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  • Ítem
    three-dimensional contouring with digital holography
    (Sociedad Colombiana de Física, 2006-01-01) Velásquez, Daniel Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
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    Long-term aerosol optical hygroscopicity study at the ACTRIS SIRTA observatory: Synergy between ceilometer and in situ measurements
    (Copernicus GmbH, 2019-01-01) Bedoya-Velásquez A.E.; Titos G.; Antonio Bravo-Aranda J.; Haeffelin M.; Favez O.; Petit J.-E.; Andrés Casquero-Vera J.; José Olmo-Reyes F.; Montilla-Rosero E.; Hoyos C.D.; Alados-Arboledas L.; Luis Guerrero-Rascado J.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    An experimental setup to study aerosol hygroscopicity is proposed based on the temporal evolution of attenuated backscatter coefficients from a ceilometer colocated with an instrumented tower equipped with meteorological sensors at different heights. This setup is used to analyze a 4.5-year database at the ACTRIS SIRTA observatory in Palaiseau (Paris, France, 2.208E, 48.713N; 160 m above sea level). A strict criterion-based procedure has been established to identify hygroscopic growth cases using ancillary information, such as online chemical composition, resulting in 8 hygroscopic growth cases from a total of 107 potential cases. For these eight cases, hygroscopic growth-related properties, such as the attenuated backscatter enhancement factor (RH) and the hygroscopic growth coefficient I3, are evaluated. This study shows that the hygroscopicity parameter 3 is negatively correlated with the aerosol organic mass fraction but shows a positive correlation with the aerosol inorganic mass fraction. Among inorganic species, nitrate exhibited the highest correlation. This is the first time that hygroscopic enhancement factors are directly retrieved under ambient aerosols using remote-sensing techniques, which are combined with online chemical composition in situ measurements to evaluate the role of the different aerosol species in aerosol hygroscopicity.. © Author(s) 2019.
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    Vortex Metrology by using Fourier Analysis Techniques: Vortex Networks Correlation Fringes
    (OPTICAL SOC AMER, 2012-10-01) Angel, Luciano; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
  • Ítem
    Recuperación de la energía radiada por conductores de corriente alterna
    (Sociedad Colombiana de Física, 2001-06-01) Marulanda, José Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
  • Ítem
    Interpretación Cuantitativa de Interferogramas Holográficos por Medición de la Fase
    (Sociedad Colombiana de Física, 2000-01-01) Velásquez, Daniel Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
  • Ítem
    Lab-made accessible full-field optical coherence tomography imaging system
    (Sociedad Espanola de Optica, 2019-09-01) Cuartas-Velez, Carlos; Ruiz-Lopera, Sebastian; Uribe-Patarroyo, Nestor; Restrepo, Rene; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    In this work, an easy to understand optical system was developed for the study of the medical imaging technique optical coherence tomography (OCT). This technique allows volumetric reconstruction of inhomogeneous, non-transparent and scattering samples such as biological tissues. The implementation was based on using non-specialized components for OCT under the scheme of a Michelson interferometer with a CCD camera to capture the interference patterns in a configuration known as full field OCT (FFOCT). Our system, explained in detail, was designed using components commonly found in most optical labs because our focus is to provide an accessible experimental setup for understanding the basics of OCT. The developed system possesses an axial resolution of 1.74 mu m and a lateral resolution of 4.5 mu m. With the described system, tomograms of two samples were obtained: a metal coin and an ex-vivo insect wing of the blattodea family.
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    Digital lensless holographic microscopy: numerical simulation and reconstruction with ImageJ
    (OPTICAL SOC AMER, 2020-07-01) Trujillo, Carlos; Piedrahita-Quintero, Pablo; Garcia-Sucerquia, Jorge; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    The description and validation of an ImageJ open-source plugin to numerically simulate and reconstruct digital lensless holographic microscopy (DLHM) holograms are presented. Two modules compose the presented plugin: the simulation module implements a discrete version of the Rayleigh-Somerfield diffraction formula, which allows the user to directly build a simulated hologram from a known phase and/or amplitude object by just introducing the geometry parameters of the simulated setup; the plugin's reconstruction module implements a discrete version of the Kirchhoff-Helmholtz diffraction integral, thus allowing the user to reconstruct DLHM holograms by introducing the parameters of the acquisition setup and the desired reconstruction distance. The plugin offers the two said modules within the robust environment provided by a complete set of built-in tools for image processing available in ImageJ. While the simulation module has been validated through the evaluation of the forecasted lateral resolution of a DLHM setup in terms of the numerical aperture, the reconstruction module is tested by means of reconstructing experimental DLHM holograms of biological samples. (C) 2020 Optical Society of America
  • Ítem
    Evaluation between methods for the color measurement in holograms by using a CMOS-RGB camera and a spectrometer.
