Practical applications of slow light methods require that one be able to controllably delay a pulse of light by many pulse lengths. In this contribution we analyze the possible limitations to the maximum achievable time delay and suggest methods for overcoming these limits.

In this paper, we attempt to find a unified framework in which the statistics of wave propagation in random media can be understood as strengths of scattering and absorption increase. First, we discuss the weak scattering, diffusive limit without absorption. In this limit, the suppression of transmission by weak localization, the distribution of total transmission and the intensity correlation functions with displacement and polarization rotation are all described in terms of the dimensionless conductance so that these effects are explicitly linked. When absorption is introduced, the dimensionless conductance can no longer serve as a fundamental scaling parameter, but the variance of the total transmission is still able to chart the changing statistical character of propagation and localization with sample size. By examining transport at a fixed time following pulsed excitation, the affect of absorption can be removed while the growing impact of localization can be clearly discerned. The functional form of probability distributions of intensity and total transmission and of the spatial and polarization intensity correlation functions in the time domain are the same as in the frequency domain. The connection of mesoscopic fluctuations to localization can be seen in the spectral correlation function of the field, which is the Fourier transform of average pulsed transmission. The spectral field correlation function can be expressed as a product of the correlation function of the field normalized to the average amplitude in a given configuration and of the square root of the total transmission.

By controlling the irradiance of an extended quasi-monochromatic, spatially incoherent source with a spatial light modulator, we generated a special optical field that exhibits a high degree of coherence with phase singularities for a specific pair of points at specified locations along the axis of beam propagation. Some local properties associated with coherence vortices, such as the Berry anisotropy ellipse describing the anisotropic degree of coherence close to a vortex core and the Dennis angular momentum rule for its associated phase, are also investigated experimentally.

We develop a new approach to materials with negative refraction index which can be implemented for optical and infrared frequencies. In contrast to conventional designs which require simultaneously negative dielectric permittivity and magnetic permeability, our system is intrinsically non-magnetic and makes use of an anisotropic dielectric constant to provide negative refractive index in waveguide geometry. The proposed approach is not limited to the proximity of a resonance and thus allows for low loss, critical for super-lensing applications.

This paper focuses on the recently established phenomenon of negative-phase-velocity (NPV) propagation of electromagnetic waves in the context of relativity, both special and general. Different observers in different states of uniform motion with respect to a material fragment may arrive at different conclusions on the possibility or impossibility of NPV propagation in that material. Also, conditions for NPV propagation may be satisfied in gravitationally affected vacuum. NPV propagation may thus be possible in scenarios encompassing space exploration, navigation, and communication; remotely guided extraterrestrial manufacturing industries; and the unraveling of the evolution of our universe after the last Big Bang.

A description of the fascinating coupling between gyrotropic media and negative refracting media will be presented. The article will address negative phase velocity media and particular types of dielectric-gyrotropic film-dielectric systems in which the applied magnetic field may result in a magneto-optic, or gyromagnetic, influence. The control features use a diverse family of dispersion curves.

A metamaterial exhibiting a negative index of refraction can be fabricated from an array of conducting wires cladded with non-magnetic dielectric and embedded in a magnetic host medium. The wires are responsible for the ε < 0 property and the magnetic medium for the μ < 0 property. A near exact calculation of the electromagnetic response of this metamaterial indicated that the bandwidth over which n < 0 depends primarily on the magnetization of the magnetic host and on the radius of the wire, the outer radius of the cladding, and the lattice constant of the wire array. For readily available materials the dissipation within the medium is mainly due to Ohmic losses within the wire and not magnetic dissipation within the magnetic host. The losses can be minimized by choosing an high conductivity metal for the wire and by having the radius of the wire and outer radius of the cladding as large as practical consistent with maintaining ε < 0.

We investigate the lasing modes in diffusive random media with local pumping. The reabsorption of emitter light suppresses the feedback from the unpumped part of the sample and effectively reduces the system size. The lasing modes are dramatically different from the quasimodes of the passive system (without gain or absorption). Even if all the quasimodes of a passive diffusive system are extended across the entire sample, the lasing modes are still confined in the pumped volume with an exponential tail outside it. The reduction of effective system volume by absoption broadens the distribution of decay rates of quasimodes and facilitates the occurrence of discrete lasing peaks.

