Artificially engineered metamaterials consisting of nanocomposites (i.e. metal- dielectric) elements in the form of metallic split ring resonators (SRRs), parallel wires or slabs can provide unique optical responses at high frequencies that not available in naturally existing materials. A variety of metamaterials have been used in many important applications such as superlenses, tunable mirrors and negative index materials. Decreasing the size of the magnetic resonators is critical if strong magnetic response is desired at optical and near- infrared frequencies. However, this scaling breaks down at high frequencies causing saturation in the magnetic response. In this study, we present a transmission line theory with models the magnetic response of pair of metallic nanostripes separated by a dielectric material. The predicted by the model magnetic susceptibility χ𝑚 and magnetic resonance frequency (MRF) are compared to exact numerical simulations showing excellent agreement. Parametric study of the MRF dependence on the resonator’s sizes show a clear saturation for small resonators
Two major types of optical cavities are in wide-use today: photonic crystals and optical microcavities. However, both of these systems have major drawbacks. Photonic crystals only operate for a certain range of wavelengths while optical microcavities can only trap light for a certain range of angles determined by the microcavity angle of total internal reflection. Here, new types of optical cavities are proposed and investigated, aiming to resolve these problems by providing Lyapunov-stable photon orbits within a specially designed inhomogeneous isotropic/anisotropic media. These types of optical traps, referred to as a Continuous Index Photon Traps (CIPTs), seek to exploit recent advances in the field of optics. Specifically, nanofabricating artificial optical materials, i.e. metamaterials, that can bend light and entrap photons in a finite spatial domain. The CIPT’s potential to provide stable photon orbits is assessed. Material realizations of the proposed photon traps are suggested and their optical properties including cavity Q-factors and decay rates are estimated. Potentialy important practical applications of the CIPTs would include optical cavities that trap light withough use of refraction index discontiniuties and hence have low scattering losses due to surface roughness.
We investigate conditions for Casimir Force (CF) reversal between two parallel half-space metamaterial plates
separated by air or vacuum at ambient temperatures. Practically, the Casimir effect can lead to stiction in
nanoscale devices, degradation and decreased performance. While material realizations of repulsive CF has been
proposed for high dielectric host materials, so far the CF reversal with air/vacuum as intermediate medium
remain challenging. Here, we propose a two plate design based on artificial electromagnetic materials known
as metamaterials. This configuration allows a simple analytical treatment that accurately describes the large
and short distance asymptotics of CF and allows extraction of important parameters such as lower and upper
cutoff gap distances that define the repulsive force window. A parametric study has been performed in terms
of the plate's dielectric and magnetic plasma frequencies, plate separation distance and temperature. The
parametric domain for achieving CF reversal is identified. If successfully implemented the proposed design could
potentially result in frictionless bio-fluid transport devices, quantum levitation and coating for ultra-clean room
A reduction of material consumption in thin-film photovoltaic devices can make solar energy economically more viable.
However, since thin films essentially absorb less light, there is an imminent need for existing technology to improve light harvesting. We present an effective approach of better light absorption, enhanced photocurrent generation and therefore higher quantum efficiency of poly (3-hexylthiophene): 1-(3-methoxycarbonyl) propyl-1-phenyl-[6, 6]-methanofullerene (P3HT:PCBM) bulk heterojunction photovoltaic/photodetector devices. We have integrated a thin semi-continuous gold film (SCGF) (~20nm) sputtered at percolation threshold between the active P3HT:PCBM layer and the indium-tin-oxide (ITO) electrode. At critical metal concentrations, i.e. percolation threshold, the light reaching the SCGF undergoes a broadband trapping with characteristic time of 200 fs, through complex interactions with fractal gold clusters. This thin SCGF together with the ITO serves as an anode. The interface between SCGF and the polymer represents the metaldielectric composite (MDC) that supports broad-band surface plasmon resonances that store electromagnetic radiation at the nanoscale and acts as an effective bulk type of concentrator without the need of increasing the photovoltaic device physical collection area. Here we report a six-fold enhancement in the integral quantum efficiency over the solar spectrum for device employing plasmon-active gold layer. Such enhancement is an important contribution for the future design of more efficient photodetecting/photovoltaic devices. The experimental results are supported by the theoretical modeling of metal-dielectric composites by block elimination method in 3D. The AC and DC responses of MDC, local field distribution, broad optical response and photon trapping in the percolating MDC were numerically calculated.
A study of a generic multishell cloaking system that conceals an object from incident electromagnetic radiation
regardless of the object shape and/or material (optical) properties is presented. Transparency conditions based
on zero permittivity materials for both cylindrically and spherically symmetric systems are derived. It has been
shown that zero permittivity material shells can be realized using noble metals. In addition, we proposed a zero-index
lowloss tunable shell design based on metal-dielectric composite material to realize the cloak. Our results
show that the proposed design can achieve cloaking across the entire optical spectral range and can decrease
the scattering-cross section by a factor of up to 103. Furthermore, a full wave analysis is performed showing the
independence of cloak performance on the object shape and material properties. The proposed approach toward
clocking does not require optical magnetism and underline the importance of zero index materials for achieving
The surface plasmons (SPs) eigenproblem which arises in inhomogeneous metal-dielectric films is studied at resonance conditions. We show that short-range correlations present in the governing Kirchhoff Hamiltonian (KH) result in delocalization of the eigenstates at the center of the spectrum. The delocalization is manifested as a power law/logarithmic singularity for the density of states and SPs localization lengths. Based on the SPs eigenproblem, analytical relationships are derived for the electromagnetic response of the semicontinuous film in resonance and off-resonance regimes. Experimental studies indirectly confirm the existence of delocalized SP states in the random system.
Anderson localization in random potential fields has been studied extensively for the last fifty years. It is commonly accepted that in 1D and 2D systems characterized by non-correlated random potential distributions, all states are exponentially localized. In this paper we investigate the eigen-problem for Surface Plasmons (SP) in random metal-dielectric films. We show that short-range correlations presented in the governing Kirchhoff's Hamiltonian (KH) result in delocalization of the eigenstates at the band center. The delocalization is shown to be manifested through power law singularities for the density of states and SP localization lengths. The study of the system size dependence of the nearest neighbor's level spacing distributions shows a gradual shift of the SP eigen-problem from a metallic phase for small system sizes into an insulating quantum phase for infinite systems. It reveals a genuine metal-insulator transition that takes place in the composite and is characterized by quantum percolation threshold Pq which is higher than the corresponding geometrical critical concentration Pc.
Analytical theory and numerical calculations for periodic arrays of metal nanoparticles indicate resonant-like enhancement of local electromagnetic field, which can be tuned by varying a ratio of particle diameter to interparticle spacing. For Raman scattering, local field enhancements on the order of 1013 and surface-averaged field enhancements on the order of 1011 can be achieved udner optimal conditions. This is several orders of magnitude greater tan that obtaiend in disordered metal-dielectric films, and suggests a new design for engineering plasmonic substrates supporting intense and spatially well-defined field patterns, with direct applications for surface-enhanced Raman scattering (SERS), and surface-enhanced optical nonlinearities.