85Rb Coherent-Population-Trapping Atomic Clock with Low Power Consumption

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In this paper, the investigation of a 85Rb coherent-population-trapping (CPT) atomic clock for low-power operation is described. The modulation profiles and CPT resonances for both 85Rb and 87Rb, the long-term frequency stabilities of the CPT resonance for both, and the feasibility of switching between low-power and high-stability operation modes are presented. The choice of 85Rb rather than conventional 87Rb is dictated by the lower ground-state hyperfine-splitting frequency, which leads to less than one-half the required RF power and more effective RF-related circuit designs. CPT resonances for both 85Rb and 87Rb can be observed separately in the same natural mixture Rb gas cell, and the linewidth is less than 120 Hz in both cases. The long-term frequency stabilities are ${<}4.0 \times 10^{-12}$/day for 85Rb and ${<}3.5 \times 10^{-12}$/day for 87Rb. These results indicate that a 85Rb CPT atomic clock has a long-term stability of ${\sim}4.0 \times 10^{-12}$/day and consumes about one-half the RF power of a 87Rb equivqlent. In addition, it is possible to switch between low-power and high-stability operation modes by changing the RF frequency and power.
2009-08-25