Theory of optical nonlinearity in pi-conjugated polymers and related materials.

Abstract

Within the framework of interacting-electron models, the optical nonlinearity in π-conjugated polymers is investigated theoretically. A complete microscopic many-body theory is developed for the mechanism of the third order nonlinearity in these materials. The universality and the predictability of the theory are well established. It is found that the bulk of the optical nonlinearity in conjugated polymers is determined by four essential states although all the excited states are involved. It is also found that electron-electron Coulomb interactions in one-dimensional systems play key roles in the nonlinear optical processes and are responsible for the observed spectroscopic features. The theoretical results are compared with experiments in wide variety of materials and excellent agreements between theory and experiments are obtained. With the essential-state theory, various experiments are explained within a single unified theory for the first time, and many controversies are resolved.