The influence of laser polarization noise on the short-term stability of CPT atomic clocks

We have completed a series of experiments examining the effect of laser polarization noise on the short-term stability of a CPT atomic clock, when the CPT signal is generated in the “standard” fashion. Specifically, we have examined CPT signal amplitudes, CPT-signal noise, and CPT linewidths for various levels of randomly fluctuating circular polarization. We find that CPT signal amplitudes increase in the presence of polarization noise due to a decreasing efficiency of trapping states. However, we also find that CPT linewidths increase, since polarization fluctuations add to atomic dephasing, and that CPT-signal noise increases. This latter effect is due to bulk population movement between trapping states when the laser polarization changes. Consequently, more sophisticated CPT signal generation schemes that eliminate the trapping of atomic population might be more resilient to laser polarization noise.