Study On Atomic Spin Polarization In Nuclear Magnetic Resonance Gyroscope

The inertial navigation system（INS）is a kind of navigation system with high privacy and autonomy,whose operation is not limited by time,environment and so on.The gyroscope is one of the key components that determine the positioning accuracy of INS.With the characteristics of easy integration,having no moving parts,high impact resistance,low power consumption and high precision,the nuclear magnetic resonance gyroscope（NMRG）is expected to be widely used in the future inertial navigation field.The operation principle of NMRGs relies on the spin polarization of the noble-gas nuclei,and the spin-exchange optical pumping（SEOP）method is routinely used to generate spin-polarized samples of noble-gas nuclei.The SEOP technique first uses the circularly polarized beam to pump electrons of alkali metal atoms,then the electronic spin polarization of the alkali metal atoms is transferred to the noble-gas nuclei through collisions which can efficiently enhance the nuclear polarization.Hence,it is of great significance for improving the working performance of NMRGs to study the spin polarization of atomic ensemble through the embedded alkali metal atomic magnetometer.Firstly,based on the interaction model of atoms with magnetic field and light field in NMRGs,the steady-state solution of the Bloch equation for the electronic spin polarization evolution of the Cesium（Cs）atoms is derived,and the influence of the three-dimensional magnetic field on the atomic magnetometer signal is explored.The optimization of the one-dimensional atomic magnetometer is realized experimentally and the optimum sensitivity at different temperatures is obtained.Secondly,the influence model of the optical power,detuning,and ellipticity of pumping laser on the polarization of Cs atoms is given through the theoretical analysis.And the experimental curves between the polarization of Cs atoms and the three parameters of the pumping laser are obtained,which lays a foundation for efficiently regulating the optical pumping polarization of alkali metal atoms.Thirdly,a new method to measure the transverse relaxation time of Cs atoms is derived theoretically based on the principle of the longitudinal-field-modulation,and the previous technique of extracting T₂from the linewidth of the modulation frequency and the traditional magnetic-resonance-broadening-fitting method are also described.The three methods are used to measure the transverse relaxation rate 1/T₂of Cs atoms at different temperatures,and the limit sensitivity of three atomic magnetometers is obtained,separately.Finally,the transverse and longitudinal relaxation time of the noble-gas nuclei are measured based on the free induction decay method,and the efficiency factor of Cs-¹²⁹Xe spin-exchange rate coefficient under the weak magnetic field is obtained,which provides the basis for optimization of the gyroscope performance.