Experimental Research On Vibration Related Effects In Gravity Measurements By Atom Interferometry

Precision gravity measurements not only play an important role in scientific research,such as fundamental physics,metrology and geophysics,but also have strategic significance in the fields of resource exploration and inertial navigation.The performance of the absolute gravimeter based on atomic interferometry has already been comparable to that of the traditional free-falling corner-cube absolute gravimeter.For absolute gravity measurements by atom interferometry,vibration noise is one of the main factors affecting the sensitivity of gravity measurements.And systematic error may be also induced in the process of vibration noise suppression.This paper focuses on the vibration related effects in atom-interferometry based gravity measurements.The main research contents and achievements are listed as follows.(1)The single-stage active vibration isolation system is analyzed in detail,and the suppression of vibration noise by two orders of magnitude is realized.Based on the loop modeling and analysis of the single-stage active vibration isolation system,the transfer function of the loop is measured,and the feedback filter is designed accordingly.Finally,vibration noise suppression by two orders of magnitude in the frequency band of 0.01-1Hz is achieved,and the loop noise is measured.(2)A two-stage active vibration isolation system is built,and effective isolation of violent vibration noise is preliminarily realized.Based on the single-stage active vibration isolation system,two-stage vibration isolation system is modeled theorectically and then built.The suppression effects of vibration noise by single-stage vibration isolation system and two-stage vibration isolation system noise under normal and earthquake conditions are compared.The measurement results show that the developed two-stage active vibration isolation system has the potential to effectively isolate large vibration noise,which lays a foundation for uninterrupted absolute gravity measurement by atom interferometry in the future.(3)The systematic error related to seismometer during the vibration noise suppression is found and evaluated.It is found that the seismometer is affected by the periodic magnetic field generated by the magnetic field coil of the magneto-optical trap,resulting in false vibration signals,which may introduce a systematic error in atom-interferometry based gravity measurements.In this paper,taking vibration noise suppression by the correction method as an example,the response of the seismometer to the change of external magnetic field is analyzed in detail,and the magnetic field coil current of magneto-optical trap is modulated.Finally,the systematic error induced by the seismometer in atom-interferometry based gravity measurements is evaluated,which can reach a level of 10 μGal.The above research on vibration related effects in atom-interferometry based gravity measurements carried out during my Ph.D.study is presented in detail in this paper,and the research lays a good foundation for improving the performance of precision gravity measurements by atom interferometry.