Abstract not available.

In recent years, researchers have demonstrated that various types of optical spectroscopy can be used to perform noninvasive, real-time and in-situ diagnosis of tissue pathologies, especially cancer. In this overview of the topic, various spectroscopic methods are described. The promises and hopes, as well as the difficulties of these developing techniques are discussed. UV-induced fluorescence spectroscopy and elastic-scattering spectroscopy are addressed at some length, and infrared-absorption spectroscopy and Raman spectroscopy are more briefly discussed.

The second-order hyperpolarizabilities of two groups of organic materials, retinal derivatives and mesoionic compounds, are obtained through measurements of nonlinear optical susceptibilities. The Z-scan technique was employed to characterize the sign and magnitude of the third-order nonlinear optical coefficient, whilst the Kerr Gate method was employed to infer the response time of the nonlinearity with 60 fs resolution. From these measurements, supported by quantum chemical theoretical calculations, the origin of the nonlinearity was determined for both materials.

Severe communications based on chaos have been investigated for some years, especially in the area of radiofrequency transmissions. Signal decoding and decoding is then generally achieved using a RF carrier whose amplitude fluctuates chaotically. Recent advances have also been reported in the field of optical telecommunications. Optical chaos produced by random fluctuations of laser power is then used to encrypt signals. However most of the systems reported so far are plagued by their low flexibility which makes difficult the key to be changed easily. We report experiments in which chaos in wavelength, rather than in power, is advantageously used to encrypt signals. The latter are encrypted as chaotic fluctuations of the wavelength of a tunable semiconductor laser driven by a generator of chaos. Decoding makes use of another generator of chaos operating as a local oscillator synchronized on the first one. The first results are reported in the wavelength range of 1550 nm.

We introduce the beam coherence-polarization matrix as a tool for dealing with beam shaped fields that are at the same time partially coherent and partially polarized. Such matrix can capture differences between physically distinct beams that would appear identical in a scalar description. Examples are given.

We review amplification and lasing without inversion (AWI and LWI) in homogeneously broadened closed three-level systems in the framework of both density-matrix and quantum- jump formalisms. With the density-matrix formalism: (1) we study the nature of quantum interference in these systems; (2) determine analytically the conditions for AWI and locate the position of maxima and minima in the probe absorption spectrum; and (3) study various regimes of lasing, namely, continuous wave, self-pulsing and giant pulse lasing. Within the quantum-jump formalism we calculate the relative probabilities of the various physical processes responsible for probe field amplification and absorption.

Several years after the discovery of Raman scattering of light, solid state Raman lasers are beginning to reach the stage of commercial applications. This talk will review the basic concepts of Raman gain with a special emphasis on Raman laser crystals. Examples of spectroscopic properties of important materials are presented. The use of these materials in shared-, coupled,- and external-resonator Raman laser systems is described. Design parameters affecting efficiency, beam quality, and temporal pulse width are discussed. Examples will be presented of the use of these lasers for transmitters in atmospheric lidar, marine imaging lidar, adaptive optics guide-stars, and materials processing applications.

Fourier optics, with early developments in the 1940s through the early 1960s, was introduced to optics educators largely through the appearance in 1968 of the book Introduction to Fourier Optics by Joseph Goodman. Over the past three decades evolutionary changes in perspective on the subject and its teaching have led to changes in the classroom, and continuing can be expected. This paper presents the historical background for those evolutionary changes and documents some of them. It concludes with a discussion of directions the teaching of this important subject might take.

Gaussian beams are an important fundamental concept of optics. They occur naturally in the treatment of laser beams and resonators, and can also be used as a basis for study of general diffraction problems. However, a limitation of the usual formulation of Gaussian beams is that they are derived using a paraxial approximation. This breaks down when beam divergence is large. Moreover, for investigation of the polarization properties of beams a vectorial treatment is necessary. Numerous authors have considered correction terms which extend the validity of the beams to higher divergence angles. An alternative is to derive a form of beam which is an exact solution of the wave equation for the scalar case or Maxwell's equations for the vectorial case. This can be accomplished using the complex source point method. However, this leads to the presence of unphysical singularities. These can be avoided by introducing complex sink-source pairs. The resulting solution is a rigorous solution of Maxwell's equations which reduces to a conventional Gaussian beam for small angles of divergence. The resonance conditions for a resonator can be derived. Various different polarizations can also be considered, including plane polarized, transverse electric and transverse magnetic modes.

Color cameras usually have a device called white balance that allows one to capture a white reference without predominant colors. In this work we analyze the compensating mechanism of white balance in a color CCD camera to evaluate if the compensation permits to establish resemblances with the process of color constancy that takes place in the human visual system. We use common lightings and a camera with dichroic mirrors and three CCD sensors to capture a color image with color quality.

In the present work Bi thin films were obtained by Pulsed Laser Deposition, using Nd:YAG lasers. The films were characterized by optical microscopy. Raman spectroscopy and X-rays diffraction. It was accomplished the real time spectral emission characterization of the plasma generated during the laser evaporation process. Highly oriented thin films were obtained.

