Study Of Highly Sensitive Atomic Magnetometer Based On Spin Polarization

Alkali metal atomic magnetometers use the atomic spin polarization in the external field to measure the magnetic field.At present,the sensitivity of the best atomic magnetometer has become better than that of the superconducting quantum interference device（SQUID）magnetometer,achieving magnetic field sensitivity of 0.16 f T/Hz^1/2.The atomic magnetometer has broad application prospects.This paper mainly studies the working principle,parameter optimization and sensitivity evaluation of atomic magnetometer based on spin polarization of Cs atoms.Firstly,the research background and progress of the atomic magnetometer and the sensitivity have been introduced.Three common atomic magnetometers are introduced,which are the spin-exchange relaxation free（SERF）magnetometer,the nonlinear optical magnetometer and the magnetic resonance-based magnetometer.The atomic magnetometer uses a spin-polarized atom to measure the magnetic field.Here,the circularly polarized light is used to pump polarized atoms,and the steady solution of the Bloch equation for spin evolution under quasi-static magnetic field is obtained,and the analytical expressions of optical rotation and spin polarization are given.Considering the distribution of spin-polarized Cs atoms on the ground state hyperfine structure,the relationship between the detuning of the probe light and the optical rotation is theoretically given and verified experimentally.It is found experimentally that the distribution of spin-polarized atoms in the ground state of hyperfine structure can be controlled by pump light detuning,and the relationship between the spin polarization distribution and the pump light detuning is obtained.Spin relaxation is a key factor in determining the sensitivity of a magnetometer.Theoretically,the spin relaxation of Cs atoms is analyzed.Experimentally,the detuning and optical power of the probe light,the detuning and optical power of the pump light,the magnetic field and other conditions are optimized to obtain the best working conditions of the magnetometer.Highly sensitive Cs atomic SERF magnetometer has a lower operating temperature.The relationship between the magnetic sensitivity of Cs atomic SERF and temperature has not been studied in detail in the past.This paper has done this work,giving the sensitivity of the work of the magnetometer from 70°C to 130°C.Magnetic field measurement sensitivity is often limited by quantum noise,such as photon-shot noise,atomic spin projection noise,and light shift noise.Finally,the quantum noise analysis and sensitivity measurement of the atomic magnetometer are completed,and photon-shot noise,atomic spin projection noise,and light-shift noise evaluation results are given.When the temperature of the chamber is 110℃,the magnetic field measurement sensitivity is 2.2 f T/Hz^1/2,the spin projection noise is 1.4f T/Hz^1/2,the photon shot noise is 0.8 f T/Hz^1/2,and the light shift noise is 1.2 f T/Hz^1/2.The high-precision measurement of the polarization of the pump light was completed experimentally,and the sensitivity of the polarization measurement of the pump light was 3.8×10^-8 rad/Hz^1/2.