    (SPIE-INT SOC OPTICAL ENGINEERING, 2013-07-01) Velásquez, Daniel Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
  • Ítem
    Characterization of SrTiO3 thin films at microwave frequencies using coplanar waveguide linear resonator method
    (John Wiley & Sons Inc., 2011-07-01) Marulanda, José Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
  • Ítem
    Mejoramiento del desempeño de un sistema de comunicaciones ópticas FFH-OCDMA utilizando redes de bragg apodizadas fuertes
    (Sociedad Colombiana de Física, 2006-04-01) Marulanda, José Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
  • Ítem
    Understanding the Physical Optics Phenomena by Using a Digital Application for Light Propagation
    (2011-02-01) Angel, Luciano; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
  • Ítem
    Noise and bias in optical coherence tomography intensity signal decorrelation
    (OPTICAL SOC AMER, 2020-04-15) Uribe-Patarroyo, Nestor; Post, Anouk L.; Ruiz-Lopera, Sebastian; Faber, Dirk J.; Bouma, Brett E.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    Functional optical coherence tomography (OCT) imaging based on the decorrelation of the intensity signal has been used extensively in angiography and is finding use in flowmetry and therapy monitoring. In this work, we present a rigorous analysis of the autocorrelation function, introduce the concepts of contrast bias, statistical bias and variability, and identify the optimal definition of the second-order autocorrelation function (ACF) g((2)) to improve its estimation from limited data. We benchmark different averaging strategies in reducing statistical bias and variability. We also developed an analytical correction for the noise contributions to the decorrelation of the ACF in OCT that extends the signal-to-noise ratio range in which ACF analysis can be used. We demonstrate the use of all the tools developed in the experimental determination of the lateral speckle size depth dependence in a rotational endoscopic probe with low NA, and we show the ability to more accurately determine the rotational speed of an endoscopic probe to implement NURD detection. We finally present g((2))-based angiography of the finger nailbed, demonstrating the improved results from noise correction and the optimal bias mitigation strategies. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
  • Ítem
    Microwave Frequency Characterization of Barium Titanate Films Obtained Via Sol-Gel
    (Rev. Fac. Ing, 2019-12-03) Marulanda-Bernal, Jose-Ignacio; Gallo-Castrillon, Wilson-Henry; Mosquera-Palacio, Diana-Marybel; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    The present work focuses on the structural, morphological and dielectric characterization of barium titanate films (BTO or BaTiO3 due to its chemical formula) deposited by spin coating on crystalline silicon (Si) substrates and CPW resonators using the Sol-Gel technique with a Ba/Ti molar ratio of 0.5/0.5. The coplanar waveguides were manufactured on alumina substrates (Al2O3) with 3 mu m of gold (Au) metallization using the laser ablation technique. The scanning electron microscopy (SEM) with X-ray energy dispersion spectrometry (EDS) showed the existence of a BTO film with an elementary composition of 14.62% barium and 5.65% titanium, with a thickness of 0.77 mu m measured using the profilometric mode of the atomic force microscopy (AFM). Dielectric characterization was carried out by comparing the frequency response (parameter S-21) of a CPW resonator with deposited BTO film and another reference resonator (without film) using a network vector analyzer (VNA). These measurements are compared in turn with computational simulations to obtain the dielectric properties. For the BTO film was determined a relative dielectric constant constant (epsilon r) of 160 with a loss tangent (Tan delta) of 0.012 for a frequency of 3.60 GHz. The dielectric constant constant and the ferroelectric property of the material produced are quite promising for applications in microwave circuits, such as miniaturization and tuning.
