Nonlinear properties of dense coherent media

Properties of coherent media in the regime of electromagnetically induced transparency (EIT) are studied. A study of the shape and width of the EIT resonance is presented for coherent media with buffer gas. Observation of an absorption-like resonance for large one-photon detunings in a medium with buffer gas and its properties are shown. The regime of ``slow'' and ``fast'' group velocities are studied. Observation of narrow resonances with a phase broadened probe field is presented, and possible application of this regime are outlined