FRD - Investigación - Ciencia y Tecnología

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Author: search.filters.author.Torga, Jorge Román

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    Time Fourier domain low coherence interferometry
    (2022-04) Cerrotta, Santiago; Torga, Jorge Román; Morel, Eneas Nicolás
    We presented a new system that combine Time Domain and Fourier Domain Low Coherence Interferometry. Moving one interferometer arm the Fourier Transform can be detected in the photodiode. Maths and experimental results are shown.
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    Fabry Perot detector for low coherence interferometry
    (2023-06) Cerrotta, Santiago; Torga, Jorge Román; Morel, Eneas Nicolás
    Se proponen dos diseños teóricos de detectores de intensidad para distintas longitudes de onda basados en cavidades Fabry Perot para ser aplicados en la técnica de interferometría de baja coherencia en el dominio de las frecuencias (FD-LCI). Un detector axial unidimensional que consta de una cavidad variable con un fotodiodo y otro detector radial con cavidad fija y con un array lineal o cámara. Se demostró su factibilidad teórica realizando simulaciones de haces gaussianos propagándose a través de cavidades con diferentes características. Se optimizaron los parámetros para que los detectores estén centrados en 850 nm, con rangos de 60 nm y resolución por debajo del nanómetro para haces de 500 µm de cintura, condiciones típicas de las fuentes y detectores usadas en FD-LCI. Además, el diseño contempla la posibilidad de usarlos simultáneamente.
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    Long-range frequency domain low-coherence interferometry detector for industrial applications
    (2023-01) Cerrotta, Santiago; Torga, Jorge Román; Morel, Eneas Nicolás
    A low-cost long-range frequency domain low-coherence interferometry (LCI) detector is presented: time Fourier domain LCI (TFD-LCI). Combining ideas of time domain and frequency domain techniques, the TFD-LCI detects the analog Fourier transform of the optical interference signal with no limitation for the maximum optical path, measuring the thickness of several centimeters with micrometer resolution. A complete characterization of the technique is presented with a mathematical demonstration, simulations, and experimental results. An evaluation of repeatability and accuracy is also included. Measurements of small and large monolayer and multilayer thicknesses were done. Characterization of the internal and external thicknesses of industrial products such as transparent packages and glass windshield is presented, showing the potentiality of TFD-LCI for industrial applications.
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    Resultados numéricos y experimentales para el análisis de vibraciones libres en una placa rectangular delgada
    (2012-11) Carrizo, Marcos; Raffo, Javier Leandro; Morel, Eneas Nicolás; Torga, Jorge Román
    El análisis de vibraciones libres en estructuras es una condición fundamental de diseño en ingeniería. Es ampliamente conocido que las frecuencias naturales y sus correspondientes formas modales son los valores a obtener en este tipo de análisis. Es por eso que el presente trabajo se enfoca en la obtención de estas magnitudes desde dos puntos de vista: el análisis numérico y las mediciones experimentales. Específicamente, los resultados de ambas técnicas se muestran para el análisis de las vibraciones libres de una placa rectangular delgada isótropa con restricción en uno de sus bordes manteniendo los otros libres. Para realizar el análisis numérico se utilizaron dos modelos: el primero se desarrolló aplicando el método de Ritz al cálculo de vibraciones libres y el segundo consistió en la modelización numérica en elementos finitos. En ambos casos se obtuvieron las frecuencias naturales y sus correspondientes formas modales. Para las mediciones experimentales también se emplearon dos técnicas: se empleó la técnica de interferometría óptica coherente, utilizando una configuración del tipo Michelson y se midieron las primeras frecuencias naturales mediante el uso de acelerómetros y técnicas de análisis de vibraciones mecánicas. Se discute la concordancia entre los resultados obtenidos por ambos métodos numéricos y ambas técnicas experimentales.
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    Inclination shift signal: thickness or index measurement in transparent media by transmission of generally astigmatic Gaussian beams
    (2021-04) Aguilar, Andres; Torga, Jorge Román
    The focus error signal is a widespread optical technique that harnesses the shape of a simply astigmatic Gaussian beam to produce an output signal with a well-defined linear range used for many different applications. However, general astigmatic Gaussian beams have not been extensively used for measuring purposes even though they have been known for decades. These beams have interesting properties which were used in this work as a mean to measure a change in the optical path and recover sample information. In this text, the formulae presented by E. Kochkina to represent generally astigmatic Gaussian beams are summarized, the principles of the proposed technique are set forth and two experimental results are presented as a validation of the proposal. A brief introduction to a different approach that enables the setup to perform simultaneous measurements of the thickness and refractive index is also given.