  • Ítem
    Holoprinter: study and development of a direct write synthetic full parallax holographic system
    (Sociedad Espanola de Optica, 2018-12-01) Madrid-Sanchez, A; Velasquez-Prieto, D; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    Holoprinters based on holographic stereograms (HS) have been developed to synthesize holograms by using 2D images with perspective information of 3D objects. The objects can be real or computer generated. HS has been applied to different fields such as engineering, medicine and military because the high visual impact of the tridimensional and multi-view images it presents. To implement a Holoprinter requires development of three components: i) 2D images generation, ii) optical system design for HS recording and iii) mechanical and control implementation. Therefore, we design and develop each of the components, which integrated compose a holoprinter to synthesize full parallax HS. This paper studies basis for production of this kind of holograms and describes the computational and opto-mechanical design and implementation that we have made. Experimental HS were obtained to validate the system.
  • Ítem
    Hygroscopic growth study in the framework of EARLINET during the SLOPE i campaign: Synergy of remote sensing and in situ instrumentation
    (Copernicus GmbH, 2018-05-18) Bedoya-Velásquez A.E.; Navas-Guzmán F.; Granados-Muñoz M.J.; Titos G.; Román R.; Andrés Casquero-Vera J.; Ortiz-Amezcua P.; Antonio Benavent-Oltra J.; De Arruda Moreira G.; Montilla-Rosero E.; Hoyos C.D.; Artiñano B.; Coz E.; Olmo-Reyes F.J.; Alados-Arboledas L.; Guerrero-Rascado J.L.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    This study focuses on the analysis of aerosol hygroscopic growth during the Sierra Nevada Lidar AerOsol Profiling Experiment (SLOPE I) campaign by using the synergy of active and passive remote sensors at the ACTRIS Granada station and in situ instrumentation at a mountain station (Sierra Nevada, SNS). To this end, a methodology based on simultaneous measurements of aerosol profiles from an EARLINET multi-wavelength Raman lidar (RL) and relative humidity (RH) profiles obtained from a multi-instrumental approach is used. This approach is based on the combination of calibrated water vapor mixing ratio (r) profiles from RL and continuous temperature profiles from a microwave radiometer (MWR) for obtaining RH profiles with a reasonable vertical and temporal resolution. This methodology is validated against the traditional one that uses RH from co-located radiosounding (RS) measurements, obtaining differences in the hygroscopic growth parameter (?) lower than 5% between the methodology based on RS and the one presented here. Additionally, during the SLOPE I campaign the remote sensing methodology used for aerosol hygroscopic growth studies has been checked against Mie calculations of aerosol hygroscopic growth using in situ measurements of particle number size distribution and submicron chemical composition measured at SNS. The hygroscopic case observed during SLOPE I showed an increase in the particle backscatter coefficient at 355 and 532nm with relative humidity (RH ranged between 78 and 98%), but also a decrease in the backscatter-related Ångström exponent (AE) and particle linear depolarization ratio (PLDR), indicating that the particles became larger and more spherical due to hygroscopic processes. Vertical and horizontal wind analysis is performed by means of a co-located Doppler lidar system, in order to evaluate the horizontal and vertical dynamics of the air masses. Finally, the Hänel parameterization is applied to experimental data for both stations, and we found good agreement on ? measured with remote sensing (?532 0.48 ± 0.01 and ?355 0.40 ± 0.01) with respect to the values calculated using Mie theory (?532 0.53 ± 0.02 and ?355 0.45 ± 0.02), with relative differences between measurements and simulations lower than 9% at 532nm and 11% at 355nm. © Author(s) 2018.
