Search results for "Names"
showing 10 items of 6843 documents
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…
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.
Nondiffracting Bessel plasmons.
2011
We report on the existence of nondiffracting Bessel surface plasmon polaritons (SPPs), advancing at either superluminal or subluminal phase velocities. These wave fields feature deep subwavelength FWHM, but are supported by high-order homogeneous SPPs of a metal/dielectric (MD) superlattice. The beam axis can be relocated to any MD interface, by interfering multiple converging SPPs with controlled phase matching. Dissipative effects in metals lead to a diffraction-free regime that is limited by the energy attenuation length. However, the ultra-localization of the diffracted wave field might still be maintained by more than one order of magnitude. This research was funded by the Spanish Mini…
Local structure relaxation in nanosized tungstates
2014
Abstract The atomic structure of nanosized and microcrystalline tungstates MeWO 4 (Me=Co, Ni, Cu, Zn), synthesized by co-precipitation technique, has been studied by x-ray absorption spectroscopy at the W L 3 -edge and Co/Ni/Cu/Zn K-edges, x-ray diffraction, Raman and Fourier transform infrared spectroscopies. The distortion of metal–oxygen octahedra is caused by the electron–lattice coupling and is further enhanced in nanosized tungstates due to formation of the double tungsten–oxygen bonds at the nanoparticle surface.
RF magnetron-sputtered coatings deposited from biphasic calcium phosphate targets for biomedical implant applications
2017
Bioactive calcium phosphate coatings were deposited by radio-frequency magnetron sputtering from biphasic targets of hydroxyapatite and tricalcium phosphate, sintered at different mass % ratios. According to Raman scattering and X-ray diffraction data, the deposited hydroxyapatite coatings have a disordered structure. High-temperature treatment of the coatings in air leads to a transformation of the quasi-amorphous structure into a crystalline one. A correlation has been observed between the increase in the Ca content in the coatings and a subsequent decrease in Ca in the biphasic targets after a series of deposition processes. It was proposed that the addition of tricalcium phosphate to th…
Shaping graphene with optical forging: from a single blister to complex 3D structures
2020
Properties of graphene, such as electrical conduction and rigidity can be tuned by introducing local strain or defects into its lattice. We used optical forging, a direct laser writing method, under an inert gas atmosphere, to produce complex 3D patterns of single layer graphene. We observed bulging of graphene out of the plane due to defect induced lattice expansion. By applying low peak fluences, we obtained a 3D-shaped graphene surface without either ablating it or deforming the underlying Si/SiO2 substrate. We used micromachining theory to estimate the single-pulse modification threshold fluence of graphene, which was 8.3 mJ cm−2, being an order of magnitude lower than the threshold for…
FeMoO4 Revisited: Crosslike 90° Noncollinear Antiferromagnetic Structure Caused by Dzyaloshinskii–Moriya Interaction
2021
The ground state of Fe2+ (S = 2) in α- and β-FeMoO4 is investigated by experiments including X-ray diffraction, Raman scattering, and 57Fe–Mossbauer spectroscopy below 300 K and evaluated by theore...
The Poisson Ratio in CoFe2O4Spinel Thin Films
2012
The response of epitaxial CoFe2O4 thin films to biaxial compressive stress imposed by MgAl2O4 and SrTiO3 single crystalline substrates is studied using X-ray diffraction and Raman spectroscopy. It is found that the Poisson ratio ν signals a non-auxetic behavior and depends on the substrate used. The Raman modes show an increase in frequency when increasing compressive strain by reducing film thickness; this is due to the shrinking of the unit cell volume. Such behavior is in qualitative agreement with recent ab initio calculations, although the measured values are significantly smaller than predictions. In contrast, the measured Poisson ratio is found to be in good agreement with expectatio…
Static and dynamic properties of low-temperature order in the one-dimensional semiconductor(NbSe4)3I
2016
We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor ${({\mathrm{NbSe}}_{4})}_{3}\mathrm{I}$ by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a well-documented pseudo-Jahn-Teller ferrodistortive structural transition at ${T}_{C}=274$ K, where the displacements of Nb ions lead to ferroelectric (FE) in-chain polarization with opposite direction in adjacent chains, all methods suggest an additional lowering of symmetry at ${T}^{*}\ensuremath{\approx}160$ K. Although antiferroelectric (AFE) phase is partially formed at ${T}_{C}$, our results consistently point to an enhancement of the interchain or…
Raman scattering as a tool for the evaluation of strain inGaN∕AlNquantum dots: The effect of capping
2007
The strain state of $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}$ quantum dots grown on $6H\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}$ has been investigated as a function of AlN capping thickness by three different techniques. On the one hand, resonant Raman scattering allowed the detection of the ${A}_{1}(\mathrm{LO})$ quasiconfined mode. It was found that its frequency increases with AlN deposition, while its linewidth did not evolve significantly. Available experiments of multiwavelength anomalous diffraction and diffraction anomalous fine structure on the same samples provided the determination of the wurtzite lattice parameters $a$ and $c$ of the quantum dots. A very good agreement is …