Speckle arises from interference of many waves with random phase relationship. In spite of its random appearance its statistical properties are independent of surface roughness of diffusers and depend only on macroscopic parameters of optical systems under usual conditions of observation. In this article we first discuss the size distribution of speckle from physical viewpoints. Then we describe the dynamic behaviors of speckle that are caused by displacement and deformation of diffuse surfaces as well as by change in optical system. Finally we overview applications of these properties of speckle to measurement of displacement and deformation.

In speckle pattern interferometry the starting phase is distributed randomly. Furthermore the background intensity and the modulation also are structured stochastically. This leads to a significant amount of noise in the interferogram analysis. Low modulated speckles are more difficult to evaluate than high modulated ones. We report on a method to reduce this problem. The principle is to use more than one wavelength at the same time and to separate the different wavelengths in the recording plane. With this method the precision can be improved by factor up to 2.3. Our first experiments show the high potential of this method.

First, the principles of large deformation analysis in holographic Interferometry are briefly outlined. Modifications at the reconstruction should recover the invisible fringes. The spacing and the contrast are characterized by the fringe and visibility vectors. The relevant derivative of the path difference involves the polar decomposition of the deformation, affine connections, the image aberration and changes of geodesic and surface curvatures. These specific considerations lead in a second part to similar aspects for hypersurfaces and to an interpretation of the Schwarzschild-solution by virtual deformations. Remarks concerning nonspherical gravitational fields including null-geodesics or light rays are added. Third, an approach to the Kerr-solution for rotating bodies and aspects of the TOV-equation for the interior are given.

Speckles can be classified as -- laser generated virtual speckles and artifically generated real speckle. An additional type termed Sampled Speckles has arisen due to the discrete nature of digital recording. Alternatively speckles are classed as -- objective speckles which are limited by the resolution of the recording medium and subjective speckles which depend on the cut-off frequency of the recording lens. Sampled speckles are limited by the sampling frequency of digital recorders. The generation of these speckles and their applications will be discussed in this paper.

Image correlation techniques developed for speckle metrology have recently been applied to a wide range of ballistics and explosives studies at the Cavendish Laboratory. White-light image correlation applied to quasi-static testing of explosives, at a range of magnifications, is discussed. High-speed ballistic measurements were performed using Digital Speckle Radiography (DSR): a combination of iamge correlation with flash X-rays to study the movement of a plane of X-ray opaque filings within a sample. DSR operates by capturing one image before and a second during the event, allowing the displacements on the plane to be measured to sub-mm accuracy. Varying the delay time and the depth of the seeded plane gives a full three-dimensional flow field in the sample. The use of two X-ray heads stereoscopically increases accuracy by allowing all three components of displacement to be determined. Measurements at velocities ranging from 100 m s^-1 to 6 km s^-1 have been achieved using this technique.

In this paper the use of laser speckle correlation as a mean to measure the micro-structural changes in paper exposed to a changing environment will be presented. Of particular interest will be changes in humidity and crack propagation. Speckle correlation is a technique that calculates the local structural change in a speckle pattern as the object deforms in real time. The response of the technique is the local rate of micro-structural change in the material. Speckle correlation is hence a complement to other speckle metrology techniques. The paper starts with a short introduction to speckle correlation but will focus on applications of the technique on paper. Results from studies of wetting of printing paper at the flock scale, dynamic response in copy paper when exposed to a sudden change in humidity and crack propagation in a notched sheet of Kraftliner are included.

The record of the interference pattern of the object wave and the reference wave is done by the application of high resolution photoplates in holography. After developing the photoplate the reconstruction of the object wave can be realized illuminating the hologram by the reference beam. In digital holography the photographic process is eliminated for the interference patterns are recorded by a CCD camera and the reconstruction can be done virtually using a computer. In general in-line reference beam is used coding the phases for the low resolution of the available CCD devices. The phase-shift technique (or application of two reference beams) can be applied to recover the phase and the amplitude of the image wve at the plane of the CCD matrix. The FFT algorithm is widely used for the reconstruction. Now it is proposed to apply the Monte-Carlo method simulating the diffracted wave to get the intensity distribution at the image plane. The application of Monte-Carlo simulation has a drawback, that is it can be slower than FFT, but its advantages can be significant, namely the intensity pattern of the diffracted wave can be determined along an inclined plane, just a part of the object can be examined if it is required and additionally there are no difficulties in extending it to phase holograms and 3-D objects.

The authors introduced in 2002 a different approach to record a digital complex hologram. A phase-shifting shearing interferometer is used in such a way that no explicit reference wave is required. Twelve different images are acquired and three phase difference patterns are calculated: (a) the phase difference between the two wave fronts with no shearing, (b) the phase difference between two neighbor pixels in the x direction and (c) the phase difference between two neighbor pixels in the y direction. This information is combined to compute the amplitude and phase components of each pixel of the digital complex hologram. A plane wave is used to remove imperfections of the optical components and misalignment errors. In this mean time a new phase propagation algorithm was developed and some advances were achieved in the experimental side. The quality of the complex digital hologram was dramatically improved as well as the reconstructed image. This paper presents the recent progress and results and analyses some possibilities to apply this technique in non-isolated environment.

Commonly, optical systems are called coherent, if a laser is used (right), and incoherent if other sources come into play (wrong). Most opticists are not aware that parasitic spatial coherence is ubiquitous, even if it is unobvious. The pretended incoherent approach may lead to significant quantitative measuring errors of illumination or reflectivity, 3d shape, size or distance. On the other hand, a favorable property of spatial coherence is that among the "speckle noise" we may reveal useful information about the object, by white light interferometry. This report will discuss simple rules to estimate the occuring errors and how to reduce spatial coherence. We will further discuss the complex signal formation in white light inteferometry and roughness measurements far beyond the bandwidth limit of the observing optics.

