Effect of extinction on the high-energy optical response of photonic crystals

An analysis of the optical response of photonic crystals in the high-order band energy range is herein presented. High and abruptly fluctuating specular reflectance is predicted for perfect lattices at those energies even in the absence of any photonic gap or pseudogap. As optical extinction is gradually introduced, it is possible to reproduce experimental results found in the literature and which have recently been the subject of an intense debate. Band structure calculations demonstrate that extinction is extraordinarily amplified in the high-energy range and is responsible for the features so far observed in that range in real crystalsConsejo Superior de Investigaciones Científicas 2005AR0070Universidad de Buenos Aires ANPCYT-BID 802Agencia Nacional de Promoción Científica y Tecnológica OC-AR03-14099Ministerio de Educación y Ciencia MAT2005-0302

Interplay between crystal-size and disorder effects in the high-energy optical response of photonic crystal slabs

Experimental reflectance spectra have been obtained for colloidal crystals whose widths ranged from one to several sphere monolayers, and their features in the higher order band energy range have been reproduced theoretically. In order to fit the measured data, optical extinction has been introduced in the theoretical model, which accounts for structure imperfections and disorder, the main sources of losses in an actual measurement. A complex spectrum in the high frequency region is observed even for one ordered monolayer, being this peak structure gradually modified as more layers are piled up. This allowed us to identify which peaks are reminiscent of the optical reflectance features of a single close-packed layer and which are the result of building up a three dimensional periodicity. A clear correlation between the amount of extinction introduced in the fitting and the slab width has been found, which demonstrates that wider real crystals produce less diffusely scattered light. At the same time, we find that the optical response of thinner crystals is more robust against the introduction of extinction than that of thicker ones, for which the effect is dramatic.Consejo Superior de Investigaciones Científicas 2005AR0070Universidad de Buenos Aires ANPCYT-BID 802Agencia Nacional de Promoción Científica y Tecnológica OC-AR03-14099Ministerio de Ciencia y Educación MAT2005-0302

Physical origin of the high energy optical response of three-dimensional photonic crystals

The physical origin of the optical response observed in three-dimensional photonic crystals when the photon wavelength is equal or lower than the lattice parameter still remains unsatisfactorily explained and is the subject of an intense and interesting debate. Herein we demonstrate for the first time that all optical spectra features in this high energy region of photonic crystals arise from electromagnetic resonances within the ordered array, modified by the interplay between these resonances with the opening of diffraction channels, the presence of imperfections and finite size effects. AU these four phenomena are taken into account in our theoretical approach to the problem, which allows us to provide a full description of the observed optical response based on fundamental phenomena as well as to attain fair fittings of experimental results.Consejo Superior de Investigaciones Científicas 2005AR0070Universidad de Buenos Aires ANPCYT-BID 802Agencia Nacional de Promoción Científica y Tecnológica OC-AR03-14099Ministerio de Ciencia y Educación MAT2005-0302

Towards a full understanding of the growth dynamics and optical response of self-assembled photonic colloidal crystal films

Recent advances in the comprehension of the growth dynamics of colloidal crystal films opens the door to rational design of experiments aiming at fabricating lattices in which the density of intrinsic defects is minimized. Since such imperfections have a dramatic effect on scattered light of wavelength smaller than the lattice constant, the evaluation of the experimental optical response at those energy ranges, based on the comparison to rigorous calculations, is identified as the most sensitive guide to accurately evaluate the progress towards the actual realization of defect-free colloidal crystals.Ministerio de Ciencia y Educación MAT200503028Consejo Superior de Investigaciones Científicas 2005AR007

Experimental evidence of localized oscillations in the photosensitive chlorine dioxide-iodine-malonic acid reaction

The interaction between Hopf and Turing modes has been the subject of active research in recent years. We present here experimental evidence of the existence of mixed Turing-Hopf modes in a two-dimensional system. Using the photosensitive chlorine dioxide-iodine-malonic acid reaction (CDIMA) and external constant background illumination as a control parameter, standing spots oscillating in amplitude and with hexagonal ordering were observed. Numerical simulations in the Lengyel-Epstein model for the CDIMA reaction confirmed the results

A comparison of Monte Carlo-based Bayesian parameter estimation methods for stochastic models of genetic networks

