AC Stark-shift in CPT-based Cs miniature atomic clocks

We report on studies on the light-shift in cae-sium miniature atomic clocks based on coherent populationtrapping (CPT) using a micro-fabricated buffer-gas cell(MEMS cell). The CPT signal is observed on the Cs D1-lineby coupling the two hyperfine ground-state Zeeman suble-vels involved in the clock transition to a common excitedstate, using two coherent electromagnetic fields. These lightfields are created with a distributed feedback laser and anelectro-optical modulator. We study the light-shift phe-nomena at different cell temperatures and laser wavelengthsaround 894.6 nm. By adjusting the cell temperature, con-ditions are identified where a miniature CPT atomic clockcan be operated with simultaneously low temperaturecoefficient and suppressed light-shift. The impact of thelight-shift on the clock frequency stability is evaluated.These results are relevant for improving the long-term fre-quency stability of CPT-based Cs vapour-cell clocks.