Showing papers in "Optics and Laser Technology in 1990"
TL;DR: In this paper, the incorporation of laser diodes and monomode fibre optics into an Electronic Speckle Pattern Interferometer (ESPI) has led to the development of a novel holographic surface contouring system.
Abstract: The incorporation of laser diodes and monomode fibre optics into an Electronic Speckle Pattern Interferometer (ESPI) has led to the development of a novel holographic surface contouring system. Height contours are obtained by switching between two laser wavelengths. Contour intervals from 0.5–5 mm have been generated by modulating the injection current of a single laser diode source and are demonstrated on an automotive disc brake hub.
43 citations
TL;DR: In this article, a description of metal surface roughness has been obtained by introducing dispersion of the roughness distribution as a new parameter, and the optical reflectance of nickel, aluminium, copper and brass specimens have been investigated experimentally using HeNe and Ar + lasers.
Abstract: A description of metal surface roughness has been obtained by introducing dispersion of the roughness distribution as a new parameter. The optical reflectance of nickel, aluminium, copper and brass specimens have been investigated experimentally using HeNe and Ar + lasers. From the wavelength dependence of reflectance observed for nickel and aluminium specimens, it is feasible that an industrial on-line system could be used to monitor surface roughness.
41 citations
TL;DR: In this article, the authors present a review of the development of fiber-optic sensors for measuring blood flow and Brownian-induced translatory diffusion in colloidal suspensions, respectively.
Abstract: ‘Photon correlation spectroscopy’ has become a standard method in applied science for analysing the properties of submicron particles in a fluid environment. The fast, local fluctuations in the intensity of the light scattered from such particles are recorded and analysed in terms of the local motions. This has led to the use of the method both to characterize particle geometry and to monitor particle translation as a marker for fluid flow. The advent of fibre-optics has enabled portable, small, remote and more flexible systems to be established in recent years. This paper reviews those instrument designs which have represented advances in the development of fibre-based systems. Emphasis is laid on instruments (a) for monitoring blood flow and (b) for measuring Brownian-induced translatory diffusion in colloidal suspensions.
33 citations
TL;DR: In this paper, the effect of electron reradiation was included in the Lorentz-Drude (LD) model and by applying the least-squares fitting method the values of the characteristic parameters (ωp, Г, τ) of electrons in aluminium were determined.
Abstract: The effect of electron reradiation was included in the Lorentz-Drude (LD) model and by applying the least-squares fitting method the values of the characteristic parameters (ωp, Г, τ) of electrons in aluminium were determined. The values of these parameters allowed the determination of optical properties of aluminium for light of wavelengths λe[43.5 nm, 200 μm]. By including the reradiation of electrons the precision of the LD model has been increased in the infra-red region of wavelengths λe[1 μm, 200 μm]. In addition, the reradiation of electrons gives the square frequency dependence for damping frequency [ Г′(ω) = Г +τω 2 ], enabling the suitable application of the LD model in the broad range of wavelengths λe[43.5 nm, 200 μm]. It was estimated that the short wave limit at which the LD model can be used for aluminium occurs at about λmin = 43.5 nm.
31 citations
TL;DR: In this article, a double-exposure hologram through fiber optics is described and the contouring fringes can be visualized on the object surfaces, where singlemode fibres are used to transfer both object and reference beams.
Abstract: In this paper holographic contouring by the movement of the object beam through fibre optics is described. The contouring fringes can be visualized on the object surfaces. This contouring technique is based on a double-exposure hologram through fibre optics. Single-mode fibres are used to transfer both object and reference beams. Between the two exposures the object illumination fibre is displaced. The fringe type is analysed and several experimental results are given.
23 citations
TL;DR: In this article, a ZnSe coated Ag hollow waveguide of short length was constructed and it was shown that it has a lower loss than a Ge coated waveguide for CO 2 laser light.
Abstract: A condition for reducing transmission loss of a dielectric-coated metallic hollow waveguide is shown theoretically when the inner metallic surface is not perfect. It is also shown that the transmission loss for CO 2 laser light is 10.6 μm wavelength is able to be estimated from an attenuation spectrum of a short waveguide. By fabricating a ZnSe coated Ag hollow waveguide of short length, we have shown that it has a lower loss than a Ge coated waveguide for CO 2 laser light.
