Non linear optical properties of nanostructured metallic surfaces

Nano-patterned metal surfaces on dielectric substrates are become very important in nanoscale optical devices such as molecular sensors, second harmonic emitters, negative index materials. Among these, self-organised approaches are a promising alternative to the conventional lithographic or scanning lithography methods, since allow low cost patterning of large macroscopic surface in a single step event. The possibility to construct tailored artificial nanostructures by acting on simple experimental parameters opens new exciting possibilities in the nanoscale technology. In this work we explored the second harmonic emission properties in transmission of self-organized gold nanowires on dielectric substrates. Second harmonic emission from thin metal surfaces is limited by several constrains: for example the emission is forbidden at normal incidence and the emission is always polarized along the plane of incidence of the pumping light. In our samples selected morphology allows to overcome such constrains leading to high emission at normal incidence, polarization of the emission guided by the wires orientation. The angular dependence of the generation efficiency was measured on test samples whose thicknesses of the wires range from 5 nm to 40 nm. The efficiency results of a value larger with respect to samples with equivalent thickness and different morphology.