Study of pulsed optically pumped Rb frequency standard

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.