Showing papers in "Pure and Applied Optics: Journal of The European Optical Society Part A in 1992"
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TL;DR: In this paper, the authors investigated the properties of the Fresnel diffraction field produced by a Cantor bars aperture and found that intensity distributions on the optical axis have a periodicity which includes symmetry, when plotted against a 2/( lambda z) where a is the length of an object, lambda is the illumination wavelength and z is the distance of an observation point from the object.
Abstract: Some properties of the Fresnel diffraction field produced by a Cantor bars aperture are investigated by numerical evaluations of the Fresnel integral It is found that intensity distributions on the optical axis have a periodicity which includes symmetry, when plotted against a2/( lambda z) where a is the length of an object, lambda is the illumination wavelength and z is the distance of an observation point from the object The period depends on the level of Cantor bars and shows a ninefold increase as the level of the object increases by one Furthermore, as the level of Cantor bars increases, intensity distributions on the optical axis become invariant gradually from the far- to the near-field region
57 citations
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TL;DR: In this paper, the Fourier transform method of interference pattern analysis is used for phase measurements of 3D surfaces, free from errors caused by highfrequency disturbances and the variation of background intensity.
Abstract: A Fourier transform method of interference pattern analysis is a powerful tool for automatic phase measurements. The technique is free from errors caused by high-frequency disturbances and the variation of background intensity. The method is particularly useful for waviness and roughness profile reconstruction of 3D surfaces.
42 citations
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TL;DR: In this paper, the role played by thermal post-effects in the holographic recording process on photopolymerizable materials was revealed and clarified and it was confirmed that the key phenomenon which controls the building up of the hologram image in such systems is the balance between the photochemically initiated polymerization and the diffusion of unreacted species from the dark to the bright regions of the record.
Abstract: For pt.II see ibid., vol.1, no.5, p.251-68 (1992). The use of a time-modulated laser source allows the role played by thermal post-effects in the holographic recording process on photopolymerizable materials to be revealed and clarified. It is confirmed that the key phenomenon which controls the building up of the holographic image in such systems is the balance between the photochemically initiated polymerization and the diffusion of unreacted species from the dark to the bright regions of the record. From a practical viewpoint, the use of intermittent or pulsed laser writing sources proves to be very effective in achieving a fast and extensive polymerization of the monomers used in the photosensitive formulation a property which goes along with a good stability of the records.
31 citations
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TL;DR: In this article, the operation of spatially variant optical interconnections using microlenses was demonstrated using an afocal pair of lenses in which lateral displacement of the second lens controlled the angular deviation of the bundle of rays.
Abstract: The authors have demonstrated the operation of spatially variant optical interconnections using microlenses. Each connection is made by imaging an element of the source onto an element of the detector by an afocal pair of lenses in which lateral displacement of the second lens controls the angular deviation of the bundle of rays. They used microlenses of 250 mu m diameter made by melting photoresist and have demonstrated an 8*8 one-dimensional cyclic shift, a two-dimensional cyclic shift and a two-dimensional perfect shuffle.
27 citations
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TL;DR: In this paper, the authors investigated self-developing formulations requiring only short exposure and which are, therefore, specially suited for real-time interferometry, and obtained a spatial resolution better than 30 mm-1.
Abstract: Photopolymers have been the subject of special attention during recent years. Since these materials can be used for recording optical information, many studies were devoted to the evaluation of their characteristics in this respect. This paper is aimed at investigating new self-developing formulations requiring only short exposure and which are, therefore, specially suited for real-time interferometry. Well contrasted interferograms can be obtained with a recording system which does not need any post-treatment. The holographic exposure requires a few seconds with a power density of 5 mW cm-2. A practical application in which the dissolution (and the concentration gradient thereof) of a crystal is studied as a function of the time, reveals a spatial resolution better than 30 mm-1.
26 citations
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TL;DR: In this paper, the tensor properties of chi gratings induced in bulk glass under different polarization conditions were explored and the results pointed out the presence of a static electric field recorded in proportion to E(EE).
Abstract: The authors explored tensor properties of chi (2) gratings induced in bulk glass under different polarization conditions. Three cases were studied: recording of gratings by waves with parallel, orthogonal and 45 degrees -tilted polarizations. The results obtained point out the presence of a static electric field recorded in proportion to E(EE).
19 citations
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TL;DR: In this article, a comparison between the two-and multiple-beam microinterferometric methods for the determination of refractive indices and birefringence of polypropylene fibres is given.
