<title>Nonlinear optical response of interacting excitons</title>

Abstract

In the vicinity of the direct intrinsic absorption threshold in semiconductors nonlinearity of the optical response is dominated by manybody interaction effects in the polarization cloud accompanying the propagation of the electromagnetic field. This polarization is essentially the system of electron-hole pairs. Its evolution with increasing density (radiation intensity) is analyzed in the framework of simplified model substituting effective short range pseudopotential instead of real Coulomb potential. At moderate densities excitonic resonance is essentially modified by the formation of excitonic molecules. Multistable behavior arise. Transient processes are discussed including gradual formation of bound state-excitons and excitonic molecules. The latter manifest themselves in anomalously large four-wave mixing amplitude.