Study On Optically Pumped Cesium Magnetometer Weak Signal Detection Technology

Magnetic field measurement technology is an important means on the study of magnetic phenomena and related physical phenomena.There are many metrics in magnetic field measurement such as the strength of the magnetic field.Different measurement methods are used in actual measurement,according to the magnetic field strength,magnetic field properties and accuracy requirements.Optical pumping magnetometer is a kind of high-precision weak magnetic detection instruments,based on the atom under the external magnetic field of the Ziehmann effect,with optical resonance principle.It is used in many fields,including the military field,geographical exploration,space magnetic measurement and biomedical science.The work elements used in optical pumping magnetometer include Helium(He),rubidium(Rb),cesium(Cs),potassium(K)and mercury(Hg)and so on.At present,the performance of domestic helium pump magnetometer is acceptable,but has a certain gap compared with foreign products.The research level of domestic cesium optical pump magnetometer is obviously lagging behind abroad.Therefore,at present,it is of great significance and urgency to improve the research of weak signal detection technology of cesium optical pump magnetometer in our country.In this paper,the theory of physics of the cesium optical pump magnetometer system is studied.The actual construction of the optical system is completed.The self-excited cesium optical pump magnetometer detection circuit is designed and realized.It includes feedback loop and frequency measurement module.The main works are as follows:(1)The optical detection method for optical pumping magnetometer is discussed.The physical principle of self-excited optical pump magnetometer is studied,including Larmor precession,Seaman effect,optical pumping action and magnetic resonance,The principle and effect of magnetic resonance are analyzed emphatically.The magnetic moments and optical signals are analyzed in detail and the expressions are deduced.(2)The structure and functions of the optical system of the self-excited cesium optical pump magnetometer are discussed.The working mechanism of the optical system is analyzed.The components of the optical system are studied and designed.The actual optical system was built.(3)The principle and process of self-excited oscillation of self-excited cesium optical pump magnetometer are analyzed.The circuit scheme and parameters of self-oscillation circuit are designed,and the actual circuit is debugged to ensure the normal operation of the whole system.(4)The measurement method of magnetic resonance frequency measurement is studied,and an improved full synchronous frequency measurement method is proposed,which reduces the maximum error to half.Based on FPGA,the actual frequency measurement system is implemented and debugged.