Spatial distribution of enhanced optical fields in one-dimensional linear arrays of gold nanoparticles studied by scanning near-field optical microscopy.

We visualized the enhanced optical field distributions in one-dimensional linear array structures of gold nanospheres by using scanning near-field optical microscopy. The characteristic field distribution depends on the chain length of the one-dimensional structures. The distribution of optical field is reproduced qualitatively by model calculations based upon finite-difference time-domain (FDTD) method. From the analysis, we have found that the characteristic distribution of the enhanced field arises from interparticle interactions, which cause propagation of the plasmon excitation in the inner part of the linear array, and trapping of it by a localized mode at the edges.