The propagation of light through nanometer-sized structures is studied computationally by use of multiple-multipole method. A two-dimensional scanning near-field optical microscope structure is chosen as an example. The relevant near and far fields as well as some imaging properties are determined for the two principal polarizations. Strikingly different results are obtained for the two principal polarizations: for s polarization, strong field confinement in the gap region, high sensitivity of the radiation pattern to the presence of an object, and high contrast; for p polarization, higher signal level with low contrast. At small gap widths a substantial amount of radiation is coupled into the substrate at angles larger than the critical angle. Line scan simulations for λ = 488 nm indicate a resolution of approximately two times the optical slit width. Resolution and contrast can be optimized by the appropriate choice of detector orientation and angle of acceptance. Coherent superposition of the radiation emitted into different directions permits further improvements.
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