Optical amplification enhancement in photonic crystals

Improving and controlling the efficiency of a gain medium is one of the most challenging problems of laser research. By measuring the gain length in an opal based photonic crystal doped with laser dye, we demonstrate that optical amplification is more than twenty-fold enhanced along the Gamma-K symmetry directions of the face centered cubic photonic crystal. These results are theoretically explained by directional variations of the density of states, providing a quantitative connection between density of the states and light amplification

Variations in the basic biokinematic pattern in three breeds of horses at the hand-led walk

In this study the lineal and temporal parameters of the stride of andalusian (n=10), angloarabian (n=6) and arabian (n=7) mature horses were compared at the walk. The speeds were similar in the three breeds (1.63±0.10 m/s), for what the Archivos de zootecnia vol. 48, núm. 183, p. 328. GALISTEO ET AL. statistical comparisons were carried out by an analysis of the variance, and a means comparison test (Tukey test). The stride lenght was shorter in arabians and andalusians than in angloarabians, while the overtracking lenght was bigger in the arabians. The duration of the forelimb cycle was bigger in angloarabians due to a bigger duration in this breed of the stance phase. The midstace position (expressed as a percentaje of the stride duration) differed among the three breeds, indicating that each one shows times of braking and propulsion of the forelimb different to the other ones; but not in the instant in which the hoof reaches the highest point in its trajectory. In the hind limb the differences were much less marked, since small differences were detected in the duration of the cycle between arabians and angloarabians, while the stride duration was longer in andalusians and angloarabians than in the Arabians; the braking and propulsion phases (determined by the position along the stride of the midstance position) didn’t differ among breeds, the same with the instant in which the hindhoof reach the highest point in its trajectory. It can be concluded that marked differences exist between equine breeds in the lineal parameters of the stride at the walk, and the temporal parameters of the forelimb, while in the hind limb are less marked, probably because this member is functionally committed in the propulsion of the horse.En este estudio se compararon los parámetros lineales y temporales del tranco de paso de caballos adultos de Pura Raza Española (n=10), Angloárabe (n=6) y Árabe (n=7). Las velocidades fueron similares en las tres razas (1,63±0,10 m/s), por lo que las comparaciones estadísticas se realizaron mediante un análisis de la varianza y un test de comparación de medias (Test de Tukey). La amplitud de tranco fue más corta en Árabes y Españoles que en Angloárabes, mientras que la longitud de sobrehuella fue mayor en los Árabes. La duración del ciclo del miembro torácico fue mayor en Angloárabes debido a una mayor duración en esta raza de la fase de apoyo. La posición de apoyo medio (expresada porcentualmente a la duración total del ciclo) difirió entre las tres razas, indicando que cada raza presenta tiempos de frenada y propulsión del miembro torácico diferentes a las demás; no así en el instante en el que el casco alcanza el punto más alto de su trayectoria. En el miembro pelviano las diferencias fueron mucho menos marcadas, ya que se detectaron pequeñas diferencias en la duración del ciclo entre Árabes y Angloárabes, mientras que la duración del tranco fue mayor en Españoles y Angloárabes que en los Árabes; los tiempos de frenada y propulsión (determinada por la posición a lo largo del tranco del apoyo medio) no difirió entre razas, lo mismo que el instante en que el casco pelviano se encuentra en el punto más alto de su trayectoria. Se puede concluir que existen marcadas diferencias entre razas equinas en los parámetros lineales del tranco al paso, al igual que sucede con los parámetros temporales del miembro torácico, mientras que en el pelviano son menos marcadas, probablemente porque este miembro está funcionalmente más comprometido que el torácico en la propulsión del caballo

Tunable magneto-photonic response of nickel nanostructures

In this letter, we present both experimental and numerical studies of the magneto-optical (MO) properties of nickel infiltrated opals. Ni can show interesting MO properties that can be controlled by nanostructuration through colloidal crystals templating. Nanostructuration allows the coupling of light to surface plasmon modes of Ni, and a clear dependence of the MO response as a function of the structural parameters of the template has been observed. This dependence can be used in future tunable devices such as switchers or MO modulators. © 2011 American Institute of Physics.This work has been partially supported by EU FP7 (NoE Nanophotonics 4 Energy Grant No. 248855 and NMP3-SL-2008-214107-Nanomagma); the CSIC PIF08-016, the Spanish MICINN (CSD2007-0046-Nanolight.es, CSD2008-00023-Funcoat, MAT2009-07841-GLUSFA, MAT2008-06765-C02-01/NAN-MAGPLAS) and Comunidad de Madrid (S2009/MAT-1756-PHAMA and S2009/TIC–1476- MICROSERES).Peer Reviewe

