Investigation On The Coherent Population Trapping (CPT) Magnetometer

Magnetometry is an important method which is used to study physical magnetic phenomena. The technology of the weak magnetic field measurements often plays an important role in many fields, such as scientific research, national defense, industry, bio-medical sciences, and areas of daily life. At present, there are several kinds of magnetometers whose applications are limited or inhibited because of their large weigh, size and power consumption or low resolution. Coherent population trapping (CPT) magnetometer which we will discuss in this thesis has many advantages, including high resolution, small size and low power consumption. Therefore, it has been paid more and more attentions from the scientists all over the world.In this thesis, many properties of a CPT magnetometer is investigated, including generalized principles, experimental setup, analyses of experimental results and the methods of experimental improvement.First, we mainly introduce the measurement of weak magnetic field, which has extensive applications and plays a very important role. Then some kinds of weak magnetic field magnetometers are described, as well as their generalized concept, principle, advantage and disadvantage, application and so on. We also review the development of CPT magnetometer, and suggest the significance of independently developing high-performance magnetometer. Meanwhile, the main research contents and the significance of this thesis are also summarized.Second, the basic principle of CPT magnetometer is analyzed theoretically by discussing the interaction between light field and atoms. The characteristics of rubidium and Zeeman Effect in the magnetic field are introduced. And we describe the theoretical expression of the relationship between the splitting and the magnetic flux density. Then we introduce coherent population trapping, analyze the quantum mechanics of the physical phenomenon, explain its essence and characterize the generalized principles of CPT magnetometer. Third, according to the generalized principles of CPT magnetometer, a set of experimental setup is established, including the laser source part, magnetic sensor part and signal detection devices part. We focus on their performance, principles and parameters. What's more, to make CPT magnetometer smaller, compact and integrated, we design a series of magnetometer package case which can make all above three parts together.Finally, we achieve the experimental study of the CPT magnetometer:measure a series of magnetic flux installed by Helmholtz coil under different conditions and geomagnetic magnetic flux. The resolution of the system is approximately 1.43nT that is less than 2nT. We experimentally detect and theoretically analyze dependence of multiple CPT resonance on relative orientation of magnetic field and light propagation. At last, we test and analyze some factors affecting the performance of CPT magnetometer, and analyze the causes and propose the method for the improvement.