  • Ítem
    Seasonal analysis of the atmosphere during five years by using microwave radiometry over a mid-latitude site
    (Elsevier Ltd, 2019-01-01) Bedoya-Velásquez A.E.; Navas-Guzmán F.; de Arruda Moreira G.; Román R.; Cazorla A.; Ortiz-Amezcua P.; Benavent-Oltra J.A.; Alados-Arboledas L.; Olmo-Reyes F.J.; Foyo-Moreno I.; Montilla-Rosero E.; Hoyos C.D.; Guerrero-Rascado J.L.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    This work focuses on the analysis of the seasonal cycle of temperature and relative humidity (RH) profiles and integrated water vapor (IWV) obtained from microwave radiometer (MWR) measurements over the mid-latitude city of Granada, southern Spain. For completeness the study, the maximum atmospheric boundary layer height (ABLHmax) is also included. To this end, we have firstly characterized the HATPRO-RPG MWR errors using 55 co-located radiosondes (RS) by means of the mean-bias (bias¯) profile and the standard deviation (SDbias) profile classified under all-weather conditions and cloud-free conditions. This characterization pointed out that temperature from HATPRO-MWR presents a very low bias¯ respects RS mostly below 2.0 km agl, ranging from positive to negative values under all-weather conditions (from 1.7 to -0.4 K with SDbias up to 3.0 K). Under cloud-free conditions, the bias was very similar to that found under all-weather conditions (1.8 to -0.4 K) but with smaller SDbias (up to 1.1 K). The same behavior is also seen in this lower part (ground to 2.0 km agl) for RH. Under all-weather conditions, the mean RH bias ranged from 3.0 to -4.0% with SDbias between 10 and 16.3% while under cloud-free conditions the bias ranged from 2.0 to -0.4% with SDbias from 0.5 to 13.3%. Above 2.0 km agl, the SDbias error increases considerably up to 4 km agl (up to -20%), and then decreases slightly above 7.0 km agl (up to -5%). In addition, IWV values from MWR were also compared with the values obtained from the integration of RS profiles, showing a better linear fit under cloud-free conditions (R2 = 0.96) than under all-weather conditions (R2 = 0.82). The mean bias under cloud-free conditions was -0.80 kg/m2 while for all-weather conditions it was -1.25 kg/m2. Thus, the SDbiasfor all the statistics (temperature, RH and IWV) of the comparison between MWR and RS presented higher values for all-weather conditions than for cloud-free conditions ones. It points out that the presence of clouds is a key factor to take into account when MWR products are used. The second part of this work is devoted to a seasonal variability analysis over five years, leading us to characterize thermodynamically the troposphere over our site. This city atmosphere presents a clear seasonal cycle where temperature, ABLHmax and IWV increase from winter to summer and decrease in autumn, meanwhile RH decreases along the warmer seasons. This city presents cold winters (mean daily maximum temperature: 10.6 ± 1.1 °C) and dry/hot summers (mean daily maximum temperature of 28.8 ± 0.9 °C and mean daily maximum of surface RH up to 55.0 ± 6.0%) at surface (680 m asl). Moreover, considering temporal trends, our study pointed out that only temperature and RH showed a linear increase in winters with a mean-rate of (0.5 ± 0.1) °C/year and (3.4 ± 1.7) %/year, respectively, from ground to 2.0 km agl, meanwhile IWV presented a linear increase of 1.0 kg·m-2/year in winters, 0.78 kg·m-2/year in summers and a linear decrease in autumns of -0.75 kg·m-2/year. © 2018 Elsevier B.V.
  • Ítem
    Evaluation of a liquid crystal based polarization modulator for a space mission thermal environment
    (Elsevier B.V., 2017-10-15) Silva-López M.; Bastide L.; Restrepo R.; García Parejo P.; Álvarez-Herrero A.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    The Multi Element Telescope for Imaging and Spectroscopy (METIS) is one of the remote sensing instruments to be onboard the future NASA/ESA Solar Orbiter mission. The science nominal mission orbit will take the spacecraft from 0.28 to 0.95 astronomical units from the Sun, setting challenging and variable thermal conditions to its payload. METIS is an inverted-occultation coronagraph that will image the solar corona in the visible and UV wavelength range. In the visible light path a Polarization Modulation Package (PMP) performs a polarimetric analysis of the incoming solar light. This PMP is based on liquid crystal variable retarders (LCVR) and works under a temporal modulation scheme. The LCVRs behavior has a dependence on temperature and, as a consequence, it is critical to guarantee the PMP performance in the mission thermal environment. Key system specifications are the optical quality and the optical retardance homogeneity. Moreover, the thermally induced elastic deformations of the mechanical mounts and the LCVRs shall not produce any performance degradation. A suitable thermal control is hence required to maintain the system within its allowed limits at any time. The PMP shall also be able to reach specific set-points with the power budget allocated. Consequently, and in order to verify the PMP thermal design, we have experimentally reproduced the expected thermal flight environment. Specifically, a thermal vacuum cycle test campaign is run at the different mission operational conditions. The purpose is both to check the stability of the thermal conditions and to study the optical quality evolution/degradation. Within this test transmitted wavefront measurements and functional verification tests have been carried out. To do that we adapted an optical interrogation scheme, based on a phase shifting interferometric technique, that allows for inspection of the PMP optical aperture. Finally, measurements obtained at nonoperational temperature conditions are also shown. These results demonstrate that the device meets the specifications required to perform its operational role in the space mission environment. (C) 2017 The. Authors. Published by Elsevier B.V.
