Spectrally resolved white light interferometer for measuring dispersion in the visible and near infrared range

We design a spectrally resolved interferometer to measure the refractive index of transparent samples over a broad spectral range of 400–1550 nm. The measuring device consists of a Michelson interferometer whose output is analysed by means of three fibre spectrometers: a homemade prism spectrometer which obtains the interferogram generated by the sample in the 400–1050 nm range, a homemade transmission grating spectrometer that measures the interferogram in the 950–1550 nm near infrared range, and a commercial Czerny-Turner spectrometer used to make high-precision measurements of the displacement between the Michelson mirrors. The whole system is illuminated by a white-light source with an emission spectrum similar to that of a black body. We test the instrument on solid and liquid samples achieving accuracy of up to 10−4 in the refractive index after fitting it with the Cauchy formula.Ministerio de Economía y Competitividad – Spain (MINECO) (MAT2014-57943-C3-2-P); Xunta de Galicia and ERDF (AGRU 2015/11 and GRC ED431C 2016/001).S

Refractive index measurements in absorbing media with white light spectral interferometry

White light spectral interferometry is applied to measure the refractive index in absorbing liquids in the spectral range of 400–1000 nm. We analyze the influence of absorption on the visibility of interferometric fringes and, accordingly, on the measurement of the refractive index. Further, we show that the refractive index in the absorption band can be retrieved by a two-step process. The procedure requires the use of two samples of different thickness, the thicker one to retrieve the refractive index in the transparent region and the thinnest to obtain the data in the absorption region. First, the refractive index values are retrieved with good accuracy in the transparent region of the material for 1-mm-thick samples. Second, these refractive index values serve also to precisely calculate the thickness of a thinner sample (~150 µm) since the accuracy of the methods depends strongly on the thickness of the sample. Finally, the refractive index is recovered for the entire spectral rangeMinisterio de Economía y Competitividad (MINECO) (MAT2014-57943-C3-2-P, MAT2017-89239-C2-1-P); Xunta de Galicia and ERDF (AGRU 2015/11, GRC ED431C 2016/001 and ED431D 2017/06)S

Non-additive electronic polarizabilities of ionic liquids: charge delocalization effects

Electronic charge delocalization on the molecular backbones of ionic liquid-forming ions substantially impacts their molecular polarizabilities. Density functional theory calculations of polarizabilities and volumes of many cations and anions are reported and applied to yield refractive indices of 1216 ionic liquids. A novel expression for the precise estimation of the molecular volumes of the ionic liquids from simulation data is also introduced, adding quadratic corrections to the usual sum of atomic volumes. Our significant findings include i) that the usual assumption of uniform, additive atomic polarizabilities is challenged when highly mobile electrons in conjugated systems are present, and ii) that cations with conjugated large carbon chains can be used together with anions for the design of ionic liquids with very high refractive indices. A novel relation for the polarizability volume is reported together with a refractive index map made up of the studied ionic liquidsThis work was supported by Ministerio de Economia y Competitividad (MINECO) and FEDER Program through the project MAT2017-89239-C2-1-P; Xunta de Galicia and FEDER (ED431D 2017/06, ED431E2018/08, GRC 508 ED431C 2020/10). C. D. R. F. thanks the support of Xunta de Galicia through the grant ED481A-2018/032. We also thank the Centro de Supercomputacion de Galicia (CESGA) facility, Santiago de Compostela, Galicia, Spain, for providing the computational resources employed in this workS

