FRD - Investigación - Ciencia y Tecnología
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Item Fabry Perot detector for low coherence interferometry(2023-06) Cerrotta, Santiago; Torga, Jorge Román; Morel, Eneas NicolásSe 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.Item Scanning optical coherence tomography applied to the characterization of surfaces and coatings(El Sevier, 2014) Cerrotta, Santiago; Morel, Eneas Nicolás; Torga, Jorge RománThis paper shows the technique of optical coherence tomography in the frequency domain (OCT-FD) to obtain surface topography and tomography of surface coatings. The setup is based on a superluminescent diode centered on 849 nm with an spectral wide of 50 nm as the light source, a single-mode fibre Michelson interferometer and a spectrometer as the detector system. This scheme allows having compact and robust equipments that was designed to be used in an industrial environment. With this system it can be obtain a tridimensional image acquired point by point with a maximum range of 20 mm width and length and 2 mm depth. Images obtained from the topography of metal samples and tomography of polymer based coatings is presented. Also it is shown that is possible to obtain, from these images, parameters of interest of the sample, such as roughness, flatness and characteristic distances. As an example to show the potential of the method the dimensions of a metal surface modified after laser ablation were measured from a topography image obtained with this technique. A second example presented was the image obtained of a roughness pattern made on a metal surface. Finally it was presented a tomography image of a modified polyurethane coating deposited on a metal surface. Thickness and refractive index of the coating were obtained after the image analysis.Item Extending low-coherence interferometry dynamic range using heterodyne detection(2020-08) Cusato, Leslie; Cerrotta, Santiago; Torga, Jorge Román; Morel, Eneas NicolásLow-coherence interferometry (LCI) technique is generating considerable interest in industrial applications where there is a need for larger measurements with high resolution. Conventional Fourier domain systems reach a limiting depth of around 3 mm, mainly due to the spectrometers used as detectors. In this work, we present an optical detection system that performs the Fourier transform of the LCI signals, based on a spatial heterodyne spectrometer. This device avoids the fall-off effect of the spectrometer, allowing to reach measurable optical depths of almost 5 cm without losing resolution. We describe the theory underlying this detection system and present experimental results which are in great accordance.Item Accuracy and Mechanistic Details of Optical Printing of Single Au and Ag Nanoparticles(2017-08-30) Cerrotta, Santiago; Garjiulo, Julian; Violi, Lanina; Chvatal, Lukas; Cortes, Emiliano; Perassi, Eduardo; Diaz, Fernando; Zemánek, Pavel; Stefani, Fernando D.;Optical printing is a powerful all-optical method that allows the incorporation of colloidal nanoparticles (NPs) onto substrates with nanometric precision. Here, we present a systematic study of the accuracy of optical printing of Au and Ag NPs, using different laser powers and wavelengths. When using light of wavelength tuned to the localized surface plasmon resonance (LSPR) of the NPs, the accuracy improves as the laser power is reduced, whereas for wavelengths off the LSPR, the accuracy is independent of the laser power. Complementary studies of the printing times of the NPs reveal the roles of Brownian and deterministic motion. Calculated trajectories of the NPs, taking into account the interplay between optical forces, electrostatic forces, and Brownian motion, allowed us to rationalize the experimental results and gain a detailed insight into the mechanism of the printing process. A clear framework is laid out for future optimizations of optical printing and optical manipulation of NPs near substrates.Item Room evacuation through two contiguous exits(Physica A: Statistical Mechanics and its Applications, 2017-05-15) Sticco, Ignacio; Frank, Guillermo; Cerrotta, Santiago; Dorso, ClaudioCurrent regulations demand that at least two exits should be available for a safe evacuation during a panic situation. Although the "faster is slower" effect is expected to take place near the exits, the evacuation time will improve because of the additional exits. However, rooms having contiguous doors not always reduce the leaving time as expected. We investigated the relation between the doors separation and the evacuation performance. We found that there exists a separation distance range that does not really improve the evacuation time, or it can even worsen the process performance. To our knowledge, no attention has been given to this issue in the literature. This work reports how the pedestrians dynamics differ when the separation distance between two exit doors changes and how this affects the overall performance.Item Feasibility and analysis of a system of two in tandem interferometers for optical coherence tomography(IEE Explore Digital Library, 2017-12-18) Cerrotta, Santiago; Morel, Eneas Nicolás; Alvira, Fernando; Torga, Jorge RománA signal obtained from a combined system of two interferometers of low coherence in the frequency domain is presented and analyzed. This system allows to expand the range of measurement offered by the conventional optical tomography system of a single interferometer with a spectrometer as a detector.Item Large Axial Range Frequency-Domain Optical Low Coherence Interferometry(2019-01-15) Cerrotta, Santiago; Morel, Eneas Nicolás; Alvira, Fernando; Torga, Jorge RománIn this paper, we propose a new experimental setup to extend the measurement range of frequency-domain low coherence interferometry (FD-LCI) from 3 mm to 2 cm. The FD-LCI can be extended to the technique of frequency domain optical coherence tomography (FD-OCT) by performing additional lateral scanning. This new and simple arrangement just attaches an extra interferometer before the spectrometer in a typical FD-LCI setup. With this configuration, it is possible to overcome the limitation of the dynamic range of the conventional technique. This allows us to measure the optical path difference of the sample of interest, which is outside the detection range of the spectrometer, using an extra interferometer as a tuner system. In addition, this tuning allows significant minimization of the effects produced by the fall-off. The accuracy of the new system is obtained by adding the FD-LCI and the tuning micrometric translator accuracies. In our experimental setup, this value is 20 μm.