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The ever-increasing requirements of product quality and reliability demand more efficient measuring and test methods that must be online, nondestructive, wholefield and without contact. Optical methods seem to be ideal for such purposes. The interferometric technique of ESPSI (Electronic Speckle Pattern Shearing Interferometry), or Shearography, is a coherent-optical measuring and test method that is similar to holographic interferometry. However, this method displays many advantages for industrial applications, due to its relative insensitivity to environmental disturbances. Shearography measures the gradient of the deformation, not the deformation itself as holography does. Consequently, shearography measures strain information directly. Based on the above, Shearography was adapted for the surface strain measurement in graphene-reinforced composite materials; the information was evaluated at each point from our sample observed area. Defect inspections with shearography on fiber-reinforced plastics parts, widely used in aircrafts, ships, chemical and oil and gas industries, are often performed outside of the lab. An optical system capable of measuring the strain fields in and out of plane was developed based on electronic speckle interferometry. The obtained interferogram images were processed using the phase-stepping technique. A specific specimen geometry and an optical arrangement based on the Michelson interferometer are proposed to measure the deformation along two orthogonal axes due to sensibility in and out of plane. The advantages of the system include its high sensitivity and stability. The experimental setup and approach for estimating the strain fields was validated using a membrane based on polylactic acid reinforced with cellulose microcrystalline as sample with and without graphene.

An optical system capable of simultaneously grabbing three phase-shifted interferometric images was developed for dynamic temperature field measurements outside of a thin flame. The polarization phase shifting technique and a Michelson interferometer that is coupled to a 4-f system with a Ronchi grating placed at the frequency plane are used. This configuration permits the phase-shifted interferograms to be grabbed simultaneously by one CCD. The temperature field measurement is based on measuring the refraction index difference by solving the inverse Abel transform, which requires information obtained by the fringe order localization. Experimental results of a dynamic event are presented varying in time.

In this work, we present a novel Panoramic Fringe Projection system (PFP) to retrieve the three-dimensional topography of quasi-cylindrical objects along their full length and around the entire circumference. The proposed procedure uses a 45° concave conical mirror to project a circular sinusoidal fringe pattern onto a specimen placed coaxially to the mirror and at the same time to image the modulated fringe pattern diffused from the object surface. In order to obtain the required sensitivity, an axicon is used to create a divergent fringe pattern with constant pitch. By processing the phase map, information on the radius over the full 360° surface of the sample can be obtained by using a single-view series of images captured from a single camera. To verify the feasibility of the PFP technique, a tubular sample with shape discontinuities has been tested. The proposed method demonstrated to be able to retrieve the accurate topography of quasi-axial-symmetric samples with complex geometries for a large variety of applications.

The structured light technique is useful to evaluate the topography of an object. By using the Fourier transform, the phase of a fringe pattern is obtained from a single image. With the phase information and the sensibility vector of the optical system, the value z(x, y) at each point of the object can be determined. It is known that color is a subjective sensation, and it changes depending on the observer. In order to make an association of real color and texture, it is necessary to calibrate and profile the optical devices involved in the process. Thus, we ensure that the color detected by a camera is the same displayed on the monitor and perceived by the observer, so it is possible to associate the color of the target object in addition to the evaluation of topography. On the other hand, 3D visualization is possible by using a stereoscopic system that provides two different images of the same object (one for each eye). One possible technique is that known as the anaglyph method, based on the binocular disparity of two images obtained with different color filters. Each one of the images is taken with complementary colors (red-blue or red-green), and the tri-dimensional shape can be seen through the use of special glasses; this way, each eye sees an image from its own angle. Object topography is obtained with the fringe projection technique, and then one image is selected and pseudo colored; then, the second image is taken, slightly changing the perspective of the tridimensional display and pseudo coloring it with a complimentary color. A computational algorithm is developed to evaluate and visualize the object in real time.

The development of this work is important in the morphological study of plant parts, specifically in the study of the cuticle of fruits or leaves. The implemented optical technique for fringe projection can identify potential fracture zones which damage the presentation of the fruits impacting business as well as producing them. Specifically, we obtained information on the thickness of a cuticle corresponding to the abaxial surface of a leaf of apple (Malus domestica) of the variety Golden Delicious.

Electronic speckle pattern interferometry is a useful technique in the measurement of displacement fields and topography. Traditionally, arrangement with dual collimated illumination to topography measurement is used. In this case, the object analysis is limited to the size of optical collimating lens. In the case of large objects, an optical system with divergent illumination can be used. It is known that displacement fields and the phase are related by the sensitivity vector. At once, to compute the sensitivity vector, illumination sources position and superficial shape need to be considered. The last condition becomes an impediment to surface contouring. In a published work 1 , a simple iterative algorithm based on the Gauss-Seidel technique is presented to compute contouring measurement. In the present work, the uncertainty associated to the measurement of the topography is calculated by using the Monte Carlo method.