Abstract: The paper deals with the determination of refractive indices and birefringence of polymer fibres using both two- and multiple-beam microinterferometry. Different techniques of interferometry are given together with their applications in investigating the optical properties of fibres. An analysis of the microinterferograms of fibres with irregular transverse sections is given. The optomechanical properties of polymer fibres, measured dynamically by interferometry, are dealt with. Lateral birefringence of fibres is also given. A mathematical expression is derived to determine the refractive indices, birefringence and the index profile of a cylindrical fibre taking into consideration the refraction of the incident beam by the fibre. This expression is applied with the two-beam microinterferograms produced for polypropylene fibres. A comparison between the two- and multiple-beam microinterferometric methods for the determination of refractive indices and birefringence of fibres is given. Both methods are evaluated. Microinterferograms are given for illustration.
19 citations
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TL;DR: In this article, photoinduced optical absorption (PA) in chalcogenide glass fibres has been investigated in terms of a multiple trapping model, which enables the authors to evaluate the characteristic energy of localized states distribution.
Abstract: Measurements are reported on photoinduced optical absorption (PA) in chalcogenide glass fibres. Experimental results on kinetics and stationary state characteristics are presented. The analysis of experimental results in terms of a multiple trapping model enables the authors to evaluate the characteristic energy of localized states distribution.
18 citations
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TL;DR: In this paper, the difference between mass diffraction and surface diffraction is presented and illustrated through clear and easy experiments based on the fundamental difference between the concepts of dimension and codimension.
Abstract: In the frame of a generalized functions analysis, it is shown that the light scattered by fractal objects has fractal properties. The difference between mass diffraction and surface diffraction is presented and illustrated through clear and easy experiments based on the fundamental difference between the concepts of dimension and codimension.
18 citations
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TL;DR: In this paper, a new configuration for a wide ultraviolet range high resolution monochromator has been analyzed, which consists of a first off-axis paraboloidal mirror collimating the radiation beam from the source, followed by a couple of plane optical elements, a mirror and a grating, constituting the dispersive system, and by a second offboard mirror focusing a selected portion of the dispersed radiation beam on a fixed exit slit.
Abstract: A new configuration for a wide ultraviolet range high resolution monochromator has been analysed. It consists of a first off-axis paraboloidal mirror collimating the radiation beam from the source, followed by a couple of plane optical elements, a mirror and a grating, constituting the dispersive system, and by a second off-axis paraboloidal mirror focusing a selected portion of the dispersed radiation beam on a fixed exit slit. Since in the extreme ultraviolet region it is necessary to use the optical elements in grazing incidence to have a good reflectivity, the two paraboloidal mirrors can be used in the so-called sagittal focusing to minimize the slope error induced aberrations in the dispersive plane. As an example, the monochromator performances when applied to a synchrotron radiation source in the range 250-1250 eV (9.9-49.6 AA) are shown.
17 citations
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TL;DR: In this paper, the authors investigated the propagation and stability of light pulses under the combined influence of the optical Kerr effect, dispersion and diffraction by adopting a variational procedure, and found that radially symmetric pulses propagating without distortion are not necessarily unstable under perturbations which do not maintain radial symmetry.
Abstract: Propagation and stability of light pulses under the combined influence of the optical Kerr effect, dispersion and diffraction are investigated by adopting a variational procedure. In particular, it is found that 'light bullets', i.e. radially symmetric pulses propagating without distortion, are not necessarily unstable under perturbations which do not maintain radial symmetry.
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TL;DR: In this paper, the phase functions of aspheric recording wave fronts of a thick HOE in the presence of a wavelength shift are given, and a simple least squares fitting algorithm is used to compute analytic expressions of these phase functions.
Abstract: Equations for tracing rays through (aspheric) holographic optical elements (HOE) are reviewed, and, in addition, the diffraction efficiency of a thick HOE is taken into account. Expressions for calculating the phase functions of aspheric recording wave fronts of a thick HOE in the presence of a wavelength shift are given. A simple least squares fitting algorithm is used to compute analytic expressions of these phase functions. Finally, a method to calculate a focus of rays is described.
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TL;DR: In this paper, the concept of absorption in a Fabry-Perot (FP) interferometer is revisited, where the FP is modelled as a medium in the cavity formed by two semi-reflecting absorbing films (typically, two metallic coatings with finite thickness).
