Search results for "Lens"
showing 10 items of 948 documents
Single-zone-plate achromatic fresnel-transform setup: Pattern tunability
1997
Abstract White-light point-source illumination results in the chromatic blurring of the optical field diffracted by an aperture. In this paper, broadband dispersion compensation for a continuous set of Fresnel diffraction patterns associated with an arbitrary input transparency is carried out, in a sequential way, by means of a single on-axis blazed zone plate. The input is illuminated with a white-light converging spherical wavefront and the diffractive lens is inserted at the virtual source plane. We recognize that the position of the input along the optical axis permits to achieve a different achromatic Fresnel diffraction pattern with low residual chromatic aberrations. The theory deriv…
Totally incoherent optical processing operations with achromatic diffraction-based setups
2000
We report on a novel family of totally incoherent, chromatic-dispersion compensated hybrid (refractive-diffractive) lens setups for implementing, in the Fraunhofer or in the Fresnel diffraction region, different achromatic diffraction-based processing operations.
High-contrast white-light Lau fringes
2004
We present a new optical assembly with which to achieve Lau fringes with totally incoherent illumination. Gratinglike codification of the spatially incoherent source combined with an achromatic Fresnel diffraction setup allows us to achieve Lau fringe-pattern visibility of almost 100% with broadband light. The white-light character to our proposed setup is in stark contrast to previous monochromatic implementations. Potential implications of this fact are identified.
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.
Superresolved Holographic Microscopy
2008
Superresolution methods in digital holographic microscopy provide a useful tool to overcome the Abbe's diffraction limit when using modest microscope lenses. The process improves the cutoff frequency of the microscope lens by means of the generation of a synthetic aperture based on time multiplexing and using 3 main stages: optical coding, optical decoding, and digital postprocessing. After the whole process, a superresolved image is obtained by Fourier transformation of the synthetic aperture.
Multiplexing THz Vortex Beams With a Single Diffractive 3-D Printed Lens
2019
[EN] We present a novel method for experimentally generating multiplexed THz vortex beams by using a single three-dimensional printed element that combines a set of radially distributed spiral phase plates, and a binary focusing Fresnel lens. With this element, we have experimentally demonstrated that THz multiplexing can be tailored to fit within a small space on an optical bench. Results are presented beside numerical simulations, demonstrating the robust nature of the experimental method.
Britu diplomātija 2. Pasaules kara priekšvakarā un sākumā (1938-1941): izmaiņas politiskajā retorikā
2020
Pētījumā tika analizētas Lielbritānijas diplomātiskā resora pārstāvju runas, paziņojumi un fiksētās liecības no divu metodoloģisko konceptu pozīcijām – miera un kara retorikām - laika posmā no 1938. gada 12. marta (Austrijas aneksijas) līdz 1941. gada 22. jūnijam (PSRS kara pieteikums Vācijai). Lielbritānija Otrā Pasaules kara priekšvakarā un sākumā nebija gatava karam un vēlējās darīt visu iespējamo diplomātiski, kas bija iespējams, lai to novērstu. Saskaroties ar dažādiem apstākļiem, Lielbritānija kļuva par Eiropā vadošo demokrātiju un miera aizstāvi gan pirms, gan arī kara laikā. Premjerministru un viņu Kabinetu vērstās retorikas izmaiņas bija iespējams konstatēt hronoloģiskā veidā un ab…
Subjetivación y Feminismo: Análisis de un manifiesto político
2004
The theme of this article is the the Italian feminist movement of the 1980s. That movement was characterised by political transformation and a crtitique of identity. The article takes as its point of departure the inaugural speech of the movement, the manifesto "Piu donne che uomini" (1983). The analysis that we present is inspired in the work of Michel Foucault. It aims to show to that the production of new feministic subjectivities, when fighting the symbolic dimension of masculine domination, has an intrinsically political character. In the 1980s, in the Italian context and particularly in the feminist movement, the rules of the political game set up by the events of 1968 materialized. T…
Generalized probabilistic modus ponens
2017
Modus ponens (from A and “if A then C” infer C) is one of the most basic inference rules. The probabilistic modus ponens allows for managing uncertainty by transmitting assigned uncertainties from the premises to the conclusion (i.e., from P(A) and P(C|A) infer P(C)). In this paper, we generalize the probabilistic modus ponens by replacing A by the conditional event A|H. The resulting inference rule involves iterated conditionals (formalized by conditional random quantities) and propagates previsions from the premises to the conclusion. Interestingly, the propagation rules for the lower and the upper bounds on the conclusion of the generalized probabilistic modus ponens coincide with the re…
Objective assessment of the effect of pupil size upon the power distribution of multifocal contact lenses
2017
AIM: To analytically assess the effect of pupil size upon the refractive power distributions of different designs of multifocal contact lenses. METHODS: Two multifocal contact lenses of center-near design and one multifocal contact lens of center-distance design were used in this study. Their power profiles were measured using the NIMO TR1504 device (LAMBDA-X, Belgium). Based on their power profiles, the power distribution was assessed as a function of pupil size. For the high addition lenses, the resulting refractive power as a function of viewing distance (far, intermediate, and near) and pupil size was also analyzed. RESULTS: The power distribution of the lenses was affected by pupil siz…