The Effects Of Laser On Sensitivity At Magnetometry With Cs Vapor

The accurate detecting technology of weak magnetic field plays an irreplaceable role in many fields such as medicine, military, geophysics and industry. Researchers have kept improving the sensitivity of magnetometer since 1950s. In 1960s, based on Josephson Effect theory, superconducting materials were used to produce the superconducting quantum magnetometer, whose sensitivity was up to 10-15T·Hz-1/2. However, its deficiency is also very obvious. It requires the rigorous working condition of low-temperature environment in liquid nitrogen. Then, scientists found that the spin-exchange relaxation-free (SERF) magnetometer could be implemented using Cs vapor as the working substance in the working condition of about 100℃.This thesis analyze the spin-exchange relaxation-free magnetometer with Cs vapor based on the phenomenological theory, and show the change curves of atom transverse relaxation and line width going with pressure of buffer gas He and temperature of Cs cell. Then, according to analyze the curves, optimal working parameters of the Cs atom SERF magnetometer are given. When the temperature of Cs cell is about 105℃and the pressure of buffer gas He is 600 Torr, the maximum breadth of spectrum line of the spin-exchange relaxation-free magnetometer with Cs vapor is about 24.2 Hz. Because the Cs atom spin-exchange relaxation-free uses the polarized electron spin to detect week magnetic field, pump and probe intensities limit its sensitivity. Therefore, it is need to find out the best pump and probe intensities. From the results of numerical calculation, they are 52mW/cm2 and 0.6mW/cm2, respectively. At the same time, this work also analyze the factors effecting sensitivity of spin-exchange relaxation-free magnetometer with Cs vapor including spin projection noise, photon shot noise and optical frequency shift. The relation of three noises and laser frequency detuning has been calculated. The results show that the spin projection noise is about 1.23fT·Hz-1/2, the photon shot noise is about 1.0fT·Hz-1/2, the optical frequency shift is about 0.12fT·Hz-1/2 and the total noise is about 1.6fT·Hz-1/2. This research has provided the necessary theoretical basis for the following experimental study on the spin-exchange relaxation-free magnetometer with Cs vapor.This thesis is divided into five parts. The first chapter introduces the research background and research status internationally and domestically of the Cs atom spin-exchange relaxation-free magnetometer. The second chapter describes the physical fundamentals and the basic working principles of the spin-exchange relaxation-free magnetometer with Cs vapor. The third chapter gives the numerical calculation results of the resonance spectral line width of the spin-exchange relaxation-free magnetometer with Cs vapor and discusses the best pump optical power and the best detection optical power. The fourth chapter theoretically discusses the factors effecting sensitivity of the spin-exchange relaxation-free magnetometer with Cs vapor, and puts forward the research target of the Cs atom spin-exchange relaxation-free magnetometer with high sensitivity. The fifth chapter summarizes the research work and looks forward to broad application prospects of the Cs atom magnetometer with high sensitivity.