The modern achievements in optical measurement techniques applied in experimental mechanics, the increasing resolving power of data recording systems, combined with digital image processing techniques yield more and better informations on the mechanical reactions of structures and structural elements than at any time before, together with an ever increasing amount of data, provided for further evaluation. No matter which optical method will be used generally the observed and recorded optical phenomena are not identical with the finally wanted informations, mainly informations on the stress-state. Hence it is necessary to calculate the final results, introducing the measured and digital data, obtained from image processing, as input data into proper and advanced mathematical procedures. According to the discrete nature of these data the mathematical algorithms are transformed into discrete numerical procedures, like finite element method and boundary element method. Such a combination of experimental and numerical analysis, named hybrid method, warrants a higher reliability and accuracy of results, which are closer to reality also because experiments represent the reality more easily than theory only. The application of hybrid methods presuppose the availability of complex measuring-, on-line-processing--and sufficient computer capacity. The principle of hybrid methods will be explained and demonstrated by some examples of application.

Computational and experimental methodologies have unique features for the analysis and solution of a wide variety of engineering problems. Computations provide results that depend on selection of input parameters such as geometry, material constants, and boundary conditions which, for correct modeling purposes, have to be appropriately chosen. In addition, it is relatively easy to modify the input parameters in order to computationally investigate different conditions. Experiments provide solutions which characterize the actual behavior of the object of interest subjected to specific operating conditions. However, it is impractical to experimentally perform parametric investigations. This paper discusses the use of a hybrid, computational and experimental, approach for study and optimization of mechanical components. Computational techniques are used for modeling the behavior of the object of interest while it is experimentally tested using noninvasive optical techniques. Comparisons are performed through a fringe predictor program used to facilitate the correlation between both techniques. In addition, experimentally obtained quantitative information, such as displacements and shape, can be applied in the computational model in order to improve this correlation. The result is a validated computational model that can be used for performing quantitative analyses and structural optimization. Practical application of the hybrid approach is illustrated with a representative example which demonstrates the viability of the approach as an engineering tool for structural analysis and optimization.

We demonstrate temperature-insensitive strain measurement in a carbon fiber composite panel using a sensor based on broad-band interferometry in highly-birefringent optical fiber. The sensing element forms an unbalanced Fabry-Perot cavity in the measurement arm of a tandem interferometer. This is interrogated using an LED source and a scanning Michelson interferometer, producing three distinct interferograms, two of which relate to the group delay (GD) of the eigenmodes of the sensing element, the other providing a zero-OPD reference in the scanning interferometer. We measure the GD of each interferogram by dispersive Fourier-transform spectroscopy. Changes in strain and temperature in the measurement fiber affect the group delays of the sensing interferograms, but do not affect the zero-OPD interferograms, which is therefore used as the origin for group delay measurements. We determine a linear transformation relating the measured group delays to strain and temperature. Inverting this transformation then provides a means of recovering strain and temperature from measurements of group delay. We apply this technique to the simultaneous measurement of strain and temperature in the composite panel. Typical measurement errors are 7 microsecond(s) train and 0.7 K. The measured values are independent, and the strain values show no evidence of thermal-apparent strain.

A mathematical algorithm is proposed for fast determination of residual stress in blind hold drilling method. Computer simulation of this algorithm has been made. Comparing of theoretical interference pattern with experimental interferogram is presented.

TV-Holography has been applied for NDT and vibration measurement of engineering components and structures in the last few years. The main limitation of the technique arises from its sensitivity against rigid body movement and the rapid increases in fringes depending on the displacement, which makes it difficult to interpret the fringe pattern. An approach which is insensitive against rigid body motion and provides a wider and more controllable sensitivity range is performed by digital shearography. Instead of measuring displacement, digital shearography measures directly displacement derivatives. With the support of the digital image processing and phase shifting techniques, digital shearography allows the shearogram to be observed in real time and to be evaluated quantitatively and automatically. Thus, this technique is suited well for nondestructive testing and strain measurement. For the vibration measurement, shearogram depicts the full-field information of dynamic deformation derivatives. By applying the phase shifting technique in conjunction with the laser light modulator, the shearogram can be evaluated quantitatively. Thus, the dynamic deformation field (w) and dynamic flexural strain field can be also obtained by integrating or differentiating the phase map of shearogram. This paper presents the principle of the method. Its applications in nondestructive testing, strain measurement and dynamic analysis are shown.

