Scanning laser polarimetry with enhanced corneal compensation for detection of axonal loss in band atrophy of the optic nerve

PURPOSE: To compare the abilities of scanning laser polarimetry (SLP) with enhanced corneal compensation (ECC) and variable corneal compensation (VCC) modes for detection of retinal nerve fiber layer (RNFL) loss in eyes with band atrophy (BA) of the optic nerve. DESIGN. Cross-sectional study. METHODS: Thirty-seven eyes from 37 patients with BA and temporal visual field defect from chiasmal compression and 40 eyes from 40 healthy subjects were studied. Subjects underwent standard automated perimetry and RNFL measurements using an SLP device equipped with VCC and ECC. Receiver operating characteristic (ROC) curves were calculated for each parameter. Pearson correlation coefficients were obtained to evaluate the relationship between RNFL thickness parameters and severity of visual field loss, as assessed by the temporal mean defect. RESULTS: All RNFL thickness parameters were significantly lower in eyes with BA compared with normal eyes with both compensation modes. However, no statistically significant differences were observed in the areas under the ROC curves for the different parameters between GDx VCC and ECC (Carl Zeiss Meditec, Inc, Dublin, California, USA). Structure-function relationships also were similar for both compensation modes. CONCLUSIONS: No significant differences were found between the diagnostic accuracy of GDx ECC and that of VCC for detection of BA of the optic nerve. The use of GDx ECC does not seem to provide a better evaluation of RNFL loss on the temporal and nasal sectors of the peripapillary retina in subjects with BA of the optic nerve.

Deriving the magnitude of niobium off-center displacement in ferroelectric niobates from infrared spectroscopy

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Diseño y fabricación de dispositivos basados en cristal líquido polimérico

