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https://hdl.handle.net/10784/1123

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Features on photorefractive registered speckles
(SPIE, 1999-04-29) Ángel-Toro, Luciano; Bolognini, Néstor; Tebaldi, Myrian; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
The recording and read-out of a volume speckle pattern is investigated for transmission geometry. The modulation of the 3D speckle grains appears when the image of a coherently illuminated random diffusor is formed onto the crystal by an optical system whose pupil consists of two identical holes. The intensity distribution of the speckle pattern imaged onto the BSO crystal leads to a space-charge field by drift of photocarriers, resulting in a refractive index modulation. The main features of diffracted read-out light at the Fourier plane are discussed. © (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Photorefractive optical processing: some proposals
(SPIE, 1999-04-29) Ángel-Toro, Luciano; Bolgnini, Néstor; Tebaldi, Myrian; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
Some proposals on Lau and Talbot fringes formation based on a grating registered as birefringence modulation in a photorefractive crystal, will be presented. In the Talbot case, the stored grating can be replicated if read-out with coherent light. The system for the Lau arrangement behaves as a combination of an amplitude and a birefringence phase grating. In both cases, it is possible to control the visibility and to produce a contrast reversion of fringes by using an analyzer. Besides, Lau and Talbot interferometers based on the mentioned approach and their alternative experimental arrangements will be discussed. © (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Contrast inversion in the Lau phenomena implemented with a photorefractive grating
(SPIE, 1999-07-06) Ángel Toro, Luciano; Tebaldi, Myrian Cristina; Bolognini, Néstor Alberto; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
It was implemented the Lau effect with a grating registered in a BSO crystal. Two different arrangement were analyzed. In both cases, it is possible to control the visibility and to produce the contrast inversion of fringes, by properly setting the pass plane orientation of an analyzer located at the crystal output.
Talbot and Lau phenomena implementation via a photorefractive converter
(SPIE, 1999-07-06) Tebaldi, Myrian Cristina; Ángel Toro, Luciano; Bolognini, Néstor Alberto; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
We propose a novel implementation of the Lau and Talbot effects. It employs a grating registered as modulation of birefringence in a Bi12SiO20 crystal. The systems proposed allow to control the visibility and in particular to reverse the contrast of the self images and Lau fringes by rotating an analyzer. A theoretical approach is outlined and the predicted behavior is confirmed by results obtained under different experimental conditions. We have taken advantage of the arrangements to demonstrate some applications.
Double aperture speckle method using a BSO crystal for in plane displacement
(SPIE, 1999-07-06) Trivi, Marcelo Ricardo; Tebaldi, Myrian Cristina; Bolognini, Néstor Alberto; Ángel Toro, Luciano; Tebaldi, Myrian Cristina; Bolognini, Néstor Alberto; Trivi, Marcelo Ricardo; Ángel Toro, Luciano; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
The possibility of using a BSO crystal as a recording medium of specklegrams with carrying frequency fringes, to storage multiple interferograms, for uniform in-plane displacements, is presented. Experimental results are shown.
Speckle photography through different multiaperture pupils
(SPIE/ 18th Congress of the International Commission for Optics, 1999-07-19) Ángel Toro, Luciano; Tebaldi, Myrian Cristina; Bolognini, Néstor Alberto; Trivi, Marcelo Ricardo; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
An image multiplexing method based on the internal modulation of speckle grains by employing different multiple aperture pupils for recording is proposed. The interferometric fringes profile and visibility in the Fourier plane, for uniform in-plane displacement double- exposed specklegrams through different pupils recording, are analyzed in terms of the geometric parameters of the pupils. Experimental evidences are presented.
Logic operations by using modulated speckle
(SPIE, 2001-08-14) Tebaldi, Myrian; Ángel-Toro, Luciano; Trivi, Marcelo; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
An alternative image multiplexing technique is proposed. In the arrangement implemented, the input is imaged by introducing a multiple aperture pupil in the imaging lens. Then, the speckle pattern is modulated by several system of fringes. The input images are sequentially encoded by using a different pupil during each exposure. The pupil arrangements implemented are selected to concentrate in each spot the spectral information corresponding to not more than two exposures. The spectral amplitude components for a pari of exposures are added into the common diffraction spots. All the diffraction spots contain information about a pair of inputs. Then, an image binary operation can be carried out in each spot. The technique is implemented by using as recording media photographic films and photorefractive crystals. The BSO crystal as recording medium is quite adequate in the applications proposed because it permits multiple storage in real time. However, due to its volume nature, each speckle grain exhibits angular selectivity in addition to those features observed in bidimensional media. © (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Double exposure specklegrams obtained by using scaled aperture pupils
(SPIE, 2001-08-14) Angel-Toro, Luciano; Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
In speckle photography the pupil aperture is usually not modified between exposures. In our work, the change of the pupil aperture scale between exposures is analyzed on the basis of double-exposed image speckle, before and after a diffuse in-plane displacement is done. The apertures have the same shape but its scale is modified between exposures. Note that the relative position of the aperture is maintained. In particular, we analyze a simple case that uses a circular aperture whose diameter is modified for recording each image. The intensity in the image plane and the fringe visibility are evaluated, in terms of the geometric characteristics of the pupils. © (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Soap film analysis by speckle interferometer
(SPIE-INT SOC OPTICAL ENGINEERING, 2003-01-01) Tebaldi, M.; Ángel, L.; Trivi, M.; Bolognini, N.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
In this paper a soap film is characterized by using a speckle interferometer. The arrangement consists of a double-exposure specklegram obtained through a double-aperture system, by introducing a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and the changes experimented by the interferometric fringe visibility in the Fourier plane due to the introduction of a soap film in each exposure are analyzed.
