We investigate the effects of geometric anisotropy on the optical nonlinearity of metal nanocrystals in a dielectric host. By invoking the effective medium approximation for anisotropic composite media, we calculate the spectral density as a function of volume fraction and anisotropy. The results show that anisotropy not only changes the spectral function substantially and thereby has a pronounced effect on the nonlinearity, but also separates the absorption peak from the nonlinearity enhancement peak so that the figure of merit may be increased by orders of magnitude. We propose the use of electrorheological effect ͑e.g., during annealing͒ to realize these gains in optical nonlinearity. ͓S1063-651X͑97͒51008-7͔

We study intrinsic optical bistability in nonlinear composites of coated spheres, motivated by a recent experiment on small-particle heterogeneous systems. A self-consistent theory is applied to calculate the local fields in composites of coated spheres with a nonlinear dielectric core and a metallic shell, embedded in a linear host. To study the resonance response, we use the spectral representation and find that the local field in the core generally consists of two resonant terms, each of which has a form similar to that in the case of spherical inclusions but with a pole whose location and residue depend strongly on the dielectric constant of the core material as well as on the thickness of the shell. Thus by tuning the relevant microstructure parameters, it may be possible to reduce the threshold applied field and enhance the bistable response. Model calculations on various physical quantities are performed in accord with the experimental conditions.

No abstract

The effective-medium approximation (EMA) is developed to study the bulk effective response of a class of strongly nonlinear conducting composite media which obey a current-field ( J-E) relation of the form J=y~E~eE, where y is the nonlinear coefficient of the medium and p) 0. First, a variational approach is invoked for solving the electrostatic boundary-value problem of a spherical inclusion embedded in a host medium. Explicit asymptotic behaviors of the field distribution are derived at both large and small ratios between the coefficients of the constituents. Second, in an attempt to extend the approximation to the vicinity of a percolation threshold, we formulate the EMA for a two-component strongly nonlinear composite from the asymptotic behaviors of the field distribution. Scaling forms of the effective response are extracted and compared to a general scaling theory and an excellent agreement is found.

We investigate the polarization dependence of optical nonlinearity enhancement for a uniaxial anisotropic composite of metal nanocrystals in a dielectric host. Three cases are distinguished depending on whether the polarization is parallel, perpendicular or unpolarized with respect to the axis of anisotropy.