Study on double-modulation coherent population trapping resonance

Spectroscopy studies of coherent population trapping (CPT) with constructive polarization modulation are presented. In these studies, the effects of modulation frequency and laser intensity on the CPT contrast of the clock transition are investigated. We experimentally show that no CPT transition with Δm_F=2 is excited. Moreover, the constructive polarization modulation CPT signals are observed in both cases, with excited levels F´=3 and F´=4 in the Dl line of Cesium. Our studies show that this scheme, with potential to implement a compact and high performance clock, could also be applied to high pressure buffer gas cell, e.g., chip scale atomic clock.