Características básicas do sistema detector

Titulación: Grao de Óptica e Optometría -- Materia: Óptica Visual e PercepciónO proceso da visión pode dividirse en 3 etapas: 1. Formación da imaxe, o ollo funciona como un sistema óptico que forma imaxes dos obxectos exteriores sobre a súa parte posterior: a retina. 2. Adquisición da imaxe, i.e. a transdución dos sinais ópticos en sinais neurais, que se leva a cabo nas células fotorreceptoras da retina. 3. Tratamento das imaxes, que se realiza en parte na propia retina, mais fundamentalmente no córtex visual. Estas 3 etapas permiten que o noso sistema visual constrúa, en tempo real, unha representación mental do mundo exterior, elaborada coas imaxes que se están formando continuamente nas nosas retinas, mais tamén e dun xeito decisivo, con outra información que ten almacenada o noso cerebro correspondente a imaxes retinianas anteriores. Esta representación mental depende loxicamente das características físicas e fisiolóxicas do noso ollo, especialmente da nosa retina. Nos temas I a V estúdase a primeira etapa da visión , entanto os temas VI a IX están dedicados as otras dúas etapas. Cómpre esclarecer que a adquisición e o tratamento das imaxes están íntimamente ligados, e o seu estudo resulta moi complexo e necesariamente multidisciplinar, para o cal é preciso utilizar coñecementos e técnicas de varias disciplinas da física, da medicina e da psicoloxía. O presente tema serve como unha introducción a esta difícil e apaixonante materia. Está divido en 4 seccións nas que se estudan: — a retina humana dun punto de vista funcional; — a fotometría, i.e. a ciencia da medida da radiación electromagnética por un fotodetector particular, o ollo humano; — a iluminación retiniana, como se calcula en función da fonte de luz e a súa relación coa pupila; e finalmente — a notábel capacidade de adaptación do ollo a iluminación ambiental, aproveitando para presentar o concepto de limiar luminoso, absoluto e diferencial.Universidade de Santiago de Compostela. Servizo de Normalización Lingüístic

Charge delocalization and hyperpolarizability in ionic liquids

In this work the role that charge delocalization plays in the non-linear optical response of ionic liquids is evaluated. The first hyperpolarizability for the non-linear process of second harmonic generation (SHG) and second hyperpolarizability for the non-linear process of electro-optical Kerr-Effect (EOKE) of a large number of ionic liquid forming ions were estimated by means of density functional theory calculations. The results point to that both charge delocalization and molecular geometry are the key features that govern their hyperpolarizabilities. Our findings show that some of the most commonly used anions in ionic liquids are expected to present strong non-linear responses while common cations present a much more limited performance. However, this limitation can be overcome by a proper tailoring of cations to present charge delocalization over large molecular regions. The hypothesis of additivity of hyperpolarizabilities in ionic liquids is tested and exploited to obtain a map of second and third order non-linear susceptibilities of 1496 ion combinations. This map is intended to be a guide for future works on the hyperpolarizability of ILsThis work was supported by Ministerio de Economia y Competitividad (MINECO) and FEDER 17 Program through the projects (MAT2017-89239-C2-1-P); Xunta de Galicia and FEDER (GRC ED431C 2016/001, ED431D 2017/06, ED431E2018/08). C. D. R. F. thanks the support of Xunta de Galicia through the grant ED481A-2018/032. We also thank the Centro de Supercomputacion de Galicia (CESGA) facility, Santiago de Compostela, Galicia, Spain, for providing the computational resources employed in this workS

An Experimental and Computational Study on Material Dispersion of 1-Alkyl-3-Methylimidazolium Tetrafluoroborate Ionic Liquids

The material dispersion of the [Ckmim][BF4] (k = 2,3,4,6,7,8,10) family of ionic liquids is measured at several temperatures over a broad spectral range from 300 nm to 1550 nm. The experimental curves are fitted to a modified three-resonance Sellmeier model to understand the effect of temperature and alkyl chain length in the dispersion. From the parameters of the fitting, we analyze the influence that the different constituents of these ionic liquids have in the dispersion behaviour. In addition, a semi-empirical approach combining simulated electronic polarizabilities and experimental densities for predicting the material dispersion is successfully tested by direct comparison with the experimental results. The limitations of this method are analyzed in terms of the structure of the ionic liquids. The results of this work aim to increase our knowledge about how the structure of an ionic liquid influences its material dispersion. Understanding this influence is fundamental to produce ionic liquids with tailored optical properties.Comment: 34 pages, 12 figure

Does the composition of the board matter? On the relationship between corporate governance and value creation

This paper studies the effect of corporate governance on value creation for listed companies. It also examines whether the fact that a business is owned or partly owned by a family has an impact on this variable as well as the behavior of companies at different stages of the economic cycle. Our research makes use of a dataset consisting of the companies in the IBEX-35 for the period 2005/12. It carries out a sub-analysis for the periods 2005-2008 and 2009-2012, to evaluate the effect of the crisis. The results indicate that neither the presence of women on boards of directors nor family ownership affect value creation in the companies analyzed. The size of the entity revealed a statistically significant and negative coefficient for the entire period under analysis. However, recorded profitability revealed a statistically significant and positive coefficient only for the pre-crisis period and not for the later period. In contrast, board size and the percentage of independent board members are both relevant and reveal a positive coefficient for the crisis period. Although its starting point is agency theory, complemented by resource dependence theory, the paper resorts to the sociological theory of the strength of weak ties, to explain its results. Gender diversity and family ownership do not seem to have an impact on value creation, while the level of independence of the governance bodies has a positive effect throughout the crisis period. This result supports the notion that board structure is much more relevant in difficult and challenging times. In addition to increasing the number of independent directors, it is also crucial that a minimum percentage be reached in order to influence the board and generate value. According to the empirical evidence, in times of crisis, it seems advisable and more efficient to increase board size with more independent directors, regardless of gender. Gender equality does not harm value creation

