Electromagnetic force on a metallic particle in the presence of a dielectric surface

By using a method, previously established, to calculate electromagnetic fie lds, we compute the force of Light upon a metallic particle. This procedure is based on both Maxwell's stress tensor and the couple dipole method. Wit h these tools, we study the force when the particle is over a flat dielectr ic surface. The multiple interaction of light between the particle and the surface is fully taken into account. The wave illuminating the particle is either evanescent or propagating depending an whether or not total internal reflection takes place. We analyze the behavior of this force on either a small or a large particle in terms of the wavelength. A remarkable result o btained for evanescent field illumination is that the force on a small silv er particle can be either attractive or repulsive depending on the waveleng th. This behavior also varies as the particle becomes larger.