Hybrid architectures made of nonlinear-active and metal nanostructures for plasmon-enhanced harmonic generation

Abstract Generation of laser light harmonics is one of the nonlinear optical phenomena offering unique opportunities for the development of applications in fields like photonics, materials science, chemistry, or medicine. Traditional nonlinear crystals are millimetre-scale, thus current trends of device miniaturization require alternative strategies for generating harmonics from micro- and nano-scaled objects. Recently, several research groups showed that plasmonic metal nanostructures can be useful for generating harmonics from nanoscale volumes. As a more efficient alternative to full metallic nanostructures, an increasing amount of effort is currently put into the study of hybrid nano-architectures, obtained by combining a nonlinear-active material - as the source of harmonics, and a plasmonic nanostructure - as the amplifier of the generated harmonics. Here, we review the current state of the art concerning laser harmonics generation with hybrid nonlinear/noble metal nanostructures. After giving brief introductions into the fields of harmonics generation and plasmonics, we highlight the different kinds of hybrid nanostructures that were successfully employed to generate enhanced second-, third- or higher harmonics. We describe nanofabrication approaches, but also findings related to the physical mechanisms involved in the enhancement process, such as correlations between surface plasmon resonances and harmonic generation efficiency or the origin of the enhanced signal.