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

A theory of optical, infrared, and microwave response of metal-dielectric i nhomogeneous films is developed. The generalized Ohm's law is formulated fo r the important case, when the inhomogeneity length scale is comparable wit h or larger than the skin (penetration) depth in metal grains. In this appr oach electric and magnetic fields outside a film can be related to the curr ents inside the film. Our computer simulations, with the use of the general ized Ohm's law approximation, reproduce the experimentally observed promine nt absorption band near the percolation threshold. Calculations show that t he 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 a lso shown that transmittance of a regular array of small holes in a metal f ilm is strongly enhanced when the incident wave is in resonance with surfac e polaritons in the film. In addition, there is a skin resonance in transmi ssion, which is of a purely geometrical nature.