Spin Polarization Process In Magnetic Resonance System

In recent years,with the continuous development and progress of precision measurement,a precise measurement based on quantum mechanics has gradually become a research hotspot.It is of great significance to study the dynamic evolution process in quantum system for the design and optimization of precision measurement technology.The requirements for high accuracy and sensitivity of magnetic field measurement can be achieved by studying and optimizing the parameters in the process of atomic spin dynamics evolution.The research of this paper mainly focuses on the following aspects:1.The physical properties of rubidium,an alkali metal element,including its fine structure and hyperfine structure are introduced.The principle of Zeeman splitting of atoms in a magnetic field,the process of spin polarization by optical pumping and depolarization by applying a resonant RF field are also introduced.2.The time characteristics of the spin polarization process of rubidium atoms in a magnetic resonance system were experimentally analyzed and studied.The magnetic resonance system has not only a constant magnetic field and an orthogonal resonance RF field,but also a left-handed circularly polarized light.We find a correlation between the polarization process when RF is turned off and the probe optical power by monitoring the transmitted optical signals under different probe optical power.We also fitted the experimental curve and obtained the time constant of its completion of polarization.Through analysis,it is concluded that the larger the probe optical power,the smaller the time constant for completing polarization.3.The semiclassical density matrix theory is introduced by taking the interaction between the atom of a two-level system and a single-mode field as an example.In addition,the calculation process of density matrix equation is deduced in detail in Schrodinger picture and interaction picture.In order to theoretically analyze and verify the experimental results,we utilized a three-level model and calculated the numerical solution of the model based on the density matrix theory.The theoretical time constant is also obtained by fitting the numerical solution image.The obtained laws are consistent with the experimental results,which can basically explain the experiment and show the rationality of the theoretical model.At present,the research on the dynamics of atomic spin state has gradually become a focus of attention.This research has potential significance in the field of magnetic field precision measurement.We hope that our theory and experiment can provide help for this research.