In order to investigate deterioration processes in the paint layers on the famous 2000-yr-old Chinese Terracotta warriors, a low coherence ESPI system was designed. In this modified set-up a short-coherent superluminescence diode instead of a laser is used. By changing the path length of one of the interfering beams it is possible to select a region limited in depth where deformations are measured even if it is below the surface. Results on an artificial test object and on original terracotta fragments demonstrate the limits and the capabilities of the new method.

Low Coherence Speckle Interferometry (LCSI) combines the depth-resolved measurement of Low Coherence Interferometry (LCI) with the high-accuracy deformation measurement of Electronic Speckle Pattern Interferometry (ESPI). Depth-resolved deformation measurement enables the characterization of the behavior of interfaces in multi-layer materials or structures while changing the ambient conditions. In this paper LCSI is introduced as a new tool for characterization of adhesion. The experimental set-up and the principle of work are described. A FEM-model of an adhesive bonded aluminum joint is developed to analyze the behavior of the Al-adhesive interface during mechanical testing. Some recent results are shown. This application demand measurements on a microscopic scale (camera field of view down to 500 x 500 μm).

We present a technique to calculate the mechanical amplitude and phase of an ultrasonic plane wavefield of nanometric amplitude that propagates on a surface. Our aim is to detect perturbations of the initially smooth wavefronts that indicate the presence of flaws in the material. We use bursts of Rayleigh waves and a double-pulsed TV Holography system that records two correlograms separated down to 1.5 microseconds. The phases of the correlograms are calculated separately using the spatial Fourier transform method (SFTM), and subtracted. In the resultant phase map, the field of instantaneous displacements of the surface (that comprises several periods of the surface acoustic wave) acts as a modulated spatial carrier, now related to the mechanical phase and amplitude, that are extracted applying the SFTM again.

By using new theoretical point of view on cross-spectral density function of the field, the propagation of partially coherent beam produce by a plane source is investigated. Then we show, experimentally, the coherence length in the source plane can be measured directly from the far zone intensity distribution. The effects of the size and coherence of the source on beam directionality will be discussed. Our experimental results will be compared with the special case when the beam is the Gaussian Schell-Model type and it is shown that our prediction has a good agreement.

Phase shifting digital speckle pattern interferometry (PDSPI) is well suited for micrometric displacement measurements. It is non-intrusive and without contact for the object under investigation. Speckle is generated when a beam of coherent light impinges the surface of an optically rough object. Designing the system with off-the-shelf components implies the full understanding of speckle generation, image acquisition and processing. This paper will describe the main components and their contribution to the final result, from the speckle effect to the unwrapping of the phase. The designed PSDSPI set-up allows the study from small to large areas and can produce quantitative displacement maps using phase shifting principle. As an application the object is a flat circular steel membrane closing a depression chamber. The size of the membrane is about 20 mm in diameter. The membrane deformation is measured using step by step PSDSPI process while decreasing pressure in the chamber. The results show a typical displacement of about 1 μm for 1 mbar. Quantitative profiles of the membrane deformation can be obtained. Further applications will be presented, including measurement corrections by shape of the object. Phase discontinuities will be discussed.

Using a multiband light source in Speckle Shearography makes dispersion effects become an issue. Since the fringe pattern of a shearographic measurement depends on the wavelength, the fringe modulation decreases if a light source with a very broad band is used. Therefore, in this paper we propose to make the fringe distance of the resulting shearogram independent of the wavelength using a dispersive optical component. To demonstrate this method, a shearing interferometer is presented, which creates a shear that is proportional to the wavelength. Provided that the object deformation along the shear is linear to the first order, the wavelength dependent shear is obtained by inserting a wedge prism into a Michelson Interferometer with the object in the input plane and the detector array in the output plane. An important prerequisite to this technique is that the refractive index of the wedge prism has a linear characteristic within the observed spectral range. Since the experimental investigations were performed with a mercury arc lamp, nBK7 is shown to be a suitable material within the range of 435 nm to 546 nm.

Among interferometric techniques for analyzing mechanical properties and behaviors of microelements and microsystems time-averaged interferometry deserves particular attention because of its relative simplicity and data video display for arbitrary vibration frequency. This communication presents an implementation of the approach of Petitgrand et al. to quantitative analysis of vibration mode shapes based on the calibration of the fringe contrast variation as a function of the vibration amplitude. Fringe contrast maps for static and resonant frequency states are determined using the four-frame method with the phase shift of π/2 between the frames. Then the dynamic map is divided by the static one to obtain the square of the modulus of the characteristic fringe function. For sinusoidal vibrations it is the zero-order Bessel function J₀ squared with the vibration amplitude encoded in its argument. The simplicity of our approach and speed of calculations are to be emphasized. The fringe processing method proposed is suitable for conventional two-beam and digital speckle interferometry. The results of experiments carried with silicone cantilever beams used in AFM resonant sensors are presented.

