Cold Atom Molasses Preparation And Parameter Measurement In Cesium Atomic Fountain Clock

Cesium atomic fountain clock, as the Time Frequency Standards device which redefines the"second" with high accuracy and stability, has been widely applied in aerospace, precisionpositioning, basic physics, geodesy and other fields. The cesium atomic fountain clock employscold atoms molasses as the working medium; preparation of great number of atoms withextremely low temperature is the key point to the development of cesium atomic fountainclock. In addition, the detection efficiency will directly impact on the performance evaluation ofcesium atomic fountain clock.This thesis focuses on the cesium atomic fountain clock, and mainly studies preparation ofcold atoms sample employing low velocity atomic beams, together with the design andimplementation of the signal detection.Analyses of the required vacuum conditions in the vacuum system of the atom clock havebeen done; afterwards, the corresponding structure scheme is proposed and accomplished.Vacuum condition of the cold atoms molasses preparation better than1.6×10^-7Pa, atomic flightzone vacuum better than3.8×10^-7Pa are obtained, individually.During the cooled optical system design and calibration, an integration of laser beamexpanders design is proposed to complete the adjustment of the cooling light with high qualities.Based on this system, the preparation of the cold atomic molasses has been achieved, with thediameter of cold atomic sample about6mm, and the measured steady-state atomic number to be（1.8±0.3）×10⁸, the temperature of10.72±0.69μK.Impacts of different experimental parameters on the atomic number of the cold atomicsample are studied, and the best experimental parameters are demonstrated to be the cooling lightdetuning of-14.3MHz, Optical power of8mW.By analyzing the characteristics of two-level fluorescence detection construction for thedetection of the program, based on this, a proper detecting structure of the optical system isdesigned and realized.Designing and accomplishing the fluorescence collection system, with detectionefficiency of4%to5%.Based on the cold atom prepared by magneto-optical trap, the symbol for fountain clock-Ramsey fringes have been obtained in the experiment.