Effective medium approximation for weakly nonlinear metal/dielectric composites with shape distribution

The effective linear and nonlinear optical properties of metal/dielectric composite media in which the components possess certain shape distribution are investigated. Based on a self-consistent condition of zero net dipole moment, we derive Bruggeman-type effective medium approximation with shape distribution, which has been established using the reciprocity theorem [Solid State Commun. 106 (1998) 83]. Spectral density functions are analytically obtained to obey the requirements of Bergman spectral representation. The real part of the effective conductivity, the energy-loss function and the linear optical absorption are calculated accordingly. By invoking the mean-field approximation, we further evaluate the effective optical nonlinearity enhancement. Numerical results show that the nonlinearity enhancement maximum is separated from the optical absorption one especially at large volume fraction. Moreover, the optical nonlinearity enhancement and the figure of merit are found to be greatly enhanced near the bulk plasma frequency. (C) 2003 Elsevier Science B.V. All rights reserved.