Holography provides the possibility to record and to reconstruct the complete information of optical wave fields. Recording holograms directly on CCD targets allows the numerical reconstruction of phase and intensity by the computer. Interferometric techniques such as 3d-displacement analysis and 3d-contouring can be implemented in this way easily and with high flexibility. In addition to the numerical reconstruction, the digitally recorded holograms can be transmitted via telecommunication networks and optically reconstructed at any desired place using LCD displays or DMDs. This possibility opens new experimental approaches with respect to the investigation of similar objects at different places by using principles of comparative holography. Moreover, the direct access to all relevant components of the digitally stored wave front allows the application of principles of active vision to coherent metrology. In this article the principles of digital holography are explained shortly. After that the combination of digital holography with principles of active metrology are discussed. Finally some practical examples are given to illustrate this combination.

Lensless Fourier-Transform Digital Holography through an aperture has been demonstrated some years ago. This technique allows to record and reconstruct images of large objects placed at short distances from the camera. In this paper we show that the distance between the aperture plane and the camera can be used to control the field of view and, therefore, moving the camera away from or towards the aperture has an effect similar to zooming a lens in and out, respectively. We also show that the F/# number of the aperture must be kept constant to hold the relative lateral resolution, i.e., to have a constant speckle size while zooming. With this improvement, Lensless Fourier-Transform Digital Holography provides a functionality similar to Image-Plane Digital Holography. Both involve practically the same computational cost. The former has the benefit of its experimental simplicity but has the drawback of not providing a real-time image of the object, which is useful for alignment, as the latter does.

The paper explains the benefits and the application limits of micro speckle interferometry (MSI) and it shows the potential for improvements when a deep UV laser source is used. For the experiments, a new deep ultraviolet micro speckle interferometer (DUV-MSI) was designed operating at 266 nm of wavelength. The implemented optics enables for the measurement of both, in-plane and out-of-plane movements on the microparts. A number of practical examples are shown in the paper in order to illustrate the advantages of a shorter wavelength in speckle interferometry.

Three systems based on digital holographic interferometry in combination with endoscopy are described. The three compact systems (using rigid, flexible endoscopes and miniaturized head) have been developed and used for the measurement of dynamical deformations on both mechanical and biological surfaces, where measurements need to be performed at "hidden" surfaces or inside more or less closed objects. A Q-switched pulsed laser is used. Two digital holograms of the test object, corresponding to the two laser pulses, are captured at separate video frames of the CCD-camera, transferred in a frame grabber and further processed in a PC. If during the interval between the two laser pulses (usually in the range of 5-600 μs) the object undergoes a vibration, a fringe pattern will result from the difference between the two holograms. This fringe pattern has the information needed to quantitatively evaluate the vibration.

Endoscopic Electronic-Speckle-Pattern Interferometry (endoscopic ESPI) is a tool for the detection and the measurement of displacements and movements in technical and biological cavities. For an adequate measurement accuracy additional to the geometry of imaging and illumination, information about the shape and curvature of the investigated cavities is required. Investigations to measure the surface topometry by endoscopic ESPI combined with a two-wavelength method have been carried out. The advantage of this arrangement, which uses commercial endoscope imaging systems, is that it is possible to obtain object shape and displacement data with the same endoscopic interferometric measurement system. Therefore, in a first step, the phase difference distribution effected by the change of the illumination wavelength and the object shape is detected by spatial phase shifting and in a second evaluation step, the radial distortions of the endoscope imaging system are corrected and the geometry of endoscopic off-axis illumination is taken into account by an approximation.

Shearography is a full-field non-contact optical technique usually used to measure displacement gradient. Correlation fringes sensitive to displacement gradient are generated by the correlation of speckle interferograms recorded before and after object deformation. Shearography is sensitive to a component of displacement gradient that is determined by the illumination and viewing directions and by the direction of applied shear. The sensitivity of shearography to displacement gradient is determined by the magnitude of the applied shear and by the optical wavelength. In general, to perform a multi-component measurement three components of displacement gradient are measured, by using three illumination, or viewing, directions, followed by a coordinate transformation to an orthogonal coordinate system. The coordinate transformation procedure relies on good quality data from all three measured channels. The adddition of a fourth measurement channel gives duplicate measurements for all the surface displacement gradient components. A good agreement between duplicate measurements gives a high level of confidence in the measurement accuracy. A fourth measurement channel also allows the surface strain to be fully characterized when correlation fringe quality is poorer, or when one of the views is obstructed as a result of the object shape. In this paper a theoretical analysis of multi-component shearography using four measurement channels is given and the issues and benefits are discussed.

Graphite-epoxy laminates are subjected to the "incremental hole-drilling" technique in order to investigate the residual stresses acting within each layer of the composite samples. In-plane speckle interferometry is used to measure the displacement field created by each drilling increment around the hole. Our approach features two particularities (1) we rely on the precise repositioning of the samples in the optical set-up after each new boring step, performed by means of a high precision, numerically controlled milling machine in the workshop; (2) for each increment, we acquire three displacement fields, along the length, the width of the samples, and at 45°, using a single symmetrical double beam illumination and a rotary stage holding the specimens. The experimental protocol is described in detail and the experimental results are presented, including a comparison with strain gages. Speckle interferometry appears as a suitable method to respond to the increasing demand for residual stress determination in composite samples.

The comparative analysis of the digital speckle-displacement measurement technique and the optical speckle-displacement correlation technique is carried out. Some versions of a joint transform correlator (JTC) architecture, namely a conventional JTC, a JTC with median thresholding, a JTC with subset median thresholding, and a fringe adjusted filter JTC, are used for study of in-plane rigid body displacements. The systematic and random errors of speckle pattern's mean displacement calculated by using the mentioned above techniques are compared. The robustness of the digital speckle-displacement measurement technique and four JTC versions to input noise of speckle patterns and output noise of a correlation response is studied.