Recent observation of two-mode lasing in random lasers is discussed in the context of the problem of distinguishing between lasing with coherent and non-coherent feedback. A general semiclassical theory of lasing in cavities with a spatially non-uniform dielectric constant is developed. It is shown that the non-uniformity causes a radiative coupling between modes of the empty cavity, which results in a renormalization of the coefficients responsible for non-linear interaction between lasing modes. One of the consequences of this renormalization is the enhancement of the effects of spatial hole burning and promotion of the multi-mode lasing.

We demonstrate first anti-Stokes laser in which only one pumping photon is required to produce one higher-energy emission photon. The difference of energy is drawn from phonons. This regime is realized in GaAs random laser. We also propose a laser system based on an anti-Stokes laser, which can be pumped by heat only. The temperature of the heater does not need to be high. The heat pumping energy (at practically no cost) can be provided via thermal contact of the laser element with an ambient environment, such as atmosphere, ocean, ground, etc.

In recent years there has been a significant evolution in the development of high purity growth methods for nanoparticles in the 10 nm size range. Concurrently, new processing methods have led to the emergence of laser quality transparent ceramics prepared from rare-earth-doped nanopowders. Output powers and efficiencies of ceramic lasers have been reported to compare very well with those of crystal laser systems, causing interest both in nanoscale and macro-scale optical ceramics. In this paper, we first describe highly scattering oxide powders that generate continuous-wave random laser action, are able to store light, exhibit quantum size effects, and sinter to transparency at exceptionally low temperatures. Quantum size effects and modified dopant interactions in transparent ceramics processed from these powders are then considered, and their potential relevance to problems in laser cooling and the engineering of nanostructured ceramics for solid state lasers and nonlinear optics are evaluated.

We discuss theoretical predictions for ultrafast (femtosecond) linear and nonlinear optical phenomena in metal nanostructures. We show that very strong (orders of magnitude in local-field intensity) ultrafast concentration of energy on nanoscale is possible. In metal/semiconductor quantum dot nanostructures, we consider a fascinating possibility of quantum generator due to spaser (surface plasmon amplification by stimulated emission of radiation). Various applications are discussed. We discuss recent experiments where the coherent control on the nanoscale has been observed and present the corresponding theoretical interpretation. We also discuss a proof-of-principle experiment on observation of the spaser published recently.

Localized surface plasmon excitations in metallic nanoparticles with either absorbing or amplifying media are analyzed. In the case of absorption, we present the first direct measurements of enhanced absorption in two dimensional films of dyes and isolated metallic nanoparticles. These results are of particular importance for enhancing the performance of low cost solar cells by allowing for a reduction in the thickness of amorphous layers that have poor conduction properties. Materials specific to the application of plasmon enhancement of TiO₂ dye sensitized solar cells are also described. The situation where the surrounding medium is capable of amplification is studied and the required gains for real metals are determined. In addition, the enhancement of local fields in such systems is estimated and discussed in terms of further enhancing Surface Enhanced Raman Spectroscopy processes for molecular detection.

We present a unified framework for a first-principles calculation of the electric force acting on dielectric or metallic nanospheres suspended in a dielectric host and subject to a uniform external electric field. This framework is based on the spectral representation of the local electric field in a composite medium. The quasi-static (or "surface-plasmon") eigenstates of a cluster of spheres are first calculated, numerically. Then those are used to calculate the force on any sphere as the gradient of the total electrostatic energy with respect to the position of that sphere. This approach is applicable even when the spheres are very closely spaced, and even when they are metallic: No infinities ever appear. The forces are not limited to dipole-dipole forces. Moreover, the force acting on any sphere is not a simple sum of two-body forces: When the inter-sphere gaps are small, complicated many-body forces appear. This is due to the fact that, when a sphere center is displaced slightly, the electric polarization of all the other spheres is changed. Consequently, the total electrical energy is changed in a way that cannot be represented as a sum of two-body energy changes. Explicit calculations of these forces for a few selected sphere clusters are presented. The results are quite different from what is obtained in the dipole approximation.