PZT thin films were deposited by laser ablation at high vacuum and at room temperature. After that, some of the samples were annealed at air in the temperature range 450 degree(s)C - 550 degree(s)C. The samples were characterized by XPS and X-ray diffraction. A decrease in the oxygen composition of the as-deposited sample was observed. In the as-deposited film metallic lead (Pb) appeared. The as-deposited analyzed film showed a weak crystallization. A posterior annealing of the as-grown films improved their crystalline structure. This annealing treatment provoked the disappearance of the metallic Pb bonds in the films.

Polycrystalline SrFe₁₂O₁₉ thin films were deposited on Si (100) substrates by PLD using a Nd-YAG laser ((lambda) equals 1064 nm). During the deposition process substrates were kept at room temperature. As-deposited films were annealed in air at temperatures between 600 degree(s)C and 840 degree(s)C. Samples were characterized by AES, ESCA, SEM, AFM, x-ray diffraction and VSM. It is presented the relevance of the preparation of the target surface on the film quality. Some differences in the chemical composition of as-deposited films, compared with the target and the annealed films, were observed. The x-ray diffraction spectra show a textured as- deposited films. Samples annealed at 600 degree(s)C, and below, showed a very weak magnetic response. In contrast annealing in the temperature range 700 degree(s)C - 840 degree(s)C led to the formation of a nanocrystalline particle system (average particle size 150 - 350 nm) which behave as a single domain in the thermally demagnetized state. The obtained coercivities (5750 - 6850 Oe) are among the highest values reported for films, powders and sintered samples.

A generalization of Talbot effect to the case of a tapered gradient index medium is considered. An initial linear periodic object illuminated by a coherent light beam is shown to repeat through this medium. Self-image positions are changed by a function depending on the taper profile parameter, the illumination parameters and the object period.

A novel and efficient method for Bessel beams generation is proposed. It relies on using a toroidal zone plate as an element forming the ring focus and subsequent Fourier transforming of the ring focus into the Bessel beam. The proposed solution, thanks to focusing of all illuminating wave into the ring focus allows to achieve greater efficiency than earlier solutions. Moreover it enables to generate higher order Bessel beams by adding a linear angular phase term to the transmittance of the zone plate. The proposed method is confirmed by numerical simulations.

The aim of this work is to generalize the fact that the diffraction efficiency of an holographic volume grating is different for the E-mode polarization and the H-mode polarization in the situation of incidence within the grating recording plane, to the case of incidence in conical mounting. It is shown, from both a theoretical and an experimental point of view, the influence of the angle that forms the incidence vector wave with the recording plane in the diffraction efficiency of two orthogonal reference polarizations and the way the hologram rotates the light polarized in a direction into light oscillating in the orthogonal one.

We present experimental results of the Mueller matrix associated to GaAs on the (001) direction, with a Si concentration of 8 X 10¹⁷ cm^-3. Laser light of 632.8 nm wavelength was used and there were taken measurements on the scattered light employing an scatterometer of the Angle-Resolved Scattering type and for an incidence angel of 10 degree(s).

Here a method for data storage by means of multiplexing 3D holograms is considered. The method consists in shifting the recording material with respect to a reference speckle wave. The experimental data on the dependence of the diffraction efficiency of the hologram with respect to the shift is presented. The general scheme of data storage in 3D-speckle shift hologram is considered and presented. It's shown that this kind of hologram substantially outperforms all other types for the number of cells (pixels) in which information can be stored. At the same time, the noises that are inherent in a 3D-speckle shift hologram restrict the density of the information storage.

The theoretical and experimental study of the diffraction efficiency of a volume transmission diffraction grating when illuminated by an arbitrary direction reconstruction beam was realized. It was found that on the contrary of what is usually expected, the diffraction efficiency could be increased by a rotation of the grating around its K vector, although the exact Bragg condition is no longer satisfied. Theoretically, the diffraction efficiency can be increased up to 100% for any grating, if we discard the reflection on the grating boundary, and absorption on the holographic media.

By using the transfer matrix's method we present an analysis of the transient dynamics of the fundamental mode resonating in a self-adaptive holographic laser oscillator. The resonator consists of a nonlinear medium in a self- intersecting geometry, a lens and an output coupler mirror. We find that the mode exhibits an stable evolution through the self-consistent solutions. Additionally we present useful results for the spatial control of the mode and the improvement of the phase conjugation process.

We present gratings that use pseudorandom sequences for obtaining missing diffraction orders, with high light throughput. We report first experimental verifications.

The learning process requires always an active critical participation of the students. This is specially true for science and technology students. In this communication we will present the results of a pedagogical experiment undertaken, since 1995, within the classes of Image Processing of the Applied Physics undergraduate course of the Physics Department of the University of Minho. We decided to center students' learning process of the basics of digital image processing on simple applied research programs. To the students is given almost entire liberty and responsibility. We limited ourselves to assess the development of the project orienting them and point out different or pertinent points of view only when strictly necessary.