Sophisticated technique for reliable quantitative deriving residual stress values from initial experimental data, which are inherent in combined implementing the hole drilling method with both holographic and speckle interferometry, is described in detail. The approach developed includes both possible ways of obtaining initial experimental information. The first of them consists of recording a set of required interference fringe patterns, which are resulted from residual stress energy release after through hole drilling, in two orthogonal directions that coincide with principal strain directions. The second way is obtaining a series of interrelated fringe patterns when a direction of either observation in reflection hologram interferometry or dual-beam illumination in speckle interferometry lies arbitrary with respect to definite principal strain direction. A set of the most typical both actual and analogous reference fringe patterns, which are related to both reflection hologram and dual-beam speckle interferometry, are presented.

The study of light scattered from changing surfaces is of great interest because of its application in aging control of mechanical components and other problems. In many situations it is important to know the roughness changes in dielectric or metallic surfaces. Often, this roughness variation must be determined in a non-destructive way. In this work it is reported some new results related with the study of roughness variations. In recent works were presented some aspects of a developed theoretical model that relates the speckle correlation with changes in the surface roughness. This model is valid for dielectric or metallic surfaces, however, for the sake of simplicity, it is studied a translucent diffuser. It is recorded the transmitted speckle pattern for a translucent rough surface before and after it suffers a change, and then it is calculate the correlation between both speckle patterns. The roughness is changed in a controlled way by means of immersion liquids of different refractive indices. A good agreement between the theoretical description and experimental results obtained in quasi-real time is achieved.

This paper provides an overview of the current state-of-the-art in fringe pattern analysis, with a particular emphasis on recent developments in digital speckle pattern interferometry (DSPI) and digital speckle photography (DSP). The main topics covered are as follows: spiral transform for analysis of fringe patterns without spatial carriers, real-time analysis, dynamic DSPI, three-dimensional phase unwrapping, combined DSPI/DSP techniques, and three-dimensional DSP. Several interesting applications outside mainstream speckle metrology are also described, including fingerprint analysis, and measurement of both strain and magnetic fields within the human brain using phase contrast magnetic resonance imaging (MRI).

Instead of the intensity information used in conventional speckle metrology, we explore new possibilities of making use of the phase information of speckle patterns. We propose a new technique of displacement measurement that makes use of the phase singularities in the analytic signal of the speckle pattern, which is generated by Hilbert filtering. Experimental results are presented that demonstrate the validity and the limitation of the proposed technique.

It is generally acknowledged that it takes at least three phase-stepped speckle patterns to obtain quantitative phase information. However, if only a phase change has to be determined, a two-bucket approach can be followed, under certain conditions. The background of the two-bucket algorithm, and the requirements with respect to the use of it, are explained. Examples of modeled and measured phase stepped speckle intensity data, showing numerical instability when conditions are not met are presented. It is also shown that two phase-stepped speckle pattern pairs, taken before and after an event can be sufficient to determine phase changes invoked by the event.

In this paper we proposed a Hilbert Transform to calculate the phase map. The data processing is performed in temporal domain, considering the temporal history of the interference signal at every single pixel. This results in a relatively high spatial resolution of the phase map. In addition, the phase method enables a fully automatic and does not require human interaction. The final results give a temporal development of two-dimensional deformation field. To reduce the influence of the fluctuations of bias intensity on the calculated phase, it was removed prior to performing the Hilbert Transform. The proposed method for analysis of the phase of dynamic ESPI was examined in two different experiments, i.e., plastic deformation studies, and thermal expansion studies. The dynamic range of measurements is increased from several tens of nanometers to several micrometers, which makes the method very attractive for dynamic measurement.

A previously observed optical interferometric band pattern interpreted as representing localized strain is compared with a mechanical band structure known as the Luders' line. The interferometric band pattern is observed in fringe systems formed with the subtraction method of electronic speckle-pattern interferometry applied to in-plane displacement of plastically deforming metal specimens. The Luders' line is known to be representing localized strain. Experiments have been carried out to compare the locations of the optical band pattern and the Luders' line under the same stress condition. The experimental results indicate clear coincidence of the optical band pattern and the Luders' line, confirming the previous interpretation that the optical band pattern represents localized strain. It has been observed that the optical band pattern begins to appear at 11% lower stress than the Luders' line, indicating that strain localization occurs prior to the appearance of the first Luders' line.

In this paper we analyze the application of a chirped Gaussian wavelet transform to retrieve the phase distribution in digital speckle pattern interferometry (DSPI). The performance of this method is evaluated using computer-simulated fringes, approach that allows an accurate determination of the phase map encoded by the fringe pattern. It is shown that the local chirp-based approximation does not give good results in the neighborhood of stationary phase points. To overcome this limitation, we compare the wavelet analysis by applying a smoothed time-frequency distribution. We show that the application of this distribution allows the determination of the phase map where the local chirp-based approximation fails. We also discuss the influence of the filtering process to smooth the DSPI fringes and some additional limitations that emerge when these methods are applied.

Phase measurements require the measurement of interferogram intensities. In this paper it is investigated how the validity of the evaluated phase is affected by the averaging of the interferogram intensities across the pixels of a CCD-array. In our previous works it has been shown numerically that the validity of the phase values depends on the topology of the speckle field. Here, it is examined analytically how the topology influences the phase evaluation with respect to averaging. One result is that in certain cases the absolute value of the phase gradient can be determined solely from the intensity of the speckle field, without any reference beam. Based on this result the phase error at intensity maxima, saddle points and for stationary points of the phase is examined.