We compare three state-of-the-art Bayesian inference methods for the estimation of the unknown parameters in a stochastic model of a genetic network. In particular, we introduce a stochastic version of the paradigmatic synthetic multicellular clock model proposed by Ullner et al., 2007. By introducing dynamical noise in the model and assuming that the partial observations of the system are contaminated by additive noise, we enable a principled mechanism to represent experimental uncertainties in the synthesis of the multicellular system and pave the way for the design of probabilistic methods for the estimation of any unknowns in the model. Within this setup, we tackle the Bayesian estimation of a subset of the model parameters. Specifically, we compare three Monte Carlo based numerical methods for the approximation of the posterior probability density function of the unknown parameters given a set of partial and noisy observations of the system. The schemes we assess are the particle Metropolis-Hastings (PMH) algorithm, the nonlinear population Monte Carlo (NPMC) method and the approximate Bayesian computation sequential Monte Carlo (ABC-SMC) scheme. We present an extensive numerical simulation study, which shows that while the three techniques can effectively solve the problem there are significant differences both in estimation accuracy and computational efficiency

Dynamics of Turing patterns under spatio-temporal forcing

We study, both theoretically and experimentally, the dynamical response of Turing patterns to a spatio-temporal forcing in the form of a travelling wave modulation of a control parameter. We show that from strictly spatial resonance, it is possible to induce new, generic dynamical behaviors, including temporally-modulated travelling waves and localized travelling soliton-like solutions. The latter make contact with the soliton solutions of P. Coullet Phys. Rev. Lett. {\bf 56}, 724 (1986) and provide a general framework which includes them. The stability diagram for the different propagating modes in the Lengyel-Epstein model is determined numerically. Direct observations of the predicted solutions in experiments carried out with light modulations in the photosensitive CDIMA reaction are also reported.Comment: 6 pages, 5 figure

Sobre la subjetividad para el consumo de sustancias psicoactivas

En el tema de las sustancias psicoactivas, lícitas o ilícitas, hay un medio ambiente que no es neutro y que, por tanto, fija tanto las reglas de su producción, distribución y venta así como construye las representaciones que definen culturalmente su consumo. De esta forma cumple un papel tanto en el uso como en el abuso. Los grupos sociales responden a esta acción, aceptando o rechazando. La vulnerabilidad frente a las presiones que implica la exposición a estas fuerzas del medio se expresa por lo grupal y por lo personal. En lo grupal se encuentran los espacios necesarios para contener las ansiedades sociales, parte de nuestra estrategia de sobrevivencia como especie gregaria. Este espacio incluye lo familiar, la vecindad y la comunidad con sus diversas organizaciones. Su precariedad está relacionada con la incompletud de su estructura o con la insuficiencia de los roles familiares o vecinales para darle contención a sus miembros. En ese caso la resistencia final a las presiones de la exposición recae en lo personal y en su labilidad o consistencia para manejarse en el campo cognitivo y emocional

Anomalous Light Propagation, Finite Size-Effects and Losses in Real 3D Photonic Nanostructures

The propagation of light through 3D ordered photonic nanostructures is strongly affected by real aspects of actual crystals, especially at the spectral range where the wavelength of light is on the order of the lattice parameter. We perform a theoretical study on anomalous light propagation in finite thin artificial opal slabs made of a reduced number of layers. The vector KKR method we use accounts for the finite character of the structure and for different sources of losses. We show that an interplay between finite-size effects and losses engineers group velocity at this high energy range. Only depending on the crystal size and extinction, light propagation can either be superluminal (positive or negative) or approach zero for certain frequencies. The numerically calculated group index is in good agreement with experimental results some of which remained partially unexplainedPeer reviewe

Anomalous group velocity at the high energy range of a 3D photonic nanostructure

We report on a study of electromagnetic waves propagation in thin periodically ordered photonic nanostructures in the spectral range where the light wavelength is on the order of the lattice parameter. The vector KKR method we use allows us to determine the group index from finite photonic structures including extinction providing confirmation of recently emerged results. We show that for certain frequencies the group velocity of opal slabs can either be superluminal or approach zero depending on the crystal thickness and the unavoidable presence of losses. In some cases, group velocity can be negative. Such behavior can be clearly attributed to the finite character of the three-dimensional structure and reproduces previously reported experimental observations. Calculations show that contrary to the predictions of extraordinary group velocity reductions for infinite periodic structures, the group velocity of real opals may exhibit strong fluctuations at the high energy range. Hence, a direct identification between the calculated anomalous group velocities, for an actual opal film, and the predicted propagating low dispersion modes for an ideal infinite ordered structure seems difficult to establish. © 2010 Optical Society of America.Peer Reviewe