Investigation On The Laser Polarization Modulated Bell-Bloom Optically Pumped Magnetometer And Its Gradiometer

Magnetic field is widely existed in the space. The precise measurement of magnetic field is of great importance in many application fields, such as geological exploration, military navigation, clinical diagnosis and industrial detection, etc.. Therefore, the research on the high-precision magnetometer becomes one of the key investigation fields worldwide. With the development of atomic physics and laser technology, the study of atomic magnetometer made great progresses in the past decades.Optically pumped magnetometer (OPM) is a widely used magnetometer with high sensitivity and high precision. In this thesis, the Bell-Bloom OPM (hereafter noted as BB-OPM) for the detection of weak magnetic fields is investigated. The BB-OPM is based on the light modulation resonance technique instead of optical radio-frequency resonance technique that is often used in typical OPM. In the research on gradiometer or multichannel magnetometer, it can successfully avoid the cross talk noise. Besides, with the comparative experiments between the BB-OPMs with frequency-modulated and polarization-modulated light, we found that the later gained a higher sensitivity. Finally, we studied a gradiometer which consists of two identical magnetometers and analyzed its performance in non-shielded environment.In the first chapter, we describe the importance of magnetic field measurement and introduce some typical atomic magnetometers. The second chapter describes the principle of BB-OPM. In the chapter three, the details of the BB-OPM setup, including the light source, the sensor part and the signal detecting part is introduced. We analyzed the resolution of magnetometer by detecting the magnetic step signals with the amplitude of 0.5nT,0.2nT,0.1 nT and 0.05nT. And by analyzing the noise power spectrum, our magnetometer attained a sensitivity of 2pT/Hz1/2 at 10Hz. We also detect the different frequencies of simulated cardio-magnetic fields whose amplitude is about 400pT with the optimized system. In the chapter four, we present a gradiometer system and analyze its performance in non-shielded environment. Finally, the overall work is summarized and the developing trend of magnetometer is discussed.