Showing papers in "Optics and Laser Technology in 1991"
TL;DR: In this article, the authors reviewed the study of time-varying speckle phenomena observed in light-fields scattered from living objects and introduced methods for evaluating blood flow in the skin surface, internal organs, and ocular fundus.
Abstract: The study of time-varying speckle phenomena observed in light-fields scattered from living objects is reviewed. The laser speckles produced from living objects may be called ‘bio-speckles’ and fluctuate temporally due to various physiological movements such as blood flow. The time-varying properties of the bio-speckles are experimentally investigated from the analyses of the power spectrum and the autocorrelation function. Based on the knowledge of dynamic bio-speckles, some methods are introduced for evaluating blood flow in the skin surface, internal organs, and ocular fundus. The experimental results show that the degree of blood flow is reflected sensitively by the time-varying properties of the bio-speckles and this can be utilized for monitoring the blood flow.
249 citations
TL;DR: In this paper, the authors used time-average shearography to detect and size of flaws such as debonds or delaminations in glass fiber reinforced plastic beams, where the component has to be excited at the resonance frequencies of the flaws.
Abstract: Results on flaw detection of glass fibre reinforced plastic beams using time- average shearography are presented here. Detection and sizing of flaws such as debonds or delaminations are successfully carried out using this technique. For easy detection of flaws, the component has to be excited at the resonance frequencies of the flaws. As the flaw gets smaller, a higher frequency is required. For flaws of the same exterior size, a deeper one will also require a higher frequency.
56 citations
TL;DR: This procedure of spatial phase stepping has been implemented on a fast microcomputer, enabling quantitative results to be obtained in a particularly simple qay.
Abstract: In a two-beam optical interferometer, introduction of a tilt between the beams produces a set of nominally straight and equispaced fringes. The phase information represented by deformations in this fringe pattern can then be calculated at each point in a video image by using intensity samples from a group of neighbouring positions. Deformations of a linear grid pattern as encountered in moire methods can be analysed in the same manner. This procedure of spatial phase stepping has been implemented on a fast microcomputer, enabling quantitative results to be obtained in a particularly simple qay.
45 citations
TL;DR: In this article, a dual field grating has been introduced for use in Talbot interferometry, and the results of an experimental investigation on setting sensitivity when using these gratings for testing are presented.
Abstract: A dual field grating has been introduced for use in Talbot interferometry. We report here results of an experimental investigation on setting sensitivity when using these gratings for testing.
33 citations
TL;DR: In this paper, an optical refracting system was designed to transform an input Gaussian laser beam into a diffraction-free Bessel beam, which was optimized for ease of fabrication.
Abstract: An optical refracting system has been designed to transform an input Gaussian laser beam into a diffraction-free Bessel beam. The optical systems characteristics are optimized for ease of fabrication.
29 citations
TL;DR: In this article, the authors used particle image velocimetry to image seeding particles at up to 2.5 m from the flow in a large-scale transonic wind tunnel.
Abstract: Velocity measurements have been made in a large-scale transonic wind tunnel using particle image velocimetry. Diffraction-limited optics have been used to image seeding particles at up to 2.5 m from the flow. A practical system to record the data has been constructed such that the camera can be remotely focused on the plane of interest. Particle images were recorded onto 35 mm film. Results were obtained from Mach numbers 0.2 to 0.8, and automatically analysed to produce vector maps of the planar velocity field. It has also been shown that particle image velocity data can be successfully recorded onto a charged coupled device image sensor at transonic speeds. This approach eliminates the need for photographic processing and allows real time data acquisition in a digital form. The potential is then apparent for automatic, and near real-time processing, of particle image velocimetry data.
26 citations
25 citations
TL;DR: In this paper, a simple method for measuring the radius of curvature of a spherical surface using compensation of a collimated beam is described, which can also be used for the determination of the focal length of the collimating lens employed.
Abstract: A simple method for measuring the radius of curvature of a spherical surface using compensation of a collimated beam is described. The same method can also be used for the determination of the focal length of the collimating lens employed. Results of the measurements using this technique are presented. Investigations on the achievable accuracies and the proper choice of parameters are carried out and the results discussed.