Abstract: The concept of absorption in a Fabry-Perot (FP) interferometer is revisited. The FP is modelled as a medium in the cavity formed by two semi-reflecting absorbing films (typically, two metallic coatings with finite thickness) and not merely by two interfaces. Starting from this model the concept of absorption for an isolated metallic film and for each one of the coatings of the FP is discussed. Due to the coupling between the reflected waves in the coatings, the expressions for both cases are essentially different. Furthermore, even if the two coatings of the FP were identical, the absorption takes different values in each of them. The phase lag in the reflection from the coatings depends on the angle of incidence and on their thickness, causing a shift in the position of the maxima of the transmitted and reflected irradiances.
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TL;DR: In this paper, a double-grating shearing interferometric technique has been developed to increase the dynamic range of shape measuring interferometry, and the interference takes place between two wavefronts diffracted from two high density sinusoidal gratings.
Abstract: In order to increase the dynamic range of shape measuring interferometry, a double-grating shearing interferometric technique has been developed. The interference takes place between two wavefronts diffracted from two high density sinusoidal gratings. Phase stepping by means of lateral shifting was introduced to obtain automatic fringe analysis. The surface shape is reconstructed from the first derivative of the phase distribution with the assumption of a rotationally symmetric object. This assumption is reasonable for testing diamond-turned surfaces. The measurement accuracy depends upon the surface size and the shear amount. The authors have experimentally measured a spherical diamond-turned mirror shape with an accuracy of lambda /2 ( lambda =0.6328 mu m), and a theoretical dynamic range of hundreds of lambda .
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TL;DR: In this paper, the capabilities and problems of interference microscopy in the UV region are discussed and a two-step procedure is proposed to reduce the wavelength in the interference by a factor of about 10.
Abstract: The authors discuss the capabilities and problems of interference microscopy in the UV region. The motivation is obvious: as the dimensions in electronics, mechanics and optics become smaller and smaller, measuring principles are required which provide lateral resolutions in the sub- mu m and longitudinal resolutions in the nm range. Due to its limited resolution optics using visible light as to cede the field to scanning electron microscopy. However, if it were possible to enhance the resolution using UV light, optics has some advantageous features: parallel data acquisition with freedom from special preparation methods and, therefore, no destruction of the object. One can think of a two-step procedure to reduce the wavelength in interference microscopy by a factor of about 10.
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TL;DR: In this article, the authors present a formalism of the two-dimensional electromagnetism covariant under the pseudo-orthogonal group SO(2,1) for diffraction by plane obstacles as well as electromagnetic wave propagation in waveguides.
Abstract: Starting with a discussion of the two-dimensional scalar and spinor wave equations, the author presents a formalism of the two-dimensional electromagnetism covariant under the pseudo-orthogonal group SO(2,1). He proves that this covariant formalism makes it easier and more unambiguous to discuss diffraction by plane obstacles as well as electromagnetic wave propagation in waveguides.
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TL;DR: In this article, a generalized van Cittert-Zernike theorem was proposed to describe the spatial coherence of wave fields with respect to the source radiance in a generalized quasihomogeneous wave model.
Abstract: The analogy between the van Cittert-Zernike theorem and diffraction in focal regions is discussed. For wavefields that can be approximated by a generalized quasihomogeneous wave model, the spatial coherence is described by a generalized van Cittert-Zernike theorem even close to the source. The main difference between the classical and the generalized theorem is that the source intensity in the former is replaced by the source radiance in the direction of the observation point in the latter. The spatial coherence is related to the source radiance by a modified Debye integral, which implies that the wave energy is propagated according to the laws of classical radiometry. No assumption of source incoherence is involved, and the results apply to radiation from both primary sources and secondary sources like rough scattering objects or illuminated apertures in optical systems.
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TL;DR: In this paper, a single beam technique for measuring both the nonlinear refractive index and nonlinear absorption of transparent materials has been proposed by Sheik-Bahae et al. This technique has been applied to evaluate both the thermal and electronic non-linear changes of refractive indices and of absorption of some Schott semiconductor doped glasses by using the CW and pulsed regime.
