We report the design and fabrication of a multilayered macroscopic fiber preform and the subsequent drawing and optical characterization of extended lengths of omnidirectional dielectric mirror fibers with submicrometer layer thickness. A pair of glassy materials with substantially different indices of refraction, but with similar thermomechanical properties, was used to construct 21 layers of alternating refractive index surrounding a tough polymer core. Large directional photonic band gaps and high reflection efficiencies comparable to those of the best metallic reflectors were obtained. Potential applications of these fibers include woven fabrics for radiation barriers, spectral authentication of cloth, and filters for telecommunications.

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Interest in the possibility of compact, low-threshold lasers has motivated investigations of the emission of active materials embedded in photonic crystal (PC) structures. The sharp decrease in the group velocity of light at the photonic band edge increases the interaction time of the light with the gain medium, enhancing optical gain. [1,2] Such gain enhancements have been observed in a variety of PC systems, including onedimensional (1D), [3] two-dimensional (2D), [4] and three-dimensional (3D) [5] structures. We focus on opals, which are 3Darrangements of spheres packed in a face-centered cubic (FCC) lattice. While colloidal nanocrystals (NCs) have been infiltrated into opals [6] and such materials have demonstrated modification of the spontaneous emission of the NCs, [7,8] amplified spontaneous emission (ASE) from a colloidal NC/opal material has not been demonstrated before. We present novel materials consisting of a titania sol-gel/CdSe or PbSe NC nanocomposite [9,10] infiltrated into polystyrene opal PCs. We demonstrate that these sol-gel/NC/PC composites exhibit efficient ASE at decreased thresholds relative to the reference sol-gel/NC materials despite the lower volume loading of NCs in the photonic structure. This observation indicates an effective increase of the optical gain as a result of the influence of the first L-point gap edge in the opal. This L-point gap corresponds to the lowest energy gap for light traveling in the <111> direction within the FCC opal structure (referred to as simply the L-point gap). In this work, opal samples are prepared via the vertical deposition technique from polystyrene particles of both 269 and 600 nm in diameter.[11] The opal growth occurs in the <111> direction. Both the volume fraction of particles in the precursor solution and the particle size dictate the number of resulting opal layers. After slow evaporation on a vibration-isolation table, strong opalescence is observable in the samples, with a 40 to 50 % maximum reflectivity. These opals are sintered at 100°C for 2 h to prevent them from falling apart during infiltration and then combined with sol-gel/NC composites via controlled dipping and withdrawal.[12] Sol-gel/NC composites are very attractive infiltration materials because of their large NC volume fractions and stable photoluminescence (PL) quantum yields. While these materials do not provide sufficient index contrast to open a complete photonic bandgap, [13,14] the resulting L-point gap still modifies the emission properties of the NCs. Figure 1a shows a typical micrograph of an infiltrated 269 nm opal sample. The sol-gel/NC composite does not infiltrate into pores and cracks, leaving a seemingly uniform coating on the polystyrene surfaces. The L-point gap is manifested as a strong peak in the reflectance spectra. After infiltration with the CdSe NC/titania sol-gel composite, the normal incidence opalescence changes from green to bright red, closely matching the color of the raw sol-gel by eye. The dipping process used to combine the sol-gel/NC composi...

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We propose a new type of ordered colloid, the "ionic colloidal crystal" (ICC), which is stabilized by attractive electrostatic interactions analogous to those in atomic ionic materials. The rapid self-organization of colloids via this method should result in a diversity of orderings that are analogous to ionic compounds. Most of these complex structures would be difficult to produce by other methods. We use a Madelung summation approach to evaluate the conditions where ICC's are thermodynamically stable. Using this model, we compare the relative electrostatic energies of various structures showing that the regions of ICC stability are determined by two dimensionless parameters representing charge balance and the spatial extent of the electrostatic interactions. Parallels and distinctions between ICC's and classical ionic crystals are discussed. Monte Carlo simulations are utilized to examine the glass transition and melting temperatures, between which crystallization can occur, of a model system having the rocksalt structure. These tools allow us to make a first-order prediction of the experimentally accessible regions of surface charge, particle size, ionic strength, and temperature where ICC formation is probable.

Dielectric reflectors that are periodic in one dimension, also known as one-dimensional photonic crystals (1DPCs), have become extremely useful tools in the optics industry due to the presence of wavelength-tunable photonic bandgaps. However, little is known about the practical effects of manufacturing defects, such as interfacial roughness, on this technologically useful property of 1DPCs. We employ a finite-difference time-domain code to gain further insight into the effect of interfacial roughness on the reflectivity of quarter-wave-tuned 1DPCs in the center of the bandgap at normal incidence. This provides an estimate of the magnitude of the effect of the roughness for even the most-robust incidence conditions.

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The study of shock-driven ejecta production has focused on Richtmyer–Meshkov instability (RMI) growth from geometric features of the material surface. Extensive study of this mechanism under both single- and multiple-shock conditions has found that the ejected mass tends to be closely associated with the shocked surface phase, and its temperature is not dramatically greater than the hydrodynamic shock temperature of the bulk. In this work, we propose and demonstrate a new ejecta production mechanism that can occur under multiple-shock conditions based on the collapse of bubbles near the free surface of the material. This mechanism produces ejected mass that is much greater in quantity than observed in the RMI case. The particles are much hotter than predicted by the shock Hugoniot state, and the ejected mass does not appear to be strongly dependent upon initial surface finish. The ejecta source extends into the material with no clear remaining free surface. We name this mechanism Shallow Bubble Collapse (SBC) and discuss the conditions under which it activates. We demonstrate resolved modeling methods that enable the calculation, design, and study of SBC as a mechanism and perform a series of experiments to compare with the models. Under some multiple-shock conditions, SBC ejection produces ten times more ejected mass than RMI growth.