New methods for optical information processing in life science
Author(s):
Tatiana Alieva
Show Abstract
The application of optoelectronic techniques, based on Fourier transform, bilinear distributions, fractional transformations, for biomedical information processing: filtering, segmentation and classification of biomedical images, characterization of optical manipulators, recovering of statistical tissue properties, is discussed.
Laser-induced lipolysis on adipose cells
Author(s):
Efrain Solarte;
O. Gutierrez;
Rodrigo Neira;
J. Arroyave;
Carolina Isaza;
Hugo Ramirez;
Aldo F. Rebolledo;
Willian Criollo;
C. Ortiz
Show Abstract
Recently, a new liposuction technique, using a low-level laser (LLL) device and Ultrawet solution prior to the procedure, demonstrated the movement of fat from the inside to the outside of the adipocyte (Neira et al., 2002). To determine the mechanisms involved, we have performed Scanning and Transmission Electron Microscopy studies; Light transmittance measurements on adipocyte dilutions; and a study of laser light propagation in adipose tissue. This studies show: 1. Cellular membrane alterations. 2. LLL is capable to reach the deep adipose tissue layer, and 3. The tumescence solution enhances the light propagation by clearing the tissue. MRI studies demonstrated the appearance of fat on laser treated abdominal tissue. Besides, adipocytes were cultivated and irradiated to observe the effects on isolated cells. These last studies show: 1. 635 nm-laser alone is capable of mobilizing cholesterol from the cell membrane; this action is enhanced by the presence of adrenaline and lidocaine. 2. Intracellular fat is released from adipocytes by co joint action of adrenaline, aminophyline and 635 nm-laser. Results are consistent with a laser induced cellular process, which causes fat release from the adipocytes into the intercellular space, besides the modification of the cellular membranes.
Photophysical and photochemical properties of Bauhinia megalandra (Caesalpinaceae) extracts as new PDT photosensitizer
Author(s):
Franklin Ramon Vargas Tovar;
C. Rivas;
O. Estrada;
Aristides Alfredo Marcano O.;
Lorenzo Echevarria;
Yrene Diaz;
I. Alexander;
L. Rodriguez;
L. Padron;
I. Ramon Rivera
Show Abstract
Recently new photosensitizers, chlorophyll "a and b" derivatives, for photodynamic therapy (PDT) have been presented. It already passed complete pre-clinical investigations. This prompted us to carry out an extensive study of photophysical properties of chlorine derivatives, important both for optimization of their clinic applications and for study of mechanisms of chlorine PDT&. The fresh leaves of Bauhinia megalandra (Caesalpinaceae) were extracted with methanol by percolation, and re-extract with a mixture of methanol-water (1:1), the insoluble fraction was then separated by column chromatography [RP18/hexane-ethylacetate (9:1)] to obtain four fractions named 1 to 4. These compounds were identified by NMR data. We found that 3 and 4 efficiently generates singlet oxygen when irradiated with visible light. Detection of the singlet oxygen was fulfilled by its reaction with histidine and detected by bleaching p-nitrosodimethylaniline under 440 nm irradiation. The quantum yields of singlet oxygen determined by us were 0.088 (1), 0.151 (2), 0.219 (3) and 0.301 (4). We measured absorption and fluorescence spectra of compounds 1 to 4 (Mg-chlorophyll-a, Pheophytin, Mg-chlorophyll-b and chlorophyll-b respectively) in different media and in aqueous solutions of human serum albumin. The association constant of the compounds 1, 2, 3 and 4 in the presence of HSA were estimated. The binding and quenching studies suggest that only 1 and 3 may serve as a useful fluorescence probe for structure/function studies of different chlorophyll binding proteins. No photoinduced binding was observed after irradiation by all the studied compounds in presence of human serum albumin.
Particle image velocimetry applied to study of a ventricular assist device
Author(s):
E. Ferrara;
Mikiya Muramatsu;
I. A. Cestari
Show Abstract
The Ventricular Assist Devices (VADs) are being used to auxiliary the blood circulation in clinical situation where the blood pumped by the ventricle doesn't attend the demand of patient. During the use of VADs there is the probability of occur thrombosis and hemolysis due to stagnation regions and high shear stress in flow. Therefore, the study of velocity flow field inside the VAD is essential for developing of a device to long using. This study can be made through the optics technique called of Particle Image Velocimetry, which consists in the determination of flow displacement through light scattering pattern by particles suspended in the fluid. In this work, a Particle Image Velocimetry was developed to study VADs with beating frequencies up to 30 bpm. The scattering pattern was obtained through particles that were added to fluid and illuminated by an Argon laser source (2W). Images were captured with a CCD acquisition system and velocity distributions are obtained from cross correlation method.
Optical detection of Trypanosoma cruzi in blood samples for diagnosis purpose
Author(s):
Elvio Alanis;
Graciela Romero;
Liliana Alvarez;
Carlos C. Martinez;
Miguel A. Basombrio
Show Abstract
An optical method for detection of Trypanosoma Cruzi (T. cruzi) parasites in blood samples of mice infected with Chagas disease is presented. The method is intended for use in human blood, for diagnosis purposes. A thin layer of blood infected by T. cruzi parasites, in small concentrations, is examined in an interferometric microscope in which the images of the vision field are taken by a CCD camera and temporarily stored in the memory of a host computer. The whole sample is scanned displacing the microscope plate by means of step motors driven by the computer. Several consecutive images of the same field are taken and digitally processed by means of image temporal differentiation in order to detect if a parasite is eventually present in the field. Each field of view is processed in the same fashion, until the full area of the sample is covered or until a parasite is detected, in which case an acoustical warning is activated and the corresponding image is displayed permitting the technician to corroborate the result visually. A discussion of the reliability of the method as well as a comparison with other well established techniques are presented.
The effect of low-intensity laser therapy on wound healing in Streptozotocin-induced diabetic rats
Author(s):
Sylvia Bicahlo Rabelo;
Antonio Guillermo Jose Balbin Villaverde;
Miguel A. Castilho Salgado;
Milene da Silva Melo;
Renata Amadei Nicolau;
Marcos Tadeu Tavares Pacheco
Show Abstract
Diabetes Mellitus is a condition that results in a delay of the wound healing process, that is associated with an insufficient production of collagen, a decrease of the amount of collagen fibrils and deficient blood flow in the wound area. It is sugested that Low Intensity Laser Therapy acts by improving wound healing in normal organisms, accelerating tissue regeneration. The aim of this work was to investigate the biostimulatory effect of the HeNe laser irradiation, at 632.8 nm, on wound healing in 15 male rats suffering from diabetes induced by Streptozotocin, compared to 15 control diabetic animals. Irradiation parameters were: laser power of 15mW, exposition time of 17 s., irradiated area of 0.025 cm2 and laser energy density of 10 J/cm2. Full-thickness skin squared samples, with 5 mm of non-injured tissue around the wound, were obtained at 4, 7 and 15 days after wounding procedure (5 treated and 5 control animals each time). The histopathologic analysis performed by haematoxylin-cosin staining. Results suggested that the irradiation of diabetic rats was efficient for wound healing. Treated group presented better quality of the wound tissues by the macroscopic observation than control group and the microscopic analysis demonstrated that treated animals had better histopathologic evaluation than non treated.
Study of the failure of the time-independent diffuse equation near a point source
Author(s):
Luis Marti-Lopez;
J. Bouza-Dominguez;
Jeremy C. Hebden
Show Abstract
The diffusion equation (DE) is widely used in biomedical optics for describing light propagation in tissue. However, the DE yields inaccurate results near sources. This drawback is important in practical situations, when it is of primary interest to calculate the dose of light applied or to retrieve the optical properties of the tissue near the light source, e.g., the distal end of an optical fiber. To study this problem we derived a diffusion equation for constant refractive index and rays of arbitrary divergence (DErad) from a modified radiative transfer equation for spatially varying refractive index. We solve the DErad for a time-independent point source in near field and far field, which are defined by a parameter Rcrit. The far-field solution is the solution to the time-independent DE, the near-field solution agrees well with Monte Carlo simulation results and the Rcrit coincides with the reported radius of inaccuracy of the DE. These results suggest that the inaccuracy of the time-independent DE near a point source is due to a non-negligible ray divergence.
Deriving the inverse square law from radiative transfer equations
Author(s):
Luis Marti-Lopez;
J. Bouza-Dominguez;
Jeremy C. Hebden;
Rene A. Martinez-Celorio
Show Abstract
The radiative transfer equation (RTE) is the fundamental equation of the radiative transfer theory and one of more important theoretical tools in biomedical optics for describing light propagation in biological tissues. The RTE assumes that the refractive index of the medium is constant and the ray divergence is zero. These assumptions limit its range of applicability. To eliminate this drawback three new RTE have been proposed recently. Obviously, those equations must be carefully studied and compared. With that aim we solve the standard RTE and the new radiative transfer equations for the specific case of a time-independent isotropic point source in an infinite non-absorbing non-amplifying non-scattering linear medium with constant refractive index. The solution to this problem is the well-known inverse square law of geometrical optics. We show that only one of those equations gives solutions consistent with the inverse square law for the irradiance, due to its ability to model non-negligible ray divergence near a point source.
Transmittance and scattering during wound healing after refractive surgery
Author(s):
Santiago Mar;
C. Martinez-Garcia;
J. T. Blanco;
R. M. Torres;
V. R. Gonzalez;
S. Najera;
G. Rodriguez;
J. M. Merayo
Show Abstract
Photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) are frequent techniques performed to correct ametropia. Both methods have been compared in their way of healing but there is not comparison about transmittance and light scattering during this process. Scattering in corneal wound healing is due to three parameters: cellular size and density, and the size of scar. Increase in the scattering angular width implies a decrease the contrast sensitivity. During wound healing keratocytes activation is induced and these cells become into fibroblasts and myofibroblasts. Hens were operated using PRK and LASIK techniques. Animals used in this experiment were euthanized, and immediately their corneas were removed and placed carefully into a cornea camera support. All optical measurements have been done with a scatterometer constructed in our laboratory. Scattering measurements are correlated with the transmittance -- the smaller transmittance is the bigger scattering is. The aim of this work is to provide experimental data of the corneal transparency and scattering, in order to supply data that they allow generate a more complete model of the corneal transparency.
Near-infrared Raman spectroscopy to detect the calcification of the annular mitral valve
Author(s):
Rick Rocha;
E. P.U. Otero;
M. S. Costa;
Antonio Guillermo Jose Balbin Villaverde;
P. M.A. Pomerarantzeff;
Marcos T. Tavares Pacheco
Show Abstract
Cardiac valves are subjected to high repetitive mechanical stresses, particularly at the hinge points of the cusps and leaflets due to the over 40 millions cardiac cycles per year. These delicate structures can suffer cumulative lesions, complicated by the deposition of calcium phosphate mineral, which may lead to clinically important disease. Near Infrared Raman Spectroscopy gives important information about biological tissues composition and it is being used for diagnosis of some pathologies. The aim of this work was to detect trough the use of the Raman Spectroscopy technique the mitral annular calcification. A Ti:sapphire laser operating at the near infrared wavelength of 785 nm was used for the excitation of the valve samples and the Raman radiation was detected by an optical spectrometer with a CCD liquid nitrogen cooled detector. In all, ten samples of normal and pathologic tissues were studied. They were approximately squared with the lateral size of 5 mm. It was observed that the Raman spectrum of the calcified mitral valve showed different behavior, when compared to normal tissues. Results indicate that this technique could be used to detect the deposition of the calcium phosphate mineral over the mitral valve.
Multispectral tracking of phytoplankton in the Colombian Caribbean
Author(s):
V. V. Ojeda Caicedo;
Arturo Plata
Show Abstract
In a quantitative research study, the concentration and circulation of group of micro-organisms "phytoplankton" have been found through the images of the ocean color in the Colombian Caribbean Sea. These images have been observed through the Sea Star satellite. The method logical procedure was to collect a number of ocean images at the 1A level of the sensor SeaWifs. This only covered the geographical area of study and the seasons of the year. The selection criterion was to give priority to the absence of clouds in the area. Afterwards, the images were analyzed to create mosaics in convenient periods to visualize the periodical changes of the micro-organisms. Thus, places with higher concentration of phytoplankton in the study site were identified. This led to quantitative analyses of the concentration level of the subject of study. To analyze the images analytic algorithms were used to fit the sensor. The atmospheric correction of the SeaWifs images was made with the SeaDas software to obtain levels two and three of the images. This was done to calculate the primary production of phytoplankton.
Light stress effect and by nitrogen deficiency in plants of Petiveria alliacea measured with two-chlorophyll-fluorescence technique
Author(s):
H. Zuluaga;
A. Oviedo;
Efrain Solarte;
E. J. Pena
Show Abstract
The chlorophyll fluorescence was studied in Petiveria alliacea plants exposed to different nitrogen concentrations and light radiation, the response was measured by two different forms; (1) measuring the photosynthetic efficiency with a pulse amplitude modulated fluorometro (PAM) emitted by a 650 nm diode and (2) measuring the fluorescence spectra caused by high power 452 nm diode with a SD2000 spectrometer. It was found out that the photosynthetic efficiency decreased in the plants exposed to high radiance and low nitrogen. Two chlorophyll fluorescence peaks were observed on 684 nm and 739 nm, the intensities in this wavelengths are inversely related with the light radiance. The correlation between the FIR and photosynthetic efficiency was very strong (r2 = -0.809, p <<0.01); this let us conclude that the fluorescence spectral analysis induced by the diode (excitation at 452 nm) is an efficient technique to detect stress by high light intensity and nitrogen in P. Alliacea plants.
Advances in the processing of policromat images as diagnostic method to determine white spot syndrome virus in white shrimp (Litopenaeus vannamei)
Author(s):
Cristina M. Chavez-Sanchez;
Josue Alvarez-Borrego;
L. Montoya-Rodriguez;
A. Garcia-Gasca;
Emma Josefina Fajer Avila;
R. Pacheco-Marges
Show Abstract
White spot syndrome (WSSV) is a viral disease which affects many crustacean species including commercial shrimps. Adequate, precise and quick methods to diagnose on time the presence of the disease in order to apply different strategies to avoid the dispersion and to reduce mortalities is necessary. Histopathology is an important diagnostic method. However, histopathology has the problem that requires time to prepare the histological slides and time to arrive to some diagnosis because this depend on the nature of the tissues, the pathogen(s) to find, the number of organisms, number of slides to analyze and the skill of the technician. This paper try to demonstrate the sensibility of one digital system of processing and recognition of images using color correlation with phase filters, to identify inclusion bodies of WSSV. Infected tissues were processed to obtain histological slides and to verify that the inclusion bodies observed were of WSV, in situ hybridization were carried out. The sensibility results of the recognition of the inclusion bodies of WSSV with the color correlation program was 86.1%. The highest percentage of recognition was in nervous system and tegument glands with 100%. The values in the stomach epithelium and heart tissue was 78.45% of recognition. Tissues with the lowest recognition values were lymphoid organ and hematopoietic tissue. It is necessary further studies to increase the sensibility and to obtain the specificity.
Optic system for the measurement of metrological parameters of the foot
Author(s):
A. Patino;
J. Meneses
Show Abstract
Taking into account the need to characterize the foot in its dimensions with the objective to prevent and correct deformities, an optical system that allows its 3D reconstruction using the laser triangulation principle was created. Parameters are measured on the digitalized 3D image that is obtained of the foot.
Digital image analysis in the design and implementation of a visual inspection system for fruit grading
Author(s):
L. Pencue Fierro;
M. Patino Velasco;
C. Zambrano Velasco;
Jaury Leon-Tellez
Show Abstract
An automated vision system to classify fruits according to the visual characteristics of the surface like: size, color, shape, texture and external defects content and distribution is described. The system works with wide range characteristics of citrus that are classified by means of an artificial neural network.
Image processing of standard grading scales for objective assessment of contact lens wear complications
Author(s):
Elisabet Perez-Cabre;
Maria Sagrario Millan;
Hector C. Abril;
E. Otxoa
Show Abstract
Ocular complications in contact lens wearers are usually graded by specialists using visual inspection and comparing with established standards. The standard grading scales consist of either a set of illustrations or photographs ordered from a normal situation to a severe complication. In this work, an objective assessment of contact lens wear complications is intended by applying different image processing techniques to two standard grading scales (Efron and CCLRU grading scales). In particular, conjunctival hyperemia and papillary conjunctivitis are considered. Given a set of standard illustrations or pictures for each considered ocular disorder, image preprocessing is needed to compare equivalent areas. Histogram analysis allows segmenting vessel and background pixel populations, which are used to determine the most relevant features in the measurement of contact lens effects. Features such as color, total area of vessels and vessel length are used to evaluate bulbar and lid redness. The procedure to obtain an automatic grading method by digital image analysis of standard grading scales is described.
Ray tracing in the human eye: measurement and modeling of optical aberrations
Author(s):
Rafael M. Navarro;
P. Rodriguez;
L. Gonzalez;
J. Aporta;
J. L. Hdez-Matamoros
Show Abstract
The rapid development of cataract and refractive surgery requires new methods to assess the optical quality of the eye. The optimized optical design of custom treatments to improve the optical performance of individual eyes requires, at least, to have the technology to (1) measure the geometry (anatomy) of the optics of the eye; (2) measure the optical performance (refractive state, aberrations, etc); (3) Build a custom optical and anatomical model of the individual eye to treat; (4) Optimal design of custom treatments. In this communication we will present the work carried out by our group to develop methods for measuring and modeling the optical performance of the eye. In particular, we will focus, first, on the Laser Ray Tracing method that we have developed to measure the optical aberrations of the eye, as a physical in vivo implementation of the classical numerical ray tracing used by optical designers; and second, on the development of custom optical models of the eye to perform that numerical ray tracing which predicts with a high fidelity experimental measurements. The methods developed have been applied to design both custom surgery and optical aids to improve optical performance.
Efficient numerical modeling of the cornea, and applications
Author(s):
L. Gonzalez;
Rafael M. Navarro;
J. L. Hdez-Matamoros
Show Abstract
Corneal topography has shown to be an essential tool in the ophthalmology clinic both in diagnosis and custom treatments (refractive surgery, keratoplastia), having also a strong potential in optometry. The post processing and analysis of corneal elevation, or local curvature data, is a necessary step to refine the data and also to extract relevant information for the clinician. In this context a parametric cornea model is proposed consisting of a surface described mathematically by two terms: one general ellipsoid corresponding to a regular base surface, expressed by a general quadric term located at an arbitrary position and free orientation in 3D space and a second term, described by a Zernike polynomial expansion, which accounts for irregularities and departures from the basic geometry. The model has been validated obtaining better adjustment of experimental data than other previous models. Among other potential applications, here we present the determination of the optical axis of the cornea by transforming the general quadric to its canonical form. This has permitted us to perform 3D registration of corneal topographical maps to improve the signal-to-noise ratio. Other basic and clinical applications are also explored.
Chromatic saturation on simple reaction time
Author(s):
B. M. O'Donell;
Elisa M. Colombo;
V. Zimmerman
Show Abstract
This study examined the influence of chromatic saturation stimulus on simple reaction times (RTs). The saturation on the chromatic stimulus was modulated along red-green and blue-yellow opponent axes. RTs are sensitive to chromatic saturation of the stimulus, the highest saturation the smaller RTs. For yellow stimuli the dependence of RT with saturation is lesser than the other colors.
A new design of a fundus camera for the human eye using the Hartmann test
Author(s):
Lizbeth A. Castaneda-Escobar;
Daniel Malacara-Hernandez
Show Abstract
The wavefront aberrations in the human eye have been studied by means of different quantitative methods. The knowledge of the wavefront shape is very useful in optics in general and particularly, in the ophtalmological area. In the latter, it is possible to optimize the results of the corneal surgery, correcting the power errors and high-order aberrations in the human eye by means of the Hartmann test; with this in mind we show a new design of a fundus camera.
Digital analysis of microscopic images of blood cells for pathological diagnostics
Author(s):
C. Zambrano Velasco;
F. Correa;
L. Pencue Fierro;
M. Patino;
Jaury Leon-Tellez
Show Abstract
In this work the implementation of a computation vision system that classifies blood cells images obtained by means of optical microscopy techniques are described. The classifier is a neural network fed with the feature extracted obtained from images, such as its shape, size and cellular nucleus configuration.
Direct led-fluorescence method for Mao-B inactivation in the treatment of Parkinson's
Author(s):
Jimmy A. Castillo;
Jannett Hung;
M. Rodriguez;
E. Bastidas;
I. Laboren;
A. Jaimes
Show Abstract
A led-fluorescence spectroscopy method determinate the inhibitory effects of probe compounds on MAO-B activity is described. In this assay, we demonstrate the possibility of determinate the activity of MAO-B efficiently and rapidly without the use of reference substrate. Measuring variations in fluorescence intensity of MAO-B enzyme during the reaction with inhibitors, L-deprenyl and berberine IC50 and KI values were obtained. For L-deprenyl (IC50 = 0.017 μM and KI = 0.019 μM) and berberine (IC50 = 90 μM and KI = 47 μM) were in agreement to the values obtained with a standard method and literature reported.
Novel applications of photoacoustic spectroscopy in life sciences
Author(s):
S. Stolik
Show Abstract
The Photoacoustic Spectroscopy, based on the generation of acoustic waves following the absorption of the modulated light by an enclosed material, was discovered in 1880 by Alexander Graham Bell. There are a lot of remarkable achievements in this topic since those days. It has been intended to present a relatively new tool to the researchers in biological areas and, simultaneously, to propose new fields of investigation to those who have been attracted by physics. The application of Photoacoustic trace gas detection to the determination of ethylene content in mice exhalation is described as a biomarker of free radicals production. It has been demonstrated the feasibility of studying the lipid peroxidation in vivo by this technique. Specifically, the results of δ-aminolevulinic acid administration in mice are presented. This drug has been used to induce Protoporphyrin IX production and ultimately to apply the Photodynamic Therapy, a recent method in cancer treatment. A kinetic study of Protoporphyrin IX production in mice skin and blood after δ-aminolevulinic acid administration in different doses is also shown. This study was performed using Photoacoustic Spectroscopy in solids.
Colloidal structural evolution of asphaltene studied by confocal microscopy
Author(s):
Jannett Hung;
Jimmy A. Castillo;
A. Reyes
Show Abstract
In this work, a detail analysis of the flocculation kinetic of asphaltenes colloidal particles has been carried out usng confocal microscopy. The colloidal structural evolution of the asphaltene flocculated has had varies postulated; however, the aggregation process of asphaltene is still not fully understood. In a recent paper, using Confocal microscope (homemade), we reported high-resolution micrographic images of asphaltenes flocculated and the correlation between crude oil stability and flocculation process. This technique permitted visualizes directly the physical nature of asphaltene flocculated. In this work, a detail analysis of the flocculation kinetic of asphaltene colloidal particles has been carried out using confocal microscopy. The physical nature of asphaltene flocculated from different crude oils is showed through of high-resolution image micrographies and its colloidal structural evolution.
Fiber optic sensor of leaks of petroleum that uses bend loss
Author(s):
Georgina Beltran-Perez;
Evgueni Anatolevich Kuzin;
Juan Castillo-Mixcoatl;
I. Huixtlaca-Cuatecatl
Show Abstract
We present results of measurements of fiber bend losses induced by periodic distortions in a single-mode and a multimode fiber having step and graded index profile. These bends are caused by soft and swellable materials with various moduli of Young. We found that the attenuation increases for longer periods of perturbations. The transition losses and pure bend losses have been calculated. Our experimental conditions show that the purebend loss is higher than the transition loss, i.e. the mode coupling mechanism of the loss is low in our experiments. These results may be used to choose suitable materials and construction for assembling a fiber optics sensor based in bend losses.
Quantitative evaluation of blisters in polymer-coated steels by three-dimensional optical reconstruction
Author(s):
Z. Milena Perez;
L. A. Romero;
Jaime E. Meneses
Show Abstract
In the industrial application field, the presence of blisters in coated steel is an important quality factor of the protection coating applied on the surface. In this work, an optical system of three-dimensional reconstruction for the detection quantitative evaluation of blisters in polymer coated steel was implemented. The implemented optical system explores a region of 4 x 3 mm with a resolution of 10 μm, using the fringe projection method. The experimental evaluation was realized using six test samples of different protection coating. The test samples were continually exposed to controlled saline atmospheres and they were periodically measured. The presence of first blisters on the surface was determined. Also, the quantitative parameters were measured as maximum height and mean width of blisters, after 566 hours of exposition.
