plasmon-enhanced second harmonic generation: from individual antennas to extended arrays

We analyze the emission yield of the second harmonic generation (shg) from dense ordered arrays of l-shaped au nanoantennas within a well-defined collection angle and compare it to that of the isolated nanostructures designed with the same geometrical parameters. thanks to the high antenna surface density, arrays display one order of magnitude higher shg yield per unit surface with respect to isolated nanoantennas. the difference in the collected nonlinear signals becomes even more pronounced by reducing the collection angle, because of the efficient angular filtering that can be attained in dense arrays around the zero order. albeit this key-enabling feature allows envisioning application of these platforms to nonlinear sensing, a normalization of the shg yield to the number of excited antennas in the array reveals a reduced nonlinear emission from each individual antenna element. we explain this potential drawback in terms of resonance broadening, commonly observed in densely packed arrays, and angular filtering of the single antenna emission pattern provided by the array 0th order.