21 citations
TL;DR: In this paper, a retroreflective tape covered PZT-element is used to remove the sign ambiguity in surface velocity, which is inherent in the form of Doppler detection used in laser vibrometers.
Abstract: This paper introduces a new design of laser vibrometer which allows high sensitivity, noncontact measurement of normal-to-surface target motion. The design includes use of a retro-reflective tape covered PZT-element to remove the sign ambiguity in surface velocity, which is inherent in the form of Doppler detection used in laser vibrometers. Utilization of this element offers the potential for a compact, cost effective design, suitable for portable, on-site use in engineering situations.
20 citations
TL;DR: In this article, an experimental set-up for measuring two displacement components by digital speckle pattern interferometry (DSPI) was described for metal-ceramic components under thermal stress.
Abstract: An experimental set-up is described for measuring two displacement components by digital speckle pattern interferometry (DSPI). Experimental results are given for metal-ceramic components under thermal stress. Emphasizing quantitative evaluation, the effective thermal expansion coefficient was determined.
18 citations
TL;DR: In this article, a short review of the spectrally modulated and dual wavelength referenced, intensity modulated optical sensors is presented, followed by descriptions of particular WDM optical sensor system developments in order to illustrate the approaches currently adopted.
Abstract: Wavelength division multiplexing (WDM) offers a potentially powerful technique for use within single optical fibre sensor systems and multiple sensor networks. The paper commences with a short review of the spectrally modulated and dual wavelength referenced, intensity modulated optical sensors. A WDM system employing multimode fibre and LED sources is then discussed. This is followed by descriptions of particular WDM optical sensor system developments in order to illustrate the approaches currently adopted. Potential network topologies for WDM multiple sensor networks are then introduced, with some description of the major implementational constraints to provide an indication of possible future developments.
17 citations
TL;DR: A video speckle interferometer has been demonstrated which uses a spherical surface of small radius at the centre of the camera aperture to simplify the alignment of the reference beam and is able to display phase-stepped interferograms of good quality with a repetition rate approaching one second.
Abstract: A video speckle interferometer has been demonstrated which uses a spherical surface of small radius at the centre of the camera aperture to simplify the alignment of the reference beam. In combination with a fast microcomputer, this gives a compact and relatively inexpensive system which is able to display phase-stepped interferograms of good quality with a repetition rate approaching one second. The software for phase stepping and unwrapping has novel features and can be applied to other types of interferometer.
17 citations
TL;DR: In this article, single CO 2 laser pulses, of 10.6μm wavelength, are used to form blind microvias (holes in electronic boards for throughplating conducting paths) in copper-clad epoxy-glass laminates.
Abstract: Single CO 2 laser pulses, of 10.6μm wavelength, are used to form blind microvias (holes in electronic boards for through-plating conducting paths) in copper-clad epoxy-glass laminates. The microvia dimensions depend on pulse energy and duration, the thicknesses of the epoxy-glass laminate and copper cladding, and the distribution of glass within the epoxy-glass laminate. The useful range of laser parameters, especially pulse energy, is primarily determined by the ability to metallize subsequently the blind microvias. Several conclusions can be drawn from the data. The pulse enegy should be within ±20% of the optimum value in order to form vias with a cylindrical geometry. For 300 μm thick laminates, the thickness of the copper on the bottom should be 18 μm or more. A larger range of pulse energies could be used if the glass fibre density was more uniform and if subsequent copper metallization of the blind vias could be improved.
TL;DR: In this article, a method of refractive power mapping of a lens is presented which is based on Talbot interferometry and utilizes a digital image processor, where a test lens is placed in front of two collinearly arranged gratings and the light passing through the test lens produces a shifted Talbot image of the first grating on the second grating and generates moire fringes.
Abstract: A method of refractive power mapping of a lens is presented which is based on Talbot interferometry and utilizes a digital image processor. By adding a digital image processing system, fast measurement of a lens power distribution is feasible. A test lens is placed in front of two collinearly arranged gratings. The light passing through the test lens produces a shifted Talbot image of the first grating on the second grating and generates moire fringes. Given the inclination angle of moire fringes, the refractive power of the lens can be calculated. The calculation is performed using a digital image processor. This method is effective in finding the refractive power distribution of progressive power lenses.
TL;DR: In this paper, an acoustic technique is described to detect laser weld defects and the feasibility of using the acoustic signal in a real-time knowledge-based system for the control and monitoring of laser welding is shown.
