Proceedings Volume 3407

International Conference on Applied Optical Metrology

Pramod Kumar Rastogi, Ferenc Gyimesi
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Proceedings Volume 3407

International Conference on Applied Optical Metrology

Pramod Kumar Rastogi, Ferenc Gyimesi
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 29 September 1998
Contents: 15 Sessions, 77 Papers, 0 Presentations
Conference: International Conference on Applied Optical Metrology 1998
Volume Number: 3407

Table of Contents

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Table of Contents

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  • State of the Art in Optical Metrology I
  • Progress in Phase Measurement Interferometry
  • State of the Art in Optical Metrology II
  • Holographic Interferometry
  • Colloquium in Recognition of Zoltan Fuzessy: International Tribute I
  • Colloquium in Recognition of Z. Fuzessy: International Tribute II
  • Colloquium in Recognition of Z. Fuzessy: Hungarian Tribute I
  • Colloquium in Recognition of Z. Fuzessy: Hungarian Tribute II
  • State of the Art in Optical Metrology I
  • Speckle Metrology I
  • Optical Methods for the Testing of Microsystem Elements
  • Fiber Optic Sensors and Applications
  • Speckle Metrology II
  • Specialized Techniques and Applications I
  • Grating and Moire-Related Techniques
  • Specialized Techniques and Applications II
State of the Art in Optical Metrology I
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Nature of the optical information recorded in speckles
The process of encoding displacement information in electronic Holographic Interferometry is reviewed. Procedures to extend the applicability of this technique to large deformations are given. The proposed techniques are applied and results from these experiments are compared with results obtained by other means. The similarity between the two sets of results illustrates the validity for the new techniques.
Large deformation measurement and analysis on related curved surfaces
Walter Schumann
In the field of holographic Interferometry the technique with two holograms and modifications at the reconstruction is investigated in case of large deformations of an opaque body. The recovering of previously invisible fringes and the strain determination is briefly outlined. Two conditions for the smallness of the first derivative of the optical path difference should ensure locally a proper spacing and a sufficient contrast of the fringes. The three linear forms from the first derivative are analyzed with the polar decomposition, some affine connections and the transverse ray aberration. Frenet's curvature relations, an involution from the shell theory, the changes of geodesic curvature and the integrability are involved. The latter points to the dislocation theory. The principal subject is the second derivative of the path difference to analyze the fringe curvature. Three quadratic forms appear besides terms with the fringe and visibility vectors. They contain the derivatives of the dilatation and the curvature change of the object surface and the virtual deformation of the images. The duality of the aberration permits the elimination of some bilinear forms. In the appendix the previous relations of curvature change are illustrated by a short extension to the Ricci tensor and to geodesics in general. An interpretation by a virtual deformation of Schwarzschild's solution of the field of gravitation is added as a simple example.
Deformation measurement by optical field methods in material testing and for verification of numerical simulation
Reinhold Ritter
Optical field methods are suitable for deformation measurements of all visible points on a considered object surface. Using the deformation values the strain tensor for the case of plane deformation state of all points can be determined. Applying an adapted strength hypothesis to its components produces a reference strain. In order to dimension an object the reference value has to be smaller than the allowed strain measured by a one-dimensional tensile test. The electronic speckle pattern interferometry and the object grating method are particularly suitable for material testing and for verification of numerical simulation. The electronic speckle pattern interferometry is especially applied, if the two compared deformation states differ from each other only by a small amount and if the expected strain values are small. The application of the object grating method is not limited by the two considered deformation states. The limitation is given more by the accuracy of the digital image processing algorithms or the grating structure. The strain values to be determined have to be greater than 0.1%. Furthermore the object grating method is applicable for the case of very small object surfaces which take only few micrometer squared and at high temperatures up to approximable 1000 degrees Celsius. Several practical examples of the application of these two methods in material testing and for verification of numerical simulation are presented.
Real-time phase distribution analysis of fringe patterns
A phase-shifting scanning moire method and a phase-difference scanning moire method are developed by the authors. They provide smooth equal-height contours and equal-displacement contours, respectively, in real-time. A phase-shifting method using correlation with rectangular is also developed. It uses the correlation of the rectangular brightness of a projected grid and two rectangular functions to determine a phase. It can provide accurate phase distributions in real-time.
Near-field optical metrology
Michel Spajer
The relations of Near Field Optics with Metrology are of two kinds. First, it shifts the resolution limit towards the nanometer scale. This improvement is due to a strong interaction between the probe and the sample and its consequence for the quantitative interpretation is a non- linear relation between the image and the object. Secondly, Near Field Optics uses some of the classical detection methods of metrology such as heterodyne interferometry and image processing.
Measurement devices with and for micro-optics at the University of Erlangen
Several devices for the measurement of micro-optical elements will be presented. These are a Mach-Zehnder interference microscope for the measurement of the wave aberrations of microlenses in transmission using a HeNe laser (633 nm wavelength) and a shearing interferometer for the measurement of microlenses in transmission in the near infrared (1319 nm). This shearing interferometer uses two Ronchi gratings to provide a lateral shear and is therefore very compact and stable. We also describe a Twyman-Green interference microscope for the measurement of (nearly) spherical surfaces in reflection using partially coherent illumination. Microlenses can be also used to build measurement devices from micro- and macro-optics. We will present a Shack-Hartmann wavefront sensor with microlenses for the measurement of quite arbitrary wavefronts and a confocal set-up which uses an array of microlenses and stops to provide a confocal measurement without a lateral scanning of the object. This confocal set-up can be used to measure the surface profile of micro-optical structures like gratings or microlenses.
Progress in Phase Measurement Interferometry
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Fringe pattern analysis methods: up-to-date review
The paper is intended to be a review of fringe pattern analysis, FPA methods and their capabilities to analyze extended class of fringe patterns. The special emphasis is paid to the distinction between passive and active methods and the general trend to hybridization of the approaches in FPA. More detailed description is given to the general description of the most commonly used FPA methods, namely: temporal and spatial carrier phase shifting methods. Latter various approaches to absolute phase determination basing an application of additional means or modification of system parameters and including fringe numbering, phase unwrapping or hierarchical unwrapping are analyzed and compassed.
Design of algorithms for phase measurement
Yves Surrel
A large number of optical measurement methods provide a fringe pattern which must be processed in order to extract the fringe phase, where the physical information is. Today, phase- stepping has become the standard method for fringe processing. A set of fringe patterns is digitized, where the fringe phase is varied by a known amount from frame to frame. The 'algorithm' is the mathematical formula which relates the set of recorded images to the phase field. However, it is desirable that this algorithm be independent of some well- known systematic sources of error: nonsinusoidal profile of the fringes, miscalibrated phase shifts, bias variation and so on. Some procedures to design such an algorithm have been proposed recently. Among them, the characteristic polynomial theory has proved to be a simple tool which allows to fully customize the algorithm, so that the most efficient use of the recorded frames is done. Apart from the simplicity of the computations which are necessary, one of the most interesting features of the theory is that it is possible to give analytical formulae for the residual phase errors, thus allowing a fully metrological approach. The present paper give the basics of the theory, and practical rules to design fully customized algorithms.