Laser shock processing system by underwater irradiation (532 nm) in metal surface
Author(s):
G. Gomez-Rosas;
Jose Luis Ocana;
Carlos Rubio;
Carlos Molpeceres;
W. Chi-Moreno;
Miguel Morales;
Z. Castellanos;
Juan Antonio Porro;
G. Rodriguez-Vilomara
Show Abstract
Laser shock processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results in the LSP concept for metal surfaces treatments in underwater laser irradiation at 535 nm. A convergent lens is used to deliver 0.9 J/cm2 in an 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG Laser with spots of a 1.5 mm in diameter moving forward along the workpiece. A LSP configuration with experimental results using a pulse density of 2 500 pulses/cm2 and 5 000 pulses/cm2 in 6061-T6 aluminum samples are presented by 532 nm. High level of compressive residual stresses are produced (600 MPa-750 MPa) with a depth of 1.2 mm. It has been shown that surface residual stress level is comparable to that achieved by conventional shot peening, but with greater depths. This method can be applied to surface treatment of final metal products.
Determination of textile local defects by digital image processing
Author(s):
N. Aguilar;
Johnson Garzon Reyes;
Angel Rodrigo Salazar Martinez;
F. R. Perez
Show Abstract
An algorithm based on image processing for detecting local defects in fabrics is presented. These defects may be considered as broken threads or double yarns, which can be viewed as straight lines in the fabric's background. Their detection is performed using the Radon transform on images previously preprocessed.
Inspection of fabrics with fluffy appearance by NIR image analysis
Author(s):
Maria Sagrario Millan;
Jaume Escofet
Show Abstract
Some fabrics, either woven or knitted, show a fibrous, fluffy appearance that hides their thread interlacing structure. In such a case tasks related with inspection of the fabric structure, identification, classification and fault detection are difficult to carry out. A remarkable improvement can be obtained when the fabric image to evaluate is captured under near infrared (NIR) illumination. NIR illumination penetrates in the material more than visible illumination and the reflected image contains more information about its structure. Although humans are not sensitive in this region, we can observe a NIR image of a fabric by exploiting the residual sensitivity of a conventional monochrome camera that reaches up to 1000 nm. The light source used is an array of NIR LEDs emitting in a band to which the camera is still sensitive. This inexpensive image acquisition system is completed with a monochrome TV monitor to display the NIR image and a computer for image analysis. Some results obtained by applying Fourier analysis to the fabric image obtained under either visible or NIR illumination are provided and discussed.
NIR imaging of non-uniform colored webs; application to fabric inspection
Author(s):
Maria Sagrario Millan;
Jaume Escofet
Show Abstract
Fabric inspection is improved using near-infrared (NIR) illumination and a conventional monochrome camera. It takes advantage of the residual sensitivity of a monochrome camera that commonly reaches up to 1000 nm. Fabrics having a superstructure of colored squares, bands, etc. superimposed to the basic web structure can be advantageously analyzed because the contrast of the superstructure signal appears reduced under NIR illumination.
Optical fiber sensor for gasoline blend quality control
Author(s):
Rosane Falate;
E. Cacao Jr.;
Marcia Muller;
Hypolito Jose Kalinowski;
Jose Luis Fabris
Show Abstract
This work shows the use of a long period grating to analyze the quality of a commercial gasoline blend. Samples with different single and double solvent proportions are characterized. It is shown that the addition of controlled amounts of a standard solvent allows differentiating legal blends from tampered blends. With the proper choice of that solvent, it is possible to shift the LPG operation towards a higher sensitivity range, and even samples that deviate little from the legal gasoline blend can be identified.
Mouse vision: PC mouse control using neural networks
Author(s):
David Miranda;
E. Silva;
A. Patino
Show Abstract
We have developed a system to control the PC's Mouse using the ocular movement. This system allows incapacitated people use the PC for many purposes; on the other hand, this system is ideal to play virtual games due to its interactivity with the user.
An application of stereoscopy and image processing in forensics: recovering obliterated firearms serial number
Author(s):
L. C. da Silva Nunes;
Paulo Acioly Marques dos Santos
Show Abstract
We present an application of the use of stereoscope to recovering obliterated firearms serial number. We investigate a promising new combined cheap method using both non-destructive and destructive techniques. With the use of a stereomicroscope coupled with a digital camera and a flexible cold light source, we can capture the image of the damaged area, and with continuous polishing and sometimes with the help of image processing techniques we could enhance the observed images and they can also be recorded as evidence. This method has already proven to be useful, in certain cases, in aluminum dotted pistol frames, whose serial number is printed with a laser, when etching techniques are not successful. We can also observe acid treated steel surfaces and enhance the images of recovered serial numbers, which sometimes lack of definition.
Application of two-photon polarization spectroscopy to the study of combustion processes
Author(s):
M. I. de La Rosa;
Conception Perez;
Ana Belen Gonzalo;
Klaus Grutzmacher;
Andreas Steiger
Show Abstract
In this work two-photon polarization spectroscopy has been applied to determine absolute number densities of atomic hydrogen in a welding flame. The technique, with high spatial and temporal resolution, is very well suited for real combustion processes because is not limited by quenching, pressure, or temperature. The great potential of the technique comes together with a laser radiation of high spectral quality. The results allow mapping the distribution of atomic hydrogen along two perpendicular directions of the flame.
Verification of the authenticity of handwritten signature using structure neural-network-type OCON
Author(s):
M. L. Molina;
N. A. Arias;
Oscar Gualdron
Show Abstract
A method in order to carry out the verification of handwritten signatures is described. The method keeps in mind global features and local features that encode the shape and the dynamics of the signatures. Signatures are recorded with a digital tablet that can read the position and pressure of the pen. Input patterns are considered time and space dependent. Before extracting the information of the static features such as total length or height/width ratio, and the dynamic features such as speed or acceleration, the signature is normalized for position, size and orientation using its Fourier Descriptors. The comparison stage is carried out for algorithms of neurals networks. For each one of the sets of features a special two stage Perceptron OCON (one-class-one-network) classification structure has been implemented. In the first stage networks multilayer perceptron with few neurons are used. The classifier combines the decision results of the neural networks and the Euclidean distance obtained using the two feature sets. The results of the first-stage classifier feed a second-stage radial basis function (RBF) neural network structure, which makes the final decision. The entire system was extensively tested, 160 neurals networks has been implemented.
Estimate of the weight in bovine livestock using digital image processing and neural network
Author(s):
N. A. Arias;
M. L. Molina;
Oscar Gualdron
Show Abstract
A procedure inside the context of artificial vision that estimates the weight in bovine livestock was developed and designed. The input data to the system are images obtained by a videotape camera to color. These images are digitized and preprocessing using filters of elimination of noise; later are implemented and evaluated different segmentation methods that allow to obtain the contour of the animal in semiautomatic form. This process consists of an automatic binarization in its initial stage and an eventual manual adjustment. Later the characteristics that have a strong correlation with the weight of the animal are extracted. These are extracted in a form that is independent of the orientation of the object inside the image. Such characteristics include: the superior area, perimeter, wide of abdomen, wide of haunch, wide of scapula. The estimate of the weight of the animal is made by means of a neural network type feedforward whose inputs feed with the extracted characteristics of the image. Finally the system is evaluated in the number and type of characteristics kept in mind and in the structure of the neural network utilized.
Fabric's cover factor measurement by image thresholding
Author(s):
Montserrat Tapias;
Manuel Rallo;
Jaume Escofet
Show Abstract
Fabric cover factor is the ratio of the area covered by the yarns to the whole area of the fabric. In this work we propose a straightforward method to evaluate the fabric cover factor by automatic thresholding of a digital image of the fabric.
Laser techniques in conservation of stone and metals
Author(s):
Renzo Salimbeni;
Roberto Pini;
Salvatore Siano
Show Abstract
After 30 years since the first experiment we may say that laser techniques are being widely employed today by conservators and restorers as the best choice for the most important tasks: (1) diagnostics about the state of conservation; (2) restoration intervention in the crucial cleaning phase; (3) monitoring of the deterioration processes. Many important experiences have been carried out in Europe along these topics, with significant validation cases and sustainable technology transfer. In this paper the activity carried out in the Tuscany Region will be reported with the monitoring of the most advanced activities carried out by the EC Action COST G7 "Artworks Conservation by Laser."
Study of thermo-optical properties or surfactants in aqueous solution by interferometry
Author(s):
M. Di Lorenzo;
Rafael A. Escalona Z.
Show Abstract
Although a variety of surfactant based processes of technological importance occur in the presence of temperature gradients, very little information is available on the thermal diffusion of these macromolecules in solution. In this work optical interferometry is applied to the study of photothermal properties of aqueous solutions of surfactants. This technique allows to visualize spatio-temporal changes of the refractive index of the samples produced by the local heating of the solvent and the solute redistribution set up by thermal diffusion. We present preliminary results on the photothermal response to absorption of cw laser radiation of aqueous solutions of ionic and nonionic surfactants in the presence of trace amounts of the malaquite green dye.
Passive sensor for wheat reflectance measurements
Author(s):
C. Weber;
F. Videla;
D. C. Schinca;
Jorge O. Tocho
Show Abstract
A low cost portable spectroradiometer able to operate in the 4 bands of the satellite system Landsat MSS was developed. The radiometer was designed to measure the spectral reflectance of spatially extended targets. Spectral bands were selected with 10 nm bandwidth filters. Measurements were made during 2003, from seedtime to harvest, on an experimental plot of wheat. The culture was divided in parcels that received different treatments (seed variety, fertilizer, herbicide and fungicide). Weekly measurements with the detector at nadir and the sun near midday were made. As result of the spectral measurements of reflectance, the normalized difference vegetation index (NDVI) was calculated. As a comparison, LAI, chlorophyll concentration and diverse gravimetric determinations, were carried out. The results were analyzed by means of statistical techniques and showed a good correlation between the optical index and the culture variables. In the future the geometry of the measurement will be improved to reduce the effect of the canopy and other channel in the near infrared will be added to distinguish water and nitrogen stress.
Relative intensity noise reduction on mode-locked external cavity lasers
Author(s):
Nuran Dogru;
Sadettin M. Ozyazici
Show Abstract
The relative intensity noise (RIN) of hybrid soliton pulse source (HSPS) utilizing different fiber Bragg gratings (FBGs) are described. The HSPS is modeled by a time-domain solution of the coupled-mode equations including spontaneous emission noise, and RIN is calculated using numerical solutions of these equations. RIN reduction up to 4 dB has been demonstrated for the mode-locked HSPS using a suitable window function such as Gaussian apodized and introducing appropriate linear chirp value into gratings.
Operational characteristics of different electrode systems in fast-transverse-flow CO2 lasers
Author(s):
M. G. Gonzalez;
Guillermo D. Santiago
Show Abstract
Time-consuming, trial and error methods have usually been key tools in the design and search of optimum performance of the electrodes in fast-transverse-flow CO2 lasers. These tests sought a large, uniformly pumped volume and high small-signal gain. The later is determined by a complex interaction between the electron density, the flow speed and the electron generation and recombination processes that have not been taken into account in previous reports. In order to overcome these problems we have developed a simple analytical model that includes the above mentioned processes. The results enabled us to evaluate the performance of several electrode systems using data obtained in our laboratory and from other authors' reports. The first experiments were carried out with an already tested electrode set; afterwards we developed a new electrode profile that provided an expanded, uniformly pumped volume and higher small-signal gain. The predictions of the model were verified through the measurement of the spatial gain distribution.
Superfluorescence three-level neodymium-doped fiber source
Author(s):
Romeo J. Selvas-Aguilar;
M. A. Martinez-Gamez;
A. Martinez-Rios;
X. Sanchez-Lozano;
Miguel A. Basurto-Pensado;
Johan Nilsson
Show Abstract
We report on a new type of cladding-pumped neodymium-doped fiber which enables strong ASE emission at the wavelength region of 940 nm with a highly reduced emission in the four-level transition at 1060 nm when is pumped by an 806 nm source. This ASE source delivers a total emission power of 60 mW from 500 mW of absorbed pump power. The arrangement setup consisted in a pump diode emitting at 806 nm with a total output power of 1.5 W, a collimated and focused lenses and a dichroic mirror. The broadband of the neodymium source was measured to be 25 nm. Moreover, a numerical simulation for the ASE source is also discussed.
Laser emission in proton implanted Nd:YAG waveguides
Author(s):
E. Flores-Romero;
Gloria Veronica Vazquez;
Heriberto Marquez;
Raul Rangel-Rojo;
J. Rickards;
R. Trejo-Luna
Show Abstract
In this work we report the performance of CW Nd:YAG waveguide lasers operating at 1064 nm at room temperature. The waveguides were fabricated by proton implantation and the main differences in the process of fabrication were the angle of implantation and the total dose implanted. The characterization of the waveguide refractive index profile induced by proton implantation and the main laser characteristics i.e. slope efficiency and threshold are presented. The results indicate that the optical properties of the waveguide in comparison with the bulk material are preserved after the implantation process and that this is a potential technique to develop compact and efficient lasers.
Novel-pump-design fiberized high-power single-mode double-clad ytterbium-doped fiber laser
Author(s):
A. Martinez-Rios;
I. Torres-Gomez;
Gilberto Anzueto-Sanchez;
Romeo Selvas-Aguilar;
Hong Po
Show Abstract
A novel design in the inner cladding of a cladding-pumped ytterbium-doped fiber is presented. The fiber includes a modification of the inner cladding by the insertion of four D-shaped holes distributed around the core in a square configuration. This novel fiber structure makes the device efficient in absorbing the pump power while keeping the overall circular structure. As a result, up to 5 W of single mode at 1095 nm from a 7 W of absorbed pump power was achieved; the slope efficiency was 60% wrt. launched pump power and the beam quality was measured to be 1.2 implying that our laser has a diffraction limited output beam.
Pulsed high-power single-mode UV lasers for two-photon spectroscopy
Author(s):
M. I. de La Rosa;
Conception Perez;
Ana Belen Gonzalo;
Klaus Grutzmacher;
Andreas Steiger
Show Abstract
In this contribution we summarize the work of our team in the last years, which is devoted to the principle, development and applications of a new spectroscopic technique: two photon polarization spectroscopy. This technique is suitable for the diagnostic of plasmas even in far off thermodynamic equilibrium conditions. Up to now, working with hydrogen and deuterium in different kind of media, such as laboratory plasmas or industrial flames, we have been able to measure the absolute density and kinetic temperature of the hydrogen atoms, the electric field in the dark space of a hollow cathode discharge, and the Stark broadening of the 2S level of hydrogen isotopes. The full potential of this technique requires tuneable pulsed high power UV laser radiation of single longitudinal mode. To achieve this powerful tool we have modified a commercial laser and we will pay special attention to this system. The whole experimental arangement provides plenty of new and promising possibilities such as the study of industrial interest elements like oxygen, carbon, or nitrogen.
Diffusion-cooled transversally microwave-pumped CO2 laser
Author(s):
Carlos F. Mosquera;
Ignacio J. Rios;
Guillermo D. Santiago
Show Abstract
We present a prototype of a diffusion-cooled, microwave-excited CO2 laser. The microwave power, generated by a 2.45 GHz CW magnetron, excites the CO2:N2:He mixture in a discharge cavity. The magnetron is linked up to the cavity through a launching guide and two cascaded horns that couple the microwave power to the cavity. The excess heat is mainly extracted by diffusive cooling to the cavity walls. Measurements of the small signal gain and the output power as function of the gas pressure are shown.
High-efficiency acoustic-induced Q-switched erbium-doped fiber laser
Author(s):
Nelida A. Russo;
S. Noriega;
Dobryna Zalvidea;
Ricardo Duchowicz;
Martina Delgado-Pinar;
Antonio Diez;
Jose Luis Cruz Munoz;
Miguel V. Andres
Show Abstract
We report a high efficiency and high repetition rate acoustic-induced Q-switched Er-doped-fiber laser. Two fiber Bragg gratings were used as cavity mirrors, whilst the active Q-Switching was performed by temporally controlling the Q-cavity factor by coupling light from the core mode to cladding modes using flexural acoustic waves. The acousto-optic attenuator was implemented by applying a RF signal to a piezoelectric disc and using an aluminum horn to focus the acoustic wave in a tapered fiber. The RF signal that drives the piezoelectric disc was amplitude modulated with a rectangular wave of variable frequency and duty cycle. Q-switched laser pulses of ~ 1 W peak power, 0.1 - 2 μs pulse width and continuously variable frequency up to 100 kHz, were obtained. The laser efficiency of energy conversion was as high as 20%.
High-efficiency emission at 2950 nm in a holmium-doped fluoride fiber laser pumped with a fiber Raman laser at 1064 and 1175 nm
Author(s):
J. Efrain Mejia-Beltran;
D. Talavera Velazquez
Show Abstract
We have demonstrated laser emission at ~2950 nm when pumping a holmium-doped fluorozirconate fiber laser by a fiber Raman laser that emits at 1064 and 1175 nm. The optical-to-optical conversion efficiency was 31% and the maximum CW output power was 290 mW. To the best of our knowledge, this efficiency is the highest reported in the literature for this system. Beam characterizations revealed a uniform intensity profile (single-mode). When the fiber laser was held at a ~3 mm from a paper surface, it was possible to burn micro-holes. Since this wavelength coincides with the absorption peak of water at 2950 nm whose absorption coefficient is ~16 times the corresponding to 2712 nm (emission of Er3+:ZBLAN fiber lasers), the 290 mW obtained here might replace a high-power (~4.6 W) Er3+:ZBLAN fiber laser for cutting samples with high moisture content. Moreover, the low intensity guided in the fibers is important since these fibers melt at high intensities. The main advantage of this pumping scheme, compared to previous results is the non-simultaneous oscillation at 2100 nm. This laser has a great potential in micromachining and microsurgery applications.
Power scaling of Q-switched fiber lasers in a multi-arm resonator
Author(s):
Daniel Sabourdy;
Agnes Desfarges-Berthelemot;
Alain Barthelemy;
Vincent Kermene;
M. T. Flores-Arias
Show Abstract
Q-switched erbium doped fiber lasers offer a simple and robust way for the generation of high energy nanosecond pulses at wavelengths about 1550 nm, which are suitable for a large number of applications. Nevertheless, pulse peak power is limited taking into account the specific characteristics of the fiber lasers such as their long cavity length and the low level of pump power with the core pumping technique. Recently, we have demonstrated highly efficient coherent combining of radiations emitted by two amplifying fibers inside a common cavity in the continuous wave regime. The principle of this method is based on the self-organization property of lasers ensuring operation on modes of lowest losses in a Mach-Zehnder interferometer resonator geometry. We have shown that the output power level is twice the one of a unique laser. We report the power rising of an actively Q-switched erbium doped fiber laser by using two coupled cavities with amplifying fibers in an interferometer configuration. This study shows that the pulse peak power obtained is 1.7 higher than in a case of a unique laser. This concept brings some novel perspectives for scaling the output peak power of monomode Q-switched fiber lasers.
Microsphere laser in Er3+-doped oxide glasses
Author(s):
Carole Arnaud;
M. Boustimi;
Massimo Brenci;
Patrice Feron;
Maurizio Ferrari;
Gualtiero Nunzi-Conti;
Stefano Pelli;
Giancarlo C. Righini
Show Abstract
We have succeeded in continuous-wave laser oscillation on 4I13/2 → 4I15/2 transition of Er3+ ions around 1550 nm in microspheres fabricated with Erbium doped posphate "Schott" and silica "Baccarat" glasses. The microsphere lasers have been studied under pumping at 1480 nm. Whispering Gallery Mode laser spectra were analyzed for different sphere diameters. Wavelength Red-shift effect of both fluorescence and laser spectra was experimentally observed in Er3+ doped phosphate glass when the pump power was increased, originating from thermal effects.
Coherent soliton propagation in a mixture of two-level atoms
Author(s):
A. F.C. Moreira;
W. R. Nascimento;
Solange B. Cavalcanti;
A. M. Kamchatnov
Show Abstract
Exact soliton solutions of a coupled system of Maxwell-Bloch equations are obtained analytically within the inverse scattering transform scheme. The equations describe a light pulse coherently propagating through a mixed ensemble of two-level atoms characterized by two slightly different detuning parameters. The solution illustrates the information about the detailed atomic properties which are impressed on both phase and velocity of the pulse during propagation, with potential applications in high resolution spectroscopy.
Using the intermodal beating frequency to interrogate a multipoint fiber Bragg grating laser sensor
Author(s):
R. A. Vazquez-Sanchez;
Evgueni Anatolevich Kuzin;
Jorge L. Camas-Anzueto;
Sergio Mendoza-Vazquez;
Baldemar Ibarra Escamilla;
Manuel May-Alarcon
Show Abstract
A multipoint fiber laser sensor, which consists of two cavities coupled based in three Bragg gratings of fiber optics and interrogated by the longitudinal mode beating frequency is presented. We used one Bragg grating (reference) and two Bragg gratings (sensors), which have the lowest reflection wavelength. The reference grating with the two sensors grating make two cavities: first one is the internal cavity which has 4230 m of length and the next one is the external cavity which has 4277 m of length. Measuring the laser beating frequency with a radio frequency (rf) analyzer for a resonance cavity and moving the frequency peaks when the another cavity are put in resonance, we prove that the arrangement can be used as a two points sensor for determining the difference of temperature or stress between these two points. On the other hand, one principal peak and three harmonics with bandwidths of 52 Hz were obtained with the rf analyzer. Their bandwidth was controlled by an intra-caivty fiber Optical Delay Line (ODL) and was measured with the rf analyzer.
Link control protection of surviving channels in distributed fiber Raman amplifier cascades
Author(s):
V. Pincheira;
H. Soto;
Ricardo Olivares
Show Abstract
In this work, by means of numerical simulation, the application of the link control protection technique on power transient suppression in cascades of distributed fiber Raman amplifiers (DFRAs) is investigated. The results point out that for a 10 DFRA's cascade, the power excursion in the surviving channels, at the 10th amplification stage, is reduced by 2.15 dB to 0.037 dB, when 8 out of 10 channels are involved in add/drop operations.
Observation of new modal patterns in experiments with Hermite-Gaussian and Laguerre-Gaussian laser modes
Author(s):
K. Contreras;
Guillermo Baldwin-Olguin;
F. De Zela;
Enrique J. Galvez
Show Abstract
We present several experiments that allow us to show the intensity and phase structure of transverse modal patterns, Hermite-Gaussian and Laguerre-Gaussian laser modes and dynamical transverse patterns. These new spatial configurations of the light depend on the dynamics of laser resonator, and on the boundary conditions. The Laguerre-Gaussian modes are obtained either by the direct conversion of Hermite-Gaussian modes using a modal converter or with a computer-generated hologram. The modal coverter is based on a cavity of cylindrical lenses. We analyze the phase structure and optical phase singularities of laser modes with a Mach-Zehnder interferometer. The resulting interference patterns clearly illustrate the azimuthal phase dependence of the Laguerre-Gaussian modes, which is the origin of the orbital angular momentum associated with each one of them. Moreover, we try to give an explanation of the new modal patterns observed.
Two-qubit quantum gates in an optical lattice with polarization gradient
Author(s):
M. A. Duenas;
Angela Maria Guzman
Show Abstract
We study a dipole-dipdole collision between two atoms confined in adjacent minima of the two sublattices of an optical lattice with polarization gradient. A qubit consists of the two lowest atomic vibrational states of the optical lattice potential. The inter-atomic distance is changed adiabatically by rotating the polarization of the lasers that originate the optical lattice. In an elastic collision the two-qubit quantum states undergo controllable phase shifts that allow for the implementation of quantum gates. We obtain the truth-table for a quantum logic phase gate and calculate probability losses caused by the non-hermitian effective dipole-dipole interaction Hamiltonian.
