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September 1986 - June 2015
Publications
Publications (37)
Dynamic optical sensors, as those based on the reflectivity of isotropic dielectrical interfaces, can be useful for measuring small changes in the refractive index of fluid media. Exact and approximated explicit formulas for their sensitivity are developed. These expressions clarify the influence of each of the constructive parameters of the device...
A study on the influence of multiple reflections on the transmission coefficients of uniaxial plane–parallel plates is presented. Two representative models are analyzed: one that considers only the first transmission, and a rigorous one, taking into account the multiple reflections within the plate. Modules, phases, and the interference between $p$...
This work studies the adverse effects, as regards noise, of immersing in water an integrating line piezoelectric detector devoted to optoacoustic imaging. We found that the sensor, in conjunction with the acoustic coupling medium (water), behaves as a resonant dielectric antenna. This phenomenon limits the performance of the system because it effic...
In this work, the first and second order effects for reflected and transmitted pulses with a Gaussian distribution of frequencies are analytically developed and interpreted. They show some peculiar characteristics that bear certain parallelism with those of monochromatic beams with a Gaussian distribution of amplitudes. However, when the former are...
El estudio detallado de la respuesta de los materiales lineales anisótropos ante campos electromagnéticos tiene como uno de sus fines el de diseñar nuevos dispositivos de interés en Óptica, Optoelectrónica y Electrónica. En este trabajo presentamos una herramienta numérica sencilla que es capaz de determinar las características de la propagación de...
El estudio detallado de la respuesta de los materiales lineales anisótropos ante campos electromagnéticos tiene como uno de sus fines el de diseñar nuevos dispositivos de interés en Óptica, Optoelectrónica y Electrónica. En este trabajo presentamos una herramienta numérica sencilla que es capaz de determinar las características de la propagación de...
This work presents a detection system for optoacoustic tomography based on a polymer piezoelectric sensor and a transimpedance amplifier. The results of the electrical and acoustic characterization show that the system has a large bandwidth (63 MHz), high sensitivity (1630 {\mu}V/Pa) and low equivalent noise pressure (1 Pa). The described sensor de...
En este trabajo se presenta la resolución analítica de las ecuaciones de Maxwell y las condiciones de contorno para la reflexión y transmisión de ondas planas en interfaces isótropo-uniaxial y uniaxial-isótropo cuando la incidencia se da en alguno de los planos principales (eje óptico en el plano de incidencia o eje óptico perpendicular al plano de...
In this paper we present a method to determine the spatial resolution and sensitivity of systems for optoacoustic tomography (OAT). The method consists of obtaining the image of a sample based on a transparent film embedded in agarose. The film has a certain pattern made with a laser printer that allows to obtain the system spatial resolution. More...
Los láseres pueden operar en dos regímenes: modo continuo ó pulsado. En los casos más simples, el modo continuo se corresponde a haces monocromáticos con distribución de amplitudes gaussiana (es un haz limitado en el espacio); mientras que el modo pulsado corresponde a haces policromáticos con distribución gaussiana de frecuencias (pulso limitado e...
En este trabajo se presenta el desarrollo de un software que permite calcular la dirección de propagación, fase, amplitud y polarización del campo reflejado y transmitido a través de un cristal uniaxial cuando una onda plana monocromática incide desde un medio isótropo. El software grafica los resultados en 3D y permite reproducir las condiciones e...
We present a method to determine the thermal boundary conductance of gold nanoparticles in aqueous solution. The novel approach consists of two steps: first, measuring photoacoustic signals originated by laser-induced nanobubbles at different energies and, second, fitting the experimental data with a nanobubble generation model developed in a previ...
The detection system for optoacoustic tomography (OAT) usually employs broadband piezoelectric sensors based on polymeric materials. Polyvinylidene fluoride (PVDF) and its copolymers are amongst the most popular ones. Within our knowledge, the existing reconstruction algorithms for OAT neglect the electrical and mechanical relaxation processes of t...
Las ondas planas monocromáticas permiten describir adecuadamente muchas de las propiedades de la radiación propagada, reflejada y transmitida a través de medios de distintas propiedades ópticas. Sin embargo, algunas características solo aparecen considerando haces y/o pulsos limitados. En este trabajo determinamos y analizamos algunas característic...
En este trabajo se presentan mediciones que revelan cambios en la respuesta en frecuencia de un fotodetector tipo PIN debida al cambio en la intensidad de la luz que llega al detector. En particular, se observan dos efectos a altos niveles de iluminacion: el ancho de banda del detector disminuye y se modifica su respuesta de fase. Para bajas intens...
Optoacoustic imaging is a hybrid technique with a rapid evolution within the area of biomedical imaging. It combines the rich and versatile optical contrast with the high spatial resolution associated with the low-dispersion ultrasonic wave propagation nature. Its application raises a series of difficult problems that require further developments....
The generation of nanobubbles by laser irradiation of nanoparticles is of great interest in various applications in biophotonics. In a previous work we presented a model that adequately describes the phenomenon at low concentration of nanoparticles (<0.1 nM) and low repetition rate laser pulses (<0.5 Hz). The model is based on the classical nucleat...
La generación de nanoburbujas por irradiación laser de nanopartículas presenta gran interés para diversas
aplicaciones en biofotónica. En un trabajo previo presentamos un modelo que describe adecuadamente el
fenómeno para bajas concentraciones de nanopartículas (< 0.1 nM) y bajas tasas de repetición de pulsos láser (< 0.5 Hz). El mismo está basado...