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    Volumetric non-local-means based speckle reduction for optical coherence tomography
    (OSA - The Optical Society, 2018-07-01) Cuartas-Vélez, C.; Restrepo, R.; Bouma, B.E.; Uribe-Patarroyo, N.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    We present a novel tomographic non-local-means based despeckling technique, TNode, for optical coherence tomography. TNode is built upon a weighting similarity criterion derived for speckle in a three-dimensional similarity window. We present an implementation using a two-dimensional search window, enabling the despeckling of volumes in the presence of motion artifacts, and an implementation using a three-dimensional window with improved performance in motion-free volumes. We show that our technique provides effective speckle reduction, comparable with B-scan compounding or out-of-plane averaging, while preserving isotropic resolution, even to the level of speckle-sized structures. We demonstrate its superior despeckling performance in a phantom data set, and in an ophthalmic data set we show that small, speckle-sized retinal vessels are clearly preserved in intensity images en-face and in two orthogonal, cross-sectional views. TNode does not rely on dictionaries or segmentation and therefore can readily be applied to arbitrary optical coherence tomography volumes. We show that despeckled esophageal volumes exhibit improved image quality and detail, even in the presence of significant motion artifacts. © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.
  • Ítem
    Plataforma de simulación de aberraciones ópticas vía implementación de las características de un SLM y reconstrucción de fase usando algoritmos basados en los sensores de Hartmann-Shack
    (2015-10-01) Ramirez, Natalia; R. Restrepo; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    Dada la importancia que hoy día presenta dentro del ámbito de la óptica, la implementación y conocimiento de dispositivos capaces tanto de generar aberraciones ópticas bien caracterizadas como de sensarlas, en este artículo se presenta el funcionamiento
  • Ítem
    Application software for teaching the polarization ellipse
    (Sociedad Espanola de Optica, 2018-09-01) Cano, Camilo; Echeverri-Chacon, Santiago; Cuartas-Velez, Carlos; Angel, Luciano; Restrepo, Rene; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    This paper describes the development of a computational application that calculates the configuration of a polarization state generator, according to the parameters of a desired polarization ellipse. The most general way to describe the polarization state of light is an ellipse, however, it is rarely used in practical courses in which applications are limited to the case of linear or circular polarization. To generate a desired polarization ellipse, a polarizer and a pair of retarders of ?/2 and ?/4 can be used, the problem is to determine the angle of rotation of the retarders. We present an open source algorithm to calculate these angles by using a minimization method applied to the Jones calculus description of polarizing elements. This development aims to help research and education activities to promote a more practical understanding of the polarimetric properties of light. © Sociedad Española de óptica.En este trabajo se presenta el desarrollo de una aplicación computacional que permite determinar la configuración de un generador de estados de polarización en función de los parámetros de una elipse de polarización deseada. La manera más general de describir la polarización de la luz es una elipse, sin embargo, este estado rara vez se aborda en un curso práctico en los cuales las aplicaciones se limitan al caso de la polarización lineal o circular. Para generar una elipse de polarización deseada se puede utilizar un polarizador y un par de retardadores de ?/2 y ?/4, el problema está en determinar a qué ángulo deben estar ubicados los retardadores. Se presenta un algoritmo de acceso libre que calcula estos ángulos mediante un método de minimización aplicado al cálculo de Jones. Este desarrollo va dirigido a actividades de investigación y educación, para promover una comprensión práctica de las propiedades polarimétricas de la luz. © Sociedad Española de óptica.
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