Search results for "Diffraction"
showing 10 items of 1584 documents
Fine tuning of thermoelectric performance in phase-separated half-Heusler compounds
2015
Two successful recipes to enhance the thermoelectric performance, namely carrier concentration optimization and reduction of thermal conductivity, have been combined and applied to the p-type (Ti/Zr/Hf)CoSb1−xSnx system. An intrinsic micrometer-scale phase separation increases the phonon scattering and reduces the lattice thermal conductivity. A substitution of 15% Sb by Sn optimizes the electronic properties. Starting from this, further improvement of the thermoelectric properties has been achieved by a fine tuning of the Ti to Hf ratio. The microstructuring of the samples was studied in detail with high-resolution synchrotron powder X-ray diffraction and element mapping electron microscop…
Addressing subphthalocyanines and subnaphthalocyanines features relevant to fluorescence imaging
2018
International audience; A series of new synthetic subphthalocyanines bear structural features aimed at allowing either fluorescence activation or a bathochromic shift of the absorption band towards the near-infrared window, relevant to optical imaging. X-ray diffraction studies of four subphthalocyanines are reported. Spectrofluorimetric studies on subnaphthalocyanines and activatable subphthalocyanine pro-fluorophores are reported.
Photoluminescence in Carborane–Stilbene Triads : A Structural, Spectroscopic, and Computational Study
2016
A set of triads in which o- and m-carborane clusters are bonded to two stilbene units through Ccluster -CH2 bonds was synthesized, and their structures were confirmed by X-ray diffraction. A study on the influence of the o- and m- isomers on the absorption and photoluminescence properties of the stilbene units in solution revealed no charge-transfer contributions in the lowest excited state, as confirmed by (TD)DFT calculations. The presence of one or two B-I groups in m-carborane derivatives does not affect the emission properties of the stilbenes in solution, probably due to the rather large distance between the iodo substituents and the fluorophore. Nevertheless, a significant redshift o…
Self-similar focusing with generalized devil's lenses
2011
[EN] We introduce the generalized devil's lenses (GDLs) as a new family of diffractive kinoform lenses whose structure is based on the generalized Cantor set. The focusing properties of different members of this family are analyzed. It is shown that under plane wave illumination the GDLs give a single main focus surrounded by many subsidiary foci. It is shown that the total number of subsidiary foci is higher than the number of foci corresponding to conventional devil's lenses; however, the self-similar behavior of the axial irradiance is preserved to some extent. (C) 2011 Optical Society of America
Structural evolution of LiOH: evidence of a solid–solid transformation toward Li2O close to the melting temperature
1998
Abstract The structural evolution of LiOH has been studied between 10 K and 1670 K using a combination of neutron and X-ray diffraction and calorimetric measurements. The room temperature tetragonal phase of LiOH has been observed down to 10 K. Above the room temperature a dehydration of solid LiOH into solid Li2O is observed at a temperature and speed which strongly changes with the thermal history and the partial pressure of water vapour. Depending on these conditions the transformation of LiOH in to Li2O before the fusion temperature can be complete, partial or suppressed. In this latter case, as previously reported in the literature, a first order structural phase transition of LiOH is …
Analytical solution for multisingular vortex Gaussian beams: The mathematical theory of scattering modes
2016
We present a novel procedure to solve the Schr\"odinger equation, which in optics is the paraxial wave equation, with an initial multisingular vortex Gaussian beam. This initial condition has a number of singularities in a plane transversal to propagation embedded in a Gaussian beam. We use the scattering modes, which are solutions of the paraxial wave equation that can be combined straightforwardly to express the initial condition and therefore permit to solve the problem. To construct the scattering modes one needs to obtain a particular set of polynomials, which play an analogous role than Laguerre polynomials for Laguerre-Gaussian modes. We demonstrate here the recurrence relations need…
Crystal structure of 4,6-O-ethylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine
2002
4,6-O-Ethylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine was synthesized and characterized using analytical, spectral and single-crystal X-ray diffraction methods. The anomeric nature of the saccharide moiety was proposed based on 1H NMR studies and was confirmed by the crystal structure. The lattice structure of this compound was compared with that of its analogues.
Accurate expansion of cylindrical paraxial waves for its straightforward implementation in electromagnetic scattering
2017
Abstract The evaluation of vector wave fields can be accurately performed by means of diffraction integrals, differential equations and also series expansions. In this paper, a Bessel series expansion which basis relies on the exact solution of the Helmholtz equation in cylindrical coordinates is theoretically developed for the straightforward yet accurate description of low-numerical-aperture focal waves. The validity of this approach is confirmed by explicit application to Gaussian beams and apertured focused fields in the paraxial regime. Finally we discuss how our procedure can be favorably implemented in scattering problems.
Structure solution with automated electron diffraction tomography data: different instrumental approaches
2011
Summary Over the past few years automated electron diffraction tomography has become an established technique for structure solution of nano-crystalline material. The intentional choice of an arbitrary tilt axis and thus, the use of nonoriented diffraction patterns (off-zone acquisition) together with fine equidistant sampling of the reciprocal space result in high quality intensity data sets. Coupling automated electron diffraction tomography with electron beam precession (Vincent & Midgley, 1994) enables sampling of intensities between the static slices of reciprocal space and therefore enhances the quality of intensity data further; relatively complex structures have been solved using 3D…
New photonic devices for ultrafast pulse processing operating on the basis of the diffraction-dispersion analogy
2008
The space-time analogy is a well-known topic within wave optics that brings together some results from beam diffraction and pulse dispersion. On the above basis, and taking as starting point some classical concepts in Optics, several photonic devices have been proposed during the last few years with application in rapidly evolving fields such as ultrafast (femtosecond) optics or RF and microwave signal processing. In this contribution, we briefly review the above ideas with particular emphasis in the generation of trains of ultrafast pulses from periodic modulation of the phase of a CW laser source. This is the temporal analogue of Fresnel diffraction by a pure phase grating. Finally, we ex…