We present experimental results obtained by using phase-shifting interferometry by polarization to measure the radial slope of transparent samples, by implementing a Radial-Shear interferometer and using a grating to replicate the interference patterns modulated by polarization; the interferometer is capable to process the optical phase data by obtaining four interferograms in one-shot. The experimental results for transparent samples are presented in this research.

Stereo Vision is a powerful tool used to make a 360° scan of an object in order to obtain topography details or getting the spatial position of interest points, but the process could be slow due to the computing time. In this work we present the alternative of using high reflective markers, which are used as reference points to track an object movement. The advantage of these markers is that their detection is faster than a full scene correlation and it is done by comparing the position of the centroids of each marker without using pixel-pixel analysis.

Three-dimensional object topography is obtained by using the fringe projection technique. In fringe projection technique, digitalization is done when black and white lines are projected over the sample object and the image is captured by the CCD. It is applied the phase shifting method to evaluate the phase of the projected fringes. In this paper it is proposed a method in which red, green and blue fringes are projected sequentially. It is obtained the topography to each color (RGB) and finally the three obtained shapes are averaged. By using this method, we obtain information about color, texture and topography details of the object.

Due to non-destructive optical techniques allows surface measurement with high accuracy, a Common Path interferometer based on a Michelson configuration was implemented to analyze phase objects by using polarization simultaneous phase-shifting interferometry. Each beam of the interferometer has a birefringent wave plate attached in order to achieve nearly circular polarization of opposite rotati ons one respect to the other. The system is coupled to a 4- f arrangement with Bi-Ronchi gratings collocated in the Fourier plane. The interference of the fields associated with replicated beams, centered on each diffr action orders, is achieved varying the b eams spacing with respect to the grating period. The optical configuration allows obtaining n-interferograms simultaneously. The phase reconstruction is performing by a three steps phase shifting algorithm. Experimental results are pr esent for a phase object. Keywords: Ronchi grating, phase shifting interfe rometry, polarization, phase objects.

In this work we present a parallel polarizing phase shifting interferometer based in a Double Cyclic Interferometer (DCSI) to analyze transparent samples. This system has the advantage of generating four beams that can interfere properly; this can reduce the number of captures needed in phase shifting interferometry. The interferometric system generates two π-shifted interferograms, which are recorded by the CCD camera in a single-shot. For the processing of the optical phase data map, a parallel phase shift can be generated by placing a linear polarizer covering two patterns. We analyze the cases of four patterns with arbitrary shifts captured in two shots. The unwrapped phase is processed by Kreis methods. Experimental results obtained by the proposed interferometer are presented.

An interferometric method to measure the slope of phase objects is presented. The analysis was performed by implementing of a polarizing phase shifting cyclic shear interferometer coupled to a grating interferometer. This system can obtain four interference patterns with adjustable phase shifts and variable lateral shear. In order to extract the slope of a phase object, is analyzed the optical phase applying the classical method of phase extraction.

A Mach Zehnder (MZ) interferometer was implemented to analyze a phase object using polarization phase-shifting interferometry. The Mach Zehnder interferometer produces two beams with circular polarization of opposite rotations one respect to the other. The system is coupled to a 4-f system with phase grating in the Fourier plane, interference of the fields associated with replicated beams centered on the diffraction orders is achieved by a proper choice of the beams spacing with respect to the gratings period. The optical configuration allows obtaining n-interferograms in one shot. The configuration presented does not require micro-polarizer arrays or additional software to eliminate noise caused by vibration, as the system is stable itself and uses conventional polarizing filters. Considering the object under study a thin phase object, experimental results are presented.

We measured the topography of lens by using a technique of diffuse reflection (fringe projection technique) and by a method based on specular reflection technique (similar to Placido disk system). The obtained results with both techniques are compared with those obtained with a spherometer. The retrieval of the three-dimensional shape of the lens is an issue of great interest for wide medical application, particularly in ophthalmology.

In this work, a dual illumination beam system is used to obtain the strain intensity factor in mode one (mode I) to mechanical elements during tension testing. The displacement field is obtained by means of a phase stepping technique, and deformations are calculated by the Stokes differentiation method. Results are compared using a finite element analysis technique.

It is measured the topography of a large object by using structured light. The type of fringes generated are equivalent to the produced by divergent beams. In this case the relation between the phase and the height is not linear. In this work it is proposed an iterative estimation to the topography measurement. It is taken in account the variation of period in xdirection of the projected grating and the perspective problem of CCD camera. The shape obtained is compared with the measurements realized with a commercial scanner. The stop criterion value c in the algorithm was chosen of .1 mm. This value corresponds to resolution in z of commercial scanner. To this case, three iterations are enough to reach the value of c. It is observed that after three iterations, the value of z is approximately the same. It is obtained a great discrepancy to the topography measurement when does not use correction in perspective and in the period variation due to divergent projection of the fringes. The main contribution of this work is show that it is important consider the variation of period and the perspective problem in the measurement of the topography to large objects.