Esta tesis se centra en el estudio y desarrollo de dispositivos de aplicación basados en cristal líquido polimérico. Las propiedades de los cristales líquidos los hacen interesantes para su uso en el desarrollo de dispositivos de seguridad para autenticación de productos y marcas, y detección y prevención de falsificaciones. Asimismo, pueden ser muy útiles para fabricar dispositivos basados en CLs dispersos en polímero, los cuales tienen a su vez múltiples aplicaciones. La orientación de las moléculas de cristal líquido y la birrefringencia son las dos características principales que afectan a las propiedades de estos dispositivos. Un dispositivo de cristal líquido estándar consiste en un sándwich formado por dos sustratos de vidrio transparente, dotados con electrodo de ITO (Indium Tin Oxide) en su superficie interna, que confinan el cristal líquido en su interior. En la primera parte de esta tesis se describen las características más importantes que describen una célula de cristal líquido. Esta introducción básica en necesaria para la correcta comprensión de los capítulos posteriores en los que se detalla el desarrollo concreto de los dispositivos desarrollados en la investigación llevada a cabo. Por ejemplo, en el caso de los dispositivos de seguridad se han eliminado los sustratos de vidrio (en la última fase de su desarrollo) para conseguir dispositivos flexibles. En la segunda parte de la tesis se incluye la descripción completa de los dispositivos fabricados, así como de los protocolos de fabricación seguidos y diseñados específicamente para ello. También se detallan en esta parte los resultados obtenidos, así como las propiedades ópticas y electroópticas en cada caso, y el/los equipos de caracterización utilizados. Utilizando cristal líquido nemático y colorante dicroico, se han desarrollado dispositivos que contienen múltiples imágenes latentes en cada cara del mismo. Utilizando distintas técnicas de alineamiento se consigue crear cualquier tipo de motivo latente, ya sean símbolos sencillos, figuras, logotipos o incluso imágenes con escala de gris. Cuanto más complejo es el dispositivo, mayor es la dificultad para reproducirlo en una eventual falsificación. Para visualizar e identificar los motivos es necesario emplear luz polarizada, por ejemplo, con la ayuda de un sencillo polarizador lineal. Dependiendo de si el polarizador está colocado delante del dispositivo o detrás del él, se mostrarán las imágenes generadas en una u otra cara. Este efecto es posible gracias al colorante dicroico añadido al CL, a la orientación inducida sobre las moléculas, y a la estructura de twist utilizada en los dispositivos. En realidad, para ver el efecto de los dispositivos no es necesario el uso de un polarizador, basta con el reflejo de una superficie dielétrica (percialmente polarizado), o la luz emitida por la pantalla de dispositivos de consumo comunes como un televisor LCD, un monitor de ordenador o un “smartphone”. Por otro lado, utilizando una mezcla entre un CL nemático polimérico y un CL nemático no polimérico es posible fabricar dispositivos LCPC (Liquid Crystal Polymer Composite) con propiedades electroópticas muy interesantes, que funcionan a tensiones de conmutación bajas. El CL polimérico conforma una estructura de red en el interior del sándwich que mantiene confinado al CL nemático en pequeños microdominios. Se han fabricado dispositivos LCPC con conmutación inversa utilizando tanto alineamiento homogéneo como homeotrópico. Debido a que tanto la estructura de CL polimérico como el CL nemático que rellena los microdominios están orientados en una misma dirección de alineamiento preinducida, la luz dispersada por el dispositivo se encuentra polarizada. La dirección de polarización coincide con la dirección de alineamiento. La innovación aportada por esta investigación: un nuevo dispositivo LCPC inverso de respuesta ultrarápida y polarizada basado en la mezcla de dos CL nemáticos y, un dispositivo de seguridad y autenticación, patentado internacionalmente, basado en CL nemáticos dopados con colorante dicroico. Abstract This thesis is centered on the availability to use polymerizable liquid crystals to develop non-display application LC devices. Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes, and also to achieve polymer dispersed LC devices to be used for different applications that will be studied here. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in these devices. A standard liquid crystal device is a sandwich consisting of two parallel glass substrates carrying a thin transparent ITO (Indium‐Tin‐Oxide) electrode on their inner surfaces with the liquid crystal in the middle. The first part of this thesis will describe the most important parameters describing a liquid crystal cell. This basis is necessary for the understanding of later chapters where models of the liquid crystal devices will be discussed and developed. In the case of security devices the standard structure of an LC device has been modified by eliminating the glass substrates in order to achieve plastic and flexible devices. The second part of the thesis includes a detailed description of the devices achieved and the manufacturing protocols that have been developed ad-hoc. The optical and electrooptical properties and the characterization equipment are described here as well. Employing nematic liquid crystal and dichroic colorants, we have developed devices that show, with the aid of a polarizer, multiple images on each side of the device. By different alignment techniques it is possible to create any kind of symbols, drawings or motifs with a grayscale; the more complex the created device is, the more difficult is to fake it. To identify the motifs it is necessary to use polarized light. Depending on whether the polarizer is located in front of the LC cell or behind it, different motifs from one or the other substrate are shown. The effect arises from the dopant color dye added to the liquid crystal, the induced orientation and the twist structure. In practice, a grazing reflection on a dielectric surface is polarized enough to see the effect. Any LC flat panel display (LCD TV, computer, mobile phone) can obviously be used as backlight as well. On the other hand, by using a mixture of polymerizable and non-polymerizable nematics liquid crystals it is also possible to achieve LCPC (Liquid Crystal Polymer Composite) devices that show really interesting electrooptical characteristics using low switching voltages. Polymerizable LC creates a hollow structure inside the sandwich glass cell that keep nematics liquid crystal confined creating microdomains. Homogeneous and homeotropic alignments have been used to develop inverse switching mode LCPCs. Due to the double LC oriented structure, the outgoing scattered light from these devices is already polarized. The polarization axis coincides with LC molecules director, the alignment direction promoted. The novelties derived from the investigation presented here, new ultrafast inverse LCPC with polarized outgoing scattered light based on oriented nematic LC mixture, and an internationally patented security and authentication device based on nematics (doped with dichroic dye) oriented polymerizable LC.

Polarization vision and its role in biological signaling

Visual pigments, the molecules in photoreceptors that initiate the process of vision, are inherently dichroic, differentially absorbing light according to its axis of polarization. Many animals have taken advantage of this property to build receptor systems capable of analyzing the polarization of incoming light, as polarized light is abundant in natural scenes (commonly being produced by scattering or reflection). Such polarization sensitivity has long been associated with behavioral tasks like orientation or navigation. However, only recently have we become aware that it can be incorporated into a high-level visual perception akin to color vision, permitting segmentation of a viewed scene into regions that differ in their polarization. By analogy to color vision, we call this capacity polarization vision. It is apparently used for tasks like those that color vision specializes in: contrast enhancement, camouflage breaking, object recognition, and signal detection and discrimination. While color is very useful in terrestrial or shallow-water environments, it is an unreliable cue deeper in water due to the spectral modification of light as it travels through water of various depths or of varying optical quality. Here, polarization vision has special utility and consequently has evolved in numerous marine species, as well as at least one terrestrial animal. In this review, we consider recent findings concerning polarization vision and its significance in biological signaling.