Abstract: Recently a single beam technique for measuring both the non-linear refractive index and non-linear absorption of transparent materials has been proposed by Sheik-Bahae et al. IEEE J. Quantum Electron., vol.26, p.760, 1990; in which the transmittance of a sample is measured through a finite aperture in the far field as the sample is moved along the propagation path of a focused Gaussian beam. The sign and magnitude of the non-linear refractive index and the value of absorption changes can be deduced from the transmittance curve. In the present paper this technique has been applied to evaluate both the thermal and electronic non-linear changes of refractive index and of absorption of some Schott semiconductor doped glasses by using the CW and pulsed regime.
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TL;DR: In this article, transient gratings induced in a homogeneous Kerr nonlinear medium by soliton beams are used to obtain a diffraction efficiency of 70% using carbon disulphide.
Abstract: The authors report experimental results on transient gratings induced in a homogeneous Kerr nonlinear medium by soliton beams. These stable self-trapped waves of high intensity are not subject to the usual problem of beam filamentation and permit refractive index gratings of high modulation, significant length, and hence high efficiencies. Moreover the probe beam is also trapped in the soliton induced waveguide which enhances its overlap with the grating. By this method a diffraction efficiency of 70% has been experimentally obtained, using carbon disulphide for the nonlinear medium. Efficient ultrafast all-optical deflection of light has been demonstrated with this material.
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TL;DR: The use of colour reversal film applied to polychromatic pattern recognition is studied in this paper, where the authors test the effects on the discrimination capability of the recognition system due to the differences between the reflectance of real diffuse objects and the transmittance of their recorded images in the slide.
Abstract: The use of colour reversal film applied to polychromatic pattern recognition is studied Colour slides contain the input information of the target and the scene for the generation of the matched filters and for the multichannel optical correlation The authors test the effects on the discrimination capability of the recognition system due to the differences between the reflectance of real diffuse objects and the transmittance of their recorded images in the slide The response of several commercial films is analysed: firstly, through experimental transmittance curves of slides which reproduce uniform colour stimuli with different exposures; secondly, through computer results obtained for the recognition of polychromatic images The suitability of each film for colour pattern recognition purposes is discussed
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TL;DR: In this paper, a simple method for determining both the size and the refractive index of spherical transparent particles, being larger in size than the wavelength of illuminating light, is proposed on the theoretical basis of geometrical optics of light scattering.
Abstract: A simple method for determining both the size and the refractive index of spherical transparent particles, being larger in size than the wavelength of illuminating light, is proposed on the theoretical basis of geometrical optics of light scattering. In the theory, the intensity distribution of scattered light at a certain off-axis angle range of a few degrees can be recognized as interference fringes due to two dominant light rays from the particle. The ratio between the interference fringe contrasts of the scattering patterns in parallel and perpendicular polarization components is used to determine the refractive index of particles, whereas the size of particles is evaluated from the fringe pitch. Experiments were performed to confirm the validity of the proposed method. The validity range of the method is also discussed in terms of the light rays scattered into the observation angle. The present method has the advantage that measurements of the absolute intensity are not required to obtain the size and the refractive index of particles.
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TL;DR: In this article, the authors considered the implementation of spherical geodesic processors without any conventional waveguide and showed that the guided propagation is assured by the whispering gallery modes due to the curvature.
Abstract: The implementation of spherical geodesic processors without any conventional waveguide is considered. The guided propagation is assured by the whispering gallery modes due to the curvature. The electric field distributions of these modes are given in the approximation of small bending losses, that is when the sphere radius rho >> lambda (in practice rho =1-20 mm). The dispersion equation of the modes and the attenuation due to the path curvature were also found. Experiments were carried out on a BK7 glass quarter of sphere ( rho =15 mm) at lambda =0.63 mu m and on a GaAs hemisphere ( rho =9.2 mm) at lambda =1.31 mu m.
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TL;DR: In this article, a hollow cathode He-Kr+ laser was operated at 469.4 nm and was excited by a 50 Hz near-square wave, maximum 10 A, 500 mu s duration current pulses.
Abstract: Operation characteristics of a short, 10 cm active length hollow cathode He-Kr+ laser were investigated. The laser operated at 469.4 nm and was excited by a 50 Hz near-square wave, maximum 10 A, 500 mu s duration current pulses. The lowest threshold current observed was 0.9 A and a maximum laser power of 2.7 mW was obtained. Laser oscillation was also observed at high He pressures, at 104 mbar the output power was 1.5 mW. The shape of the laser pulse showed a characteristic change with increasing He pressure. Saturation of laser power with increasing discharge current was observed even at high He pressures. The saturation is considered to be caused by the appearance of sputtered Al vapour.
