  The long-wavelength optical properties of a plasmonic crystal composed of
gold nanorod particles have been studied. Because of the strong coupling
between the incident light and vibrations of free electrons, bulk polariton
excitation can be induced and a polaritonic stop band will be created. An
analytical model has been established,which was confirmed by the numerical
simulations. The similarity between the plasmonic and ionic crystals, as well
as various optical properties, may be of both fundamental and practical
interests.
