Reaching the dipole limit in second-harmonic generation from gold nanoparticles

Second-harmonic generation from arrays of gold nanoparticles exhibits interference between electric-dipole and higher multipole (magnetic-dipole and electric-quadrupoles) effects. We show that improved sample quality suppresses the role of higher multipole effects in second-harmonic generation from L-shaped gold nanoparticles, thereby opening the possibility of reaching the pure dipole limit. This is a prerequisite for nonlinear metamaterials with tailorable properties.