We report spatial domain measurements of the damping of surface-plasmon excitations in metal films with periodic nanohole arrays. The measurements reveal a short coherent propagation length of a few microm inside nanohole arrays, consistent with delays of about 10 fs in ultrafast transmission experiments. This implies that the transmission spectra of the entire plasmonic band-gap structure are homogeneously broadened by radiative damping of surface-plasmon excitations. We show that a Rayleigh-like scattering of surface plasmons by the periodic hole array is the microscopic origin of this damping, allowing the reradiation rate to be controlled.

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When light illuminates a thick metal film perforated with small holes, shadows appear. At the nanoscopic level, however, light can be emitted predominantly from the metal surfaces between the holes—shadows can be indeed brighter than the lighted holes. The symmetry of the near-field emission pattern is determined by the symmetry of the surface plasmon waves. Surprisingly, these nanoscopic emission patterns from the metal can be preserved to the far-field region, where the pattern becomes sinusoidal. This unusual behavior of light emission from the shadows is explained by efficient wave vector selection.

We report experimental observation of Fabry-Perot resonances and Fabry-Perot-induced band-structure flipping in quasi-one-dimensional plasmonic crystals. Angle-resolved transmission spectra of nanoslit arrays in metal films demonstrate band-gap formation resulting from surface plasmon polariton couplings mediated via nanometer-sized waveguide channels. Tuning the waveguide dielectric function and thickness allows for a pronounced resonant enhancement of the coupling strength and band-gap energy and may even induce changes in sign of the coupling-i.e., an effective band-gap flipping. Our results indicate an interesting route towards band-gap engineering in plasmonic crystals.

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