We present a physical model for the conversion of the evanescent photons into propagating photons detectable by an imaging system. The conversion mechanism consists of two physical processes, near-field Mie scattering enhanced by morphology dependant resonance and vectorial diffraction. For dielectric probe particles, these two processes lead to the formation of an interference-like pattern in the far-field of a collecting objective. The detailed knowledge of the far-field structure of converted evanescent photons is extremely important for designing novel detection systems. The model is also applicable for determination of the near-field force exerted on small particles situated in an evanescent field. This model should find broad applications in near-field imaging, optical nanometry and near-field metrology.
A mathematical model for understanding near-field Mie scattering, as used in optical trap nanomery for single molecule detection, is developed. Both perpendicular and parallel polarization states of incident electromagnetic waves have been considered. Simulations under different incident angles, and refractive indices of trapped particle have been investigated. Half-space signal strength is studied on the base of the calculated three-dimensional scattered electromagnetic field.