Dipolar second order nonlinear effects from gold nano-antennas by controlling radiation phase

A recurring theme in nanophotonics is the ability of metal nanostructures to imbue artificial materials with new function. Here we explore metallic nano-antennas as the building blocks of second order nonlinear optical metamaterials. While nonlinear effects in natural materials must gradually accumulate weak nonlinearity across macroscopic crystal dimensions, a small volume of metamaterial, and even isolated antennas, can create surprisingly strong effects. We show that the nonlinear selection rules that typically prevent dipolar SHG from nano-antennas can be engineered so they effectively radiate SHG. This provides access to other second order optical processes, which we have recently observed.