When two microwaves with frequencies close to each other are applied simultaneously to a 87Rb gas cell, which is optically pumped by 85Rb lamp, the beat in the resonance signal of 0-0 transition of 87Rb gro und state is observed. Theoretical explanation is presented.
An optical pumping device, consisting of only 85Rb lamp and 87Rb absorption bulb, is used. The 0-0 transition resonance signal of 87Rb ground state is found to be greater than that in the conventional optical pumping device, in which the 87Rb lamp, 85Rb filter and 87Rb absorption bulb are used. In a definite temperature range, a negative resonance signal is observed. Up to now, it has not been explained yet. The line-width and optical frequency shift are measured. The possibility of applying this device in 87Rb atomic frequency standard is discussed.
The pulsed optically pumped(POP) 87Rb vapor-cell frequency standard was studied based on the detection of free induction microwave signal or optical absorption signal.In POP operation the pumping,interrogation,and detection phases are separated in time,avoiding the coupling between microwave and optical coherence.The theoretical results show that an oscillation period doubled with respect to the classical Ramsey method which leads to a doubled atomic quality factor Q,and the reduction of optical shift and cavity pulling shift will be obtained,when the atoms are submitted to π/2 Ramsey microwave pulse.In experiment Ramsey fringes were obtained with a clock prototype based on 87Rb in buffer gas,with bandwidth of 65 Hz and 150 Hz for microwave and optical signal respectively.The frequency stability achieved was 1.2×10-12 for measurement times up to 100 s.