85Rb D1-Line Coherent-Population-Trapping Atomic Clock for Low-Power Operation

A Rb-85 D1-line coherent-population-trapping (CPT) atomic clock with a natural-mixture Rb gas cell is demonstrated. D1-line excitation can generate a larger CPT resonance amplitude, and the choice of 85Rb rather than conventional Rb-87 is because of its lower ground-state hyperfine-splitting frequency. The frequency deviation for the D1 line was measured using the same experimental setup as that for the D2 line except for the vertical-cavity surface-emitting laser (VCSEL) wavelength and RF power. In the case of D1-line excitation, the CPT resonance amplitude was 1.5 times that for the D2 line, and the light shift sensitivity was one-half that for the D2 line. The Allan standard deviations for the 85Rb D1 line, estimated from the frequency deviations, are <2.5 x 10(-12) per day. In addition, the required RF is 1.5 GHz and its power is only -8.0 dBm. (C) 2010 The Japan Society of Applied Physics DOI: 10.1143/JJAP.49.062801