The London-van der Waals interaction in the presence of evanescent waves
Author(s):
Angela Maria Guzman
Show Abstract
The London-van der Waals potential experienced by an atom under reflection from an atomic mirror is modeled as a quantum dipole-dipole interaction between the atomic dipole induced by the evanescent wave and its image dipole in the dielectric mirror. The quantum dipole-dipole interaction arises from the combined effect of the evanescent field and spontaneous emission. It depends on the electronic structure of the atom and is described by an effective non-Hermitian Hamiltonian that yields dissipative effects under reflection. The analytical expression obtained here preserves the power-law dependence of the static van der Waals interaction at distances close to the wall, but its long-distance behavior reflects that of the evanescent wave.
Comparison of two different configurations of multipass amplifier for chirped pulse amplification
Author(s):
Alexandro Ruiz de la Cruz;
Raul Rangel-Rojo
Show Abstract
We present the results of two different multi-pass designs for the amplification stage of a chirped pulse amplifier system. The first design is a typical one, where all of the beam paths that pass through the amplifying medium are in the same plane. The second one distributes the same number of passes in two planes, reducing the angle between the pump beam and the signal, thus increasing the overlap and the energy extraction efficiency.
Experimental observation of optical feedback effect on emission frequency and optical output power in a laser diode
Author(s):
J. Villanueva;
Guillermo Baldwin-Olguin
Show Abstract
We analyze the effects of optical feedback in a laser diode in the frequency of emission and optical output power. We observe experimentally that the dynamics properties of injection laser are affected by the interference between light of the laser diode cavity and backscattered light. We demonstrate that the light intensity shows hysteresis and discrete shifts of frequency according to feedback light and/or forward current variations condition due at non-linear active layer.
Optical design based on genetic algorithm of distributed fiber Raman amplifier cascades
Author(s):
H. Soto;
V. Pincheira;
Ricardo Olivares
Show Abstract
In this work, we use evolutionary techniques to optimize the design of Distributed Fiber Raman Amplifier (DFRA) cascades inserted in WDM (Wavelength Division Multiplexing) optical networks. Applying genetic algorithms to a cascade of 10 DFRAs, each link being 50 km-long, we achieved a gain ripple less than ± 0.5 dB at the end of the cascade for a bandwidth of 80 nm using 8 pump signals.
Fractal dimension of turbulent laser beam wandering
Author(s):
Dario G. Perez;
Luciano Zunino;
Mario Garavaglia
Show Abstract
We analyze the fractal (box-counting) dimension of laser beam wandering. The wandering is due to the light travelling across a path filled by laboratory generated turbulence. The laser's centroid position is collected by a continuous position detector -- "light-tracker." We determine the box-counting dimension by means of two independent algorithms. The first method calculates the Hurst exponent of each axis, within the fractional Brownian model, and then the fractal dimension is determined applying a theoretical result. For the second one a new algorithm is proposed to estimate it directly. These results are compared.
Experimental study and theoretical modeling of a self-Q-switched all-fiber Erbium laser
Author(s):
Alexander V. Kir'yanov;
Yuri O. Barmenkov;
M. A. Martinez-Gamez;
Nikolai N. Il'ichev
Show Abstract
A self-Q-switched diode-pumped Erbium fiber laser is implemented in an all-fiber configuration. The laser operates in a stable regime of giant pulses in a broad range of pump powers and does not require additional intra-cavity elements except the active fiber and fiber Bragg gratings as output couplers. A modeling of the laser is developed, implying that the mechanism of self-Q-switching is the power-dependent thermo-induced lensing in Erbium active fiber that stems from the excited-state absorption at the laser wavelength.
Dynamics of an erbium-doped fiber laser subjected to harmonic modulation of a diode pump laser
Author(s):
Alexander N. Pisarchik;
Alexander V. Kir'yanov;
Yuri O. Barmenkov;
R. Jaimes Reategui
Show Abstract
An erbium-doped fiber laser is shown to operate as a bistable or multistable nonlinear system under harmonic modulation of the diode pump laser. Phase- and frequency-dependent states are demonstrated both experimentally and in numerical simulations through codimensional-one and codimensional-two bifurcation diagrams in the parameter space of the modulation frequency and amplitude. In particular, generalized bistability results in doubling of saddle-node bifurcation lines where different coexisting attractors born. The laser model describes well all experimental features.
Periodically switched erbium-doped fiber laser for enhanced temperature sensitivity in a fiber sensor
Author(s):
Keith P. De Souza
Show Abstract
When a pulse of light is launched down a single-mode optical fiber, with a peak power below the threshold for nonlinear effects, backscattered Rayleigh and spontaneous Brillouin signals are generated. The Brillouin signal is temperature sensitive while the Rayleigh signal shows comparatively negligible sensitivity but serves as a backscattered signature for fiber attenuation and loss mechanisms. Ratioing one signal to the other extracts the temperature information. Optical separation of the Rayleigh and Brillouin signals of our sensor requires a source with bandwidth less than 90 pm. However, the narrowband Rayleigh signal generated is noisy due to coherent Rayleigh noise. A broader source generates a Rayleigh signal with reduced coherent Rayleigh noise. A Q-switched erbium-doped fiber-optic laser containing a fiber-optic switch in the laser cavity, which allows switching and selection of a narrow (<90 pm) or broad (~3 nm) bandwidth output coupler has been developed. Periodic switching should allow virtually simultaneous capturing of Brillouin and broadband Rayleigh signals thus ensuring that the spontaneous Brillouin signal is correctly referenced even if fiber attenuation, splice or bend losses should vary during extended data collection cycles.
Effects of out-coupling in fiber lasers
Author(s):
Jesus Escobedo-Alatorre;
Romeo J. Selvas-Aguilar;
A. Martinez-Rios;
Daniel A. May-Arrioja;
Miguel A. Basurto-Pensado;
Jose Javier Sanchez-Mondragon
Show Abstract
An analysis of out-coupling in a laser shows an optimum way of subtracting more output power by choosing an appropriate cavity arrangement from a high-power fiber laser. This investigation consisted in resolving analytically the effect of different cavities in our laser system and one thing that outcome was to know that a fiber laser can operate with high efficiency even with high losses in one end of the cavity (e.g. at an external diffraction grating), only if the feedback in the out-coupling end is low. Moreover, it was also found that is possible to improve the output power by reducing the feedback in the out-coupling end. Parameters considered in this resolved method are 0.1 NA, 10 μm diameter core, 200 μm inner-cladding diameter and 10 dB small-signal absorption. The fiber laser was doped with ytterbium and lases at 1080 nm, when pumped at 915 hm. The maximum pump power was set to 10 W.
A new tensor theoretical formalism to treat matter-radiation interaction
Author(s):
Pedro A. Pineda;
Celso Luis Ladera
Show Abstract
Starting from Maxwell's equations it is possible to define a tensor whose components represents the electric polarization and the magnetizacion of a given medium. Each component of this tensor is a bilinear form which is related to the basic quantum object constituent of the medium. The formalism is applied the case of EIT propagation.
The first hyperpolarizability of some chiral carboxylates by hyper-Rayleigh scattering measurements and theoretical calculations
Author(s):
O. Castellano;
X. Hernandez;
N. Cubillan;
M. Giffard;
Mamadou Sylla;
Xuan Nguyen Phu;
H. Soscun;
Aristides Alfredo Marcano O.
Show Abstract
We report the quadratic hyperpolarizability βs of newly synthesized chirals carboxylates salts. These nonlinear optical coefficients have been measured using Hyper-Rayleigh scattering (HRS) technique in solution. Before nonlinear measurements, the different compounds under study were characterized by resonance magnetic nuclear of protons and absorption spectra. They were shown to be completely transparent to the absorption in the UV-Visible and near-infrared region of the spectrum: spectra of solutions in methanol, recorded on an ATI-UNICAM spectrometer in range 250 - 1100 nm show no absorption above 350 - 400 nm. HRS measurements are made by using methanol as solvent and the values of the nonresonant hyperpolarisabilities obtained are of the same order of magnitude that that of the paranitroaniline and are located beween 30x10-30 esu and 60x10-30 esu.
Two-beam conical diffraction in a Kerr medium
Author(s):
Marcio A.R.C. Alencar;
Cid B. de Araujo
Show Abstract
A new conical diffraction phenomenon was observed when two beams of the same or different frequencies intersect as they pass through a CS2 cell. Light is emitted on the surface of a circular cone that is centered in each one of the two beams and has an angular extent equal to twice the crossing angle between the incident beams. The origin of this effect is discussed and a quantitative study of the conical emission intensity is given.
Angular selectivity behavior of a grating imaging in thick photorefractive media
Author(s):
Myrian C. Tebaldi;
K. Contreras;
Nestor A. Bolognini
Show Abstract
It is well known that a thin phase grating holographically produced exhibits Raman-Nath behavior and a thick phase grating shows Bragg behavior in the diffraction process. In the Raman-Nath regime several diffracted waves are produced. Usually, in a photorefractive material such as a sillenite BSO crystal, volume phase holograms are stored by means of the interference of two coherent beams intersecting inside the crystal. In our work, we analyze the diffraction properties of gratings incoherently stored in a photorefractive medium. To this purpose, an input Ronchi grating is incoherently imaged in a thick BSO crystal. The grating is stored on a birefringence modulation basis. In the reconstruction step, when a collimated beam impinges perpendicularly to the crystal input face several diffracted orders appear in accordance with the Raman-Nath regime. As far as the read-out beam direction is rotated the diffraction efficiency of each order changes. The angular selectivity behavior of the grating in terms of the crystal thickness and the grating period is analyzed. The adequate selection of the write-in parameters allow to highlight a determined order and to achieve multiple storage, without cross-talk.
Single three-level atoms for quantum information
Author(s):
J. Mompart;
R. Garcia;
Ramon Corbalan
Show Abstract
A single three-level atom in interaction with a single longitudinal mode of a high-Q cavity is used to quantum engineer the intracavity field. In our proposal the quantum bit states correspond to the vacuum and single photon Fock states of each of two circular polarization states of the longitudinal mode. We show that for particular velocities of the three-level atom crossing the cavity it is possible to implement in one single step a two-qubit quantum phase gate between the two circular polarization states. Fidelity against several decoherence mechanisms such as atomc velocity fluctuations or the presence of a weak magnetic field along the cavity axis is analyzed.
Numerical and experimental analysis of Raman effect in optical fiber
Author(s):
S. Mendoza Vazquez;
Sabino Chavez-Cerda;
Evgueni Anatolevich Kuzin;
Jorge L. Camas-Anzueto;
R. A. Vazquez-Sanchez;
Baldemar Ibarra Escamilla;
J. Gutierrez Gutierrez
Show Abstract
The fiber Raman amplifier employs the intrinsic properties of silica fiber to obtain the amplification, thus they use the transmission fiber as the amplification medium, where the gain is created along the transmission line. The amplification is realized by Stmulated Raman Scattering (SRS). This nonlinear process occurs when a sufficiently powerful pump is within the same fiber as the signal. In this paper, we showed experimental and numerical analysis of SRS in optical fibers. We obtain a continuous spectral when we plot the energy content in each Stokes sublines with the wavelength, which are self-pump between them. The numerical results are in agreement with the experimental results, just as the waveform in the time of optical fiber end and the energy is transferred from the signal pump to the Stokes sublines. With the simulations, we can obtain several parameters of this optical amplifier like the optical fiber effective length to obtain the amplification.
Time-gated imaging through scattering media by using efficient THG in organic films
Author(s):
Gabriel Ramos-Ortiz;
Myoungsik Cha;
Stephen Barlow;
Gregory Walker;
Seth R. Marder;
Bernard Kippelen
Show Abstract
We report on efficient third-harmonic generation (THG) with large spectral and angular bandwidths in polymer thin films doped with conjugated organic molecules. Using the efficient THG exhibited by these organic films, we demonstrate real-time, time-gated, direct imaging of objects immersed in highly scattering media by using femtosecond pulses tuned at the eye-safe and telecommunication-compatible near-infrared spectral region (1550 nm). By using a low cost detection system we resolved THG time-gated images of objects immersed in media with a scattering attenuation of 14 mean-free paths, equivalent to an attenuation of six optical densities.
Optical properties of gold metallic nanostructures
Author(s):
R. J. Delgado-Macuil;
V. Lopez Gayou;
M. Rojas Lopez;
J. F. Sanchez Ramirez;
V. Camacho-Pernas
Show Abstract
In this work we analyze the optical properties from nanostructures metallic surfaces of gold-palladium, for this we used light in the visible spectrum. The analysis is based in the width of the films grown and of the ratio of concentration of gold/palladium in films. Transmission spectrum and Z-Scan technique are used to observe the optical properties of these metallic nanostructures.
Dynamics of energy transfer and frequency upconversion in Tm3+-doped fluoroindate glass
Author(s):
Vladimir A. Jerez;
Cid B. de Araujo;
Younes Messaddeq
Show Abstract
Blue and ultraviolet upconversion (UC) emissions at 455 and 363 nm were observed from Tm3+ doped fluoroindate glasses pumped with a 650 nm pulsed dye laser. The temporal behavior of the fluorescence signal originate from the 1D2 manifolds was studied for different Tm3+ concentrations. The fluorescence measurements revealed the origin of the UC process as well as allowed to quantify the interaction between Tm3+ ions. The results indicate that a two-step absorption process is responsible for the UC emission and the dominant interaction contributing for ET among of active ions is the dipole-dipole interaction.
Light-induced photorefractive and thermal lens effect in lithium niobate crystals
Author(s):
Marcos R. R. Gesualdi;
C. J. da Silva;
Tomaz Catunda;
Mikiya Muramatsu
Show Abstract
In this work, we study self-focusing and self-defocusing effects, determination of photorefractive and thermal parameters in LiNbO3 and LiNbO3:Fe crystals using light-induced photorefractive and thermal lens with double-beam of mode-mismatched technique. Beyond to establish a best understand of photorefractive and thermal effects, their relations and limits in theses materials. And obtained good results in thermal lens effect (self-focusing) in LiNbO3 crystals and the photorefractive lens effect (self-focusing and self-defocusing).
Coherent blue light generation: quasi-phase-matched second harmonic generation in KTiOPO4 waveguides
Author(s):
Noureddine Melikechi
Show Abstract
Two issues which limit continuous wave second harmonic generation in quasi phase matched KTiOPO4 periodically segmented waveguides are discussed. The first is the thermal loading caused by the fundamental and the second harmonic beams which degrades the quasi-phase matching condition and as a result corrupts the spectral quality of the second-harmonic field. We show that a carefully designed external temperature gradient leads to an enhancement of the conversion efficiency and control of the spectral lineshape of the output field. The second issue discussed is the poor optical coupling into quasi phase matched periodically segmented waveguides. We show that using optical interference, it is possible to increase th efficiency of the generated second harmonic significantly over coupling a single beam with the same total power. Finally, we show that using optical interference, it is also possible to considerably enhance the optical coupling efficiency into single mode fibers.
Generating tunable microwave signals (1 to 25 GHz) by optical mixing
Author(s):
Alejandro Garcia-Juarez;
Celso Gutierrez-Martinez;
Jose Alfredo Torres-Fortiz;
Jocobo Meza-Perez
Show Abstract
In this work we report the generation of microwave signals using photo-mixing of two laser beams. In this case, one laser beam is single mode and the other one shows a multimode spectrum. Due to spectral separation between the two lasers, microwave signals can be generated and tuned between 1 and 25 GHz, the bandwidth of the generated signal is approximately 2.5 GHz; however, using narrow-band microwave filters, the photo generated signal can provide microwave information carriers for high-speed telecommunication systems.
Analysis of the phase conjugation reflectivity for volume speckle patterns in a BSO crystal
Author(s):
A. Salazar;
Myrian C. Tebaldi;
Nestor A. Bolognini
Show Abstract
When a diffusing surface is illuminated by a coherent light beam, speckles are formed in the space in front of the surface. These speckles have a three-dimensional structure. However, in spite of this three-dimensional nature, two-dimensional recording media are usually used for applications in optical metrology. Since 80's, the photorefractive crystals were widely employed for optical processing and metrology in particular concerning speckle applications. Furthermore, we have taken advantage of the three-dimensional photorefractive medium to store three-dimensional speckle distributions. In our case, the phase conjugation theory, within the transmission grating approximation, is applied to study the phase conjugation reflectivity when speckle patterns are stored in a BSO photorefractive crystal. It is numerically shown that the beam coupling theory is adequate to explain the reflectivity behavior in terms of the average modulation of the registered speckles and the average speckle length. The knowledge of the reflectivity behavior when speckle patterns are considered, allows to optimize interferometric system based on real-time speckle pattern correlation and to improve speckle applications in optical signal processing.
Analysis of the wavelet-matched filtering in a four-wave mixing arrangement
Author(s):
A. Salazar;
R. Goez;
D. Sierra;
Johnson Garzon Reyes;
F. R. Perez;
H. Lorduy
Show Abstract
In image processing, the wavelet transform is useful to enhance the local features of images, so that, the correlation of a target with a reference signal can be improved by wavelet filtering. The wavelet filtering operation and correlation can be photorefractively performed if a crystal is used as a dynamic holographic recording medium. In particular, the sillenite family of photorefractive crystals have a high photosensitivity and high carrier mobility which allow a fast response that makes them attractive for real-time image processing and optical phase conjugation. We analyze a real-time wavelet-matched optical correlator using phase conjugation in a four-wave mixing arrangement. The robustness of the correlator to the noise due the finite crystal depth is improved using a proper wavelet filter.
Surface-plasmon bandgaps observed in the diffuse background of metallic gratings
Author(s):
Ricardo A. Depine;
Silvia A. Ledesma
Show Abstract
Due to the excitation of surface plasmons, the diffuse background of a microrough metallic grating can present intensity maxima called diffuse light bands. We reexamine this phenomenon within the framework of recent studies on photonic surfaces and show that it provides an experimental technique for mapping the dispersion relation of surface plasmons, including the gap that, under appropriate circumstances, opens up in the reciprocal grating space.
Beam propagation in magnetic atomic guides
Author(s):
K. Rodriguez;
Angela Maria Guzman
Show Abstract
We study modal propagation of cold atomic gases in a straight magnetic waveguide consisting of a current wire and a uniform magnetic field. This configuration is known to generate a transverse confining potential for atoms with magnetic dipole moment oriented anti-parallel to the magnetic field. The potential has azimuthal symmetry to first order in powers of the atomic distance to the waveguide axis. We obtain the modal dispersion curves by means of the WKB quantization method, and introduce a parameter Q that characterizes symmetric atomic waveguides as the parameter V does in optical fibers. We simulate propagation of cold atomic beams by means of the BPM (Beam Propagation Method) and show the spatial evolution of transverse monomode and multimode profiles obtained for different values of Q and arbitrary input beam profiles. We demonstrate, analytically and numerically, the existence of a threshold Q-value for guidance of matter waves analogous to the V-threshold for propagation in a TE00 mode in optical fibers and obtain that, under the experimental conditions reported in the literature, the already observed Gaussian profile of guided atomic beams corresponds to multimode propagation. RIAO/OPTILAS'04.
Solvent effects over optical properties of a two-level molecular system
Author(s):
J. L. Paz;
M. Gorayeb;
A. J. Hernandez
Show Abstract
The solvent effects over optical properties of a two level system in presence of an electromagnetic field was modeled in this work. The system-field interaction was considered by using the dipolar-electric approximation, assuming negligible the molecular permanent dipole moments. The solvent effects were included in the formalism in a stochastic form, through the induced shifts over the Bohr molecular frequency. The coherence was calculated from the optical stochastic Bloch equations (OSBE), and later, it was averaged over all realizations of the stochastic molecular variable. To do that, it was applied the convolution theorem, which was resolved using direct and inverse Fourier transforms.
Study of the optical properties of a molecular system interacting with a high-intensity electromagnetic field
Author(s):
M. Gorayeb;
J. L. Paz;
A. J. Hernandez
Show Abstract
It was studied the solvent influence over a two level system interacting with an electromagnetic field using an stochastic treatment. It was considered a high-intensity electromagnetic field which is capable to produce local saturations. The induced coherence in the two electronic states, was averaged in the usual form, through both, Lorentzian and Gaussian probability density. From that, analytical expressions for susceptibility and optical properties were obtained. Numerical calculations were carried out to construct surfaces corresponding to this properties as a function of the field variables and the distributions parameters.
Study of the optical susceptibilities of a two-level molecular system in four-wave-mixing-spectroscopy: local regime
Author(s):
J. L. Paz;
M. Gorayeb;
A. J. Hernandez
Show Abstract
It was studied the solvent influence over a two level system in the four wave mixing spectroscopy. the solvente effect was incorporated to the model in a stochastic form, through the broadening of the upper molecular level. Two intense waves of the same frequency, ω1, and another wave with minor intensity and ω2 frequency, were considered coupled to the nonlinear system, generating a new signal whose frequency is ω3, and where the wave-vectors follow the relation vector k1 + vector k1 = vector k2 + vector k3. Using the dipolar-electric and the rotating wave approximations, it was calculated the average of the coherence at the ω1, ω2 and ω3 frequencies. From that results, analytical expressions to the susceptibilities at the studied frequencies were obtained. Linear, coherent and coupled processes were identified.
Exact nonlinear response of a harmonic oscillator
Author(s):
J. Recamier;
W. Luis Mochan;
Jesus A. Maytorena
Show Abstract
A harmonic oscillator may display a nonlinear behavior when forced by an inhomogeneous field. We calculate the response of harmonic molecules adsorbed on a surface to a monochromatic electric field employing algebraic methods. The field inhomogeneity, due to image effects, produces harmonics which we evaluate non-perturbatively as a function of the intensity and frequency of the field and the distance to the substrate. We compare the results with those obtained using perturbation theory.
Propagation studies of the four wave mixing for a two-level system: stochastic treatment of the solvent
Author(s):
M. Gorayeb;
J. L. Paz;
A. J. Hernandez
Show Abstract
Propagation of a four wave mixing through a molecular system interacting with thermal reservoir was carried out. From that, analytical expressions to the absorption coefficient at different frequencies were obtained. Surfaces to that property and to the refractive index were exhibited. Saturation effect due the field can be viewed as well as the attenuation of the optical properties when the molecule-solvent coupling increases. That permit us to define an effective relaxation time which includes a parameter that measures the molecule-solvent interaction.
Nonlinear optical nanoscope with depth resolution
Author(s):
W. Luis Mochan;
Catalina Lopez-Bastidas;
Jesus A. Maytorena;
Bernardo S. Mendoza;
Vera L. Brudny
Show Abstract
Existing optical scanning microscopes don't allow the determination of the depth below the surface of the sample under which where scatterers might be located, due to the simple exponential decay of their evanescent probing field. We propose a nonlinear near field microscope which would allow three dimensional images of buried structures with nanometric resolution along all dimensions.
Real-time optical monitoring of the dip coating process
Author(s):
Alexandre F. Michels;
T. Menegotto;
Hans-Peter P. Grieneisen;
C. V. Santilli;
S. H. Pulcinelli;
Flavio Horowitz
Show Abstract
A significant part of film production by the coating industry is based on wet bench processes, where better understanding of their temporal dynamics could facilitate control and optimization. In this work, in situ laser interferometry is applied to study properties of flowing liquids and quantitatively monitor the dip coating batch process. Two oil standards -- Newtonian, non-volatile, with constant refractive indices and distinct flow properties -- were measured under several withdrawing speeds. The dynamics of film physical thickness then depends on time as t-1/2, and flow characterization becomes possible with high precision (linear slope uncertainty of ±0.04%). Resulting kinematic viscosities for OP60 and OP400 are 1,17 ± 0,03 St and 9,9 ± 0,2 St, respectively. These results agree with nominal values, as provided by the manufacturer. For more complex films (a mutli-component sol-gel Zirconyl Chloride aqueous solution) with a varying refractive index, through a direct polarimetric measurement, allowing also determination of the temporal evolution of physical thickness (uncertainty of ± 0,007 microns) is also determined during dip coating.
Input image magnification versus read-out visibility in BSO crystals
Author(s):
Lia Maria Zerbino;
Myrian C. Tebaldi;
Nestor A. Bolognini
Show Abstract
Image conversion is an interesting operation that can be a useful tool in image processing. In this paper we analyze the output readout visibility behavior of input images stored in a BSO photorefractive crystal. The output visibility versus the input visibility in terms of the slit width stored images of the input transparencies employed are analyzed. In this communication, non-holographic distributions with several magnifications are stored as modulation of birefringence in the crystal. In particular, the relation between the image magnification and the read-out visibility is studied. Preliminary experimental results under extinction configuration obtained by using intensity normalized slit images are described.