Fourier analysis of phase-shifting algorithms
The analysis of phase detection algorithms in the Fourier domain provides information about the overall performance characteristics for complex, non-ideal signals encountered in real-world instruments. Thus phase algorithms can be optimized and adapted to the particular application at hand. After a review of the basic Fourier description of phase algorithms, several cases are discussed demonstrating this ability. These cases include phase shift error, non-sinusoidal.
Progress in phase unwrapping
Jonathan Mark Huntley, C. R. Coggrave
This paper reviews some of the main developments in numerical phase unwrapping techniques that have been introduced over the past five years. In quality control applications of wholefield optical techniques it is often necessary for the phase unwrapping to be both robust and performed within a guaranteed time period of a few seconds or less. Deterministic algorithms that have data-independent run times are therefore desirable. The temporal phase unwrapping algorithm has been implemented on a pipeline image processor which is able to calculate phase maps from phase-shifted fringe patterns acquired at 30 frames s-1, and to unwrap the resulting phase maps in real time. One application of the system is measurement of surface profile. The fringe patterns are projected at 30 frames s-1 using a high resolution data projector. The spatial frequency is reduced exponentially from the maximum value. The sequence of phase values at a given pixel is then unwrapped independently of the other image pixels, and all the intermediate phase values contribute in a least squares sense to the final range estimate for the pixel. A total acquisition and processing time of 0.7 s has been achieved for a maximum spatial frequency of 16 fringes across the field of view.
State of the Art in Optical Metrology II
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Surface topometry by multiwavelength technique and temporal Fourier transformation
Hans J. Tiziani, Bernhard Franze, Pascal Haible, et al.
Absolute interferometry can be a powerful tool for distance and shape measurement. Two and more wavelengths can be used to increase the range of unambiguity in interferometry. Furthermore it leads to the possibility to apply interferometric methods to measure optical rough surfaces. A continuously tunable laser in a two beam unequal path interferometer is used to overcome the ambiguity problem of classical interferometric methods. While the laser wavelength is tuned continuously, the variation of the interference intensity is recorded sequentially. At each image pixel the frequency of the signal modulation is analyzed, giving the absolute depth information for the corresponding object point. The wavelength tuning step governs the depth of measurement whereas the tuning range determines the depth resolution to be obtained. The method can be applied for optical as well as for technical surfaces. In the latter case, the intensity variation is observed independently in each speckle. However, the resolution of the measurement of optically rough surfaces is limited by the surface roughness. The continuous tuning of the wavelengths is performed with a diode laser with external cavity where a frequency variation of 30 nm can be obtained without mode hops within one second. Furthermore a novel method to measure the shape and steps heights by rotating the object and using temporal evaluation of the speckles' modulation is presented. Currently a temporal Fourier- transformation is used, similar to the evaluation method used in wavelength scanning interferometry.
New applications of in-plane, shadow, and reflection moire methods
Fu-Pen Chiang, M. L. Du, I. M. Kao
This paper describes some recent applications of the classical moire methods. The first is the use of in-plane moire method to monitor crack tip strain during cyclic loading. A new model predicting the crack growth rate using crack tip strain as a parameter is proposed. The second is the development of a modified shadow moire method for mapping warpage of silicon wafers due to the presence of residual stress. Talbot effect is introduced to enhance the sensitivity of the shadow moire method. The third example is the use of a modified reflection moire method to monitor the quality of thin films deposited on substrates.
Whole-field digital analysis of photoelastic fringe patterns
Terry Y. Chen
Digital approaches for fringe multiplication, determination of fringe order and principal stress direction in photoelasticity are presented. Relevant theories are described. The scheme developed allows for: (1) multiply the fringes to a factor of 16; (2) automatic determination of the fringe orders with or without zero-order fringes in the fringe patterns, (3) directly determining the principal stress angles in the range (pi) /2. Test results are reported.
Diffractive optical element in materials testing
Raimo Veil Johannes Silvennoinen, Kai-Erik Peiponen
The object of this paper is to present a sensor based on diffractive optics that can be applied for the materials testing. The present sensor, which is based on the use of a computer-generated hologram (CGH) exploits the holographic imagery. The CGH-sensor was introduced for inspection of surface roughness and flatness of metal surfaces. The results drawn out by the present sensor are observed to be in accordance with the experimental data. Together with the double exposure holographic interferometry (DEHI) and digital electronic speckle pattern interferometry (DSPI) in elasticity inspection, the sensor was applied for the investigations of surface quality of opaque fragile materials, which are pharmaceutical compacts. The optical surface quality was observed to be related to the porosity of the pharmaceutical tablets. The CGH-sensor was also applied for investigations of optical quality of thin films as PLZT ceramics and coating of pharmaceutical compacts. The surfaces of PLZT samples showed fluctuations in optical curvature, and wedgeness for all the cases studied. For pharmaceutical compacts, the optical signals were observed to depend to a great extent on the optical constants of the coatings and the substrates, and in addition to the surface porosity under the coating.
Optical interferometry techniques in electrochemistry and corrosion
In the present investigation, an optical corrosion-meter has been developed for materials testing and evaluation of different corrosion phenomena. The idea of the optical corrosion-meter was established based on principles of 3D- holographic interferometry for measuring microsurface dissolution, i.e. mass loss, and on those of electrochemistry for measuring the bulk electronic current, i.e. corrosion current of metallic samples in aqueous solutions. In the present work, images of 3D-interferometric microscopy of stainless steel samples were obtained by the optical corrosion-meter during different stages of electrochemical behaviors of stainless steel in different aqueous solutions. In fact, an early stage of the anodic dissolution behavior of the stainless steel samples was monitor during the anodic polarization measurement in 5N sulfuric acid. In addition, an early stage of pitting corrosion of stainless steel samples was monitored in situ by the optical corrosion-meter during the cyclic polarization test in seawater. The observations of pitting were basically interferometric perturbations detected only on the surface of the stainless steel in seawater. The interferometric perturbations interpreted as a localized corrosion in a form of an early pittings, of a depth ranged between 0.3 micrometer to several micrometers.
Roughness parameters and surface deformation measured by coherence radar
Peter Ettl, Berthold E. Schmidt, M. Schenk, et al.
The 'coherence radar' was introduced as a method to measure the topology of optically rough surfaces. The basic principle is white light interferometry in individual speckles. We will discuss the potentials and limitations of the coherence radar to measure the microtopology, the roughness parameters, and the out of plane deformation of smooth and rough object surfaces. We have to distinguish objects with optically smooth (polished) surfaces and with optically rough surfaces. Measurements at polished surfaces with simple shapes (flats, spheres) are the domain of classical interferometry. We demonstrate new methods to evaluate white light interferograms and compare them to the standard Fourier evaluation. We achieve standard deviations of the measured signals of a few nanometers. We further demonstrate that we can determine the roughness parameters of a surface by the coherence radar. We use principally two approaches: with very high aperture the surface topology is laterally resolved. From the data we determine the roughness parameters according to standardized evaluation procedures, and compare them with mechanically acquired data. The second approach is by low aperture observation (unresolved topology). Here the coherence radar supplies a statistical distance signal from which we can determine the standard deviation of the surface height variations. We will further discuss a new method to measure the deformation of optically rough surfaces, based on the coherence radar. Unless than with standard speckle interferometry, the new method displays absolute deformation. For small out-of-plane deformation (correlated speckle), the potential sensitivity is in the nanometer regime. Large deformations (uncorrelated speckle) can be measured with an uncertainty equal to the surface roughness.
