Strong Nonlinear Efficiency Enhancement in the Visible and UV Ranges from Plasmonic Gold Nanogratings

Nonlinear frequency conversion in metals has been a subject of theoretical and experimental research since the emergence of nonlinear optics, partially motivated by their high third order nonlinearities and despite its high absorption in the visible and near infrared spectral ranges. Enhancement of harmonic generation from gold surface has been demonstrated in different nanostructures, especially when excited by plasmonic resonances, and represents nowadays an active field of research with applications to functional nano-photonic devices. However, most of experimental results presented in literature often show only qualitative aspects of this enhancement, do not quantify the efficiency (presenting only arbitrary units) and are not in good agreement with the theoretical models set forward. Understanding the properties of light propagation and localization at the nanoscale, when light-matter interaction displays completely new and interesting physical phenomena, which are not well explained by conventional approximations, is a crucial step to design structures capable of enhancing the naturally low efficiency of harmonic generation in metals in the visible and UV ranges.