Applications of artificial neural network in holographic interferometry and speckle metrology have been presented. Back-propagation neural network has been used for defect detection. Self-organizing networks has been successfully applied to determine interferometric fringe centerlines.

In this paper the dynamic processing of interferometric fringe patterns obtained by real-time optical measurement methods like holographic interferometry is shown. A hologram of the tested component is superimposed with the hologram of the stressed component. The achieved fringe patterns vary according to the degree of stress applied. To evaluate these varying fringe patterns in real time, dynamic filtering is required. A hybrid opto-electronic sytem with a digital image processing and optical correlation module based on liquid-crystal spatial light modulators gives us the possibility to use dynamic filters and input images. In order to process interferometric fringes the adaptive wavelet transformation is applied.

We investigate digital holography method as metrological tool for inspection and characterization of MEMS structures. The efficiency of the digital holography is demonstrated measuring out of plane deformations due to the intrinsic residual stress. Microstructures under investigation are of two different types: the first are made of a single polysilicon layer, whereas the second are bimorph structures with a thin silicon nitride layer over the polysilicon one. These structures exhibit an out-of-plane deformation owing to residual stresses between the different layers. The characterization of these deformations is instrumental to study and understand the effect of residual stress on the deformation of the single microstructures. To this aim digital holography has been applied as metrological tool in order to obtain the profile of the microstructures. These data are employed in analytical and numerical model to evaluate residual stress inside the investigated structures. Moreover, digital holography has been employed to evaluate MEMS behavior when subjected to thermal load. Profile of cantilevers, with dimensions from 1 to 50 μm, has been measured.

Speckle Pattern Interferometry has emerged from the experimental substitution of holographic interferometry to become a powerful problem solving tool in research and industry. The rapid development of computer and digital imaging techniques in combination with minaturization of the optical equipment led to new applications which had not been anticipated before. While classical holographic interferometry had always required careful consideration of the environmental conditions such as vibration, noise, light, etc. and could generally only be performed in the optical laboratory, it is now state of the art, to handle portable speckle measuring equipment at almost any place. During the last decade, the change in design and technique has dramatically influenced the range of applications of speckle metrology and opened new markets. The integration of recent research results into speckle measuring equipment has led to handy equipment, simplified the operation and created high quality data output.

Holographically recorded diffractive optical elements are described, which can be used to implement very simple self-aligning electronic speckle pattern interferometers (ESPI) and holographic interferometers requiring only a laser source and a CCD camera in the optical set-up. The ESPI systems can utilize transmission or reflection holographic optical elements (HOEs). The HOEs are essentially amplitude beamsplitters and recombiners whose recording and reconstruction parameters can be adjusted to optimize the ratio of reference and object beams reconstruction so as to maximize subtraction fringe contrast. The HOEs are recorded using a 4-component photopolymer system. In addition the HOEs can be recorded at visible wavelengths but used in ESPI systems, which incorporate at diode laser. The diode can be wavelength modulated. In this way we can incorporate digital speckle pattern interferometry (DSPI) or amplitude and phase modulation of the optical path difference for time-averaged speckle interferometry.

A "handheld" speckle interferometer for measuring out-of-plane displacements on reflective as well as diffusely scattering object surfaces is presented. The interferometer is a nearly path length compensated set-up which uses diffuse illumination of the object in combination with a speckled reference. The reference wave is established by reflecting a part of the diffuse object illumination from a glass plate located just in front of the object. The glass plate is mounted on a piezoelectric translator in order to control the phase of the reference wave when using phase stepping algorithms. The coherent light source is a laser diode. A web camera with a Universal Serial Bus (USB) interface is employed as the image-capturing device. Likewise, is the piezoelectric translator controlled through the USB interface. The necessary size of the optical set-up depends on the size of the object. The interferometer presented here is a compact version of the set-up, which is capable of measuring displacments of small objects, having either a specularly reflecting- or a diffusely scattering surface. The small optical set-up together with the use of the popular USB-communication for acquiring the images and controlling the phase of the reference wave constitutes a compact "handheld" instrument and eliminates the need for installing extra hardware, such as frame grabber and Digital to Analog converter, in the host computer.

We will present the basic properties of photorefractive crystals and show how they can be used efficientl in holograpic interferometry experiments. We then will present some holographic systems and their numerous applications. With continuous illumination, we will show classical non destructive testing (defect detection), displacement metrology, vibration mode shape visualization, as well as a study for the use of photorefractive crystals in microgravity monitoring of fluid (FSL) experiment aboard the International Space Station). With pulsed illumination we will present the possibilities of the photorefractive crystals in vibration measurement (and will introduce the ongoing EC-funded PHIFE research project). The purpose of the paper is to unmystify photorefractive crystals and to show that they could be a good alternative to traditional speckle-based techniques for highly demanding applications. For that we will highlight the highest resolution achieved as well as the high temporal dynamics of the holographic recording.

A laboratory measurement system based on electronic speckle pattern interferometry is described which is intended to measure the deformation fields developed in Ball Grid Arrays (BGAs) and other high density electronic packages and interfaces under thermal load associated with production and normal use. The die and substrate generally have widely differing coefficients of thermal expansion, which results both in residual stress in the assembly on cooling and stress during operation cycles. The instrument currently under development at EMPA uses a NIR laser diode source to illuminate the device under test. The instrument involves edge-on illumination of the outer row of solder balls fo a BGA. A novel imaging scheme is employed with a linear array of coherent fiber bundles being used to transfer the images of the individual solder balls to the object plane of the camera. We report on the tests we have performed on different types of bundles, both flexible and rigid, to evaluate the characteristics for optimum image quality in optical setups relevant to our micro-imaging ESPI-application: modulation transfer function (MTF), limiting resolution, cross-talk between adjacent fibers, optical transmission quality. We report first fringe phase maps taken with the ESPI setup.

