Collective many-body resonances in condensed phase nonlinear spectroscopy

The optical response of assemblies of electronic and vibrational chromphores may show two types of collective resonances induced by either direct short-range coupling (multiple quantum coherence) or by long-range macroscopic local field and cascading processes. Using a unified approach for both types of resonances, we demonstrate how specific signatures in line shapes, phase profiles, and density dependence may be used to distinguish between the two. New high harmonic resonances at combinations and multiples of optical frequencies of the single exciton transitions are predicted in the k1+k2−k3 four wave mixing signal for several model systems.