20 citations
19 citations
TL;DR: In this paper, the performance characteristics of three unique optically-addressed spatial light modulators (SLMs) have been experimentally investigated and measured parameters include resolution, visibility, imaging response time, and write light sensitivity.
Abstract: The performance characteristics of three unique optically-addressed spatial light modulators (SLMs) have been experimentally investigated. The measured parameters include resolution, visibility, imaging response time, and write light sensitivity. The modulators investigated include two relatively new technologies, the ferroelectric liquid crystal (FLC) SLM from the University of Colorado-Boulder and the amorphous silicon photoconductive twisted nematic liquid crystal SLM from GEC-Marconi Research, and a well-established industry benchmark, the Hughes Liquid Crystal Light Valve (LCLV).
11 citations
TL;DR: In this paper, a new and simple technique of phase retardation measurement is presented based on computer-aided analysis of diffraction patterns generated by phase objects, which is suitable for techniques where a phase modulation is obtained by the exposure of a photo-sensitive medium.
Abstract: This paper presents a new and simple technique of phase retardation measurement. it is based on computer-aided analysis of diffraction patterns generated by phase objects. Special flatness of the object substrate is not required for this method. The method is especially suitable for techniques where a phase modulation is obtained by the exposure of a photo-sensitive medium. The method can aid the prediction of the desired phase shift from the exposure. The phase retardation measurement method is described for an efficient kinoform manufactured using a simple, well known photochemical (silver-halide) process. Experimental results are presented.
TL;DR: Experimental results in edge extraction for both binary and grey-scale transmissive objects are reported, achieved using morphological transformations and a threshold decomposition technique.
Abstract: Real-time non-linear image processing has been achieved using an active optical scanning technique This paper reports experimental results in edge extraction for both binary and grey-scale transmissive objects Binary edge extractionis achieved using morphological transformations, while grey-scale edge extraction is achieved using a threshold decomposition technique Advantages and limitation of both techniques are identified
TL;DR: In this paper, it was shown that films of the order of a nanometre in thickness are detectable in the presence of an exponentially decaying evanescent wave in the fluorescing medium.
Abstract: If the interface between a dielectric surface and an adjacent, fluorescing, medium of lower refractive index is illuminated by a collimated light beam, an exponentially decaying evanescent wave is generated in the fluorescing medium. The electric field of the evanescent wave generates easily measurable fluorescence. If part of the surface is covered with a dielectric film, the fluorescence generated is smaller, since some of the decaying wave occurs in a non-fluorescing medium. Measurement of the difference between the fluorescing signals enables the non-destructive measurement of the film thickness to be made. Several questions arise, for example (i) what angle of incidence should be used, (ii) how is the sensitivity influenced by the substrate refractive index, (iii) should p-or s-polarized light be used, (iv) what sensitivity is attainable? This paper answers these questions and indicates that films of the order of a nanometre in thickness are detectable.
TL;DR: In this paper, the development of a high-energy, pulsed Nd:YAG laser system for materials processing and medical applications is reported. And an automatic operation system using a microprocessor-based driver/controller enables safe operation of the laser system and automatic material processing when integrated in a laser/robot system.
Abstract: The development of a high-energy, pulsed Nd:YAG laser system for materials-processing and medical applications is reported here. A variable pulse width in the range of 0.3–10 ms and a variable pulse repetition rate up to 50 pps are provided. An automatic operation system using a microprocessor-based driver/ controller enables safe operation of the laser system and automatic material processing when integrated in a laser/robot system.
TL;DR: In this paper, the refractive fringe diagnostic was applied to a spherical shock wave in air generated by an arc discharge, where a pulsed ruby laser was used as the probe beam.
Abstract: The refractive fringe diagnostic was applied to a spherical shock wave in air generated by an arc discharge. A pulsed ruby laser, synchronized with the shock generation, was used as the probe beam. Both fine and coarse fringes were observed and were modelled computationally. Agreement with the broad features of the density profile predicted by theory was obtained, but the gradient of the theoretical shock rear was found to be too shallow. The shock tail was seento be stationary over a duration of hundreds of microseconds.
