Periodicity-induced effects in the scattering and absorption of light by infinite and finite gratings of circular silver nanowires

Rayleigh anomaly induced phase gradients in finite nanoparticle chains

Collective optical interactions in infinite nanoparticle arrays have been studied intensively over the past decade. However, analysis of finite arrays has received significantly less attention. Here, we theoretically and numerically show that the collective interaction in finite nanoparticle chains can support phase gradients that shift the diffraction pattern with respect to infinite chains. Specifically, we demonstrate that this phenomenon occurs for resonating nanoparticles in a narrow spectral range around the Rayleigh anomaly condition, i.e., when a certain diffraction order radiates at a grazing angle. This reveals that the Rayleigh anomaly, which is associated with intensity changes, can also induce angular anomalies in finite arrays. To study the effect theoretically, we develop a novel analytical approach based on the discrete dipole approximation. Within this framework, we find an approximate closed-form solution to the particles' dipole moments. We show that our solution can be expressed in two different ways, one based on a combinatorial calculation, and the other on a recursive calculation, and discuss the unique physical interpretation emerging from each of them. Our results are of potential importance in a wide range of practical applications from LIDARs to beam shaping schemes.

Surface Lattice Resonances in THz Metamaterials

Diffraction of light in periodic structures is observed in a variety of systems including atoms, solid state crystals, plasmonic structures, metamaterials, and photonic crystals. In metamaterials, lattice diffraction appears across microwave to optical frequencies due to collective Rayleigh scattering of periodically arranged structures. Light waves diffracted by these periodic structures can be trapped along the metamaterial surface resulting in the excitation of surface lattice resonances, which are mediated by the structural eigenmodes of the metamaterial cavity. This has brought about fascinating opportunities such as lattice-induced transparency, strong nearfield confinement, and resonant field enhancement and line-narrowing of metamaterial structural resonances through lowering of radiative losses. In this review, we describe the mechanisms and implications of metamaterial-engineered surface lattice resonances and lattice-enhanced field confinement in terahertz metamaterials. These universal properties of surface lattice resonances in metamaterials have significant implications for the design of resonant metamaterials, including ultrasensitive sensors, lasers, and slow-light devices across the electromagnetic spectrum.

Slow-light effect via Rayleigh anomaly and the effect of finite gratings

In this Letter, we investigate the slow-light effect of subwavelength diffraction gratings via the Rayleigh anomaly using a fully analytical approach without needing to consider specific grating structures. Our results show that the local group velocity of the transmitted light can be significantly reduced due to the optical vortex, which can inspire a new mechanism to enhance light-matter interactions for optical sensing and photodetection. However, the slow-light effect will diminish as the transmitted light propagates farther from the grating surface, and the slowdown factor decreases as the grating size shrinks.

Effect of finite metallic grating size on Rayleigh anomaly-surface plasmon polariton resonances

Rayleigh anomalies (RAs) and surface plasmon polaritons (SPPs) on subwavelength metallic gratings play pivotal roles in many interesting phenomena such as extraordinary optical transmission. In this work, we present a theoretical analysis of the effect of finite metallic grating size on RA-SPP resonances based on the combination of rigorous coupled wave analysis and finite aperture diffraction. One-dimensional arrays of gold subwavelength gratings with different device sizes were fabricated and the optical transmission spectra were measured. As the grating size shrinks, the broadening of the RA-SPP resonances is predicted by the theoretical model. For the first order RA-SPP resonances, the results from this model are in good agreement with the spectra measured from the fabricated plasmonic gratings.

Scattering of light by gratings of metal-coated circular nanocylinders on a dielectric substrate

Light scattering by a grating of the metal (Ag)-coated nanocylinders supported on the dielectric substrate is investigated using an accurate and rigorous formulation based on the recursive algorithm combined with the lattice sums technique. The proposed approach could be applied easily to the various configurations of the grating composed of the metal or metal-coated nanocylinders with different types and locations of the excitation sources. Special attention is paid to the three types of resonances: (a) surface plasmon resonances associated with the metal nanocylinders, (b) Rayleigh anomalies related with the periodic nature of the grating, and (c) resonances due to the coupling between the grating and the dielectric substrate. Near-field distribution of the magnetic field, which is parallel to the axis of the nanocylinders, is investigated numerically. Physical insight is given to the localization of the field along the interfaces of the metal nanocylinders, formation of the strong reflected field by the grating, and the field enhancement at the surface of the dielectric substrate. The accuracy of the numerical analyses has been tested based on the principle of the energy conservation. All these features are technologically important and have wide practical application from the viewpoint of the flexible design and fabrication of the plasmonic optical devices.

Seeing the order in a mess: optical signature of periodicity in a cloud of plasmonic nanowires

We consider the two-dimensional (2-D) problem of the H-polarized plane wave scattering by a linear chain of silver nanowires in a cloud of similar pseudo-randomly located wires, in the visible range. Numerical solution uses the field expansions in local coordinates and addition theorems for cylindrical functions and has a guaranteed convergence. The total scattering cross-sections and near- and far-zone field patterns are presented. The observed resonance effects are studied and compared with their counterparts in the scattering by the same linear chain of wires in free space.

Collective phenomena in photonic, plasmonic and hybrid structures

Preface to a focus issue of invited articles that review recent progress in studying the fundamental physics of collective phenomena associated with coupling of confined photonic, plasmonic, electronic and phononic states and in exploiting these phenomena to engineer novel devices for light generation, optical sensing, and information processing.