamber to complete the atomic polarization.

[0009] In the above solution, the plasma detection system includes a dotted box composed of an acousto-optic modulator, a lens, a filter, and a CCD or spectrometer; In the above solution, the differential detection system includes a dotted box composed of a polarization beam splitter prism, a photodetector PD1, and a photodetector PD2.

[0010] The present invention also provides a plasma detection device for a magnetometer, including: A DBR laser for emitting a detection laser with adjustable frequency; An acousto-optic modulator, optically connected to the DBR laser, for frequency modulating the detection laser; An alkali metal atom gas chamber for receiving the detection laser modulated by the acousto-optic modulator, and a heating structure is provided outside the gas chamber to maintain the atomic density in the gas chamber; A fluorescence detection module, including a lens, a filter, and a CCD / spectrometer arranged in sequence along the outgoing direction of the gas chamber, for collecting the fluorescence signal induced by the laser; A differential detection module, including a 1 / 2 wave plate, a polarization beam splitter prism located on the outgoing light path of the gas chamber, and photodetectors PD1 and PD2 corresponding to the two split beams of light; A signal processing unit, including a transimpedance amplifier, a lock-in amplifier, a data acquisition card, and a computer, for synchronously processing the differential signal and the fluorescence signal; The acousto-optic modulator is connected to the CCD / spectrometer through a time domain synchronization control module to achieve the same-frequency locking of fluorescence signal acquisition and laser modulation.

[0011] In the above solution, in the differential detection module: The polarization beam splitter prism splits the detection beam into two orthogonally polarized lights, which are received by PD1 and PD2 respectively; The differential signals output by the two photodetectors are amplified and noise-suppressed through a transimpedance amplifier and a phase-locked amplifier, and are connected to a data acquisition card.

[0012] The plasma detection method and device for a magnetometer provided by the present invention solve the plasma effect problem caused by high atomic density during the miniaturization of the magnetometer through innovative technical means, and effectively improve the sensitivity and stability of magnetic field detection. The specific beneficial effects are as follows: 1. Break through the traditional technical bottleneck and achieve the collaborative optimization of plasma effect and magnetometer performance The present invention first incorporates the plasma effect into the design and detection system of the magnetometer. By analyzing the enhancement effect of the plasma on the atomic spin polarization rate and the light-spin coupling efficiency, the problem of limited sensitivity caused by neglecting the plasma effect in traditional research is solved. Combining real-time detection with parameter modeling, not only suppresses the negative impact of the plasma, but also utilizes its collective effect to improve the magnetic field detection sensitivity, providing a theoretical and technical basis for the miniaturization and high performance of the magnetometer.

[0013] 2. Non-invasive plasma detection technology to avoid interfering with the measurement of extremely weak magnetic fields Using the laser-induced fluorescence (LIF) technology, synchronously controlling the detection laser frequency and fluorescence signal acquisition through an acousto-optic modulator, and combining a narrowband filter and differential signal processing, realizes non-invasive real-time detection of the plasma. Compared with traditional probe methods or microwave methods, the present invention does not need to introduce external devices to interfere with the internal magnetic field environment of the gas chamber, and is especially suitable for high-sensitivity extremely weak magnetic field detection scenarios (such as magnetocardiogram and magnetoencephalogram medical detections).

[0014] 3. High-precision synchronous control and noise suppression, significantly improving the detection signal-to-noise ratio Through the time-domain synchronous locking technology of the acousto-optic modulator and the CCD / spectrometer, combined with the narrowband filtering characteristics of the phase-locked amplifier, background noise and common-mode interference are effectively suppressed. At the same time, the combination of the polarization beam splitter prism and the differential detection system further eliminates the interference of factors such as environmental temperature and light intensity fluctuations, improving the accuracy of plasma threshold detection to the sub-microtesla level, meeting the requirements of high-resolution magnetic field measurement.

[0015] 4. Multi-parameter fusion analysis, real-time dynamic monitoring of plasma and magnetic field states By establishing a relationship model between the detected laser frequency parameters and the fluorescence intensity characteristics, and combining the magnetic field parameters obtained in real time by the differential detection system, the dynamic correlation analysis of the plasma generation state and the magnetic field change is realized. This technology can synchronously determine the plasma threshold, magnetic field intensity, and gas chamber stability index, providing a basis for closed-loop feedback control for the long-term stable operation of the magnetometer.

[0016] 5. Compact structure and strong compatibility, promoting the chip development of the magnetometer The device adopts a modular design, integrating the fluorescence detection module (lens, filter, CCD) and the differential detection module (polarizing beam splitter prism, photodetector) into the same optical path. Combining a miniaturized acousto-optic modulator and a heating structure significantly reduces the system volume. This design is compatible with the existing SERF magnetometer architecture and can be directly applied to the detection of high-density atomic environments in chip-level gas chambers, laying a foundation for the development of the next generation of portable high-sensitivity magnetometers.

