Surface-plasmon-enhanced nonlinearities in percolating 2-D metal-dielectric films: Calculation of the localized giant field and their observation in SNOM

The surfaces of percolating random 2-D metal-dielectric films consist of several spectral resonances, which have been calculated and afterward observed by near-field optical microscopy. These films show anomalous optical properties which are investigated in the first section. Nonlinear electrical and optical properties of metal-dielectric film percolation composites, though recognized very early, were not well understood. It is only recently that calculation of local fields in semicontinuous films allows us to define the enhancement factors of optical nonlinearities. These calculations are outlined from basic principles in the second section and compared with experimental results. An insightful approach to the same problem is to use a network description to represent the random system and discretize the equations satisfied by the scalar potential of the electrical field. We recall in the third section how such discretization leads to a Hamiltonian which is paradigmatic in the theory of Anderson localization. The imaging and spectroscopy of localized optical excitation in gold-on-glass percolation films was performed using near-field optical microscopy (SNOM), and the fourth section recalls the basic features of the experimental technique and describes the first experimental observation of ''hot spots'' in a nanometer-scale area.