Optical properties of TiO2-x thin films studied by spectroscopic ellipsometry: substrate temperature effect
Author(s):
M. A. Camacho-Lopez;
Celia A. Sanchez-Perez;
A. Esparza-Garcia;
E. Ghibaudo;
S. Rodil;
S. Muhl;
L. Escobar-Alarcon
Show Abstract
Titanium oxide thin films were obtained by reactive dc-magnetron sputtering. A target of titanium (Lesker; 99.9% pure) and a mixture of argon and oxygen gases were used to deposit titanium oxide films onto silicon and glass substrates. The substrate temperature was varied between 200 and 400°C. Optical constants have been determined by spectroscopic ellipsometry and by using the optical transmittance data from UV-Vis spectrometry. The effect of substrate temperature on the optical properties is analyzed. Results indicate an increase in the refractive index of the films with substrate temperature, which is attributed to changes in the oxygen content, density and degree of crystallization of the films.
Growth of metallic Ag nanoparticles in fluoroborate glasses doped with rare-earth ions and their optical characterization
Author(s):
L. P.N. Riano;
Cid B. de Araujo;
O. L. Malta;
P. Santa Cruz;
Marcos A. Couto dos Santos
Show Abstract
Fluoroborate glasses have been prepared containing silver nanoparticles (NP) and rare-earth (RE) ions. Optical techniques were used for analysis of the surface plasmon (SP) band formation and to determine the influence of the NP on the RE ions luminescence. Electron microscopy was applied to measure the particles concentration and their size distributions. The techniques used allowed to identify the presence of Ag particles with diameters in the range of 5 - 200 nm. The absorption band of SP is centered at 425 nm for samples doped with Eu3+ and centered at 416 nm for samples with Pr3+. The ions luminescence shows enhancement or quenching for metallic particles of different sizes.
Polarization holographic element using an azobenzene polymer
Author(s):
Geminiano Martinez-Ponce;
Cristina E. Solano;
Sergio Calixto-Carrera;
Ludmila Nikolova;
Todor Todorov;
Tsveta Petrova;
Natalia Tomova;
Violeta Dragostinova
Show Abstract
A holographic lens is recorded superimposing two beams with orthogonal linear polarizations on an azobenzene polymer film. The polarization pattern on the interference plane induces two modulations in the media: the volume and the surface modulation. The spatial frequency of the surface relief is twice the one for the volumetric modulation resulting in a holographic lens with two different focal lengths. Additionally, because of the modulated anisotropy induced in the medium, the polarization at the longer focus distance is orthogonal to the polarization at the shorter one. We propose this polarization element to send or detect information in two planes simultaneously or separately by using an analyzer behind the holographic lens.
Titanium dioxide thin films: refractive index variation as a function of the deposition rate
Author(s):
G. Galvez;
Guillermo Baldwin-Olguin;
Francisco Villa
Show Abstract
The present work studies the variation of refractive index of titanium dioxide thin films due to changes in the evaporation rate during the deposition process under high vacuum. The experiments were done by depositing thin films on a glass disk of 45 cm in diameter for different deposition rates. To characterize thin films the spectral transmittance in the visible range was measured at different points along of two perpendicular radii. The refractive index profile was then determined from these data by using an inverse synthesis method. The results permitted us to obtain the refractive index variation as a function of evaporation geometry for different deposition rates.
Characterization of composite tube junction by ESPI
Author(s):
Alfredo Moreno Yeras
Show Abstract
The introduction of new materials in Mechanical Engineering is one of the main tasks of scientists and engineers. At present new technologies that allow the study, characterization and measurement of important mechanical states in new materials are being developed continuously. These techniques include the Optical Techniques of Measurement that use laser as an important tool in the information processing and interpretation. These techniques also involve the Electronic Speckle Pattern Interferometry (ESPI). The present investigation shows the development and implementation of ESPI technique in the study and characterization of composite tube junction. The technical characteristics related to this technique implementation are included in this paper. The strain field caused by different applied actions is also presented. The advantages and disadvantages of the use of this technique are shown and they are compared to other traditional and optical measurement techniques.
Phase measurement in digital speckle pattern interferometry using wavelet transforms: recent developments
Author(s):
Alejandro Federico;
Guillermo H. Kaufmann
Show Abstract
This presentation reviews recent developments carried out by the authors to evaluate phase distributions in digital speckle pattern interferometry (DSPI) using wavelet analysis. The advantage of this approach is that it requires only one interferogram to be analyzed and does not need the application of a phase unwrapping algorithm neither the introduction of carrier fringes in the interferometer. In particular, it is presented an approach that takes into account the second order contribution of the phase map. It is also presented the application of a smoothed time-frequency distribution which improves the accuracy of the results obtained in the neighborhood of stationary phase points and also when the generated DSPI fringes present discontinuities in the first derivative of the phase map.
Experimental interferogram analysis using evolutionary computation
Author(s):
Juan J. Sanchez-Escobar;
Pascual Alonso;
Sergio Vazquez-Montiel
Show Abstract
We report the experimental verification of an alternative method to the conventional least squares fit method for obtaining the phase of real interferograms, making an automatical polynomial fitting on exprimental data in accurate form. The process can be realized solving an optimization problem using an evolutionary algorithm, where the solution to the irradiance equation should be considered like an inverse problem and an objective function should be minimized. In this work we review the fundamental concepts comparing the performance of the least squares fit method and the evolutionary algorithm used in the experimental interferogram analysis.
Focal length assessment by self-imaging
Author(s):
Myrian C. Tebaldi;
Nestor A. Bolognini;
Alberto A. Tagliaferri;
Roberto Daniel Torroba
Show Abstract
Several classical and modern approaches were developed in the literature for measuring the focal length of a lens. We focus our attention on those that employ self-imaging methods. In our proposal, a collimated laser beam illuminates a test lens. After the lens, the wavefront becomes convergent or divergent according to the lens power. Attached to the lens, we place a Ronchi grating. This procedure gives rise to several classical Talbot images, although magnified due to the non-parallel illumination. Key to our presentation is the use of the property that the pitch of each self-image is directly related to the focal length of the collimating lens. To obtain the pitches, a lensless CCD camera is positioned in any two consecutive self-images planes. The respective images are captured and processed. We designed software that allows first to precisely focus each self-image plane by a best-contrast algorithm, and then takes an intensity histogram along a direction perpendicular to the grating lines. By measuring the distance between consecutive self-image planes and their pitches, the focal length is determined. This method provides a reference testing with higher setting sensitivity and an increase in the accuracy compared to previous methods. Note that the proposed method represents a practical improvement over other existing methods.
Algorithm geometric-radiometric to generate an aberrated image irradiance pattern
Author(s):
N. Bautista-Elivar;
Carlos I. Robledo-Sanchez
Show Abstract
Using the intensity law of geometrical optics we propose an algorithm to obtain the transverse distribution of the irradiance in an optical system affected by aberrations. This method can be used as alternative to recovery the phase in an optical system.
Microstructured surface element for high-accuracy position measurement by vision and phase measurement
Author(s):
Patrick Sandoz;
Bertrand Trolard;
D. Marsaut;
Tijani Gharbi
Show Abstract
In interferometry sub-wavelength resolutions are achieved thanks to phase computations. The number of measurement points resolved per fringe depends on the signal to noise ratio and may vary from tens to billions. In this work, that principle of fringe interpolation by phase computation is applied to image processing for the construction of accurate position sensors based on vision. A micro-structured pattern is etched on a surface element and is used as a phase-reference signal similar to an interference fringe pattern. This surface element is fixed on the moving target of interest and is observed by a static vision system. Then target displacements are reconstructed and measured with a high accuracy by locating the phase-reference in the recorded images. In a first configuration in-plane position is retrieved with a resolution of about 10-2 pixel for horizontal and vertical coordinates and about 10-4 radian for the orientation. Thus nanometer displacements can be controlled by a diffractive optical system and micrometer-sized surface patterns. Furthermore, this method is self-calibrating since the phase-reference pattern dimensions are known accurately and then provide us with a size reference available in each recorded image. Different configurations allow the position measurement along the three-space directions while an interferometric set-up is able to locate the position versus the six degrees of freedom. Several measurements per second are performed with an up-to-date microcomputer thanks to the dedicated software developed.
Using 3D virtual environments to visualize wave interference phenomena
Author(s):
M. H. Gimenez;
J. Riera;
A. Vidaurre;
Juan A. Monsoriu;
Carlos J. Zapata-Rodriguez
Show Abstract
Information and Communication Technologies have demonstrated to be extremely effective in the transmission of scientific knowledge. Nowadays, the development of software and hardware makes it possible to simulate physical processes as close to reality as required. Furthermore, complex physical processes benefit from graphical simplicity in order to emphasize the main points for a complete understanding. In this work we focus our attention on the interference of coherent scalar waves in homogeneous media. Digital simulations have been designed in order to help the students to understand this phenomenon. Examples of interference of plane waves and cylindrical waves are visualized in sapce-time scales as the main advantage over traditional teaching resources.
Wavelet coefficients thresholding method applied to the correlation of noisy scenes
Author(s):
Javier E. Mazzaferri;
Silvia A. Ledesma
Show Abstract
The distortion of a signal due to noise contamination can be overcome by using a decomposition of the signal in a base of wavelets. If the decomposition coefficients are small compared with the noise, the scene is dominated by the distortion. On the contrary, if they are bigger in absolute value, the signal is stronger that the noise. A way of reconstructing an image with a lower level of noise is accomplished neglecting the coefficients which values are lower than a threshold, and replacing them by zero. In this work we present a method that applies the thresholding of the wavelet coefficients in order to perform pattern recognition of noisy scenes. The method could be implemented in optical processing by using a Vander Lugt correlator architecture operating with liquid crystal displays. The function to be recognized is decomposed in sub-bands based on the Gabor decomposition, in the frequency plane. Hard thresholding is performed and the threshold is generated with accurate support functions in the filter plane. The criterion for the threshold selection is chosen to optimize the signal to noise ratio in the output plane. Numerical simulations results are shown and comparisons with other filters are made.
Extraction of topographic information based on equal color fringes of white light interferogram
Author(s):
E. Aguilera;
Arturo Plata
Show Abstract
C.I.E. chromaticity diagram has been used as a mean that permits to associate standard visual color perception with several interesting physics quantities: Temperature, characterization of lighting sources, thickness of thin films, and the amount of material in alloys and paintings. In specific, who works in interferencial microscopy knows the relation between isocolor curves, which are produced in a white light interferogram and the topography of the object under observation. A study about locus of these colors into the Chromaticity diagram is done in this work. Colors are produced by interference among plane wave fronts of white light with different delays. By this study, standard clibration that permits to extract topography information from some real interferograms can be obtained.
Realization and characterization of multilayer mirrors for Fabry-Perot interferometry in optic communication systems
Author(s):
Alejandro Garcia-Juarez;
Celso Gutierrez-Martinez;
J. Pedraza-Contreras;
F. Garcia Temich
Show Abstract
A theoretical design and experimental realization of multi-layer mirrors for Fabry-Perot interferometry and optical telecommunications is described in this work. The mirrors were designed and fabricated by 13 successive thin layers to achieve very high reflectance at optical wavelengths around 1300 nm. Thin layers are ZnS y MgF2 presenting high and low refractive index respectively. Layer thickness are of λo/2 at λo = 656 nm. Experimental results include the characterization of the transmittance of mirrors around 1300 nm. Additionally the mirrors were integrated in a Fabry-Perot interferometer to characterize optical sources emitting at 1300 nm. Finally to show a practical application, optical phase modulation was analyzed, using the fabricated mirrors.
Study of speckle interferometry techniques in a photorefractive crystal BGO: conventional holography and double aperture
Author(s):
D. Caraballo L.;
L. Maria del Carmen Lasprilla
Show Abstract
The study of speckle patterns by photography or digitally have been used in a wide variety of events of measures of displacements, vibrations or small deformations, from almost static situations until high speeds. In this work, a comparative analysis of experimental arrangements of speckle techniques is presented: a conventional holography and double aperture, for micro displacements of objects, in both cases, the speckle is modulated by Young strips, of such form that the first case makes reference to a modulation to high frequency, and in the second case show a low frequency, also it is had in the two techniques it is made double-exposure, one for the starting point of the object and the other for the object displacement. The registration and the reading are carried out in almost-real time in holographic arrangements using a photorefractive crystal; the information in these crystals is codified like one variation local of refraction index. In the two cases it is considered the nature in volume by registers of the speckle. The contrast of the interference fringes is analyzed in terms of the diffraction efficiency of the readout beam and of the registration parameters. The results are presented for each configuration.
Three-illumination-source position optimization for interferometry
Author(s):
Amalia Garcia Martinez;
J. A. Rayas;
Ramon Rodriguez-Vera;
Hugo J. Puga
Show Abstract
When it is carried out to perform a three dimensional evaluation of displacements, it has been proposed ESPI systems which uses three illumination beams or the use of three sensors. The same technique has been used by digital holography and shearography. The different sensitivity vectors associated to each illumination beam let us permit to calculate the displacement in each direction by sensitivity matrix. In the present work, it is showed the sensitivity components for each source in the case of optical set-up with three divergent iluminating beams, where the sources position makes possible measure the u, v and w components with a weight factor approximately equal respecting to set-up sensitivity.
Interferometric measurement of temperature profiles inside a transparent solid
Author(s):
Liliana Alvarez;
Elvio Alanis;
Graciela Romero;
Carlos C. Martinez;
G. Lesino
Show Abstract
Electronic speckle pattern interferometry technique (ESPI) was applied to the determination of temperature profiles inside a solid block made of a transparent material. The block is a component of a scaled-model intended to simulate a solar energy storage-collector wall (Trombe wall) and its adjacent room. In order to obtain the speckle correlation fringes, a Mach-Zehnder interferometer was used, in whose object arm the model was put. By means of an electrical heater a constant heat flux is supplied through one of the wall faces, maintaining the opposed face at a constant temperature, until a steady state is reached. The temperature profiles for several intermediate states are determined by measurements on the corresponding speckle correlation fringes. The experimental results are compared with the analytical solutions of the differential equation of heat conduction, with the appropriate initial and boundary conditions.
Optical direct observation of Gouy phase shift
Author(s):
Patricio Fluxa;
Lia Maria Zerbino;
Mario Garavaglia
Show Abstract
This paper considers the anomalous propagation of phase through the focus of an optical system. We observed the interference rings produced by two collinear spherical waves coming from the same laser source with different focal points. Then three regions are determined along the optical axis: R1, befor focuses; R2 between focuses; and R3, after focuses. In each of them we pictured interference rings which are complementary in intensity with a CCD camera. The complemnetary relationship is caused by the sudden change of phase by π through each focus.
A simple and low-cost technique to fabricate and experience interference birefringent filters
Author(s):
Pablo Velasquez;
Ignacio Soriano Moreno;
M. del Mar Sanchez-Lopez;
D. Puerto
Show Abstract
In this work we propose and demonstrate a very simple method to produce interference birefringent filters. We use the birefringence properties of usual commercial scotch, which acts as a uniaxial material. By superimposing several scotch layers with parallel orientation, and placing them between two crossed polarizers oriented at 45 degrees, we can measure the birefringence of the material. We use a portable fiber spectrophotometer to characterize the layers birefringence in the visible range. We developed a software to calculate the transmission properties of different types of birefringent filters, including folded and fan Solc filters. In the simulations we include the information of the material birefringence that we obtain experimentally, thus leading to a precise description of the transmission properties in the entire visible range. A very simple system permits to align the scotch layers with the proper angles and create a birefringent filter. We have designed several filters with different spectral properties. The measurement of the transmission obtained with the portable spectrophotometer confirms experimentally the prediction given by the simulation software.
Measurement of the Mueller matrix of an elliptical-mirror scatterometer
Author(s):
Neil Charles Bruce;
Oscar Rodriguez-Herrera
Show Abstract
We have recently developed a scatterometer which uses an elliptical mirror to direct the light scattered from a rough surface onto a CCD camera. This scatterometer is faster than the traditional arm based devices, and can measure the bi-dimensional scatter pattern. In the present work we present results for the calculation of the Mueller matrix of the elliptical mirror with the aim of using this information to correct the measured Mueller matrix for the instrumental contribution, to obtain the Mueller matrix of the scattering process.
Resolving power of a hybrid zone-plate/gradient-index lens system
Author(s):
Jose Manuel Rivas-Moscoso;
Carlos C. Gomez-Reino
Show Abstract
Following the Rayleigh criterion for resolution, we analyze the resolving power of a hybrid optical structure composed of a zone plate and a gradient-index lens at focal planes inside and outside the lens in terms of the type and number of zones of the zone plate. The Fraunhofer approximation can be invoked to study the irradiance at the Fourier planes inside the lens. In all other cases, the Fresnel diffraction integral must be used, although the resolution defined by the Rayleigh criterion still holds. We compare the limit of resolution for the hybrid structure with the resolution of a lens with the same aperture diameter as a function of the number of zones, stating that both coincide for a large number of zones. Finally, we present irradiance profiles with both approximations at various planes inside the lens and compare the results with those obtained by the use of zone plates in free space.
Configurations of LED arrays for uniform illumination
Author(s):
Ivan Moreno
Show Abstract
Solid state lighting is becoming the preferred choice for many lighting applications that require homogeneous illumination distribution. Light-emitting-diode (LED) sources for lighting are usually composed of several individual LEDs. Nevertheless, packaging density of LED arrays is limited by cost, available space, and particularly by thermal problems. This paper presents an investigation of the effects on illumination uniformity of light sources consisting of multiple LEDs due to different array configurations and packaging density of LEDs. The performance of various array configurations is analyzed using a radiometric analysis and experimental results.
A unified model for polarimetric magnitudes
Author(s):
J. J. Gil
Show Abstract
The physical magnitudes involved in polarimetric phenomena are studied under a unified mathematical model based on coherency matrices. These magnitude arise as the real coefficients of the expansion of the coherency matrices on the basis constituted by n-1 the generators of SU(n) group and the nxn identity matrix. The states of polarization of light beams are analyzed in the general case where the three components of the wave field must be considered. The 3D polarization magnitudes are obtained and two non-dimensional invariant magnitudes are defined to represent the stability of the polarization ellipse and the stability of the propagation direction. These "indices of purity" derive in the well known degree of polarization when the propagation direction does not fluctuate. The model is also applied to the polarimetric properties of material media, where three non-dimensional invariant "indices of purity" are defined to represent the mixture of pure components resulting in depolarization behavior of the media as a whole.
Variable optical attenuator using active multimode interference waveguide
Author(s):
Daniel A. May-Arrioja;
Romeo J. Selvas-Aguilar;
Jesus Escobedo-Alatorre;
Patrick LiKamWa;
Jose Javier Sanchez-Mondragon
Show Abstract
We propose a new structure for an integrated variable optical attenuator using InGaAsP multiple quantum wells. The principle of operation relies on the self-imaging properties of multimode interference (MMI) waveguides. The device consists of a MMI region that is 12 μm wide by 350 μm long, with input and output waveguides that are 2 μm wide. The dimensions of the MMI are calculated such that an image of the input field is produced at the output waveguide. The last statement is true as long as the phase relation between the modes in the MMI section is kept constant. Therefore, by selectively perturbing the refractive index within the MMI section, the phase relation of the modes is altered, thereby modifying the interference properties at the output of the device. We present numerical simulations using the Finite-Difference Beam Propagation Method (FD-BPM), and demonstrate that optical attenuation is possible by selectively modulating the refractive index of a narrow region within the MMI section. A dynamic range of -37 dB can be easily obtained at a wavelength of 1.55 μm with a device insertion loss of 0.3 dB. The effects of electro-absorption on the device performance are also investigated.
Replication of diffractive optical elements by injection molding
Author(s):
E. J. Carvalho;
Edmundo S. Braga;
Lucila H. D. Cescato
Show Abstract
In this paper we describe the replication processes of DOE carried out at the Diffractive Optics Laboratory/UNICAMP for replicating DOE. In particular we present the results obtained in the replication by injection molding of microlens array, diffraction gratings and polarizing elements. The measurements of the geometric dimensions of the DOE masters, the nickel shims and the replicated structures were accomplished by perfilometry, AFM and SEM microscopy. The optical properties of both the DOE masters and their replicas were evaluated by measuring of the diffraction efficiency as a function of the incident wavelength, for orthogonal polarizations.
Physical theory of Ronchi-grams unequal strip-widths rulings
Author(s):
N. I. Toto-Arellano;
Gustavo Rodriguez Zurita;
Alejandro Cornejo-Rodriguez
Show Abstract
In this paper we inspect some further properties of diffraction Ronchi rulings and its effects in Ronchigrams. Our considerations are based on the physical theory of gratings with different strip-widths geometry. Under scope are absorptive gratings, phase gratings and mixed gratings. The presented analysis and respective results are illustrated here with the use of an advanced mathematics software pack. Some possible applications in optical testing, imaging processing and nanolithography are considered.
Digital optical switches with reconfigurable output waveguide branches in InP
Author(s):
Pedro J. Barrios;
Siegfried Janz;
Andre Delage;
Ilya Golub;
W. Ross McKinnon;
Philip J. Poole;
Shawkat M. Abdalla;
Dritan Celo;
Sandy Ng;
Tom J. Smy;
Barry A. Syrett
Show Abstract
A compact Y-junction waveguide switch with electrically reconfigurable output waveguide arms is demonstrated in InGaAsP/InP. Simulations indicate that the plasma effect or the thermo-optic effect can be used as the active switching mechanism, as corroborated by experimental tests. For the plasma effect the induced index change under the electrode, Δn, is negative. The Y-junction device has a measured switch contrast ratio ~ 20 dB, with a response time of ~ 5 ns. Using the thermo-optic effect Δn is positive and the observed contrast ratio is better than 10 dB. The highly localized nature of the thermal gradient in these devices yields thermo-optic switching into the hundred of nanoseconds range, several orders of magnitude faster than the overall thermal response time. This is the fastest thermo-optic switch reported to date. Fabrication of these switches, and in particular the use of O+-ion implantation to provide electrical isolation of the waveguide branches, is described.
Holographic lithography for electroforming submicrometric structures
Author(s):
L. E. Gutierrez R.;
Lucila H. D. Cescato;
E. J. Carvalho
Show Abstract
In this paper we proposed and demonstrated the association of holographic lithography with electroforming to produce submicrometric metallic structures. To demonstrate the potential of the technique, different types of submicrometric metallic structures were generated: periodic lines, nano-tunnels and arrays of holes. Such structures can met different applications from optics to micromechanical systems.
Autofocus algorithm using one-dimensional Fourier transform and Pearson correlation
Author(s):
A. Bueno Mario;
Josue Alvarez-Borrego;
L. Acho
Show Abstract
A new autofocus algorithm based on one-dimensional Fourier transform and Pearson correlation for Z automatized microscope is proposed. Our goal is to determine in fast response time and accuracy, the best focused plane through an algorithm. We capture in bright and dark field several images set at different Z distances from biological organism sample. The algorithm uses the one-dimensional Fourier transform to obtain the image frequency content of a vectors pattern previously defined comparing the Pearson correlation of these frequency vectors versus the reference image frequency vector, the most out of focus image, we find the best focusing. Experimental results showed the algorithm has fast response time and accuracy in getting the best focus plane from captured images. In conclusions, the algorithm can be implemented in real time systems due fast response time, accuracy and robustness. The algorithm can be used to get focused images in bright and dark field and it can be extended to include fusion techniques to construct multifocus final images beyond of this paper.
Axial resolution of a chromatic dispersion confocal microscopy
Author(s):
Johnson Garzon Reyes;
J. Meneses;
Arturo Plata;
Gilbert M. Tribillon;
Tijani Gharbi
Show Abstract
An analysis of the axial resolution of a chromatic dispersion confocal microscopy is presented. The system is based on the principle of focus multiplexing by wavelength encoding due to a phase Fresnel lens. The axial resolution is related with the measure of the FWHM value of every spectral response.
