Molecular Nonlinear Optical Susceptibilities in Condensed Phases

摘要

A unified microscopic theoretical framework for the calculation of optical excitations in molecular and semiconductor materials was developed. The hierarchy of many-body density matrices for a pair-conserving many-electron model and the Frenkel excitons model was rigorously truncated to a given order in the radiation field. Closed equations of motion were derived for five generating functions representing the dynamics up to third order in the laser field including phonon degrees of freedom as well as all direct and exchange- type contributions to the Coulomb interaction. By eliminating the phonons perturbatively, we obtained equations that, in the case of the many-electron system, generalize the semiconductor Bloch equations, are particularly suited for the analysis of the interplay between coherent and incoherent dynamics including many-body correlations, and lead to thermalized excitons (rather than single-particle) distributions at long times. A complete structural equivalence with the Frenkel excitons model of molecular materials was established.