Surface profilometry by wavelength scanning interferometry
Ichirou Yamaguchi, Akihiro Yamamoto, Masaru Yano
Parallel and absolute measurement of surface profiles are realized on objects including diffuse surfaces and discontinuities such as steps and holes. Sensitivity and range of measurements have been examined by using a dye laser with tuning range of 4.2 nm. Their dependences on axial positions and tilt angle are investigated experimentally for diffuse objects and milled ones. A narrow dip and a screw head that cannot be measured by other methods could be analyzed by the present method.
Holographic Interferometry
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Pulsed TV holography system: development and some results
Nils-Erik Molin
In TV holography (also called ESPI or DSPI), temporal phase stepping is a common method. It allows quantitative evaluation of high quality interferograms of quasi-static events and of harmonic vibrations. To study transient and rapid events, pulsed lasers with pulses of short duration (about 25 ns) are instead employed. This 'freezes' most mechanical and acoustic events, such as propagating transient bending waves and acoustic fields. A recently developed pulsed TV holography system allows all-electronic recording and evaluation of interferograms. Two object state recordings are captured on subsequent frames using a CCD-camera connected to a PC computer. The time separation can be set from 20 microseconds to 700 microseconds using a double pulsed ruby laser. Phase maps are calculated and unwrapped to give 3D-plots of the deformation or pressure fields. Recordings of bending wave propagation in plates and transient sound fields in air will illustrate the system performance.
Flow diagnosis by using holographic interferometry
Sheng-Mao Tieng
Holographic interferometry is employed to diagnose an unsteady natural convection flow. The advanced optical diagnostic technique not only clearly reveals the thermal boundary, thermal intrusion, circulating flow, stratified distribution of the steady flow, and their developing behaviors, but also facilitates a quantitative analyses of the temperature distribution, the thickness of the thermal boundary layer and the intrusion.
Digital holography: methods and applications
Thomas M. Kreis, Werner P. O. Jueptner, Juergen Geldmacher
Fresnel or Fraunhofer holograms recorded on CCD arrays can be numerically reconstructed either by the discrete finite Fresnel transform or by solving the diffraction integral using the convolution theorem. Applications in holographic interferometric deformation measurement with effective digital filtering to enhance the interference phase are presented. The detection, location, and size determination in holographic particle analysis can use reconstructed images which are orthogonally oriented with respect to the hologram plane or employ different angular views reconstructed from a single hologram in a tomographic approach.
Contour mapping of the shape difference between two objects by holographic interferometry with reduced sensitivity
The survey of main trends in holographic study of the surface shape for diffusely reflective objects is made in the paper. These methods are the basis for the different methods for direct contour mapping of deviation in shape of the object under study from the master one. The description and comparison of these methods and technique is done in the paper. The dependence of the resulting contour map contrast on the shift of the speckle fields of object and reference wave between the exposures is calculated.
Holographic interferometry of strain waves as a tool for nondestructive testing
Galina V. Dreiden, A. V. Porubov, Alexander M. Samsonov, et al.
The paper presents a new approach to detect impurities, inhomogeneities and anisotropy in condensed matter based on laser generation and holographic observation of nonlinear waves in solids, both transparent and opaque. This approach uses the two phenomena recently discovered by us. First is generation of so-called Poisson waves in a medium surrounding the solid when the strain wave propagates inside it. Second, our studies have proved the physical possibility to generate and observe waves of a new type -- longitudinal strain solitons in nonlinearly elastic waveguides. The soliton detection and recording allows to introduce a new one-pulse technology in nondestructive testing, to determine intrinsic physical properties of nonlinearly elastic materials.
Combined implementation of holographic and speckle interferometry for comparative local stress analysis at different vibration modes
Sergey A. Novikov, Vladimir S. Pisarev, Alexander S. Dzuba, et al.
New capability of combined application of time-averaged holographic interferometry and defocused speckle photography, allowing us a comparative analysis of local stresses corresponding to different vibration modes, is considered. The main aspects of the technique developed are illustrated by using as an example bending oscillations of thin square plate with a large central circular hole. Experimental results are compared with corresponding numerical data obtained by means of the MSC/NASTRAN software.
Colloquium in Recognition of Zoltan Fuzessy: International Tribute I
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Holography for the investigation of technical systems
Industrial application of holographic interferometry may be taken as the headline to describe the research work of Zoltan Fuzessy. Under this general theme investigations from the material properties determination to vibration measurements at running motors are included. In the field of quality control the differential holography has to be mentioned a specialty of his research group, which might have a lot of power in the control of components shape. In this paper a few topics are reported connected with the research work of Zoltan Fuzessy under headline 'Application of Holography for the Investigation of Machines and Systems.' In addition to his work results from other research groups are cited, which may be influenced by him or follow the same ideas.
Applications of pulsed cineholographic interferometry
Paul Smigielski
A new cineholographic system working at 25 Hz with double exposure and double reference beam allows to determine as a function of time the deformation map of a structure under stressing. This set-up includes a double YAG-laser system and a phase stepping device allowing to obtain quantitative results in the reconstruction process. Two types of applications have been investigated with such a system: (1) fast non-destructive testing on site, mainly in the aeronautic field, (2) on-site vibration analysis of structures. It is this last type of application which is the object of this paper. The fact of disposing of a map of the displacements (occurring during a very short space of time) with a high spatial resolution and also as a function of time (25 Hz) allows new very interesting possibilities in the field of on- site vibration analysis of structures: (1) determination of phase and magniture maps for vibration flow measurements. For a complex vibration resulting of the superimposition of n sinusoidal excitation it is possible to know the magnitude and the phase of each frequency by recording 2n double-exposure holograms using the cineholographic system described before (2) calculation of the structural intensity which describes the transfer of vibrational energy by elastic waves and calculation of the divergence of the structural intensity vector to localize mechanical zones and to understand the dynamic behavior of the structure. Structural intensity created by flexural waves in a plate can be expressed using only the normal vibrational velocity component. However, the principal difficulty in obtaining it experimentally arises from the fact that it contains spatial derivatives of this normal velocity up to the third order. Use of double-exposure holographic interferometry is very suitable to calculate this structural intensity due to the fact that the holographic method gives directly the normal vibrational velocity at a very high number of points on the structure under investigation. Therefore, spatial derivatives can be calculated with enough precision.
Pulsed digital holography for vibration analysis
Pulsed digital holography is very useful for vibration analysis. In order to increase the temporal resolution a ruby laser producing up to four pulses has been used. The separate digital holograms (one hologram for each pulse) of an object under test are recorded in few microseconds on three CCD sensors. The images of the recorded holographic interference patterns are captured digitally with a framegrabber inside a Personal Computer. The reconstruction of the holograms is performed digitally by means of computer. For the later quantitative evaluation of the reconstructed holograms, the Fourier method is used. The optical phase of each hologram is obtained from the complex amplitude and the deformation between two laserpulses is calculated from phase subtraction and phase unwrapping of these two holograms. Experimental results are presented.
