Abstract

We present a microscopic mechanism of optical nonlinearity in organic conjugated polymers. We show that the bulk of the nonlinearity is determined by only two well-de fined channels, even though an infinite number of channels are possible in principle. Our results are valid for arbitrary Coulomb interactions, both short-range (extended Hubbard) and long-range (Pariser-Parr-Pople). We are able to explain the chain-length dependence of the third-order susceptibility in finite polyenes. We also explain the complete frequency dependence of the third-harmonic generation in trans-polyacetylene and in several polydiacetylenes within the same theoretical model.

© 1990 Optical Society of America