Showing papers in "Optics and Laser Technology in 2000"
251 citations
TL;DR: In this paper, the potential power of digital holography in particle measurement and its expected development in the near future is described, and the basic concept and procedure of digital in-line holographY are shown mainly for particle depth measurement and the performance test results obtained in numerical simulations and experiments are demonstrated.
Abstract: This paper describes the potential power of digital holography in particle measurement and its expected development in the near future. In digital holography, image reconstruction is carried out numerically on a computer using observed hologram patterns and some quantitative information can be derived from the reconstructed images. In this paper, the basic concept and procedure of digital in-line holography are shown mainly for particle depth measurement and the performance test results obtained in numerical simulations and experiments are demonstrated to examine the potential of the present method.
232 citations
TL;DR: In this article, the effects of Brownian motion on particle image velocimetry were analyzed and a weighting function was derived to describe the contribution of the measured velocity as a function of position.
Abstract: In particle image velocimetry applications involving either low velocities or small seed particles, Brownian motion can be significant. This paper addresses the effects of Brownian motion. First, general equations describing cross-correlation particle image velocimetry are derived that include Brownian motion. When light-sheet illumination particle image velocimetry (PIV) is used Brownian motion diminishes the signal strength. A parameter describing this effect is introduced, and a weighting function describing the contribution to the measured velocity as a function of position is derived. The latter is unaffected by Brownian motion. Microscopic PIV Brownian motion also diminishes the signal strength. The weighting function for microscopic PIV is found to depend on Brownian motion, thus affecting an important experimental parameter, the depth of correlation. For both light-sheet illumination and microscopic PIV, a major consequence of Brownian motion is the spreading of the correlation signal peak. Because the magnitude of the spreading is dependent on temperature, PIV can, in principle, be used to simultaneously measure velocity and temperature. The location of the signal peak provides the velocity data, while the spreading of the peak yields temperature.
121 citations
TL;DR: In this article, the basic concepts that govern infrared thermography together with some particular aspects linked to its use are reviewed and different operating methods together with their implementations are also discussed, as well as the capability of IR to deal with several simple, or complex, fluid flow configurations.
Abstract: During the past several years infrared thermography has evolved into a powerful investigative means of thermo-fluid-dynamic analysis to measure convective heat fluxes as well as to investigate the surface flow field behaviour over complicated body shapes. The basic concepts that govern this innovative measurement technique together with some particular aspects linked to its use are herein reviewed. Different operating methods together with their implementations are also discussed. Finally, the capability of infrared thermography to deal with several simple, or complex, fluid flow configurations is analysed.
106 citations
TL;DR: A review of laser Doppler anemometry (LDA) and particle image velocimetry (PIV) with their application to the measurement of sound is presented in this paper.
Abstract: A review of laser Doppler anemometry (LDA) and particle image velocimetry (PIV) with their application to the measurement of sound is presented. The fundamental principles behind LDA and PIV are discussed and extended to the application of sound measurement. Special attention is paid to analysis of LDA signals including the Hilbert transform, which enables amplitude information to be obtained about various frequency components of a signal and wavelet analysis, which allows non-stationary signals to be accurately analysed. The influence of the refractive index variations in a medium due to a sound wave on the laser beams of an LDA signal is discussed. Attention is also paid to acoustic streaming which arises due to high-intensity sound, and PIV results are presented to demonstrate the effect.
85 citations
TL;DR: In this article, a characterisation and analysis of spatter deposition during laser drilling in Nimonic 263 alloy for various laser processing parameters using a fiber-optic delivered 400 W Nd:YAG laser is presented.
Abstract: This paper reports on the characterisation and analysis of spatter deposition during laser drilling in Nimonic 263 alloy for various laser processing parameters using a fibre-optic delivered 400 W Nd:YAG laser. The principal findings are a large proportion of the spatter (approx. > 70%) was deposited due to the initial laser pulses (before beam breakthrough) required to drill a through-hole. Short pulse widths, low peak powers and high pulse frequencies generated smaller spatter deposition areas. At high pulse frequencies, the spatter distribution/thickness can be altered as a result of laser-ejected material interaction. Focal plane positions between −0.5 and +1.5 mm produced relatively similar spatter areas of about 14 mm 2 . As a result of the reduction in the material removed per pulse, a longer focal length of 160 mm generated smaller areas of spatter deposition in comparison to a shorter focal length of 120 mm . In addition, a generic relationship between the spatter area and dentrance/dexit with increasing total laser energy has been established.
