John S. Derov

Negative Refraction and Left-Handed Electromagnetism in Microwave Photonic Crystals

We demonstrate the negative refraction of microwaves in a metallic photonic crystal prism. The spectral response of the photonic crystal prism, which manifests both positive and negative refraction, is in complete agreement with band-structure calculations and numerical simulations. The validity of Snells law with a negative refractive index is confirmed experimentally and theoretically. The negative refraction observed corresponds to left-handed electromagnetism that arises due to the dispersion characteristics of waves in a periodic medium. This mechanism for negative refraction is different from that in metamaterials.

Advantages of microsphere-assisted super-resolution imaging technique over solid immersion lens and confocal microscopies

We demonstrate a series of advantages of microsphere-assisted imaging over confocal and solid immersion lens microscopies including intrinsic flexibility, better resolution, higher magnification, and longer working distances. We discerned minimal feature sizes of ∼50-60 nm in nanoplasmonic arrays at the illumination wavelength λ = 405 nm. It is demonstrated that liquid-immersed, high-index (n ∼ 1.9-2.1) spheres provide a superior image quality compared to that obtained by spheres with the same index contrast in an air environment. We estimate that using transparent microspheres at deep UV wavelengths of ∼200 nm might make possible imaging of various nanostructures with extraordinary high ∼30 nm resolution.

Large pyroelectric response from reactively sputtered aluminum nitride thin films

We report the pyroelectric response of c-axis oriented, undoped, wurtzite, aluminum nitride reactively sputtered onto polished silicon wafers. The voltage between a metallic contact on the AlN surface and the n + -doped silicon substrate was monitored during pulsed infrared, radiant heating. From analysis of the data, a pyroelectric voltage coefficient, P v , in excess of 0.5 × 10 6 V/m/K was extracted for films in the 600 to 2500 A thickness range.

Optical microscopy with super-resolution by liquid-immersed high-index microspheres

We study super-resolution capability of liquid-immersed high refractive index (n~1.9–2.1) barium titanate glass microspheres with diameters from several microns up to hundreds of microns. Imaging is provided in a conventional upright microscope with the spheres placed in a contact position with various semiconductor and metallic nanostructures. Using a commercial Blu-ray disk, we demonstrate an ability to discern 100 nm feature sizes which cannot be resolved by conventional microscopy. Using silver nanowires with diameter about 100 nm, we demonstrate ~1.7 times improvement in spatial resolution compared to conventional diffraction-limited far field microscopy. Using two-dimensional nanoplasmonic arrays, we demonstrate high resolution imaging by using objectives with surprisingly small numerical apertures. The last property is attractive for high-resolution imaging at long working distances. This imaging technique can be used in biomedical microscopy, microfluidics, and nanophotonics applications.

Plasmonic Superpixel Sensor for Compressive Spectral Sensing

In multispectral and hyperspectral sensing, there is a growing need for a versatile sensor capable of adapting response and improving detection of hard-to-find dynamic targets of interest in contested environments. Such on-the-fly adaptivity in current systems requires significant data resources and computation time for data analysis. In order to implement practical systems with this capability, sensors that reduce data loads and computational requirements while maintaining performance are required. To this end, we report a novel hybrid algorithm sensor method using plasmon-based tunable superpixels and a compressive spectral sensing (CSS) algorithm for the next generation of hyperspectral sensors. The benefit of our hybrid approach is that it enables us to effectively sense a minimal data set and only performs simple arithmetic such as linear superposition to extract spectral features of a target without requiring actual spectral filters. In this paper, we focus on the selection of a minimum basis of plasmonic spectral bands, the configuration of superpixels using selected plasmonic structures, and finally the generalization of a CSS algorithm to process superpixel data for feature extractions. The performance of algorithm-driven superpixels has been successfully demonstrated with the context of reconstructing infrared spectral signatures.

Negative index metamaterial for selective angular separation of microwaves by polarization

Materials with simultaneously negative electric permittivity and magnetic permeability are referred to as left handed, and are also called backward wave and double negative media. The first experimental demonstration of such a metamaterial combined metallic split ring resonators with posts etched on opposite sides of dielectric boards. The boards are usually stacked in parallel planes with insulating spacers to form highly anisotropic prisms. We have demonstrated that this anisotropic. prism exhibits both positive and negative refractive indices and can split an incident beam into two components. The positive and negative indices are accessible by the choice of polarization of the electric field. Using an electric field parallel to the posts, negative refraction is observed. Rotating the electric fields 90/spl deg/ yields a positively refracted signal. Intermediate angles of polarization can achieve refraction in both negative and positive directions simultaneously, or the receiver polarization can be chosen to select either signal separately, The values of the positive and negative index and the wedge angle of the prism determine the separation angle of the output beams. This effect has potential application for a unique type of angular beam splitter.

Optimum design of antennas using metamaterials with the efficient global optimization (EGO) algorithm

EGO is an evolutionary, data-adaptive algorithm which can be useful for optimization problems with expensive cost functions. Many antenna design problems qualify since complex computational electromagnetics (CEM) simulations can take significant resources. This makes evolutionary algorithms such as genetic algorithms (GA) or particle swarm optimization (PSO) problematic since iterations of large populations are required. In this paper we discuss multiparameter optimization of a wideband, single-element antenna over a metamaterial ground plane and the interfacing of EGO (optimization) with a full-wave CEM simulation (cost function evaluation).

Heating of large-area substrates for in situ deposition of YBCO

We have developed a radiant technique for substrate heating which we found particularly useful for the in situ deposition of high temperature superconducting films. Using this technique, large area YBa/sub 2/Cu/sub 3/O/sub x/ films were deposited, using off-axis sputter deposition, onto lanthanum aluminate and sapphire substrates, the latter using an yttria-stabilized zirconia buffer layer. For both types of substrates we were able to obtain c-axis oriented films. The DC and microwave properties of the films deposited on lanthanum aluminate are presented along with the DC measurements of the films deposited on sapphire. The motivation for employing this method of heating are discussed, along with our current plans for scaling up the process to produce even larger area films.<<ETX>>

High throughput, large scale, broadband, plasmonic nanostructure fabrication for optical sensors

Plasmonics have the potential to enhance the performance of detectors. A thermal metal dewetting process was developed which can be easily scaled for high throughput production. Through this process, plasmonic nanostructures were fabricated providing broadband plasmon resonance tunable over a 1000 nm wavelength range. The plasmonic media and their integration into fluorescence-based sensors will be described.

Validation of Negative Refraction in a Metamaterial Wedge using QPSK Modulated Signals

The phenomenon of negative refraction in a Metamaterial wedge is known to be relatively narrowband. Here, we first experimentally estimate the negative refraction bandwidth of a Metamaterial wedge using a slab and a series of CW measurements. We subsequently measure the RF bandwidth of the Metamaterial wedge using a series of simple QPSK modulated signals. The measured RF bandwidth correlates well with the bandwidth estimate made using the slab and CW measurements.