Design of highly focused fields that remain unpolarized on axis

Research on the properties of highly focused fields mainly involved fully polarized light, whereas partially polarized waves received less attention. The aim of this Letter is to provide an appropriate framework, for designing some features of the focused field, when dealing with incoming partially polarized beams. In particular, in this Letter, we describe how to get an unpolarized field on the axis of a high numerical aperture objective lens. Some numerical results that corroborate theoretical predictions are provided.

Nanoantenna enhanced emission of lightharvesting complex 2: the role of resonance, polarization, and radiative and non-radiative rates

Nanoantennae show potential for photosynthesis research for two reasons; first by spatially confining light for experiments which require high spatial resolution, and second by enhancing the photon emission of single light-harvesting complexes. For effective use of nanoantennae a detailed understanding of the interaction between the nanoantenna and the light-harvesting complex is required. Here we report how the excitation and emission of multiple purple bacterial LH2s (light-harvesting complex 2) are controlled by single gold nanorod antennae. LH2 complexes were chemically attached to such antennae, and the antenna length was systematically varied to tune the resonance with respect to the LH2 absorption and emission. There are three main findings. (i) The polarization of the LH2 emission is fully controlled by the resonant nanoantenna. (ii) The largest fluorescence enhancement, of 23 times, is reached for excitation with light at λ = 850 nm, polarized along the long antenna-axis of the resonant antenna. The excitation enhancement is found to be 6 times, while the emission efficiency is increased 3.6 times. (iii) The fluorescence lifetime of LH2 depends strongly on the antenna length, with shortest lifetimes of [similar]40 ps for the resonant antenna. The lifetime shortening arises from an 11 times resonant enhancement of the radiative rate, together with a 2–3 times increase of the non-radiative rate, compared to the off-resonant antenna. The observed length dependence of radiative and non-radiative rate enhancement is in good agreement with simulations. Overall this work gives a complete picture of how the excitation and emission of multi-pigment light-harvesting complexes are influenced by a dipole nanoantenna.

Far infared reflectance along the C-axis of the charge stripe superconductor La1.875Ba0.125CuO4.

Reflectance measurements along the c-axis of La1.875 Bao.125CU04 at temperatures above(6K) and below(O.5K) the bulk superconducting transition temperature(3K) were performed using a Bruker rapid scan spectrometer and a Martin-Puplett polarizing spectrometer. It was found that when polarized light reflected from a sample the Bruker rapid scan spectrometer has a low frequency cutoff of lOcm-1 while the Martin-Puplett polarizing spectrometer has a low frequency cutoff of 6cm-1 A superconducting pla ma edge was absent in all measurements taken. It was concluded that if a superconducting plasma edge exists in La1.875Bao.125CU04 it is below 6cm-1.

a-b axis-oriented lanthanum doped Bi4Ti3O12 thin films grown on a TiO2 buffer layer

a-b axis-oriented, lanthanum doped Bi4Ti3O12 (BLT) thin films with a TiO2 rutile buffer layer deposited on Pt/Ti/SiO2/Si substrates were grown by the soft chemical method. Butterfly dielectric behavior has been achieved and can be ascribed to the ferroelectric domain switching. The remanent polarization and the coercive voltage for the film deposited on TiO2 buffer layer were 22.2 mu C/cm(2) and 1.8 V, respectively. Random-oriented BLT films showed a reduction in switching polarization when compared to the a-b axis-oriented films. Due to the excellent physical properties, these films are a promising candidate for use in lead-free applications in ferroelectric devices. (c) 2006 American Institute of Physics.

