Low power 85Rb CPT atomic clock

This paper outlines the features of the ⁸⁵Rb vapor cell atomic clock, the coherent population trapping (CPT) resonance in an ⁸⁵Rb/⁸⁷Rb mixed vapor cell, and the results of the frequency stabilities of a pilot system. The experiments were performed with a sealed vapor cell containing a natural mixture of Rb isotopes and a buffer gas. Excitation of the CPT resonance was accomplished using a vertical-cavity surface-emitting laser modulated at 1.5, 3.0, 3.4 and 6.8 GHz, which corresponded to the full- and half-ground-state hyperfine frequencies of ⁸⁵Rb and ⁸⁷Rb. The results show that the CPT resonances at both ⁸⁵Rb and ⁸⁷Rb can be observed separately. The frequency stabilities of the output signals for each CPT resonance were <10x10^-12/day for ⁸⁵Rb and <6x10^-12/day for ⁸⁷Rb. In addition, the RF modulation signal power for ⁸⁵Rb was 1.1 dB less than that of ⁸⁷Rb, which was 3.4 GHz.