Metamaterial structures designed to have simultaneously negative permittivity and permeability are known as left-handed materials. Their complexity and our understanding of their properties have advanced rapidly to the point where direct applications are now viable. We present a radial gradient-index (GRIN) lens with an index-of-refraction ranging from -2.67(edge) to -0.97(center). Experimentally, we find the lens can produce field intensities at the focus that are greater than that of the incident plane wave. These results are obtained at 10.45 GHz and in excellent agreement with full-wave simulations. This lens is a demonstrate an newly pioneered advanced fabrication technique using conventional printed circuit board (PCB) technology which offers significant design, mechanical, and cost advantages over other microwave lens constructions.
In recent years there has been an enormous development in the understanding of light transport in disordered materials, in particular in systems with optical gain. A phenomenon termed random lasing can be observed, which can be used to realize a random laser. We will describe the behaviour of these fascinating new light sources that resemble in various respects a regular laser while the lasing process is based on light diffusion.
We consider plasmonic nanoantennas immersed in active host medium. Specifically shaped metal nanoantennas can
exhibit strong magnetic properties in the optical spectral range due to the excitation of Magnetic Resonance Plasmons
(MRP). A case when a metamaterial comprising such nanoantennas can demonstrate both "left-handiness" and negative
permeability in the optical range is considered. We show that high losses predicted for optical "left-handed" materials
can be compensated in the gain medium. Gains required to achieve local generation in such magnetic active
metamaterials are calculated for real metals
Investigations of ZnO random lasers spectra due to single shot of nanosecond pumping were performed using CCD camera Videoscan-285. It was obtained that these spectra essentially differ from lasing spectra under picosecond pumping: as a rule the line widths are significantly larger, often spectra have quite smooth shape; often spectra essentially change from shot to shot in random manner on the same pumping spot. From our point of view it can be the result of many lasing acts appearance during single pumping pulse and of lasing lines frequency changing in every lasing act.
Negative phase velocity metamaterials (NPM) are engineered media currently enjoying a surge of interest due to their interesting properties and potential applications. Their nonlinear behaviour will be intrinsic to the Holy Grail quest for power control. This is a hot topic that is only just being explored as evidenced by a rapidly increasing number of publications over the past few years. With the introduction of power comes the possibility of solitons and it is important to recognise that damping, arising from both the environment and the material, must be offset by the introduction of gain. In this context the investigation considers what are known as dissipative solitons, within a pumping, multi-stable configuration, designed as a ring or Fabry-Perot cavity. Several exciting scenarios will be presented and particular attention is devoted to the nonlinearity displayed by well-known 'artificial' molecules such as split rings and omega particles. The desire to create metamaterials that reach out to optical frequencies is acknowledged through a discussion of scalability. Detailed studies of the cavity stability regimes lead to some novel possibilities for cavity control. The presentation will be rounded off with a generalised theory of metamaterial behaviour in nonlinear environments that is based upon a novel approach using what is sometimes called the nonlinear Lorentz lemma. Extensive new numerical results will be used to illustrate the concepts outlined above.
Metamaterials demonstrating a negative phase velocity for light usually consist of arrays of wires and cut-ring structures. Such media are characterized by both the permittivity and permeability being negative. Calculations of the Ohmic loss associated with the wires alone indicate that dissipation can be minimized by making them of metal of the highest possible conductivity and by having the largest possible wire radius. Replacement of the cut-ring structures with a ferrite further reduces losses since ferrites can be less lossy than typical conductors. The upper limit to the wire radius is ultimately set by the requirement that the permittivity be negative. The calculations take into account the skin depth within the wires. Although bigger wires lead to more volume in which Ohmic losses are present, these wires are more effective in shorting out the electric field and thereby decreasing the Ohmic loss. An array made of large diameter and high conductivity wires leads to a strong electromagnetic response and a well defined plasma frequency for the wire array.
Proc. SPIE 6320, An adaptive Fourier Bessel split-step method and variational techniques applied to nonlinear propagation in negative index materials, 63200E (27 September 2006); doi: 10.1117/12.675638
Starting from a simple dispersion relation that models negative index materials, we derive and develop the underlying
partial differential equation for wave propagation in such a medium. In the first part we study the linear characteristics of
wave and beam propagation in NIMs. In the second part we heuristically perform a nonlinear extension of the linear
partial differential equation by adding cubic nonlinear terms as in the nonlinear Klein Gordon equation, and (d+1+1)-
dimensional envelope solitary wave solutions are derived. Also, using variational techniques and an adaptive Fourier
Bessel split-step numerical method, we show that nonlinearity management through a periodic variation of the
nonlinearity coefficient helps in stabilization of spatial solitons.