78 citations
TL;DR: In this paper, an investigation into the laser processing of medium-density fiberboard (MDF) was carried out using an established experimental methodology developed to study the interrelationship between and effects of varying laser set-up parameters.
Abstract: This paper details an investigation into the laser processing of medium-density fibreboard (MDF). Part 1 reports on the determination of process parameter settings for the effective cutting of MDF by CO2 laser, using an established experimental methodology developed to study the interrelationship between and effects of varying laser set-up parameters. Results are presented for both continuous wave (CW) and pulse mode (PM) cutting, and the associated cut quality effects have been commented on.
55 citations
TL;DR: In this paper, the results from the successful application of the particle imaging velocimetry (PIV) technique to both the blade passage region of a transonic axial compressor and the diffuser region of high speed centrifugal compressor are presented.
Abstract: Digital particle imaging velocimetry (DPIV) is a powerful measurement technique, which can be used as an alternative or complementary approach to laser doppler velocimetry (LDV) in a wide range of research applications. The instantaneous planar velocity measurements obtained with PIV make it an attractive technique for use in the study of the complex flow fields encountered in turbomachinery. The planar nature of the technique also significantly reduces the facility run time over point-based techniques. Techniques for optical access, light sheet delivery, CCD camera technology and particulate seeding are discussed. Results from the successful application of the PIV technique to both the blade passage region of a transonic axial compressor and the diffuser region of a high speed centrifugal compressor are presented. Both instantaneous and time-averaged flow fields were obtained. The averaged flow field measurements are used to estimate the flow turbulence intensity. The instantaneous velocity vector maps obtained during compressor surge provide previously unobtainable insight into the complex flow field characteristics occurring during short lived surge events. These flow field maps illustrate the true power of the DPIV technique.
47 citations
TL;DR: In this article, the authors present the design of a suitable test apparatus for laser welding thin polymer films to a heavier substrate, and shows the results of an investigation into the feasibility of laser welding multi-layer polymer film lids to tubs for the manufacture of aseptic food containers.
Abstract: Keyhole laser welding of polymers is a subject well covered and researched, but relatively little information exists regarding the welding of thin polymer films, particularly to a heavier substrate. This paper presents the design of a suitable test apparatus for laser welding thin film to a heavier substrate, and shows the results of an investigation into the feasibility of laser welding multi-layer polymer film lids to tubs for the manufacture of aseptic food containers. A consistent weld, free from defects, is the key to process success. Typical welding defects have been synthesised in order to investigate, and consequently remove, their cause. The result is a reliable welding method based on even film clamping. With careful attention to machine design, a seal of high mechanical strength and chemical integrity is possible.
42 citations
TL;DR: In this paper, a line-of-sight speckle photography of transparent media is used for quantitative measurements of the instantaneous temperature fields in 3D unsteady flows and the subsequent specklegram treatment uses the Young's fringes method as well as cross-correlation analysis of small interrogation areas of the recordings.
Abstract: The line-of-sight speckle photography of transparent media is used for quantitative measurements of the instantaneous temperature fields in 3D unsteady flows. Both electronic and photographic methods are employed for specklegram recording. The subsequent specklegram treatment uses the Young's fringes method as well as cross-correlation analysis of small interrogation areas of the recordings. Experimental data for three different heat transfer configurations are obtained and discussed. The first one is natural convection over extended vertical heated plates with forward facing steps, the second is unsteady 3D convective flow around a suddenly heated vertical thin wire, and the third one is a convective plume above a multi-jet flame. Both local and global Nusselt numbers are determined via measuring local surface temperature gradients for these convective flows. The results are compared with Ostrach's theory for a single vertical plate and with the data obtained by Mach–Zehnder interferometry. The 3D temperature fields are reconstructed for axisymmetric convective flows around a suddenly heated vertical wire using quasi-double projection measurement and the Radon inversion. 3D temperature distributions above the combustion zone are reconstructed using multi-projection speckle photography measurements and computerised tomography.
