We prepare arrays of gold nanoparticles that include both noncentrosymmetric particles with a second-order nonlinear optical response (active particles) and centrosymmetric particles with no second-order response (passive particles). The plasmon resonances of the active and passive particles are at distinct wavelengths, yet the passive particles modify the electromagnetic modes of the structure in such a way that second-harmonic generation from the active particles is enhanced. Our results provide a completely new concept for optimizing the nonlinear responses of metamaterials.
Czaplicki, R., Husu, H., Siikanen, R., Mäkitalo, J., Kauranen, M., Laukkanen, J., Lehtolahti, J., & Kuittinen, M. (2013). Enhancement of second-harmonic generation from metal nanoparticles by passive elements. Physical Review Letters, 110(9), . https://doi.org/10.1103/PhysRevLett.110.093902