Although materials exhibiting negative permeability and permittivity, referred to as metamaterials or left-handed materials (LHMs), have been postulated for many years, it is only recently that such materials have been physically realized. Previous attempts to model these structures embedded a material with a negative index of refraction as a black box and utilized the effective index approximation. While such attempts are sufficient for demonstrating the concepts of negative refraction, they do not utilize physically realizable elements to build LHMs and, hence, cannot account for various spectral and temporal material properties. Thus, in order to determine the frequency range over which such structures exhibit a negative refraction, a rigorous numerical modeling of the LHM is necessary. However, this is a non-trivial task, given the level of detail that is required in the model, which translates into massive computational size and time. Thus, there is a clear need for a numerical platform capable of handling such computationally intense problems. To this end, we have developed a novel, hardware-based platform to analyze LHM structures. This platform has demonstrated performance comparable to a 100-node PC cluster at a fraction of the power, area, and cost. In this paper, we describe this platform and its application to LHM structures. Specifically, the hardware accelerator is used to calculate the transmission spectra of an LHM structure, too large to be modeled using standard software simulation tools, in order to identify the frequency regions where the permittivity and permeability are negative. The hardware platform is then used to demonstrate negative refraction.
The macroscopic electro-optic activity of organic materials is linearly related to molecular first hyperpolarizability of individual chromophores, chromophore number density, and the acentric order parameter describing chromophore order. When strong chromophore-chromophore intermolecular electrostatic interactions (e.g., dipole-dipole interactions) are present, the latter two quantities are not independent. In previous publications, we have demonstrated how electro-optic activity can be systematically improved by control of chromophore shape in chromophore/polymer composite materials and by the nanoscopic engineering of single- and multi-chromophore-containing dendrimer materials, where steric interactions and covalent bond potentials are used to inhibit centrosymmetric ordering of chromophores. In this communication, we demonstrate how doping a second chromophore into a chromophore-containing material can lead to dramatically improved electro-optic activity. This work also provides insight into the affect of surrounding lattice on solvatochromic shifts and line broadening that can lead to increased optical loss.
A hyper-branched molecule, such as a dendrimer, has a repeated structure consisting of molecules with low molecular weights. As it is possible to produce relatively large and well-defined macromolecular structures, these structures are suitable for use as frameworks for controlling nanoscale intermolecular interactions. We discuss about managing intermolecular interactions among optical responsive molecules using the framework of super molecular structures, such as dendrons and dendrimers. The dendrimer works as a nano-sized cage, which is effectively protect photoactive choromophores from photobleaching and quenching. The dendron works as a cone-shaped anchor, which leads effective surface modification with photoactive molecules on gold.
Charge relaxation in dispersive materials is often described in terms of the stretched
exponential function (Kohlrausch law). The process can be explained using a "hopping"
model which in principle, also applies to charge transport such as current conduction.
This work analyzed reported transient photoconductivity data on functionalized pentacene
single crystals using a geometric hopping model developed by B. Sturman et al and
extracted values (or range of values) on the materials parameters relevant to charge
relaxation as well as charge transport. Using the correlated disorder model (CDM), we
estimated values of the carrier mobility for the pentacene samples. From these results, we
observed the following: i) the transport site density appeared to be of the same order of
magnitude as the carrier density; ii) it was possible to extract lower bound values on the
materials parameters linked to the transport process; and iii) by matching the simulated
charge decay to the transient photoconductivity data, we were able to refine estimates on
the materials parameters. The data also allowed us to simulate the stretched exponential
decay. Our observations suggested that the stretching index and the carrier mobility were
related. Physically, such interdependence would allow one to demarcate between
localized molecular interactions and distant coulomb interactions.