A 3D digital terrain model oriented to design a clutter predictor for the Mexican Republic
Author(s):
E. Gonzalez-Ramirez;
I. D. Cluckie;
Margarita Tecpoyotl-Torres;
M. A. Rico-Ramirez;
G. Cerda-Villafana;
Jesus Escobedo-Alatorre;
Jose Javier Sanchez-Mondragon
Show Abstract
The variation of rainfall intensity with height makes mandatory to look at the rainfall as close to the ground as possible, when scanning the atmosphere by means of weather radars. Weather radar measurements contain many errors, which reduce the quality of the rainfall data. In particular, ground clutter has a strong relationship with the beam elevation angle and the Digital Terrain Model (DTM) around the radar site. Clutter is present when the radar beam intercepts obstacles creating a beam blockage reflecting back part of the incident energy. Due to this relationship, it is possible to predict clutter from a DTM by calculating the amount of this "blocked" energy. We present a software tool able to manipulate a DTM in order to design a clutter predictor for weather radar. This software allows the exploring of the image (rotation, zoom in and out), calculate geographic parameters and have functions to deal with the radar propagation through the atmosphere. The software developed here, in addition, has the possibility to combine the propagation beam with the DTM in order to design a cultter predictor as well as display weather radar products to become the way standard in which all the information is viewed.
Optical design and analysis of a noncontact profiler using diffractive optical elements (DOE)
Author(s):
J. A. Hernandez;
Sergio Vazquez-Montiel
Show Abstract
In this work we present an alternative to design a noncontact profiler using diffractive optical elements in substitution of the traditional optical elements (refractive, reflective). With these elements we have lenses with large numerical aperture and high control of the spherical aberration that is most important in the case of the profilers. In this work, the optical design of a profiler is presented that will be used in a large coordinate measuring machine. The optical design allows to this profiler scan the surface in a continuous way. We also present the algorithms for recovering the form of the surface starting from the date obtained with the profiler.
Telescopic system design using hybrid elements (refractive-diffractive) for people with visual weakness
Author(s):
O. Garcia Lievanos;
Sergio Vazquez-Montiel
Show Abstract
People with visual weakness, besides the typical refraction problems as myopia (shortsightedness), lose much of the light that enters to their eyes because their retina has many useless cones. For this reason the traditional ophthalmic lenses cannot solve the problem of these people, therefore, we are required of optical systems that collect a big quantity of light, we also need these systems to be of small dimensions and lightweight so they can be used for a long time. In this work we propose the optical design of telescopes using hybrid components, using this new optical components we have obtained compact and lightweight optical systems without decreasing the optical quality of the images. We present the optical design of telescopes for three different magnifications, as well as the analysis of the quality of their images.
Ray tracing in a plane-parallel uniaxial plate
Author(s):
M. Avendano-Alejo;
M. J. Orozco-Arellanes;
Orestes Nicholas Stavroudis
Show Abstract
Ray tracing formulas in a plane-parallel uniaxial plate bounded by an isotropic medium is analyzed when the crystal axis lies in the incident plane, and when its orientation is arbitrary. We present the behavior of the critical angle for the extraordinary ray as a function of the crystal axis position with respect to the normal to the refracting surface.
Wavefront coding technology in the optical design of astronomical instruments
Author(s):
Rosario Porras;
Sergio Vazquez-Montiel;
J. Castro
Show Abstract
The new astronomical instruments; spectrographs, cameras, focal reducers, telescopes, etc., requires to work in more and more wide spectral ranges and with very large fields of vision. Therefore, the chromatic aberrations and the field curvature are aberrations very difficult to correct and to balance in the process of optical design. For that problem, in the stage of optical design is necessary to add more optical components in the instrument, also we need to use more aspherical surfaces and we need more time of optical design, etc. In this work we propose to use the technique of wavefront coding using a cubic phase mask to obtain optical systems with an extended depth of field that corrects the chromatic aberration and the field curvature automatically. In this paper we present preliminary results of this technique.
The construction of a prototype of a 50-MBS free-space laser optic transmitter
Author(s):
Nicolas Alberto Gomez Montoya;
B. Sepulveda;
C. Florez;
F. Betancur
Show Abstract
Light emitting diodes or LEDs, which are special for telecommunications, and laser diodes were characterized. A free space optical data transmitter and its corresponding receptor were built. A power of 10 mW semiconducting laser with a wavelength of λ = 640 nm was tested. It was possible to modulate this laser with a digital signal at a speed of 40 Mbs and to transmit the information for a distance of 250 meters. A LED of high power was tested. With this LED it was possible to increase modulation speed with frequencies higher to 50 Mbs, but the distance covered by this laser was of only 180 meters due to light diffraction. The LED generates at the wavelength of λ = 650 nm. The diffraction phenomenon was corrected using the appropriate optics.
Highly compact temperature-insensitive phase-shifted and multiple-phase-shifted long-period fiber gratings by use of a CO2 laser
Author(s):
Yinian Zhu;
Ping Shum;
X. Chen;
C. H. Tan;
Hui-Wen Bay;
C. Lu
Show Abstract
We demonstrate the first fabrication of highly-compact and temperature-insensitive phase-shifted and multiple phase-shifted long-period gratings using the focused pulses of CO2 laser with point-by-point technique. By introducing the 3π/2, π, or π/2 phase shifts in the different location of the gratings with 480 μm of a period-length and total number about 16 - 21 periods, the symmetrical and asymmetrical pandpass filters based on those gratings can be obtained. The temperature sensitivity of formed gratings is about 8.8 pm/°C at a temperature range of 23°C - 190°C. Such fiber grating component could be used as an all-fiber oscillator in the laser cavity. Long-period gratings with different phase shifts are also investigated with various notches of resonance attenuations. All gratings fabricated are compactness to be packaged into the fiber-optic based devices.
Tunable optical source for the interrogation of Bragg gratings via spectral scanning
Author(s):
Aleksander S. Paterno;
Jose Luis Fabris;
Hypolito Jose Kalinowski
Show Abstract
This paper describes the implementation of an interrogation system with a tunable Erbium doped fiber ring-laser (EDFL). The EDFL is used to illuminate optical devices like Bragg gratings, so that it can also be used as an interrogation system to determine the spectral characteristics of the devices. An intra-cavity Fabry-Perot filter, driven by a dedicated voltage ramp generator, tunes the EDF laser. The resulting optical signal is captured by a photodetector and analyzed in a personal computer. The apparatus can be used as an optical spectrum analyzer for passive components and as an interrogation system for multiplexed fiber Bragg grating based sensors. As an application example, the temperature inside a concrete beam submitted to systematic heating and vibrations has been remotely measured with the system.
Reconfigurable 1x4 optical switch in InGaAsP multiple quantum wells
Author(s):
Daniel A. May-Arrioja;
Nathan P. Bickel;
Patrick LiKamWa
Show Abstract
We report on an integrated 1 x 4 optical switch that operates using the principle of carrier-induced refractive index change in InGaAsP multiple quantum wells. The device is very simple, requiring only the currents applied to two electrodes for complete operational control. An area-selective zinc in-diffusion process is used to channel the current into the multiple quantum wells, thereby enhancing the efficiency of the carrier based effects. As a result, the electrical power consumption of the device is significantly reduced, allowing the switch to be operated uncooled and under d.c. current conditions. Our initial 1 x 4 switch exhibits a -8 dB crosstalk between channels. However, improvements on the switch design and better control during the device fabrication process will significantly enhance this value.
Integrated electro-optic Mach-Zehnder switch realized by Zinc in-diffusion
Author(s):
Daniel A. May-Arrioja;
Patrick LiKamWa
Show Abstract
We demonstrate the use of an area selective zinc in-diffusion technique to fabricate an integrated InP/InGaAsP Mach-Zehnder optical switch. The zinc in-diffusion process using a semi-sealed open-tube diffusion furnace was characterized to enable the creation of p-n junctions at a precise depth in selected areas of the device sample. The method is simple, yet highly controllable and reproducible; with the crystal quality remaining intact after the diffusion process is complete. Using this technique an integrated 1 x 2 Mach-Zehnder optical switch has been fabricated. Our preliminary devices show a switch contrast ratio of 12 dB with a voltage swing of ±2.5 volts. Improving our fabrication process will further optimize the performance of the switch. Nevertheless, very good electrical isolation is obtained between the contacts, which demostrates the potential of the technique for the fabrication of Photonic Integrated Circuits.
Reconstruction of refractive index profile of optical waveguides by the finite element method
Author(s):
Sigifredo Solano G.;
Catalina A. Ramirez;
Javier Morales;
Pedro Ignacio Torres;
Nicolas Alberto Gomez Montoya
Show Abstract
We show that the refractive-index profile (RIP) of optical waveguides can be determined by analyzing the transmitted near-field pattern with the finite element method. The first step consists in determine the initial guess for the RIP. Then, the selected guess is improved applying a reconstruction procedure with the finite element method. The procedure has been evaluated by comparing the obtained results with experimental measurements obtained by the RNF and m-lines techniques on a pure-silica single-mode fiber and slab waveguide, respectively.
Electrically controlled Bragg grating in microstructured fiber with internal electrode
Author(s):
Pedro Ignacio Torres;
H. Arsalane;
Fredrik Carlsson;
A. Claesson;
Walter Margulis
Show Abstract
Microstructured fibers with internal electrode provide a new, flexible means for shaping the spectral properties of intracore gratings. In particular, control of the current that is applied to electrode permits modifies the central wavelength and the birefringence of the grating. The fabrication procedures for this type of device and experimental results related to its operation are described.
Modeling of photonic crystal fibers with the scalar finite element method
Author(s):
V. H. Aristizabal;
F. J. Velez;
Pedro Ignacio Torres
Show Abstract
A numerical model based on the scalar finite element method is applied to analyse the dispersion properties of photonic crystal fibers having a solid core and a cladding region with multiple air-holes. A correction which accounts for the polarization effects due to the large refractive index difference between silica materials and air holes is included in the analysis. The obtained numerical results show a good agreement with full-vector ones reported in literature.
Nonlinear microstructured fibers with ultrahigh birefringence
Author(s):
Arturo Ortigosa-Blanch;
Antonio Diez;
Martina Delgado-Pinar;
Jose Luis Cruz Munoz;
Miguel V. Andres
Show Abstract
We present the fabrication and characterization of a microstructured fiber with ultrahigh birefringence. The fiber, consisting on a small elliptical core suspended from thin silica bridges, has been fabricated adapting the stack and draw method for microstructured fibers to the well known fabrication procedure for conventional elliptical core optical fibers. The ellipticity of the core and the air-hole array has been achieved by controlling the lateral tension between the preform and the jacketing tube. The group index birefringence has been measured using a frequency-domain modulated carrier method and a modal interferometer method. Both methods proved appropriate and showed consistent results. A group index birefringence higher than 7 x 10-3 is demonstrated, being this value higher than those reported to date.
Fiber laser hydrogen sensor codified in the time domain
Author(s):
Yuri O. Barmenkov;
Arturo Ortigosa-Blanch;
Antonio Diez;
Jose Luis Cruz Munoz;
Miguel V. Andres
Show Abstract
A novel scheme for a fiber optic hydrogen sensor is presented. The sensor is based on an erbium-doped fiber laser with a Pd-coated tapered fiber within the laser cavity acting as the hydrogen-sensing element. When the sensing element is exposed to a hydrogen atmosphere, its attenuation decreases changing the cavity losses, which leads to a modification of the switching-on laser transient. The hydrogen concentration can be obtained by a simple measurement of the build-up time of the laser. This technique translates the measurement of hydrogen concentration into the time domain. Sensing techniques translating the measurement to the time domain offer the possibility to acquire and process the information very easily and accurately using reliable and low-cost electronics. We have also studied the influence of the pumping conditions. We have found that changing from a 100% modulation depth of the pump to biasing the laser with a certain pump power (being this value always below the laser threshold) the sensitivity of the sensor is substantially enhanced. Hence the sensitivity of the fiber laser sensor can be adjusted to certain requirements by simply controlling the pump. Relative build-up times variations of up to 55% for 10% hydrogen concentration are demonstrated.
Effective-area measurement in a single-mode optical fiber
Author(s):
J. Gutierrez Gutierrez;
Evgueni Anatolevich Kuzin;
Baldemar Ibarra Escamilla;
Sergio Mendoza-Vazquez
Show Abstract
The effective area (Aeff) of the single-mode fiber is an important measurement parameter. It is the area of the cross section of the beam into the fiber. Therefore, their evaluation requires the measurement of the field distribution in the fundamental mode LP01. In this work, we present a method to measure the effective area in the single mode fiber (SMF) and dispersion shifted fiber (DSF) using a 1550 nm wavelength in the input beam. The Direct Far Field (DFF) scan technique was used, making an accurately measure of the angular distribution of the intensity of the field from the single-mode fiber. The near field and far field for a circularly symmetric fiber are related through the inverse Hankel transform of order zero. Since this cannot be resolved analytically, we process our data obtained experimentally with a numerical integration to evaluate Hankel transform. If we know the near field, we can obtain the effective area from these data and equally of numerical integration.
Spectral birefringence characterization of erbium-doped monomode optical fibers: relative values of the linear and the circular birefringence
Author(s):
Diana Tentori-Santa Cruz;
Cesar Ayala-Diaz;
Fernando Trevino-Martinez;
Javier Mendieta-Jimenez
Show Abstract
Erbium-doped monomode optical fibers are widely used to build amplifiers, lasers, incoherent light sources and sensors. Since the performance of these devices can be modified by its spectral birefringence, it is important to characterize it. In the case of an elliptical retarder the determination of the sign of the linear birefringence and the relative value of the linear and circular distributed birefringence is not obvious. In this work we analyze the anisotropic response of erbium fibers assuming that they are uniform and behave as a distributed retarder with linear and circular birefringence. Taking advantage of the geometric properties of the Poincare sphere it is possible to separate the linear birefringence contribution from that of the circular birefringence and to determine their signs and relative values.
Method for measuring erbium-doped fiber parameters
Author(s):
R. Tellez-Garcia;
H. Sanchez H.;
Jorge L. Camas-Anzueto;
Evgueni Anatolevich Kuzin;
Baldemar Ibarra Escamilla;
O. Pottiez
Show Abstract
We develop a simple method to measure the set of parameters of an erbium-doped fiber which is needed to elaborate the numeric model of an amplifier when a 980-nm pump is used. We start from the Rate Equations and field propagation equations for signal and pump and shows the necessity of the attenuation coefficients at low powers for pump and signal and the knowledge of four parameters (defined as A, B,C, D) which include cross sections and overlap factors for signal and pump, erbium-doped concentrations, lifetime, and effective area. Our experimental procedure allows measuring the ABCD parameters without the knowledge of all parameters of a fiber. The ABCD parameters obtained experimentally were applied to a computer program to calculate the characteristics of amplifiers and then the calculation results were compared with the experimental characteristics of amplifiers. The comparison showed reasonably good agreement of the calculated and measured characteristics.
A wavelength demultiplexer based on waveguide broadening in silicon-on-insulator platform
Author(s):
Oscar Martinez Matos;
Maria L. Calvo;
Pavel Cheben;
Andre Delage;
Siegfried Janz;
Dan-Xia Xu
Show Abstract
We propose a modified arrayed waveguide grating (AWG) demultiplexer formed by an array of parallel ridge waveguides of equal length fabricated in silicon-on-insulator (SOI). Each waveguide contains two sections with different widths. The lengths of the two sections are modified from a waveguide to the adjacent waveguide, resulting in a wavelength dispersive phase array. With an appropriate demultiplexer output geometry, the light is focused in the output slab waveguide combiner. The focal position is wavelength dependent in the transverse direction, so that the optical signal is demultiplexed into separated output channels corresponding to different spectral bands. This device does not require bending waveguide sections which are essential in a conventional AWG demultiplexer, yielding very compact devices with potentially low loss. Numerical simulations have been carried out to evaluate the influence of waveguide parameters such as lengths and widths of different waveguide sections on demultiplexer performance.
Devices, components, and applications of low cost using polymer optical fibers
Author(s):
Mauro Lomer;
Guillermo Baldwin-Olguin
Show Abstract
Low-cost optical devices, components a polymer optical fiber (POF) are demonstrated using technical of polished. Potentially low-cost components fabrication processes are described. Several components and devices are proposed for applications in comunications or industrial applications. Experimental results obtained with POF and diffraction grating are presented.
Design and fabrication of 2D photonic crystals by holographic lithography
Author(s):
F. Quinonez;
Elso Luiz Rigon;
Lucila H. D. Cescato;
V. F. Rodriguez-Esquerre;
Hugo E. Hernandez-Figueroa
Show Abstract
Two dimensional photonic crystals slabs can be recorded using a double exposure of a photoresist film to an interference fringe pattern. In order to present an expressive PBG (photonic band gap) for a desired region of the electromagnetic spectrum, the geometry of the 2 dimensional structures must be appropriately defined. Besides the geometric requirements, the material itself, in which the structures are recorded, must be transparent and present high refractive index in electromagnetic region of the PBG. In this paper we design and fabricate two dimensional (PC) Photonic Crystals) in dielectric films on glass substrates. The use of optical materials instead of semiconductors allows the devleopment of processes able to produce P.C. for the visible part of the spectrum.
Optimization of 16x2.5 Gbit/s metro CWDM transmission over 65 Km of standard fiber
Author(s):
C. M. B. Lopes;
Eunezio A. De Souza
Show Abstract
We present a simulation of a 16 channels coarse wavelength division multiplexing (CWDM) system operating at 2.5 Gbit/s transmitted over 65 Km of standard fiber. The channel space was optimized in order to improve the use of the operation spectrum and to avoid the water peak. The results demonstrate the feasibility of 40 Gbit/s total capacity CWDM system operation using the S, C and L bands with bit error rate (BER) better than 10-9.
Simultaneous measurement of temperature and pressure using single fiber Bragg grating and fixed filter demodulation technique
Author(s):
Luiz C. S. Nunes;
L. C. G. Valente;
R. W. A. Llerena;
Arthur M.B. Braga;
A. L. C. Triques
Show Abstract
Fiber Bragg grating (FBG) sensors offer many advantages for monitoring strain and temperature, other physical parameters can be measured through the use of mechanical transducers. However, FBGs are sensitive to strain and temperature and, in many cases, it is difficult to discrminate both measurements. To overcome this problem several techniques have been proposed, most of them employing more than one grating. This work demonstrates the possibility to discriminate temperature and pressure measurements using only one FBG sensor and a low cost demodulation technique based on two fixed filters. A pressure transducer has been used to transfer a lateral force to the fiber, proportional to the applied pressure, generating birefringence in the Bragg grating. The system allowed to measure pressure in the range of 0 to 400 psi with uncertainty of 4 psi and, simultaneously, measure temperature in a range of 22°C with uncertainty of 0.1°C.
Improvement of performance in FFH-OCDMA systems by using strong apodized fiber Bragg gratings
Author(s):
J. I. Marulanda;
Pedro Ignacio Torres;
Catalina A. Ramirez
Show Abstract
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.
Photomixing of two laser diodes for generating tunable microwave signals (1 to 25 GHz) with applications to high-speed telecommunication systems
Author(s):
Alejandro Garcia-Juarez;
Celso Gutierrez-Martinez;
A. Torrez-Fortiz;
Jocobo Meza-Perez
Show Abstract
In this work we report the generation of microwave signals using photomixing of two diodes lasers. With this technique we can mix two optical signals that come from two different lasers. One laser is a single mode and the other laser is a multimode. Due to spectral separation between two lasers, microwave signals can be generated and tuned between 1 and 25 GHz. The bandwidth of the generated signal is approximately 2.5 GHz, however with the design and realization of microwave filters we can filter the photo generated signal and in this way, it is possible to obtain a radio frequency signal that can be used as a high frequency information carrier.
Silicon quadrant detector in CMOS technology
Author(s):
Alicia Vera-Marquina;
Alfonso Torres Jacome
Show Abstract
An optoelectronic device that detect visible light is designed in silicon technology, peaking in 650 nm wavelength. The quadrant detector (QD) derive photocurrents by projecting a light spot on four photodiodes placed close to each other on a silicon common substrate. The photodetector is square shaped with 2.25 mm2 per active area by each quadrant and the size of the device is 9 mm2. This work describes a technology to develop position sensitive detectors of four quadrant optimizing geometry to increase sensitivity. We propose to integrate sensor into complementary metal-oxide-semiconductor (CMOS) technology in order to improve photodetector out signal, reducing noise generated when photodetector is so far from data acquisition system.
A wavelength multiplexed fiber optic hydrogen sensor
Author(s):
Dobryna Zalvidea;
Antonio Diez;
Jose Luis Cruz Munoz;
Miguel V. Andres
Show Abstract
We present a novel configuration of a fiber-optic hydrogen sensor suitable for wavelength multiplexing. It is based on a palladium-coated tapered fiber and a fiber Bragg grating. This scheme allows sensor's multiplexing, which increases the capability to implement multipoint sensor networks for volumetric detection. Moreover, the sensitivity of the sensor is enhanced since light interacts twice with the palladium layer.
Design, implementation, and characterization of a low-cost phase shifter device
Author(s):
M. Patino;
L. Pencue;
C. Zambrano Velasco;
J. Leon
Show Abstract
The design, implementation and the used technique to characterize a phase shifter device constructed from an extracted piezoelectric element of a tweeter commercial are described in this paper. Interferograms obtained with a Mach-Zender interferometer, where one of the mirrors was replaced by the implemented device are shown.
CR (III) and CR (VI) detection in water environment using an optical fiber grating sensor
Author(s):
Ricardo C. Kamikawachi;
G. R.C. Possetti;
Marcia Muller;
Hypolito Jose Kalinowski;
Jose Luis Fabris
Show Abstract
This work shows the application of an optical sensor to detect the presence of Cr(III) and Cr(VI) oxidation states in water solutions. The sensing device is a long period grating produced in a standard telecommunication optical fiber by applying a suitable number of point-to-point electrical arc discharges from a fusion splicer. In order to analyze the Cr(III) and Cr(VI) solutions, the sensing device is kept into a recipient under constant longitudinal stress and the Chromium solution samples are added to it. The results show that the sensor can not only detect the presence, but also differentiate between the two-oxidation states. Samples with Chromium concentrations from 0.16 mg/l to 5.2 mg/l are analyzed, leading to maximum wavelength shifts (relative to the LPG in pure water) of 0.14 nm and 0.26 nm for Cr(III) and Cr(VI), respectively. A comparison between the results obtained for both solutions shows that is possible to identity any of the Chromium oxidation states present in the sample until a lower limit concentration of 2.6 mg/l for the employed set-up.
Optical fiber detector based on light diffraction
Author(s):
Aristides Alfredo Marcano O.;
L. Rodriguez;
J. Ramirez
Show Abstract
We describe a new kind of fiber optics device, which detects directly sound and other perturbations with high sensitivity. The fiber works as a sound transducer able to detect human voice of low power levels. The phase changes, induced by sound waves in the propagating through the fiber light beam, generate amplitude changes after the beam is diffracted at the exit end of the fiber. A specially designed electronic system processes the signal which can be used for sound reproduction and detection. The system can also be used as an all purposes detector for the registration of subsonic and ultrasonic acoustic waves, direct pressure, temperature changes and other external fields.
Analytic description of dispersion-managed fiber systems
Author(s):
M. H. de Sousa;
Mario F.S. Ferreira;
E. Marti-Panameno
Show Abstract
A variational method with an arbitrary ansatz is used to reduce the governing equation in the case of a periodic dispersion-managed fiber system to a coupled set of nonlinear ordinary differential equations. The phase-plane dynamics of the reduced system and the main characteristics of the dispersion managed pulses, namely the possibility of propagation when the average dispersion is zero or normal, are examined.
Generalized guided-wave mode calculations in graded-index fibers
Author(s):
E. Castro;
J. Puerta;
P. Martin
Show Abstract
In this paper a novel approximated method is introduce to calculate guided-wave modes in graded-index fibers. Useful solutions have been obtained on the whole range of r for the corresponding scalar wave equation, using two-point quasirational approximations. This approach is better than the WKB approximation which is good only for the ray optic pictures and when the phase changes at the caustic are ignored. Here an adequate change of variables have been found that allows determine power series and asymptotic expansions suitable for application of the two-point quasi-rational approximant method. The results presented here agree very well with the numerical solutions.