A quasi distributed optical fiber sensor is proposed, aimed to measure strain in electrical power conductor cables. The sensor uses a series of Bragg gratings as optical transducer elements along the conductor. Preliminary results are presented.

A technique for the extraction of laser rate equation parameters to be used in the simulation of high-speed optical telecommunication systems is described. The simulation using the extracted parameters exhibits good agreement with the experimental results, even for a large current modulation and soliton pulses. A model, which represents the parasite effect introduced by the mount fixture, was built. The model presented here is ready to use in the simulation of high-speed lightwave systems.

We have combined a fusion-pulling technique and a standard metal-coating technique to fabricate in-line single-mode fiber filters, polarizers and sensors. The reduction of the core and cladding diameters in a tapered fiber causes the evanescent field to extend beyond the outer boundary. Thus, when a metal film is evaporated on a tapered fiber, the surface plasma modes cause coupling to the fiber mode.

It was used an optical fiber with a 100 mm long chirped Bragg grating to compensate the chromatic dispersion of data transmission systems. Dispersion compensated transmission over 80 Km standard single mode telecommunication fiber is demonstrated. The results show that may not be necessary the control of the chirp of the transmitted optical pulses.

Recent developments in the construction of Erbium-doped fibers have seen parallel progress in the measurement techniques to characterize these fibers. In this paper, we discuss a simple method of obtaining threshold power amplification of Erbium-doped fibers. The method can be used to measure the threshold power of this particular fiber. As a result, the predicted threshold power value is in very good agreement with the experimental results obtained. We have based our measurements of the amplified spontaneous emission on both the forward and the backward directions of the fiber axis. We also report on other parameters such as Erbium doping concentration, the spectrum of absorption, and cross sections, with the objective of obtaining data for comparison of predicted threshold amplification with actual threshold amplification, when the Erbium-doped fibers are used in laser systems.

In this work we present an analysis of the birefringence effects induced by external fields on passive fibers and, on the basis of this information, we propose an explanation for some effects observed in active fibers. To modify the passive fiber birefringence we have used external forces. The photo-elastic description of the birefringence induced by simple stresses is verified for short circuit cylindrical samples of silica glass (step-index and GRIN). Phase and polarization changes of light transmitted through these samples were studied using holographic interferometry and polarimetry. Using these results, a proposal is made to understand the polarization sensitivity of EDFAs. In the case of active fibers its birefringence was altered changing its geometrical shape. The amplifying performance of an EDFA built with a helically-wound active fiber was compared with that of an EDFA built with an irregularly wound erbium fiber.

White light interferometry can be seen as a multichannel process since each wavelength constitutes an independent information carrier. The simultaneous observation of different wavelengths allows the absolute evaluation of optical path differences (OPD). Two basic detection schemes are available which are chosen as a function of the application requirements. In the first one, all wavelengths are superimposed on the photodetector and we get a single composite output signal. Therefore, the OPD has to be scanned in order to detect the interference fringe pattern which appears only for OPD shorter than the light source correlation length. The second scheme consists to separate optically the different wavelengths for a parallel detection and to measure the absolute value of the OPD without any mechanical displacement of the interferometer. This paper explores the case of surface profilometry for the presentation of the latest proposed signal processing algorithms and to compare the capabilities and perspectives of those two approaches.

Digital speckle pattern interferometry (DSPI) is used to produce a fringe pattern representing speckle correlation changes. This fringe pattern has the same interpretation as that obtained with holographic interferometry. Remarkable features of this technique are the possibilities of real- time processing and software treatment. Due to these characteristics, DSPI becomes an attractive option to the non-destructive testing an evaluation. Through different analysis of the fringes, it is possible to get quantitative information about the correlation changes that gave rise to the pattern. We are going to introduce three alternatives of digital speckle to precision measurements: focal length (fringe positional changes), angle measurements (fringe visibility changes), and topography (digital fringe generation by moire). Theoretical demonstrations will be outlined and experimental results will be presented.

We have developed a program for phase shift measurement on fringes pattern. Our program has capability to measure displacement of vertical fringes, tilted, curvy, and circular fringes, because of the use of pattern correlation.

A novel method of phase reconstruction from high-spatial- frequency intensity patterns incorporates the technique of line integration of phase gradient to find the first approximation to the phase and the algorithm of successive approximations to find exactly the unknown phase. The error function is constructed to incorporate the measured intensity to assure rapid convergence.

The possibility of using a BSO crystal as a recording medium of specklegrams with carrying frequency fringes, to storage multiple interferograms, for uniform in-plane displacements, is presented. Experimental results are shown.

