Abstract
Field enhancement due to localized surface plasmons excited in nanosize Ag and coated Ag spheres has been numerically studied using the Mie theory. It has been found that light intensity enhancement becomes maximum at an appropriate diameter of spheres. This maximum has been expected to be determined from mediation of a size-dependent light-confinement effect and a size-dependent dielectric constant of Ag spheres. Such field enhancement should play a crucial role in observing strong nonlinear optical effects. For a nanosize metal sphere coated with a Kerr-nonlinear film, we have succeeded in finding optical switching and optical bistability phenomena using the modified Mie theory.