The Development And Systematic Errors Evaluation Of The Portable Atomic Gravimeters

The Earth's gravitational acceleration g is position dependent and time varying.The high-precision measurement.of g in real time and different locations is widely ap-plied in basic researches and engineering fields.For the gravity sensors,the absolute gravimeter based on atom interferometry can continuously measure g in a high repeti-tion rate and with high sensitivity and stability.So the atomic gravimeter is a combina-tion of absolute and relative gravimeter,which makes it an increasingly wide utilization in the world.But it requires the atomic gravimeter to be miniaturized,integrated and portable.To obtain an high accuracy and verify it,it's also necessary for the systematic errors evaluation and the comparison with other absolute gravimeters.These are also the emphases in this thesis.In this thesis,the significance of precise gravity measurement and the research progress of all kinds of gravimeters domestic and overseas,especially portable atomic gravimeters,are reviewed.The theoretical bases of the laser cooling of atoms,the sim-ulated Raman transitions and the interference of atoms involved in atomic gravimeter are introduced,as well as the methods of deriving g and analyzing the noises.In this thesis,the design and building process of our two generations of portable atomic gravimeters,USTC-AG01(02)and USTC-AG11(12),are introduced in detail.The design of embedded welding optical window is adopted in the vacuum system.Assuming that the light source is a point in the center of the detection area,the fluores-cence collection efficiency can reach 39%.The right-angle reflection structure makes the optical system of the sensor head more compact.The fresnel lenses are applied in the probe system,which realize an atomic fluorescence collection efficiency of 12.8%for any one of the atomic state with a compact construction.The spatial inhomogene-ity of the bias magnetic field for the Raman interference is less than 0.3%.The size of AG11(12)' s sensor head is only 0.3×0.3 ×0.65 m3.It basically meets the requirements of miniaturization.In January 2019,AG02 and AG 12 were transported over 1300 km to Changping?Campus,the National Institute of Metrology(NIM).After a quick local recovery,the g measurement sensitivities were 35.?Gal/(?)and 42.5 ?Gal/(?)respectively.After averaging for 2000 s,the stabilities reached 0.8 ?Gal and 1.3 ?Gal,respectively.The contributions of the noise sources were also calculated.These results verify the mobility and robustness of our atomic gravimeters to some extent.To improve and verify the accuracies of the two atomic gravimeters,the sign of the Raman chirp rates was alternating to eliminate the wave-independent errors in real time at NIM,and the analysis is also given.With the home-made adjustment device for directions of the Raman lights,the multi rounds iteration adjustment method was applied to eliminate the cross term between the two tilt angles of the incident and reflected lights,and made g compensation due to the tilt drift.Measuring g varying the Rabi frequency to fit in line,so that the systematic errors induced by the two-photon light shift were obtained.With the difference method of measuring g in two opposite directions of the sensor head,the biases caused by the Coriolis effect were obtained.With the finite element analysis and the path integral method,the self-attraction effects on the g measurements were accurately calculated out.Also with the path integral method,the effective heights of g measurements were given,which are much more accurate than the calculating results from the approximation formula.For the g values measured by AG02 and AG12,after correcting by the total systematic errors and the biases from the environmental effects,two comparisons with the reference values measured by an optical absolute gravimeter NIM-3A show that the the degrees of equivalence(DoE)are 3.7(15.2)?Gal and-12.5(15.4)?Gal,respectively.