Complex media can be grown, found in nature, or manufactured.. Holography is one way of fabricating such media. Here I review some examples of holographically manufactured complex media and speculate about some that could be made.

Photoresponsive nanocomposite organically modified silica (ORMOSIL) films were prepared by solution sol-gel processing of organically modified silicon alkoxide compounds. Waveguiding at 488 nm proceeds with simultaneous self-inscription and permanently inscribed waveguides can be revealed by wet etching. Under certain conditions, self-inscription becomes chaotic, and filamentation is observed. A counterpropagating beam set-up allows simple optical devices like crosses and y-junctions to be created. Soliton-like behavior is exhibited at low laser power where counterpropagating self-inscribed beams undergo mutual trapping. The ORMOSIL films exhibit interesting patterns which may be associated with the relief of stress in the films. These patterns can be controlled to some extent by depositing self-inscribed features in the glassy medium.

The homogenization of three-phase particulate dielectric composites provides the setting for our theoretical study. We implement an extension of the widely used Bruggeman homogenization formalism which takes account of the sizes, shapes, and orientations of the component particles. Thereby, the relationships between the geometric attributes of the component particles and the constitutive parameters of the homogenized composite are investigated. In particular, we consider interactions between percolation thresholds associated with conducting and nonconducting component particles. Anisotropies in percolation thresholds and their interactions are explored via numerical examples.

We show that a chiral film that is not matched to the refractive indices of the surrounding media behaves as a Bragg resonator for elliptically polarized light with a given handedness, ellipticity, and axial alignment. Equations are derived for the polarization parameters, auxiliary angle (chi) and azimuthal angle (alpha), of the polarization ellipse. Thickness modulated chiral films and chiral-birefringent composite media are considered as elliptical Bragg mediums. Experimental results are presented for coatings fabricated with titanium oxide.

A general framework for the analysis of chiral electromagnetic media is discussed via the analysis of Maxwell's equations in a coordinate system that rotates uniformly along the z-axis. We are motivated in this study by the knowledge that exact solutions exist in at least two canonical cases: (a) natural optical activity and (b) structurally chiral dielectrics. In the latter case the so-called Oseen transformation has previously been used to render a completely analytic solution. However, we show that this transformation is not a true rotation of real physical space, but that when such a rotation is applied via the helical transformation, identical solutions are generated. These ideas provide a basis for constructing solutions in chiral media in general, and it is speculated how they can be applied in novel contexts.

In the field of optical energy harvesting it has long been known that the efficient capture of radiation by suitably designed absorbers is by no means the sole criterion for an effective collection system. The optical energy acquired by an absorbing medium is of little value at its absorption site; useful devices require that the energy rapidly and non-diffusively relocates to traps or reaction centers. Storage is then achieved by driving charge separation or another more complex reaction. The principles that operate over the crucial mechanisms for inter-site energy transport are now well understood, and materials can be engineered to expedite and control an optimally directed, multi-step flow of energy. In this paper the salient principles drawn from nanophotonics, fluorescence spectroscopy, molecular electronic structure and nonlinear optics are exhibited with reference to a number of recently devised energy harvesting materials and systems, prominently featuring dendrimeric organic polymers. It is also shown how the elementary transfer mechanism can be tailored to more efficiently direct the flow of excitation energy.

Mobility in single-grain and polycrystalline organic field-effect transistors (OFETs) is of interest because it affects the performance of these devices. While reasonable values of the hole mobility has been measured in pentacene OFETs, relatively speaking, our understanding of the detailed transport mechanisms is somewhat weak and there is a lack of precise knowledge on the effects of the materials parameters such as the site spacing, the localization length, the rms width of the density of states (DOS), the escape frequency, etc. This work attempts to analyze the materials parameters of pentacene OFETs extracted from data reported in the literature. In this work, we developed a model for the mobility parameter from first principle and extracted the relevant materials parameters. According to our analyses, the transport mechanisms in the OFETs are fairly complex and the electrical properties are dominated by the properties of the trap states. As observed, the single-grain OFETs having smaller values of the rms widths of the DOS (in comparison with the polycrystalline OFETs) also had higher hole mobilities. Our results showed that increasing the gate bias could have a similar but smaller effect. Potentially, increasing the escape frequency is a more effective way to raise the hole mobility and this parameter appears to be affected by changes in the molecular structure and in the degree of "disorder".

