Progress in rubidium fountain clock research at SIOM

A laser-cooled rubidium fountain clock is studied at Shanghai Institute of Optics and Fine Mechanics (SIOM). One important characteristic of the setup was, instead of six laser beams used in normal fountains, a fold optical path (FOP) was used to trap, cool, and launch atoms, which decreased laser power by 60% and the optical system was simplified greatly. This fountain clock had been operated with the center Ramsey fringe of line-width of 1Hz and the signal noise ratio (SNR) of 100. Recently, some evaluations of the fountain clock systematic uncertainty have been finished. By comparing with an H-maser (VCH-1003A), the evaluation of the frequency instability was obtained by 8×10^-13τ^-1/2 and 6×10^-15 in one day. The system errors (type-B uncertainty) had been evaluating, and some results, such as second-order Zeeman shift and blackbody radiation shift, had been achieved. Some experiments of ⁸⁵Rb fountain were also reported in this paper.