Abstract
In this work, the first hyperpolarizability of Au x @Ag 100-x core-shell nanoparticles with x the gold molar fraction in percent and the gold core of which is 12 nm in diameter, is determined and compared to that of their corresponding laser annealed nanoparticles using hyper Rayleigh scattering experiments. Laser annealing transforms the initially composite Au x @Ag 100-x core-shell nanoparticles into alloyed Au x Ag 100-x homogeneous nanoparticles, providing a reference for comparison. It is observed that the evolution with the relative molar ratio between gold and silver of the first hyperpolarizability magnitude of both the Au x @Ag 100-x core-shell and the alloyed Au x Ag 100-x nanoparticles is driven by the SPR resonance enhancement occurring at the harmonic wavelength due to red shifting of the SPR band away from the harmonic wavelength. Furthermore, the first hyperpolarizability magnitude of the Au x @Ag 100-x core-shell nanoparticles is found to be about three orders of magnitude larger than that of the annealed alloyed Au x Ag 100-x nanoparticles. This feature may be attributed to the existence of the two nonlinearities, namely the surface nonlinearity due to the surrounding mediumsilver layer interface and the silvergold metal -metal interface constructively contributing due to their close localization. The core-shell morphology is thus highly beneficial in view of applications as compared to the alloyed one.