  We describe both theoretically and experimentally the existence and
excitation of confined modes in planar arrays of gold nanodisks. Ordered 2D
lattices of monodispersive nanoparticles are manufactured, embedded in a silica
matrix, and exposed to evanescent prism-coupling illumination, leading to dark
features in the reflectivity, which signal the presence of confined modes
guided along the arrays. We find remarkable agreement between theory and
experiment in the frequency-momentum dispersion of the resonances. Direct
excitation of these modes reveals long propagation distances and deep
extinction features. This characterization of guided modes shows the great
potential of metallic particle arrays for optical signal processing and distant
sensing applications.