Since 1996 a lidar station is operated routinely at CEILAP (CITEFA-CONTCET), located in Buenos Aires suburb. The scientific objectives are related to environmental and atmospheric radiative budget studies. Two backscatter lidars operating at 532 nm and 308 nm are used to document the atmospheric boundary layer dynamics, and cirrus clouds and tropospheric aerosols radiative properties. The lidar measurements are made in conjuction with visible radiometer measurements on the same site and radiosoundings made twice daily at the nearby meteorological station. Atmospheric boundary layer measurements during daytime are conducted since 1996 on a regular basis using the backscatter lida.r operating at 532 nm, and more recently using a second lidar on the same site operating at 308 nm. Similarly, cirrus clouds and tropospheric aerosols measurements are conducted during clear days (e.g. without low clouds) since 1996 using the backscatter lidars. Since the late 1997 more interest is given to urban ABL dynamics in connection with pollution events, and biomass burning taking place in the tropical South America. It happened that such plumes can be frequently transported over the Buenos Aires area by large scale circulation

Nonlinear optical properties in thin layers are investigated near a phase conjugate mirror. By using a rigorous electromagnetic theory of volume gratings the wave distortion correction by phase conjugation is examined in a nonlinear Kerr medium and Agarwal's theorem is numerically demonstrated. At specific incidence angles guided modes are formed inside the layered structure. When the nonlinearity is increased optical bistability is observed in waveguide resonances. An analytic solution is developed to explain the numerical data.

We propose a new method for the measurement of nonlinear susceptibility of an optical material based on the recording of the total distortions of the wave-front of a light wave propagating through the medium. We compare the method with the usual Z-scan and EZ-scan techniques and demonstrate theoretically and experimentally the better sensitivity of the new method.

Mode locked Ti:Sapphire laser represent an important source of femtosecond pulses. In particular bidirectional ring lasers are useful tools for some measurements, such as: rotation sensors, and nonreciprocal optical effects. We have developed a numerical model to calculate the stability of a ring laser. We use this method to design bidirectional Kerr Lens Mode (KLM) Locked Ti:Sapphire laser. As a first step, in this work we test the accuracy of our model by comparing it with a unidirectional KLM locked Ti:Sapphire ring laser, which we designed and built in our laboratory.

We have shown the vortex structure of the dislocation appearing in a laser beam passing through a Gaussian lens induced in a cubical, non-linear media during self-action. We make such studies using focusing and defocusing Gaussian lenses both theoretically and experimentally.

We present a new variation of the Z-scan technique, which provides a sensitive method for measurement of the nonlinear refractive index of materials. The method is based on imaging of a top hat beam onto a blocking disk; therefore, it is very sensitive. In addition to greater sensitivity the method offers the advantage that it does not require a Gaussian beam, therefore it can be used with low energy lasers with any beam profile.

We propose a novel implementation of the Lau and Talbot effects. It employs a grating registered as modulation of birefringence in a Bi₁₂SiO₂₀ crystal. The systems proposed allow to control the visibility and in particular to reverse the contrast of the self images and Lau fringes by rotating an analyzer. A theoretical approach is outlined and the predicted behavior is confirmed by results obtained under different experimental conditions. We have taken advantage of the arrangements to demonstrate some applications.

An image synthesis from images of a pilled fabric sample illuminated under different orientations is proposed to improve the input used for pilling evaluation by image analysis. The image synthesis is based on the Karhunen-Loeve transform.

This paper presents a segmentation technique for sandstone microscopic images. A sintetized image is obtained by means of operations with three images captured by a CCD camera at a specific wavelength and different polarization angles between polars and analyzer. Thus it is possible to obtain some characteristics to define size and shape of sandstone grains.

We present a technique to implement the Boolean logic gates in polarization architecture using a dual beam arrangement. The method is based on the intensity beam modulation of linearly polarized laser light, through an array of polarizers placed in each beam path. These arrays are the inputs to the logical operations, which are achieved by the rotation of the incident light polarization direction. The output is represented by the superposition of shadowgrams resulting when both beams are brought together on a screen.

Intensity moments of any order are proposed and moments of low order (less than 2) are shown to be suitable for overcoming the problem of lack of data, due to turbulence non-stationarity, for correctly measuring higher order integer moments in atmospheric optical scintillation.

Optical methods are used to study the following problems in Fluid Mechanics: (1) propagation of solitary waves in water channels; (2) thermoconvective flow of petroleum-in-water emulsions; (3) flow distribution in combustion chambers; and (4) propagation of blood in human veins.

Pseudorandom sequences are strings of binary numbers with a binary autocorrelation function. This property is here exploited for implementing a lensless, nonshadow casting correlator for Theta-decoding.

We employ the Lau effect for substantially reducing the influence of binary multiplicative noise, on periodic patterns.

This paper presents a digital implementation of an out-of- plane target location system by means of a joint transform correlator (JTC). A sequence of images of the 3D scene is coded into a single performing an integration of each frame in the vertical sense. The coded sequence is used as the input plane of the JTC after binarization, Fourier transform is performed followed by removal of the DC term from joint power spectrum; finally correlation is evaluated.

It was implemented the Lau effect with a grating registered in a BSO crystal. Two different arrangement were analyzed. In both cases, it is possible to control the visibility and to produce the contrast inversion of fringes, by properly setting the pass plane orientation of an analyzer located at the crystal output.

