Investigation of the nonlinear optical response from arrays of Au bowtie nanoantennas

We demonstrate that the optical response of a single Au bowtie nano-antenna (BNA) can be favorably modified to increase the local intensity by a factor of 103in the feed gap region when a periodic array of BNAs are used. We use the periodicity of the arrays as an additional degree of freedom in manipulating the optical response and investigate the behavior of the resultant nonlinear emission, which include second harmonic generation (SHG), two-photon photoluminescence (TPPL), and an additional photoluminescence that cannot be attributed to a single multiphoton process. We discuss the effects of the array with respect to the nonlinear emission and also find that the considerable field enhancement of our antenna system leads to a broadband continuum whose spectral response is highly controllable. Resonantly excited arrays of BNAs were seen to exhibit a remarkably uniform emission over 250 nm of the visible spectrum. In addition, our analysis suggests that high field enhancements, as well as resonance matching, may not be the only preconditions for enhanced nonlinear emission. To our knowledge, this is the first report of implementing optical antennas in an array to favorably augment its optical response.