| In recent years,the research on laser detection of alkali metal atomic magnetometers is a frontier subject that has attracted much attention in the fields of quantum precision measurement and quantum sensing technology.The semiconductor laser pumped self-oscillating atomic magnetometer has the advantages of miniaturization,low power consumption,etc.,and can quickly respond to magnetic field changes.Therefore,the development of portable self-oscillating laser-pumped magnetometers is a hot spot in the current application of atomic magnetometers.However,there are still many problems to be studied in the process of miniaturization and engineering of magnetometers:Whether the difference between the first harmonic of the magnetic resonance signal and the radio frequency magnetic field is 90 degrees is the key to the accurate measurement of the magnetic field.Therefore,it is necessary to deeply explore many factors in the miniaturization process of the self-oscillating magnetometer(laser power,radio frequency magnetic field power,atomic cell linewidth,etc.)influence on the phase,find the best working conditions after the miniaturization of the instrument.A variety of commercial instruments are used in the exploration experiment of the principle of magnetometer,so in the process of miniaturization and engineering,it is necessary to study new technologies and algorithms to realize the relevant functions of the instruments and integrate them.The accurate measurement of the frequency of the magnetic resonance signal by the frequency meter is also the key to high-precision magnetic field measurement,and the self-oscillating magnetometer outputs a sinusoidal analog signal,so it is necessary to develop a high-precision frequency meter that matches it and integrate it into the magnetometer.In order to meet the needs of miniaturization and engineering of high-precision and highsensitivity quantum magnetometers,this work deeply studies the working principle of laser-pumped self-oscillating cesium atomic magnetometers,factors that affect the sensitivity,and key techniques for engineering.In this work,a portable self-oscillating atomic magnetometer with a VCSEL pumpprobe structure and a miniaturized frequency meter are designed and developed.It provides a certain value for promoting the engineering application of laser-pumped self-oscillating atomic magnetometer in various fields.The main work and innovative achievements are briefly described as follows:1.The optimal working conditions of the self-oscillating cesium atomic magnetometer with laser pump-probe structure are studied both theoretically and experimentally.The multipole moment evolution equation of the system is obtained through atomic multipole moment theory,quantum mechanics perturbation theory and master equation theory,and the signal of self-oscillating atomic magnetometer is theoretically analyzed.On the one hand,considering the coupling between the higher-order moment and the first-order moment under strong optical power,the steady-state analytical formula of the multipole moment of the system is solved and the absorption spectrum is calculated.Numerical fitting of the relationship between the first harmonic of the absorption spectrum of the cesium atoms driven by left circularly polarized light and a magnetic field(magnetostatic field and radio frequency field),the angle,the detuning,the amplitude of the radio frequency magnetic field,the atomic cell linewidth and other factors.On the other hand,under the conditions of resonance,detuning,weak light and strong light,the influence of the RF signal amplitude,atomic cell linewidth(temperature,gas pressure)and other factors on the magnetometer signal amplitude and phase in the system is analyzed.Finally,a self-oscillating atomic magnetometer experimental system with a pumpprobe structure was built.The experimental results were basically consistent with the theoretical analysis,which provided theoretical support for the further engineering design of portable magnetometers.2.A number of key technologies of magnetometers have been studied,and a portable selfoscillating cesium atomic magnetometer with VCSEL pump-probe structure has been successfully developed.Including:designed and implemented the self-oscillating signal loop with low noise and automatic gain control of the magnetometer.The VCSEL source control circuit is realized,including temperature control circuit and current control circuit,which can realize the stability of the laser temperature in the range of 0.002℃,and the noise performance is better than the current output of 0.2μA/√Hz(from 0.1 Hz to 20 Hz).An algorithm of window filtering peak-finding and optimization of PID frequency stabilization is proposed,which can quickly lock the laser frequency within 30 seconds,the locked laser linewidth is about 43 MHz,and the long-term frequency drift is better than 12.5 MHz/hour.Using the atomic cell heater structure with non-magnetic alloy heat conduction,the atomic cell temperature control unit is designed and realized.The atomic cell temperature can be maintained to the set value within 10 minutes and the fluctuation is less than 0.1℃,and the temperature fluctuation range is less than 0.02℃ after long-term stability.In addition,the main structure of the magnetometer probe,cable and circuit is also designed and fabricated.The final magnetometer prototype was tested at the 1st class weak magnetic metering station of NDM.The functions are complete and the performance(3 pT/√Hz@1Hz)can reach the same level of the self-oscillating atomic magnetometer CS-3,which is marked with the commercial spectral light source abroad,and has the advantage of lower power consumption.3.The self-oscillating magnetometer converts the measurement requirements of the magnetic field into the measurement requirements of the self-oscillating frequency(Larmor precession frequency).The measurement accuracy of the signal frequency by the frequency meter directly affects the measurement accuracy of the magnetic field by the self-oscillating magnetometer.This work presents a new method for measuring frequency using FPGA and time-to-digital conversion(TDC)technology.The time difference between the rising edge and falling edge of the actual gate and the rising edge of the standard signal is directly and accurately measured by TDC,which solves the time error problem caused by non-integer cycles in equal-precision frequency measurement.The measurement error of this method is analyzed,and the main factors affecting the frequency measurement accuracy are theoretically obtained.The miniaturized frequency meter is realized in a limited space,with a volume of 70 mm in diameter and a disc shape of 15 mm in thickness,with a high degree of integration.The test shows that in the frequency range of 70 kHz～350 kHz,the output rate is 10 Hz,the range is less than 4.2 mHz,the accuracy is better than 0.56 mHz,and the sensitivity is better than 0.19 mHz/√Hz@1 Hz,which is consistent with the theoretical analysis.The portable self-oscillating laser-pumped cesium atomic magnetometer developed in this work is suitable for occasions that require sensitivity,volume and power consumption,such as marine submarine detection and UAV aeromagnetic measurement. |
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