Morphometric study of the nerve fibers of the oculomotor nerve in dog

The intracranial portion of the right oculomotor nerves was extracted from six adult German Shepherd dogs. The nerves were studied using light and electron microscopy. Nerve area was calculated, and myelinated and unmyelinated fibers were analized to determine number, diameter and area. Also in the myelinated fibers the area and diameter of the correspondent axon, and thickness of the myeline sheath were measured. The mean number of fibers was 8543.50±1231.85 for myelinated and 1402.00±241.58 for unmyelinated. The mean fiber diameter was 10.23±0.68 μm for myelinated and 0.43±0.21 μm for unmyelinated. This study demonstrated that the oculomotor nerves in dogs have structural and ultrastructural characteristics that are similar to those from other specie

Optical response with threefold symmetry axis on oriented microdomains of opal photonic crystals

The paper deals with three-dimensional photonic crystals known as artificial opals, namely, fcc lattices of dielectric spheres: such systems have been the subject of numerous investigations. Opal photonic crystals viewed along the [111] direction of the fcc structure have a threefold symmetry axis; however this microscopic symmetry is difficult to observe in optical measurements performed on macroscopic areas containing microdomains with different orientations. In this work polarized transmittance measurements on [111]-stacked silica opals with single oriented microdomains, identified by field-emission scanning electron microscopy and laser-scanning confocal microscopy, demonstrate different optical response of twin structures with the two possible vertical stacking sequences. A detailed comparison with theory shows that microtransmittance experiments probe the photonic band structure along the Gamma-L-K and Gamma-L-U orientations of the Brillouin zone, respectively, thus giving conclusive evidence for macroscopic optical response related to the presence of a threefold (instead of a sixfold) symmetry axis in the photonic microstructure. The paper arises from a collaboration between the University of Pavia and the Politecnico di Torino

Tunable anisotropy in inverse opals and emerging optical properties

Using self-assembly, nanoscale materials can be fabricated from the bottom up. Opals and inverse opals are examples of self-assembled nanomaterials made from crystallizing colloidal particles. As self-assembly requires a high level of control, it is challenging to use building blocks with anisotropic geometry to form complex opals, which limits the realizable structures. Typically, spherical colloids are employed as building blocks, leading to symmetric, isotropic superstructures. However, a significantly richer palette of directionally dependent properties are expected if less symmetric, anisotropic structures can be created, especially originating from the assembly of regular, spherical particles. Here we show a simple method to introduce anisotropy into inverse opals by subjecting them to a post-assembly thermal treatment that results in directional shrinkage of the silica matrix caused by condensation of partially hydrated sol-gel silica structures. In this way, we can tailor the shape of the pores, and the anisotropy of the final inverse opal preserves the order and uniformity of the self-assembled structure, while completely avoiding the need to synthesize complex oval-shaped particles and crystallize them into such target geometries. Detailed X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy studies clearly identify increasing degrees of sol-gel condensation in confinement as a mechanism for the structure change. A computer simulation of structure changes resulting from the condensation-induced shrinkage further confirmed this mechanism. As an example of property changes induced by the introduction of anisotropy, we characterized the optical spectra of the anisotropic inverse opals and found that the optical properties can be controlled in a precise way using calcination temperature

Dynamic light diffusion, Anderson localization and lasing in disordered inverted opals: 3D ab-initio Maxwell-Bloch computation

We report on 3D time-domain parallel simulations of Anderson localization of light in inverted disordered opals displaying a complete photonic band-gap. We investigate dynamic diffusion processes induced by femtosecond laser excitations, calculate the diffusion constant and the decay-time distribution versus the strength of the disorder. We report evidence of the transition from delocalized Bloch oscillations to strongly localized resonances in self-starting laser processes.Comment: 4 pages, 5 figure

Enhanced emission in self assembled photonic crystals by hybrid photonic-plasmonic modes

Trabajo presentado a NanoSpain 2010 celebrado en Málaga del 23-26 Marzo, 2010Surface Plamon Resonances. -- Free Standing 2D PC. -- Normal IncidencePeer reviewe