| The aim of this work is to investigate theoretically the optical properties in macroscopic inhomogeneous granular composite media.(1) The nonlinear optical response in a metal-dielectric composite containing interfacial layers is studied in dilute limit as a function of temperature. We find: (a) The effect of interfacial layers is more dominant at low temperature than at high; (b) Given frequency, more large volume fraction of metal component, and more prominent metallic property inside interfacial layers; (c) Given volume fraction, increasing frequency changes interfacial property from dielectric-like to metal-like; (d) There exits an optimum interfacial layer, which makes the effective nonlinearity exhibit a maximum. It is shown that the effective nonlinear optical response can be largely enhanced, only if the interfacial layer, incident frequency, temperature, and the volume fraction of component are chosen appropriately.(2) The particle-shape effect on the effective nonlinear optical response in a random granular composite medium is investigated, which includes two components of different linear conductivity, nonlinear exponent as well as particle shape. The effective nonlinear response is related to the granular concentration, the depolarization factor, and the conductivity of component. We study two systems, one of which is that the composite is composed of better-conductor particles ex-hibitting high-order nonlinearity. and linear poorer-conductor particles, the other of which is that the composite contains poorer-conductor particles having high-order nonlinearity, and linear better-conductor particles. In order to check the validity of this theory, we bring it into 2D. After the comparison with 2D numerical simulation data, good agreement can be found. Hence it is also possible to gain enhanced effective nonlinear optical response by choosing most suitable particle shape.(3) T-matrix approach is developed to investigate the nonlinear AC response of a Kerr composite. Inside it, parallel nonlinear cylindrical grains with or without concentric linear shells are randomly distributed in a linear host. For an applied sinusoidal field, the induced field in the composite may include components with frequencies at higher harmonics. The explicit expressions for effective linear conductivity and nonlinear susceptibilities at arbitrary order harmonic generations are derived in the dilute limit of the nonlinear component. Hence arbitrary high order harmonics can be induced from one Kerr component. It is thus concluded that not only perturbative method but also T-matrix approach can be used to deal with the nonlinear AC response.(4) Two effective-medium-approximation equations, i.e., EMA I and EMA II, derived under two different self-consistency conditions, are used to discuss the optical threshold of a certain metal-dielectric composite. All the particles shaped as ellipsoid are randomly located in this composite. With the aid of Drude model, we consider temperature effect again. The explicit expressions for percblation thresholds /c are derived, respectively. Take Au/SiO^ composite as numerical calculation. For both EMA I and EMA II, we find: (1) /* is always larger than fc, as certified by an RLC circuit; (2) Larger temperature, larger optical threshold. As for the case of spherical particle compared with those of ellipsoidal particles at a given temperature, EMA I allows fc or /* to take a maximum value, whereas EMA II a minimum one. Further discussion yields the conclusion that EMA I is more physical than EMA II, as obtained in a former work.
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