Magnetic Noise Suppression Methods And Experiment Researches Based On Ultrahigh Sensitive SERF Atomic Magnetometer

Magnetic field widely distributes in nature.Detecting weak magnetic field can promote researchers in each area to find novel phenomenon and explore new mechanisms.With the developments of quantum manipulation technology and quantum sensor technology,using atomic spin effect to measure the magnetic field becomes a new development direction.Ultrahigh sensitive quantum magnetometers,especially the optical pumping magnetometers,emerge in response to the needs of times.Among these magnetometers,the atomic spin magnetometer,which is based on the principle of spin-exchange relaxation-free(SERF),has attracted tremendous attention due to its highest theoretic sensitivity.So far,the magnetic field measurement sensitivity of 0.16fT/Hz1/2 has been achieved,which is the highest magnetic field measurement sensitivity realized by human.In this paper,based on the SERF ultrahigh sensitive magnetic field measurement device with the goal of improving the sensitivity,the magnetic noise suppression methods and experiment researches,including the establishment of the magnetic shielding optimization model with high shielding factor and the experimental research,the calibration method experimental research of the triaxial magnetic coil parameters,and on-site accurate monitoring of the atomic density number,were carried out.The main innovations are listed as follows,1.To solve the problem of the sensitivity of the SERF ultrahigh sensitive magnetic field measurement device limited by the magnetic noise,the output signal equation was established,which could be used to analyze the magnetic noise sources.Such an equation provided a theoretic foundation for the SERF ultrahigh sensitive magnetic field measurement device to promote its sensitivity.2.In order to isolate the influence of the environment magnetic field on the SERF ultrahigh sensitive magnetic field measurement device,the parameter modeling of the magnetic shielding cylinder was established.Based on this model,with other conditions steadfast but changing only one parameter,the simulations of the influences from the various parameters on the shielding factor were carried out.The shielding factor was about 105.The magnetic shielding cylinder designed by the optimization modeling approach had the advantages of small volume,light weight,low cost,high uniformity,and good shielding performance.This optimization modeling method could provide theoretical guidance to the structure optimization design of the miniaturization magnetic shielding.3.As for the problem of the calibration accuracy of the tri-axial magnetic coil constants limited by the fluxgate’s probe placement accuracy and fluxgate’s measurement accuracy.An on-site and high precision method for calibrating coil constants without any additional equipment was presented.This method could provide the basic guarantee for the SERF ultrahigh sensitive magnetic field measurement device to improve its sensitivity.The non-orthogonal angle of the tri-axial magnetic coils could lead to a deviation of magnetic field between the practical value and theoretical expectations.This deviation could affect the estimation accuracy of the sensitivity of the SERF ultrahigh sensitive magnetic field measurement device.To solve this problem,an ingenious method for measuring the non-orthogonal angle of the tri-axial magnetic coil was proposed.This method could provide practical reference for the establishment of the non-orthogonal angle error model and for the non-orthogonal angle error compensation.In order to synchronously measure the triaxial magnetic coil constants and non-orthogonal angle,an integration determination based on atomic spin Larmor precession was proposed in this paper.4.Increasing the signal response of the SERF ultrahigh sensitive magnetic field measurement device was another way to improving the sensitivity.Accurately monitoring the atomic number density had a great significance due to the atomic density number proportional to the signal of the SERF ultrahigh sensitive magnetic field measurement device.Thus,we proposed an on-site accurate monitoring of atomic density number based on the magnetic resonance linewidth.This method also could be used to measure the temperature inside the alkali metal cell.Finally,the performance measurement of the SERF atomic magnetometer was performed.A measurement sensitivity of 9.7 fT/Hz1/2 was achieved.