A caesium atomic beam microwave clock detected by distributed feedback laser diodes

A compact caesium-atomic-beam microwave clock is investigated at Peking University. The atomic beam is prepared by magnetic state selection and detected, after microwave interrogation, by means of laser-induced fluorescence. Distributed feedback laser diodes are adopted for their large mode-hopping-free ranges, which ensure a care-free long-term operation. Besides, digital servo systems can automatically relock the laser's frequency when it is off-resonant. A 45-day continuous measurement of the output frequency is carried out. The 5-day frequency stability is 2.7·10 −14 and the short-term stability is as good as those of commercial cesium clocks.