Precise Measurement Of Gravity Gradient Based On The Cold Atom Interferometer

The high-precision gravity gradient measurement is of great significance in the fields of self-navigation,resource exploration,geophysics,and fundamental physics.With the development of cold atom physics and related experimental techniques in recent years,cold atom interferometers have been applied widely in precision measurement physics.The gravity gradiometer based on cold atom interferometer,which employing ?K-level cold atoms as test mass,using atom interference phase as measuring parameters,and taking atom clock transition as frequency reference,has a high measurement sensitivity and can achieve low drift and self-calibration.In addition,it is made up of solid components in normal temperature,which bring the advantage in engineering and practical applications.Therefore,this kind of new gravity gradiometer attracts more and more attentions.The primary mission of my doctoral studies is to develop miniaturized cold atom interferometer and its application techniques for precision gravity gradient survey.In this thesis,the design and the experimental process of the cold atom interferometer,and the results of the gravity gradient measurement are presented in detail.The main works are as follows:1.Many miniature optical devices and control devices are developed,and finite element method is used to analyze the mechanical properties of homemade optical system.All optical devices are mounted in 3 small optical modules which are 50 cm×44 cmx×10 cm and 2 homemade fiber-coupled beam delivery systems,and the integration of optical system and electrical system is preliminary realized.2.A compact prototype for precision horizontal gravity gradient measurement was established.The gradiometer consists two compact cold atom interferometers which are separated by about 1 m in horizontal direction.With the interrogation time T=112.4 ms and the repetition rate of 1.75 Hz,a differential acceleration sensitivity of 131.3 mrad/?Hz and a long term resolution of 1.5 mrad@5800 s have been achieved.3.A sequential control system for gravity and gradient measurement based on Lab VIEW was developed.4.The main noise sources of atom gravity gradiometer have been analyzed and calculated,the results are in accordance with the experimental measurement.The improving scheme based on these analyses is proposed.A simple normalized detection method for cold atom interferometer is designed and implemented.The detection of the population in F=3 state or F=2 state after coherent manipulations is normalized to the blow-away fluorescence during initial state preparation.In this way,the system structure and the detection procedure are both simplified.Both the amplitude noise in atom source and the short term phase noise in interference fringes are suppressed by more than a factor of 10 with this normalized detection.