Study Of Heading Error For Mz ~4He Optically Pumped Magnetometer And Optimization Of Saturated Absorption Spectroscopy Parameters

The precise measurement of weak magnetic fields is an important method for studying magnets and analyzing the Material form and the properties of matter.Since the discovery of nuclear magnetic resonance by Bloch and Purcell in 1946,quantum magnetic detection technology has had many applications in science and technology,including military submarine detection,geophysical exploration,magnetic anomaly detection,map mapping,bio-magnetic field detection,and oil and gas pipeline detection.The common types of quantum magnetometers include proton magnetometers,superconducting quantum interference magnetometers,optically pumped magnetometers,coherent population trapping magnetometers,and so on.Among them,the optically pumped magnetometer has the advantages of a wide measurement range,high accuracy,high sensitivity,no temperature control,etc.In this Thesis,the Mz helium-atom optically pumped magnetometer is studied and the heading error difference problem arising in the system is improved.In this thesis,we introduce the current research status of quantum magnetometers and the research on the heading error of magnetometers at home and abroad and explain the significance of the research.Theoretical analysis and desktop experimental system are used to verify the causes of heading error;and the improvement method is applied to the magnetometer prototype to test the final improvement effect.The main research work and results of the thesis are summarized as follows:1.The Zeeman effect,optical pumping effect and magnetic resonance effect of ~4He atoms in the external magnetic field are analyzed,and the theoretical basis of the helium-atom optically pumped magnetometer for magnetic measurements is explained.The composition of the helium-atom light-pumped magnetometer desktop as well as the prototype system is studied,and the test and calculation methods of the light-pumped magnetometer heading error and sensitivity index are described.2.The quantum coherence effect on the saturation absorption spectroscopy is investigated theoretically and experimentally for the desktop magnetometer system.The principle of saturable absorption signal generation and the principle of quantum coherence effect are described.The effect of different polarization states of the pump light and the detection light on the saturated absorption signal is studied,The reason for this phenomenon is explained qualitatively in the context of quantum coherence effects.the frequency stabilization experiment is conducted and the Allan variance of the data is calculated to verify the frequency stabilization effect.The experimental results show that the saturation absorption signal is the largest and the frequency stabilization effect is the best when the detection light and the pump light are both linearly polarized and have the same polarization axis direction.3.Based on the actual requirements of the magnetometer index optimization project,the heading error index of laser helium pump magnetometer equipment is tested and optimized.The specific causes of the heading error were first investigated and theoretically studied,mainly including the effects of material remanence,light source and RF coil.The effect of AC Stark effect of light source and AC Zeeman effect of RF coil and the modulation coefficient of RF coil on heading error is verified by desktop experiments,and a specific method to eliminate the heading error is given,and the feasibility of the scheme is tested by external field experiments.The heading error is reduced to about 0.3nT.