Controlling electromagnetically induced transparency by the laser phase

Summary form only given. We present both theoretical and experimental investigations of the CW laser light propagation through the medium of double-/spl Lambda/ atoms. Our theoretical calculations show that optical properties of the medium-absorption and refraction-can be changed from the regular two-level behaviour to the EIT (three-level /spl Lambda/) behaviour by the change of only the phase /spl Phi/ of input laser fields. The propagation of light through an optically thick double-/spl Lambda/ medium is also non-trivial, because the phase is changed in the course of propagation, which leads to the dramatical change of the absorption and refraction. The general trend is, however, the same for different regimes: not only the atoms are prepared in the dark state, but also the laser field is prepared in the non-absorbing state. Thus, the laser phases, amplitudes and frequencies become matched after a sufficiently long propagation even in the CW regime. We note also a possibility of amplification of one laser wave in expense of the others (frequency conversion) and frequency generation (four-wave mixing) enhanced by quantum interference in such a medium. We also report here the first experimental observation of phase dependent EIT.