Second-harmonic generation of electrostatic origin from extreme nanosized bi-metal structures.

We experimentally studied the second-harmonic generation from 5 and 25 nm-sized gold nanoparticles positioned 5-75 nm away from a thick silver layer. While known theories fail, a proposed model that takes into account the quasi-static interaction of the particles with the underlying silver layer shows good agreement with measured data. This agreement points to the possibility of nonlinear optics based on the interaction between extreme nanoscaled particles, rather than emanating from the particles themselves.