Multiphoton-process-induced coherence effects in a dissipative quantum system

The work is aimed at modeling coherence effects in a dissipative quantum system under the semi-classical density matrix formalism. A number of multiphoton coherence effects have been shown to be feasible by controlling the incoherent pumping mechanism in a generic four-level model. The specialty of the model is in finding inversionless gain without any restrictions being imposed on the decay rates of the driven transitions. Many of the coherence effects, such as absorption cancellation, inversionless gain at the line center, and sidebands of an absorptive line shape accompanied by dispersive switching, are explained using the same model under different parametric conditions. Further, it is shown that modulation in the coherence effects can effectively be controlled by the two- and three-photon excitation mechanisms with the proper choice of the rates of incoherent pumping under a stimulated Raman process. Different conditions of population inversion are found for both coherent and incoherent control of stimulated Raman resonance. In addition to Raman gain, gain without inversion in any standard state basis is found to be achieved in our present model. The proposed scheme can have potential application in controlling the properties of an optical field on propagation through rare earth ion-doped fiber material or other solid-state, as well as atomic, media. (C) 2015 Optical Society of America