Abstract

The microscopic second-order ${\beta }_{ijk}^{S_n}\left(\sim {\omega }_3;{\omega }_1,{\omega }_2\right)$ and third-order ${\gamma }_{ijkl}^{S_n}\left(\sim {\omega }_4;{\omega }_1,{\omega }_2{\omega }_3\right)$ optical susceptibilities for conjugated molecular structures with real population of the S_n electronic excited state have been examined in detail and found to be generally enhanced by orders of magnitude compared to ${\beta }_{ijk}^{S_0}\left(\sim {\omega }_3;{\omega }_1,{\omega }_2\right)$ and ${\gamma }_{ijkl}^{S_0}\left(\sim {\omega }_4;{\omega }_1,{\omega }_2{\omega }_3\right)$ for systems that occupy the ground electronic state S₀. The enhancement mechanisms for excited-state nonlinear-optical processes will be discussed based on electron correlation theory of nonlinear-optical processes, which has been proven successful in explaining the ground-state susceptibilities ${\beta }_{ijk}^{S_0}\left(\sim {\omega }_3;{\omega }_1,{\omega }_2\right)$ and ${\gamma }_{ijkl}^{S_0}\left(\sim {\omega }_4;{\omega }_1,{\omega }_2{\omega }_3\right)$ for conjugated structures.

© 1991 Optical Society of America