Dielectric nanoantennas on epsilon-near-zero substrates: Impact of losses on second order nonlinear processes.

Second-harmonic generation from dielectric nanoantennas has been always studied and optimized by properly designing the radiating nanostructures. However, by placing the nanoantennas on different substrates one can optimize the amount of radiation that is back-scattered or lost in the substrate. Here we provide a detailed analysis on the properties of the substrates that can in turn enhance or suppress SHG conversion and collection efficiency from dielectric nanoantennas. More specifically, we analyzed second-harmonic generation from a cylindrical AlGaAs nanoantenna placed on epsilon-near-zero substrates with variable losses and found that the amount of radiation that is efficiently back-scattered and overall conversion efficiency strongly depends on the damping of the substrate rather than the optimization of the resonator. These results let us foresee a novel approach to improve nonlinear processes at the nanoscale and realize novel functionalities, such as beam steering and tailored antenna directivities thanks to the tunability of epsilon-near-zero materials. [ABSTRACT FROM AUTHOR]