The exciton polaritons dispersion law is analyzed in a one-dimensional multiple-quantum-well based photonic crystal. An effective approach allowing to consider structures with an arbitrary periodic spatial modulation of the dielectric function and the multilevel structure of the exciton spectrum is developed. It is shown that the condition of the Bragg resonance has to be modified to take into account the symmetry of the exciton states and the non-trivial dispersion law of the electromagnetic waves in photonic crystals. For a particular case of a one-level excitonic susceptibility it is shown that the Bragg resonance occurs when the exciton frequency falls to the high-frequency boundary of the photonic band-gap. The polariton's dispersion law is considered. The angular dependence of the spectrum is analyzed. The effect of multiple exciton levels on the polariton spectrum is discussed.

Modal solutions for photonic crystal fibers (PCFs) with circular air holes in a hexagonal matrix are presented, by using a rigorous full-vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, modal hybridness, modal birefringence and group velocity dispersion values have been determined for a range of PCFs and the results are shown and conclusions drawn.

In this paper, we explore the specific nature of wave propagation in multiple scattering media and examine how this is revealed in various aspects of the speckle pattern measured at the output surface of an ensemble of disordered media. We present near-field measurements of the speckle pattern transmitted through random samples in a quasi-one dimensional geometry. The microwave field--amplitude and phase--is measured as a function of frequency along perpendicular transverse polarizations on a close grid of points on the output surface of samples composed of randomly positioned dielectric spheres. The field spectrum is Fourier transformed to access the temporal evolution of the speckle pattern. The field and intensity correlation functions versus displacement and frequency shift are measured and reveal non-Gaussian behavior, namely long range correlation. The key distributions and correlation functions of the delay time are also measured and compared to calculations, to show the interplay between the delay time and the intensity in the speckle pattern. The widest fluctuations of the phase derivative with frequency are found at low intensity values near a phase singularity in the transmitted speckle pattern. The position of these phase singularities at which the intensity vanishes is reconstructed for the entire speckle pattern.

Second harmonic generation (SHG) was observed from yttrium orthochromite (YCrO₃) crystals with centrosymmetric structure. The origin of the SHG was determined to be a magnetic-dipole transition considering the resonant structure of SHG spectra and its polarization dependence. The intensity of SHG shows the drastic change at the Néel temperature under magnetic field and this fact suggests the effects from magnetic ordering. Along with the spectrum of the SHG intensity, phase of the nonlinear susceptibility was measured by analyzing the polarization characteristics of superposed fields from the sample and reference. The result shows that axial i-type χ⁽²⁾ value is pure imaginary at the peak wavelength. Gallium ferrite (GaFeO₃) has simultaneously four types of nonlinear optical tensors including polar i-, axial i-, polar c- and axial c-types. We observed SHG originating from c-type components by employing the experimental configuration where each contribution is separable. Structures of spectra and their relation to magnetic properties are discussed.

Simplified method of eigenmodes simulation in random media based on numerical solution of the stationary wave equation for two-dimensional (2D) medium with a random distribution of dielectric permittivity is suggested. By means of discretization the wave equation can be reduced to the system of homogeneous linear equations that includes parameter α=(2πb/λ)², where b is the spacing between the nodes of discretization, λ - the wavelength. The values of α (and corresponding b/λ) were determined as eigenvalues of this system of linear equations. The relative field amplitudes in all discretization nodes i.e. eigenvectors were calculated with this α. 2D random medium was simulated by matrix whose elements randomly take on two different values. One of them corresponds to dielectric permittivity of the material particles, the other - to permittivity of the spaces between them. Under the assumption made, elements of such matrix represent material particles and spaces between them, quantity b - particles size. All calculations were made using MATLAB. Different variants of disordered (and ordered) media were examined. It was shown that localized modes exist only in disordered systems and in a limited range of ratio b/λ . The dependence of modes character on the value of filling ratio and dielectric permittivity is estimated. Some results for one- and three-dimensional media are represented.