In recent years, white-light interferometry has been used extensively for the measurement of displacement. In this work, a novel bulk-optical Mach-Zehnder interferometer (MZI) is employed as a processing interferometer in an extrinsic fiber-optic electronically scanned white light interferometer. A Fabry-Perot interferometer was used as the sensing interferometer, whereby one of its mirrors was translated using a linear PZT stage in order to provide the displacement measurand. An electronically-scanned system was employed, which has the advantages of not requiring any moving parts, which in turn increases the mechanical stability of the system. In addition, this bulk-optical MZI configuration has the advantages of being relatively small and compact, and does not require the use of polarizers, unlike some electronically-scanned interferometers--such as Wollaston interferometer. This system has been experimentally realized to provide absolute displacement measurements with a resolution of 40 nm.

Self-mixing interference in laser diodes occurs when light is reflected from an external surface back into the laser cavity. A displacement sensor based on this effect is attractive for its simplicity and low cost; the only necessary optical components are the laser diode, collimating optics, and the reflector. This paper examines the limitations placed on such a system by the effects of thermal and mechanical instabilities. The accuracy and dynamic range of any laser diode-based interferometric sensor is limited by the sensitivity of the operating wavelength to temperature fluctuation. It is shown here that optical feedback can be used to reduce the wavelength sensitivity, and hence increase the potential accuracy, by a factor of two. In the case of misalignment of the reflector, it is shown that, although the output of a laser diode with optical feedback is normally very sensitive to the alignment, if a small alignment is introduced deliberately, feedback can be obtained from light making a double-pass of the external cavity. This leads to a reduction of the sensitivity to alignment and, at the same time, doubles the potential resolution of a sensing system.

For comparison to model predictions, measurement of the true response of weak polymeric materials requires that a non- contacting method be use. In particular, for compression tests on weak polymers it is necessary to obtain the full 3D displacement field for the specimen. In this work, the full 3D displacement field was measured using a combination of white light speckle correlation and projected fringes. To obtain the out-of-plane displacement field, a fringe pattern with frequency of 0.30 lpmm was projected onto the specimen surface using a standard slide projector. A phase-stepping algorithm was used to convert the optical fringe pattern in a contour map for the surface. Due to reflections and noise in the fringe pattern, the authors developed a robust phase unwrapping methodology based on fuzzy logic principles. Baseline tests have shown that the algorithm produces accurate contour maps even when noise and poor fringe contrast are present. For the measurements of the in-plane displacement field the polymer foam material was illuminated with a white light source and the natural character of the reflected light was used to obtain speckle images of the polymer. The images were acquired at various load levels and stored in digital form. The digital images were correlated to obtain the speckle deformation field. To increase the range of measurement and to deal with high strain, additional processing of the images using fuzzy logic algorithms was completed.

The methods of phase shifting interferometry have been applied to a number of unique optical metrology instruments which demonstrates the power of phase detection.

In a two-wavelength phase-shifting speckle interferometer for object contouring one usually obtains only the height coordinate of the object surface, which is parallel to the direction of observation. In order to measure the lateral surface coordinates x and y by the same technique the light source is shifted in two directions perpendicular to the optical axis. Two additional phase maps of parallel fringes are generated, which are then used to assign the lateral coordinates x and y to the corresponding pixels of the camera. Nevertheless the intensity distribution of speckle fields seems unfavorable in terms of precision metrology, as interferometers have to rely on a saturable photodetector and an analog-to-digital converter with finite resolution. We calculate the optimum beam ratio, modulation of the camera and lens aperture for a speckle interferometer with maximum phase-measurement accuracy. To obtain the minimum error of 10.6 mrad it is found that the mean speckle intensity ought to be adjusted to be 1/11 times the saturation intensity of the camera, the beam ratio is to be 4 and that the space-bandwidth product must be chosen 0.31. The latter is of particular practical interest, because stopping down the lens increases the need for a high-power laser. The results are valid for all kinds of speckle interferometers and are not restricted to the above- mentioned arrangement. They are confirmed by computer simulation of a two-wavelength speckle interferometer.

