Electromagnetically induced transparency: Laws of light transmission in a continuous wave experiment

We report on first measurements of the dependence of the transmission of re sonant polarized light on the optical length in a continuous wave electroma gnetically induced transparency regime. The law of light propagation is fou nd to be exponential, with an absorption coefficient smaller compared to it s value in the non-transparent case. This result is explained by a transien t character of the absorption and the presence of losses of atomic populati on to non-observable magnetic sublevels of the ground state.