Search results for "Focu"
showing 10 items of 1182 documents
Fractal-structured multifocal intraocular lens
2017
[EN] In this work, we present a new concept of IOL design inspired by the demonstrated properties of reduced chromatic aberration and extended depth of focus of Fractal zone plates. A detailed description of a proof of concept IOL is provided. The result was numerically characterized, and fabricated by lathe turning. The prototype was tested in vitro using dedicated optical system and software. The theoretical Point Spread Function along the optical axis, computed for several wavelengths, showed that for each wavelength, the IOL produces two main foci surrounded by numerous secondary foci that partially overlap each other for different wavelengths. The result is that both, the near focus an…
Devil's lenses.
2007
In this paper we present a new kind of kinoform lenses in which the phase distribution is characterized by the “devil’s staircase” function. The focusing properties of these fractal DOEs coined devil’s lenses (DLs) are analytically studied and compared with conventional Fresnel kinoform lenses. It is shown that under monochromatic illumination a DL give rise a single fractal focus that axially replicates the self-similarity of the lens. Under broadband illumination the superposition of the different monochromatic foci produces an increase in the depth of focus and also a strong reduction in the chromaticity variation along the optical axis.
Focal shift in optical waves with off-axis focus
2003
We present a formulation for a suitable description of the focal shift in optical waves that have an off-axis focus. This shift that is primarily produced along the chief axis is given in terms of the focal distance and depends only on a parameter that is named as the generalized Fresnel number. Any non-uniform, either truncated and non-apertured optical beam with off-axis focus may be considered.
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.
Superesolution in digital holographic microscopy
2011
In this contribution, we address with the possibility to overcome the limited resolving power of imaging systems beyond the limit imposed by Abbe's diffraction theory. We first review the mathematical foundations underlying superresolution (SR) from an information theory point of view and then we focus on two multiplexing approaches in digital holographic microscopy (DHM) for achieving SR by synthetic aperture (SA) generation.
Effective Fresnel-number concept for evaluating the relative focal shift in focused beams
1998
We report on an analytical formulation, based on the concept of effective Fresnel number, to evaluate in a simple way the relative focal shift of rotationally nonsymmetric scalar fields that have geometrical focus and moderate Fresnel number. To illustrate our approach, certain previously known results and also some new focusing setups are analytically examined.
CREAPP K6-12: Tool to evaluate the creative potential of app oriented to the design of personal digital storytelling
2018
An instrument is presented that allows primary school teachers to evaluate the potentiality to develop creativity that have playful online app K6-12 focused on the development of digital storytelling (DST), so they can select those that can be used in the classroom for that purpose. The instrument validated consists of 48 indicators associated with the six dimensions of the creativity: flexibility, originality, fluency, problem solving, elaboration of products and co-edition and dissemination. It was designed based on the opinions of experts in creativity and Information and Communication Technologies of the didactic field, theory of education and methodology; also with the assessments and…
Co-occurrence of discourse markers in English : from juxtaposition to composition
2019
Abstract In this paper, we report on a qualitative analysis of co-occurring discourse markers, that is, sequences of adjacent discourse markers that belong to the same unit but may express different functions. We examine several formal and functional features of these co-occurring strings on the basis of corpus examples extracted from conversational data in English. In particular, we focus on scope, meaning-in-context (or functions), syntactic category and position. Our analysis reveals several degrees of integration: differences in scope allow us to differentiate juxtaposition and combination of markers. In the case of combination, difference in meaning integration allows us to distinguish…
Unavoidable sets and circular splicing languages
2017
Circular splicing systems are a formal model of a generative mechanism of circular words, inspired by a recombinant behaviour of circular DNA. They are defined by a finite alphabet A, an initial set I of circular words, and a set R of rules. In this paper, we focus on the still unknown relations between regular languages and circular splicing systems with a finite initial set and a finite set R of rules represented by a pair of letters ( ( 1 , 3 ) -CSSH systems). When R = A × A , it is known that the set of all words corresponding to the splicing language belongs to the class of pure unitary languages, introduced by Ehrenfeucht, Haussler, Rozenberg in 1983. They also provided a characteriza…
Recognizable picture languages and polyominoes
2007
We consider the problem of recognizability of some classes of polyominoes in the theory of picture languages. In particular we focus our attention oil the problem posed by Matz of finding a non-recognizable picture language for which his technique for proving the non-recognizability of picture languages fails. We face the problem by studying the family of L-convex polyominoes and some closed families that are similar to the recognizable family of all polyominoes but result to be non-recognizable. Furthermore we prove that the family of L-convex polyominoes satisfies the necessary condition given by Matz for the recognizability and we conjecture that the family of L-convex polyominoes is non…