Speckle techniques are investigated for the characterization of pavement surface microtexture, particularly, height variations from one up to about ten micrometers in amplitude. Using the scalar diffraction theory of Kirchhoff, some simulations of the speckle contrast were carried out to bring out some patterns in case of a subjective speckle whose grains are not resolved by CCD photodetectors and in the case of a two-scale surface texture. We deduce the possibility of characterizing the fineness of the microtexture or its evolution versus wear modifying. The method is also experimentally applied to some reference surfaces (abrasive papers with various finenesses) and some models of pavement surfaces at various steps of wear.

A new optical technique based on real time holographic interferometry in trues colors has been implemented around the transonic wind tunnel of the ONERA-Lille center to analyze 2D unsteady wake flows. Tests realized in color interferometry, real time and double exposure, use simultaneously three wavelengths of a continuous waves laser (argon and krypton mixed) and holograms are recorded on silver-halide single-layer panchromatic Slavich PFGO3c plates. The very principle of real-time true color holographic interferometry uses three primary wavelengths (red, green, blue) to record, under no-flow conditions, the interference among the three measurement beams and the three reference beams simultaneously on a single reference hologram. After the holographic plate is developed, it is placed on the test setup again in the position it occupied durng exposure and the hologram is illuminated again by the three reference beams and three measurement beams. A flat, uniform color can then be observed behind the hologram. So a horizontal, vertical, or even circular fringe pattern can be formed and the achromatic central white fringe can be made out very clearly. This single color is used to determine the path difference zero on the interferograms. The flow studied was the unsteady flow downstream of a cylinder placed crosswise in the test section. A sequence of hundred interferograms was recorded on the flow around the cylinder at Mach 0.37. The vortex formation and dissipation phases can a be seen very clearly, along with the fringe beat to either side of the cylinder.

In order to measure erosion/redeposition in fusion devices, a new diagnostic based on speckle interferometry is investigated. First experiments performed on carbon fiber composite (CFC) materials have shown that this technique is able to measure a modification of the surface in the range of 1 μm. Further experiments have been performed on different materials using a second wavelength in order to carry out 3D measurements of the surface and to increase the dynamic range of the depth measurement. A diagnostic, based on two-wavelength TV-holography to measure in situ erosion/redeposition during long duration discharges on the CIEL limiter in Tore Supra, is under development at CEA Cadarache.

This paper shows the feasibility of applying digital image plane holography (DIPH) as a fluid velocimetry technique for simultaneous measurements of all three components of the velocity field. As a first approach DIPH has been set up to measure a single fluid plane. The recording apparatus is a digital speckle interferometer (DSPI) with spatial phase shifting (SPS). The speckle interferometer has an out-of-plane sensitivity and the off-axis reference beam produces a spatial modulation in the pattern (hologram) recorded by the CCD camera. From the interferometric and photographic analysis of the reconstructed object wave, the three velocity components in the fluid plane are obtained. The complex amplitude of the object wave is calculated by the application of a Fourier-transform method to the hologram. The phase change between two subsequent frames yields an out-of-plane component of the velocity field. The two in-plane components are obtained, as in digital speckle photography, by cross correlation of the reconstructed object wave's intensity. Some quantitative results in a Rayleigh-Benard convective flow are presented. In the final setup, angular multiplexing with coherence length control has been introduced in order to simultaneously measure the velocity fields in two fluid planes. Some preliminary results from the convective flow are presented.

Pulsed TV holography is an all-electronic version of pulsed holographic interferometry. Such a system was used to study ignition of pre-mixed flammable gases. The object was recorded in its undisturbed and disturbed state followed by an evaluation of the changes in refractive index field between those two states. The essential components of the set-up are an injection seeded, twin cavity double pulsed Nd:YAG laser and a CCD camera. A focused laser pulse from the same laser that was used for the recording of the digital hologram initiated the ignition of the pre-mixed gas. Results from the recordings show the ignition process. From the experimental phase maps the refractive index of the gas mixture could be determined. This method makes it possible to determine the proportion of components in a pre-mixed flammable gas in situ.

Fast and robust 3D quality control as well as fast deformation measurement is of particular importance for industrial inspection. Additionally a direct response about measured properties is desired. Therefore, robust optical techniques are needed which use as few images as possible for measurement and visualize results in an efficient way. One promising technique for this aim is the inverse pattern projection which has the following advantages: The technique codes the information of a preceding measurement into the projected inverse pattern. Thus, it is possible to do differential measurements using only one camera frame for each state. Additionally, the results are optimized straight fringes for sampling which are independent of the object curvature. The ability to use any image for inverse projection enables the use for augmented reality, i.e. any properties can be visualized directly on the object's surface which makes inspections easier than with use of a separated indicating device. The hardware needs are low as just a programmable projector and a standard camera are necessary. The basic idea of inverse pattern projection, necessary algorithms ane found optimizations are demonstrated, roughly. Evaluation techniques were found to preserve a high quality phase measurement under imperfect conditions. The different application fields can be sorted out by the type of pattern used for inverse projection. We select two main topics for presentation. One is the incremental (one image per state) deformation measurement which is a promising technique for high speed deformation measurements. A video series of a wavering flag with projected inverse pattern was evaluated to show the complete deformation series. The other application is the optical feature marking (augmented reality) that allows to map any measured result directly onto the object under investigation. The general ability to straighten any kind of information on 3D surfaces is shown while preserving an exact mapping of camera image and object parts. In many cases this supersedes an additional monitor to view results and allows an operator to investigate results on the object, directly.

