Progress of the Portable Rubidium Atomic Fountain Clock in SIOM

A portable Rb-87 atomic fountain clock has been constructed and researched in Shanghai Institute of Optics and Fine Mechanics, and some improvements have been made recently. So far, comparison data with the H -maser shows that, the Allan deviation of the relative frequency stability of this fountain clock is 5.0 x 10(-1)3 tau(-1/2), which reaches 2.6 x 10(-15) at the average time of 40000 s, and degenerates for longer time due to the frequency drift of the H -maser. The relative frequency uncertainty has been evaluated with the value of 2.4 x 10(-15). In addition, some characteristics technique has been realized on this fountain clock, including "local -oscillator -locking" which gives the error signal back to the local oscillator directly and offers the standard frequency output whose stabilities arrive at the limit determined by the Dick effect, "health safeguard", an improvement used to increase the continuous running time, and suppress the possible faults caused by frequency unlocking and power fluctuation of the laser, and "self comparing", a simple and effective way for the frequency uncertainty evaluation, which is used to evaluate the distributed cavity phase shift, collision shift, and light shift.