  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 schemes using electromagnetically induced
transparency (EIT) or coherent population trapping (CPT). Our results may be of
importance for future light storage-based precision measurements with EIT and
CPT-type devices where, in contrast to schemes using continuous exposure to
optical fields, the impact of intensity fluctuations from the signal field can
be suppressed.
