Surface integral method for second harmonic generation in metal nanoparticles including both local-surface and nonlocal-bulk sources

We propose a numerical method, based on surface integral equations (SIE), for evaluating the second harmonic (SH) scattering by metal nanoparticles (NPs) of arbitrary shape, considering both nonlocal-bulk and local-surface SH sources, induced by the electromagnetic field at the fundamental frequency. We demonstrate that the contribution of the nonlocal-bulk sources can be taken into account through equivalent surface electric and magnetic currents. We numerically solve the SIE problem by using the Galerkin method and the Rao-Wilton-Glisson basis functions in the framework of the distribution theory. The accuracy of the proposed method is verified by comparing with the SH-Mie analytical solution. As an example of a complex-shaped particle, we investigate the SH scattering by a triangular nanoprism. This method paves the way for a better understanding of the SH generation process in arbitrarily shaped NPs and can also have a high impact on the design of novel nanoplasmonic devices with enhanced SH emission.