Study On Self-Excited Feedback Loop Of Optical Pumped Cesium Atomic Magnetometer

Magnetic fields are a special substance that is both invisible and untouchable,and ubiquitous in our lives,affects our lives,so the research teams in various countries have carried out in-depth research on the precise measurement methods of magnetic fields.Atomic magnetometer,with its high sensitivity,has become the focus of research teams at home and abroad.The optical pump magnetometer in atomic magnetometer has been developed and studied rapidly in recent years because of its small size and high sensitivity.Although China’s research started late,but after years of research has also achieved certain results,shortening the gap with developed countries.However,for the self-excited oscillating optical pump magnetometer,there are few research teams in China,and there is a certain gap between the research results and those in foreign countries.Self-excited feedback loop is one of the most critical parts in the self-excited optical pump atomic magnetometer.The whole feedback loop is composed of RF coil excitation source,photoelectric conversion circuit and signal amplification phase shift feedback circuit,the coil excitation source needs to provide stable energy for the RF coil over a large frequency range,and the signal amplification phase shift feedback circuit also needs to provide a stable 90° phase delay to the phase of the input signal within a wide signal frequency range.However,at present,there are few related researches in China,the feedback phase shift accuracy is not high,the stability is not good,the feedback system is too complex is not conducive to debugging and high cost.Therefore,taking the selfexcited cesium optical pump atomic magnetometer as the research object,this paper studies a self-excited cesium light pump magnetometer composed of low cost,high stability RF coil excitation source and wide operating frequency signal amplification phase shift feedback loop.This study mainly takes cesium atom as self-excited magnetometer working material,starting from the study of the basic physical principle of the optical pump magnetometer,analyzes and studies the optical structure and optical signal characteristics of the self-excited optical pump magnetometer,and completes the construction and testing of the self-excited magnetometer optical system.According to the specification of Cesium Atomic gas chamber in Magnetometer,the Helmholtz coil and its constant current drive source are designed,The output current error of the drive source is not more than 0.5mA in the range of signal frequency from 1kHz to 1MHz,and then the signal amplification phase shift feedback loop is designed according to the optical signal characteristics in the self-excited magnetometer,and the maximum error of signal phase shift in the signal frequency 20 kHz to 360 kHz is not more than 2.9 °.The minimum error below the 220 kHz signal frequency is only 0.07 °.Finally,the whole feedback loop is combined with the optical structure of the magnetometer to complete the construction of the whole selfexcited cesium optical pump atomic magnetometer system,and the frequency values of the magnetic resonance signal measured by the magnetometer system in different magnetic field environments are measured and analyzed.