In Situ Ac Stark Shift Detection In Light Storage Spectroscopy

We report on a method for measuring ac Stark shifts observed in stored light experiments while simultaneously determining the energetic splitting between the electronic ground states involved in the two-photon transition. To this end, we make use of the frequency matching effect in light storage spectroscopy. We find a linear dependence on the intensity of the control field applied during the retrieval phase of the experiment. At the same time, we observe that the light shift is insensitive to the intensity of the signal field which is in contrast to continuously operated electromagnetically induced transparency (EIT) or coherent population trapping (CPT) experiments, where the light shifts induced by all participating optical fields have to be taken into account. Our results may be of importance for future precision measurements in addition to or in combination with current EIT and CPT-type devices which are largely compatible with our approach and could benefit from the inherent robustness regarding operational conditions, shape of the resonances or intensity fluctuations in the signal field.