Linear and nonlinear properties of high-quality L-shaped gold nanoparticles

The nonlinear optical response of metal nanostructures is sensitive to sample quality. Small deviations in the structural features of the particles result in large changes in the nonlinear response. This problem is particularly evident in second-harmonic generation, which is sensitive to sample symmetry. Local defects give rise to chiral symmetry breaking and effective quadrupole effects. Recent achievements in sample fabrication make it possible to obtain metal nanostructures with very high quality and tailorable nonlinear optical properties. Our study shows that the nonlinear optical response of high-quality samples is driven by electric-dipole interactions and is no longer uncontrollable as it was in the past for low-quality samples. Improving sample quality has also made it possible to observe the effect of higher-order resonances on the nonlinear response.