Direct observation of surface plasmon-polariton dispersion.

We describe a method to observe the directional emission of electromagnetic radiation produced by the radiative decay of surface plasmonpolaritons (SPPs) that allows the dispersion of the modes in k-space to be directly visualized. The method presented here opens up the possibility of characterizing the effect of a wide range of surface morphologies on SPP dispersion. As an example we show the formation of a stop-band for SPPs when the metal surface is modulated in the form of a diffraction grating.