Abstract: An acoustic technique is described to detect laser weld defects. The acoustic signal is compared with signals from a number of other sensors. The feasibility of using the acoustic signal in a real-time knowledge-based system for the control and monitoring of laser welding is shown.
TL;DR: In this paper, a concept for an all-optical reflection modulator is introduced for two-dimensional digital optical signal processing in an AlGaAs system employing molecular beam epitaxy.
Abstract: Dielectric interference filters incorporating an epitaxial anti-reflector structure and a concept for an all-optical reflection modulator are introduced. They are suitable for two-dimensional digital optical signal processing in an AlGaAs system employing molecular beam epitaxy. The reflection modulator concept uses dynamic band filling in multiquantum wells to obtain a bleachable absorption type optical non-linearity and promises more than 80% modulation depth. The numerical investigations are carried through with the help of two equivalent mathematical approaches which are explained in detail. Calculated results show satisfying agreement with experiments.
TL;DR: In this article, a solid state, time-resolved holographic interferometric system has been developed, where the reference beam is subdivided into several branches which illuminate the film from different angles and are individually shuttered by electro-optical light valves.
Abstract: A solid state, time-resolved holographic interferometric system has been developed. The time-dependent object beam from a strobed sequence of events impinges on a fixed area of film from a single direction, whereas the reference beam is subdivided into several branches which illuminate the film from different angles and are individually shuttered by electro-optical light valves. The reference exposure is recorded simultaneously on all images by keeping all shutters open during one pulse of the laser. For the remaining pulses the shutters are sequenced. A three-image prototype has been implemented, and has been used to record interferometric sequences of a shock wave reflecting off a model, at intervals down to 100 μs.
TL;DR: In this paper, the effect of dielectric coatings on semiconductor laser performance is investigated and it is demonstrated that the dielectrics are a powerful means of controlling the laser threshold current, external quantum efficiency, maximum output power, longitudinal mode behaviour, lasing wavelength and spectral linewidth.
Abstract: Experimental studies and theoretical analyses on the effect of dielectric coatings on semiconductor laser performance are presented. It is demonstrated that the dielectric coating technique is a powerful means of controlling the laser threshold current, external quantum efficiency, maximum output power, longitudinal mode behaviour, lasing wavelength and spectral linewidth.
TL;DR: In this paper, a simple optical technique is reported for determining the expansion coefficient of long metallic bars based on plane wavefront shearing interferometry, which produces quick and fairly accurate results.
Abstract: The dimensional changes produced in materials by temperature variations are generally very small. Hence, sensitive techniques for investigating them are required. A simple optical technique is reported for determining the expansion coefficient of long metallic bars. This newly developed method is based on plane wavefront shearing interferometry, which produces quick and fairly accurate results. The thermal expansion of an object introduces defocusing in the optical system. For calculating this focusing error or the linear thermal expansion the wave aberration function and the wave theory of aberrations have been used.
TL;DR: In this paper, a differential arrangement using a laser for the measurement of the velocity of moving surfaces is discussed and configurations of optical velocimeters with diffraction beam-splitters are shown not to be critical on the wavelength stability of a semiconductor laser.
Abstract: A differential arrangement using a laser for the measurement of the velocity of moving surfaces is discussed. Configurations of optical velocimeters with diffraction beam-splitters are shown not to be critical on the wavelength stability of a semiconductor laser. Laser meters measuring the velocity and length of rolled stock have been built on the basis of the devices considered.
TL;DR: In this paper, the laser calorimetric measurement of the absorption coefficient in a small cubic 12 × 9 × 9 mm KTP crystal has been investigated experimentally, and the measurement accuracy is within 10%.
Abstract: The laser calorimetric measurement of the absorption coefficient in a small cubic 12 × 9 × 9 mm KTP crystal has been investigated experimentally. The absorption coefficient in this crystal is 0.0121 cm -1 , and the measurement accuracy is within 10%.
TL;DR: In this article, a simple reflectometer for measurement of the absolute reflectance of plane specularly reflecting surfaces at normal incidence without using any reference standard is described, and results obtained for samples of high as well as low-reflecting surfaces using a HeNe laser source are reported.
Abstract: A simple reflectometer for measurement of the absolute reflectance of plane specularly reflecting surfaces at normal incidence without using any reference standard is described. Results obtained for samples of high as well as low-reflecting surfaces using a HeNe laser source are reported.
