Engineering the second harmonic generation pattern from coupled gold nanowires

We numerically investigated second harmonic generation from systems composed of two coupled gold nanowires. The developed method allows one to arbitrarily change the shape of the wire cross section in order to explore the generated and scattered field patterns. Our results suggest that the overall second harmonic generation is related to the electromagnetic energy per unit length stored in the gap area between the wires. These geometrical considerations make further optimization possible. As an example we discuss the possibility to select dipolar emission and/or quadrupolar emission patterns. The selection mechanism responsible for this kind of emission can be traced back to the interaction between nonlinear sources with the surface plasmon resonance of the metallic wires.