DYNAMICS OF COHERENT POPULATION TRAPPING STATES IN DENSE SYSTEMS

We investigate the characteristics of the coherent population trapping (CPT) states in a dense medium. We incorporate the local-field effect s into the density-matrix equations and numerically integrate the resu lting nonlinear equations. We find that the CPT state is essentially u naffected by the local-field effects for all ranges of field strengths ; however, states close to the CPT state are sensitive to them. We dem onstrate a dispersive behavior near the CPT state in a dense medium be sides important asymmetries and shifts of the Autler-Townes peaks in a bsorption spectra. We also study the effect of local fields on the dyn amics before CPT occurs and show that the evolution to the CPT state i s delayed due to the local fields. We extend our calculation to analyz e lasing without inversion in a dense medium of Lambda systems.