3RD-ORDER OPTICAL NONLINEARITY ENHANCEMENT THROUGH COMPOSITE MICROSTRUCTURES

Formulas for the evaluation of third-order optical susceptibility of n onlinear composites are derived in the mean-field approximation for fo ur different microstructures corresponding to those described by the M axwell-Garnett theory, the Bruggeman self-consistent theory, the Sheng theory, and the differential effective medium theory. A commonly enco untered error in the literature is pointed out, with the correct formu lation given, Anomalous dispersion, i.e., surface plasmon resonance of coated spheres, is identified as the source of large optical nonlinea r susceptibility enhancement. Examples are given that demonstrate this microstructural enhancement effect. Comparison with experimental data on AuSiO2 granular films shows that large enhancement in the third-or der Kerr-type nonlinear susceptibility can indeed be realized at compo sitions below the percolation threshold, with prediction of even large r enhancement possible. (C) 1998 Optical Society of America.