Symmetry breaking and strong coupling in planar optical metamaterials

We demonstrate narrow transmission resonances at near-infrared wavelengths utilizing coupled asymmetric split-ring resonators (SRRs). By breaking the symmetry of the coupled SRR system, one can excite dark (subradiant) resonant modes that are not readily accessible to symmetric SRR structures. We also show that the quality factor of metamaterial resonant elements can be controlled by tailoring the degree of asymmetry. Changing the distance between asymmetric resonators changes the coupling strength and results in resonant frequency tuning due to resonance hybridization

Compliant Metamaterials for Resonantly Enhanced Infrared Absorption Spectroscopy and Refractive Index Sensing

Metamaterials can be designed to operate at frequencies from the visible to the mid-IR, making these structures useful for both refractive index sensing and surface-enhanced infrared absorption spectroscopy. Here we investigate how the mechanical deformation of compliant metamaterials can be used to create new types of tunable sensing surfaces. For split ring resonator based metamaterials on polydimethylsiloxane we demonstrate refractive index sensing with figures of merit of up to 10.1. Given the tunability of the resonance of these structures through the infrared after fabrication, they are well suited for detection of the absorption signal of many typical vibrational modes. The results highlight the promise of postfabrication tunable sensors and the potential for integration

Compact silicon photonic waveguide modulator based on the vanadium dioxide metal-insulator phase transition

We have integrated lithographically patterned VO2 thin films grown by pulsed laser deposition with silicon-on-insulator photonic waveguides to demonstrate a compact in-line absorption modulator for use in photonic circuits. Using single-mode waveguides at λ = 1550 nm, we show optical modulation of the guided transverse-electric mode of more than 6.5 dB with 2 dB insertion loss over a 2-µm active device length. Loss is determined for devices fabricated on waveguide ring resonators by measuring the resonator spectral response, and a sharp decrease in resonator quality factor is observed above 70 °C, consistent with switching of VO_2 to its metallic phase. A computational study of device geometry is also presented, and we show that it is possible to more than double the modulation depth with modified device structures

Matrix cracking and stress strain behaviour of continuous fibre ceramic composite laminates.

Matrix damage and its effects on mechanical properties have been examined for SiC (Nicalon1) fibre reinforced glass and glass ceramic matrix composites under quasi-static and fatigue loading conditions. Nicalon/Pyrex laminates of different lay-ups have been tested under quasi-static tension. The elastic moduli have been measured and matrix damage monitored as a function of applied strain. The mechanical properties are strongly influenced by the presence of crystalline regions in the matrix which promote microcracking. Laminated plate theory is used to provide bounds to the moduli of the laminates. For unidirectional and simple crossply Nicalon/CAS2 laminates the quasi-static stress/strain behaviour and associated matrix damage accumulation have been examined in detail. The damage development with applied stress was quantified by counts of crack density (in both longitudinal and transverse plies), stiffness loss and cumulative residual strain. The quasi static stress/strain behaviour during continuous tests (accumulating damage) and discontinuous tests (constant damage) have been modelled using a stress analysis based on Aveston, Cooper and Kelly (ACK) theory. The continuous stress/strain behaviour of (0/90) crossply laminates has been modelled using a shear-lag analysis developed previously to describe the transverse ply cracking behaviour of polymer matrix composites. The analysis is modified to account for longitudinal ply cracking. Matrix damage development in unidirectional and (0/90) crossply laminates under quasistatic cycling and high frequency fatigue loading have been studied. For unidirectional laminates stable stress/strain hysteresis loops were obtained during quasi-static cycling, corresponding to stable matrix damage states. These and similar loops obtained after high frequency fatigue are modelled using, the discontinuous stress/strain analysis. It is suggested that the effect of high frequency fatigue is to decrease the interfacial shear strength

