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Localized plasmon-enhanced optical response: harmonic generation and polarization effects

It is now known that plasmon oscillations supported by nanostructured metal thin films of fractal morphology, can result in large local fields and strong enhancement of optical phenomena, for example Raman scattering. The localized plasmons, acting like nano-antennas, can concentrate very large electromagnetic energy in nanometer- sized areas, hot spots, and provide particularly strong enhancement of optical responses, in a very broad spectral range. Our new experimental results show up position dependence of the hot spots on the polarization state of the light. Moreover as expected from recent theoretical predictions, on this kind of thin percolating films, there is a dramatic enhancement of the second harmonic generation (2(omega) ) out of the specular directions. This unusual diffuse SHG could be connected to possible chirality of the percolating metallic films, which is expected to manifest itself as change in the hot-spot distribution for the left and right circularly polarized incident light.