Study Of Improving Sensitivity Of Atomic Magnetometry In Earht-field Range

The precise measurement of magnetic fields has attracted people's attention due to its wide application.Alkali metal-vapor magnetometers have seen tremendous progress in recent years,improving their sensitivities to below the fT/(?) level for submicrotesla fields.As one of the most sensitive magnetometry,atomic magnetometry are used in a wide variety of applications ranging from geophysics to fundamental physics and to medicine.When the atomic magnetometer works in a zero-magnetic environment,its sensitivity is already sufficient for most of applications.However,in the geophysical field range(up to100 ?T),nonlinear Zeeman(NLZ)effect can cause a signal reduction and polarization self rotation(PSR)effect can cause improvement of noise.Therefore,to solve the interference caused by these effects on the atomic magnetometer and improve the sensitivity of the atomic magnetometer in the geomagnetic environment is a crucial step for the further development of the atomic magnetometer.In this thesis we investigate the way to improve the sensitivity of atomic magnetometry in earth-field range.The sensitivity of atomic magnetometry is decided by signal amplitude,linewidth,and noise level of magnetometry.In the geophysical magnetic field range,the linewidth and signal amplitude is limited by nonlinear Zeeman effect.Meanwhile,the noise level of atomic magnetometry is limited by self-rotation effect.To solve these problems,we did researchs as follow:1.The nonlinear Zeeman effect can induce splitting and asymmetries of magnetic-resonance lines in the geophysical magnetic-field range.This is a major source of“heading error” for scalar atomic magnetometers.We demonstrate a method to suppress the nonlinear Zeeman effect and heading error based on spin locking.In an all-optical synchronously pumped magnetometer with separate pump and probe beams,we apply a radio-frequency field which is in-phase with the precessing magnetization.This results in the collapse of the multi-component asymmetric magnetic-resonance line with? 100 width in the Earth-field range into a single peak with a width of 22 Hz,whose position is largely independent of the orientation of the sensor within a range of orientation angles.The technique is expected to be broadly applicable in practical magnetometry,potentially boosting the sensitivity and accuracy of Earth-surveying magnetometers by increasing the magnetic-resonance amplitude,decreasing its width and removing the important and limiting heading-error systematic.2.Globally applied magnetic fields may lead to crosstalk between closely located sensors(as in a gradiometer)and therefore limit the applicability of this technique to sensor networks,which are important in biomedical and fundamental physics applications,such as,human heart or brain-activity mapping.Here,we present all-optical compensation of nonlinear Zeeman shift in a magnetometer using spin locking by replacing the RF field with an intensity-and polarization-modulated laser beam.This method allows to build a highly-sensitive multi-sensor magnetometer array,capable of working in the Earth's magnetic field range.3.The polarization self-rotation effect(PSR)is a fundamental source of excess quantum noise that limits the sensitivity of this technique.We studey the PSR effect on the signal-to-noise ratio(SNR)of a magnetometry with a bias magnetic field applied.We increase the SNR by introducing a phase shifter before the poarimeter to control the phase between vertical polarized light and horizontal polarized light.The implementation of the phase shifter results in improvement of SNR by up to 10 dB.