Colloquium in Recognition of Z. Fuzessy: International Tribute II
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Holography: science and art
Pierre Michel Boone
Art and science are separated by a very large distance nowadays. Long ago, e.g. in Renaissance, or even earlier, in classic Greece and Rome, or still earlier in Egypt or Mesopotamia, arts and sciences were united. Today they seem to go separate paths: science for the industry, arts for the gallery. Holography is an exception: no art without science, but also no science without art.
Selected problems of optical metrology in industry
Hans Rottenkolber
The benefit of optical metrology for testing tires is obvious. The testing principle has proven a high degree of reliability with respect to recognizing defects. The defect is indicated as a bright or dark area in a grayvalue-image of the tested area. The grayvalue-image is substituted with false colors (green/red). In order to display a tire defect e.g. as a red spot an absolute threshold has to be defined. When leaving the laboratory environment and entering the production control some unexpected problems occur regarding this absolute threshold. Typical problems include the differentiation of reinforced and defect areas, the recognition of malfunctions, compensation of Cartesian shearing vs. radial deformation and taking the individual deformation of each single tire into consideration. Some solutions of the designated problems are discussed.
Thirty-odd years of industrial hologram interferometry
Numerous technical advances have been made since the invention of holography in, which have led to widespread use of holographic interferometry in the fields of nondestructive testing and structural development. This paper reviews some of these developments for the early days when the holographic tire tester was developed to the current times of automated fringe analysis an hybrid CAH/CAE methods. This is both a historic as well as a technical overview as seen from the authors' perspective and involvement since circa 1966. References are provided for key technical publications, but only a small selection of the slide material is included in this paper.
Colloquium in Recognition of Z. Fuzessy: Hungarian Tribute I
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Estimating the shape factor of suspended particles in a liquid-borne particle counter
A new liquid-borne particle counter is described that utilizes an optimized optical set-up to determine the size distribution and concentration by two different methods and to estimate the shape-factor of the suspended particles. The aim of this optimization was to achieve the appropriate optical conditions for such type of measurement, viz. determining the geometry of the illumination and detection, and calculating the testing volume and dependence of the parameters of detected signal on the particle size for pulse height and pulse duration methods performed at the same illumination and detection conditions. The possibility of estimating the shape-factor of micron-size particles is discussed. The proposed measurement method was incorporated in a PC-controlled LQB-1-200-L-T liquid-borne laser particle counter developed on the basis of previous APC- 03-2 and APC-03-2A air-borne particle counters and a LQB-1-200 liquid-borne particle counter.
Multiwavelength ATR reflectometry of thin films
A. Hoffmann, Norbert Kroo, Z. Lenkefi, et al.
Optical parameters of metallic and non-metallic thin films (complex dielectric function and the thickness) can be determined by measurement of the attenuated total reflection (ATR) of light. In this method the first layer should be a surface-plasmon-carrying metal film as e.g. silver or gold, while the 100 - 200 angstrom thick adlayers could be both metallic or non-metallic. The basic unit of our newly developed multichannel reflectometer is a conventional ATR reflectometer, working in the Kretschmann geometry. The light source is a white lamp unit and the analysis of the reflected beam is performed using an OMA-4 multichannel optical analyzer. This instrument makes possible the determination of the angular distribution of reflectance of thin film samples in the 400 - 900 nm wavelength range in one cycle.
Size distribution measurement of particles in LDA systems using back scattering geometry
Several proposals are known for the simultaneous measurement of particle velocities and size. In this study we propose to measure the ratio of the contents of two specific channels of the Fourier transform of the autocorrelation function of the pre-detection signal corresponding to single particle transit of the sensing volume. We show that in a wide range of experimental conditions this ratio is a monotonous function of particle size. This circumstance leads to the possibility of defining calibration curves for practical devices.
Adaptive system for speckle pattern interferometry
Janos Kornis, Attila Nemeth, Nasser Moustafa
In our paper we have analyzed the application possibility of a modified version of speckle pattern interferometry: the adaptive speckle pattern interferometry (ASPI). The core of this technique is the using of the holographically reconstructed virtual images of reference waves. Using this solution an adaptive measuring system can be built. A developed prototype of the ASPI has been presented as a measuring device for various measuring tasks. Selected applications have been shown from real time holography to comparative displacement or contour measurement.
Electromagnetic field in optics
Peter Varga, Peter Torok
A linearly polarized plane wave traversing an optically transparent system rarely maintains its linear polarization. In this work we discuss two aspects of this phenomenon. First, we consider the effect of a high aperture lens on polarization. This case is of utmost importance in confocal and near field microscopy and, in general, focusing. Second, the role of the polarization in hologram reconstruction is discussed.
Colloquium in Recognition of Z. Fuzessy: Hungarian Tribute II
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Beyond the upper limit of holographic and speckle interferometry
Ferenc Gyimesi, Zoltan Fuzessy, Bela Raczkevi, et al.
Holographic interferometry has the advantage of high sensitivity but at practical loads, the fringe systems get soon too dense to be observed conveniently. One special way of overcoming this problem is provided by the comparative methods. In the present paper, comparisons of deformations up to the millimeter region will be reported in difference holographic interferometry and an extension possibility to electronic speckle pattern interferometry will be demonstrated, too. The most direct approach would be to magnify the image to the required great extent and then build up the complete fringe system from the observed tiny parts. A practical method will be suggested here which alleviates this cumbersome procedure. In addition, if the very dense fringes are already washed away by the speckles -- some integration along the fringes proves to be of real help.
Measurement of thermal gradient in solutions generated by laser illumination
Zsolt Benko, E. Farkas, Zsolt Bor, et al.
When a solution is irradiated by light, a part of that light is transmitted, the other part is absorbed and usually changed into heat energy. If the solution is fluorescent then a part of the absorbed light energy is emitted as fluorescence. The absorbed heat energy results in the change of the refractive index of the solution. If a laser beam with Gaussian spatial distribution is used for irradiation then the formation of the so called thermal lens can be observed. The thermal gradient caused by the laser beam can be calculated by measuring the focal length of the thermal lens. The effectiveness of the Moire technique and the thermal lens method were examined. The results show both methods to have about the same sensitivity, but the thermal lens method was found to be much easier to evaluate. Numerous solutions were examined. Some of them were investigated at their anti-Stokes fluorescence region to examine the possibility of cooling down a solution by means of a laser beam.
Velocity measurements in the nanosecond range realized by variably delayed dye laser exposition
Zsuzsanna Marton, Bela Hopp, Zsolt Toth, et al.