Since the intrinsic lifetime of spontaneous recombination UV radiation in zinc oxide amounts less than ~200 ps it is of interest to obtain stimulated UV radiation of powdered ZnO with pumping pulses of nanosecond duration. This will clarify the possibility of quasi-continuous laser radiation in disordered media. At the same time this effect can open the way for working out a cathodoluminescent screen with narrow spectrum and short persistence time. Investigations of UV radiation spectra of powdered zinc oxide and some disordered films were conducted. The samples were pumped by 3-rd harmonics of the two-stage Nd:YAG-laser (λ=355 nm) with pulse duration ~10 ns. Maximum density of energy of pumping pulses was about 160 mJ/cm². Spectra of spontaneous emission were registered at 300K and 77K. With some of our powdered samples we achieved lasing at 300K. The threshold values of pumping energy density occurred to be higher than that under picosecond pumping approximately for two orders of magnitude. Peculiarities of different samples lasing are demonstrated and discussed. In spectra of the ZnO films investigated at 300K UV band maximum is situated at ~382 nm, while in powders of ZnO this maximum was located at ~389 nm. Besides, in the films the long-wavelength part of the UV band broadens with increase of pumping power.

Last years nanosized gold particles attract much attention as a component of industrially perspective catalysts for some reactions as CO oxidation, NO reduction etc. We studied several systems including gold based on different synthetic zeolites pure or doped with another metals (Fe, Na). It was shown by different techniques (XPS, UV-Vis spectroscopy, TPR) that intrinsic properties of zeolites used and gold system preparation method influence significantly on the contribution of different gold species (ions, clusters and particles). For mixed Au-Me-zeolites activity level and dynamic of CO conversion with time in steam and temperature depends on nature of zeolite and specificity of Au-Me interaction. All binary metal systems were found to be activated in different degree during catalytic activity test due to mutual interaction of gold with second metal. Extremely high level of CO conversion and low dependence of activity on temperature was observed for Au- Fe- H- and Na-Y zeolites. The change in contribution of gold nanoparticles was observed after sample contact with CO.

Nanosized carbon fibers are of great importance due to its numerous technological applications. One of its disadvantages is low mechanical strength. This problem could be solved by incorporation of carbon fibers into cavities or channels of ceramic monoliths with foam or honeycomb structure. In the present work the experience of preparation of uniform carbon layer consisting from nanosized fibers onto ceramic monoliths with different geometry will be presented. Carbon fibers were produced by catalytic pyrolysis of methane over nanosized metal particles supported over ceramic monolith. Variation of preparation conditions permits to obtain carbon fibers with different density and thickness.

The application of nanosized palladium catalysts has gained growing importance over the last few years. Palladiumbased catalytic methods for fine organic synthesis permits the replacement of traditional labor-consuming techniques in multi-step organic syntheses and provides an improvement from the standpoint of cost and environmental impact. The use of activated carbon "Sibunit" as a substrate for catalysts has been fostered by the substrate's high surface area, chemical inertness both in acidic and basic media, and at the same time by the absence of very strong acidic centers on its surface which could promote undesirable side reactions during the catalytic run. A conversion of alpha-pinene derivatives to commercial biologically active compounds and fragrances as well as sun screens with ultra violet filtering properties, involves a catalytic hydrogenation as a key intermediate step. The aim of the present work is to clarify the factors favoring the dispersion of Pd metal on carbon. The effect of reduction temperature and pretreatment of the carbon surface on metal size during preparation of Pd on "Sibunit" catalysts for selective verbenol conversion was studied. The electron microscopy method (TEM) was used to show the influence on Pd metal dispersion of carbon surface oxidation by the oxidant H₂O₂, HNO₃. The catalytic activity of Pd/C catalyst samples in verbenol hydrogenation reaction was determined. Kinetic peculiarities of verbenol hydrogenation over the most active catalyst sample were obtained.