TL;DR: In this paper, the effect of atmospheric attenuation in the Raman lidar detection of pollutants is investigated and an atmospheric model is given, and the choice of a suitable laser is discussed.
Abstract: The effect of atmospheric attenuation in the Raman lidar detection of pollutants is investigated. Atmospheric transmittance is discussed and an atmospheric model is given. Optimization of the excitation wavelength for lidar detection of various pollutants is covered and the choice of a suitable laser is discussed.
TL;DR: In this article, an exponential grating was proposed for Gaussian laser beam diameter measurement, which provides accurate measurement of submicron to millimetre diameter laser beams, and is shown to be suitable for the measurement of Gaussian beam diameter.
Abstract: A novel exponential grating is proposed for Gaussian laser beam diameter measurement. The grating provides accurate measurement of submicron to millimetre diameter laser beams.
TL;DR: In this paper, a simple visual method based on the conical diffraction phenomena is described for alignment and/or determination of the tilting of a surface using the analyses of the diffraction orders' position.
Abstract: A simple visual method, based on the conical diffraction phenomena, is described for alignment and/or determination of the tilting of a surface. The method uses the analyses of the diffraction orders' position. The accuracy of this method is the same as in classical methods.
TL;DR: A survey of the literature dealing with spatial filter designs that have found application in coherent optical correlator systems is presented in this paper, where a variety of spatial filters are specified in terms derived from their Fourier transforms.
Abstract: This article presents a survey of the literature dealing with spatial filter designs that have found application in coherent optical correlator systems. Its purpose is to assist in one's choice of a spatial filter or set of filters for a particular application. A variety of spatial filters are specified in terms derived from their Fourier transforms or related transforms. Of particular and current interest are the phase-only and binary phase-only filters. Definitions of a large number of spatial filter types are presented and briefly discussed herein. Diffraction efficiency and signal-to-noise ratio evaluation criteria are also defined. For convenience a summary table of filter designs is included.
TL;DR: In this article, the operational characteristics and spectral properties of a high pressure (up to 1.2 MPa) small size (3.5 cm 3 discharge volume), high repetition frequency (10 Hz), low voltage (down to 15 kV) CO 2 TEA laser are reported.
Abstract: In this work we report the operational characteristics and the spectral properties of a high pressure (up to 1.2 MPa) small size (3.5 cm 3 discharge volume), high repetition frequency (10 Hz), low voltage (down to 15 kV) CO 2 TEA laser. A simple model for the pulling and the linewidth of the laser is given which agrees with the measured values. Linear continuous tuning is also obtained on the weaker lines.
TL;DR: In this paper, a coherent shadow projection approach for subpixel edge positioning and part sizing is described, where the Fresnel diffraction pattern at the shadow borders is used to locate precisely the edges by an iterative cross- correlation procedure.
Abstract: An approach for subpixel edge positioning and part sizing by coherent shadow projection is described. Templates matching the Fresnel diffraction pattern at the shadow borders are used to locate precisely the edges by an iterative cross- correlation procedure. A similar procedure is followed to compensate for longitudinal displacements by monitoring their effects on the diffraction pattern. The performance is analysed in the presence of mechanical, optical and electronic perturbations. A resolution of nearly 0.015 pixels and an accuracy of 0.15 pixels have been obtained.
TL;DR: In this paper, the dependence of the SNR and the signal beam gain on the crystal orientation was analyzed using a HeNe laser and it was found that orientating the crystal for maximum gain gives poor signal-to-noise ratio.
Abstract: In signal beam amplification by two-beam coupling in BaTiO 3 photorefractive crystals, beam fanning in the direction of the amplified signal reduces the signal-to-noise ratio (SNR). The dependence of the SNR and the signal beam gain on the crystal orientation are analysed using a HeNe laser. It is found that orientating the crystal for maximum gain gives poor signal-to-noise ratio. A compromise has to be made between the SNR and high gain for optimum signal amplification.
TL;DR: In this paper, a method of scaling the light intensity distribution in the Fresnel region is presented, which enables a modification of the zone plate transmittance, which leads to a scale transformation of the output focal curve.
