Near- to far-field imaging of free-space and surface-bound waves emanating from a metal nanoslit

The authors report the radiation pattern (radial and angular distribution of light intensity) of a silver nanoslit measured in the near- to far-field regimes. In most far fields, the 1/r dependence of intensity distribution, expected from a cylindrical wave emanating from a line source, is clearly observed. The glancing angle regime is found to be governed by the presence of surface plasmons, showing higher intensity closer to the metal surface. From the radiation patterns measured with a tilted-probe, radial-scan method, a branching ratio is quantitatively determined for the free-space radiation and surface plasmon components, emerging from the nanoslit. (c) 2008 American Institute of Physics.