Soap film analysis by speckle interferometer
(SPIE, 2003-11-18) Tebaldi, Myrian; Ángel-Toro, Luciano; Trivi, Marcelo; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
In this paper a soap film is characterized by using a speckle interferometer. The arrangement consists of a double-exposure specklegram obtained through a double-aperture system, by introducing a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and the changes experimented by the interferometric fringe visibility in the Fourier plane due to the introduction of a soap film in each exposure are analyzed.
Improvement of performance in FFH-OCDMA systems by using strong apodized fiber Bragg gratings
(SPIE-INT SOC OPTICAL ENGINEERING, 2004-01-01) Marulanda, JI; Torres, PI; Ramirez, CA; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
This paper shows simulations of an all-fiber fast optical code division multiple access communications system (OCDMA), using strong apodized fiber Bragg gratings (FBGs) arrays as passive encoding-decoding devices. Auto and cross-correlation functions of the user signals, and bit error rate (BER) were used as evaluation criteria. Through numerical analysis, we demonstrated that when strong Bragg gratings are used the performance of the system is increased. We obtain the BER performance for strong gratings and compare results in various cases.
Analysis of vibrations in a plate using interferometric methods
(SPIE-INT SOC OPTICAL ENGINEERING, 2004-01-01) Rueda, E.; Angel, L.; Velasquez, D.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
In this work some frequencies and modes of vibration of a thin plate were determined using interferometric methods like: real-time holographic interferometry, time-average holographic interferometry, digital speckle pattern interferometry DSPI. And the results obtained are compared with those obtained with the program of finite elements COSMOS.
Reduction of speckle noise in digital holography
(SPIE-INT SOC OPTICAL ENGINEERING, 2004-01-01) Garcia-Sucerquia, J.; Ramirez, J.A.H.; Castaneda, R.; Prieto, D.V.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
A fundamental problem in holography, as well optical as digital, is the presence of speckle noise in the reconstruction process. Many approaches have been carried out in order overcome such a problem, ranging from altering the spatial coherence (optical techniques) of the illumination to imaging processing techniques (digital techniques). This work shows the merged use of digital imaging techniques in order to reduce the speckle noise in digital reconstruction of optically recorded Fresnel's holograms. The proposed filtering techniques are illustrated with experimental results.
DC term filtering techniques in digital holography
(SPIE-INT SOC OPTICAL ENGINEERING, 2004-01-01) Garcia-Sucerquia, J.; Ramirez, J.A.H.; Prieto, D.V.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
In numerical hologram reconstruction like in optical holography, there exist different diffraction orders, which many times produce difficulties for the image visualizations. In numerical reconstruction, the filtering of the DC term, or zero order diffraction, provides an improved utilization of the dynamic range of the visualization systems, which is needed for the right displaying purposes of reconstructed images. In the case of the in-line set-ups, the zero diffraction order has even more devastating effects because it does not allow reconstructing the images itself as in Gabor's holograms, so it is necessary to attempt a filtering of this DC term. In this work is shown a qualitative assessment of different techniques of DC term filtering applied to numerical reconstruction of Fresnel's holograms recorded by means of off-line set-ups.
DC term filtering techniques in digital holography
(SPIE, 2004-10-21) Velásquez-Prieto, Daniel; García Sucerquia, Jorge Iván; Herrera Ramírez, Jorge Alexis; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
In numerical hologram reconstruction like in optical holography, there exist different diffraction orders, which many times produce difficulties for the image visualizations. In numerical reconstruction, the filtering of the DC term, or zero order diffraction, provides an improved utilization of the dynamic range of the visualization systems, which is needed for the right displaying purposes of reconstructed images. In the case of the in-line set-ups, the zero diffraction order has even more devastating effects because it does not allow reconstructing the images itself as in Gabor's holograms, so it is necessary to attempt a filtering of this DC term. In this work is shown a qualitative assessment of different techniques of DC term filtering applied to numerical reconstruction of Fresnel's holograms recorded by means of off-line set-ups.
