Surface modes in plasmonic crystals induced by diffractive coupling of nanoantennas

Lattice surface modes in two-dimensional plasmonic crystals of metallic nanoantennas are sustained by the diffractive coupling between localized plasmon resonances. We have investigated experimentally the dispersion of these modes by combining variable-angle transmittance and reflectance spectroscopy. Transmittance spectra through plasmonic crystals reveal quality factors for these modes exceeding 150 in the near infrared, 30 times higher than the quality factor associated to localized plasmon resonances. We have derived the characteristic lengths of the lattice surface modes, distinguishing a regime in which the group velocity is reduced while the mode intensity is strongly confined near the nanoantennas and a regime in which the surface mode propagates over several unit cells of the plasmonic crystal.