Realization And Research On Related Key Technique For Time-keeping Cesium Fountain Clock

Cesium atomic fountain clock, the current time and frequency primary standard, with thehighest accuracy performance. It is applied widely in time-keeping system, the field of metrology,fundamental physics research areas. With the development of new methods and newtechnologies, the continuously improving operation ability of the cesium atomic fountain clock,the cesium atomic fountain clock has the potential to be as time-keeping clock. Compared withother time-keeping atomic clock, the frequency drift and long-term stability (days) of highcesium atomic fountain clock features. As time-keeping the clock is one of the cesium atomicfountain clock application development direction. This paper focuses on this theme, the first keytechnologies of the cesium atomic fountain clock, developed with anti-vibration characteristicsof external cavity semiconductor laser, and on this basis, the development of a system withautomatic frequency stabilization function, to solve the limit of cesium atoms fountain clockcontinuous operation of the main problems of capacity; Cesium atomic fountain clock, cold atomcollision frequency shift error and stability performance are conflicting issues. It is solvedthrough the2D MOT technology for the direct preparation of cold atomic beam into an opticalmolasses, in access to low-density atoms while ensuring the same number of atoms, collisionfrequency shift smaller, while the clock stability performance is unchanged. Combined theachieving key technologies with the optical system and vacuum system, the cesium atomicfountain is realized and get a better flight time signal, and laid the foundation for the operation ofthe cesium atomic fountain. According to the order in which the work is carried out the contentand results can be summarized as the following sections:(1) Development of anti-vibration external cavity semiconductor laser, and applied to thecesium atomic fountain clock. The theoretical analysis based on the interference filter,"cat’s eye"structure of the external cavity show anti-vibration characteristics of the external cavitysemiconductor laser. Tested the spectral characteristics of the vibration of external cavitysemiconductor lasers show that the narrower linewidth and higher spectral purity.(2) The frequency tunable external cavity semiconductor lasers based on liquid crystal variable retarder. Analysis of the PZT frequency tuning inherent in the external cavitysemiconductor laser with a return error, aging and the control voltage disadvantages of theproposed program to the tune of the liquid crystal phase delay. On this basis, the DFB laser isdeveloped with a liquid crystal tunable external cavity semiconductor laser. The test showed thatthe developed lasers with a lower tuning voltage, there is no return error and mechanicalmovement. The program is proposed based on semiconductor optical amplifier chip, the LCDdelay frequency tuning,"cat eye" structure of the external cavity high-power semiconductorlaser.(3) Development of a2D MOT slow atomic beam apparatus. With a force model ofCesium atoms in the2D MOT, a numerical simulation characteristic analysis software system ofthe2D MOT process of slow atomic beam, is developed.According to the software system, acomplete slow atomic beam device is designed and implemented to obtain a better performanceslow atomic beam. The flight time method to test the flux, average speed of atom beam under theguidance of the numerical simulation results, to improve the performance of the2D MOT slowatomic beam. the phenomenon of cyclical changes of the atomic beam flow is discovered withpolarization states of push beam.(4) Development of the optical system of the cesium atomic fountain clock. Automaticfrequency stabilization of anti-vibration external cavity semiconductor laser is developed basedon the saturated absorption spectroscopy. The laser is transported through the polarizationmaintaining fiber to the integration of the expander to a collimated, circularly polarized lightoutput.(5) Development of the vacuum system of the cesium atomic fountain clock. Acomprehensive analysis of the degree of vacuum requirements of influence on the cesium atomicfountain clock performance is done according to the theory of the vacuum system design. Basisfor the design to vacuum system of cesium atomic fountain clock reach design aims.(6) Realization of cesium atomic fountain clock. Combined cesium atomic fountain clockoptical system, vacuum system, with control system, cesium atoms is cooled by the Dopplercooling mechanism, moving molassess, the polarization gradient cooling. A comprehensiveanalysis of various parameters (MOT magnetic field gradient, laser frequency, optical molassescooling time, etc.) on the temperature of cold atoms, the atom number of impact to determine the operating parameters of the cesium atomic fountain. The selected state cavity and repulsion oflight to achieve mF=0atom. The Ramsey fringe produced by interaction of9.2GHz microwaveand Caesium atoms has been realized with cold atomic fountain.