RESUMEN
Herein, we present a detailed analysis of the structure of artificial opal films. We demonstrate that, rather than the generally assumed face centered cubic lattice of spheres, opal films are better approximated by rhombohedral assemblies of distorted colloids. Detailed analysis of the optical response in a very wide spectral range (0.4 < or = a/lambda < or = 2, where a is the conventional lattice constant), as well as at perpendicular and off-normal directions, unambiguously shows that the interparticle distance coincides very approximately with the expected diameter only along directions contained in the same close-packed plane but differs significantly in directions oblique to the [111] one. A full description of the real and reciprocal lattices of actual opal films is provided, as well as of the photonic band structure of the proposed arrangement. The implications of this distortion in the optical response of the lattice are discussed.
RESUMEN
We examine quasiperiodic multilayers arranged in m-bonacci sequences, which combine ordinary positive-index materials and dispersive metamaterials with negative index in a certain frequency range. When the volume-averaged refractive index of the nonperiodic multilayer equals zero, the structure does not propagate light radiation and exhibits a forbidden band. We identify some analytical expressions to determine the upper and lower limits of the above zero-average refractive-index bandgap. We recognize that these limits are not explicitly dependent on the geometrical parameters of the stack of layers.
RESUMEN
We study surface plasmon polariton excitations and surface shape resonances in a lossy metallic grating with bivalued cavities. The modal formalism is used to solve the diffraction problem for the infinite grating and the homogeneous problem for a single cavity in a plane surface. Both polarization modes are considered. We provide curves of reflected efficiency versus wavelength as well as near-field plots. The resonances are identified as dips in the reflected efficiency, which imply significant power absorptions. Results for various depths of the cavities and for several angles of incidence are shown, where the different types of resonant behavior can be appreciated. Particular attention is paid to the changes introduced by the finite conductivity of the metal in relation to the results obtained for a perfect conductor.
RESUMEN
We have demonstrated the use of a high-repetition-rate 46.9-nm tabletop laser to characterize diffraction gratings designed for grazing-incidence operation in the soft-x-ray spectral region. The efficiencies for various diffraction orders were measured as a function of angle of incidence and compared with the results of model simulations. This measurement technique provides benchmarks with which to improve electromagnetic codes used in the design of soft-x-ray diffraction gratings. The results illustrate the potential of compact tabletop soft-x-ray lasers for use as a new tool for characterization of short-wavelength optics at the manufacturer's site.
RESUMEN
Diffraction of plane waves by a corrugated grating made of a gyroelectromagnetic uniaxial material is set up by using the T-matrix formalism. The fully vectorial treatment presented here is limited in its range of applicability by the use of the Rayleigh hypothesis. The preferred axis of the anisotropic medium is considered parallel to the mean surface of the periodic interface between the medium and the free space. The analysis is exemplified numerically by calculations performed for sinusoidal gratings.
RESUMEN
The scattering of electromagnetic plane waves incident upon a random grating whose grooves are not perpendicular to the plane of incidence is studied. The results display a new effect associated with the weak localization of surface electromagnetic waves in random surfaces. This new effect is similar to enhanced backscattering in the sense that a peak in the intensity of the incoherent component of the scattered light is in a direction opposite to the specular direction, but it differs from enhanced backscattering in that this direction does not coincide with the retroreflection direction and in that it is observed in both p and s polarizations.
RESUMEN
A bare metallic grating illuminated by a plane, S-polarized electromagnetic wave can completely absorb one of the diffracted orders. These strong absorptions have been reported to be accompanied by two different types of behavior. Here we calculate, by means of an exact differential method, the phase versus angle-of-incidence curves for cycloidal metallic gratings with different groove-depth-to-period ratios. We show that an algorithm based on the electromagnetic theory of gratings can account for the experimentally observed behavior in the vicinity of a resonant anomaly. We also show that this type of study provides additional information about the position of the zeros of the scattering matrix in the complex plane.
RESUMEN
The surface impedance boundary condition is used to include the effect of high conductivity of meals in the integral theory of perfectly conducting gratings. As an intuitive approach, the diffraction formalism proposed by Petit for the treatment of infinitely conducting gratings in P polarization is extended to highly conducting materials by introducing the concept of equivalent surface current density. Then, integral equations for both polarizations are deduced in a mathematically rigorous way. The new method is used to calculate the efficiencies of sinusoidal gratings at infrared and visible light, and the numerical results are compared with those obtained using Maxwell boundary conditions and also with the perfect conductivity model.