In many optical recognition processes a multiple filters synthesis is required. These filters are usually computer generated holograms in which it is possible to codify different objects to be detected and eventually someone to be refused. In most cases the codification of all this information in binary media produces filters with low light efficiency due to the amount of dark zones, which imposes a practical limit to the amount of information to be codified. Synthesis of composed filters in color photographic films by using a polychromatic source, would allow us to increase the capacity to storage information.

In this paper we present a multichannel optical correlator for parallel pattern recognition. This architecture takes profit of the periodic pixelated structure of the Spatial Light Modulators. This structure produces several diffraction orders and each one of them may be considered as an information channel. An additional quadratic phase introduced in the filters separates the channels in the correlation plane. We give experimental and numerical results.

We present a display showing dynamic speckle local activity as that observe when coherent light illuminates biological samples (biospeckle). Regions differing in their activity are shown as different gray levels. Results obtained with seeds and drying of paint are shown. We propose its use in the determination of seeds viability, detection of corrosion centers and local variations in surface roughness.

The drying of paints was followed using the time evolution of the activity of dynamic speckle patterns. For processing the data an alternative method based in the use of the second order moment of the modified co-occurrence matrix of the time history of its intensity was used. The experimental results obtained were compared with gravimetrical techniques. The results are discussed on the basis of the knowledge of the coating drying process.

Several studies have been conducted that involved full scale investigation of rapid crack propagation (RCP) in polyethylene (PE) pipes. Greig & Ewing showed that the critical pressure in a plastic pipe, which governs RCP, is very sensitive to temperature and that stringent controls on operating and proof test pressures are required for large diameter PE pipes. Leevers and Yayla demonstrated with the S4 (Small Scale Steady State) test excellent correlation with the full scale test on smaller diameter pipes. Vanspeybroeck changed the S4 into the S5 (Small Scale Steady State Scum) test to avoid any decompression in the pipe sample and to simulate full scale testing. In this paper, we present some preliminary results of testing aided by holographic interferometry to determine stress fields associated with RCP.

We present the results of phase transitions measurements (state and structural) in pure metals (In and Sn) and in Zn- 21Al-5Cu alloy, using a photoacoustic technique. It is based on real time monitoring of the acoustic signal with PZT sensors after an excitation of the sample with laser pulses.

Optical triangulation, as a non-contact non-destructive method, extensively proved its usefulness on the topographic and dimensional inspection of objects and surfaces of use in the industrial world. In this communication we will make a brief presentation of the issue of the micro-inspection of the relief structure of rough surfaces by optical triangulation. The microtopographers developed at the Physical Department of the Universidade do Minho will be briefly described.

This paper describes the use of optical correlation speckle patterns to detect and analyze the metallic corrosion phenomena, and shows the experimental set-up used. We present some new results in the characterization of the corrosion process using a model based in electroerosion phenomena. We also provide valuable information about surface microrelief changes, which is also useful in numerous engineering applications. The results obtained are good enough for showing that our technique is very useful for giving new possibilities to the analysis of the corrosion and oxidation process, particularly in real time.

This work describes the application of mean intensity diffusion analysis to detect and analyze metallic corrosion phenomena. We present some new results in the characterization of the corrosion process using a model based in electroerosion phenomena. Valuable information is provided about surface microrelief changes, which is also useful for numerous engineering applications. The quality of our results supports the idea that this technique can contribute to a better analysis of corrosion processes, in particular in real time.

This article describes an approach to quantify the quality of thresholding-based segmentation on Brazilian bankchecks. The checks are previously acquired by scanner and soon after, their colored patterns are decomposed according to the HSI model. Several thresholding algorithms are then applied and an automatic evaluation of the results is carried out. The evaluation methodology is based on `performance assessment' of the character recognition rate from an optical character recognition.

Various techniques based on image processing are presented for the automatic quality control of textiles. General defects (shrinking, abrasion, etc.) are detected by using operations in the frequency domain. Local defects (broken threads, mispicks, double yarns, etc.) are detected using a method based on a multiscale and multiorientation Gabor scheme that imitates the visual coding in early human vision. Also pilling resistance is automatically evaluated in wear-and-tear fabrics by a new algorithm which combines operations in both the spatial and frequency domain.

This work studies theoretically the scattering of light from cylindrical rough surfaces. It is shown, for the conical diffraction configuration, that the mean intensity on an observation plane perpendicular to the cylinder longitudinal axis, is related to the statistical parameters that characterize the surface: the roughness (sigma) and the correlation length T.

We propose a method of designing and fabricating 2D random surfaces that scatter light uniformly within a specified range of angles and produce no scattering outside that range. The proposed method is tested by means of computer simulations. Preliminary experimental results are also presented.

All solid-state laser technology has produced high efficiency, ow cost, stable and portable devices. The effort done in Argentina to acquire know-how in this field is reviewed in this article. Three diode-pumped Neodymium lasers prototypes were constructed, a continuous-wave laser, an active q-switched laser and an active mode-locked laser. All the prototypes use the same pumping diode and collimating-focusing optics. The result was a simple laser kit with an easy access to all the laser and pumping optics, representing a good compromise between performance and cost.

