If a metal film, thick enough to be totally opaque, is perforated by tiny subwavelength holes in an orderly fashion, the transmission will be enhanced extraordinarily [T. W. Ebbesen, Nature (London) 391, 667 (1998)]. Here, we investigate the transmission through an ultrathin semitransparent Au film with a square array of subwavelength holes and observe the opposite behavior: less light is transmitted through the pierced metal compared to the closed film.

Nanophotonic structures with irregular symmetry, such as quasiperiodic plasmonic crystals, have gained an increasing amount of attention, in particular as potential candidates to enhance the absorption of solar cells in an angular insensitive fashion. To examine the photonic bandstructure of such systems that determines their optical properties, it is necessary to measure and model normal and oblique light interaction with plasmonic crystals. We determine the different propagation vectors and consider the interaction of all possible waveguide modes and particle plasmons in a 2D metallic photonic quasicrystal, in conjunction with the dispersion relations of a slab waveguide. Using a Fano model, we calculate the optical properties for normal and inclined light incidence. Comparing measurements of a quasiperiodic lattice to the modelled spectra for angle of incidence variation in both azimuthal and polar direction of the sample gives excellent agreement and confirms the predictive power of our model.

Simulation models for the optical properties of 2D quasiperiodic plasmonic structures often fail due to their lack of periodicity. Therefore, it is necessary to find an appropriate model to describe the optical properties of such structures. In this paper we present a model which is able to describe the optical spectra of 2D metallic photonic quasicrystals on top of a waveguide. We take the 2D Fourier transform of the structure and consider all possible waveguide modes in the specific energy range. By utilizing the dispersion relations, the optical spectra can be calculated. The presented model is verified by measurements of a quasiperiodic lattice as well as a rectangular lattice as reference. We find distinct differences in the behavior of quasicrystalline vs rectangular lattices, in particular when investigating rotated and elongated plasmonic particles.Coupling plays a major role in plasmonics. A plethora of interesting phenomena arise from the interaction of particle plasmon resonances with other optical modes. The coupled system can exhibit Fano resonances, 1 which make such systems ideal for optical nanosensors. 2-4 The most straightforward coupled systems comprise planar plasmonic structures with 1D or 2D periodic arrangements. 5,6 In this case, the localized particle plasmons couple to evanescent grating modes. Complementary to this structure are systems which include slits or holes in a solid metal film. 7 All of these examples have in common that the arrangement of plasmonic structures or holes in the metal film is periodic. First attempts to break with this convention have been carried out by Vardeny 8 and Rockstuhl. 9 They investigated quasicrystalline arrangements of nanoholes in a metal film and associated spectral features with characteristics in the reciprocal lattice of their structure. Similarly, already in the year 2000, Zoorob et al. investigated quasicrystalline holes in a dielectric waveguide slab. 10 Other researchers examined 2D and 3D quasicrystalline dielectric photonic crystals. [11][12][13][14] Quasiperiodic structures offer the possibility to engineer significantly more isotropic photonic band gaps. 15 The hybrid system where localized plasmons are strongly coupled through waveguide modes is particularly suited to study coupling. Hybrid periodic 1D and 2D systems have shown a variety of coupling-related linear 16-18 and nonlinear properties. [19][20][21] Even disordered systems were studied. [22][23][24] Recently, these systems have been utilized in a number of exciting applications such as efficiency-enhanced solar cells 25 and subwavelength focusing of light. 26 For the simple periodic cases, it was possible to describe these systems quantitatively by using S-matrix methods which are Fourier-periodic. However, up to now, we have been lacking a possibility to describe quasiperiodic plasmonic crystals quantitatively. In all of the above-mentioned systems where quasiperiodicity played a role, only qualitative assignments of the different spectral modes to reciprocal lattice features w...

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