In moire technique there are some inherent drawbacks such as: inevitable shadow in illumination and readout, limited depth and size of measurement which obstruct its further application in topographic measurement of large object, especially with complicated shape. Our studies show that the multi-aperture overlap-scanning techniques can also be applied to moire method. Therefore, not only all these drawbacks can be removed, the problem sensitive to eccentric positioning of object and axis swing of the turntable in 360 degree(s) profilometry can also be overcome. In this paper the mathematical model for Moire pattern transformation and connection is described, and results of simulation tests are presented.

Interferometry is widely used for precision measurement of optical pathlengths and pathlength changes. Because optical pathlength can then be related to other parameters like refractive index, density, temperature, position, angle, and constituency, interferometry forms the basis of many types of sensors. In recent years such procedures have evolved to extremes, where extremely high precision measurements are required. Measurement have been reported with better than 1/10,000 wavelength resolutions, i.e. better than one angstrom. This allows the real time observation of the evolution of events that were not possible before, essentially on a molecular level. New applications include: the observation of the growth of a crystal with near single atomic layer sensitivity, the observation of minute changes in concentration and temperature of a solution, sub- microscopic changes in bubbles and particles in a solution, surface mapping to nearly atomic precision, observation of trace levels of gases, and others. New procedures that have been developed and the problems that must be overcome to push the precision of interferometric measurement to its limits will be reviewed and some recent applications of these methods will be described. These include phase shifting, heterodyne, resonance, and phase conjugate interferometry.

In this paper, a shearography approach is used to encode flow field density measurements. The fringes are projected through the flow field and automatically analyzed using the Fast Fourier Transform method. The subsequent `wrapped' phase map is `unwrapped' using the largely noise immune Minimum Spanning Tree technique. This allows the flow field to be solved despite the presence of discontinuities such as shocks. This technique was applied to the results made on a 2D transonic windtunnel at Rolls Royce, Derby where whole field measurements were made. The subsequent fringe patterns were each solved by the automatic fringe analysis technique on a Sparc-5 Sun system. The shock structures were observed to be the same as those revealed by earlier flow visualizations. The density measurements correspond well to previous holographic measurements.

This paper describes a scanning laser speckle photography (SLSP) measurement system which is an advancement of a standard laser speckle photography (LSP) technique. The new SLSP set-up enlarges the measuring area of a conventional LSP which is restricted to the used optical expansion/collimation system. This is done by a mechanical movement of a set of mirrors in the beam path of a small expanded laser beam by a precise computer-controlled XY- positioner. Thus the magnitude of the measuring area is enlarged from the relative small cross section of the expanded/collimated laser beam to the movement distance of the positioner. Furthermore an additional advantage of the SLSP is the decrease of the exposure time for a specklegram due to the increased laser light intensity of a small expanded laser beam. The established SLSP measurement set-up is used to investigate the temperature field in a thermal boundary layer of a natural convection flow of air around a slender heated vertical cylindrical tube. Therefore the axis-symmetrical temperature field of the heated tube is vertically scanned by the moved laser beam and a specklegram is fixed on a holographic film by a double-exposure. The optical SLSP arrangement is described in detail and first experimental results of temperature measurements with the SLSP are presented.

Moire tomography based on algebraic reconstruction technique (ART) is presented in this paper. The maximum entropy type ART-QMART is modified to apply to moire tomography. A new kind of ART based on Rytov approximation is also presented. Numerical results show that ART type moire tomography can be used to reconstructed 3D refractive index distribution.