An imaging system with nanosecond resolution was developed and used for investigation of excimer laser induced ablation. The photographic recordings were made by means of a videocamera equipped with a microscope. Dye laser pulses used for exposition were delayed appropriately with respect to the incidence of the excimer laser light. The movement of the plume ejected from the sample and the propagation of the mechanical waves developed in and above the sample were visualized. Using single recording pulses the distance-time functions were obtained. The velocity-time functions were calculated by derivation of those. Applying a Michelson interferometer for generating double exposing dye laser pulses with delay dt, the average velocity for dt could be measured directly. The propagation velocity of shock waves originating from the polymethyl-methacrylate surface was investigated by this technique in Schlieren arrangement. Velocities as high as 40 times the sound velocity in the air were measured. The material ablated from the polymethyl-methacrylate was observed in vacuum by single exposition transmission arrangement. During the excimer laser ablation of cornea several phenomena occur, such as shock wave in the air, shear wave on the surface, internal acoustic wave, plume ejection and so on. The characteristic velocities of these are shown. 7
Numerical simulation package for speckle metrology
Janos Kornis, Nandor Bokor, Attila Nemeth
A computer program package for numerical simulation of speckle phenomena has been developed. It is suitable for simulating both objective and subjective speckle effects in various optical setups. Several simulation results are presented in this paper. The simulations was made in UNIX and Windows NT environment.
State of the Art in Optical Metrology I
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Evolution of optical interferometry in view of practical applications
The time when Newton's rings were first observed may be considered as the beginning of optical interferometry as science. In the period of roughly 350 years a few milestones may be named and put in the time scale. At the end of the 19th and at the beginning of the 20th centuries the classical interferometry prospered, while after the invention of holography and the first laser coherent optical metrology took the lead and holographic interferometry partly outshined the classical counterpart, partly put it in another light. In the early period of its development optical schemes and interpretation methods were developed which was followed by searching computerized techniques for automated evaluation of interferogram. Holographic interferometry has become a versatile tool for basic and applied research, and instruments and systems have been developed for industrial uses. Full potentials of holographic interferometry in view of industrial application can be realized by purely optical and hybrid techniques.
Speckle Metrology I
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Digital shearography for slope measurement
Huai Min Shang, Y. M. He, Cho Jui Tay
This paper presents an electronic speckle shearing interferometry optical method for the full field measurement of the slope of an object. The object under study is placed on a rotatable platform and illuminated by an expanded laser beam. Its image is recorded by a shearing CCD camera and stored directly into a computer. By recording the two images before and after giving the object a small angle of rotation, the resulting correlation fringe pattern which represents the object surface slope can be obtained. Theory of the new method and some experimental results are presented.
Speckle interferometry with nanoparticles
Fu-Pen Chiang, Qing Wang
The sensitivity of one beam speckle interferometry (also called speckle photography) is the size of speckles that can be generated. In the early days of this technique, speckle size is essentially controlled by the aperture size of the recording camera. When laser speckle is used, the wavelength of the laser beam, the f/number of the recording lens and magnification of the system determines how small the laser speckles can be generated. When white light speckle is used, the size is determined by the resolution of the recording lens. The theoretical limits of these two approaches are actually the same in that no speckle smaller that 1/2 of the wavelength of the radiation can be recorded. However, speckles much smaller than lens resolution can be generated using either a chemical or a physical vapor deposition process. And they can be clearly recorded using an electron microscope. We have successfully created nanometer speckles and applied them to variety of solid mechanics problems of importance. Examples include characterization of mechanical properties of interphase in metal matrix composite, study of kinking failure mechanism of fibrous composite, measurement of thermal deformation of solder joint in electronic devices, etc. This nanospeckle technique has opened up a new field of investigation which heretofore was not accessible to experimentalist.
ESPI deformation measurement on lightweight structures under thermal load
Erwin K. Hack, Rolf Broennimann
We report on the application of ESPI to measure deformations induced by thermal load on lightweight honeycomb panels for space applications. The panel was mounted isostatically onto a vibration isolated table. A housing for temperature stabilization was constructed enclosing the panel, heating elements, fans and the ESPI-head made of Invar. Emphasis is put on the quantitative analysis of the deformation of this large object (0.8 X 0.8 m2) viewed from a relatively short distance of 1.1 m and illuminated sequentially from three non-orthogonal directions. Influences of laser stability, rigid body displacements, temperature inhomogeneities as well as possible deformations of the measurement head are discussed in order to derive the measurement uncertainty and to estimate corrections. Beside the sensitivity vector analysis it is important to take into account the optical light path changes due to temperature changes. Out of plane deformation fields of the panel are presented.
Optical strain gauge
Rajpal S. Sirohi, Fook Siong Chau, Siew-Lok Toh, et al.
The paper presents a technique that could be used to measure (1) in-plane displacement, (2) the velocity of a solid body using a principle similar to that used in LDA, and (3) strain at a point. Some initial results for velocity determination are presented and compared with theory.
Fiber optical single-frame speckle interferometer for measuring industrial surfaces
Jochen Kranz, Juergen Lamprecht, Andrea Hettwer, et al.
Speckle interferometry is a sophisticated technique for the non-contact, high precision measurement of form, deformation and vibration of technical surfaces. In this paper, a new single frame phase-shifting speckle interferometer for the quantitative measurement of out-of-plane-deformations is described and first measurements are presented. With a binary phase grating, six interference patterns are generated at a time. They are acquired within one frame time of a single CCD- camera, thus minimizing errors due to thermal fluctuations or vibrations. The use of fiber optics allows a flexible application of the system under industrial conditions and a compact design of the sensor head.
Shear ESPI with small objects
Rajpal S. Sirohi, Cho Jui Tay, Huai Min Shang, et al.
Shear ESPI has been applied for the NDT of objects under magnification. A method to obtain the thickness of the defect (assumed to be circular diaphragm on a rigid boundary) from the Shear ESPI data is presented. Experiments conducted on programmed defects establish the validity of the procedure; and thickness estimates with less than 10% departure from the nominal values are obtained.
Optical Methods for the Testing of Microsystem Elements
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Optical measurement methods for MEMS applications
Volker Grosser, C. Bombach, Wolf Faust, et al.
Modern microelectronics, microsystems (MEMS and MOEMS) and their components are characterized by high volume integration of a variety of materials and combinations of materials to realize very different and variable functions (sensor and actuator functions, signal processing, etc.). The reliability and the lifetime of these microproducts are strongly depending on the material properties and the thermo-mechanical design. So nondestructive optical measuring and inspection methods are widely used in the R&D process, in IC-fabrication, in manufacturing and in packaging of MEMS and microcomponents. In following some special applications are described.
Combined measurement of silicon microbeams by grating interferometry and digital holography
In this paper the methodology and instrumentation for the investigation of the silicon microbeam behavior under tensile and bending loads are described. The tests are performed by means of Automated Grating Interferometry (AGI) and Digital Holography (DH). Both methods deliver a direct approach to a highly sensitive measurement of surface displacements. In combination with simulation tools (analytical or FEM models) the material parameters can be determined. Consequently the main aim of the measurements is to determine the three Cartesian components of the displacement vector.
Holographic microscopic interferometry with respect to the estimation of stress and strain in micro-opto-electro-mechanical systems (MOEMS)
Guenther K.G. Wernicke, Oliver Kruschke, Nazif Demoli, et al.