Highly Strained Compliant Optical Metamaterials with Large Frequency Tunability

Metamaterial designs are typically limited to operation over a narrow bandwidth dictated by the resonant line width. Here we report a compliant metamaterial with tunability of Δλ ~ 400 nm, greater than the resonant line width at optical frequencies, using high-strain mechanical deformation of an elastomeric substrate to controllably modify the distance between the resonant elements. Using this compliant platform, we demonstrate dynamic surface-enhanced infrared absorption by tuning the metamaterial resonant frequency through a CH stretch vibrational mode, enhancing the reflection signal by a factor of 180. Manipulation of resonator components is also used to tune and modulate the Fano resonance of a coupled system

Testing Born-Infeld electrodynamics in waveguides

Waveguides can be employed to test non-linear effects in electrodynamics. We solve Born-Infeld equations for TE waves in a rectangular waveguide. We show that the energy velocity acquires a dependence on the amplitude, and harmonic components appear as a consequence of the non-linear behavior.Comment: 3 pages. To appear in PR

Quantification of neurodegeneration by measurement of brain-specific proteins

Quantification of neurodegeneration in animal models is typically assessed by time-consuming and observer-dependent immunocytochemistry. This study aimed to investigate if newly developed ELISA techniques could provide an observer-independent, cost-effective and time-saving tool for this purpose. Neurofilament heavy chain (NfH(SM135)), astrocytic glial fibrillary acidic protein (GFAP), S100B and ferritin, markers of axonal loss, gliosis, astrocyte activation and microglial activation, respectively, were quantified in the spinal cord homogenates of mice with chronic relapsing experimental allergic encephalomyelitis (CREAE, n=8) and controls (n=7). Levels of GFAP were found to be threefold elevated in CREAE (13 ng/mg protein) when compared to control animals (4.5 ng/mg protein, p<0.001). The inverse was observed for NfH(SM135) (21 ng/mg protein vs. 63 ng/mg protein, p<0.001), ferritin (542 ng/mg protein vs. 858 ng/mg protein, p<0.001) and S100B (786 ng/mg protein vs. 2080 ng/mg protein, N.S.). These findings were confirmed by immunocytochemistry, which demonstrated intense staining for GFAP and decreased staining for NfH(SM135) in CREAE compared to control animals. These findings indicate that axonal loss and gliosis can be estimated biochemically using the newly developed ELISA assays for NfH(SM135) and GFAP. These assays may facilitate the quantification of pathological features involved in neurodegeneration

Plasmonic nanoparticle enhanced photocurrent in GaN/InGaN/GaN quantum well solar cells

We demonstrate enhanced external quantum efficiency and current-voltage characteristics due to scattering by 100 nm silver nanoparticles in a single 2.5 nm thick InGaN quantum well photovoltaic device. Nanoparticle arrays were fabricated on the surface of the device using an anodic alumina template masking process. The Ag nanoparticles increase light scattering, light trapping, and carrier collection in the III-N semiconductor layers leading to enhancement of the external quantum efficiency by up to 54%. Additionally, the short-circuit current in cells with 200 nm p-GaN emitter regions is increased by 6% under AM 1.5 illumination. AFORS-Het simulation software results were used to predict cell performance and optimize emitter layer thickness

Tunneling and delocalization in hydrogen bonded systems: a study in position and momentum space

Novel experimental and computational studies have uncovered the proton momentum distribution in hydrogen bonded systems. In this work, we utilize recently developed open path integral Car-Parrinello molecular dynamics methodology in order to study the momentum distribution in phases of high pressure ice. Some of these phases exhibit symmetric hydrogen bonds and quantum tunneling. We find that the symmetric hydrogen bonded phase possesses a narrowed momentum distribution as compared with a covalently bonded phase, in agreement with recent experimental findings. The signatures of tunneling that we observe are a narrowed distribution in the low-to-intermediate momentum region, with a tail that extends to match the result of the covalently bonded state. The transition to tunneling behavior shows similarity to features observed in recent experiments performed on confined water. We corroborate our ice simulations with a study of a particle in a model one-dimensional double well potential that mimics some of the effects observed in bulk simulations. The temperature dependence of the momentum distribution in the one-dimensional model allows for the differentiation between ground state and mixed state tunneling effects.Comment: 14 pages, 13 figure