[0017] 6. Broad potential for cross-field applications The plasma detection method of the present invention is not only applicable to the optimization of magnetometers in the field of quantum sensing, but also can be extended to fields such as plasma physics research, semiconductor process monitoring, and nuclear fusion diagnosis. Its high-precision and non-invasive technical characteristics have important application values in scenarios such as biomedical detection (such as magnetoencephalography and magnetocardiography) and national defense and military (such as submarine magnetic anomaly detection).

[0018] In summary, through innovative technical integration and theoretical breakthroughs, the present invention solves the contradiction between the miniaturization and high sensitivity of the magnetometer, and at the same time provides a reliable means for the active regulation of plasma effects, combining theoretical innovation and engineering practicability. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the system involved in implementing a plasma detection method for a magnetometer according to the present invention.

[0020] The reference numerals are listed as follows: 1-DBR laser; 2-laser; 3-acousto-optic modulator; 4-heating structure; 5-alkali metal atomic gas chamber; 6-770 nm pump light; 7-lens; 8-filter; 9-CCD or spectrometer; 10-half-wave plate; 11-PBS; 12-PD1; 13-PD2; 14-transimpedance amplifier; 15-lock-in amplifier; 16-data acquisition; 17-computer; 18-plasma parameter detection system; 19-differential detection system. Detailed Description of the Invention

[0021] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, modifications or equivalent substitutions made to the present invention should be covered within the scope of the claims of the present invention.

[0022] In addition, for a better illustration of 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.

[0023] In current research, the plasma generated during the air chamber heating and laser pumping processes is mostly ignored. The present invention first proposes to consider the plasma effect in the alkali metal atomic magnetometer. At the same time, in traditional research, the detection methods of plasma include the probe method, microwave method, spectroscopy method, etc., but these methods will all affect the atomic magnetometer and reduce the detection sensitivity. Therefore, the present invention innovatively adopts the laser-induced fluorescence detection method to provide a non-invasive interference magnetometer plasma detection method for the deficiencies of the prior art.

[0024] The present invention discloses a plasma detection method for a magnetometer, including a DBR laser, an acousto-optic modulator, a heating structure, an alkali metal atomic gas chamber, a lens, a filter, a CCD or a spectrometer, a half-wave plate, a PBS, two photodetectors, a transimpedance amplifier, a lock-in amplifier, a data acquisition card, and a computer. The DBR laser is used to emit laser light. The laser power driver and the acousto-optic modulator are used to change the laser frequency and control the switch of the detection light and the CCD / spectrometer. The PBS and the two photodetectors use the differential detection method to extract the signals of the detection beam. The lens and the filter collect and filter the generated fluorescence signals and are acquired by the CCD. The transimpedance amplifier, the lock-in amplifier, and the data acquisition card amplify and acquire the signals. The plasma detection system and the differential detection system are carried out simultaneously and transmitted to the computer for analysis to detect the relevant parameters of the plasma and its influence on the sensitivity and long-term stability indicators of the magnetometer in real time. The plasma detection method for a magnetometer disclosed by the present invention can detect the presence of plasma in the gas chamber and the threshold value that appears. It first proposes to consider the plasma effect in the magnetometer, which is expected to solve the problem of "decreasing sensitivity with a decreasing gas chamber", and lay a solid theoretical foundation for improving the long-term stability and sensitivity of inertial and magnetic field measurements and realizing the next-generation chip-based magnetometer, which is of great significance.

[0025] Innovation Point 1: In this invention, the effects brought by the plasma are considered in the magnetometer. Different from the general magnetometer research that ignores the influence of the plasma in the gas chamber, this invention first proposes to consider the plasma effect in the magnetometer, comprehensively analyzes the possible physical processes in the alkali metal gas chamber, and finds that the plasma environment can enhance the atomic spin polarization rate in the gas chamber and improve the light-spin coupling efficiency, which is expected to solve the problem of "decreasing sensitivity with the reduction of the gas chamber", laying a foundation for the chipization of the next-generation magnetometer and the improvement of magnetometer sensitivity, and having great significance.

[0026] Innovation Point 2: This invention innovatively uses the laser-induced fluorescence detection method in the atomic magnetometer to achieve real-time measurement of the plasma. The traditional probe method calculates parameters such as electron temperature and density by measuring the inflection point potential of the current-voltage characteristic curve of the probe, and needs to insert the probe deep into the gas chamber, which destroys the internal magnetic field of the gas chamber and cannot realize the exploration of extremely weak magnetic fields in the magnetometer.