Photonic crystal fiber for chromatic dispersion compensation
Author(s):
M. A.R. Franco;
M. T. Ruggieri;
V. A. Serrao;
F. Sircilli
Show Abstract
We propose a new design of a Photonic Crystal Fiber (PCF) with high negative chromatic dispersion for compensation purpose. The proposed PCF has a hexagonal holey structure with seven air-holes rings with different diameters. For the numerical analyses a scalar finite element method was utilized. This scalar approximation describes the general behavior of the optical propagation in the PCF and yields good numerical results for the exploratory phase of new PCF designs. However, more accurate results would require a vectorial approach. For this new PCF design, values as large as D = -5000 ps/nm/km were reached at 155 μm wavelength.
Twist in the center of the loop of Sagnac interferometer of optical fiber to determine the beat length
Author(s):
J. M. Estudillo-Ayala;
A. Placencia-Villanueva;
Roberto Rojas-Laguna;
T. Toledo-Garcia;
E. Alvarado-Mendez;
Jose Amparo Andrade-Lucio;
O. G. Ibarra-Manzano;
Rene Jaime-Rivas;
Maria de Jesus Estudillo-Ayala
Show Abstract
In this work we showed an improvement in the method to measure low birefringence in optical fibers with the Sagnac interferometer published in paper previous in which the fiber twists in an end of the loop of the interferometer and the entrance of the light every time it is adjusted that twists the fiber. In this work we twist the fiber in the center of the loop of the Sagnac interferometer it is very simple and we don't need light polarization neither to adjust the axes in the entrance of the fiber. It can use for the mensuration a section of shorter fiber that a beat length. Some theoretical and experimental results are presented.
Tapered photonic crystal fiber couplers for optical integration
Author(s):
Igor A. Sukhoivanov;
Jose Amparo Andrade-Lucio;
Roberto Rojas-Laguna
Show Abstract
At the present paper the photonic crystal coupler of an optical fiber, which has been made by the adiabatic tapering of the optical fiber based on the photonic crystal is presented. In our investigation an effective refractive index model of two-dimensional photonic crystal was used. This model allows analyzing the waveguide structures, which work on the effective index waveguiding in a defect of the photonic crystal. The effective refractive indexes of such couplers were numerically found. Using this model the field distribution in these couplers were investigated and were calculated its losses. It was shown that the couplers with smaller input diameter and the fixed output diameter have smaller losses.
Gaussian beam characterization using the thermal lens method
Author(s):
O. Mendoza-Yero;
H. Cabrera Morales;
Aristides Alfredo Marcano O.
Show Abstract
We study the effects of a thermal lens generated by a pump beam on the propagation of a low power TEM00 probe beam. We show that the thermal lens affects the probe beam waist position and waist radius. The waist position is displaced forward and backward depending on the sign of the refractive index thermal gradient. We show that the waist position does not coincide with the focal plane of the thermal lens. Our results suggest that the absorption coefficient of the sample can be found measuring the time-dependent waist radius of the probe beam.
Ab initio excitation spectrum of the CO-Ar Van der Waals molecule
Author(s):
H. Castejon;
M. C. Salazar;
J. L. Paz;
A. J. Hernandez
Show Abstract
In the present contribution we performed ab initio calculations at the CCSD(T) level of theory in the framework of the supermolecule approach on the CO-Ar van der Waals (VdW) complex. The interaction energy of the ground CO(X1Σ)-Ar(1S) and excited CO(A1II)-Ar(1S) states and corresponding vertical excitation energies are therefore calculated.
Ab initio interaction and spectral properties of CO+-He
Author(s):
I. Lugo;
J. L. Paz;
M. C. Salazar;
A. J. Hernandez
Show Abstract
Ab initio calculations at the CCSD(T) level of theory in the framework of the supermolecule approach are used to study the CO+-He van der Waals (vdW) dimer in the present contribution. The interaction energy of the ground CO+(X2Σ)-He(1S) and excited CO+(A2II)-He(1S) states and corresponding vertical excitation energies are therefore calculated.
Measurement of Stark parameters of HeII P-Alpha, P-Beta and P-Gamma spectral lines
Author(s):
Santiago Mar;
F. Rodriguez;
R. J. Pelaez;
J. A. Aparicio;
V. R. Gonzalez;
Juan Antonio del Val
Show Abstract
Optical diagnostics is a known and powerful tool to obtain information concerning the processes involved inside and around plasma. In the case of helium plasmas, they are present in industrial applications, like welding or cutting processes and in scientific research, like the inertial confinement plasmas or astrophysical analysis. This work reports information on the pressure broadened profiles of the HEII Paschen-alpha (Pα), Paschen-beta (Pβ) and Paschen-gamma (Pγ) spectral lines measured in a pulsed discharge lamp. Information relative to the line shapes, full width at 1/2, 1/4 and 1/8 of the maximum intensity and the dip of the HEII 320.3 nm is provided. The electron density has been determined by two-wavelength interferometry and from the Stark width of the HEI 501.6 nm and ranges during the HeII emission from 0.54 to 0.64 1023 m-3 in the plasma. Temperature (1.7 - 2.4 eV) has been simultaneously determined from the Boltzmann-plot of HEI and from local thermodynamic equilibrium (LTE) assumptions. The final results have been compared with most of the previous existing data.
The phase space representation in the resolution of two spectral lines: the grating spectrometer case
Author(s):
Luis Raul Berriel Valdos;
J. Carranza Gallardo;
Jose Luis Juarez
Show Abstract
The aim of this work is to find a resolution value for grating spectrometers when two spectral lines are analyzed. The phase space representation is used to find this value when the following proposal is employed: If the Wigner distribution function is positive along the space frequency axis (at the origin of the space axis) then the two spectral can not be resolved; otherwise, the spectrometer resolve them.
Photothermal beam deflection applied to SO2 trace detection
Author(s):
Francisco Adriano Manzano;
V. D'Accurso;
O. Radulovich
Show Abstract
We present the application to environmental monitoring of a compact setup for in situ trace gas detection based on photothermal beam deflection (mirage effect) spectroscopy. Gas traces measurements are performed by detecting the time-varying component of the photothermal deflection of a red diode laser beam, propagating inside the region where a pollutant is excited by another laser. In this work, detection of traces of SO2 in a mixture with Nitrogen at atmospheric pressure enclosed in a glass cell, was performed using the fourth-harmonic pulses of a 10 Hz Nd:YAG laser. It was verified by FTIR spectroscopy that negligible SO2 destruction was produced after irradiation of high pressure mixtures with 105 UV pulses. Several beam sizes and propagating angles for the UV and visible laser were tested and evaluated in order to overcome parasitic signals due to unwanted absorption in optical elements. With this setup we reached a detection limit of 5 ppbV in a hundred-second averaging time span but we estimate sub-ppbV levels can be reached by simple changes in the geometry for improving the signal to noise ratio.
Raman spectroscopy applied to molecular transformation of photochromic polymers
Author(s):
R. Delgado Macuil;
V. Lopez Gayou;
M. Rojas Lopez;
A. Orduna-Diaz;
Ruben Ramos-Garcia
Show Abstract
Photochromic polymers are materials with high potential for applications in optical devices. In this work we analyzed the polymeric matrix effect in convertion and reconvertion efficiency of spiropyran trough. Raman spectroscopy and fluorescence. Argon laser in 514 nm was used as excitation source. The results show the increase of fluorescence over the illumination time, one peak in λ = 571 nm was present. The peak is associated with the molecular reconvertion from merocianine to spiropyran.
Photoacoustic systems for NO2 trace detection
Author(s):
V. Slezak;
A. Peuriot;
Guillermo D. Santiago;
J. Codnia
Show Abstract
Vast research work on visible-laser-based photoacoustic spectroscopy of NO2 in air has been performed at the CEILAP. The study of the mechanisms of acoustical energy losses in a cavity is carried out exciting with a pulsed visible laser. For precise measurements a processing method is developed which allows obtaining high resolution of the photoacoustic signal spectrum when the acquisition window is limited. Devices are shown, where the resonant excitation is obtained with either a mechanically amplitude-modulated or an acousto-optically Q-switched green laser. A simpler, more compact and cheaper acquisition system is obtained through digitizing the pre-amplified signal by the sound card of a PC. The detection limit of different setups and an application to the measurement of the NO2 content in car exhausts are presented. Moreover, a one-dimensional model for cell design and otimization of S/N ratio is developed. It is verified by measurements on NO2 mixtures in a specially built acoustic cavity with a detached Helmholtz resonator.
Implementation of a photorefractive Talbot correlator
Author(s):
J. E. Rueda;
Maria del Carmen Lasprilla;
A. Salazar
Show Abstract
In this work, the results of the implementation of an optic correlator are presented. The optic correlator allows detecting, on the exit plane, the address of rotation of the objective. The correlation filter is the hologram of the self-image of the reference object, which is materialized in a BSO crystal. During the operation of the correlator, the exit plane exhibits harmonic space20. On the other hand, while the objective changes its angular position, the harmonic of order zero and the harmonic +1 or -1 exchange energy, as it is the address of rotation of the objective.
Image transformer for spectroscopy
Author(s):
P. Garcia;
O. Cardona;
Alejandro Cornejo-Rodriguez
Show Abstract
It is necessary to optimize the slit width of a spectrometer in order to obtain the theoretical resolution, the greater amount of energy onto the detector and a better signal to noise ratio. We propose a transformer system of images for spectroscopy, which consists of a plano-convex lens cemented on one side of a parallel-plane glass plate, to transform the image formed in the focal plane of a telescope into an image of rectangular form of a specific size, with the objective that all the light passes the slit of the spectrometer without decreasing the resolution. We present the preliminary simulations and experimental results of the proposed optical system.
Ab initio study of the vibrational molecular spectra of the dimmer N2He
Author(s):
M. Llanos;
R. Lopez-Planes;
A. J. Hernandez;
M. C. Salazar
Show Abstract
Starting from the surface of potential energy obtained for the N2-He dimmer calculated under the Supermolecule approach, using the Theory of Perturbation Moller Plesset up to fourth order (MPPT4) and the pattern of the rigid rotor, the surface corresponding to the state N2(A'ΓIg)-He ('S) presents two vibrationals states e1 = 44,70 cm-1 and e2=23,27 cm-1. The longitudes of wave obtained λe1=2,23x10-1m and λe2 = 4,30x10-1m indicate us that the dimmer emits inside the UHF spectrum very near to the radar bands.
Spectroscopic analysis of signals from LIBS experiments
Author(s):
C. D'Angelo;
D. Diaz Pace;
D. Bertuccelli;
G. Bertuccelli
Show Abstract
In the LIBS experiences (Laser Induced Breakdown Spectroscopy), in particular those carried out at atmospheric pressure, the observed atomic lines present a high absorption which is a setback in order to employ the measured line intensities to calibrate the element concentration in the samples. Absorption mainly occurs in the strongest lines of the spectrum and, consequently, those with the biggest probability of detection in a multi-element plasma. With the goal of quantifying some element in a laser-induced plasma several procedures are used. The most widely known is constructing calibration curves. In contrast, free-calibration methods are already available. The latter requires knowing plasma parameters and equilibrium (LTE) and optically thin plasma conditions are assumed. In both cases the experimental measurement of absorbed lines leads to errors in the concentration calculus. In this paper, working methods under optically thick inhomogeneous plasma conditions are studied. Considering information deduced from the optical thickness of the measured spectral lines quantification of trace elements in the samples is achieved. The optical thickness is responsible of line saturation. It is related to the emitting species density, the electronic temperature and concerned spectral line.
CCI2 reactions with HCI, NO2 and O2
Author(s):
V. M. Freytes;
J. Codnia;
M. L. Azcarate
Show Abstract
The IR Multiphoton Dissociation (IRMPD) of CDCl3 different gases was studied with the flash photolysis technique using a tunable CO2 TEA laser tuned to the 10P(48) line. CDCl3 samples were irradiated in the presence of HCl to analyze a possible recombination of the primary dissociation fragments CCl2 and DCl. The IRMPD of CDCl3 was also studied in mixtures of HCl/Ar, O2/Ar and NO2/Ar. In the experiences with added HCl, CHCl3 was obtained as major product evidencing the existence of the CCl2 and DCl recombination reaction. The dissociation probabilities per pulse obtained with the addition of different gases were compared.
Laser flash photolysis with real-time mass spectrometry detection
Author(s):
J. Codnia;
Francisco Adriano Manzano;
M. L. Azcarate
Show Abstract
The laser flash photolysis technique in a flow system with real time mass spectrometry detection is a suitable tool monitor the time evolution of chemical reactions. IR and UV lasers have been used to generate radicals to initiate a chemical reaction in a gas mixture. The appropriate selection of the pressure regimes (μtorr - 760 torr), the laser pulse repetition rate and the sample residence time in the photoreactor make possible the selective detection of final and intermediate reaction products. The selection of the temporal scales enables the independent study of the different stages of a process through the elimination of certain radical reactions. The rate constants associated to the corresponding kinetic scheme can be therefore determined and the reaction channels can be established. This technique was implemented for the study of oxidation reactions of chlorofluorocarbons of atmospheric interest.
Spectroscopic analysis of signals on LIBS experiences: fit of experimental measurements
Author(s):
C. D'Angelo;
D. Diaz Pace;
D. Bertuccelli;
G. Bertuccelli
Show Abstract
In the LIBS experiences (Laser induced breakdown spectroscopy), the created plasma is far inhomogeneous and the observed lines present a high absorption. This fact gives rise to drawbacks in the performance of the technique to calibrate the content of any element in the sample. Both the most studied and easier approach to modeling such absorbed plasmas is the homogeneous model, where we consider the same temperature and density in the whole plasma plume. In this work, in order to quantify the results obtained in alloy and soil samples, we searched experimental conditions where the plasma was almost homogeneous. The minimum-squares fit method was carried out to analyze the measured lines on the homogeneous plasma framework. Two lines of the same element and ionization state were employed such a way the homogeneous zone was fully characterized and plasma parameters such as temperature, density and the generic shape of the optical thickness were determined. With these parameters we were able to quantify the percentage of any element in the sample with an uncertainty of 1%.
Backscattering spectroscopy applied to sizing particles in solution
Author(s):
F. Videla;
D. C. Schinca;
L. B. Scaffardi
Show Abstract
Optical backscattering spectroscopy offers instrumental advantages over fixed wavelength multiangle scattering measurements. We present results of backscattering spectroscopy of calibrated spherical latex micro particles in aqueous solution when a beam of white light is incident on the sample. From Mie calculations and Fourier analysis, the radius of the particles can be retrieved, both in monomodal (single particle size present) and bimodal (two particle size present) samples.
Changes in the intensity of push-pull molecules FWM spectrum under the modification of VB-CT model parameters
Author(s):
T. Cusati;
J. L. Paz;
E. Squitieri
Show Abstract
In this work we have studied the maximal intensity behavior of the FWM signal with the changes in the molecular parameters Vo (corresponding to the electronic energy gap between the states involved in the model) and q (bond length alternation coordinate), from the valence-bond charge-transfer model. We have observed maximal values for the cases of extreme representation and minimal values at the intermediate representation. Moreover, for each value of Vo and q, there exist the respective optimum values of q and f, associated to the maximal values mentioned before.
Effects of the changes in the relaxation times on the FWM response of push-pull molecules
Author(s):
J. L. Paz;
T. Cusati;
E. Squitieri
Show Abstract
In the present work we have studied the changes in the FWM signal response considering the modification in the longitudinal and transversal relaxation times T1 and T2, respectively. These changes are obtained considering three cases of rate between longitudinal and transversal relaxation times T1/T2, with three orders of magnitude between them: a) 0.1, b) 1 and c) 10. These modifications are applied to push-pull molecules, taking into account the valence-bond charge-transfer model. Moreover, we have taken into account the symmetric values of Vo = ± 1 (corresponding to the electronic energy gap between the states involved in the model). Notable changes in maximal intensity of the peaks belong to the FWM spectrum are observed with the variation in the ratio between the relaxation times.
Influence of intramolecular coupling parameters changes on dipole moments and macroscopic polarization
Author(s):
T. Cusati;
J. L. Paz
Show Abstract
We have studied the effects of the changes in the intramolecular coupling parameters S (height) to which the vibronic coupling occurs), V0 (energetic difference between the minima of the potential curves) and v (coupling parameter), considering a two levels system described by two crossed harmonic potential curves. This work has been divided into two particular cases: a) simultaneous changes in S and v and b) simultaneous changes in S and V0. In the first case we have observed an important increment of the polarization values for low values of v. In the particular case of resonance peak, an important increment of polarization values is observed with the increment of v. In the second case, an abruptly increasing in polarization values is observed to high values of S and low values of Vo. In the particular case of resonance peak we observed the contrary behaivor of the precedent case: a notable decreasing of the polarization values is observed with the increasing in v. These changes are associated to the modifications in the overlapping integral and consequently in the dipole moments of the states in the new coupled basis.
Exact decoupling of two dipole-dipole interacting dimers
Author(s):
T. Cusati;
A. Napoli;
A. M. Messina
Show Abstract
It is today possible to test many quantum mechanical predictions, even the most puzzling ones, setting up sophisticated experiments on exemplary "textbook" physical systems like a single atom or molecule or a single material quantum harmonic oscillator. It is therefore conceptually highly exciting to conceive simple but not trivial physical situations representable by exactly solvable hamiltonian models, in the grasp of the experimentalists. In this paper we study a physical system consisting of two coupled identical dimers. Each molecule possesses both fermionic and bosonic degrees of freedom and its internal non adiabatic dynamics is governed by a bilinear term conserving the total excitation number. The two molecules are assumed to interact by a dipole like term. Our main result is that the hamiltonian model representing such a composite system may be unitarily put in a form describing two fictitious uncoupled JC dimers provided the initial excitation number is less than two. The advantage of these canonical transformations is that it makes the restricted dynamical problem exactly tractable. In this way we may successfully study the time evolution of quantum correlation effects get established in the dimer-dimer system due to dipolar like coupling.
Effects of off-axis laser beam propagation on beam parameters
Author(s):
O. Mendoza-Yero
Show Abstract
Off-axis Gaussian beam propagation through ABCD optical systems is analyzed using a relation between beam moments of irradiance in off-axis and on-axis propagation, respectively. Analytical expressions to link off-axis and on-axis Gaussian beam propagation parameters (for instance squared beam radius, Kurtosis and Skewness parameters) are obtained. It is shown that off-axis propagation causes an increase of beam waist radius, a decrease of beam symmetry and it may flat beam profile.
Light propagation in chiral and magnetochiral random media: the impact of broken symmetries
Author(s):
Felipe A. Pinheiro;
B. A. van Tiggelen
Show Abstract
We investigate light transport and scattering in random media with broken mirror and/or time-reversal symmetries. Using microscopic transport theory, we demonstrate the residual circular polarization of diffuse light in chiral optical media, associated with broken mirror symmetry. We introduce a model to describe light scattering in inhomogeneous magnetochiral media, which occurs for broken mirror nd time-reversal symmetries. In such media, we define a new optical measure for the degree of chirality and calculate it for some simple chiral systems and even use it to probe the chirality of random media.
Numerical modelling of nonlinear ellipse rotation
Author(s):
Jorge Ares;
M. T. Flores-Arias;
Vincent Kermene;
Agnes Desfarges-Berthelemot;
Alain Barthelemy
Show Abstract
Numerical modeling of nonlinear ellipse rotation has been made for an optical field propagating along a linear birefringent silica optical fiber. The kernel of this model comes from expressing the coupled field as a sum of two linearly polarized modes in the direction of the principal axes of the fiber. The developed model is suitable for the design of a big number of optoelectronic devices and let easily introduce the temporal dispersion effects.
Surface inspection with optical fiber bundles
Author(s):
Jorge Ares
Show Abstract
We propose a new kind of fiber sensor for performing surface analysis. The sensor is composed of an optical fiber bundle which eventually couples the propagating light onto a discrete set of intensity detectors. Two well different ways of working are exposed. Some characteristics of its theoretical performance are also commented.
Refraction of a three-dimensional beam in uniaxial crystal-isotropic medium interfaces in presence of inhibited reflection
Author(s):
Claudia E. Vanney;
Liliana Ines Perez
Show Abstract
We propose a generalization of Artmann's method for three-dimensional beams. This generalization, that does not consider a symmetry coordinate for the incident beam, allows its use in non-isotropic interfaces. We apply it particularly to the study of the refraction of a beam that is limited in two directions and that impinges on a uniaxial crystal-isotropic medium interface in presence of inhibited reflection. As known, the direction of the energy flux of a three-dimensional incident beam can be obtained (to first order and considering paraxial approximation) from the interference patterns of two two-dimensional beams. Each beam can be obtained from the superposition of two plane waves. In the first beam, the normals to the wave fronts are contained in the same incidence plane and they impinge with different angles; in the second, they are contained in different planes of incidence but with the same angle. We show that the refracted ray, in presence of inhibited reflection, suffers a lateral displacement that is not contained in the plane of incidence. The refraction of the first two-dimensional wave packet takes into account the longitudinal displacement whereas the refraction of the second allows us to calculate the transversal displacement.
Distinguishing fine details by Fresnel domain diffraction
Author(s):
Francisco F. Medina-Estrada;
John Freddy Barrera;
Jorge Ivan Garcia-Sucerquia
Show Abstract
The capability of distinguishing fine details in simple structures by means of Fresnel domain diffraction is shown. Through numerical simulations it is shown that the bigger Fresnel's number in the diffraction considered the bigger differentiability is reached. A circular clear aperture with two fine details is employed for illustrating.
Intensity fluctuations and the degree of polarization in Gaussian random electromagnetic fields
Author(s):
Tero Setala;
K. Lindfors;
Matti Kaivola;
Jani Tervo;
Ari T. Friberg
Show Abstract
For an electromagnetic beam described by Gaussian statistics the normalized intensity fluctuations are known to depend on the beam's degree of polarization. With general non-paraxial random electromagnetic waves, such as optical near fields, a complete characterization of the polarization state requires a 3 x 3 coherence matrix and a three-dimensional degree of polarization. We demonstrate that, under the assumption of Gaussian statistics, the normalized intensity fluctuations in the three-dimensional case are expressible in terms of the three-dimensional degree of polarization. Since such a general description can be employed even for beams with only a transverse electric field, several important physical results follow from comparison of the three-dimensional and usual two-dimensional formulations. The results are expected to be particularly important in intensity interferometry.
Optical encryption method using zone plates
Author(s):
John Freddy Barrera;
Rodrigo H. Henao;
Roberto Daniel Torroba
Show Abstract
We present the implementation of an optical encryption method using zone plates. The optical security system is based on using a computer generated phase mask. In the encryption process the phase mask is placed in the Fourier plane of the object to be encrypted. The original-data recovering is performed by digital reconstruction using the conjugate of the encryption mask. Theoretical background and computer simulations are presented to demonstrate the method.
Communication modes in axicon imaging
Author(s):
Anna Burvall;
P. Martinsson;
Ari T. Friberg
Show Abstract
The communication modes are an increasingly frequently used technique for studying the radiation, propapgation, and scattering of light. The method is unusual in the way that it gives the information content and the resolution of the fields. It also allows for the possibility of including the noise considerations in the calculations. We present a brief summary of the communication modes method, together with our latest contribution: the communication modes for the axicon geometry.
Transformation of the vortex part of the orbital angular momentum in first-order optical systems
Author(s):
Tatiana Alieva;
Martin J. Bastiaans
Show Abstract
The transformation of the vortex part of the orbital angular momentum of linearly polarized, partially coherent beams during their propagation through separable first-order optical systems is analyzed. We obtain that the evolution of the vortex part depends only upon the parameters ax, ay, bx, and by of the ray transformation matrix. Isotropic systems with the same ratio b/a produce the same change of the vortex part of the orbital angular momentum.
Construction of generalized Fresnel zone plate
Author(s):
Carlos Criado;
N. Alamo;
Hector Jorge Rabal
Show Abstract
We define a generalized Fresnel zone plate as a diffraction grating device that diffracts a predetermined wave front into a spherical converging one. The device is constructed as the intersection of a family of refracting profiles with an arbitrary shaped surface. The refracting profiles are obtained as envelopes of specific families of Cartesian ovals. The classical Fresnel zone plate is a particular case of this class. This construction has several interesting applications.
