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Vargas J.,Instituto Nacional Of Tecnica Aerospacial Inta | Gomez-Pedrero J.A.,Complutense University of Madrid | Alonso J.,Complutense University of Madrid | Quiroga J.A.,Complutense University of Madrid
Applied Optics

This paper presents a deflectometric technique to measure the power of an ophthalmic lens as perceived by the user. It is based on a calibrated camera acting as a pinhole in order to measure ray deflection along the same path as the visual axis when the lens is held in front of the eye. We have analyzed numerically the accuracy of our technique, and it has been compared experimentally with a commercial "lens mapper" and with the real user power calculated from the measured topography of the lens surfaces to state the reliability and accuracy of the presented technique. © 2010 Optical Society of America. Source

Klacka J.,Comenius University | Kocifaj M.,Comenius University | Kocifaj M.,Slovak Academy of Sciences | Kundracik F.,Comenius University | And 3 more authors.
Journal of Quantitative Spectroscopy and Radiative Transfer

The explicit solution to Maxwell's equations that satisfies the continuity equation is obtained for electrically charged spherical particles. The traditional separation-of-variables method (SVM) cannot be used to solve the vector wave equation for a non-uniformly charged spherical particle. In addition, a perturbation approach to the electromagnetic scattering problem fails if a spherical particle is occupied by electric charges that are not spatially homogeneous. By incorporating a correction to the conventional surface-current density, we have refined the conductivity model and found that the Rayleigh approximation (for mode n=1) is not a valid approach for modelling the optical effects by electrically charged particles much smaller than the wavelength of an incident radiation. Theoretical analyses indicate that peak enhancements of optical signatures are usually relevant in the long-wavelength limit due to the necessity to include higher-order modes of vibration (n>. 1). © 2015 Elsevier Ltd. Source

Kocifaj M.,Slovak Academy of Sciences | Kocifaj M.,Comenius University | Kundracik F.,Comenius University | Videen G.,Instituto Nacional Of Tecnica Aerospacial Inta | Videen G.,U.S. Army
Journal of Quantitative Spectroscopy and Radiative Transfer

The dependence of the electric potential on the absorption and scattering of light by small particles has emerged as an interesting research topic, as the unexpected amplified optical signatures of a system of electrically charged particles were satisfactory predicted recently for homogeneous, uniformly charged spheres. However, natural particles are rarely of spherical shape. A comprehensive understanding of how arbitrarily shaped, charged particles interact with electromagnetic radiation has been missing. The approach we present here attempts to fill this gap by introducing a numerical formulation of the electromagnetic scattering problem for these particles. The first results from the intercomparison of numerical and analytical solutions for a pseudosphere show that the resonance features found are largely consistent, except for the magnitude and width of the peak amplitude, which may be due to inherent differences in the approaches used. © 2016 Elsevier Ltd Source

Zubko E.,University of Kharkiv | Videen G.,Space Science Institute | Videen G.,Instituto Nacional Of Tecnica Aerospacial Inta | Videen G.,University of Cantabria | And 4 more authors.
Planetary and Space Science

We examine the dispersion of the degree of linear polarization P in comets at phase angle ∼90° where the maximum amplitude of positive polarization Pmax occurs. The range of polarization observed in comets is from 7% up to more than 30%, and this cannot be explained through depolarization by gaseous emissions. Instead, we suggest that the observed dispersion of P results from different properties in cometary dust. We simulate the spectral polarimetric observations of comets using model agglomerated debris particles. The vast majority of observations can be reproduced with a mixture of weakly absorbing and highly absorbing agglomerated debris particles, which obey the same power-law size distribution. Within this extremely simple approach, polarization at side-scattering angles in a given comet is governed by the relative abundance of weakly and strongly absorbing particles. We find that in comets with the highest polarization, the weakly absorbing particles appear in proportions of only 14-23% by volume; whereas, in comets with the lowest polarization Pmax, their abundance is much greater, 82-95%. We conclude that the polarization at side-scattering angles unambiguously measures the relative abundance of Mg-rich silicates and refractory organics or amorphous carbon in comets. We put forth a hypothesis that low Pmax could be an indicator for presence of a well-developed refractory surface layer covering cometary nucleus. © 2015 Elsevier Ltd. All rights reserved. Source

Barreda A.I.,University of Cantabria | Sanz J.M.,University of Cantabria | Alcaraz de la Osa R.,University of Cantabria | Saiz J.M.,University of Cantabria | And 5 more authors.
Journal of Quantitative Spectroscopy and Radiative Transfer

We study the effect of contaminants on the resonances of silicon nanoparticles (NPs) by considering the spectral evolution of the degree of linear polarization of light scattered at right angles to the incident beam, PL(90°). From an optical point of view, a decrease in the purity of silicon nanoparticles due to the presence of contaminants impacts the NP effective refractive index. We analyze this effect for a silicon nanosphere (R=200. nm) suspended in different media. We focus on the spectral range where the quadrupolar magnetic, dipolar electric and dipolar magnetic resonances appear. The weakness of the resonances induced on the PL(90°) spectrum by the lack of purity can be used to quantify the contamination of the material. In addition, it is shown that Kerker conditions also suffer from a spectral shift, that is quantified as a function of material purity. © 2015 Elsevier Ltd. Source

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