Key Techniques Of Nuclear Magnetic Resonance Gyroscope

Inertial navigation system(INS),as a robust self-contained navigation system without the need for external references,plays an important role in the circumstance without global positioning system signals.The gyroscope in using,which is one of the key components of the INS,limits the development of the INS for high precision or compact size.Thanks to the development of the microfabrication,nuclear magnetic resonance gyroscope(NMRG)has become the most potential candidate for the high-performance gyroscope in compact size.In recent years,NMRG has become one of the hot spots in the research on INS.Since NMRG has been in application,more reaserches concentrate on the performance improvement and the minimized design.The key techniques of the NMRG are presented in this thesis to improve the performance of the NMRG.Firstly,laser systems for the NMRG using modulation transfer spectroscopy for laser frequency stabilization are developed.A statergy for the optimization of frequency locking is summarized and the instability of 1.73×10^-10 and 4.23×10^-11 are achieved at the averaging time of 1 s and 1000 s,respectively.The laser frequency can be locked continuously for more than a whole day.It can be estimated that the instability of the laser frequency leads to a fluctuation of less than 0.013%of the atomic magnetometer signal.Next,a three-axis atomic magnetometer by modulating the longitudinal magnetic field is developed.The stabilization of the magnetic field in three dimensions is realized based on the three-axis atomic magnetometer.The fluctuation of the magnetic field in three axes is less than 7 n T in a period of 5000 s,which means the fluctuation of the gyroscope signal is less than 0.08 Hz.The stabilization of the magnetic field at various cell temperatures is studied and it is found that the higher cell temperature corresponds to the lower magnetic noise.And then,the automatic measurement system for the relaxation time of the noble atoms is built up.The method of measuring the linewidth of the longitudinal magnetometer error signal and the method of detecting the free induction decay are also compared.By fitting the error signal of the longitudinal magnetometer,the transverse and longitudinal relaxation of the noble atoms are measured at the same time.Using the technique of relaxation measurement,the binary spin-exchange rate coefficient between Cs and Xe atoms and the wall relaxation are estimated by measuring the relaxation time at different cell temperatures.The polarizations of the alkali atom and the noble atom are estimated according to the atomic magnetometer signal,which leads to the estimation of the enhancement factor.Finally,a method on optimizing the gas recipe of the cell is presented based on the simulation on the best buffer gas pressure and corresponding pump laser power density.The optimization of the gas recipe can improve the polarization of the noble gas and the sensitivity of the atomic magnetometer,which leads to the improvement of the angle random walk and the bias instability of the nuclear magnetic resonance gyroscope.