Reflection of electromagnetic waves at index-matched anisotropic interfaces
Author(s):
Marina E. Inchaussandague;
Miriam L. Gigli;
Ricardo A. Depine
Show Abstract
We study the relation between the excitation of eigenmodes at isotropic-gyroelectromagnetic flat interfaces under index-matching condition and the singular behavior of the reflectivity at grazing incidences. We show that, as in the isotropic case, these eigenmodes can be excited by waves at other angles of incidence by introducing a periodic corrugation to the interface between the two media. The coupling produces strong peaks in the curves of reflectivity versus angle of incidence, whose intensity and shape depend on the height of the corrugation. Numerical examples for a particular orientation of the optic axis are presented.
Obtaining the phase in the star test using genetic algorithms
Author(s):
Marcos A. Salazar Romero;
Sergio Vazquez-Montiel;
Alejandro Cornejo-Rodriguez
Show Abstract
The star test is conceptually perhaps the most basic and simplest of all methods of testing image-forming optical systems, the irradiance distribution at the image of a point source (such as a star) is give for the Point Spread Function, PSF. The PSF is very sensitive to aberrations. One way to quantify the PSF is measuring the irradiance distribution on the image of the source point. On the other hand, if we know the aberrations introduced by the optical systems and utilizing the diffraction theory then we can calculate the PSF. In this work we propose a method in order to find the wavefront aberrations starting from the PSF, transforming the problem of fitting a polynomial of aberrations in a problem of optimization using Genetic Algorithm. Also, we show that this method is immune to the noise introduced in the register or recording of the image. Results of these methods are shown.
Numerical study of surface-enhanced Raman scattering (SERS) by a radial distribution of molecules covering a single metal spherical particle
Author(s):
F. R. Perez;
A. Salazar;
Johnson Garzon Reyes
Show Abstract
We present a computational model to analyze the electromagnetic contribution to Surface Enhanced Raman Scattering (SERS) based on Lorenz-Mie scattering for a single metal spherical particle covered by a shell of molecules, immerse, all the system, in a dielectric medium. In the model, all molecules are assumed to be an electrical dipole at fixed direction: the same of the linear polarization of the exciting plane electromagnetic field. The volume occupied for the molecules is twice the volume of the particle. A constant radial of molecular density is considered. The enhancement factor, EF is defined as the ratio of the total scattered power by the system particle-molecules to the total scattered power by the same distribution of molecules in the same dielectric medium. We study the EF for particles with radii between zero and 350 nm. Three wavelengths are used: 532, 633 and 382 nm. A comparative analysis between particles of copper, aurum and silver is presented. The 459 cm-1 Stokes line of carbon tetrachloride is studied.
Spherical aberration analysis of a uniaxial Cartesian oval
Author(s):
M. Avendano-Alejo;
M. J. Orozco-Arellanes;
Orestes Nicholas Stavroudis
Show Abstract
In early published contributions we obtain ray tracing formulas for uniaxial crystals. In the present contribution we show the ray tracing for an uniaxial cartesian oval, when the crystal axis lies in the incident plane. The uniaxial crystals have two refracted rays (ordinary and extraordinary rays). When the object is placed at infinity, the ordinary rays have a common focus called the distal focus. For the extraordinary ray the uniaxial cartesian oval show spherical aberration produced by the medium itself. In order to reduce the spherical aberration we analyze several cases for the orientation of the crystal axis, this improve the performance on this optical design.
Huygens principle in plane waves
Author(s):
J. A. Romero;
L. Hernandez
Show Abstract
The article presents results corresponding to the mathematical formulation of Huygens' principle for plane waves. We show the deduction of an integral relationship as the basis of the above-mentioned principle. By using this integral formula and the properties of the electrical field vector of the plane waves, a vectorial equation to describe Huygens' Principle is obtained. To corroborate the validity of the solution to problems, which may arise using the vectorial equation, we proved that such solutions fulfil Helmholtz' homogeneous equation. Subsequently the density of energy of the secondary waves was determined. In order to illustrate this method, we found an exact analytical equation that describes relative intensity of the diffracted light as a function of the distance from the center of the aperture. For the first maxima and minima, the intensity behavior is similar to the one predicted by Fresnel's theory. However, for distances near to the aperture, the difference is remarkable. Afterwards, we did a comparative analysis among the results obtained and Fresnel's theory, and new approaches were established. It must also be pointed out that contrary to previous methods; the present formulation is dealt with a vectorial analysis without recurring to any approximations.
Study of surface modes at gyroelectromagnetic gratings in conical mounting
Author(s):
Miriam L. Gigli;
Marina E. Inchaussandague;
Ricardo A. Depine
Show Abstract
We study the diffraction of electromagnetic waves at periodically corrugated isotropic-gyroelectromagnetic surfaces, in the index-matching situation, when the plane of incidence forms an aribtrary angle with the main section of the grating ("conical mounting"). It is shown that, under these conditions, eigenmodes can be excited at certain angles of incidence, which can be calculated. We analyze the variation of the position of the anomalies when the orientation of the plane of incidence is varied, for different orientations of the optic axis and different wavelengths.
Sampling theorem in fractional Fourier domains
Author(s):
R. Torres;
Pierre Pellat-Finet;
Yezid M. Torres Moreno
Show Abstract
The standard Fourier transform operator F is a particular case of the fractional order Fourier transform operator Fα (it is obtained for α = 1). In the same way that has been done for F, a sampling theorem for Fα is proposed for signals whose fractional Fourier transforms of order α have finite supports. An interpolation formula for fractional bandlimited functions is also deduced.
Propagation of light in structured volumetric mediums
Author(s):
B. P. Iguanero;
Gabriel C. Martinez-Nikonoff
Show Abstract
In this work we analyzed light propagation by using coupling mode theory in multiple diffractive structures. The diffraction phenomenon confines the optical field for this reason is possible to control the propagation of light throughout specific trajectory. Experimental synthesis was implemented by using arrays of linear gratings and zonal plates. The study is generalized by using the model of angular spectrum. Experimental results are also shown.
Beam-propagation method based on the fractional order Fourier transform
Author(s):
Cesar O. Torres Moreno;
Yezid M. Torres Moreno
Show Abstract
A new formulation of the classical scalar beam-propagation method is derived by use of the fractional order Fourier transform. The method relies on the fundamental fact that the coherence is transformed by a linear filter univocally connected to the filter acting on the electric field; building on this result, we solve exactly the problem of the passage of such fields through arbitrary lossless optical system characterized by their ABCD matrices.
UVB and erythemal solar radiation on tilted planes in Valencia, Spain
Author(s):
M. J. Marin;
E. Sanudo;
Maria Pilar Utrillas;
Jose Antonio Martinez-Lozano;
Fernando Tena
Show Abstract
A preliminary analysis of experimental UVB and erythemal solar radiation data measured in Valencia a Mediterranean coastal site in Spain, is made. The data have been recorded by means of four broadband radiometers YES UVB-1 recently installed by the Solar Radiation Group of the University of Valencia. One of them measures global horizontal irradiance. The second one has a shadowband for the measurement of diffuse horizontal irradiance. The other two instruments record global irradiance data on planes inclined 45° alternating North-South and East-West orientation. The results show some differences between UVB irradiation on horizontal and tilted surfaces and also among the different orientations. The irradiance received in horizontal position is higher than on the others planes and the daily maximum value is reached at noon in horizontal, North and South positions whereas on East plane it happens before the noon and after the noon in West orientation. This kind of measurements allows the evaluation of the UV Index corresponding to solar radiation on tilted surfaces with different azimutal angles. The differences between horizontal UV Index and North UV Index are of three units. In contrast on the South is of one unit at the most.
Lidar measurements of atmospheric parameters at CEILAP, Buenos Aires, Argentina
Author(s):
J. C. Dworniczak;
L. Otero;
Andrea F. Pazmino;
Eduardo Jaime Quel;
M. Raponi;
J. Salvador;
O. Vilar;
Elian Wolfram;
Pierre H. Flamant;
Javier Fochesatto;
Sophie M. Godin-Beekmann;
Jacques Porteneuve;
Pablo R. Ristori
Show Abstract
The lidar systems contribute with privileged information to study environmental pollution due to its capacity to discriminate different atmospheric parameters in time and space. In this work, three of those system were developed at CEILAP laboratory in Argentina (34° 33' S, 58° 30' W): 1) a Multiwavelength lidar to characterized the atmospheric boundary layer and tropospheric aerosols using a Nd:YAG laser (10 Hz, 650 mJ @ 1064 nm); 2) a Raman lidar to measure night-time water vapor profiles, useful as a tracer of air parcel and in understanding energy transport within the atmosphere. This system utilizes an excimer laser (XeCl) (100 Hz, 300 mJ @ 308 nm), and 3) a differential absorption lidar (DIAL) to measure the stratospheric ozone profile. Two laser are used, the same excimer laser of Raman lidar and a Nd:YAG laser (30 Hz, 950 mJ @ 1064 nm). Complementary in situ measurements are also performed with a sun-photometer (AERONET-NASA); UVA, UVB and GUV radiometers (Argentina Solar Monitoring Network), pyranometer and a pyrgeometer. Recent results and the synergy between the actives and passives instruments are showed.
Spectral distribution of the solar ultraviolet irradiance measured at Buenos Aires, Argentina
Author(s):
M. Raponi;
Elian Wolfram;
J. Pallotta;
L. Otero;
J. Salvador;
Eduardo Jaime Quel;
Ruben D. Piacentini
Show Abstract
The solar radiation at Earth surface is measured usually with instruments of narrow or large wavelengths bands. However, for different applications like the determination of irradiances related to biological actions and substance and material degradations, it is needed to know the spectrum at all wavelengths with reasonable resolution. In CEILAP (CONICET - CITEFA) placed at the Gran Buenos Aires suburbs (34° 33' S, 58° 30' W, 20 m asl), we made measurements of solar UV irradiance in clear sky days in the UV range (300 - 400 nm) range with a spectroradiometer Monospec 27 of National University of Rosario. The data represented in a 3D diagram show the variations in the solar spectrum along the day as function of the solar zenith angle. From the comparison with the results obtained employing the TUV program developed by Madronich/NCAR that solves the radiative transfer equation, it is possible to determine the influence of the ozone and aerosol atmospheric components on this irradiance. The spectra were calibrated against the absolute measurements made with an instrument GUV 541 at wavelengths of 305, 320, 340 and 380 nm, which is placed in the same building and was recently calibrated.
Radiometry through spatial coherence wavelets
Author(s):
Roman Castaneda;
Jorge Ivan Garcia-Sucerquia
Show Abstract
Generalized radiance was introduced for analyzing the behavior of radiant surfaces in any state of spatial coherence. Some of its properties make difficult to interpret it physically. In particular, generalized radiance is a Wigner distribution function that can take positive and negative values, so that it does not have the meaning of an energy flux at all. Supported on the concept of radiator pairs we will express the generalized radiance, the generalized radiant emittance and the generalized radiant intensity first proposed by Marchand and Wolf. Then, we will analyze the extreme cases of spatially coherent and incoherent sources and propose a new physical interpretation for the negative values of the generalized radiance.
Reproducibility improvement in color measurements of periodic objects
Author(s):
Jose-German R. Cortes-Reynoso;
Jose Guadalupe Suarez-Romero;
Juan Bautista Hurtado-Ramos;
Eduardo Tepichin Rodriguez;
Juan Carlos Solorio-Leyva
Show Abstract
A common and known problem in textile industry is the measurement of color and of their fabrics for quality control. Commercial equipment is limited to color measurements of objects with homogeneous surfaces. In the case of samples with no-homogeneous surfaces it is recommended the use of accessories such as an integrating sphere that averages the in-homogeneities along with the averaging of several measurements taken for different orientations of the sample. However, single measurements with these devices are still not precise enough. In order to solve this problem we proposed a novel system for color measurement of periodic objects. In a first stage we have presented novel illumination geometry capable to produce an homogeneous illumination over periodic objects. The measurements were made with a two-aperture radiometer which is coupled to the illumination setup. This system was used to measure the reflectance produced by a textile sample. In this work, we present the second stage, where the system is improved in order to measure color directly from textile samples. We present the results from a comparison between our system and a commercial one.
Interinstrumental agreement between spectrocolorimeters
Author(s):
J. Carranza Gallardo;
J. Medina
Show Abstract
The aim of this work is to generate a scheme for the intercomparation of spectrocolorimeters which have the same optic configuration of illumination/viewing, in chromatics coordinates L α b in base to the ASTM recommendation E1164-02. In order to quantify the agreement interinstrumental of these equipments, we were utilized five Materials Reference Standard (MRC), in five points of the CIEL α b color space. The scheme proposed in this work can be applied in colorimetry to discriminate the existent of variations in chromatics coordinates CIEL α b generated for samples that can not taken as standards.
The size-of-source effect in practical measurements of radiance
Author(s):
Juan Carlos Solorio-Leyva;
Jose Guadalupe Suarez-Romero;
Juan Bautista Hurtado-Ramos;
Eduardo Tepichin Rodriguez;
Jose-German R. Cortes-Reynoso
Show Abstract
One of the main sources of error when making precise measurements of radiance is the one associated to the variation in the output signal of the radiometer due to changes in the size of the source. This effect is known as the size-of-source effect (SSE). It is observed experimentally that as the size of the source increases, the output signal of the radiometer increases as well. No standard method for measuring the SSE exists. The SSE is estimated as the ratio of the output signal at a given diameter of the source to the signal at a reference diameter. One method considers this reference diameter as the diameter of an infinite source. A second method sets the reference diameter to the largest diameter experimentally possible. Commonly, the second method is the one used since it is more practical. However, the first one is a better model, even though the limit to infinite is not available experimentally. In this work, we discuss a formal method to calculate this limit. The limit can be used in the first method for a better quantification of the effect in practical measurements.
Pseudocolor engraving prints using signal processing methods
Author(s):
D. Hoelck;
J. Barbe
Show Abstract
In this contribution we propose an application for pseudo-color engraving-prints. Usually, the prints that are made with relief and intaglio techniques, are black and white images composite by a group of binary lines. Several texture and gray levels are obtained changing direction and density of lines in the print. We propose an application based signal processing methods to pseudo-color black and white prints. The proposed method can be done in real time using a white light optical correlator. The different color channels R, G and B could be encode simultaneously using a color film for filter representation. In this way the pseudo-color processing can be done in one cycle of the optical processor.
Measuring small color differences in the nearly neutral region by 3CCD camera
Author(s):
Edison Valencia;
Maria Sagrario Millan Garcia-Verela
Show Abstract
A method to evaluate the discrimination capability of a camera to measure small color differences in the nearly neutral region is proposed. We focus on the camera's performance in the nearly neutral region of the color space because: it represents a challenge for the instrument (these colors entail a similar stimulation of the RGB channels) and, second, these colors concentrate industrial interest, particularly related to materials for clothing or decorating. The method proposed has two stages. Firstly, we determine the appropriate working conditions of the acquisition system (SONY DX-9100P camera). Secondly, we select two sets of matte Munsell samples, regularly distributed in the Hue circle with low Chroma and Values. These two sets of samples are the very pale color and the dark grayish color sets. Each selected chip is compared with all its nearest neighbors of the Munsell color system under D65 illumination. CIELAB and CIEDE2000 formulae is used to estimate color differences. All the color differences are separately evaluated in pairs by the camera and by a reference instrument (spectroradiometer Photo-Research PR-715). We test the reliability of the camera's performance by comparing the results obtained by both the camera and the spectroradiometer.
Laplacian filter based on color difference for image enhancement
Author(s):
Maria Sagrario Millan Garcia-Verela;
Edison Valencia
Show Abstract
The use of the Laplacian operator to enhance grayscale images by edge sharpening is widely known. The discrete application of this operator is made by convolving a mask whose kernel computes the weighted differences between neighbor pixels. The operator was extended to color images by applying it to each R, G, B, component separately and combining the result to yield the enhanced color image. In this work we apply the Laplacian operator to a color image by computing color differences between neighbor pixels in the CIELAB (CIEDE2000) space. The perceptual channels of Luminance, Chroma and Hue are used to obtain the resulting enhanced color image. N4 and N8-neighborhoods are considered. The results are compared with those obtained using the RGB channels separately. Using the Laplacian based on color difference, we obtain improved edge sharpening and artifact reduction in the resulting image.
Segmentation of envelope address blocks through fractal-based approach
Author(s):
L. F. Eiterer;
Jacques Facon;
D. Menoti
Show Abstract
In this paper, we propose an approach to automatically locate address blocks in postal envelopes based on fractal dimension. First, the fractal dimension of a postal envelope image is computed. The K-means clustering technique is then used to label pixels as stamps, postmarks, and address blocks.
Intensity-invariant recognition, vector spaces and camouflage
Author(s):
Henri H. Arsenault;
Pascuala Garcia-Martinez
Show Abstract
From the point of view of vector spaces, intensity invariant pattern recognition corresponds to identifying vectors independently of their length, which means that such methods consist primarily on measuring angles between vectors in vector spaces. We describe a few such methods that have proven to be efficient for various intensity variations of targets in unsegmented natural scenes. The conventional wisdom for camouflage states that the best camouflage is one that breaks up the lines of objects, so most camouflage schemes are binary. We discuss the best methods of detecting such camouflage objects in natural scenes.
Unified approach for document segmentation
Author(s):
Horacio Andrés Legal-Ayala;
Jacques Facon
Show Abstract
In this paper, we propose a unified approach for document segmentation. Differently of others techniques that segment images without a priori knowledge about the classes to be segmented, this approach carries out a previous learning of what must be segmented. The learning is carried out using only two images, the original one and its ideal segmented version. This stage generates a decision matrix, which is used to extract the similar semantic information in new images. The knowledge acquired in the decision matrix is explored by means of KNN strategy. Performed tests on different types of document images, like signature, postal envelopes and old document databases for instance, showed significant and promising results. It must be emphasized that this learning segmentation approach is completely automatic, does not require heuristics, and may transform the subjective human operator's knowledge into an automatic process and reproduce it.
Numerical simulation to align a segment mirror
Author(s):
J. Fausto M. Escobar-Romero;
Fermin-Solomon S. Granados-Agustin;
Alejandro Cornejo-Rodriguez
Show Abstract
A technique of great help in the optical test is the subaperture method, this method is proposed to align the segments of a primary mirror of telescope, using the ideal form of the primary mirror, which is defined using the sagita z(x, y). When the surface under test is segmented each segment has a sagita zi(xi, yi) that is rotated and displaced with regard to the reference system of all surface, where i = 1, 2, ..., n, with n is the number of segments. Some numerical simulations are shown to align two segments of a mirror using the subapertures method using the least square algorithm to align the segments.
Applications of a holographic system with mutually incoherent polarized light beams
Author(s):
Salvador Guel-Sandoval;
L. R. Berriel-Valdos;
A. V. Zamora-Gomez
Show Abstract
Using a holographic system, where the source beam is composed of two beams incoherently superimposed, it is possible to make use of the fact that the picture-sensitive medium that registers the information is able to record several holograms simultaneously or one by one and make them to interfere at the reconstruction step. This is in fact nothing new, except when each hologram is recorded with different state of polarization. Then we can watch interference between them independently of the polarization state used during the recording step, since any reconstructed hologram always preserve the state of polarization of the recovering wave.
Fiber Bragg optimization using parallel processing and genetic algorithm
Author(s):
M. J. de Sousa;
L. Villar de Souza;
C. Sales Jr.;
Joao Claudio Chamma Carvalho;
Carlos Renato L. Frances;
Joao Crisostomo Weyl Albuquerque Costa
Show Abstract
In this work are presented two designs of fiber Bragg gratings optimized by using genetic algorithm and parallel processing. The results achieved show the robustness of that technique when applied to complex search spaces. Besides, it is shown that the use of the parallel processing improves the performance of genetic algorithm.
A technique of optical pattern recognition with rotational invariance
Author(s):
N. I. Toto-Arellano;
G. Camacho-Basilio
Show Abstract
The optical pattern recognition system of joint transform correlation has a disadvantage. It doesn't work under rotation of test object. In this work we show the experimental results of a technique for rotational invariant optical recognition which is based on a ring detector acting as filter. This correlator has the disadvantage of not present scale invariance of the objects under test. In addition, a theoretical analysis and simulation results are illustrated here with the use of an advanced mathematics software package.
Joint-transform correlator tolerant to distortions of the objects to detect
Author(s):
C. La Mela;
Claudio C. Iemmi
Show Abstract
In this work we combine the advantages of photorefractive joint transform correlators (JTCs), with synthetic discriminant function filters, giving rise to a distortion-tolerant photorefractive JTC. We use a liquid crystal television display working as pure phase modulator to represent, side by side, a phase codified scene and the generated reference.
Fractional Fourier transform of two-dimensional signal with DSP device
Author(s):
Joaquin Alfonso Cornejo;
Yezid M. Torres Moreno
Show Abstract
Taking advantage of the high speed arithmetic offers by the parallelism of the digital signal processor DSP TMS320C6711 of TI, we implemented two algorithms to find the Fourier transform of fractional order of two dimensional signals ("The discrete fractional Fourier transform" and "Fractional Fourier Transform calculation through the fast-Fourier-transform algorithm"). As a result, we have two algorithms for calculate the fractional Fourier transform of images using a DSP, the images are captured using a camera CCD and the fractional Fourier transform is display in a monitor, both are connected to the DSP device directly. Finally, the work focuses in the evaluation of this algorithms, in order to find which is best performance related to four criteria determined from the properties of the Fourier transform of fractional order: The inverse transform, fractional Fourier transform of order one or standard Fourier transform, fractional Fourier transform of order zero or operator identity and order additivity.
3D reconstruction of complicated objects by gray code method
Author(s):
J. Meneses;
D. Amaya;
Z. Valderrama
Show Abstract
In this work the Gray code method for numerical 3D reconstruction of complicated objects was implemented. Based on structured projection, the Gray code method projects in different binary patterns. Grouping this sequence, this sequence of patterns allow to describe 2n different directions of projection, where each direction corresponds to a word in binary code. Thus, each point in the observation field corresponds to a unique binary code that can be identified in the digitized image. The surface object introduces a lateral shift of each binary word in relation to the reference plane. A digital procedure that identifies each code, allows calculating the lateral shift and the corresponding height. The technique of gray code is easy to implement, it is flexible to the size of the object and it can resolve discontinuity objects. The system was designed to reconstruct human faces and was evaluated using objects of well-known form. Experimental results are presented and discussed.
Three-dimensional surface reconstruction based on laser triangulation
Author(s):
C. Lizcano;
M. Marquez
Show Abstract
At the present time, a great number of applications exist that need the reconstruction of three-dimensional surfaces, such as: medicine, reverse engineer, industrial tasks and virtual world recreation. A system of reconstruction of surfaces was made up of three parts: capture of image, calibration of the camera and generation of a mesh from the cloud of three-dimensional points (3D). The data 3D is captured using the principle of triangulation between a camera or receiver, a generator of structured light (emitting laser) and the object. The capture of the image is made through a digital camera, having used a set of algorithms developed in Borland C++ Builder5. For the camera's calibration the method of flexible calibration was implemented (Zhang, 2002), which consists of a solution of closed form, followed by a nonlinear refinement based on the criterion of maximal probability. In order to generate the three-dimensional surface a rectangular mesh was create using a set of B-spline curves.
Encryption for security using optical fractional Fourier transform
Author(s):
Z. Lizarazo;
Yezid M. Torres Moreno
Show Abstract
In this work we proposed one optical setup for encryption based in the fractional Fourier Transform. The Fourier transform of fractional order add another degree of freedom, of course the degree fractional used, for the optical encryption realization. The inverse fractional Fourier transform is perform by phase conjugation. This technique allows use the optical setup for encryption and decryption simultaneously. Based in experimental results and numerical simulations we find that is not arbitrary the use of the keys for encryption and decryption operations. The optical fractional Fourier transform has been obtained using the Lohmann type I configuration and a photorefractive crystal BGO working as mirror phase conjugation has been used.
Application of digital holography in the calculation of displacements
Author(s):
J. L. Valin;
Edison Goncalves;
Fernando F. Palacios;
J. R. Perez
Show Abstract
Digital Holography is applied to make micro-displacements determination of a steel bar and an aluminum sheet. The displacement of aluminum sheet is made under immersion conditions in water and air. An experimental installation is presented for digital holograms registration with plane reference beam, using a CCD camera as detector. The "HOLODIG" computing system was developed for digital reconstruction of the image using the direct method, the intensity and phase image and interferograms were obtained. Taking into account the phase interferogram and making the unwrapping, the phase was determined for every point of the study surface. As examples of method application the displacement of a square section steel bar, tested in air, and an aluminum sheet, tested in air and submerged in water, were determined. Experimental values of the displacement obtained agree with the applied ones. In the case of aluminum plate submerged in water, the magnitude of the measured displacement is proportional to water refraction index.