Electronic Holography or ESPI (electronic speckle pattern interferometry) is widely used for deformation analysis of complex, 3D surfaces. The sensitivity is well below 1 micron and deformations can be observed in real time. Any of those methods require either a constant phase between the interfering beams or a defined phase oscillation about a stable mean value or another controlled phase variation. The use of active control loops enhances the degree of phase constance, facilitates the defined variation of phase and permits a considerable reduction of cost for passive stabilizing installations, thus permitting the operation of an ESPI camera in an industrial production environment. By the use of a computer as active controller, autocalibration becomes feasible, a variety of stabilization parameters and algorithms can be tested easily, parameter optimization can be automized and phase perturbations can be recorded. User- guidance for failure diagnosis enhances further the user friendliness of the system. All this has been accomplished without any special or high-performance equipment, which allowed a relatively cheap realization. With an interferometer and photodiode amplifier as phase detector, a PC with a multi-I/O board and a piezo-mounted mirror with a simple, self-built driver as phase actuator, phase stabilization up to the kHz regime was demonstrated, limited by the mechanical resonances of the optical setup. The complete software has been developed by the author, using Oberon as language, operating system and development system.

Optical interferometric monitoring of spin coating (optospinography) has allowed close observation of a thin liquid film temporal evolution (at 500 -2500 rpm, 100 Hz data acquisition), from which its kinematic viscosity can be determined. The data obtained from this procedure is in good agreement with known values for two oil standards, indicating that the method is valid in the range of approx. 0.4 to 150 Stokes. Advantages and limitations are discussed.

Holographic interferometry enables the accurate measurement of 3D displacement fields. However, the determination of 3D- displacement vectors of objects with complex surfaces requires to measure the 3D-object coordinates not only to consider local sensitivities but to distinguish between in- plane deformation, i.e. strains, and out-of-plane components, i.e. shears, too. To this purpose both the surface displacement and coordinates have to be combined and it is advantageous to make the data available for CAE- systems. The object surface has to be approximated analytically from the measured point cloud to generate a surface mesh. The displacement vectors can be assigned to the nodes of this surface mesh and the components of the deformation can be evaluated for an experimental stress analysis. They also can be compared to the results of FEM- calculations. The brake saddle of a car brake is such a complex formed object where the surface cannot be described by fundamental mathematical functions. The 3D-object coordinates were measured in a separate topometric set-up using a modified fringe projection technique to acquire absolute phase values. By means of a geometrical model the phase data were mapped onto coordinates precisely. The determination of 3D-displacement vectors required the measurement of several interference phase distributions for at least three independent sensitivity directions as well as the 3D-position of each measuring point. These geometric quantities had to be transformed into a reference coordinate system of the interferometric set-up in order to calculate the geometric matrix. The necessary transformation were realized by means of a detection of object features in both data sets and a subsequent determination of the external camera orientation. This paper presents a consistent solution for the measurement and combination of shape and displacement data including their transformation into simulation systems for the car brake. This is an example, how more accurate and effective measurement techniques make it possible to bring experimental and numerical displacement analysis closer.

With the aim to characterize mechanical properties of thin films, a widely micromechanic test, bulging, is associated with two contactless and noninvasive optical methods, holographic interferometry and projected fringes. These two complementary processes are combined with phase measurement interferometry to get out-of-plane displacements. These solutions are discussed in terms of accuracy and sensitivity. An application is presented on single crystal silicon. Experimental values are compared to results obtained with finite element modeling. Considering the same principle, measurement shapes are performed on multi-layer membranes to analyze residual stresses.

The objective of this investigation is to measure surface enrichment, develop non equilibrium surface phase diagrams, and, using these phase diagrams area tools, study in situ reactions such as carbon deposition on transition metals and their alloys. Electro-Optic Interferometry (EOI) has been chosen as a nondestructive technique to monitor carbon deposition with the strains induced by the molar volume increase. Preliminary experiments have been performed by applying mechanical deformations to verify the accuracy of the EOI for monitoring strains on highly reflective, smooth surfaces. The preliminary results indicate that, using the EOI as described in this paper, full field displacements can be determined with accuracies down to 0.025 micrometers . Based on these results it can be concluded that the EOI has potential for developing surface phase diagrams and in situ studies of carbon deposition.

