Near-field optical excitation as a dipole-dipole energy transfer process

The process of fluorescence excitation in the scanning near-field optical microscope (SNOM) is considered as a dipole-dipole resonance energy transfer process between a molecule under study and a SNOM aperture, which can be treated as a magnetic-type point dipole. It is shown that such an approach satisfactorily describes the conditions of the usual SNOM fluorescence experiments. Fluorescence excitation dependence on the polarization of the incident light and medium refraction index have been obtained. The equation to calculate the resonance dipole-dipole energy transfer radius (which is a natural unit of a SNOM's longitudinal resolution) is derived. Those cases where such a radius is of the order of the SNOM aperture, and thus single dipole, can strongly influence the radiation conditions are discussed briefly.