The semiconducting conjugated polymers, poly-phenylene-vinylene (PPV), are studied using linear and non-linear optical spectroscopy methods: ultra-fast optical spectroscopy, optical absorption, and luminescence. Study of polarization resolved absorption and excitation spectra at room temperature revealed strong anisotropy of the optical responses. Microscopic interpretation of the results is based of the first principal analysis of the electronic structure of PPV using the density functional theory (DFT). The dominant contribution of the optical excitations in visible spectral range is related to the delocalized pi-electronics of the PPV chains. Time-resolved luminescence measurements indicate the separate contributions from electronic transitions associated to the localized and delocalized electrons in PPV.
The incorporation of the Pockels effect in structurally chiral materials (SCMs) engenders new modalities for
control manipulation of the circular Bragg phenomenon (CBP). The boundary-value problem of the reflection
and transmission of a plane wave due to a slab of an electro-optic SCM is formulated in terms of a 4×4
matrix ordinary dfferential equation. The SCM slab can be locally endowed with one of 20 classes of point
group symmetry, and is subjected to a dc voltage across its thickness. The enhancement (and, in some cases,
the production) of the CBP by the application of a dc electric field across the thickness of the SCM slab has
switching and circular-polarization-rejection applications in optics.
This paper reviews our recent progress of micro and nanolithography techniques for the fabrications of planar photonic meta-materials and other nano photonic structures. The nanotechnologies involved in this development include the state-of-the-art electron-beam lithography (EBL), nanoimprint lithography (NIL), hot embossing, soft lithography and hybrid lithography, which is the combination of different lithography processes. Using these technologies, various meta-materials in sizes from micrometres down to sub-100 nm were successfully fabricated. Characterisations of these meta-materials have revealed a wealth of novel phenomena in nanophotonics. This paper will also discuss the advantages, disadvantages and suitability of each technology involved, trying to give a fair judgement for the applicability of the developed techniques. It can be concluded that micro and nanolithography are capable of achieving functional planar optic meta-materials in both single layer and multiple layer. Especially the developed manufacture processes using nanoimprint lithography and hot embossing technique may lead to fast speed patterning for high throughput and low cost mass production for broad applications.
Sum Frequency Generation (SFG) spectra of nanocrystalline porous silicon (por-Si) exposed to different chemical treatments are studied. We report the first SFG studies of por-Si in direct contact with a liquid. SFG is excited by a regeneratively amplified Ti:sapphire system (787 nm, 120 fs, 1 kHz). The sum frequency is generated by combining this light with infrared that is generated with an optical parametric amplifier (OPA) that delivers 100-200 μJ pulses at 1370-1770 nm. Por-Si is made from a 10-20 Ω cm p-type Si(001) wafer. Comparisons are made to planar Si(001) as well as GaAs(001). First principle electronic structure theory based on density functional theory (DFT) is used to study the adsorption and optical response functions from the system of ethanol molecule adsorbed on Si(001) and Si(111) surfaces. Equilibrium atomic geometries are obtained through molecular dynamics and total energy minimization methods. Electron energy structure and optical properties are calculated using generalized gradient approximation method with ab initio pseudopotentials. Predicted differential optical absorption spectra for chemisorbed Si(001) and Si(111) surfaces are analyzed in comparison with SFG data measured on differently treated porous silicon. Substantial modifications of the surface atomic and electron energy structures of silicon surfaces due to chemisorption are shown to provide the dominant contributions to the SFG response.
We explore new concepts for electro-optic (EO) modulator designs based on local-field enhancement and electrodes in close proximity for improving the performance of nonlinear materials. Using nanopatterned metals or conductive materials for electrodes and plasmonic elements we show that the effective nonlinearity can be enhanced and concurrently the driving voltage reduced for electro-optic active materials. We especially devote our attention on EO modulator applications using polymers doped with active chromophores. Our substrate materials are mesoscopically patterned using focused ion beam milling. The critical dimensions of the features are smaller than a wavelength. The effective medium theory is used to analyze the results.
A very general mean-field theory is presented for a photonic crystal (either dielectric or metallo-dielectric) with arbitrary 3D Bravais lattice and arbitrary shape of the inclusions within the unit cell. The material properties are described by using a generalized conductivity at every point in the unit cell. After averaging over many unit cells for small Bloch wave vectors in comparison with the inverse of the lattice constant, we have derived the macroscopic response for the artificially structured material. In the most general case, such a response turns out to be bi-anisotropic, having terms associated with the permittivity, and permeability, and magnetoelectric tensors. We have derived explicit expressions for the four tensors in terms of the geometry and material parameters of the inclusions. Nevertheless, for a photonic crystal with inversion symmetry the magnetoelectric tensors in the bi-anisotropic constitutive relation vanish. In addition, we have verified that for cubic symmetry the system becomes bi-isotropic, being characterized by two frequency-dependent scalars, namely the permittivity and permeability. It is very important that, in general, the permittivity and permeability tensors are diagonal in different reference systems. The principal axes of the permeability tensor (unlike those of the permittivity tensor) depend on the direction of the wave vector. This necessitates the development of a new Crystal Optics for anisotropic photonic metamaterials.
