Laser-induced transparency and dark-line effects caused by three-wave mixing in atomic systems

Abstract

We study laser-induced transparency and dark-line effects in a two-level atomic system where the upper transition level is coupled by a laser field to a dressed system consisting of two lower-energy metastable states mixed by a second laser field (\ensuremath{\Pi} configuration). We show that the emission (absorption) spectrum of the two-level system develops two dynamic dark lines (transparency holes) with tunable central frequencies equal to the Rabi frequency of the second field with positive and negative signs, and widths proportional to that of the first field. The detailed evolution of these effects at low- and high-field intensities and the role of quantum interferences are discussed by presenting a model based on laser-induced continuum structure and adopting a dressed-state picture. We discuss various nonlinear processes in this system and show how the dynamics of emission and absorption spectra are determined by one- and two-photon coupling processes.