Transient CPT signals arising from rapid changes in laser polarization

Abstract

In chip-scale atomic clocks based on coherent-population-trapping (CPT), the laser of choice is a VCSEL due to its low threshold current, very high quantum efficiency, and large dynamic bandwidth. A problem with these lasers, however, is that they suffer from polarization fluctuations, which could degrade CPT signal-to-noise ratios. In previous work we found that a rapid change in laser polarization led to a multi-exponential variation of the light intensity transmitted through a resonant Rb vapor. Here, we show that this is not a systematic effect, but is a result of atomic dynamics. Specifically, we show that the change in transmitted light intensity arises from both a change in the system's trapping state and a re-establishment of the atomic coherence that is at the heart of the CPT signal.