We use the projected fringes technique to follow the changes induced in the topography of metallic sample sheets subjected to uniaxial tensile tests. Since in-plane strains are associated with out-of-plane deformations, the monitoring of thickness variation of the tensile specimens can be used to detect necking and shear band formation. A sequence of images of the fringe pattern was captured and processed by means of the Fourier transform technique. We measured the material behavior in the elastic and plastic zones during its elongation until fracture took place. We present experimental results for stainless and hot rolled steel sheets.

We report on the errors obtained by comparing the in- and out-of-plane displacements calculated from the sensitivity matrix with all its components and when it is considered only the component of the largest contributing of each one of the three interferometers. Divergent illumination is considered in the sensitivity vectors evaluation to measure displacement vector components. This analysis is made for a flat elastic target by using of Electronic Speckle Pattern Interferometry (ESPI).

We present a non-contact system for obtaining three-dimensional objects topography. The described system combines the fringe projection technique and the Talbot effect which is knowed like Talbot interferometry. In fringe projection technique, the digitalization is realized when black and white lines are projected over the object and this image is captured by the CCD. In Talbot interferometry, the object is collocated on one of the grating auto-image planes. The deformed grating image is captured by the CCD and superposed with other reference one that can be physical or computer generated (virtual/synthetic) for obtaining a moire pattern which gives information about the object topography. The topography of a coin and phalangeal articulation are obtained by using of this technique. The Spatial Synchronous Detection and Fourier Method were incorporate to retrieve the phase.

When it is carried out to perform a three dimensional evaluation of displacements and strains, it has been proposed some optical systems which uses three illumination beams or the use of three sensors. The different sensitivity vectors components associated to each illumination beam; let us permit to calculate the displacement in each direction by sensitivity matrix. In the present work, simple geometries of interferometers are discussed. It is showed the sensitivity components for each source in the case of optical set-up with three divergent illuminating beams, where we analysed the sources position that makes possible measure the u, v and w components with a maximum weight factor in each direction respecting to set-up total sensitivity. The sources position is one on x-axis, the second on y-axis and the third near to z-axis. From the theoretical predictions is proposed an interferometer which is based on the ESPI technique which has the sources configuration calculated. Experimental results of displacements are presented to an elastic surface when a rotated load is applied in the centre of the target.

The Large Millimeter Telescope (LMT) 1 is a 50 m diameter millimeter-wave telescope designed for principal operation at wavelengths between 1mm and 4mm. The LMT secondary mirror will have a diameter of approximately 2.6 meters and focal ratio of .35. The purpose of this study was to implement the incoherent fringe projection technique and the spatial phase synchronous method to measure the secondary mirror mold profiling. The obtained topography is compared with the conic surface generated synthetically. We considered that mold should be hyperboloid surface with paraxial curvature of 1764.9 mm and conic constant of -1.1474. We will discuss the preliminary results where it is obtained a RMS of 0.624 cm.

Amalia MartInez1, Raul Cordero**&, J A. Rayast, H. J. Puga*, R. RodrIguezVerattCentro de Investigaciones en Optica, A. C., Apartado Postal 1 -948, C. P. 37000, Leon, Gto.,MEXICO**Department of Mechanical and Metallurgical Engineering, Pontificia Universidad Catolica deChile, Vicufla Mackenna 4860, Santiago, CHILE

It is described a technique where different views of an object are connected to recover its three-dimensional form in a field of vision of 360°. The object is placed on a rotary motorized platform and projected a linear fringe pattern. In each angular object displacement, the projected fringe pattern is captured by a camera CCD. Each pattern is digitally demodulated providing information of depth. The format of the digital matrix, this is, the image type, is changed for one of triads ( x , y , z ). This way, a cloud of independent points of their position in the matrix is constructed. As a reference, one point in each cloud (known it a priori ), is taken. All the clouds are rotated and displaced until the reference point taking its corresponding position. Different mixed clouds of points (views) are ordered in a single triad matrix that describes the complete surface of the object surface target. Finally a mesh of quadrilaterals is built up that makes possible to generate a solid surface.

Commonly, in-plane sensitive arrangements use tow symmetrical collimated wavefronts for object surface illumination. However, this is a limitation when large objects surface have to be analyzed. In this case spherical illumination is needed. Using this kind of optical set-up, the present work shows results of fracture measuring by using moire and speckle interferometric methods. Non- collimated symmetrical dual-beams, having a sensitivity vector varying with the position are performed. These methods are capable of detecting in-plane and out-of-plane deformations due to the use of divergent beams. It is calculated the error to each component of the sensitivity vector. Experimental result of fracture measurements are shown.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.