Parametric phase shift in electromagnetically induced transparencies

Summary form only given. The field of atom manipulation using laser light has experienced a rapid growth in the recent years. By the interaction of the atoms with laser light it is possible to design media with desired optical properties such as transparent media showing negative or positive dispersion. Negative dispersive transparent media can be used e.g. to realize an optical cavity with large build up but broadband response (white light cavity) or to demonstrate superluminal light propagation. It has also been demonstrated that positive dispersive media can exhibit steep dispersion leading to small absolute values of the group velocity (slow light, see e.g.) or reducing e.g. the line width of a cavity relative to the line width of the empty resonator.We report on recent experiments on investigation the absorptive and dispersive properties of a coherent prepared media, that shows electromagnetically induced transparency on extremely narrow dark resonances. We have carried out the experimental study of a two-photon excitation via quantum interference in a three level Cs atomic system. The experiments were done on a Cs atomic beam.