Nonlinear optical response from arrays of Au bowtie nanoantennas.

We demonstrate that the optical response of a single Au bowtie nanoantenna can be favorably modified to increase the local intensity by a factor of 10(3) in the feed gap region when a periodic array of antennas are used. We find that the array periodicity can be used to modulate and shape the spectral emission. An analysis of the emission confirms the presence of second-harmonic generation and two-photon photoluminescence, typical of gold nanostructures, but also reveals a portion of the emitted spectrum that cannot be attributed to a single multiphoton process. Our investigations have important implications for understanding the role of resonant nanostructures in designing optical antennas for next-generation photonic technologies.