Spatial coherence beams, which propagate from a non-regular grating to a Fraunhofer observation plane, yield spatial coherence Moire patterns. Furthermore, as a result of the analysis of the corresponding interferogram, an effective Moire grating is proposed. In both critical and Kohler's microscope illuminations, Besselian coherence beams propagate between the exit pupil and the exit window of the illumination system. The size of their coherence patches is determined by the field stop of this system.

We show that by using a binary spatial filter, and a square law detector, all the defocused OTF's are displayed in a single picture. This unique picture has as horizontal coordinate the spatial frequency, and as vertical coordinate the amount of defocus. The gray level variations of the picture are proportional to the values of the out-of-focus MTF.

Axicons designed as a tandem of one diverging lens and one converging lens burdened with spherical aberration are analyzed in this report. The principal features of the axicon's focal segment, such as the axial intensity distribution and the central core width, are determined with the help of the nonuniform stationary phase method and compared with the numerical evaluation of the corresponding diffraction integral.

We present a comprehensive interpretation of the defocused Optical Transform Function (OTF) in terms of the Ambiguity Function and the Wigner Distribution Function. This allows us to propose a geometrical approach to the physical OTF.

We present a family of apodizers with random transmittance for achieving high focal depth, without sidelobes along the optical axis. Numerical simulations illustrate the properties of these apodizers.

Two experimental setups, using the fourth harmonic of a Nd:YAG laser (266 nm), for producing Bragg gratings by the external method are described and their results presented and discussed. The two different setups allow the fabrication of gratings of controlled spectral bandwidth (0.3 to 5 nm) with peak position between 1.3 and 1.6 micrometers . The stability of the system and the possibility of writing type IIA gratings are also discussed.

We report the development of two lab prototypes for all optical clock recovery and optical synchronization, composed by a DFB semiconductor laser driven by a ultra-fast switching current circuit. It was verified that a fast switch of the laser bias current accomplished by the strong feedback in the external cavity induce the self-pulsation needed for correct operation. In the presence of optical RZ signals, the device leaves in natural pulsation frequency synchronizing with the input data.

We study the dynamics of a vertical-cavity surface-emitting laser with polarization isotropic optical feedback using the San Miguel, Feng, and Moloney model, which considers the role of carrier spin dynamics in both the conduction and the valence bands. Two transitions coupled to right- and left- circularly polarized light are coupled by spin-flip processes, which are characterized by the spin relaxation rate, (gamma) _s. With moderately strong optical feedback and close to the solitary laser threshold the laser dynamics depend significantly on the value of (gamma) _s. For low spin relaxation rates the time-averaged intensity often shows abrupt dropouts, similar to those observed in edge- emitting semiconductor lasers. Underlying the dropouts there is antiphase competition between the time-averaged orthogonal linearly polarized components of the electric field. For large values of the spin relaxation rate the dropouts tend to disappear and the time-averaged intensity is constant or nearly constant, depending on the stability of the linearly polarized states of the laser without feedback.

We analyze the influence of the lateral carrier diffusion on the modulation response including transport effects in ridge-waveguide multiple quantum well semiconductor lasers. It is found that the lateral carrier diffusion has a significant influence on the carrier spatial hole burning and the damping factor in the modulation response, but that the modulation bandwidth of ridge structure quantum well laser does no change.

It is shown that the photoacoustic signals generated at the high reflection mirror of a pulsed laser have a linear dependence on the incident energy, this allows us to acoustically measure the output energy with the advantage that there is no interference with the beam, as in optical measurements.

Modeling and predictions of discharge initiated lasers behavior has always been quite a task, often replaced by direct trial and error approaches, and more so when the electric discharge indirectly triggers a chemical reaction leading to population inversion. We introduce a suitable model for predicting the energy contents, power and shape of the output pulse of an HF laser operating both in multiline and single line modes. We simulate by computer the chemical kinetics of the substances originated from SF₆ and C₃H₈ by an electrical discharge. The model suppose an homogeneous composition of the gas: all effects that could modify that uniformity, as temperatures gradients, arcs, etc., were overlooked. We obtain accordance with experimental results: the laser shot before the electrical discharge was finished and the cooling of the incoming gas mixture shows a significative increase of the spectral power of the laser pulse.

We show that the Montgomery objects are self-fractional- Fourier transforms. We relate, with a simple formula, the order of self-imaging with the fractional order of the Fourier transform.

The marginal cross-spectral density, a Wigner distribution function allows us to determine the structure of spatial coherence beams. The Fourier spectrum of spatially partial coherent interferograms is described by a triple correlation, which involves the cross-spectral density of the illuminating optical field and the transmittance of the aperture.

Here we study the focusing properties produced by apertures having supergaussian ring profiles, which contain the narrow ring as a limiting case. The supergaussian rings are compared with equivalent ring pupils for different amplitude transmission widths. Numerical results show that both types of pupils produce superresolution with great depth of focus (DOF). Though the annular pupil produces in general higher values of the superresolution and DOF for a given amplitude transmission width, the supergaussian ring concentrates better the energy into the focus.