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TL;DR: Using an external cavity semiconductor laser coupled to an additional empty cavity, optical pulses on the order of 100 ps duration at repetition rates of 1-2 GHz have been generated by careful adjustment of the length of the auxiliary cavity to match that of the main cavity and do not require any modulating signal to be applied to the laser diode as mentioned in this paper.
Abstract: Using an external cavity semiconductor laser coupled to an additional empty cavity, optical pulses on the order of 100 ps duration at repetition rates of 1-2 GHz have been generated. The pulses are obtained by careful adjustment of the length of the auxiliary cavity to match that of the main cavity and do not require any modulating signal to be applied to the laser diode.
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TL;DR: In this paper, the intensity pattern of an object illuminated stepwise by a movable point source with unit intensity is recorded at every step by a CCD TV camera and held in a computer memory.
Abstract: Optical mutual intensity can be controlled by the variable intensity distribution of an extended quasi-monochromatic incoherent source. A point source with a conceptually variable intensity, moving stepwise over the source plane, is capable of providing an equivalent extended incoherent source. This idea can be realized by an opto-electronic hybrid system. The intensity pattern of an object illuminated stepwise by a movable point source with unit intensity is recorded at every step by a CCD TV camera and held in a computer memory. All the memorized intensity patterns are multiplied successively with a series of weighting values from a suitable function generated in the computer. This generated function can take the same formula as the required intensity distribution of an extended incoherent source. The sum total of all the weighted elementary patterns results in an intensity pattern of the object equivalent to that formed by spatially coherence-controllable illumination. The computer-generated image patterns for a knife-edge object are in good agreement with the measured image patterns. The image pattern can be shaped with the help of such a function generated in the computer.
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TL;DR: In this paper, the effects of misalignment between optical fibres and the imaging beams illuminating them were analyzed with reference to existing and projected fiber systems. But the effects on image degradation and loss of light can arise in fiber-fed spectroscopy.
Abstract: Serious image degradation and loss of light can arise in fibre-fed spectroscopy from misalignment between optical fibres and the imaging beams illuminating them. The effects are analysed, with reference to existing and projected fibre systems.
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TL;DR: In this article, an efficient Brillouin scattering of a train of short pulses in single-mode optical fibres has been observed for the first time, and the authors have experimentally observed that the scattering is efficient.
Abstract: The authors have experimentally observed for the first time an efficient Brillouin scattering of a train of short pulses in single-mode optical fibres
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TL;DR: In this paper, the authors used multiple-beam Fizeau fringes to determine the refractive index profile of graded index optical fibres, and the dispersion of the material of the optical fibre has been studied.
Abstract: The authors use multiple-beam Fizeau fringes to determine the refractive index profile of graded index optical fibres. Some parameters affecting the determination of this refractive index profile are discussed. The dispersion of the material of the optical fibre has been studied, and the constants of Cauchy's equation for fibre cladding are also determined.
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TL;DR: In this paper, the authors analyzed a periodically modulated light beam with a square profile and showed that the improvement in the signal-to-noise ratio by measuring the moment generating function of the number of photopulses, Qn(s, T), with respect to the measurement of the second normalized factorial moment, n(2)T, was demonstrated.
Abstract: The authors show, through the analysis of a periodically modulated light beam with a square profile, the improvement in the signal-to-noise ratio by measuring the moment generating function of the number of photopulses, Qn(s, T), with respect to the measurement of the second normalized factorial moment, n(2)(T). An experimental verification in the low light level range (1-10 photoelectrons per period) for different values of the modulation factor has been made. The results and some conclusions are presented.
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TL;DR: In this paper, the structure formation in areas subjected to uniaxial stress were different from the changes observed in unstretched samples under the same conditions, and the observed peculiarities in surface morphology are explained in terms of Marangoni-type material convections governed by temperature gradient and released mechanical stress fields.
Abstract: Excimer laser induced structure formation in different polymers (polyester, polyvinylchloride,. . .) at laser fluences just below the ablation threshold has been investigated. Different surface formations of hexagon and/or roll types were registered in the irradiated regions. The laser treatment yielded a highly oriented regular structure at large scale and disordered structure at small scale. The structure formations in areas subjected to uniaxial stress were different from the changes observed in unstretched samples under the same conditions. The observed peculiarities in surface morphology are explained in terms of Marangoni-type material convections governed by temperature gradient and released mechanical stress fields.