Search results for " function"
showing 10 items of 9395 documents
White-light imaging with fractal zone plates
2007
We report the achievement of the first images to our knowledge obtained with a fractal zone plates (FraZPs). FraZPs are diffractive lenses characterized by the fractal structure of their foci. This property predicts an improved performance of FraZPs as image forming devices with an extended depth of field and predicts a reduced chromatic aberration under white-light illumination. These theoretical predictions are confirmed experimentally in this work. We show that the polychromatic modulation transfer function of a FraZP affected by defocus is about two times better than one corresponding to a Fresnel zone plate.
Super resolved optical system for objects with finite sizes using circular gratings
2015
We present a real time all optical super resolution method for exceeding the diffraction limit of an imaging system which has a circular aperture. The resolution improvement is obtained using two fixed circular gratings which are placed in predetermined positions. The circular gratings generate synthetic circular duplications of the aperture, thus they are the proper choice for a circular aperture optical system. The method is applicable for both spatially coherent and incoherent illuminations, as well as for white light illumination. The resolution improvement is achieved by limiting the object field of view. The proposed method is presented analytically, demonstrated via numerical simulat…
Broadband focused waves with compensated spatial dispersion: transverse versus axial balance.
2007
We determine the constraints an ABCD optical system must verify to achieve, at the focal region, broadband waves with compensated spatial dispersion either along the optical axis, called on-axis isodiffracting fields, or in the lateral direction, here named in-plane isodiffracting beams. An optical configuration is identified for generating both types of achromatic broadband focused wave fields. An experimental verification is also provided.
Dark spatial solitary waves in a cubic-quintic-septimal nonlinear medium
2017
We consider the evolution of light beams in nonlinear media exhibiting nonlinearities up to the seventh order wherein the beam propagation is governed by the cubic-quintic-septimal nonlinear Schr\"odinger equation. An exact analytic solution that describes dark solitary wave propagation is obtained, based on a special ansatz. Unlike the well-known $\text{tanh}$-profile dark soliton in Kerr media, the present one has a functional form given in terms of ``${\text{sech}}^{2/3}$''. The requirements concerning the optical material parameters for the existence of this localized structure are discussed. This propagating solitary wave exists due to a balance among diffraction, cubic, quintic, and s…
Structure of Liquids
2014
An Introduction to the description of the static structure of simple liquids is given. The principle quantity, which describes this structure is the structure factor, which can be measured with neutron and X-ray diffraction. The structure factor is the Fourier transform of the radial pair distribution function, which describes the statistics of the atoms around a given one. Several theories are introduced for calculating this quantities. It is shown that the structure of liquid metals is dominated by their hardcore repulsion. In the low-wavenumber limit the structure factor is related to the compressibility of the liquid. In this limit deviations from the hard-core model become importent, w…
3D printed diffractive terahertz lenses
2016
[EN] A 3D printer was used to realize custom-made diffractive THz lenses. After testing several materials, phase binary lenses with periodic and aperiodic radial profiles were designed and constructed in polyamide material to work at 0.625 THz. The nonconventional focusing properties of such lenses were assessed by computing and measuring their axial point spread function (PSF). Our results demonstrate that inexpensive 3D printed THz diffractive lenses can be reliably used in focusing and imaging THz systems. Diffractive THz lenses with unprecedented features, such as extended depth of focus or bifocalization, have been demonstrated.
First principles simulation of amorphous InSb
2013
Ab initio molecular dynamics simulations based on density functional theory have been performed to generate a model of amorphous InSb by quenching from the melt. The resulting network is mostly tetrahedral with a minor fraction ($10%$) of atoms in a fivefold coordination. The structural properties are in good agreement with available x-ray diffraction and extended x-ray-absorption fine structure data and confirm the proposed presence of a sizable fraction of homopolar In-In and Sb-Sb bonds whose concentration in our model amounts to about $20%$ of the total number of bonds.
<title>Relaxation processes in amorphous As-S and As-Se films</title>
1997
The relaxation of optical, mechanical and chemical properties of as-evaporated amorphous As-S and As-Se films while storing them at room temperature is investigated. The AsxS1-x films with arsenic content 0.3 less than x less than 0.4 are found to undergo maximal changes. It is shown that the phenomenon of dark self-enhancement of holograms (an increase of diffraction efficiency over time without any special treatment) can be used as an efficient method for investigation of relaxation processes in the amorphous chalcogenide films. The changes of diffraction efficiency in amorphous As2S3 films have been measured as a function of aging time and recording light intensity. The relaxation proces…
Diffraction-free beams in thin films
2009
The propagation and transmission of Bessel beams through nano-layered structures has been discussed recently. Within this framework we recognize the formation of unguided diffraction-free waves with the spot size approaching and occasionally surpassing the limit of a wavelength when a Bessel beam of any order n is launched onto a thin material slab with grazing incidence. On the basis of the plane-wave representation of cylindrical waves, a simple model is introduced providing an exact description of the transverse pattern of this type of diffraction-suppressed localized wave. Potential applications in surface science are put forward for consideration. Ministerio de Ciencia e Innovación (MI…
Accommodation in human eye models: a comparison between the optical designs of Navarro, Arizona and Liou-Brennan.
2017
Aim To simulate and compare accommodation in accommodative and non-accommodative human eye models. Methods Ray tracing and optical design program was used. Three eye models were designed and studied: the Navarro, the Arizona and the Liou-Brennan. In order to make the Navarro and Liou-Brennan models to accommodate, specific geometric parameters of the models were altered with values that were chosen from the literature. For the Arizona model, its' mathematical functions for accommodation were used for the same accommodative demands. The simulation included four distances of accommodation for each model: at infinity, 3, 1 and 0.5 m.The results were diffraction images of a "letter F" for graph…