Plasmon-Enhanced Second Harmonic Generation: from Individual Antennas to Extended Arrays
We analyze the emission yield of the second har-monic generation (SHG) from dense ordered a rrays of L-shaped Au nanoantennas within a well-defined collection an-gle and compare it to that of the isolated nanostructures de-signed with the same geometrical parameters. Thanks to thehigh antenna surface density, arrays display one order of mag-nitude higher SHG yield per unit surface with respect to iso-lated nanoantennas. The difference in the collected nonlinearsignals becomes even more pronounced by reducing the col-lection angle, because of the efficient angular filtering that canbe attained in dense arrays around the zero order. Albeit thiskey-enabling feature allows envisioning application of theseplatforms to nonlinear sensing, a normalization of the SHGyield to the number of excited antennas in the array reveals areduced nonlinear emission from each individual antenna el-ement. We explain this potential drawback in terms of reso-nance broadening, commonly observed in densely packed ar-rays, and angular filtering of the single antenna emission pat-tern provided by the array 0th order.