Photon management in harmonic generation at the nanoscale

Nonlinear nanophotonics has recently attracted enormous interest for light-based technologies with potential applications ranging from light sources, tunable components, and ultrafast metadevices [1–4]. Nanoscale-designed components do certainly integrate different functionalities in nanophotonics circuits by improving miniaturization and allowing the replacement of bulky components [5–7]. One key asset in nonlinear nanophotonics is the capability to achieve strong light-matter interaction through optical resonances in subwavelength nanostructures [8,9]. Differently from bulk macroscopic media, where the efficiency of nonlinear optical phenomena is mainly determined by intrinsic nonlinear properties and phase-matching conditions, in nonlinear nanophotonics the key challenge is to engineer the nonlinear scattering from nanoscale elements by molding the local electromagnetic field to achieve the desired behavior. Since the nonlinear response strongly depends on localized resonant effects in nanostructures, both modal andmultipolar control ofthe nonlinear response are extensively exploitedfor boosting the near-field interaction and designing the radiation directionality [10]. The nanoelements, also known as nanoantennas, are typically made of metallic or dielectric materials.