STUDY AND CHARACTERIZATION OF NEW RESONANCES IN THE FREQUENCY SPACE IN A 2-LEVEL SYSTEM WITH NONZERO PERMANENT DIPOLE-MOMENTS

Properties of the resonance peaks associated with the non-degenerate f our-wave mixing signal in a two-level molecular system with non-zero p ermanent dipole moments are studied in the space defined by the pump ( omega(1)) and probe (omega(2)) frequencies. An analytical expression f or the Fourier components of the nonlinear homogeneous macroscopic pol arization are obtained, where the terms responsible for the oscillatio n (at frequency omega(3) = 2 omega(1) - omega(2)) of the populations a nd coherences are also identified. Topological properties of the resul ting nonlinear spectra are studied in frequency space using three-dime nsional curves and contour plots. We have additionally identified the dominant contributions of the coherence and/or population that determi ne the intensity and the spectral linewidth. The critical quantities f or the present analysis are the transition and permanent dipole moment s when the rotating-wave approximation (RWA) is not considered.