Temporal phase-shifting speckle interferometry (TPSSI) is a technique based on the recording of a sequence of speckle interferograms throughout the entire deformation history of an object. To calculate the phase map, a controlled phase change is introduced in the reference beam as a function of time. As temporal phase unwrapping involves only one-dimensional signals, this procedure is generally easier to carry out than 2-D spatial unwrapping. TPSSI also allows large-object absolute displacement fields to be obtained. This paper provides an overview of recent developments and applications of temporal phase-shifting speckle interferometry. These include the performance of different phase-shifting algorithms when a TPSSI system is used in the presence of harmonic and random vibrations and also for measuring mechanical vibrations. A novel adaptive phase-shifting algorithm is also presented that searches for the peak of the windowed Fourier transform of the modulated intensity signal and evaluates the phase at that frequency instead of at the carrier frequency. The presentation is illustrated with an application of TPSSI to the detection of sub-surface delamination defects in carbon fiber specimens submitted to vacuum loading. It is shown that re-referencing the temporal phase unwrapping algorithm after different time intervals allows the measurement of time-varying displacements in excess of 100 μm without the limit normally imposed by speckle decorrelation.

A hybrid phase unwrapping algorithm has been proposed recently, which uses a window-based technique and two local phase unwrapping approaches to determine gradient information for each window. However, with this approach, in many practical applications, we encountered certain inconsistencies, e.g. caused by noise in the input phase map. In this paper, we present an improved window-based algorithm for unwrapping noisy phase maps. With pixel-based images, we can only obtain residues of charge one, but, with this new method, higher charges are possible. Eventually the total charge of positive and negative residues may be unequal. Therefore, we extend the set of residues by border residues until we obtain equal charges. We build connected components containing neighbors of residues using the breath-first-search method. Hereafter, we follow a minimum-cost graph-theory method determining the set of branch-cuts and computing the global minimum of the total cut-length. Every positive residue is associated to a corresponding negative residue. We connect these pairs by the path with the worst overlap error obtained by one of the local phase unwrapping approaches. Using this new method, we are able to reduce the rms-phase-error by factor 5, when comparing the results to the existing hybrid phase unwrapping algorithm.

HoloVision is a software package for performing digital holography on the Microsoft Windows platform. Basic theory for reconstruction of digitally sampled holograms is presented along with some more specific software implementation details. This includes the Fresnel method, the Convolution method and the Fourier method. A method involving a tilt of the reference wave and magnification through a numerical lens is presented to enlarge the visible region of the reconstructed image. Two different approaches for suppressing the undesired zero-order components are investigated. Examples are included for ordinary intensity images as well as for phase difference images from digital holographic interferometry.

The paper describes a simple low-cost open-loop PZT actuator and the procedures which have been developed for its calibration and alignment in order to obtain a device dedicated to phase-shifting speckle interferometry. A low-voltage multilayer PZT ceramic block was inserted between a mirror and a cube beamsplitter of a Michelson interferometer to be used in a shearometer assembled on a cube 40x40x40 mm. The PZT was driven by a supply voltage output by a 16 bit D/A converter directly connected to the parallel port of a personal computer which guarantees a very accurate output. By the analysis of the interference pattern produced by the Michelson interferometer the calibration curves (for ascending and descending input voltage) were obtained. When the whole hysteresis loop has been identified, a fairly linear working range can be chosen. The device is equipped with three setscrews acting on a leaf-spring for the compensation of the mirror tilting produced by the non uniform expansion of the PZT block. The calibration can be performed using either the interference between two smooth wavefronts (in presence of a sufficiently fine fringe pattern) or the interference between two speckle patterns. The calibration procedure can be consequently carried out directly on any speckle interferometer at the beginning of the measuring session, in this way the environmental sensitivity of the actuator can be overcome.

In this article a new automatic phase FFT filtration method is described. It is compared with other well known filtration techniques for noise removal. This automatic FFT filter is applied on interferograms obtained through one dimensional folding shear interferometry for displacements measurement of a loaded glass flask. Different algorithms have been applied for processing of digitally synthesized phase maps and the advantages of the enhanced automatic FFT filtration are shown. The phase filtered maps obtained in this way can be demodulated even with the simplest unwrapping technique.

In several applications, it is necessary to measure the surface characteristics of a wire so, it is important to do it during the manufacturing process. This work presents two main results: First, an analytical expression for the angular distribution of the mean scattered intensity from cylindrical rough surfaces as a function of the characteristic statistical parameters of the heights. This expression allows to measure the ratio T/σ between the correlation length and the roughness. Second, a quantitative relationship between the size and shape of the speckle grains in the Fraunhofer zone and the statistical properties of the cylindrical rough surface. In the first case, it is shown that the scanning process inherent to usual detection systems can be replaced by single step detection using a screen and a CCD camera. Therefore, this method can be applied to on line wire surface testing where conventional procedures are inadequate. In the second one, the experimental autocorrelation functions at different angles gives another method for measuring the parameter T/σ. Then, the study of the light scattered from cylindrical rough surfaces seem to be of great interest because of its potential application in NDT of manufacturing and finishing processes of components like pipes, junctions, wires and bearings.