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    Diseño y construcción de un módulo de microscopía de barrido por sondeo local y de un sistema de nanoposicionamiento de alta precisión para un microscopio multianálisis
    (2014) Martínez Reina, Hernán; Pujol, Miguel A.; Morel, Eneas Nicolás; Scarpettini, Alberto; Torga, Jorge Román
    Este trabajo presenta la técncia de interferometrá de baja coherencia orientada a la obtención de topografiá de superficies y tomografía de materiales. Se decribe la idea general, se presentan distintos esquemas experimentales y se muestran resultados obtenidos en distintos tipos de aplicaciones. Se pretende mostrar que esta técnica, todavía en etapa de laboratorio, puede ser en muchos casos una alternativa a las técncias convencionales o una solución a problemas por resolver, en el área de los ensayos no detructivos en materiales.
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    Improved spectral resolution in time-varying interferometry
    (2018-11) Antonacci, Julian; Morel, Eneas Nicolás; Torga, Jorge Román; Duchowicz, Ricardo; Arenas, Gustavo
    In this work, we present a procedure that allows increasing the resolution of dynamic length measurements made by spectral interferometry. The proposed scheme leads to obtaining a compact photonic instrument with the ability to measure distances, variations on positions and vibrations with a very high resolution. This measurement system includes a superluminescent source (SLED), a digital spectrometer and a Fizeau interferometer. Spectral data is processed by applying Fourier domain techniques previously applied in optical coherence tomography. The resolution of the spectral measurement system is determined by the spectrometer bandwidth and the light source employed. A signal is obtained by analysing the time evolution of a single pixel from the spectrometer CCD sensor, which is later analysed using time domain interferometry (TDI) techniques. This procedure works by detecting changes in the optical path below those that can be detected by spectral analysis. The original resolution obtained with the solely spectral techniques was 2.2 µm but was improved to 40 nm by complementary analysis of temporal signals.
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    Optical coherence tomography-based scanning system for shape determination, wall thickness mapping, and inner inspection of glass containers
    (2013-02) Morel, Eneas Nicolás; Gutierrez, Marina; Miranda, Hernán; Sambrano, Edgardo; Torga, Jorge Román
    In this work we present a method that enables simultaneous measurement of shape and wall parameters of glass containers. The system is based on the optical coherence tomography technique, employing the spectral domain configuration. The data were obtained by measuring the spatial coordinates of a sequence of points in a predefined region of a sample that includes points on the surface and in the interior of the material. Dimensional parameters, thickness mapping, and tomography studies of the interior of the sample walls can be obtained from these measurements.
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    Limitations due to the detector in the low coherence interferometry
    (2008-02-15) Morel, Eneas Nicolás; Torga, Jorge Román
    Se describirá como se generan las señales de interferometria de baja coherencia en el espacio de Fourier, se determinara las características que determinan el rango dinámico del sistema y las señales asociadas al sistema de detección y su influencia en la señal de interferencia.
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    Interferometric system based on swept source-optical coherence tomography scheme applied to the measurement of distances of industrial interest
    (2015-12-11) Morel, Eneas Nicolás; Russo, Nélida A.; Torga, Jorge Román; Duchowicz, Ricardo
    We used an interferometric technique based on typical optical coherence tomography (OCT) schemes for measuring distances of industrial interest. The system employed as a light source a tunable erbium-doped fiber laser of ∼20-pm bandwidth with a tuning range between 1520 and 1570 nm. It has a sufficiently long coherence length to enable long depth range imaging. A set of fiber Bragg gratings was used as a self-calibration method, which has the advantage of being a passive system that requires no additional electronic devices. The proposed configuration and the coherence length of the laser enlarge the range of máximum distances that can be measured with the common OCT configuration, maintaining a good axial resolution. A measuring range slightly >17 cm was d0.etermined. The system performance was evaluated by studying the repeatability and axial resolution of the results when the same optical path difference was measured. Additionally, the thickness of a semitransparent medium was also measured.