38 citations
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TL;DR: In the paraxial approach, the inequality M2⩾1 holds, if M2 is defined by the second moments as discussed by the authors, however, in some publications M2 has not been defined at all.
Abstract: M2 is now widely used to characterize the quality of laser radiation. In the paraxial approach the inequality M2⩾1 holds, if M2 is defined by the second moments. Nevertheless, in some publications M2
TL;DR: This study proposes a method by using quadtree techniques, which are able to recognize the hand shape image within an extremely short time, which uses a parallel grating to project onto the backside of a hand.
Abstract: Automated hand shape recognition has been studied over the past decade and some commercial systems have been developed. Despite these advances, there is not much open public literature discussing the hand shape verification research. This study proposes a method by using quadtree techniques, which are able to recognize the hand shape image within an extremely short time. The geometrical shape of a hand is a biometric characteristic of human beings, although it is different even for a twin sibling. This study uses a parallel grating to project onto the backside of a hand. The parallel grating will be distorted by the curvature shape of the hand and processed by image processing techniques for recognition. This study also presents our recognition results of 100 students captured over a period of time.
TL;DR: In this article, a two-deposited-metal layers method was used to manufacture electron beam grating for high-temperature use and the results verify that the Zr-Pt-type grating possesses heat resistance up to 1100°C in vacuum.
Abstract: This paper proposed new ways for producing multi-layer model grids for electron beam moire method. An electron beam lithography system was set up under scanning electron microscope which was equipped with a beam blanking device and a pattern generator. The two-deposited-metal layers method was used to manufacture electron beam grating for high-temperature use. The results verify that the Zr–Pt-type grating possesses heat resistance up to 1100°C in vacuum. A new type of composite grating with frequencies 100 lines / mm and 1000 lines / mm using three deposited layers was produced. A 10 000 lines / mm two-deposited-metal layers grating was successfully fabricated using electron beam lithography.
TL;DR: Witze et al. as discussed by the authors employed a three-component laser Doppler anemometry (LDA) system to investigate the structure of the flow inside the cylinder of a motored internal combustion engine.
Abstract: A three-component laser Doppler anemometry (LDA) system has been employed to investigate the structure of the flow inside the cylinder of a motored internal combustion engine. This model engine was reasonably representative of a typical, single cylinder, spark ignition engine although it did not permit firing. It was equipped with overhead valve gear and optical access was provided in the top and side walls of the cylinder. A principal objective was to study the influence of the inlet port design on the flow within the cylinder during the induction and compression strokes of the engine. Here, it can be noted that results obtained in an unfired engine are believed to be representative of the flow behaviour before combustion occurs in a fired engine (see P.O. Witze, Measurements of the spatial distribution and engine speed dependence of turbulent air motion in an i.c. engine, SAE Paper No. 770220, 1977; Witze, Sandia Laboratory Energy Report, SAND 79-8685, Sandia Laboratories, USA, 1979). Experimental data presented for an inclined inlet port configuration reveal the complex three-dimensional nature of the flow inside the model engine cylinder. Not surprisingly, the results also show that the inclined inlet port created flow conditions more favourable to mixing in the cylinder. Specifically, the inclined inlet flow was found to generate a region with a relatively high shear and strong recirculation zones in the cylinder. Inclining the inlet port also produced a more nearly homogeneous flow structure at top dead centre during the compression stroke. The paper identifies the special difficulties encountered in making the LDA measurements. The experimental findings are examined and the problems that arise in presenting time-varying three-dimensional data of this type are discussed. Finally, the future potential of this experimental approach is explored.
TL;DR: In this paper, a simple model has been developed to calculate the thermal focal length of a diode side-pumped solid-state laser, which is based on a thermal model with a Gaussian heat density in any cross section of a laser rod.
