Sandia National Laboratories

About: Sandia National Laboratories is a facility organization based out in Livermore, California, United States. It is known for research contribution in the topics: Laser & Thin film. The organization has 21501 authors who have published 46724 publications receiving 1484388 citations. The organization is also known as: SNL & Sandia National Labs.

Energy-transfer pumping of semiconductor nanocrystals using an epitaxial quantum well.

Abstract: As a result of quantum-confinement effects, the emission colour of semiconductor nanocrystals can be modified dramatically by simply changing their size1,2. Such spectral tunability, together with large photoluminescence quantum yields and high photostability, make nanocrystals attractive for use in a variety of light-emitting technologies—for example, displays, fluorescence tagging3, solid-state lighting and lasers4. An important limitation for such applications, however, is the difficulty of achieving electrical pumping, largely due to the presence of an insulating organic capping layer on the nanocrystals. Here, we describe an approach for indirect injection of electron–hole pairs (the electron–hole radiative recombination gives rise to light emission) into nanocrystals by non-contact, non-radiative energy transfer from a proximal quantum well that can in principle be pumped either electrically or optically. Our theoretical and experimental results indicate that this transfer is fast enough to compete with electron–hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures. Furthermore, the measured energy-transfer rates are sufficiently large to provide pumping in the stimulated emission regime, indicating the feasibility of nanocrystal-based optical amplifiers and lasers based on this approach.

Paving: A new approach to automated quadrilateral mesh generation

Abstract: This paper presents a new mesh generation technique, paving, which meshes arbitrary 2-D geometries with an all-quadrilateral mesh. Paving allows varying element size distributions on the boundary as well as the interior of a region. The generated mesh is well formed (i.e. nearly square elements, elements perpendicular to boundaries, etc.) and geometrically pleasing (i.e. mesh contours tend to follow geometric contours of the boundary). In this paper we describe the theory behind this algorithmic/heuristic technique, evaluate the performance of the approach and present examples of automatically generated meshes.

Polarization-transparent microphotonic devices in the strong confinement limit

Abstract: Microphotonic structures that strongly confine light, such as photonic crystals and micron-sized resonators, have unique characteristics that could radically advance technology1,2,3,4,5,6. However, such devices cannot be used in most applications because of their inherent polarization sensitivity; they respond differently to light polarized along different axes7,8,9. To take advantage of the distinctive properties of these structures, a general, integrated, broadband solution to their polarization sensitivity is needed. Here, we show the first demonstration of such a solution. It enables arbitrary, polarization-sensitive, strong-confinement (SC) microphotonic devices to be rendered insensitive (transparent) to the input polarization at all wavelengths of operation. To test our approach, we create the first polarization-transparent add–drop filter from polarization-sensitive microring resonators. It shows almost complete elimination of polarization sensitivity over the 60-nm bandwidth measured, while maintaining outstanding filter performance. This development is a milestone for SC microphotonics, allowing the applications of photonic-crystal and microring devices to several areas, including communications, spectroscopy and remote sensing.

Synthesis of digital holograms by direct binary search

Abstract: A new approach to the design of computer-generated holograms makes optimal use of the available device resolution. An iterative search algorithm minimizes an error criterion by directly manipulating the binary hologram and observing the effect on the desired reconstruction. Several measures of error and efficiency useful in assessing the optimality of digital holograms are defined. Methods for designing digital holograms that are based on projections and error diffusion are presented as established techniques for comparison to direct binary search.