A new method has been developed to simultaneously measure the thickness and shape of a thin film, such as a dragonfly wing. The innovation in the method is the combining of a heterodyne interferometer and a laser triangulation displacement sensor into one optical system. We confirmed the accuracy of the method by measuring the displacement of a glass plate and the thickness variation generated by a rotated glass plate. The system has a relative accuracy of 1% in the shape measurement and 1.3% in the thickness variation measurement. The method was then applied to a dragonfly wing. The results indicated that the method is very effective in biomechanics studies, such as evaluating the flight performance of dragonflies. In such evaluations, it is essential to measure the high accuracy the variations in both shape and thickness of the wing simultaneously.

High sensitivity, automatic grating interferometry system is shown as the effective experimental tool for the material structure studies and determination of local material constants. The investigations of local Poisson ratio distribution in multilayer glass fiber/epoxy composite, strain distribution around the wire actuator in smart material (carbon fiber/epoxy + optical fiber + wire actuator) and mechanical relation in the area of a few grains in two-phases austenitic-ferritic steel are described and discussed.

In quality control nondestructive techniques gain more and more importance. Holographic interferometry has the advantage of being very sensitive and can be used contactless for inspection of technical components. The interferogram contains fringes, whose pattern holds information about the surface deformation as a part subjected to the load. The detection of faulty parts is usually done by an expert who is used to interpret the interferogram. The automation of this procedure raises several problems, due more specifically to a bad discrimination of the classes of flaws. This paper describes a method for recognition of fault indicating patterns by synthesis of the interferograms, the comparison with the real pattern and modification of the simulation strategy with respect to the classification of the flaw. Taking into account the experimental conditions and a first hypothesis about the type of flaw within the object, a synthesized image of the fringes can be generated and compared to the experimental image. Based on the found hypothesis the experimental load and set-up are changed if the synthesized and experimental fringes differ. First results of this new approach are reported.

A setup for the detection and classification of inhomogeneities (scatterers) in and on transparent films is described. The setup involves the illumination of the film by a laser light sheet. The light scattered off the film is imaged onto two linear CCD arrays. The polarization of the illuminating laser is circular and the two orthogonal linear components are filtered in front of the two CCD arrays. The CCD arrays detect the hh- and the vv-components of the scattered light, as cross-polarized scattering can be neglected. It is shown that the ratio of these two components depends for certain scattering angles on the type of scatterer. The aim of the investigations was to distinguish between dust and bubbles, the two major fault sources in thin gelatin films, the typical substratum for photographic and holographic films. The system was tested with hollow glass spheres and ragweed pollen as test scatterers. The hollow spheres behave as bubbles in the gelatin film Pollen were chosen to represent organic particles. The experimental results prove the validity of the assumed method and show an adequate characterization of the two types of scatterers provided they are at the surface of the investigated film. Statistical analysis of the experimental data show that the characterization quality is diminished if the scatterers are embedded in a gelatin layer, as not all scattering angles are observable due to total internal reflection of the scattered light.

In the present investigation, holographic interferometry was utilized for the first time to measure the alternating current (A.C.) impedance of aluminum samples during the initial stage of anodization processes in aqueous solution without any physical contact. The anodization process (oxidation) of the aluminum samples was carried out chemically in different acid sulpheric acid concentrations (0.5 - 3.125% H2SO4) at room temperature. In the mean time, a method of holographic interferometric was used to measure the thickness of anodization (oxide film) of the aluminum samples in aqueous solutions. Along with the holographic measurement, a mathematical model was derived in order to correlate the A.C. impedance of the aluminum samples in solutions to the thickness of the oxide film of the aluminum samples which forms due to the chemical oxidation. The thickness of the oxide film of the aluminum samples were measured by the real time-holographic interferometry. Consequently, holographic interferometric is found very useful for surface finish industries especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film as well as the A.C. impedance of the aluminum samples can be determined in situ. In addition, a comparison was made between the obtained data of the A.C. impedance from the holographic measurements and A.C. impedance data obtained from measurements of electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data from both techniques.

