Giant field fluctuations and characteristic lengths in optical properties of nano metal-dielectric films

We show that the intensities of the local electric field in metal-dielectric granular films may exhibit giant fluctuations in the optical and infrared range when the dissipation in metallic grains is low. It is found that these fluctuations are highly correlated in space. We introduce a new correlation length xi(e) that is the generic scale for the field inhomogeneity at resonance and percolation threshold. We predict an anomalous scattering of the incident light as well as significant enhancement of Rayleigh and Raman scattering in addition to various non-linear effects in a wide frequency range from the optical to far infrared region and in a range of concentrations around the percolation threshold which depends on frequency and loss factor. For frequencies much smaller than the resonant plasmon frequency, the relevant length is the coherence length L-omega. In the intermediate frequency region where ''anomalous'' absorption and enhanced scattering effects are observed one has to consider the interplay of the field fluctuations correlation length xi(e), the coherence length L-omega and the geometric percolation length xi(p). The main object of this paper is to illustrate this situation.