Reduction of speckle noise in digital holography
(SPIE, 2004-10-21) Velásquez-Prieto, Daniel; García Sucerquia, Jorge Iván; Castañeda Sepúlveda, Román; Herrera Ramírez, Jorge Alexis; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
A fundamental problem in holography, as well optical as digital, is the presence of speckle noise in the reconstruction process -- Many approaches have been carried out in order overcome such a problem, ranging from altering the spatial coherence (optical techniques) of the illumination to imaging processing techniques (digital techniques) -- This work shows the merged use of digital i maging techniques in order t o reduce the speckle noise in digital reconstruction of optically recorded Fresnel's holograms -- The proposed filtering techniques are illustrated with experimental results --
Analysis of vibrations in a plate using interferometric methods
(SPIE, 2004-10-21) Ángel-Toro, Luciano; Prieto, Daniel Velasquez; Rueda Muñóz, Edgar Alberto; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
In this work some frequencies and modes of vibration of a thin plate were determined using interferometric methods like: real-time holographic interferometry, time-average holographic interferometry, digital speckle pattern interferometry DSPI. And the results obtained are compared with those obtained with the program of finite elements COSMOS.
Phase-difference images by digital holography applied to 3D surface contouring
(Academia Colombiana de Ciencias Exactas Físicas y Naturales, 2005-06) Velásquez-Prieto, Daniel; García Sucerquia, Jorge Iván; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
The problem to determine the 3D-contour of objects with all sizes and shapes is a hot topic in diverse fields of optical research and engineering. Through the use of the numerical reconstruction of digital recorded holograms, we propose a technique to evaluate the 3D contour of objects at least four orders of magnitude larger than the optical wavelength. The required 2π-module phase map in any contouring process is obtained by means of phase-difference image of two digital reconstructed holograms. These holograms are interferometric recordings from a still object under different angle illumination. Our proposal is supported on the theoretical analysis of the contouring system, verified by means of numerical results.
Test results. EMIR optomechanics
(SPIE-INT SOC OPTICAL ENGINEERING, 2005-08-30) Barrera, S.; González, C.; Manescau, A.; Abreu, D.; Becerril, S.; Correa, S.; Fragoso, A.; Pérez, J.; Redondo, P.; Restrepo, R.; Saavedra, P.; Sánchez, V.; Tenegi, F.; Garzón, F.; Patrón, J.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
EMIR is a NIR multiobject spectrograph with imaging capabilities to be used at the GTC. The first collimator lens in EMIR, made of Fused Silica, has an outer diameter of 490 mm, and a weight of 265 N, which make it one of the largest Fused Silica lenses ever mounted to work under cryogenic conditions. The results of the various tests being done at the IAC (with two different lens dummies) in order to validate a mounting design concept for this lens, are presented here. The radial support concept tested consists of three contact areas around the lens, one of which is a PTFE block, preloaded by coil springs and the other two are fixed supports made of Aluminum and PTFE, dimensioned in order to keep lens centered both at room temperature and under operation conditions.
EMIR: The GTC NIR multi-object imager-spectrograph
(SPIE-INT SOC OPTICAL ENGINEERING, 2006-01-01) Garzón, F.; Abreu, D.; Barrera, S.; Becerril, S.; Cairós, L.M.; Díaz, J.J.; Fragoso, A.B.; Gago, F.; Grange, R.; González, C.; López, P.; Patrón, J.; Pérez, J.; Rasilla, J.L.; Redondo, P.; Restrepo, R.; Saavedra, P.; Sánchez, V.; Tenegi, F.; Vallbé, M.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
EMIR, currently entering into its fabrication and AIV phase, will be one of the first common user instruments for the GTC, the 10 meter telescope under construction by GRANTECAN at the Roque de los Muchachos Observatory (Canary Islands, Spain). EMIR is being built by a Consortium of Spanish and French institutes led by the Institute de Astrofisica de Canarias (IAC). EMIR is designed to realize one of the central goals of 10m class telescopes, allowing observers to obtain spectra for large numbers of faint sources in an time-efficient manner. EMIR is primarily designed to be operated as a MOS in the K band, but offers a wide range of observing modes, including imaging and spectroscopy, both long slit and multiobject, in the wavelength range 0.9 to 2. 5 µm. It is equipped with two innovative subsystems: a robotic reconfigurable multislit mask and disperssive elements formed by the combination of high quality difracction grating and conventional prisms, both at the heart of the instrument. The present status of development, expected performances, schedule and plans for scientific exploitation are described and discussed. The development and fabrication of EMIR is funded by GRANTECAN and the Plan Nacional de Astronomia y Astrofisica (National Plan for Astronomy and Astrophysics, Spain).

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