| Abstract
| - Hyper Rayleigh scattering is used to investigate the second harmonic light collected from a liquid suspensionof silver metallic particles, the diameter of which ranges from 20 nm up to 80 nm. From the dependence ofthe quadratic hyperpolarizability as a function of the particle size, it is inferred that retardation effects of theelectromagnetic fields play a major role in the frequency conversion process. The hyper Rayleigh scatteringintensity was also recorded as a function of the angle of polarization of the incident fundamental wave. Forthe particles with a diameter of 20 nm, the harmonic response is dominated by the dipolar contribution arisingfrom the deviation of the particle shape from that of a perfect sphere. It is therefore concluded that the originof the nonlinear polarization for the smaller silver particle sizes arises from the surface similarly to the caseof the gold metallic particles. For larger diameter particles, retardation effects in the interaction of theelectromagnetic fields with the particles cannot be neglected any longer, and the response deviates from thepure dipolar response, exhibiting a strong quadrupolar contribution. The weighting parameter ζV is used,equaling unity for a pure quadrupolar contribution and vanishing for a pure dipolar response, in order toquantify the relative magnitude of these two dipolar and quadrupolar contributions. The size dependence ofthis parameter obtained for the silver particles is compared to the dependence previously reported for goldmetallic particles.
|