Abstract: The pump energy distribution in a diode side-pumped solid-state laser, is an overlap of propagating Gaussian beams. A simple model has been developed to calculate the thermal focal length of a diode side-pumped solid-state laser, which is based on a thermal model with a Gaussian heat density in any cross section of a laser rod. It can be seen that as the waists of pump beams increase, the energy distribution tends to be uniform and the thermal focal length tends to be long, which means a smaller thermal focusing.
TL;DR: In this paper, the authors applied wavelength scanning interferometry to Fizeau interferometer for surface profilometry, which is free from ambiguity of the sign in the measurement result.
Abstract: We have applied wavelength scanning interferometry to Fizeau interferometer for surface profilometry. This interferometer is free from ambiguity of the sign in the measurement result. It is more compact in setup than the Michelson interferometer used previously. Experimental results from a step and a dip on a mirror surface are shown. In the focal depth of imaging system, we could measure a mirror surface with less than standard deviations of 20 μm including quantization error in frequency analysis. We also could measure the surface shape of a coin. Origins of the noises appearing in the results are also discussed.
TL;DR: In this article, an experimentally-based method to evaluate the power distribution for both CW and PM cutting is presented, with different power distribution with different cutting speeds, material thickness and pulse ratios.
Abstract: Part 2 of this paper details an experimentally-based method to evaluate the power distribution for both CW and PM cutting. Variations in power distribution with different cutting speeds, material thickness and pulse ratios are presented. The paper also provides information on both the cutting efficiency and absorptivity index for MDF, and comments on the beam dispersion characteristics after the cutting process.
TL;DR: In this article, a high-resolution grating interferometer (GI) based on a transverse Zeeman laser was used to obtain a resolution of 0.7 nm using a heterodyne signal processing method.
Abstract: Metrological feasibilities of a high-resolution grating interferometer (GI) based on a transverse Zeeman laser are investigated. When the grating pitch equals 20 μm, a resolution of 0.7 nm is obtained by means of a heterodyne signal processing method. The comparison of two approaches for determining the residual nonlinearity is presented. One is to evaluate the maximum residual error by determining the amplitude modulation degree of the measurement signal. The other is to do a high precision calibration with a differential dual-frequency interferometer that has a higher precision. The experimental results show that the nonlinearity is no more than 25 nm which fits well with the estimating result. Analysis of the depolarization effect of the grating indicates that it has little influence on the measurement accuracy.
TL;DR: A new methodology to study irregular behaviours in logic cells is reported, based on two types of diagrams, namely phase and working diagrams, where sets of four bits are grouped and represented by their hexadecimal equivalent.
Abstract: A new methodology to study irregular behaviours in logic cells is reported. It is based on two types of diagrams, namely phase and working diagrams. Sets of four bits are grouped and represented by their hexadecimal equivalent. Some hexadecimal numbers correspond to certain logic functions. The influence of the internal and external tolerances, namely those appearing in the employed devices and in the working signals, may be analysed with this method. Its importance in the case of logic structures with chaotic behaviours is studied.
TL;DR: In this paper, the authors compared four kinds of currently available Nd : hosted laser passive Q-switch and mode-locking modulators: plastic dye sheet, LiF : F 2 − color center crystal, Cr +4 : YAG crystal and RG1000 colored glass filter.
Abstract: Four kinds of currently available Nd : hosted laser passive Q-switch and mode-locking modulators: plastic dye sheet, LiF : F 2 − color center crystal, Cr +4 : YAG crystal and RG1000 colored glass filter were investigated in detail and summarized for comparison for the first time. The LiF : F 2 − crystal with outstanding annealability, long lifetime, low cost and operability at high repetition rates is highly recommended.
TL;DR: In this article, the shape of transverse interference fringes formed across isotropic nonabsorbing optical fibers is also calculated, where a laser light sheet is used to illuminate and pass directly through the optical fiber.
Abstract: A new technique (El-Ghandoor et al., Opt. Laser Technol. 31(7) (1999) 481–488) has been applied to study the shape of transverse interference fringes, instead of multiple beam Fizeau fringes (Marhic, Stein, Appl. Phys. Lett. 35 (1975) 1678–1682), from a GRIN optical fiber. In this technique, a laser light sheet is used to illuminate and pass directly through the optical fiber. Theoretical expressions are derived for the optical path differences of three groups of interference beams. The first one passes through the cladding, the core, and then the cladding once again; the second passes through the cladding only, and the third passes through the surrounding air. Theoretical expressions for the shape of transverse interference fringes formed across isotropic non-absorbing optical fibers are also calculated.
