Exploring the Use of Ramsey-CPT Spectroscopy for a Microcell-Based Atomic Clock

We investigate the application of Ramsey spectroscopy for the development of a microcell atomic clock based on coherent population trapping (CPT). The dependenceof the central Ramsey-CPT fringe properties on key experimental parameters is first studied for optimization of the clock's short-term frequency stability. The sensitivity of the clock frequency to light-shift effects is then studied. In comparison with the continuous-wave (CW) regime case, the sensitivity of the clock frequency to laser power variations is reduced by a factor up to 14 and 40.3 for dark times of 150 and 450 mu s, respectively, at the expense of intensity 3.75 times higher for short-term stability optimization. The dependence of the clock frequency on the micro wave power is also reduced in the Ramsey case. We demonstrate that the Ramsey-CPT interrogation improves the clock Allan deviation for averaging times higher than 100 s. With a dark time of 450 mu s, a clock fractional frequency stabilityof 3.8 x 10(-12) at 104 s is obtained, in comparison with the level of 8 x 10(-11) obtained in the standard CW case, in similar environmental conditions. These results demonstrate that Ramsey-based interrogation protocols might be an attractive approach for the development of chip-scale atomic clocks (CSACs) with enhanced mid- and long-term stability.