Se estudió el funcionamiento de un tensiómetro de gota rotante. Para ello se obtuvieron las ecuaciones que describen la forma la gota en equilibrio. Con estas ecuaciones se realizó una simulación numérica que fue contrastada con un trabajo previo
The modeling of bubbles initiated by laser-irradiated nanoparticles is of interest for many applications. There is at present no comprehensive physical picture for all the stages of the process. We present an alternative approach with a key assumption: the vapor bubble evolves adjacent to the nanoparticle. To take into account the irreversible evol...
En experiencias de laboratorio, comunmente es deseable controlar la temperatura de un proceso. Ya sea para lograr un efecto deseado o para estudiar las propiedades físicas de un compuesto. Por ello es de interes el diseño, desarrollo e implementación de un termostato Calentador/Enfriador Programable. Este dispositivo, mediante dos actuadores, enfrí...
Los efectos no-geométricos de primer y segundo orden al reflejarse y trans mitirse un haz Gaussiano a través de una o varias superficies ha sido y sigue siendo estudiado con profundidad. Los haces limitados en el tiempo de dis tribución gaussiana de frecuencias presentan algunas características pecu liares que guardan algún paralelismo con las de l...
A critical microemulsion (AOT/decane/water, W 0 = 34.6 and g = 0.068) was studied using complex permittivity and Kerr-effect techniques. Permittivity measurements were made in the range from 150 Hz to 1.5 MHz using a circuit of a novel design. Below 100 kHz a dielectric relaxation process appears, it can be related to a Maxwell–Wagner polarization...
In this work we present an experimental setup that allows measuring, simultaneously, the electric birefringence, the electric light scattering, and the cell electrical current under the action of an external electric field. The basic design corresponds to a standard birefringence setup. The Kerr cell was built to permit the observation of 90° light...
Experimental results are presented on the electric birefringence induced in aqueous TRITON X-100 solutions near critical micelle concentration (CMC). The results show the transition from anisotropic aggregates to spherical micelles and the changes that take place in the monomers' concentration.
By following a method proposed by Kahlweit, an equilibrium diagram was determined in O/W quaternary microemulsions. These systems were formed by octanol (cosurfactant)/water/octane (oil)/alkylglucoside (surfactant). The experiment study was performed at two different temperatures (25°C and 50°C). The objective of this study work was to determine th...
Layer bending rigidities were measured for an AOT–water–iso-octane microemulsion with two methods: electric deformation and temperature dependent fluctuation mode analysis. The values of rigidity obtained, while being of the expected order of magnitude for the electric deformation method, are lower when computed with the fluctuation mode analysis....
The Kerr effect of the Xanthan (charged polyelectrolyte; 113 ppm)/DTAB (surfactant) mixture in aqueous solution was studied. The static Kerr constant (B) and mean relaxation times (τ) values as a function of surfactant concentration (CDTAB ) were determined. The observed birefringence (Δn) is not a linear function of the electric applied field (E )...
The Kerr effect of polyelectrolyte/surfactant mixtures in aqueous solutions has been measured. Investigated materials are: PAMPS (Polymer) and DTAB (surfactant). Two kinds of polymer were employed to assemble the studied systems: one of them ("System I") contains 10% (mol) charged monomer whereas the other one ("System II") contains 25% (mol). Kerr...
In order to follow the sol–gel transition in systems containing TiO2 nanoparticles rheological and optical measurements were performed. Samples were prepared adding titanium(IV) butoxide (hydrolysis and condensation processes) to water/AOT/isooctane microemulsions. We prepared different systems at constant Wo=[H2O]/[AOT] while varying R=[H2O]/[Ti(B...
Kerr effect measurements as a function of the relation [water]/[alkoxide] concentration (h) were performed. These systems were prepared from water/AOT/isooctane microemulsions by adding titanium (IV) butoxide. From a certain h value it was observed that Kerr constant values change abruptly. This behaviour is indicative of the beginning of the sol -...
The variation of the Kerr constant versus surfactant concentration in a solution of AOT in water was studied. The observed behavior shows changes when aggregates begin to form. allowing to measure the critical micelle concentration, with results coincident with those obtained through static light scattering and electric conductivity measurements. F...
For some years, several authors have tried to explain the behavior of electric field induced birefringence in some microemulsion systems. In this work we continue a line based on works by van der Linden [S. Geiger, E. van der Linden, D. Bedeaux, Physica A 156 (1989) 130; C. Roman Vas, G.J.M. Koper, E. van der Linden, J. Phys. II (France) 4 (1994) 1...
We have applied the Kerr effect technique to a five-component w/o microemulsion in order to determine the evolution of the shape of water droplets dispersed in dodecane. The analysis is made in terms of the fraction in volume of the droplets with respect to the microemulsion. The adopted model leads to the conclusion that, as the proportion of wate...
The Kerr constant was determined for the AOT-water-dodecane water-in-oil microemulsion. The goal of these experiments has been to test the validity of the theoretical approach of van der Linden, S. Geiger and D. Bedaux, Phys. A., 156 (1989) 130, which explains the electro-optical process through an elastic deformation of the droplets. The bending m...
Electric birefringence measurements were carried out in sodium di-2-ethylhexylsulfosuccinate(AOT)—water—dodecane(decane), water/oil microemulsions, along different concentration paths. The Kerr constant as a function of watercore droplet radius or the water volume fraction have been determined. This electro-optic effect was related to the droplet d...
