Preliminary Implentation And Performance Optimization Of Cesium Atomic Radio-frequency Magnetometer

High-sensitivity magnetic-field measurement has found various and numerous applications,including fundamental physics study,space exploration,mineral prospection,biomedical diagnosis,as well as earthquake prediction.The coherent precession of polarized atomic spins is used to detect and measure magnetic fields in alkali atomic magnetometers.Measurements based on alkali atomic magnetometers benefit from high sensitivity,high precision,as well as low power consumption.As a new type of atomic magnetometer,the radio-frequency atomic magnetometer enables the high-sensitivity detection of high frequency magnetic-field signal.Radio-frequency atomic magnetometers have broad application prospects in various and numerous fields,such as the detection of nuclear magnetic resonance(NMR)signal and magnetic resonance imaging(MRI).In this paper,the cesium atomic radio-frequency magnetometer is investigated,and the main works are as follows:First,the principle of cesium atomic radio-frequency magnetometer is investigated.The physical characteristics and energy level structure of cesium atom are introduced.The Larmor precession under external magnetic field is analyzed.The principle of optical pumping is described,and the spin relaxation mechanisms of polarized cesium atoms are analyzed.The cesium atomic radio-frequency magnetometer response is obtained.An optical method to detect the spin relaxation of polarized cesium atoms is introduced.Then,special attention is paid to the characterization and optimization of the cesium cell.The production technology of cesium atomic cell is first introduced.The cesium atoms density is obtained through absorption method.Three typical methods for measuring the transverse relaxation time of cesium atoms,namely,the free-induction decay method,ratio method and linewidth fitting method,are compared.The intrinsic transverse relaxation model of cesium atoms is established for the first time.The intrinsic transverse relaxation rate of cesium atoms are obtained in experiments.The effects of the absorption of cesium atoms by the glass wall and the“reservoir effect”on the intrinsic transverse relaxation are emphasized.This study enlightens the cesium atomic cell design.Special attention is paid to the suppression of the spin relaxation due to the collisions between cesium atoms and cell wall.Two methods are investigated,one is the introduction of buffer gas,and the other one is the use of antirelaxation coating.The optimal buffer gas pressure in cesium cell is determined both in theory and experiment.The effect of surface topography of cesium cell on the antirelaxation property is analyzed.The transverse relaxation time of cesium atoms has been effectively prolonged,which laid the foundation for the performance optimization of cesium atom radio-frequency magnetometer.The light narrowing effect in cesium atomic radio-frequency magnetometer is studied.By solving the evolution equation of density matrix in Liouvlle space,the theory model of light narrowing in cesium atomic radio-frequency magnetometer is built.The light narrowing effects are demonstrated in experiments at the temperatures of T=70?,T=75?,T=80?,and T=85?,and the reductions of linewidths are 17.6%,27.7%,29.4%,and 35.4%,respectively.The linewidth narrowing is due to the partially suppression of the spin-exchange relaxation of cesium atoms.The disagreements between experiment and theory are mainly due to the absorption of cesium atoms by the glass wall.Research has been conducted on the optimization of internal magnetic field in cesium atomic radio-frequency magnetometer.The theory model of the internal magnetic field is built.The distributions of the heater-induced magnetic field and the secondary field due to eddy effects are obtained through ANSYS simulation.The impact of heating frequency on the magnetometer system is investigated.The optimal heating frequencies in various cases are obtained in our experiments.The adverse effect of the superimposed magnetic field is mitigated by optimizing the heating frequency.The inhomogeneous residual magnetic field inside the magnetic-shielding cylinder is compensated by a pair of gradient coils.The transverse relaxation rate of cesium atoms has reduced from798.2s^-1 to646.2s^-1 through active compensation.The open-loop cesium atomic radio-frequency magnetometer system is investigated.The open-loop cesium atomic radio-frequency magnetometer is designed and built.The sensitivity calibration method of cesium atomic radio-frequency magnetometer is introduced.The laser powers and frequencies of the pump and probe beams,as well as the cell temperature are optimized.For the signal frequency of 55 k Hz,the sensitivity of the cesium atomic radio-frequency magnetometer has achieved at160 fT/1/2Hz.The closed-loop cesium atomic radio-frequency magnetometer system is investigated.On the basis of the open-loop system,the active tracking measurement of magnetic field signal is realized with the method of frequency lock at zero of the dispersion spectral.By optimizing the feedback parameters,the system response time is only 2.64s for a frequency variation of 1k Hz,and the system jitter is less than 23Hz.