Probing molecules adsorbed at the surface of nanometer colloidal particles by optical second-harmonic generation.

It is observed that optical second-harmonic generation from molecules adsorbed at the surface of nanometer size colloidal particles occurs at angles as large as 90 degrees away from the fundamental beam direction. This phenomenon can be rigorously described by the nonlinear Rayleigh-Gans-Debye theory and used for probing molecules adsorbed on nanometer size colloidal particles.