Coherent light scattering and resonant energy transfer in an apertureless scanning near-field optical microscope
We investigate the interaction of two molecules or nanosized particles with a nearly resonant laser field under the tip of an apertureless near-field microscope. We show that interference of several scattering channels provides means for enhanced spatial resolution. The visibility of two separate nano objects is considered, and a natural definition emerges for the resolution of the apertureless microscope operating under conditions of nearly resonant illumination. The probe tip creates an additional coupling channel between the two molecules, and thus affects the energy transfer between them. We demonstrate that the tip can either enhance or suppress this transfer. Two models for the tip geometry are considered: a simplified pointlike dipole, and a more realistic elongated spheroid. Quantitative results are obtained for the dependence on irradiation frequency and tip position for dielectric as well as metallic tips. In particular, specific results are obtained for a silver tip under conditions of plasmon resonance, and we show that under fully resonant conditions the tip may enhance the intermolecular energy transfer by nearly two orders of magnitude.