Figure 7. Characterization of randomness in optical near-fields by the angular spectrum-based theoretical analysis.

(a,b) A differently-specified dipole pair gives a different angular spectrum. (a) Moderate randomness yields significantly different spectra, whereas (b) less randomness gives nearly identical spectra. (c) The incidence patterns of the near-field electric field intensity, given by the integral of the angular spectrum, based on dipole pairs that follow random statistics show some variation even as the distance from the silver nanostructures increases. (d) On the other hand, with less-random dipole pairs, such a tendency is not observed. These are clear manifestations of the hierarchical attributes of optical near-fields.