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The collective effects in a periodic array of plasmonic double-antenna meta-molecules are studied. We experimentally observe that the collective behavior in this structure substantially differs from the one observed in their single-antenna counterparts. This behavior is explained using an analytical dipole model. We find that in the double-antenna case the effective dipole-dipole interaction is significantly modified and the transverse long-range interaction is suppressed, giving rise to the disappearance of Wood's anomalies. Numerical calculations also show that such suppression of long-range interaction results in an anomalous spatial dispersion of the electric-dipolar mode, making it insensitive to the angle of incidence. In contrast, the quadrupolar mode of the antenna pair experiences strong spatial dispersion. These results show that collective effects in plasmonic metamaterials are very sensitive to the design and topology of meta-molecules. Our findings envision the possibility of suppressing the spatial dispersion effects to weaken the dependence of the metamaterials' response on the incidence angle.

We examine the Wood's anomaly in arrays of nanorod pairs and find an apparent strong coupling between longitudinal plasmon modes and an oscillating dipole moment perpendicular to the plane of the substrate.

We measure, simulate, and analyze the optical transmission through arrays of Ag nanorod pairs and U-shaped nanostructures as a function of polarization and angle of incidence. The bianisotropic nature of the metamaterials is exhibited in data and in simulations, and we argue that the electric field rather than the magnetic field excites the low frequency "magnetic" mode. We also observe spatial dispersion in the form of frequency shifts as a function of incident angle which we attribute to coupling effects between neighboring structures. A simple model based upon coupled electromagnetic dipoles is found to provide a qualitative description for the main features observed in the spectra.

We report on the near-field optical microscopic (NSOM) imaging of single-crystal Nd1/2Sr1/2MnO3 near the first-order phase transition from the CE-type charge-ordered insulator (COI) to the ferromagnetic metal (FMM) at 165 K. Using polarized light, the measurements are sensitive to twin domains through optical anisotropy and to hysteretic inhomogeneous strain associated with the phase transition. Optical evidence for strain relaxation and multiphase coexistence is observed through the transition from 150 to 165 K. The multiphase coexistence is seen as the formation of FMM "nanoneedles" with widths less than 100 nm and lengths of at least several micrometers at temperatures well below TC. The work demonstrates polarized NSOM as a technique for the study of first-order solid-state phase transformations on the nanometer spatial scale.

We report on factors affecting the performance of a broadband, mid-IR absorber based on multiple, alternating dielectric / metal layers. In particular, we investigate the effect of interface roughness. Atomic layer deposition produces both a dramatic suppression of the interface roughness and a significant increase in the optical absorption as compared to devices fabricated using a conventional thermal evaporation source. Absorption characteristics greater than 80% across a 300 K black body spectrum are achieved. We demonstrate a further increase in this absorption via the inclusion of a patterned, porous anti-reflection layer.

We propose a periodic multilayer structure of dielectric and metal interlayers to achieve a near-perfect broadband absorber of mid-infrared radiation. We examine the influence of four factors on its performance: (1) the interlayer metal conductance, (2) the number of dielectric layers, (3) a nanopatterned antireflective layer, and (4) a reflective metallic bottom layer for backreflection. Absorption characteristics greater than 99% of the 300 K and 500 K blackbody spectra are found for the optimized structures. Incident angle and polarization dependence of the absorption spectra are examined. We also investigate the possibility of fabricating a nanopatterned antireflective layer to maximize absorption.

We systematically investigate the resonant behavior of arrays of Ag nano-structures ranging from isolated simple rods, to U-shapes, to single split ring structures. We show that the lowest order plasmonic resonance associated with a rod red shifts as we create a U and SRR into the position normally associated with a simple LC mode. A second mode red shifts and grows in intensity as we extend the arms of the U-shape, and a third mode appears in the spectra as we close the arms and form a split ring structure. We performed simulations of the structures and examine the E-field and current density. The simulations show that the current path is different for these modes. We examine the behavior of the lowest order mode in detail, discuss the effects of skin depth, and present an improved LC model to describe this resonance.

A novel, chemical-etching technique produces very high throughput, polarization-maintaining probes for near-field, scanning, optical microscopy (NSOM). The process includes coating the tips with aluminum and forming the apertures with a focused ion beam (FIB). The elliptical core fibers used resulted in elliptical apertures for the probes. The throughput of the probes depends on the incident polarization. For polarization parallel to the minor axis, the tip presents an insertion loss of only 20 dB for aperture widths of 55 nm. Probes have a typical polarization extinction of 100 to 1 in the far field. These tips produced NSOM images of gold dots on a GaAs substrate in reflection mode.