TL;DR: In this paper, various techniques used for multiline operation of TEA CO 2 lasers are reviewed with particular reference to the multilines laser parameters of interest in laser applications.
Abstract: The various techniques used for multiline operation of TEA CO 2 lasers are reviewed with particular reference to the multiline laser parameters of interest in laser applications.
TL;DR: In this paper, the fracture behavior of a four-point bend surface-coated ceramic specimen with a through-the-thickness crack was experimentally investigated, and the influence of the glaze on the fracture behaviour of the composite material was shown.
Abstract: The fracture behaviour of a four-point bend surface-coated ceramic specimen with a through-the-thickness crack was experimentally investigated. Speckle photography was used to measure opening displacements over the specimen surface and across the crack line. For a glazed and unglazed specimen, stress-intensity factors were experimentally determined by means of a method that uses data not restricted to the singularity-dominated zone. Stress-intensity factors were numerically calculated using a three-dimensional finite element analysis and their variations along the crack front were also evaluated. Experimental results agree reasonably well with the numerical results. Results show the influence of the glaze on the fracture behaviour of the composite material.
TL;DR: In this paper, the ionizing effect of γ radiation on a dc CO2 laser is analyzed from an experimental point of view, and the authors develop a simple model that qualitatively explains the laser behaviour.
Abstract: The ionizing effect of γ radiation on a dc CO2 laser is analysed from an experimental point of view. Electron temperature and density are compared with laser output variations and total gas pressure of the maximum output. These parameters allow us to develop a simple model that qualitatively explains the laser behaviour.
Abstract: Transformation of F centres in irradiated NaCl crystals to colloidal (or C) centres by a thermo-optic process is employed to write information into the crystals using a HeCd laser. Hurter-Driffield curves of the storage are constructed and optimum parameters for writing are determined.
TL;DR: In this article, a 2.1 μm Cr 3+, Tm 3+, Ho 3+ : YAG laser is operated with an output power of 20 W at 12 Hz.
Abstract: A 2.1 μm Cr 3+ , Tm 3+ , Ho 3+ : YAG laser is operated with an output power of 20 W at 12 Hz. The laser output is successfully transmitted through a silica fibre. The laser system was designed based on the technology of an alexandrite laser oscillator.
TL;DR: In this article, the problem of spatial coherence applied to confocal optical systems is investigated and the coherence factor or the mutual coherence intensity, assuming perfectly coherent illumination and partially coherent detection, is calculated.
Abstract: The problem of spatial coherence applied to confocal optical systems is investigated. The coherence factor or the mutual coherence intensity, assuming perfectly coherent illumination and partially coherent detection, is calculated. This detection step is dependent upon the pinhole diameter of the receptor. The optimal diameter of the pinhole receptor is discussed.
TL;DR: In this article, an analytical study has been carried out to investigate the effect of various material and structural parameters on the properties of InGaAsP/InP buried heterostructure semiconductor laser diodes (BH-LDs) emitting at 1.3 μm and 1.55 μm.
Abstract: An analytical study has been carried out to investigate the effect of various material and structural parameters on the properties of InGaAsP/InP buried heterostructure semiconductor laser diodes (BH-LDs) emitting at 1.3 μm and 1.55 μm. In particular the influence of the active layer thickness d, the width W and cavity length L are discussed. Also, the effect of the relative refractive index difference δ = (n a − n c ) n a (where na and nc are the active and cladding layer's indices) on (1) the effective refractive index ne, (2) the single-transverse mode condition, (3) the facet reflectivity R0, (4) the mirror loss αmo and (5) the beam divergences both in the direction parallel to, and perpendicular to the junction plane are considered. The analysis which is based on effective index approach has been performed for the fundamental TE0 and TM0 modes. The results can be used to design semiconductor laser diodes and amplifiers for optimum operation.
TL;DR: In this paper, a simple and reliable automatic fringe-counting interferometer featuring a real-time display of cw laser wavelengths is described. But the accuracy of the system is better than one part in 106.
Abstract: We describe a simple and reliable automatic fringe-counting interferometer featuring a real-time display of cw laser wavelengths. The wavemeter and its reference laser constitute a compact construction and offer easy operation. The accuracy of the system is better than one part in 106.