title: Theory of nondegenerate nonlinear optical susceptibilities of graded composites with high-volume fractions.
abstract: We present a theory for the effective nondegenerate third-order nonlinear optical susceptibility (NDTNOS) of composite media in which the graded metallic particles with weak nonlinearity and the linear dielectric grains are randomly distributed. In combination with an effective medium approximation, the recently established nonlinear differential effective dipole approximation (NDEDA), which is valid for the degenerate third-order optical nonlinearity of the composites in the dilute limit, is generalized to deal with the effective NDTNOS of graded composites of high-volume fractions. Numerical results show that for high-volume fractions, the presence of gradation makes the effective NDTNOS enhanced, but the linear optical absorption reduced, thus, yielding an attractive figure of merit. In addition, by using NDEDA and Maxwell-Garnett approximation, we study the effective NDTNOS of the graded composite media with the Hashin-Shtrikman microgeometry. The nondegenerate optical nonlinearity enhancement is found to be sensitive to the composite topology.
authors.affiliation: Department of Physics, The Chinese University of Hong Kong, Shatin, NT, Hong Kong. lgaophys@pub.sz.jsinfo.net
authors.forename: Lei
authors.initials: L
authors.lastname: Gao
authors.forename: K W
authors.initials: KW
authors.lastname: Yu