Nonlinear circular dichroism in self-organized metal nanowires arrays

Metal nanostructures supported on dielectric substrates have attracted great interest as building blocks of nanoscale optical devices such nano-plasmonic devices or planar metamaterials. In this framework artificial circular dichroism [1] is investigated for developing novel devices for active polarization controllers, like rotators and modulators and high efficient molecular sensors. Here we report the experimental observation of nonlinear extrinsic chirality [2] (circular dichroism) of the second harmonic (SH) field generated by self-organized gold nanowire arrays with sub-wavelength periodicity [3]. In this material the chirality arises from the curvature of the self-assembled wires, producing a lack of symmetry at oblique incidence [2]. Such circular dichroism in the SH field is the evident signature of the sample morphology and can be used in order to develop more efficient molecular sensors, based on metal enhanced fluorescence or surface enhanced Raman scattering.