Electronic speckle pattern interferometry (ESPI) is discussed for the detection of out-of-plane deformations in small objects. For increasing the resolution in object space a laser source of small wavelength is combined with a microscope with a high numerical aperture. Fringe quality is increased by using spatial phase-shifting and the Fourier transform method to allow deformation detection also under non-optimum conditions. The efficacy will be shown in some measurements on different specimens where deformations are successfully recorded in areas down to a few micrometers in size.

The introduction of new materials in Mechanical Engineering is one of the main tasks of scientists and engineers. At present new technologies that allow the study, characterization and measurement of important mechanical states in new materials are being developed continuously. These techniques include the Optical Techniques of Measurement that use laser as an important tool in the information processing and interpretation. These techniques also involve the Electronic Speckle Pattern Interferometry (ESPI). The present investigation shows the development and implementation of ESPI technique in the study and characterization of composite tube junction. The technical characteristics related to this technique implementation are included in this paper. The strain field caused by different applied actions is also presented. The advantages and disadvantages of the use of this technique are shown and they are compared to other traditional and optical measurement techniques.

We propose a multiplexing/demultiplexing technique in digital Fresnel holography for the simultaneous measurement of two dimensional deformations. The spatial multiplexing uses the incoherent mixing of 2x2 coherent waves. The optical arrangement of the setup gives access simultaneously to the out of plane and the in plane component of the displacement field. For this, we use a twin polarizing Mach-Zehnder interferometer which produces the simultaneous incoherent addition of two holograms of the object. The digital holograms are reconstructed using the discrete Fresnel transform. Each object phase encodes the in plane and out of plane component of the displacement field vector. In order to exract the mixing of the 2D measurement, we use a spatial demultiplexing of the holograms. Its principle is based on the use of the spatial autocorrelation function. The spatial coordinate of one of its three lobes is used for the demultiplexing of the second hologram on the first. This numerical demultiplexing is based on the two dimensional Fourier transform and the application of the so called delay theorem. After demultiplexing, the sum of the two phase change gives access to the out of plane component and their difference to the in plane one. Experimental results dealing with the study of the mechanical behavior of composite materials are presented.

In this study, we are developing optical methods to monitor the condition of plant, i.e., biological activity or growth, aiming to investigate the influence of the environmental conditions. The statistical interferometry developed by the authors has been applied to measure the growth of the plant. This method utilizes the statistical properties of a fully developed speckle field and has the advantage of simple optical system to achieve measurements with an extremely high accuracy. In the experiments to demonstrate the validity of the method, the growth speeds of the plants were measured under various environmental conditions of watering and light illumination. It has been clearly demonstrated that the statistical interferometry has a high sensitivity for monitoring the growth of the plant at a nanometer scale with a high temporal resolution of second scale.

This study deals with the measurement of the deformation of sheets of recycled paper subjected to tensile loads using an electronic speckle pattern interferometry (ESPI) technique. Specimens with fibers, which constitute a sheet of paper, parallel and perpendicular to the direction of paper making are used to investigate the effect of the arrangement of fibers on the tensile property. The deformation of recycled paper is compared with that of virgin pulp paper. Results reveal that a large two-dimensional deformation of recycled paper can be measured using the ESPI technique, and that the directions of fibers, which constitute a sheet of paper, have a significant effect on the two-dimensional deformation of recycled paper.

Non-destructive testing of rubber by optical means presents a challenge because rubber has different mechanical properties from conventional solids when subjected to stress. The size of flaws introduced in rubber during the manufacturing process is an important characteristic as they increase the stress in the specimen when it is in use. The use of electronic speckle pattern interferometry, electronic speckle pattern shearing interferometry and white light interferometry for non-destructive material characterization of rubber is presented. It is shown that electronic speckle pattern shearing interferometry can be of some use for visualization of flaws on the rubber surface under thermal stress. White light interferometry gives a complete profiling of the elastomer surface and it is only one of the three interferometric techniques for measuring flaws on the rubber surface.

We investigate the propagation of a partially coherent beam produce by a plane source. By utilizing Helmholtz equation, the intensity of the source in plane z = 0, and plane z are obtained. Then by considering new theoretical prediction on cross-spectral density function of the field in the plane z = 0, the root-means square (rms) beam radius, as a function of distance z are calculated. The effects of the size and coherence of the source on beam directionality will be then discussed. In the special case when the beam is the Gaussian Schell-Model type, our results reduces to well known expression.

Speckle interferometry has been introduced in Civil Engineering at CUJAE in 1988 as a useful technique in research work. This paper describes some applications of speckle interferometry in civil engineering. Speckle photography has been utilized to study deformation in shearwalls, and also studding of behavior building model under concentrate loading. Displacements were numerically calculated using a finite element method. Electronic Speckle Pattern Interferometry (ESPI) has been used for the measurement of the Young's modulus in mortars and concrete. Obtained values of the Young's modulus are in good agreement with reported for mortars or measured by a static compressive technique for concrete.

Speckle noise is inherent to laser barcode scanners since barcodes are usually printed on diffusive surfaces which generate speckle when illuminated by spatially coherent beams. In this paper statistical properties of barcode signals corrupted by speckle noise are analyzed. We derive closed form expressions for the autorcorrelation function and power spectral density of speckle noise for scanning beams with arbitrary field distributions. Since differentiation is often used for enhancement of barcode edges, we also analyze the properties of differentiated speckle noise. We derive estimates for signal-to-noise ratio when a laser beam scans over an edge. The random edge jitter in a barcode signal caused by speckle noise is also analyzed. The theory is illustrated by applying the results to Gaussian beams.