The Development of 85Rb Atomic Fountain Clock in SIOM

A 85Rb atomic fountain clock is under construction in SIOM. The 85Rb AFC shares a laser source with 87Rb AFC. The power spectral density of the sideband phase noise of microwave synthesis chain is -90 dBc/Hz @ 1Hz, which is 15 dB lower than the absolute phase noise of the local oscillator. The early physical experiments are finished. The atomic numbers of 3 × 105 and the temperature of $4\mu \text{k}$ are calculated from the time of flight signal. At present, the Ramsey interference fringe is observed with FWHM of 0.95 Hz. The measured 85Rb ground-state hyperfine splitting has a deviation of +5.8 Hz from the published frequency. Further optimization and evaluation work is in progress.