We obtain that the irradiance impulse response along certain axes of an optical imaging system, that suffers from primary spherical aberration and longitudinal chromatic aberration, can be calculated from 1D integrations in a single 2D phase- space representation, the Wigner distribution function associated with a certain azimuthally-averaged version of the pupil of the system. This result is applied to study the response along the optical axis of unstable laser resonators and optical systems working under polychromatic illumination.

By means of the rigorous integral equations describing the electromagnetic wave scattering, not subject to the constraints of electrostatic and/or dipolar approximations, we calculate the scattered electromagnetic field in the vicinity of random fractal metal surfaces. We study the classical electromagnetic enhancement, due to the excitation of surface plasmon polaritons, responsible in part for the SERS. The dependence of the field enhancement on substrate, excitation wavelength, fractality, and polarization is analyzed.

A new and simple method, the dynamic angle limited integrated scattering measurement technique is developed to examine light scattered from clean optically smooth reflective surfaces with random roughness. We present three new systems which have several advantages over the conventional angle resolved scattering (ARS) system. As scattered light is collected in a given solid angle, the measurement system does not require a detection unit with an extremely dynamic range. Unlike in the common ARS measurement system, in this method a linear movement is adopted to scan scattered light. This technique can be applied to the in-workshop inspection of the optical polishing process.

We describe a ray picture for predicting the irradiance distribution generated by Zernike's three-slits experiment.

We present an overview of recent experiments we have done concerning the observation of photoassociative ionization in a cold sample of trapped sodium atoms. In a second stage, the process is used as a prototype to demonstrate the possibility of optical manipulation of interatomic collisions. This effect could be explored to manipulate the thermodynamical properties of a sample of degenerated quantum gas.

We review an extension of the optical coherence theory to the case of atomic Schrodinger waves, and show that this requires the introduction of several classes of coherence. Optical methods to manipulate the coherence of matter-wave fields are discussed.

A general description of the Quantum Trajectories is presented, both from the Montecarlo and Stochastic Schrodinger equation viewpoint. Also a physical interpretation of these trajectories is given. The example is a mode of the electromagnetic field in a cavity interacting with a beam of two or three level atoms, the field playing the role of the small system and the atomic beam standing for a reservoir at finite temperature. We show that the evolution of the field states, under continuous monitoring of the state of the atom which leave the cavity can be described with the Monte-Carlo method or a diffusion equation, depending on the configuration of the system.

We perform modal analysis and ultracold atomic beam propagation in hollow optical fibers. The eigenmodes and modal propagation constants of the atomic waveguide are determined by numerical solution of the Schrodinger equation for the center-of-mass motion. The existence of a threshold de Broglie wavelength for the fundamental mode is predicted. Beam propagation is performed by modal expansion of the wavefunction on a truncated basis of eigenmodes of the atomic waveguide. The evolution of the atomic probability density profile along the waveguide for a non cylindrical atomic beam is shown.

Bright atomic resonators have been proposed as `atom-laser' cavities, where dipole-dipole interaction in the relevant mechanism to populate a translational eigenstate of the resonator. We study here dipole-dipole collisions inside a bright atomic resonator under two different laser arrangements. We show how collisional matrix elements depend on whether a longitudinal laser field is added or not to a 2D-linlin configuration. We conclude that the laser field configuration inside the resonator might allow for manipulation of collisional cross-sections with lasers.

Deceleration of an atomic beam of calcium was achieved by using the radiation of a frequency double diode laser at 845.2 nm. In order to enhance the violet beam generation the doubling crystal, KNbO₃, is placed inside an external build-up cavity. The laser beam at 423 nm, counter- propagating with the atomic beam, is put into resonance with the ¹S₀ yields ¹P₁ transition of Ca. To keep the laser in resonance with the atomic transition during the cooling process, the Zeeman technique is used.

Photoluminescence (PL) from (Al, Ga)As quantum-wire arrays grown on vicinal (111)B GaAs substrates by molecular beam epitaxy is reported for the first time. A peak at 1.826 eV is attributed to excitonic recombination in the built-in quantum-wire array, and a peak at 1.759 eV and a low PL emission band also originate from the serpentine superlattice structure. For comparison, the epilayers were also deposited on (100) GaAs substrates simultaneously. But the PL results indicate that they are the alloy-well structures. We explain these PL results with a model and draw a conclusion that steps on (111)B surface can play a very important role in crystal growth.

This work reports information about the temporal evolution of the equilibrium departure in a high current pulsed arc. An argon plasma has been created in a linear lamp by discharging a capacitor bank on its electrodes. Very careful diagnostics techniques have allowed us to determine electron density N_e (2.0 - 9.5 X 10²² m^-3) and ArII excitation temperature which has been assumed to be equal to kinetic electron temperature T (13000 - 26000 K). By making ArII/ArI intensities ratio at each instant of the plasma life, it is possible to obtain a parameter which gives an idea of the departure of ionization-recombination processes from local thermodynamic equilibrium conditions.

