High contrast signal in a coherent population trapping based atomic frequency standard application

A polarization-selective method is developed for detecting a coherent-population-trapping (CPT) resonance signal in a vapor cell. The method uses a single laser beam with frequency modulation to induce CPT resonance and to control the AC Stark shift. The method provides a CPT resonance signal with a high contrast of 22%. Using this method, a CPT-based rubidium vapor cell frequency standard demonstrates a measured short-term stability of 1.4/spl times/10/sup -12//spl tau//sup - 1/2 /.