System Design Of All Optical Cs Atomic Magnetometer

The detecting techniques of weak magnetic field develop rapidly and have been used inmany practical applications, such as geological surveys, oil and gas mineral exploration,archeology, material defect detection, submarine cable survey, looking for underwatershipwrecks, bio-magnetic field detection and so on. The first high-sensitivity magnetometer,developed in the Second World War, is the flux-gate magnetometer, then protonmagnetometer, Overhauser effect magnetometer, optical pumped magnetometer,superconducting quantum interference device(SQUID) emerge in secession and the sensitivityincreases quickly. In recent years, the atomic magnetometer has become the most sensitivemagnetometer. In this paper we explain its basic principle and demonstrate an all opticalatomic magnetometer system. The main topics of this thesis are as follows.(1) The Cs atoms are used as the material. We analyze the theory of magnetic fielddetecting process of atomic magnetometer and discuss the process of atomic polarization. Theresulting circular dichroism of the atomic polarization is detected by measuring ellipticity ofthe probe light, the detailed proof is given in the paper. We calculate the various relaxationtechniques of the depolarization as well.(2) The external cavity semiconductor laser is used as light source. We discusspolarization spectroscopy and dichroic atomic vapor laser lock (DAVLL) in theory andexperiment based on the rate equation. The calculation is agreement with the experiment. Theadvantages and disadvantage of the techniques are analyzed.(3) The Cs vapor cell is the core component of the atomic magnetometer. According tothe relaxation technique of Cs-He spin destruction collision and wall collisions we discuss theinfluence of vapor cell diameter and He pressure to atomic magnetometer and design the Csvapor cell. According to pressure broadening effect, we propose the method of measuring cellvapor pressure through testing Cs absorption spectrum.(4) In order to increase the density of Cs atoms, we use hot air heating means to heat theCs vapor cell. The method can avoid the magnetic noise and has been used in theexperimental system successfully with temperature stability of0.1°C.(5) A highly sensitive detecting system is designed. The polarizing beamsplitter and Faraday modulator techniques are used to detect small rotation angle, both methods canachieve10-7rad small angle detecting. The polarizing beamsplitter used in practical systemcan achieve higher response rate.We build all-optical Cs atomic magnetometer successfully and discuss the influence ofpumping beam frequency, pumping intensity, probing intensity, temperature, duty cycle ofpumping beam modulation and magnetic field. We have achieved the sensitivity of magneticmeasurement of0.3pT/Hz1/2at100nT. How to improving the sensitivity is discussed at theend of the paper.The innovative results of this paper include:(1) We build all-optical Cs atomicmagnetometer based on dual optical beam structure and have achieved the most sensitivemagnetic measurement of0.3pT/Hz1/2at home.(2) The linear polarized light is used to detectcircular dichroism of the atomic polarization.(3) We adopt pressure broadening effect tomeasure the pressure of the Cs vapor cell.(4) We design the non-magnetic heating systemusing hot current.