Surface contribution to the electric dipole moment near an interface, and its effect on power emission.

Abstract

When a small particle is located near an interface, its electric dipole moment can be induced by laser irradiation. Since the laser light reflects at the interface, this leads to an interference pattern, and the dipole moment is determined by this total field. In addition, the dipole radiation emitted by the particle reflects at the interface, and this field adds to the external field. In this fashion, the dipole moment is altered by the field it emits, and as such the emitted radiation modifies its own source. We have derived a simple expression to take this back action into account. We introduce two resolvent functions, Υ‖(h) and Υ⊥(h), which depend on the dimensionless distance h between the particle and the interface. These functions exhibit resonance features due to the underlying back-action mechanism. It is shown that two, one, or no resonance peaks appear in the induced dipole moment. Whether these peaks are present depends on the parameters under consideration. The power emitted by the particle depends on h due to interference between the source radiation and the reflected radiation. With the surface induced contribution to the dipole moment included, an additional h dependence appears. This dependence shows the resonance peaks, which may be amenable to experimental observation.