[0027] Innovation Point 3: This invention first uses an acousto-optic modulator or a chopper. By changing the frequency of the detection laser, synchronizing the CCD or spectrometer, and acquiring the fluorescence signal through the acquisition system, a relationship model between the laser frequency, fluorescence intensity, and plasma parameters is established to detect the presence of the plasma and the threshold at which it appears (the final result of this invention is to detect whether it appears and the threshold point). The measurement result is more accurate and avoids the influence of external factors on the experimental result, greatly suppressing the common-mode noise and achieving the purpose of accurately detecting the plasma.

[0028] Innovation Point 4: The plasma parameter detection system and the differential detection system run simultaneously, which can detect the parameters related to the plasma in real time and their influence on the sensitivity and long-term stability indicators of the magnetometer.

[0029] Figure 1 Schematic diagram of the system structure involved in a plasma detection method for a magnetometer to implement this invention.

[0030] A plasma detection method for a magnetometer includes the following steps: Step 1, the DBR laser 1 emits a laser beam 2. After being modulated by the acousto-optic modulator 3, the beam I enters the alkali metal atomic gas chamber 5 (the heating structure 4 heats the gas chamber 5, and the pumping light 6 has pumped the alkali metal atoms in the alkali metal atomic gas chamber 5 to complete atomic polarization). The laser beam 2 is affected by a weak magnetic field and becomes the detection beam I' carrying parameter information such as the change of the weak magnetic field inside the gas chamber.

[0031] Step 2: Detect that after the light beam I' passes through the half-wave plate 10, it is split by the polarization beam splitter prism 11 (PBS). After being interfered by the external weak magnetic field and air temperature, the precession direction of the atoms in the alkali metal gas chamber deflects, thereby changing the polarization direction of the light. At this time, the differential signal of the two light beams split by the polarization beam splitter 11 is no longer 0. The photodetector PD1 12 and the photodetector PD2 13 will detect a differential signal. After extracting the differential signal information, the detection of the internal magnetic field change information of the gas chamber 5 can be realized. Without a magnetic field, the differential signal is 0. If there is magnetic field interference inside the gas chamber, the differential signal is no longer 0. Using parameter inversion, that is , is the differential detected signal, and k is the coefficient. In this way, the magnetic field magnitude inside the gas chamber can be obtained through the differential signal.

[0032] Step 3: Using the laser-induced fluorescence scattering detection technology, the frequency or on / off of the laser beam 2 can be changed through the laser power driver and the acousto-optic modulator, so that the laser beam 2 is transformed into the detection beam I. After the lens 7 focuses the fluorescence induced by the detection beam I, the filter 8 filters out the light with the same wavelength as the pump light and the detection light, and only allows the newly induced fluorescence to enter the CCD or the spectrometer 9 to obtain the fluorescence signal (the realization depends on the characteristics of the optical filter 8. Through the selective transmission of the band-pass filter (narrow-band transmission characteristics), only the fluorescence wavelength is allowed to pass, while blocking the pump light / detection light / light with the same wavelength). After the signal is amplified and collected by the transimpedance amplifier 14, the lock-in amplifier 15 and the data acquisition card 16, it is transmitted to the computer 17 for plasma characteristic spectral line matching and signal-to-noise ratio analysis of the collected fluorescence signal, so as to obtain whether the plasma exists and its appearance threshold. The CCD / spectrometer 9 acquires the signal and is in the same frequency or controls the time delay with the acousto-optic modulator 3, greatly reducing the background noise and improving the signal-to-noise ratio. In this way, a relationship model between the laser frequency, the fluorescence intensity and the plasma parameters is established. The plasma parameter detection system and the differential detection system run simultaneously, and the relevant parameters of the plasma and its influence on the sensitivity and long-term stability index of the magnetometer can be detected in real time.

[0033] Purpose of the invention: Aiming at the current situation in the research that the plasma effect is ignored and there are limitations in further improving the sensitivity of the magnetometer and miniaturizing the gas chamber, the present invention innovatively proposes to consider the plasma effect into the magnetometer and use the laser-induced fluorescence scattering detection technology to detect its threshold. Since plasma will definitely be generated during the gas chamber heating and laser pumping processes, this research is very important, laying a solid theoretical foundation for improving the sensitivity and long-term stability of inertial and magnetic field measurements, and realizing the next-generation chip-based magnetometer, which has great significance in many fields such as national defense and military, biomedicine, etc.