Holographic microscopy with conjugate reconstruction for the interferometric determination of three-dimensional displacement was used for the investigation of the mechanical behavior of micromechanic and microelectronic components. An experimental set-up for the exposure of the holographic interferograms was used for the application of the spatial heterodyne technique, for the application of phase shifting, and for electro-optic holography. Three holograms for different illumination directions recorded on one holographic plate are reconstructed conjugately, and spatial heterodyne technique a well as phase shift technique were used to evaluate the interferograms. Only by conjugated reconstruction it is possible to obtain a perfectly optimized interferometer for the static evaluation method. The evaluation of interferograms which are strongly disturbed by speckle noise can be performed successfully. A comparison of the results of the application of both techniques is given. The influence of the speckle effect on the resolution was investigated.
Fiber Optic Sensors and Applications
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Distribution sensing by synthesis of the optical coherence function
Kazuo Hotate, Takashi Saida, Zuyuan He
Current modulation of a laser diode produces a change in the emission frequency. Hence, modulating the driving current with white noise, we can control the linewidth, that is, the coherence length of the source. Several commercial tunable laser products have a function of tuning the coherence length by this way. While, we have proposed and studied a method to control not only the coherence length but also the shape of the coherence function. We have called this technique as 'the synthesis of the optical coherence function.' In this paper, at first, the principle of the synthesis of the coherence function is explained. Next, as the application of this technique, a high resolution reflectometry, a distributed fiber-optic stress sensor, a multiplexed fiber-optic interferometric sensor, and optical parallel information processing are described.
Applications of distributed Brillouin fiber sensing
Luc Thevenaz, Marc Nikles, Alexandre Fellay, et al.
Long-range distributed strain and temperature measurements along an optical fiber is presented, using a novel optical sensor based on stimulated Brillouin scattering. The optical effect only depends on the fiber material, so that the bare fiber itself acts as sensing element without any special fiber processing or preparation. The sensor accuracy is plus or minus 1 degree Celsius for temperature and plus or minus 20 (mu) (epsilon) for deformation. The spatial resolution is 1 meter and the sensor range is more than 20 km. Successful monitoring of a concrete dam element has been performed using an embedded standard cabled fiber. The temperature dynamics of lake waters have been also observed by simply laying a cable over the lake bed.
Structural analysis of bridges and beams using long-gage fiber optic sensors
Daniele Inaudi, Nicoletta Casanova, Pascal Kronenberg, et al.
The security of civil engineering works demands a periodical monitoring of the structures. The current methods (such as triangulation, water levels, vibrating strings or mechanical extensometers) are often of tedious application and require the intervention of specialized operators. The resulting complexity and costs limit the frequency of these measurements. The obtained spatial resolution is in general low and only the presence of anomalies in the global behavior urges a deeper and more precise evaluation. There is therefore a real need for a tool allowing an automatic and permanent monitoring from within the structure itself and with high precision and good spatial resolution. In many civil structures like bridges, tunnels and dams, the deformations are the most relevant parameter to be monitored in both short and long-terms. Strain monitoring gives only local information about the material behavior and too many such sensors would therefore be necessary to gain a complete understanding of the structure's behavior. We have found that fiber optic deformation sensors, with measurement bases of the order of one to a few meters, can give useful information both during the construction phases and in the long term. In the case of beams and bridges, long-gate sensors can be used to evaluate the curvature variations and calculate the horizontal and vertical displacements by double integration of the curvatures.
Application of optical fiber sensors on the power dam of Luzzone
Rolf Broennimann, Philipp M. Nellen, Peter Anderegg, et al.
The hydro-electric power dam of Luzzone in Switzerland has been heightened by 17 m to 225 m. Distributed fiber optical sensors, based on wavelength multiplexed Bragg gratings, have been embedded in the concrete to monitor temperature and strain evolution. The sensors were designed to make them suitable for embedding and operation in this harsh environment. Data taken during curing and the first year afterwards are presented.
Testing of the Swiss Expo 2001 structural models by fiber optic and whole field optical methods
Andrea Pedretti, Ezio Cadoni, Daniele Inaudi
In the frame of the Forum project for the Swiss Expo2001 an experimental program on structural models is in progress. The structures of the Swiss Expo 2001 exhibition will be based on the Tensegrity concept. The behavior of these structures is highly geometrically non-linear and is relatively complicated to calculate and simulate. This pointed to the necessity of extensive testing and permanent monitoring of the structures. The tests are carried out on 1:10 scale models. In the paper the authors shows the application of fiber optic and whole field optical methods to control and monitoring the tests.
Speckle Metrology II
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Speckle interferometry to investigate degradation processes of stressed solid materials
Degradation processes of stressed solid materials was investigated by newly developed speckle interferometry. Sequence of speckle correlation fringes were obtained by subtracting couples of interfering speckle patterns successively acquired. The behavior of plastic deformation and fracture were observed on a video monitor as moving fringe patterns of in-plane deformation components. In experiments of a specimen of carbon steel S45C, we observed a characteristic white band which can be interpreted as a Luder's band sweeping over the specimen in the yielding state of the loading test. In experiments of an aluminum alloy specimen, complicated movement of a white and was found corresponding to load serration.
Measurement of stress distribution in fiber-glass-reinforced timber joint
Chi-Jen Chen, Pramod Kumar Rastogi
Electronic speckle pattern interferometry is applied to examine stress distributions on a fiberglass reinforced doweled joint with increasing load levels. The dowel is embedded in the reinforced wood and is loaded in compression. The observation of the in-plane deformations on reinforced wood specimens is obtained in real-time. A continuous monitoring of the specimen enables one to detect the development of stresses in the axial direction of load. The stress distributions around the hole of unreinforced and reinforced bolted joints are compared.
Application of ESPI technique to evaluate the crack propagation zone of prenotched clay elements
Ezio Cadoni, Brian W. Bowe, Daniel Albrecht
Optical interferometric techniques are being increasingly used in laboratory test and can usefully substitute other classical techniques when great accuracy in measuring displacement is required. In particular, Electronic Speckle Pattern Interferometry (ESPI) technique has aroused lively interest by the industrial and research users because does not require excessive environmental stability and does not necessary photo processing. In the paper the authors show the results obtained applying the ESPI methods to mechanical characterization of clay materials used to manufacture blocks for composite floors.
Specialized Techniques and Applications I
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Scanning optical microscopy and its applications to nondestructive materials testing
Peter Torok, L. Mule Stagno
In this work we discuss the applications of confocal microscopy to non-destructive materials testing. After the introduction we briefly consider some important theoretical aspects of the microscope. We then move to discuss the possible imaging modes available for both surface and bulk microscopy. We present experimental images obtained with various types of imaging modes. Finally, an experimental confirmation for the theoretically predicted contrast mechanism is discussed.
Effect of anomalous particle light scattering on PIV image quality
J. Kostas, J. Cater, J. Soria
Optical mastermind techniques, such as PIV, are finding more frequent use in experimental fluid mechanics laboratories. The continuing development of both imaging technology and image processing algorithms over the past twenty years have extended its measurement capabilities. Developments in high power pulsed lasers, such as Nd:YAG have also contributed to extending the applicability of the technique to a variety of flows. It has been found that for measurements in water, problems arise due to a combination of the very high light intensity supplied by a high powered pulsed Nd:YAG laser and Mie scattering effects of sub-micron sized particles inherently present in un-distilled water (e.g. mains water supply). This creates problems for obtaining consistent PIV images. These problems arise when using large water tunnel facilities for which it is not feasible to use distilled water. In addition to this, particle selection is of prime importance when one wishes to use orthogonally polarized dual laser systems. Experimental results will be presented to illustrate the degradation in image quality due to these ubiquitous effects. Recommendation regarding particle selection and optimum laser polarization states will be presented for conditions in distilled and typical mains water supply.
