Excitonic Optical Nonlinearity in Two- and Three-Dimensional Semiconductors

Recently, excitonic optical nonlinearities in direct-gap-semiconductors have attracted much attention and have been studied extensively [1]. Of particular interest are the nonresonant excitonic nonlinearities for their potential applications to ultrafast all-optical devices. The nonlinear optical properties of exciton systems result, in general, from the deviation of excitons from non-interacting ideal bosons. Not only the mutual interaction between excitons, but also the anharmonic excitonphoton interaction, contribute to the excitonic optical nonlinearity. In this paper we develope a simple theory for nonresonant excitonic optical nonlinearity in two- and three-dimensional semiconductors, treating the above mentioned two kinds of anharmonicity on an equal basis.