Resonant Bragg scatter of surface plasmons on nanohole arrays

Using microscopic imaging, we study the generation and propagation of beams of surface plasmons ( SPs) on a hexagonal metal nanohole array. We discuss the wavelength-dependent propagation, a Fano-type interference and the possibility to generate focused SP beams. Prominent forking of these beams is attributed to resonant ( Bragg) scattering from consecutive lattice planes. This claim is supported by a coupled-mode model.