Experimental and numerical analysis of the thermal deformation of composite tubes
Daniel Holstein, Petra Aswendt, Roland Hoefling, et al.
The thermally induced deformation of anisotropic composite tubes with different thicknesses is studied by means of Finite-Element-Analyses and interferometric measurement techniques. Of particular interest are the differences in the deformation behavior in comparison to isotropic tubes. It is shown that characteristic bending phenomena appear at the shell surfaces of the tubes, due to the three-dimensional stress state near the edges. The simulated thermal deformation is experimentally verified by means of holographic as well as speckle interferometry. The results of this work show that the implemented micro- and macromechanics of both used Finite- Element systems enables to predict the thermal deformation of composite tubes properly, if a suitable model is used. Nevertheless, especially for thin tubes significant discrepancies between the simulated and the measured deformation could appear, due to the disregarding of the complex microscopic structure in the simulation. Thus experimental verifications with fullfield measurement techniques should generally be performed.
Laser generation and detection of ultrasound for materials characterization
The authors describe the application of laser-ultrasonic sources in combination with interferometric detectors to monitor ultrasonic Lamb waves propagating in metal and composite structure plate samples. Using a high powered pulsed laser source, and temporally and spatially sampling the resultant acoustic field, it was possible to directly measure the Lamb wave phase velocities of several modes simultaneously. A further development has been the demonstration of a low power CW laser source capable of generating Lamb waves in a steel sample at a power density well below the ablation damage threshold.
Optical testing of cylindrical surfaces by grazing incidence interferometry in the infrared region
Roland Schreiner, Sven Brinkmann, Thomas Dresel, et al.
Interferometric testing of technical, optically rough surfaces is disturbed by high contrast speckle noise. Grazing incidence interferometry is an appropriate tool to increase the effective illuminating wavelength. This leads to dramatically reduced speckle noise. Increasing of the wavelength from the visible region to the infrared is another opportunity to diminish speckle. An IR-interferometric combining both methods is presented. The advantage of the IR-interferometer compared to the VIS-interferometer is the reduced anamorphotic distortion of the image, which increases the resolution in the z-direction of the cylinder and enables the measurement of rougher surfaces. The interferometric set-up consists of two diffractive axicons with the test piece in between. The axicons serve as references for the cylindrical test samples and as beam splitters and combiners. The plane wave of the 0- th diffraction order is the reference beam whereas the conical wave of the first order is deflected onto the object. After reflection from the cylindrical test sample the first order contains wavefront deformations due to deviations of the test sample from cylindricity. After recombination of the object and the reference beam by the second axicon a low frequency interference pattern is detected by a high resolution PtSi focal plane array. The surface deviations can be reconstructed with the methods of phase shift interferometry.
Hologram reconstruction using liquid crystal spatial light modulators
Denis Lebrun, Samir Belaid, Cafer Ozkul
High-speed in-line holography is used to visualize the trajectories fibers which are drawn out in a turbulent flame. In order to improve the SNR, the images are not observed by a conventional reconstruction setup. In our case, the holographic plate is directly placed on the input plane of a wavelet-transform optical system. This processing system is based on a VanderLugt correlator including an Electrically Addressed Spatial Light Modulator (EASLM). The shape of matched filters is deduced by successive rotation and dilatation operations of wavelet functions in the Fourier domain. The 3-D location of a fiber element and its orientation are estimated by searching the daughter wavelet which yields the maximum intensity on the output plane of the correlator, which also contains the reconstructed image. The results are compared with those obtained by a conventional optical reconstruction. The SNR of the images observed on the output plane is improved. Moreover, it is shown that the axis coordinate accuracy is improved to (Delta) z equals plus or minus 50 micrometer, instead of plus or minus 0,5 mm for holographic reconstruction.
Two-frequency laser measuring technique with high axis velocity
Fengzhou Fang, Bryan Kok Ann Ngoi
Interferometers using heterodyne techniques are now widely employed for displacement measurements. Heterodyne interferometric techniques involve the use of two beams derived from the same laser, one of which has its frequency shifted by a specified amount. A helium-neon laser is forced to oscillate simultaneously at two frequencies separated by a constant difference of about 2 MHz, by applying an axial magnetic field. But the axis-velocity with this method is not able to be increased for a small frequency difference. An effective way of introducing such a frequency shift is by means of an acousto-optic modulator. It is studied in detail after a few methods are discussed for increasing the frequency difference. The measuring system will be used widely in displacement, objective with high speed motion of 1.8 m/s and on-line measurement.
Determination of precise optical surface roughness parameters using ARS data
Valentina V. Azarova, U. N. Lokhov, K. Malitsky
The comparison of different methods of measuring surface roughness parameters, i.e. angle-resolved scattering (ARS) technique and atomic force microscope (AFM) profilometry, was performed for quartz precise optical surface, obtained by different polishing processes. The functions of power spectral density, calculated from ARS, using vector scattering theory, and from AFM data are in good agreement in the range of polar scatter angles 30..75 degrees. In this range the angular scattering is well predicted using the exponential autocorrelation function, with parameters, calculated from surface profile. The autocorrelation length, calculated from ARS data is above range using exponential statistics, remains practically constant for different surfaces, obtained by the same polishing process. The latter allows to consider it as the characteristic parameter of certain polishing process.
Grating and Moire-Related Techniques
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Digital moire: techniques and applications
The proliferation of digital imaging techniques has permeated in the Experimental Mechanics arena as well. More so the fact that since digital imaging records information in discrete and periodic intervals, this system lends itself nicely as a moire reference grating in the various moire techniques. The aliasing feature, which is generally avoided in traditional digital image and signal processing, now can be used to analyze the deformed specimen grating for deformation studies. This paper will discuss the use of digital moire techniques and demonstrate their application for the range of moire methods. Furthermore the use of phase shifting, one of the most powerful fringe processing technique will also be discussed in conjunction with this.
Color-encoded fringe projection and phase shifting for 3D surface contouring
Peisen S. Huang, Qingying Hu, Feng Jin, et al.
A color-encoded fringe projection and phase shifting technique is proposed for rapid 3-D surface contouring applications. A color fringe pattern whose RGB components comprise three phase-shifted fringe patterns is created by software on a computer screen and then projected to an object by a novel computer-controlled digital projection system. The image of the object is captured by a digital camera positioned at an angle different from that of the projection system. The image is then separated into its RGB components, creating three phase-shifted images of the object. These three images are used to retrieve the 3-D surface contour of the object through the use of a phase wrapping and unwrapping algorithm. Only one image of the object is required to obtain its 3-D surface contour. Thus contouring speed, limited only by the frame rate of the camera, can be dramatically increased as compared to that of the traditional phase shifting techniques. The technique is especially useful in applications where the object being contoured is going through quasi-static or dynamic changes. This paper describes the principle of the technique and presents some preliminary experimental results.
