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.

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.

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.

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.

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.

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.

We report on a new source of coherent red-light with perspective applications in laser photodynamic therapy. The red light is generated through stimulated Raman scattering (SRS) process by acetone of a frequency-doubled Nd:YAG nanosecond laser radiation (532 nm). The Stokes transition is found at 630 nm and with spectral line narrowing similar to the pump one. When pumping using the radiation from a Rhodamine-6G Dye laser (560 - 575 nm), tuning between 640 and 670 nm is demonstrated. Conversion efficiencies up to 50% are reported.

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 R_crit. 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 R_crit 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.

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.

Porphyrins can be degraded by light. Photogem is a photosensitizer used in PDT in Brazil. Photogem irradiation at 514 and 630 nm change its fluorescence and absorption due to photodegradation and photoproducts formation (new absorption band in 640 nm). Irradiated Photogem was incubated with tumor or non-tumor cells. The low toxicity suggests that the photoproducts of Photogem are less cytotoxic than the original formulation.

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.

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.

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.

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.

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.

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.

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.

In this paper, we will describe a method used to obtain the power error distribution map for a spherical well corrected ophthalmic lens. The proposed method uses a computer to perform a null test compensation to probe the real refractive correction state of the lens under test. The Hartman test is used to probe an ophthalmic lens and subtract the ideal power distribution map corresponding to the same lens design. In this way we obtain the power error distribution map of the lens. The proposed method may be useful in mass production of spherical ophthalmic lenses.

This paper describes a simple Hartmann test data interpretation that can be used to evaluate the performance in spherical ophthalmic lenses. Considering each spot of the Hartmann pattern like a single ray, using traditional ray tracing analysis it is possible to calculate the value of the spherical power in the point corresponding with each spot. The values of spherical power for each spot obtained by this procedure are used to obtain a spherical power distribution map of the entire lens.

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.

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.

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.

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.

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.

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.

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 K_I values were obtained. For L-deprenyl (IC₅₀ = 0.017 μM and K_I = 0.019 μM) and berberine (IC₅₀ = 90 μM and K_I = 47 μM) were in agreement to the values obtained with a standard method and literature reported.

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.

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.

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.

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 (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.

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.

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.

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.

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.

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.

In this work, we show a simple single lens system using laser light illumination to observe flow dynamics. It is based on a phase contrast technique in which the filter is made of a nonlinear optical material, therefore it is self-aligned and depends mainly on the illuminating intensity. Due to these characteristics, the resulting setup is extremely robust and builds up within a few milliseconds.

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.

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.

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.

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 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.

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."

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.

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.

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.

In this communication we demonstrate the implementation of an external cavity fiber grating laser with a side mode suppression ratio higher than 40 dB utilizing a Fabry-Perot laser diode with a facet containing an antireflection coating which thickness is controlled by a technique allowing the direct observation of the laser resonance behavior during the application process.

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.

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.

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.

We present a design of an Er-doped fiber amplifier (EDFA) with high amplification. The purpose of the device is amplification of low power pulses from laser diodes to powers sufficiently high for investigations of optical fiber nonlinear processes. The optical amplifier consists of two stages. As the first stage we use the reflecting configuration where a signal is amplified twice in the same Er-doped fiber. The second stage works as a high power amplifier. The input pulses have pulse duration of 1 ns - 100 ns, and wavelength 1549.1 nm. The maximum amplification of this design is 50 dB. We obtained the output pulses with maximum power of 50 W. These pulses were used successfully to investigate the NOLM and SRS.

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.

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.

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.

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%.

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.

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.

A wavelength-switchable fiber ring laser that includes a Bragg grating-based acousto-optic modulator is reported. When a longitudinal acoustic wave propagates along a fiber grating, it modulates periodically the effective period, which causes that additional bands of reflection appear on both sides of the Bragg wavelength. Wavelength switching of the laser emission is achieved by dynamic adjust of the peak reflectivity of the different bands.

We have succeeded in continuous-wave laser oscillation on ⁴I_13/2 → ⁴I_15/2 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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

We consider the propagation of a pulse light in a given medium and in the case of electro-magnetic induced transparency. It is showed that the propagation regime is superluminar or subluminar depending upon the difference between the Rabi frequency and the sum of the reciprocals of the lower states lifetimes in the so-called Lambda configuration scheme.

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.

We show how to study the fine and hyperfine structure spectral properties of an exciton in a semi-conductor quantum dot using the standard formalisms of quantum mechanics.

We have developed a method which yields the real and the imaginary parts of third-order susceptibility of material media. We have applied this method to determine the nonlinear refractive index (n₂) of new synthesized organic materials in the picosecond regime (30 ps pulse duration at 1064 nm wavelength). The results obtained show the efficiency of this technique for measuring low values of the nonlinear refraction coefficient n₂ in diluted materials.

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.

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.

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.

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.

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.

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.

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.

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.