Polarization in heavy quark decays

In this thesis I concentrate on the angular correlations in top quark decays and their next--to--leading order (NLO) QCD corrections. I also discuss the leading--order (LO) angular correlations in unpolarized and polarized hyperon decays. In the first part of the thesis I calculate the angular correlation between the top quark spin and the momentum of decay products in the rest frame decay of a polarized top quark into a charged Higgs boson and a bottom quark in Two-Higgs-Doublet-Models: $t(uparrow)rightarrow b+H^{+}$. The decay rate in this process is split into an angular independent part (unpolarized) and an angular dependent part (polar correlation). I provide closed form formulae for the ${mathcal O}(alpha_{s})$ radiative corrections to the unpolarized and the polar correlation functions for $m_{b}neq 0$ and $m_{b}=0$. The results for the unpolarized rate agree with the existing results in the literature. The results for the polarized correlations are new. I found that, for certain values of $tanbeta$, the ${mathcal O}(alpha_s)$ radiative corrections to the unpolarized, polarized rates, and the asymmetry parameter can become quite large. In the second part I concentrate on the semileptonic rest frame decay of a polarized top quark into a bottom quark and a lepton pair: $t(uparrow) to X_b + ell^+ + nu_ell$. I analyze the angular correlations between the top quark spin and the momenta of the decay products in two different helicity coordinate systems: system 1a with the $z$--axis along the charged lepton momentum, and system 3a with the $z$--axis along the neutrino momentum. The decay rate then splits into an angular independent part (unpolarized), a polar angle dependent part (polar correlation) and an azimuthal angle dependent part (azimuthal correlation). I present closed form expressions for the ${mathcal O}(alpha_{s})$ radiative corrections to the unpolarized part and the polar and azimuthal correlations in system 1a and 3a for $m_{b}neq 0$ and $m_{b}=0$. For the unpolarized part and the polar correlation I agree with existing results. My results for the azimuthal correlations are new. In system 1a I found that the azimuthal correlation vanishes in the leading order as a consequence of the $(V-A)$ nature of the Standard Model current. The ${mathcal O}(alpha_{s})$ radiative corrections to the azimuthal correlation in system 1a are very small (around 0.24% relative to the unpolarized LO rate). In system 3a the azimuthal correlation does not vanish at LO. The ${mathcal O}(alpha_{s})$ radiative corrections decreases the LO azimuthal asymmetry by around 1%. In the last part I turn to the angular distribution in semileptonic hyperon decays. Using the helicity method I derive complete formulas for the leading order joint angular decay distributions occurring in semileptonic hyperon decays including lepton mass and polarization effects. Compared to the traditional covariant calculation the helicity method allows one to organize the calculation of the angular decay distributions in a very compact and efficient way. This is demonstrated by the specific example of the polarized hyperon decay $Xi^0(uparrow) to Sigma^+ + l^- + bar{nu}_l$ ,($l^-=e^-, mu^-$) followed by the nonleptonic decay $Sigma^+ to p + pi^0$, which is described by a five--fold angular decay distribution.

Modeling Framework for the Establishment of the Apical-Basal Embryonic Axis in Plants

The apical-basal axis of the early plant embryo determines the body plan of the adult organism. To establish a polarized embryonic axis, plants evolved a unique mechanism that involves directional, cell-to-cell transport of the growth regulator auxin. Auxin transport relies on PIN auxin transporters 1], whose polar subcellular localization determines the flow directionality. PIN-mediated auxin transport mediates the spatial and temporal activity of the auxin response machinery 2-7] that contributes to embryo patterning processes, including establishment of the apical (shoot) and basal (root) embryo poles 8]. However, little is known of upstream mechanisms guiding the (re)polarization of auxin fluxes during embryogenesis 9]. Here, we developed a model of plant embryogenesis that correctly generates emergent cell polarities and auxin-mediated sequential initiation of apical-basal axis of plant embryo. The model relies on two precisely localized auxin sources and a feedback between auxin and the polar, subcellular PIN transporter localization. Simulations reproduced PIN polarity and auxin distribution, as well as previously unknown polarization events during early embryogenesis. The spectrum of validated model predictions suggests that our model corresponds to a minimal mechanistic framework for initiation and orientation of the apical-basal axis to guide both embryonic and postembryonic plant development.

Experimental measurements of the scattered-light polarization from different liquid flows

An experimental system designed to measure very low optical powers, of the order of a few picowatts, is presented. Its main aid is to detect the polarisation state of scattered light from a fluid flow, in different angular directions with respect to the longitudinal axis of the flow. A laser beam incident linearly polarized crosses the fluid flow orthogonally. The scattered light is detected by means of a photodetector situated behind a lineal polarizer whose orientation can be rotated. The outgoing electrical signal is amplified by means of a Mode-lockin amplifier and is digitally processed.