Spectrally resolved white light interferometry to measure material dispersion over a wide spectral band in a single acquisition

In this paper we apply spectrally resolved white light interferometry to measure refractive and group index over a wide spectral band from 400 to 1000 nm. The output of a Michelson interferometer is spectrally decomposed by a homemade prism spectrometer with a high resolution camera. The group index is determined directly from the phase extracted from the spectral interferogram while the refractive index is estimated once its value at a given wavelength is known.Ministerio de Economia y Competitividad (MINECO) (MAT2014-57943-C3-1-P, MAT2014-57943-C3-2-P); Xunta de Galicia and FEDER (R2014/015, AGRU 2015/11)S

Experimental Device to Measure the Ionic Conductivity Anisotropy in Liquid Crystal Hydrogel Based In [EMIM] Alkyl Sulfate Ionic Liquids

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] We have built an experimental device with the aim to measure the expected electrical conductivity anisotropy in a liquid crystal, obtained from the gelation of the ionic liquid 1-ethyl-3-methyl imidazolium decyl sulfate, [EMIM][DSO4]. This ionic liquid has the particularity that it transits to a semi-solid gel state at room temperature when it contains water, naturally adsorbed from the environment until a balance is reached between the concentration of water in the IL and the atmospheric humidity grade. The quantity of water adsorbed to form the hydrogel at room temperature varies from about 5 to 30 wt%, each composition giving place to different smectic phases. In the gel state, the ionic liquid ions and the water molecules self-organize into micro-sized mesophases that resemble the structures of a liquid crystal. Our device is a closed 2D sample holder (with sides 150 times longer than its thickness), with a single narrow window open to the atmosphere, and four copper contacts on the sides. The dried ionic liquid is tempered at 40 °C to increase its fluidity when injected into the cavity, and then, it can only adsorb water through the narrow opening. Thus, water adsorption is unidirectional and slow, so the transition of the IL to the gel phase happens progressively. A metastable giant mesophase appears as an orientated macrodomain in the form of a striped pattern. In this state, we measure the electrical conductivity of the confined film in directions parallel and perpendicular to the observed strips, finding a difference of up to 26% between both values of the conductivity. If the sample freezes (below 10 °C) or it liquefies (above 50 °C) the meso structure is broken and the observed anisotropy destroyed. We can return the sample to gel state by varying the temperature, but the ordered macroscopic state is no longer recovered. This research must give clues to solve the charge transport mechanism quiz in ionic liquids and semi-solid coductors.This work was supported by Ministerio de Economia y Competitividad (MINECO) and FEDER Program through the projects MAT2017–89239-C2–1-P, MAT2017–89239-C2–2-P and RED2018–102679-T; Xunta de Galicia and FEDER (GRC 508 ED431C 2020/10). Funding for open access charge: Universidade da Coruña/CISUGXunta de Galicia; GRC 508 ED431C 2020/1

Accuracy of refractive index spectroscopy by broadband interferometry

Uncertainties of refractive and group index in dispersion measurement by spectrally resolved white light interferometry are deeply analyzed. First, the contribution to uncertainty of the different parameters affecting both indices is identified. Afterwards, results are presented for a 1.5 mm thick fused silica sample over a broad spectral range, from 400 to 1000 nm, and the effects that mostly deteriorate the measurement accuracy are established. Finally, the different contributions are quadratically combined to determine the total uncertainty of the two indicesThe financial support of the Spanish Ministry of Economy and Competitiveness through the coordinated grants MAT2017-89239-C2-1-P is gratefully acknowledged. Moreover, this work was funded by the Xunta de Galicia and FEDER (ED431D 2017/06, ED431E2018/08, GRC 508 ED431C 2020/10)S