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 LiNb_O3 crystals and the photorefractive lens effect (self-focusing and self-defocusing).

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.

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.

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.

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.

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.

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.

We present the polarization dependence in the formation of dark spatial waveguides in nonlinear liquids like CS₂. Our experimental and numerical results about the formation of dark waveguides show the dependence between the polarization and the formation of multiple waveguides. With a polarization angle between 100° - 120° for the incident beam we show that the wide of the waveguide is minimum and even dark spatial waveguides are formed. A discussion about waveguides formation is presented for others polarization angles. In this work we show an improvement in the method to measure low birefringence in optical fibers.

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.

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.

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.

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 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.

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.

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.

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.

We analyze diffraction gratings behavior recorded on a phase holographic emulsion. This emulsion is composed with resin and bromophenol blue dye (BPB) they have a diffraction efficiency (η) from 0.22 to 0.615% order, and their thickness are different in the holographic emulsion.

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.

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.

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.

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.

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.

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.

This paper presents a combined system based on DSPI and local heating, which alows the evaluation of residual stresses. To determine the residual stress values, a finite element analysis (FEA) of the thermomechanical process is carried out. The feasibility of this approach is demonstrated by comparing the results obtained from measurements in a preloaded specimen and the stress values introduced in it.

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.

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.

In this work some frequencies and modes of vibration of a thin plate were determined using interferometric methods like: real-time holographic interferometry, time-average holographic interferometry, digital speckle pattern interferometry DSPI. And the results obtained are compared with those obtained with the program of finite elements COSMOS.

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.

We present a new algorithm that applies the correlation functions to phase shifting interferometry to recover the phase of a test surface. In this work we make numerical simulations to test the algorithm and the results are verified with real interferograms. The correlation algorithm recovers the phase value with 5% accuracy.

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.

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.

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.

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.

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 λ_o/2 at λ_o = 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.

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.

Nowadays there are a lot of optical interferometric tests, but there is no doubt the most used, among the lateral shear interferometry is the Ronchi test. In this work we implement the Bi-Ronchi test by generating a square Ronchi ruling onto a LCD. Phase shifting interferometry and a matrix method were used to recover the wavefront aberration. Plots of the surface under test and wavefront abberations are also shown.

The nonlinear common path interferometer is a simple and robust single lens optical processor using an intensity dependent medium placed on its geometrical focal plane to observe deformed wavefronts. It is described either as a nonlinear inteferometer or as an image processor. We demonstrate that this system requires excess surrounding illumination beyond the geometrical boundaries of the disturbance to operate. We discuss recent progress on this setup. In particular, the effect of large phase changes in the filter and the dynamics of the filter formation.

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.

The interferometric techniques of lateral shearing and white light scanning interferometry are combined to determine the variations of thickness of phase objects and the thickness of such objects is approximated through B-splines functions.

Xiang developed a method for the measurement of radii of curvature of optical surfaces greater than one meter, this method is used for spherical concaves and convexes surfaces, at the vertex; the error is of 0.1%. In this work are carried out some innovations to the method of Xiang, for measurements of local radius of curvature of conical concaves and convexes surfaces. Some results obtained are for a parabolic surface.

We propose a novel spatial light modulator (SLM) characterization method based on ellipsometric techniques, in which the Jones matrix describing the SLM polarization capabilities can be obtained and then used for any arbitrary configuration of the device. We have used it to characterize a reflecting SLM (analogue ferroelectric liquid crystal from Boulder Nonlinear Systems).

An implemented system to evaluate the deformations that a CD under thermal loads undergoes is described, and the developed software of evaluation is discussed. Interferograms obtained for each deformation state are showed and the graphs of deformation like relief maps, with the height of the deformations codified in color code, too.

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.

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.

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.

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.

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.

We experimentally investigated the transmission variation of a nonlinear optical loop mirror (NOLM). We analyzed the transmission evolution of the NOLM based on the input intensity. The NOLM is formed by a symmetrical coupler, 500 m of highly twisted low-birefringence fiber and a quarter-wave retarder plate in the loop. If we rotate the quarter-wave retarder plate is possible to change the transmission behavior. Using circular polarization of the input beam is possible to get a high contrast between the maximum and minimum of the transmission. With this characteristic, we have the possibility to reduce the amplitude fluctuations and the pedestal in a train of optical pulses.

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.

This paper is about a numerical investigation of the NOLM (non optical loop mirror) with low birefringence fiber and a 0.5/0.5 coupler. We induce birefringence to the loop fiber bias macro bendings considering self-rotation polarization of the input beam. This is done in order to find its possible advantages as an optical switch.

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.

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.

We present the first results of nano-patterning in poly-methyl methacrylate (PMMA) photo-resist using a 46.9 nm tabletop extreme ultraviolet (EUV) laser. As a proof of principle, we recorded a Fresnel diffraction pattern of a copper mesh with 19 μm square holes. Results of ongoing interference experiments will also be presented.

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.

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.

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.

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.