Inverse projected-fringe technique with automatic pattern adaption using a programmable spatial light modulator
This paper deals with a new active technology in optical shape measurement called inverse projected-fringe-technique. Using a programmable liquid crystal spatial light modulator (LCD- SLM) with digital pixel control a precise sinusoidal grating with arbitrary topology can be created and projected onto the object under test. In this case the grating can be adapted to the shape of the object not only to overcome possible problematic areas such as saturated regions and nonresolved fringes but to generate also a so called inverse pattern that causes straight and uniform fringes on the object if it is observed by the camera. This technique is of special advantage for shape control in the production line since only certain deviations from the uniform pattern have to be detected if the object has to be classified as good or bad. In that case a fast optical correlator can be used that needs almost the same simple filter mask for a broad variety of test objects.
Grating microinterferometer for local in-plane displacement/strain field analysis
Micromechanical elements analysis require the local approach to their behavior and material constants. In the paper the automated grating microinterferometer GMI for in-plane displacement/strain measurement in a region smaller than 1 X 1 mm2 is presented. It is based on the concept of achromatic grating interferometer combined with glass block waveguide and designed for the work with standard optical microscopes. The interferogram obtained may be modified and design for both temporal and carrier frequency phase shifting methods. The methodology of measurement is described and the example of GMI application is given.
Hybrid FEM/grating interferometry analysis of displacement fields in mechanical elements
In the paper the concept of interactive implementation of grating interferometry and FEM is proposed in order to provide additional information to properly design and control both numerical and experimental procedures. At first the information from global FEM approximate model is used to design interferogram and adjust experimental setup. Having the best fitted experimental conditions, the measurement is performed. The results are used to improve the FEM parameters e.g. size and shape of FEM grid and fit local experimental data to modified FEM model. To provide the proper experimental tool, grating interferometry with two-channel acquisition module (for instantaneous u and v displacement measurement) is applied. The concept is tested on the examples of analysis of bending ceramic-to-metal joint and laser beam weldment under tensile semiaxial load.
Grating diffraction for strain measurement in a microscope
In this paper, a compact microscope system for direct strain measurement is presented. It involves the grating diffraction method coupled with microscopy and image processing technique. A Leitz optical transmitting microscope with white light source is reconstructed by developing a loading and recording system. Gratings with median density from 40 - 200 l/mm are used. With the help of a Bertrand lens, the Fourier spectrum of the grating, not the grating image is formed on the CCD sensor plane with high image quality. A software which can precisely, quickly and automatically determine the diffraction spot centroids is developed. The local strain is measured with high spatial resolution. A discussion on improving the sensitivity in multiple ways is suggested.
Specialized Techniques and Applications II
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Problems in complex modulation of wavefronts using LCTV displays in optical correlation measurements
Nazif Demoli, Guenther K.G. Wernicke, Alexander Hirsch, et al.
Optical-hybrid correlator systems use electronically addressed spatial light modulators (SLMs) to improve the flexibility in data manipulation. By using the SLMs we must add to the optical setup such elements like polarizers and retarders, or enlarging lenses to match the scales in the system. These optical elements as well as the SLMs themselves cause the wavefront distortions. The problems and solutions to minimize the wavefront distortions throughout an optical-hybrid frequency plane correlator are discussed.
Adaptive conversion of visual information by noncomputing method
Andrew E. Gorodetsky, Mikhail E. Kompan
A new method of visual information processing is discussed. As a particular example, porous silicon is considered as a material, characterized by progressively decreasing luminescence quantum yield at constant excitation intensity. Discrimination of moving object was shown to be possible when visual information is displayed using a luminescent screen, made of a such material.
Application of shape-measuring optical methods in animation
Malgorzata Kujawinska, Michal Pawlowski
The methodologies and tools used recently in animation are presented and their most significant problems are recognized. It includes creating of libraries of realistic 3D objects and describing the models of animation in 3D space. As a solution optical methods using structured light are proposed for gathering information about shape of 3D objects. The fringe projection system is applied for determination of absolute co- ordinate of 3D objects in respect to their global shape and local texture. Additionally the measurements at sequential stages of the object movements are performed. This information is the base to calculate the trajectories of points' movement, and latter to predict the model of animation. The concept described above is experimentally tested on simple 3D objects. The further works required to apply the methodology presented for description of complex, realistic objects are discussed.
Optoelectronic recognition of mobile objects
A. N. Alexandrin, Irina L. Tarasova
The estimation of various optoelectronic methods of recognition of objects is resulted in this work. Optoelectronic system for the recognition of images, using a method integrated fluctuation is considered. A problem of automatic allocation such systems of mobile object on a background motionless and their recognition is put. The problem is decided by introduction in system self-adaptive element from a new material -- porous silicon. Self-adaptive element is designed as the screen from porous silicon. Is shown, that application of physical adaptation of system element initiates additional adaptive properties of system. Possible directions of use of new system are specified. Optoelectronic system, recognition of image, recognition of moving objects, porous silicon, degradation of porous silicon, selfadaptive element, porous silicon screen, method of integral fluctuation, allocation (contrasting) of dynamic information, system for recognition of moving objects.
Aberrations of an optical system in the field heterodyne interferometer
Heterodyne interferometry method for shape measurement based on the fringe projection is presented. Fringe pattern is displacing in the measurement field due to the interference of beams with slightly shifted frequencies. The phase difference of signals detected by matrix of detectors gives the information about the shape of surface under investigation. Phase measurement errors generated by imaging optical system are given.
High-resolution cross-correlation PIV on photographic film
J. Cater, J. Kostas, A. Fouras, et al.
An adaptation of current image shifting techniques has been developed that permits cross-correlation PIV analysis of non- overlapping images recorded on photographic media. The image acquisition technique utilizes pulsed lasers to produce two singly exposed sub-images of particles in one photographic frame. The technique can also provide images suitable for cross-correlation analysis on digitally recorded images without the need for a specialized camera. An adaptive cross- correlation PIV analysis method is employed to extract the in- plane velocity field information with high velocity sampling resolution and large velocity dynamic range. Further capabilities and limitations of the technique are presented as well as an analysis of the associated measurement errors. Some of the more interesting problems that were encountered during the development of the experimental technique are also discussed. The application of this method to the unsteady flow of a vortex ring will be illustrated as an example. High spatial resolution measurements using film recording have yielded the detailed instantaneous 2-D velocity and vorticity fields. Measurements made from digital recordings using this technique provide the evolution of instantaneous in-plane velocity and vorticity fields.
Precision laser element metrology
Valentina V. Azarova, N. A. Efremova, Vaytcheslav N. Svirin, et al.
This paper presents complex method and the description of the setup based on it that allows to control different parameters of ring laser cavities for gyro sensors during the technological process of manufacturing. First of all this is accuracy of mono-block cavity manufacturing, accuracy of mirror alignment, the level of cavity selection, the control of sphericity of cavity, measurement of diffraction cavity losses, back scattering and the active substance gain in the cavity. Complex method combines the analysis of cavity transmission spectrum, measurement of the resonance transmission peak and measurement of radiation decay time in the cavity. The analysis of the influence of cavity characteristics on the accuracy of laser gyros is carried on.