TV holography is used to measure the components of the deformation vector, whereas TV shearography is used to obtain the derivatives of the displacement components. In this paper, we highlight a novel approach to split the CCD into two parts which enables to extract entirely different information from a single experimental configuration. A holo-shearography configuration provides simultaneous measurement of out-of-plane displacement and its slope change in real time. Similarly a holo-comparative configuration multiplexes an out-of-plane displacement configuration and a comparative interferometric configuration. Few experimental results using both these configurations are presented. In addition TV holography is implemented for vibration studies on an Indian classical musical instrument--Veena. The preliminary studies on a model veena are demonstrated.

Two simple Electronic Speckle Pattern Interferometer (ESPI) configurations have been devised based on diffused reference beam which provides out-of-plane displacement data over the whole field. Both configurations use a tiny diffuser to generate the reference beam. This makes the system insensitive to reference beam misalignment, simplifies the construction of ESPI setup and allows larger area of observation unlike the conventional ESPI system. Thermal deflection studies on a cantilever plate have been carried out. Experimental results and features over the conventional ESPI system are discussed.

This paper describes an high precision in-process optical surface profilometer system. The measurement principle of the profilometer is based on phase comparison of optical heterodyne signals. Disturbance from environment vibration and mechanical instability of the interferometer was effectively eliminated by using optical and electronic common-mode rejection techniques. Measuring light can be automatically focused on the surface by a moving-coil lens during the sample scanning process. The size of the profilometer is small since a laser diode is used instead of a big He-Ne laser. This profilometer is suitable for use on machine. The height sensitivity is of the order of 1 nm and lateral resolution is 0.8 micrometers .

A new type of non-contact heterodyne profilometer with annular lens is described in this paper. The surface can be measured without the separated reference surface. The theoretical lateral resolution of this system becomes much higher of 1 m. The optical structure is easy to set up.

Small dew droplets, which deposited on the mirror surface of a copper plate, were measured by using an interference microscope to evaluate the quality of dew deposited on the mirror surface of the dew-point hygrometer. A He-Ne laser of 10 mW and an optical fiber cable of 3 mm in diameter and 120 cm in length were used as a light source and an optical guide to the microscope. The fiber cable was shaken slightly with an acoustic speaker to reduce speckle noise in the interference images. A shape of dew droplet deposited on the mirror surface of the copper plate was obtained from the interference fringes, and the mass thickness of dew droplets was also obtained by numerical calculation of the volumes of each dew droplet deposited and was of the order of 10^-5 g/cm². The deposition velocities of dew on the surface under slow wind velocity were also measured.

Fine particulates are usually analyzed physically and chemically. Most important of the physical analyses is the particle size determination. Particle size data for the same fine particulate can vary depending on the instrument and method used. The basic reason for such discrepancies is the phenomenon of particle shape. Usually the particulates are of irregular shape and their size and size distribution are based on measurement of certain properties such as length, volume, mass, settling rate, total or projected surface area, sieve aperture, etc. The methods of particle size analysis provide identical or similar analysis results for spherically shaped, non-agglomerated particles only. The various principles used to measure particle size respond differently to changes in particle shape and agglomeration. In this paper the particle size analysis methods based on laser scattering phenomena are discussed. Sample data are presented for metallic, ceramic, and polymer particulates to compare the laser scattering results with others such as scanning electron microscopy, coulter counter, sedimentation, etc.

Small laser interferometer are designed. Interferometer consists of two very small convex or concave mirrors and small flat mirror attached. Well-known Dall method of testing concave aspherical mirrors can be used with this interferometer. Concave ellipsoid mirrors can be tested as well as spherical one. It is possible to design very simple modification of the interferometer using only one very small convex mirror. A few interferometers can be used in a very large spectral range as they consist of mirror surfaces only. It is possible to use the interferometers to test optics, for testing transparent matter, to watch gas or liquid streams. Interferometers are very cheap and easily can be made in quantity. The interferometers are very small that is why they are especially recommended for testing optics in the Space.

Based on a number of technological experiments, the optimization proposal of CCOP was presented and the theoretical control model was properly modified to improve the polishing precision and efficiency. In addition, on a home-made CNC optical fabrication center FSGJ-1, a parabolic surface with a diameter of 200 mm was polished to 0.025 m rms within 30 hours.