Correlation between visual acuity and pupil size
Author(s):
Silvia A. Comastri;
Rodolfo M. Echarri;
T. Pfortner
Show Abstract
The eye suffers from aberrations that are pupil size dependent and reduce visual performance. Pupil size is often disregarded when visual performance is clinically determined. Considering 23 normal eyes, under natural viewing conditions, visual acuity is here related to pupil size when each subject reads monocularly a Snellen chart of constant luminance placed at 2m.
Full retrieving of the complex degree of spatial coherence through the spot moments
Author(s):
Roman Castaneda;
Jorge Ivan Garcia-Sucerquia;
J. F. Carrasquilla
Show Abstract
In this work a method for retrieving the magnitude and phase of the complex degree of spatial coherence is shown. To apply it only the recording of the spot intensity is required. Afterwards, centered reduced moments of the spot are calculated, in order to use them as coefficients of a series to expand the complex degree of spatial coherence. Experimental results for Schell-model spots are shown. The Fourier spectra corresponding to the experimentally recorded sots, are calculated in order to show the equivalency between the proposed method and the Fourier one.
DC term filtering techniques in digital holography
Author(s):
Jorge Ivan Garcia-Sucerquia;
J. A. Herrera Ramirez;
Daniel Velasquez Prieto
Show Abstract
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
Author(s):
Jorge Ivan Garcia-Sucerquia;
J. A. Herrera Ramirez;
Roman Castaneda;
Daniel Velasquez Prieto
Show Abstract
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.
Anamorphic holographic lenses composed by two volume holographic elements
Author(s):
Manuel V. Collados;
Jesus Atencia;
J. Tornos;
Manuel Monton Quintanilla
Show Abstract
We design and construct anamorphic holographic lenses composed by two volume holographic elements. We study their efficiency and their capability to perform the multi-channel Fourier transformation. We test the behavior of an anamorphic optical processor constructed with these holographic lenses.
Lateral displacement of the refracted beam in an isotropic-unixial interface
Author(s):
Liliana Ines Perez;
Maria C. Simon
Show Abstract
The comprehension and determination of the properties of limited beams that propagate or reflect and refract on all kind of interfaces, have become of the greatest interest because of the present and future applications in linear and non-linear optics. As it is known, when there is total reflection on an isotropic or an anisotropic interface, the reflected ray suffers a displacement on the interface that has been studied by a great number of authors. However, if an isotropic-uniaxial interface is considered, the condition of total reflection for one of the refracted rays can be fulfilled whereas the other subsists as a propagating wave. This leads to the existence of a complex displacement of the maximum associated to the propagating beam. We analyze this displacement and its relation with the phase shifts that the waves that synthesize the propagating beam suffer. We consider a beam with symmetric distribution of amplitudes that impinges on a general isotropic-uniaxial interface (i.e. without separation of modes).
Photorefractive speckle pattern amplification
Author(s):
Myrian C. Tebaldi;
Nestor A. Bolognini;
L. Arizmendi
Show Abstract
Photorefractive crystals make possible an efficient energy transfer from the pump beam (reference) into the signal beam. The coupling of interacting beams in dynamic hologram recording in photorefractive media can be utilized to produce an image amplification whose action is based on a light-induced change of the refractive index. A speckle distribution is characterized by a randomly varying intensity and phase. In our case, we consider a speckle distribution and a plane wave as the interfering beams inside a BSO crystal. The incident beam ratio of the two interfering beam depends on the speckle beam intensities and an statistical distribution of the beam ratio appears in the crystal. Under this condition, the speckle amplification is analyzed. When the reference beam is phase shifted, a local amplification is observed in the reconstructed speckle beam. The amplification is studied in terms of the input mean intensity of the speckle beam, the pupil aperture diameter of the imaging lens and the external applied voltage.
Coma-free diffractive optical element
Author(s):
Juan M. Simon;
Silvia A. Comastri
Show Abstract
Holographic optical elements recorded employing an object beam originated at a point can act as image forming systems free from aberrations if the reconstruction and reference beams coincide. However if these beams are tilted, aberrations often appear. In this article, a diffractive optical element free from coma is predesigned and numerically tested.
Interference and diffraction effects generated by multiple apertures
Author(s):
Orlando Quintero;
John Freddy Barrera;
Rodrigo H. Henao;
Francisco F. Medina-Estrada
Show Abstract
The effects of interference and diffraction produced by a bidimensional structure composed of multiple and identical apertures are studied. The apertures have different shapes, sizes and spatial distribution. Such effects are competitive during the propagation, that is, in some planes the interference effects are more visible, while in others prevail the diffraction ones.
Influence of the off-axis illumination and the finite object dimensions in the Talbot effect in a tapered GRIN media
Author(s):
M. T. Flores-Arias;
Carlos C. Gomez-Reino;
Maria Victoria Perez Martin;
Carmen Bao
Show Abstract
The irradiance at Talbot images in tapered gradient-index (GRIN) media for ideal periodic objects is presented. The effects on Talbot images due to off-axis illumination and finite object dimension are considered. Results have been applied to a hybrid structure composed by a divergent linear tapered GRIN medium and a sinusoidal amplitude grating to show transverse shift and finite apperture diffractive effect on the Talbot images as well as the walk-off effect.
Resonant modes in nested diffraction gratings
Author(s):
Angela N. Fantino;
Susana I. Grosz;
Diana C. Skigin
Show Abstract
The diffraction problem of a plane wave impinging on a grating formed by nested cavities is presented. The nested cavities are formed by layers of perfectly conducting sheets that describe rectangular profiles. The problem is solved by means of the modal method, for s and p polarization modes. The electromagnetic response of the grating is analyzed, paying particular attention to the generation of resonances within the structure. The dependence of the resonances on the geometrical parameters of the grating is studied, and results of far and near field are shown. The results were checked and found in good agreement with those available in the literature for certain limit cases.
Speckle pattern illumination: two applications
Author(s):
Fernando Perez Quintian;
Maria A. Rebollo
Show Abstract
The speckle pattern produced by a translucent diffuser which is itself illuminated by another speckle pattern is studied. The decorrelation of the resultant speckle pattern by a lateral displacement of the diffusing surface is shown to be related to the standard deviation of the slope's distribution and to the illuminating speckle grain size. Therefore, measuring the intensity decorrelation as a function of the surface displacement it is possible to obtain information about the diffuser slope distribution. Reciprocally, we show that a statistically characterized diffuser can be used to measure the mean size of the illuminating speckle grain.
Varifocal zone plates obtained by moire
Author(s):
Rodrigo H. Henao;
A. Mira;
Zbigniew Jaroszewicz;
Andrzej Kolodziejczyk
Show Abstract
Moire patterns in the form of equilateral hyperbolic zone plates have been studied. They are created by a mutual rotation of basic grids which turn out to be zone plates described by conic curves and include as a special case hyperbolic and elliptical zone plates. The obtained moire zone plates change their focal length in function of the rotation's angle between the superposed grids that generated them and therefore they can be of interest in three-point method used for determination of small displacements of great engineering structures. Simulations as well as experimental results are presented.
Two-source method in digital holographic contouring
Author(s):
J. R. Perez;
Edison Goncalves;
R. de Souza;
Fernando F. Palacios;
Mikiya Muramatsu;
J. L. Valin;
Marcos R. R. Gesualdi
Show Abstract
Using digital holography the two-source method was applied for shape determination of a groove on an Aluminum plate. The electric component of the electromagnetic field, on the image plane, was reconstructed using the Fresnel-Kirchoff integral and Fourier method and digital holograms were captured changing the fiber optic position with a micro positioner. The phase interferogram was filtered by means of the sine/cosine filter and for the unwrapping process was applied the branch-cut method. This object present real discontinuity and the experimental results agree with the expected one, with high quality intensity image. The quasi-3D phase presentation shows the object shape.
Real-time holographic interferometry using photorefractive Sillenite crystals with phase-stepping technique
Author(s):
Marcos R. R. Gesualdi;
Diogo Soga;
Mikiya Muramatsu
Show Abstract
This work applies a holographic interferometer setup that it uses the photorefractive Bi12SiO20 crystals for Real-Time Holographic Interferometry (RTHI) in diffusive regimen with configuration exhibiting difraction anisotropy. This device is connected with an interferogram-analysis method that uses the phase-stepping technique for quantitative measurement of changes on object. So we captured holographic interferograms from test surface, and calculated the phase map, using images by Four-Frame Method, and removed the wrapping of tangent function (unwrapping), using the Cellular-Automata Technique. We are obtained good results in applications in basic research, dentistry and technological areas.
Simple method for multiplexing channels in a Fourier optical processor
Author(s):
S. Palma;
J. Barbe;
Juan Campos;
Claudio C. Iemmi
Show Abstract
One of the most popular devices used into optical processors to display the images are the liquid crystal spatial light modulators (LCSLMs). Many applications in signal procession tasks use images with less resolution than the modern LCSLMs can be support. In this contribution we propose a new method based in a spatial multiplexing that uses the high resolution of the modern LCSLMs to introduce several channels in an optical correlator. The proposed method for the channels codification is based onto multiresolution analysis. Given an RGB image, before it will be displayed in LCSLM screen, a computer decompose the image in R, G and B channels and for each channel calculates a set of 50%, 25% and 12.5% scaled replicas. Then, in the place of the image, the computer send to LCSLM screen a composite scene with the original image and its replicas. Each of the images displayed in the scene defines one different channel in the optical correlator. In order to prove the method we develop an application based on signal analysis using a bank of 16 Gabor filters, that decompose the signal in 16 frequency channels (four orientations 0°, 45°, 90°, 135° and four frequencies 1/4, 1/8, 1/16, 1/32 cycles/pixels). With the proposed channels codification, a complete set of 16 filtered R, G and B images can be obtained using only 4 cycles of the optical processors, that minds that we increased the speed of the processor by factor 4.
Testing conical surfaces using digital superposition of Ronchi-grams
Author(s):
B. Cabrera-Perez;
J. Castro-Ramo;
Alfonso Padilla-Vivanco;
Alberto Cordero-Davila
Show Abstract
In optical workshops, Ronchi test is used to determine the optical quality of any concave surface while the surface is in the polishing process its quality is verified based on the technician experience. We describe a method based on digital image superposition between a real Ronchigram with an ideal obtained by a computer simulation program. The real Ronchigram image is processed by an erosion algorithm to obtain its skeleton. We supposed a linear relationship between the separation of each fringe for both experimental and ideal fringes, to obtain in this way the desired surface. Such method allows us to compute in a direct way the transversal aberration of the surface under test.
Study of signals from dynamic speckle patterns
Author(s):
Angel G. Augier Calderin;
A. Rolo Naranjo;
D. Rivero Ramirez
Show Abstract
In study of dynamic processes, information on parameters of system can be obtained from the changes in corresponding dynamic speckle pattern. Examples of these processes are biological, chemical or biochemical reactions, changes in molecular populations, changes in absorption, reflection properties or refraction index of a medium, superficial dynamics process, crystal dissolution, particle movement and others. In the present work the generation and counting of pulses corresponding to signals obtained from dynamic speckle patterns, and a study of some signal processing methods, in particular the analysis of pseudo-phase portrait are shown.
Numerical holography computing by using the fractional Fourier transform: a ping-pong-pang algorithm
Author(s):
R. Torres;
Pierre Pellat-Finet;
Yezid M. Torres Moreno
Show Abstract
An iterative algorithm for computing holograms is presented: it is based on the fractional order Fourier transform. It allows us to generate diffraction patterns which are not in the Fourier plane. It also makes possible the design of computer generated holograms providing two beforehand given illumination patterns on two preselected planes. Holograms have been calculated according to the proposed method and have been engraved by photolithography. Experimental results are given. A speckle reduction technique is also explained.
Pseudoscopic white-light imaging by means of two bi-dimensional diffracting elements and a pinhole
Author(s):
Jose Joaquin Lunazzi;
D. S. F. Magalhaes
Show Abstract
Diffracted images with inverted depth were first reported by the authors where a lens or slit intermediated the white-light double diffraction process. The diffracting elements were simple straight line diffraction gratings and the image could be seen but not projected due to its strong astigmatism. The generalization of the symmetry properties to bi-dimensionally defined diffracting elements allows to produce projected images with circular gratings intermediated by a pinhole. Acting as a focusing element, the possibility of enlargement is reported here with experimental results.
Orthoscopic white-light imaging by means of two bi-dimensional diffracting elements and a pinhole
Author(s):
Jose Joaquin Lunazzi;
Noemi Ines Rodriguez Rivera
Show Abstract
Diffracted images with inverted depth were first reported by the authors where a lens or slit intermediated the white-light double diffraction process. The appearance of an image with orthoscopic relief was reported, generated with the same system consisting of simple straight line diffraction gratings. We report now that the generalization of the symmetry properties to bi-dimensionally defined diffracting elements eliminates the vertical astigmatism of the images.
Cantor fractal zone plates: numerical simulation and experimental characterization
Author(s):
J. A. Rodrigo;
Tatiana Alieva;
Maria L. Calvo;
Jeffrey A. Davis;
L. Ramirez
Show Abstract
We study experimentally and by numerical simulation the Fresnel diffraction on the recently introduced fractal zone plates (ZPs) associated with Cantor sets. The focusing properties of these ZPs and the evolution of the intensity patterns at the plane transversal to the propagation direction are discussed. As it follows from numerical simulation the series of conventional and doughnut-like secondary focuses are observed around the principal focus. The position, depth and the size of these focuses depends on the type of Cantor set and the level of the fractal, which are directly related to the number of the corresponding Fresnel zones. The results obtained by numerical simulations are verified in the experiments. The fractal Cantor ZPs of different levels are implemented with a liquid crystal display and with the diapositives. The experimental results obtained by both types of the dispositives are in good agreement with the theory and numerical simulations.
Fractal diffraction properties in tapered GRIN media
Author(s):
Osvaldo J. Trabocchi;
Carlos C. Gomez-Reino
Show Abstract
This paper analyzes the light propagation in a tapered gradient-index medium when the input signal is a binary fractal function. Analtical expressions for the diffracted field at the Fourier transform plans of the inhomogeneous medium are obtained. The results show self-similarity properties at specific plans of the GRIN.
Temporal evolution of speckle in foams
Author(s):
A. Martinez;
C. Ortiz;
Hector Jorge Rabal;
Ricardo A. Arizaga;
Marcelo Trivi
Show Abstract
When an optically rough surface illuminated by a laser evolves in time the scattered light gives rise to a dynamic speckle pattern and its variation depends on the activity of the sample. Biological samples show this behavior but it also can be observed is some other dynamic processes such as drying of paint, corrosion, heat exchange, blood flow, vibrations, etc. In this work we present a dynamic speckle phenomenon that occurs in the development of foams. The experimental results show the time evolution of the samples and offer a potential applicability of this measurement technique to the assessment of this type of processes.
Focusing of a chirped pulse train in phase opposition through linear chirped fiber grating (LCFG)
Author(s):
L. Chantada;
Carlos R. Fernandez-Pousa;
M. T. Flores-Arias;
Carmen Bao;
Maria Victoria Perez Martin;
Carlos C. Gomez-Reino
Show Abstract
There exists a well-known analogy between the paraxial or one-dimensional Fresnel diffraction and the propagation of pulses in linear dispersive medium with negligible attenuation. Under this analogy, the envelope of a pulse is equivalent to the distribution of complex amplitude of the light in diffraction. In this context, we study the propagation of a train of identical Gaussian chirped pulses arranged in time in the same way as the Fresnel zones of a phase zone plate, in a highly dispersive guiding medium. From this study we find that the input train focuses in an only pulse, for certain values of total dispersion. We establish the focusing condition and characterize the output signal through its width and peak intensity.
Study of the surface roughness in metals with different surface finishing by two-dimensional correlation of laser speckle pattern
Author(s):
Miguel Asmad;
Guillermo Baldwin-Olguin;
C. Maczeyzik;
Fernando Mendoza Santoyo;
Carlos Perez-Lopez
Show Abstract
In this work we use an experimental setup implemented in the Optical Physics Laboratory of PUCP, in order to study and to measure the roughness of surfaces with different surface finishing as milling, turning, etc. The measurement method is based on a two-dimensional scan of scattered light like from rough metal surface when the surface is illuminated by laser light. The light is scattered likes speckle in all space and arrives onto the CCD of a digital camera. The speckle images of rough surfaces are captured at different angles of illumination. We have analyzed the dependence between the structure of speckle and the surface roughness. Using two-dimensional Fast Fourier Transform it has been possible to compute the correlation between speckle pattern images and find out the relationship between surface roughness and speckle patterns decorrelation for different metal surface finishing.
Speckle contrast dithering simulations
Author(s):
G. H. Sendra;
Hector Jorge Rabal;
Marcelo Trivi;
Ricardo A. Arizaga
Show Abstract
Algorithms used to process a speckle image are limited by the resolution of the CCD camera and the employed digitalization system. We propose the use of dithering procedures to increase the intensity discrimination and improve the contrast resolution. This technique consists in decreasing the quantification error by performing several measurements to which a random value is added in each measurement before detection. Hence, it is possible to find a more approximated value to the real one. The precision increase results from the use of multiple images to which a determined white-light intensity has been added. This work shows the results of applying dithering to improve the precision of methods that use speckle contrast. It is a frequently used quantity in the implementation of activity images and in the determination of surface roughness. Numerically simulated images were used to verify the reliability of the technique whose intensities were later quantified for processing. The observed mean squared error is lower when this technique is employed, and the level of improvement depends on the size of the used windows. A device for the experimental verification of the results is in the design stage.
Refraction holodiagrams with birefringent elements
Author(s):
Karin V. Gottschalk;
Hector Jorge Rabal;
Maria C. Simon
Show Abstract
Holodiagrams developed by Abramson and known as tools that permit the analysis of the geometrical aspects related to different optical phenomena are here extended using them when the elements that change the direction of light propagation are refractive and are composed by both isotropic and birefringent materials. Given the role of the optical axis in birefringent materials, the constructed holodiagrams consider the case when it is in the direction joining the two foci (source and point of observation). The curves obtained, representing the loci of constant optical path have a complicated shape that differs from the already known for isotropic materials. The total reflection phenomenon in the interface between such materials is also considered.
The digital fractional correlator utilized for character recognition: a comparative study
Author(s):
Cesar O. Torres Moreno;
Lorenzo Mattos Vasquez;
G. Mestre;
Yezid M. Torres Moreno
Show Abstract
Some properties of digital correlation based of the fractional Fourier transform are analyzed. We generalize the architecture of a VanderLugt correlator to achieve the VanderLugt fractional Fourier transform correlator such that fractional correlation can be obtained. In this situation the Fourier transform in the classical VanderLugt is replaced by the fractional Fourier transform, and four different VanderLugt fractional architectures can be implemented. The performances of such a correlator are analyzed according to the standard criteria of signal-to-noise ratio, correlation sharpness, peak-to-correlation energy, and Horner efficiency. Here the binary image of a character is used for the test.
Analysis of multi-element resonators using the fractional Fourier transform
Author(s):
Cesar O. Torres Moreno;
Yezid M. Torres Moreno
Show Abstract
In this paper we demonstrate that the propagation of a light wave into multi-element optical system can be treated in the framework of the fractional Fourier transform. This result provide new insight into wave propagation and multi-element resonators as well as the possibility of exploiting this result as a mathematical tool in analyzing such systems. This mathematical formulation gives the direct relationship between input and output of the light field, the confinement stability condition, the diameters of the beam at the mirrors and the diameter of the beam waist.
Laboratory teaching in optics: formation x information and the physics and engineering students
Author(s):
Armando Dias Tavares;
R. J.M. da Fonseca;
L. P. Sosman;
L. A.C.P. da Mota
Show Abstract
The way laboratory work should be conducted and the effectiveness of the two major usual approaches for doing that are discussed. The mapping of problems presented by both these methods is discussed in the context of their application in the Education of physicists and engineers at undergraduate level. The challenges posed by trying to teach as much as possible, in as little as possible time, for as much as possible people are analyzed and some solutions are proposed.
JAVACOLOR: an instructional model for teaching the physics of color
Author(s):
A. Villamarin;
O. Alvarez;
E. Orozco;
R. Munoz
Show Abstract
In this work we applied the Gagne instructional model to the design and development of a JAVA web page by teaching and learning of the basic physics of the color address to undergraduates optics courses. The color simulations were development interactive and friendly for running at different operative systems. The pages were structured in two parts: (1) Theory: Color, Physics of color, Digital Color; (2) Practice, Simulation of additive mixture, color models, color matching and separation mechanism. The page includes links to specialized sites. The instructional design was validated using experts criteria and tested with learners of third years optics course at the Universidad De Carabobo.
Northwest Argentinean archeoptics: nanotechnology?
Author(s):
Pablo Ixtaina;
D. C. Schinca;
Mario Garavaglia
Show Abstract
In an excavation performed in 1999 at the Campo del Pucara, Alamito site, which belongs to the Condorhuasi Culture (from 0 to 500 AD), and is placed near the frontier of Catamarca and Tucuman provinces in the Northwest of Argentina, Victor Nunez Regueiro and Marta Tartusi Paz found an intriguing archaeological artifact: Remains of a thin slab of schist covered by a mica sheet, dated from 360 and 480 AD. The mica was analyzed by photometric and interferometric procedures and experimental results suggest that it behaves as an interferential dielectric mirror.
Structural characterization of microcrystalline-amorphous hydrogenated silicon samples prepared by PECVD method
Author(s):
A. Orduna-Diaz;
M. Rojas Lopez;
V. L. Gayou;
R. J. Delgado-Macuil;
V. H. Mendez-Garcia;
R. E. Perez-Blanco;
E. Rosendo
Show Abstract
Microcrystalline-amorphous doped hydrogenated silicon (μc n+ a-Si:H) samples were prepared by using plasma enhanced chemical vapor deposition (PECVD) method. The samples were deposited on corning substrates at 270°C and then were annealed at 250°C during several hours. Raman scattering spectroscopy was employed to study the amorphous-microcrystalline (μc/a) phase transition and the subsequent microcrystallization process as a function of the annealing time. It was found that the conductivity of the material is closely related to the normalized Raman intensity of the LO mode. In this work, such relation is explained in terms of the impurities activation and by the hydrogen effusion, which takes place during the annealing process. Samples morphology was characterized by atomic force microscopy (AFM). Crystallized silicon islands were observed with an average diameter depending on the annealing time.
Laser-induced phase changes of metallic Ti and W thin films
Author(s):
Rodger Evans;
Santiago Camacho-Lopez;
Raul Rangel-Rojo;
M. A. Camacho-Lopez;
Celia A. Sanchez-Perez;
A. Esparza-Garcia
Show Abstract
In this work we present experimental findings in the field of laser matter interaction on the topic of laser induced oxidation and crystalline structure change. It has been shown in the past few years that lasers can be used to induce both oxidization of metals as well changes the crystal in the crystalline structure of the metal oxide. Conventional theory has proven to be mildly successful in predicting these effects with a thermal model; drawing its influence from the traditional method of inducing material change by baking the metal. We reformed a scan of varying values of laser intensity and accumulated fluence. We will show evidence of an increase in the oxygen content in Ti and W thin films irradiated by a frequency doubled Nd:YAG laser source with a pulse duration of 4 ns and per pulse energies of 26 to 60 μJ (peak intensities of 1.7 x 107 to 3.8 x 107 W/cm2). We will also show that other effects, that may include crystalline structure change, are also occurring.
Calculations of the light scattered from an infinite-sloped surface using the Kirchhoff approximation
Author(s):
Neil Charles Bruce
Show Abstract
Recently a modification of the Kirchhoff approximation was presented to permit the calculation of the multiple scattered light in rough surfaces with infinite slopes. Here we present a brief description of the method and examples of the scattering of light from rough surfaces with rectangular grooves. The examples presented here show how the scattering pattern changes from a periodic surface to a random surface. The randomness is added to the groove width, separation and depth separately to investigate the effect of each of these parameters on the scattering.
