Progress on the construction of an atomic cesium fountain at NIM

An atomic cesium fountain has been designed for a new primary standard of frequency in China. Cold atomic clouds collected in the magneto-optical trap (MOT) were previously reported (1995). To further improve the performance of the MOT we have optimized the laser-optical system and operation of the MOT. Some optical elements were replaced with new ones with better quality; frequency stabilization of lasers and arrangement of the optical system was modified; and polarization maintaining (PM) optical fibers were adopted to transfer lights from the optical system to MOT. We also installed the fluorescence detecting - amplifying assembles to take the time of flight (TOF) measurement of the cold atoms.