Claims

1. A plasma detection method for a magnetometer, characterized in that: include: (a) emitting a frequency-adjustable detection laser to a heated alkali metal atom gas cell, wherein the detection laser is frequency modulated by an acousto-optic modulator; (b) synchronously collect the fluorescence signal induced by the laser in the gas chamber, and keep time domain synchronization with the acousto-optic modulator during collection; (c) establishing a corresponding relationship model between detection laser frequency parameters and fluorescence intensity characteristics; (d) Real-time monitoring of the changes in the magnetic field parameters of the gas chamber through a differential detection system; (e) Determine the plasma generation state and threshold parameters by combining the relationship model with the changes in magnetic field parameters.

2. The detection method according to claim 1, characterized in that: include: Step 1, the DBR laser (1) emits a laser beam (2), which is modulated by the acousto-optic modulator (3) and enters the alkali metal atom gas chamber (5). The laser beam (2) is affected by a weak magnetic field and becomes a detection beam I′ carrying information on changes in gas chamber parameters. Step 2, after the detection light beam I′ passes through the 1 / 2 wave plate (10), it is split by the polarization splitting prism (11). After being disturbed by the external weak magnetic field and temperature, the direction of motion of the atoms in the alkali metal gas chamber is deflected, thereby changing the polarization direction of the light. At this time, the differential signal of the two light beams split by the polarization splitting prism (11) is no longer 0, and the photodetector PD1 (12) and the photodetector PD2 (13) will detect a differential signal. After extracting information from it, the internal information of the gas chamber (5) can be detected; Step 3, using laser induced fluorescence scattering detection technology, the frequency or on / off of the laser beam (2) can be changed to become a detection beam I through a laser power driver and an acousto-optic modulator. After the lens (7) focuses the fluorescence induced by the detection laser, the filter (8) filters out the light of the pump light and the detection light wavelength, and only allows the newly induced fluorescence to enter the CCD or spectrometer (9) to obtain the fluorescence signal. The signal is amplified and collected by a transimpedance amplifier (14), a phase-locked amplifier (15) and a data acquisition card (16), and then transmitted to a computer (17). The collected fluorescence signal is matched with the plasma characteristic spectrum line and the signal-to-noise ratio is analyzed by using existing software tools to obtain the existence of plasma and the threshold value of its occurrence. The CCD / spectrometer (9) acquires the signal and synchronizes the frequency with the acousto-optic modulator (3) or controls the time delay to reduce the background noise. A relationship model between the laser frequency, the fluorescence intensity and the plasma parameters is established. The plasma parameter detection system and the differential detection system are operated simultaneously, and the plasma related parameters and their influence on the sensitivity and long-term stability index of the magnetometer can be detected in real time.

3. The detection method according to claim 1, characterized in that: The heating structure (4) heats the gas chamber (5), and the pumping light (6) pumps the alkali metal atoms in the alkali metal atom gas chamber (5) to complete the atomic polarization.

4. The detection method according to claim 2, characterized in that: include: The plasma detection system includes a dotted frame consisting of an acousto-optic modulator (3), a lens (7), a filter (8), and a CCD or a spectrometer (9); The differential detection system includes a dotted frame consisting of a polarization beam splitter prism (11), a photodetector PD1 (12), and a photodetector PD2 (13).

5. A plasma detection device for a magnetometer, characterized in that: include: A DBR laser (1) for emitting a detection laser with adjustable frequency; an acousto-optic modulator (3), connected to the optical path of the DBR laser (1) and performing frequency modulation on the detection laser; An alkali metal atom gas chamber (5) receives a detection laser modulated by an acousto-optic modulator (3), wherein a heating structure (4) is provided outside the gas chamber (5) to maintain the atomic density in the gas chamber; A fluorescence detection module, comprising a lens (7), a filter (8) and a CCD / spectrometer (9) arranged in sequence along the emission direction of the gas chamber (5), and used for collecting fluorescence signals induced by the laser; A differential detection module comprises a 1 / 2 wave plate (10) located on the outgoing light path of the air chamber (5), a polarization beam splitter prism (11), and photoelectric detectors PD1 (12) and PD2 (13) corresponding to the two paths of light after the light splitting; A signal processing unit, comprising a transimpedance amplifier (14), a phase-locked amplifier (15), a data acquisition card (16) and a computer (17), for synchronously processing the differential signal and the fluorescence signal; The acousto-optic modulator (3) is connected to the CCD / spectrometer (9) via a time domain synchronization control module to achieve frequency locking of fluorescence signal acquisition and laser modulation.

6. The device according to claim 5, characterized in that In the differential detection module: The polarization beam splitter prism (11) splits the detection light beam into two orthogonal polarized lights, which are received by PD1 (12) and PD2 (13) respectively; The differential signals output by the two photoelectric detectors are amplified and noise-suppressed through a transimpedance amplifier (14) and a phase-locked amplifier (15), and are connected to a data acquisition card (16).

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