TL;DR: A novel arithmetic unit is proposed consisting of a pipelined optical ripple carry adder that adds two words with bits multiplexed by different wavelengths on a single fiber.
Abstract: A novel arithmetic unit is proposed consisting of a pipelined optical ripple carry adder that adds two words with bits multiplexed by different wavelengths on a single fiber. The addition result is returned to a fiber bus in the same format as the incoming words. The corresponding operand bit pairs are split off the fiber using wavelength division demultiplexers. Full adders compute the sum for each bit pair and the carry from the next lower significant bit pair. The full adder uses couplers and NOT, NOR and novel XOR logic gates constructed using semiconductor optical amplifiers for gain and wavelength shifting.
TL;DR: In this article, the effects of 60 W HPDL beams on the removal of chlorinated rubber (CR) paint from concrete surfaces and the ash particles generated from this process were determined using optical microscopy and image analysis.
Abstract: This paper describes the effects of 60 W High Power Diode Laser (HPDL) beams on the removal of chlorinated rubber (CR) paint from concrete surfaces and the ash particles generated from this process. The physical characteristics, including shape and size distribution of the removed and collected airborne CR particles, down to a size of around 1 μm in diameter, were determined using optical microscopy and image analysis. The shape of the particles observed was highly irregular, displaying no symmetry. The size distribution of the collected particles was found to range between 1–2000 μm, with the maximum concentration being found between 29 and 60 μm. The chemical characteristics of the CR ash particles were investigated by means of ESEM and EDX techniques. From a comparative analysis, it was found that the concentration of chlorine within the CR material was significantly reduced after HPDL treatment. This, together with DTA/TGA results indicated a combustive degradation of the CR polymer through the interaction with the process gas, oxygen, and the laser irradiation. Also, a strong correlation between laser power and average particle sizes has been found, with higher powers generally producing larger particle sizes. Opposite effects have been found by changing the oxygen flow rate, with higher oxygen flow producing, on average, smaller particles. An interpretation of the combustion process, as well as a brief discussion on operational safety and environmental impact of the products is attempted.
TL;DR: In this paper, a simple interferometric phasemeter which can be used as a proximity sensor is described, based on the measurement of the phase shift between the p- and s- components of a field caused by the processes of attenuation in total internal reflection.
Abstract: A simple interferometric phasemeter which can be used as a proximity sensor is described. It is based on the measurement of the phase shift between the p- and s- components of a field caused by the processes of attenuation in total internal reflection. The role of the interferometer is to restore the p- and the s- components from the resultant totally reflected field, with minimum amplitude and phase distortions and to let them interfere. The phase shift as a function of the attenuation of the total internal reflection can be determined from the interference signal. The interferometer is of a common path polarization shearing type, consisting of Rochon beamsplitter and a linear polarizer. An experiment for measuring the distance between glass plane surface and a plane attenuater made of Si mono-crystal is described. A good agreement between theory and experiment for separations less than 300 nm is observed. This device can be applied in research and metrology. After further modifications, the optical system could be used for proximity sensing, surface geometry control, variable optical retarders, contamination monitoring, etc.
TL;DR: In this paper, the relationship between the heat intensity in a laser slab and the heat transfer coefficient has been studied by considering the variations of thermal conductivity and expansion coefficient of the laser slab with temperature.
Abstract: Thermal heating is a major limiting factor in scaling the average power of a solid-state laser. The relationship between the heat intensity in a laser slab and the heat transfer coefficient has been studied by considering the variations of thermal conductivity and expansion coefficient of the laser slab with temperature. In this paper, the laser rod has been studied by including its thermal, stress and optical aberration effects. It is pointed out that different heat transfer coefficients should be adopted according to different heat intensities inside the laser rod in order to obtain better pumping input as well as to optimize the cooling effects.
