Dispersion of the nonlinear susceptibility in gold nanoantennas

Optical nanoantennas are excellent tools for accessing the nonlinear response of noble metals owing to the strong enhancement of light-matter interaction occurring in the near-field. For example, excitation of gold nanostructures with intense radiation triggers both coherent and incoherent phenomena such as third-harmonic generation (THG) [1] and multi-photon photoluminescence (MPPL), respectively [2, 3]. In this work, we study the interplay between these frequency conversion mechanisms in order to unveil the effective 2 (3) nonlinear response of metals.