Research On Key Technology Of High Sensitive Miniature Optical Weak Magnetic Sensor

In recent years,with the rapid development of weak magnetic sensors,magnetic weak sensors based on the structure of the atomic magnetometer have achieved the highest magnetic field sensitivity in the field of weak magnetic sensors on a theoretical level.Especially the magnetometer based on spin-exchange relaxation free(SERF)theory,its sensitivity has surpassed superconducting quantum interferometer(SQUIDs),and its low-cost and miniaturized advantages have made it high expectations in the field of weak magnetic detection.The SERF atomic magnetometer eliminates the effects of spin exchange collisions.It has ultra-high sensitivity because of the spin exchange broadening component improves the coherence between alkali metal atoms.Weak magnetic detection technology has applications in many fields such as geophysical exploration,ore exploration,and medicine.Especially in the measurement of brain magnetism,it is expected to surpass the superconducting quantum interferometer magnetometer to become a new generation of magnetoencephalogram and magnetocardiogram magnetic sensor.The main research work of this thesis is as follows:1.The development history and research significance of weak magnetic sensors are introduced in this thesis;then the current mainstream weak magnetic sensors are introduced,and the current status of the development of weak magnetic sensors is mainly explained.2.The theoretical basis of the weak magnetic sensor is analyzed;the atomic spin evolution equation based on the Bloch equation is established,and the method of increasing the signal of the magnetometer is discussed from the equation.Using the relaxation mechanism in the atomic vapor cell,an atomic vapor cell with suitable buffer gas pressure is designed.3.A weak magnetic sensor system is designed and built,using a single-beam optical atomic magnetometer structure.The 795 nm circularly polarized light is used to pump the rubidium atomic vapor cell,and 1550 nm laser is used as the heating gas cell.The entire vapor cell is made by glass blowing.The weak magnetic sensor probe is made with 3D printing technology.A lock-in amplifier is used to process the collected signal.After demodulation,a signal that is linearly dispersed with the external magnetic field is obtained.4.The parameters that affect the performance of the weak magnetic sensor are optimized,Inckuding the optical pumping rate,the frequency and amplitude of the modulated magnetic field,and the ellipticity of the pump light.The slope of the demodulated dispersion curve near zero magnetic field region is the conversion coefficient.Perform noise power spectrum analysis on the background noise of the weak magnetic sensor.The noise power spectrum is divided by the conversion coefficient to obtain the sensitivity.The sensitivity is 400 f T/?.The factors affecting sensitivity are analyzed and methods to improve sensitivity are proposed.A lot of work has been done in the miniaturization of the entire sensor probe.Based on the existing sensor head design,the miniaturized probe has been reduced in size by several tens of times.Corresponding optical devices and electrical components are designed to fit the size of the miniature probe.The use of a more stable pump light source optimizes the noise of the light source and reduces the line width of the system.Finally,the sensitivity is 60fT(?).