Time-dependent phase shift of a retrieved pulse in off-resonant EIT-based light storage

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-photon resonance, and provide numerical simulations of the full dynamical Maxwell-Bloch equations, which allow us to account for the experimental results.