Electromagnetic field fluctuations and optical nonlinearities in metal-dielectric composites

A scaling theory of local held fluctuations and optical nonlinearities is d eveloped for random metal-dielectric composites near a percolation threshol d. The theory predicts that in the optical and infrared spectral ranges the local fields are very inhomogeneous and consist of sharp peaks representin g localized surface plasmons (s.p.). The localization maps the Anderson loc alization problem described by the random Hamiltonian with both on- and off -diagonal disorder. The local fields exceed the applied field by several or ders of magnitudes resulting in giant enhancements of various optical pheno mena. A new numerical method based on the developed theory is suggested. Th is method is employed to calculate the giant held fluctuations and enhancem ent of various optical processes in 2D metal-dielectric composites - semico ntinuous metal films. The local field fluctuations appear to be highly corr elated in space. These fluctuations result in dramatically enhanced Rayleig h and Raman light scattering. The scaling analysis is performed to describe the giant light scattering in a vicinity of the percolation threshold. The developed theory describes quantitatively enhancement of various nonlinear optical processes in percolation composites. It is shown that enhancement depends strongly on whether nonlinear multiphoton scattering includes an ac t of photon subtraction (annihilation). The magnitudes and spectral depende ncies of enhancements in optical processes with photon subtraction, such as Raman and hyper-Raman scattering, Kerr refraction and four-wave mixing, ar e dramatically different from those processes without photon subtraction, s uch as sum-frequency and high-harmonic generation. Electromagnetic properti es of metal-dielectric crystals and composites beyond the quasistatic appro ximation are also studied. Equations of macroscopic electromagnetism are pr esented for these systems. Both linear and nonlinear optical responses are considered in the case of a strong skin effect in metal grains. It is shown that the magnetic field undergoes giant spatial fluctuations. Scaling prop erties of the local magnetic field and its high-order moments are analyzed. (C) 2000 Elsevier Science B.V. All rights reserved.