The results obtained for contaminant detection in water, with the recently implemented LIBS technique, are presented. A Q-Switched Nd-YAG laser (1.06 micrometers ) was used, focusing its output on the sample. Two experimental set-ups are used; in the first spark was generated in the bulk of the liquid, while in the second it was generated at its surface. We found the latter useful because it gave more information on several ionic elements present in the aqueous solution. The linearity of the system and its limits of detection were checked with know concentrations of Mg, Ca and Na.

Stark widths of 28 OII spectral lines have been measured as functions of electron density in a pulsed discharge plasma. The electron density, which ranges from 1 to 8 X 10²² m^-3 in the plasma, has been determined simultaneously by one-wavelength interferometry, using the 514.0 nm transition of an Argon ion laser, and from Balmer- alpha Stark broadening. The OII excitation temperature (22000 - 48000 K) has been determined from Boltzmann-plots. The measured data are compared with other works found in the literature.

We report a study of spectrum the Xe VIII obtained by a pulsed spectral source. We observed and classified new spectral lines which allowed us to resolve some multiplets. We are studying diffuse lines belonging to transitions to the continuum states as well as laser transitions in this ion. We also study Rydberg series and made theoretical Hartree-Fock calculation including core excited configurations.

The low to high-field transition in KZnF₃:Cr³⁺, induced by external pressure was observed through photoluminescence measurements at room temperature, T equals 90 K and T equals 20 K. Direct measurement of the lowest electronic level separation (Delta) , was accomplished through the low temperature experiments. Pressure coefficients of (Delta) are given. Emission spectra of KZnF₃:Cr³⁺ obtained at several pressures and temperatures in the range [20 K - 90 K] allow for the construction of a Tanabe-Sugano type diagram illustrating the transition from low- to high-crystal-field regime for cubic and distorted centers. Assignments of sharp lines are given based on the analysis of these diagrams, time-resolved spectroscopy and transition lifetime. Emission measurements were performed at atmospheric pressure and low temperature outside the pressure cell and also at several pressures for KZnF₃:Co³⁺. Comparing the zero-phonon line positions and using the phonon dispersion relation of the host material and fine structure in the emission spectrum of KZnF₃:Co²⁺ was identified. Pressure coefficients were obtained for several among the emission lines from which the values for zero-phonon lines were deduced. Analysis show that the spin-orbit parameter changes with pressure are negligible in KZnF₃:Co²⁺.

The Laboratory of Coherent Optics possesses the following lines of investigation laser material processing, holography, image processing, biomedical applications of laser, speckle techniques and other optical measuring techniques. In the present paper, some of the most important results obtained in the last three years are described.

This paper summarizes the research activities of the optical communications group at University of Aveiro and Institute of Telecommunications-Aveiro pole. Several activities like clock recovery systems, both electrical and all optical, electrical equalizers for very high bit rate DST systems, post-detection filters for multigigabit optical receivers, soliton systems, simulation work on WDM, DST, EDFA and short pulse generation for high bit rate systems are presented.

We present some of the experimental and theoretical studies in lasers and optics that have currently been performed in our country. We present an overview of several active areas of research that include nonlinear optic spectroscopy, applied optics, and theoretical modeling of laser dynamics.

This communication introduces the Optics and Signal Processing Group from Universidad Industrial de Santander at Bucaramanga, Colombia. First, a brief description of how the group was formed, its strategic importance and also some of its more important achievements are presented. Then, the main scientific domains where the group carries out its research are described and finally, some guidelines about future research work in the group are given.

In this article we present the different groups of investigation which work at the Department of Optics and Applied Physics of the University of Valladolid (Spain). The areas covered by these groups are the following: (1) optical diagnostic techniques in plasmas, (2) calculation of spectral line shapes, (3) atmospheric optics, (4) radiometry and photometry, and (5) history of science and techniques.

The research projects at the Laser Technology Laboratory of Havana University are devoted to Nd:YAG lasers development and to the implementation of new laser applications in different fields. Relative to the lasers research the objective is the development of compact, light and relative low-cost lasers. This development is based on a vertical integration strategy that establishes the own elements production as pumping cavities, multilayer mirrors and filters, power supplies control units and others. Several investigations are carried out using these lasers: thin film deposition of semiconductor, ferroelectric and magnetic materials by laser ablation, subsurface laser marking of transparent materials, pulse laser surface silicon texturing and laser cleaning of art works.

In this work we summarize some of the work of our team in the last years, devoted to the use of spatial light modulators (SLM) in optical correlators and optical image processors. We have built an optical processor that uses two liquid crystal SLMs, one to implement the image to be processed and a second one to implement a Fourier filter. We analyzed the advantages of the use of SLMs, but also the restrictions they impose. We proposed several architectures and filters design to take profit of this SLM based optical processor.

The fiber loop mirror constructed from a low-birefringent twisted fiber was numerically examined. The non-linear ellipse rotation effect have been included in the consideration. We have shown, that in this configuration the nonlinear variation of the transmission coefficient is possible even with a 0.5/0.5 coupler. By appropriate choice of the fiber twist, birefringence, and length, variety of different characteristics of the interferometer can be achieved. Some of the configurations manifest polarization independent operation.