We report measurements of the time-dependent phases of the leak and retrieved pulses obtained in EIT storage experiments with metastable helium vapor at room temperature. In particular, we investigate the influence of the optical detuning at two-phot
on resonance, and provide numerical simulations of the full dynamical Maxwell-Bloch equations, which allow us to account for the experimental results.
We report the experimental observation of Coherent Population Oscillation (CPO) based light storage in an atomic vapor cell at room temperature. Using the ultranarrow CPO between the ground levels of a $Lambda$ system selected by polarization in meta
stable $^4$He, such a light storage is experimentally shown to be phase preserving. As it does not involve any atomic coherences it has the advantage of being robust to dephasing effects such as small magnetic field inhomogeneities. The storage time is limited by the population lifetime of the ground states of the $Lambda$ system.
Electromagnetically induced transparency (EIT) in metastable helium at room temperature is experimentally shown to exhibit light storage capabilities for intermediate values of the detuning between the coupling and probe beams and the center of the a
tomic Doppler profiles. An additional phase shift is shown to be imposed to the retrieved pulse of light when the EIT protocol is performed at non-zero optical detunings. The value of this phase shift is measured for different optical detunings between 0 and 2 GHz, and its origin is discussed.
