Optical response of metal-dielectric inhomogeneous films is considered. A Generalized Ohm's Law is formulated to relate the electric and magnetic fields outside to the currents inside the film. Computer simulations 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. Optical transmittance through a periodically inhomogeneous metallic film is strongly enhanced when the incident wave is in resonance with surface plasmon polaritons excited in the film, and can be exploited for optical switching. An analytical theory for extraordinary light transmittance through an optically thick metallic film with subwavelength holes is developed. The transmittance has sharp peaks due to the internal resonances in the holes. At a resonance, electric and magnetic fields are dramatically enhanced in the holes. These resonances are proposed to circuit light over a metallic film for distances on the nanometer length scale.
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