In suitably designed nanoscale systems the ultrafast migration of uv/visible electromagnetic energy, despite its near-field
rather than propagating character, can be made highly directional. At the photon level such energy migration
generally takes a multi-step form, with each step signifying the transfer of an electromagnetic quantum between
chromophores playing the transient roles of source/donor and detector/acceptor. There is much interest in nanophotonic
devices based on such mechanisms, although the excitation transfer is usually subject to losses such as radiative decay,
and possible device applications are compromised by a lack of suitable control mechanisms. Until recently it appeared
that only by inefficient and kinetically frustrated means, such as chromophore reorientation or movement, could
significant control be effected. However in a system constructed to inhibit near-field propagation by geometric
configuration, the throughput of laser pulses can facilitate energy transfer through a process of laser-assisted resonant
energy transfer. Suitably configuring an arrangement of dipoles, it proves possible to design parallel arrays of optical
donors and acceptors such that the transfer of energy from any single donor, to its counterpart in the opposing plane, is
switched by throughput laser radiation of an appropriate intensity, frequency and polarization. A detailed appraisal of
some possible realizations of this system reveals an intricate interplay of electronic structure, optical frequency and
geometric factors. In the drive to miniaturize ultrafast optical switching and interconnect devices, the results suggest a
new basis for optically activated transistor action in nanoscale components, with significant parallel processing
We re-examine some the assumptions underlying low frequency scattering of electromagnetic
waves. We find an inconsistency in the basic field expansions, and propose a new ansatz
through which the inconsistency is addressed. We illustrate by comparing the two methods
for scattering of plane waves by a perfectly conducting cylinder, for which the exact solution
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.
Surface plasmon-like (SPL) modes are the electromagnetic surface eigenmodes on structured perfect-conductor
surfaces. The standard eigenvalue-solving method is adopted to solve these modes. The fields of the SPL
modes are maximal on the conductor surface and decay exponentially into both the air and the structured
conductor. On thin structured conductors, the SPL mode splits into a high-frequency anti-symmetric mode and
a low-frequency symmetric mode. The SPL modes are slow-wave modes with the frequencies that approach an
equivalent surface-plasmon frequency at large in-plane wavevectors. However, the interhole interaction
prevents the dispersion relation from being generally described by an analytic equation.
In this paper, we calculated the propagation constant β, the group velocity, the group velocity dispersion, and the optical field distribution in straight or curved nanometer-waveguide by means of the scale FDTD method. From the calculated results, we can find that the curve of nanometer-waveguide has influence on the dispersion of the waveguide, when the radius of nanometer-waveguide is smaller, the influence is larger. The evolutions of group velocity vg and group velocity dispersion Dw obtained by us are different from the results obtained in other papers. And the field distribution of curved waiveguide slopes towards the outside of the bend radius, smaller the bend radius is, the larger the slope of the field distribution is.
The structural origin of the weak iridescence from the very peculiar ribbon-shaped feathers of the African
open-bill stork, Anastomus lamelligerus (Ciconiidae) is investigated, using a combination of spectrophotometry,
electron microscopy, and theoretical modelling. The cortex of these feathers can be described as a slab of keratin,
transformed into a multilayer by the insertion of thin parallel planes containing harder nodules, disposed sideby-
side and oriented along the feather axis. These nodules each show a sperically capped cylindrical shape. An
empty cylindrical channel - the vacuole - occupies the long axis of the nodule. These nodules act in a collective
and individual way to produce the frequency selection giving rise to the observed dark-green coloration of these
In this paper we study theoretically the superlensing phenomenon of light by photonic crystal structures. The light wave
at any space point is calculated by using the multiple scattering method. By carefully analyzing the influences of a
number of parameters on the imaging characteristics, we find that negative refraction is not directly related to the
subwavelength imaging phenomenon.