Abstract: The paper presents a method of scaling the light intensity distribution in the Fresnel region. This can be useful in the design of computer generated diffractive optical elements. In particular, the method enables a modification of the zone plate transmittance, which leads to a scale transformation of the output focal curve. The approach is useful in those cases where the focal curve to be transformed is localized in the plane parallel to that of the zone plate and the complex amplitude of the focusing element is known in an analytic form. The theoretical description is based on the similarity property of the Fourier transform. The method is demostrated by obtaining computer generated zone plates with elliptic and hyperbolic focal curves.
TL;DR: In this paper, the surface slopes of some thin plates are measured using moire interferometry, which can be used with any thin plates having different shapes and which are subjected to complicated extra forces.
Abstract: In this paper, the surface slopes of some thin plates are measured using moire interferometry. This method can be used with any thin plates having different shapes and which are subjected to complicated extra forces — situations difficult to do by theoretical calculation. The method is simple and has high sensitivity.
TL;DR: In this article, a gigahertz mode-tunable waveguide CO2 laser operating with high-pressure He-free mixtures (⩽0.4 bar), with a long pulse (20 μs) high repetition rate (1 kHz) radio-frequency discharge was presented.
Abstract: This paper reports on a gigahertz mode-tunable waveguide CO2 laser operating with high-pressure He-free mixtures (⩽0.4 bar), with a long pulse (20 μs) high repetition rate (1 kHz) radio-frequency discharge. Single-mode tuning at 0.92 GHz with good mean laser linewidth (<40 MHz) and large peak power (150 W) have been obtained over 40 laser lines, with 0.3 W mean power. By using standard He reach mixtures both the laser line number and mean power are slightly increased.
TL;DR: In this article, an alexandrite-laser rod was actively Q-switched in the transversal fundamental mode at λ = 758 nm with an double crystal KD ∗ P Pockels cell.
Abstract: An alexandrite-laser rod was actively Q-switched in the transversal fundamental mode at λ = 758 nm with an double crystal KD ∗ P Pockels cell. Pulse width, pulse energy and optical pulse delay (the build-up time of the photon field in the resonator) were measured as functions of pumping energy, rod temperature and reflectivity of the output coupling mirror. As the laser gain of alexandrite strongly depends on temperature, the pulse width and pulse energy were also investigated as functions of the temperature of the active material. A comparison of experimental data with theory was made.
TL;DR: The design of a new ophthalmoscope which may be used both to survey the whole retina, using a wide field of view, and also to perform a detailed inspection at a higher magnification over a smaller field of sight is described.
Abstract: At present clinicians use two types of opthalmoscope to examine the retina. These are the direct ophthalmoscope (for small field of view, high magnification) and the indirect ophthalmoscope (for large field of view, low magnification). This paper describes the design of a new ophthalmoscope which may be used both to survey the whole retina, using a wide field of view, and also to perform a detailed inspection at a higher magnification over a smaller field of view. The new optical system employs a two-conjugate zoom system to provide continuous coverage over the full magnification and field ranges of the existing direct and indirect ophthalmoscopes.
TL;DR: In this article, glass and scintillator damage has been induced using CO2 and Nd3+: YAG lasers, and analyzed both with an optical microscope and analytical calculus.
Abstract: Glass and scintillator damage has been induced using CO2 and Nd3+: YAG lasers, and analysed both with an optical microscope and analytical calculus. The analyses of possible theories and effects are also presented.
TL;DR: In this article, it was shown that the Nd:YALO 3 crystal is a useful kind of laser crystal to operate in a pulsed laser at 1341.4 nm.
Abstract: On the basis of a measured stimulated emission cross-section for the 4 F 3/2 - 4 I 13/2 transition of the Nd 3+ ion in a YAP crystal, it is shown that the Nd:YALO 3 crystal is a useful kind of laser crystal to operate in a pulsed laser at 1341.4 nm. Output energy of 5.31 J with an overall efficiency of 1.84% at 1341.4 nm has been achieved by using a 6 mm diameter and 101 mm long A-axis YALO 3 rod with 1 at.% Nd 3+ ion.