Colloidal silica spheres with 200nm, 250nm, and 290nm diameters were self-assembled with single crystal crystallites 4-5mm wide and 10-15mm long. Larger spheres with diameters between 1000-2300nm were self-assembled with single crystal crystallites up to 1.5mm wide and 2mm long. The silica opals self-assembled vertically along the [100] direction of the face centered cubic lattice resulting in self-templated opals. Inverse opal photonic crystals with a partial band gap possessing a maximum in the near infrared at 3.8μm were constructed from opal templates composed of 2300nm diameter spheres with chalcogenide Ge₃₃As₁₂Se₅₅ (AMTIR-1), a transparent glass in the near infrared with high refractive index. Inverse gold and gold/ polypropylene composite photonic crystals were fabricated from synthetic opal templates composed of 200-290nm silica spheres. The reflectance spectra and electrical conductance of the resulting structures is presented. Gold was infiltrated into opal templates as gold chloride and heat converted to metallic gold. Opals partially infiltrated with gold were co-infiltrated with polypropylene plastic for mechanical support prior to removal of the silica template with hydrofluoric acid.

Using the density-functional theory, the Ginzburg Pitaevskii Gross (GPG) equation for Bose-Einstein (BE) condensate, confined in a magnetic trap, is modified to include contribution from three-body collisions in the strongly interacting regime a>>l, 'a' is the scattering length and 'l' being the characteristic low energy length scale. This generalized GPG equation has been solved numerically using the analytically derived Thomas-Fermi order parameter, which also includes three-body interactions. The order parameter, chemical potential, extent of correlation and other ground state properties are computed when the aspect ratio, λ, is varied from1.0 to 0.05 (λ represents the anisotropy of the magnetic trap). As λ is varied from 1.0 to 0.05, the condensate shape changes from isotropic three-dimensional (3-D) to highly anisotropic quasi one-dimensional (1-D). The stability of the BE condensate increases with decrease in λ, which is also borne out by the behavior of chemical potential and the total energy per particle, as there is a decrease of about four times for a=5000 a₀ as well as for a=7000 a₀, 'a₀' being the Bohr radius. The extent of correlations, however, increases by more than five folds, showing that quasi 1-D BE condensate is highly correlated. Both two- and three-body interaction energies show a decrease with decrease in λ: three-body interaction energy staying below two-body interaction energy for a=5000 a₀ while for a=7000 a₀, a cross-over occurs between the two at λ ~ 0.35. As one goes from 3-D to quasi 1-D, the percentage difference for various physical quantities, computed between only two-body interactions and when both two- and three-body interactions are considered, shows a decrease, suggesting that the effect of three-body collisions become increasingly less significant in agreement with the recent study.

Multiphase composite nanoparticles presenting core-shell structures have been investigated by performing a detailed correlation between their synthesis parameters and the structural and magnetic properties. Basically in all the experiments iron pentacarbonyl as iron precursor and ethylene as laser energy transfer agent and as a secondary carbon source have been used. The capability of the synthesis technique to form nanocomposite particles by varying laser power density, inlet geometry, pressure in reactor chamber and gas precursors' ratio was tested. The results proved that the laser pyrolysis can produce particles between 4 and 10 nm diameters. Their sizes may vary according to the reactor pressure and gas flows but their size distributions remain sharp as long as an optimized geometry of the reactor is used. As a second step, the structure and magnetic properties were studied by different techniques such as TEM, HREM, SAED, XRD, FT-IR and Raman spectroscopy. The investigations reveal that, depending on the input parameters, some samples exhibit a nanocomposite structure consisting of iron / iron carbides (Fe3C or Fe2C5) core wrapped in a shell of amorphous or turbostratic carbon. The different magnetic phase identification was performed using Mossbauer spectroscopy and thermo-magnetic analysis.