Abstract

Metal island films consist of ultrasmall oblate spheroidal particles, typically 20 nm in diameter. In such particles incident light can resonantly drive localized plasma oscillations, which lead to an enhanced field inside and at the surface of the particles. Therefore, optical second harmonic generation (SHG) originating at the surface of the particle due to the strong discontinuity of the normal component of the incident light field and to symmetry breaking of the surface is also enhanced. On the other hand, if the particles have rotational symmetry due to the preparation technique used so far at vertical incidence of the fundamental beam, all contributions to the SH radiation compensate. At oblique incidence, however, the nonlinear polarization has an appropriate component, and SHG is observed in reflection similar to properties at a flat metal surface.

© 1990 Optical Society of America