Local electric and magnetic fields in semicontinuous metal films: Beyond the quasistatic approximation

A theory of optical, infrared, and microwave response of metal-dielectric inhomogeneous films is developed. The generalized Ohm's law is formulated for the important case, when the inhomogeneity length scale is comparable with or larger than the skin (penetration) depth in metal grains. In this approach electric and magnetic fields outside a film can be related to the currents inside the film. Our computer simulations, with the use of the generalized Ohm's law approximation, reproduce the experimentally observed prominent absorption band near the percolation threshold. Calculations show that the local electric and magnetic fields experience giant spatial fluctuations. The fields are localized in small spatially separated peaks: electric and magnetic hot spots. In these hot spots the local fields (both electric and magnetic) exceed the applied field by several orders of magnitude. It is also shown that transmittance of a regular array of small holes in a metal film is strongly enhanced when the incident wave is in resonance with surface polaritons in the film. In addition, there is a skin resonance in transmission, which is of a purely geometrical nature.