In-fiber linear polarizer based on UV-inscribed 45° tilted grating in polarization maintaining fiber

We report an in-fiber linear polarizer structured by UV-inscribing a 45° tilted fiber grating (TFG) into polarization maintaining (PM) fiber along its principal axis. The polarization extinction ratio (PER) achieved by a 48 mm long 45° TFG has reached 46 dB at 1550 nm and the overall PER is >40 dB over a 50 nm wavelength range. Such 45° TFG based polarizers have many advantages over conventional products, including low loss, low cost, simple fabrication process, and no physical modification to the fiber, thus offering high stability and capable of handling high power.

Broadband tunable all-fiber polarization interference filter based on 45° tilted fiber gratings

We have theoretically and experimentally designed and demonstrated an all-fiber polarization interference filter (AFPIF), which is formed by a polarization-maintaining (PM) fiber cavity structure utilizing two 45° tilted fiber gratings (45°-TFGs) inscribed by UV laser on the PM fiber. Such a filter could generate modulated transmission of linear polarization status. It has been revealed that the modulation depth of the transmission depends on the coupling angle between the 45°-TFGs and the PM fiber cavity. When the two 45°-TFGs in PM fiber are oriented at 45° to the principal axis of the PM fiber cavity, the maximum modulation depth is achievable. Due to the thermal effect on birefringence of the PM fiber, the AFPIF can be tuned over a broad wavelength range just by simple thermal tuning of the cavity. The experiment results show that the temperature tuning sensitivity is proportional to the length ratio of the PM fiber cavity under heating. For 18 and 40 cm long cavities with 6 cm part under heating, the thermal tuning sensitivities are 0.616 and 0.31 nm/° C, respectively, which are almost two orders of magnitude higher than normal fiber Bragg gratings. © 1983-2012 IEEE.

UV inscribed long period gratings with femtosecond ablated axial fibre slots for polarization control

We present data on the development a new type of optical fibre polariser and the characterisation of its wavelength properties. The device is fashioned using a two step process. Firstly, a standard UV long period grating (LPG) with a period of 330μm is inscribed into hydrogenated SMF-28, followed by femtosecond laser ablation of a groove parallel to the fibre axis. The UV inscribed LPGs have inherently low birefringence. However, the removal of the cladding layer parallel to the location of the LPG within the fibre core (as a result the ablation) modifies the cladding modes that couple with the LPG. Furthermore, the groove breaks the fibre symmetry introducing a non-uniform stress profile across the fibre cross section leading to significant birefringence. We show that increasing the depth of the groove increases the birefringence, and this behaviour coupled with the ability to control the wavelength location of the LPGs attenuations peaks results in a polariser able to operate at almost any wavelength and birefringence. The maximum birefringence reported here as polarisation mode splitting was approximately 39±0.1nm with a polarisation loss of 10dB. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Type Ia supernovae from violent mergers of carbon-oxygen white dwarfs: polarization signatures

The violent merger of two carbon-oxygen white dwarfs has been proposed as a viable progenitor for some Type Ia supernovae. However, it has been argued that the strong ejecta asymmetries produced by this model might be inconsistent with the low degree of polarization typically observed in Type Ia supernova explosions. Here, we test this claim by carrying out a spectropolarimetric analysis for the model proposed by Pakmor et al. for an explosion triggered during the merger of a 1.1 and 0.9 M⊙ carbon-oxygen white dwarf binary system. Owing to the asymmetries of the ejecta, the polarization signal varies significantly with viewing angle. We find that polarization levels for observers in the equatorial plane are modest (≲1 per cent) and show clear evidence for a dominant axis, as a consequence of the ejecta symmetry about the orbital plane. In contrast, orientations out of the plane are associated with higher degrees of polarization and departures from a dominant axis. While the particular model studied here gives a good match to highly polarized events such as SN 2004dt, it has difficulties in reproducing the low polarization levels commonly observed in normal Type Ia supernovae. Specifically, we find that significant asymmetries in the element distribution result in a wealth of strong polarization features that are not observed in the majority of currently available spectropolarimetric data of Type Ia supernovae. Future studies will map out the parameter space of the merger scenario to investigate if alternative models can provide better agreement with observations.