LIGHT-PROPAGATION THROUGH NANOMETER-SIZED STRUCTURES - THE 2-DIMENSIONAL-APERTURE SCANNING NEAR-FIELD OPTICAL MICROSCOPE

The propagation of light through nanometer-sized structures is studied computationally by use of multiple-multipole method. A two-dimensiona l scanning near-field optical microscope structure is chosen as an exa mple. The relevant near and far fields as well as some imaging propert ies are determined for the two principal polarizations. Strikingly dif ferent results are obtained for the two principal polarizations: for 8 polarization, strong field confinement in the gap region, high sensit ivity of the radiation pattern to the presence of an object, and high contrast; for p polarization, higher signal level with low contrast. A t small gap widths a substantial amount of radiation is coupled into t he substrate at angles larger than the critical angle. Line scan simul ations for lambda = 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 accept ance. Coherent superposition of the radiation emitted into different d irections permits further improvements.