Second Harmonic Generation from Gold and Silver Nanoparticles in Liquid Suspensions

A general review of the second harmonic (SH) light scattered from aqueous suspensions of small gold and silver metallic particles is presented. The first part is devoted to the general theory of the SH generation from particles in order to discuss the incidence of the shape of the particles and the retardation effects of the electromagnetic fields on the total SH scattered field. The next part focuses on the problem of the polarization fields, a problem rather specific to metallic particles. Because of their strong polarizability and the possibility of resonance enhancements through surface plasmon (SP) excitations, the exciting field cannot be taken as the incident field only but rather as the superposition of the incident and the polarization fields. An illustration of this problem is presented with the determination of the exact origin of the SH response from metallic particles. This experimental section presents two different sets of data: the size dependence of the SH intensity and the polarization patterns recorded in the geometrical configuration of Hyper Rayleigh Scattering. SP resonance enhancements of the absolute values of the hyperpolarizabilities are then discussed before a presentation of the SH response of aggregating suspensions of particles and their possible applications is given