TL;DR: In this article, the effect of atmospheric optical turbulence on ultraviolet (UV) radiation with a wavelength of 253.7 nm was investigated using a UV scintillometer with a path length of 185 m and it was found that the scintillation predicted by currently available models which take into account the effects of inner scale, saturation and aperture averaging was in good agreement with the measurements made under various conditions in weak turbulence.
Abstract: We investigate the effect of atmospheric optical turbulence on ultraviolet (UV) radiation with a wavelength of 253.7 nm. The normalized irradiance variance (scintillation index) was measured using a UV scintillometer with a path length of 185 m. The dependence of the UV scintillations on the atmospheric turbulence structure parameter and inner scale was determined through simultaneous measurements of these quantities made with a visible laser scintillometer. The dependence of the UV scintillation index and its probability density function on receiver aperture size was also measured. It was found that the scintillation predicted by currently available models which take into account the effects of inner scale, saturation and aperture averaging was in good agreement with the measurements made under various conditions in weak turbulence.
TL;DR: In this article, Coupland et al. introduced conjugate reconstruction, a new method of holographic recording and reconstruction that allows a constant image shift to be introduced to the particle image displacement.
Abstract: Holographic recording techniques have recently been studied as a means to extend two-component, planar particle image velocimetry (PIV) techniques for three-component, whole-field velocity measurements. In a similar manner to two-component PIV, three-component, holographic PIV (HPIV) uses correlation-based techniques to extract particle displacement fields from double-exposure holograms. Since a holographic image contains information concerning both the phase and the amplitude of the scattered field it is possible to correlate either the intensity or the complex amplitude. In previous work we have shown that optical methods to compute the autocorrelation of the complex amplitude are inherently more tolerant to aberrations introduced in the reconstruction process, Coupland, Halliwell, Proc. Roy. Soc. 453 (1960) (1997) 1066. In this paper we introduce a new method of holographic recording and reconstruction that allows a constant image shift to be introduced to the particle image displacement. The technique, which we call conjugate reconstruction, resolves directional ambiguity and extends the dynamic range of HPIV. The theory of this method is examined in detail and a relationship between the image and object displacement is derived. Experimental verification of the theory is presented.
TL;DR: In this article, the CIE color difference formula was applied to evaluate four types of material surfaces; anodized aluminium, stainless steel, poly-butylene tetra-phthalate (PBT), and phenol formaldehyde, viewed under three common modes of illumination; tungsten, fluorescent and daylight.
Abstract: In this paper, the CIE color difference formula was applied to evaluate four types of material surfaces; anodized aluminium, stainless steel, poly-butylene tetra-phthalate (PBT), and phenol formaldehyde, marked using a Nd:YAG laser, and viewed under three common modes of illumination; tungsten, fluorescent and daylight. The color difference values were based on the spectral reflectance readings obtained from a spectrophotometer. Each material exhibited different color difference trends in relation to marking speed for the different modes of illumination. Nevertheless, general comparisons could be made in terms of operational marking speeds and the maximal color difference values for each material.
TL;DR: In this paper, the design and operation of a laser scanning system based on a synchronized scanning geometry is described and results for scanning plane and cylindrical surfaces are reported, and deviations of the experimental results from that of the expected theoretical ones are presented.
Abstract: Design and operation of a laser scanning system based on a synchronized scanning geometry is described. Results for scanning plane and cylindrical surfaces are reported. Deviations of the experimental results from that of the expected theoretical ones are presented. The described system offers a good reproducibility and results agree well with the theory. The results obtained from our system are satisfactory and show a promise in order to be used in the real applications. The reported approach can also be used in the design of a three-dimensional vision system.
TL;DR: In this paper, the Poincare sphere representation of polarization states is used to derive two auxiliary equations for phase retardance measurements, in addition to another two previously derived equations, allowing for extending the range of validity of a model for calibrating phase plates in pairs.
Abstract: The Poincare sphere representation of polarization states is used to derive two auxiliary equations for phase retardance measurements. These equations, in addition to another two previously derived equations, allow for extending the range of validity of a model for calibrating phase plates in pairs. In another application, the sphere is used to explain a new method for identifying the principal axes of two birefringent phase plates during their calibration.