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Showing papers on "Speckle imaging published in 2006"


Journal ArticleDOI
TL;DR: In this paper, Malbet et al. developed two analytical methods for wave front sensing and control that aim at creating "dark holes", i.e., areas of the image plane cleared of speckles, assuming an ideal coronagraph and small aberrations.
Abstract: High-contrast imaging from space must overcome two major noise sources to successfully detect a terrestrial planet angularly close to its parent star: photon noise from diffracted starlight and speckle noise from starlight scattered by instrumentally generated wave front perturbation. Coronagraphs tackle only the photon noise contribution by reducing diffracted starlight at the location of a planet. Speckle noise should be addressed with adaptive optics systems. Following the tracks of Malbet, Yu, and Shao, we develop in this paper two analytical methods for wave front sensing and control that aims at creating "dark holes," i.e., areas of the image plane cleared of speckles, assuming an ideal coronagraph and small aberrations. The first method, "speckle field nulling," is a fast FFT-based algorithm that requires the deformable-mirror influence functions to have identical shapes. The second method, "speckle energy minimization," is more general and provides the optimal deformable mirror shape via matrix inversion. With an N × N deformable mirror, the size of the matrix to be inverted is either N2 × N2 in the general case or only N × N if the influence functions can be written as the tensor product of two one-dimensional functions. Moreover, speckle energy minimization makes it possible to trade off some of the dark hole area against an improved contrast. For both methods, complex wave front aberrations (amplitude and phase) are measured using just three images taken with the science camera (no dedicated wave front sensing channel is used); therefore, there are no noncommon path errors. We assess the theoretical performance of both methods with numerical simulations including realistic speckle noise and experimental influence functions. We find that these speckle-nulling techniques should be able to improve the contrast by several orders of magnitude.

274 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate a coherent imaging technique that enables them to image the complex field at the focus of an X-ray zone plate without the need for conventional Xray lenses, and they show that there are no fundamental limits on the resolution of this lensless imaging technique other than the wavelength of the X-rays themselves.
Abstract: The rapid development of new sources of coherent X-rays, such as third-generation synchrotrons, high-harmonic-generation lasers1 and X-ray free-electron lasers2, has led to the emergence of the new field of X-ray coherent science. The extension of coherent methods to the X-ray regime makes possible methods such as coherent diffraction, X-ray photon-correlation spectroscopy, speckle interferometry and ultrafast probing at atomic resolution and femtosecond timescales. Despite rapid improvements in the resolution that conventional X-ray optics can achieve, new methods for manipulating X-rays are required to push this to the atomic scale3. Here we demonstrate a coherent imaging technique that enables us to image the complex field at the focus of an X-ray zone plate without the need for conventional X-ray lenses. There are no fundamental limits on the resolution of this lensless imaging technique other than the wavelength of the X-rays themselves. The ability to characterize the beam with one measurement makes the method ideally suited to characterizing the fields generated by pulsed coherent X-ray sources.

200 citations


Journal ArticleDOI
TL;DR: Analysis of transverse and longitudinal intensity distributions of a volume speckle field for the SBMIR technique is presented and enhancement of the resolution method by shifting the camera a distance of a half-pixel in the lateral direction improves the sampling of Speckle patterns and leads to better quality reconstructions.
Abstract: The recording of the volume speckle field from an object at different planes combined with the wave propagation equation allows the reconstruction of the wavefront phase and amplitude without requiring a reference wave. The main advantage of this single-beam multiple-intensity reconstruction (SBMIR) technique is the simple experimental setup because no reference wave is required as in the case of holography. The phase retrieval technique is applied to the investigation of diffusely transmitting and reflecting objects. The effects of different parameters on the quality of reconstructions are investigated by simulation and experiment. Significant enhancements of the reconstructions are observed when the number of intensity measurements is 15 or more and the sequential measurement distance is 0.5 mm or larger. Performing two iterations during the reconstruction process using the calculated phase also leads to better reconstruction. The results from computer simulations confirm the experiments. Analysis of transverse and longitudinal intensity distributions of a volume speckle field for the SBMIR technique is presented. Enhancing the resolution method by shifting the camera a distance of a half-pixel in the lateral direction improves the sampling of speckle patterns and leads to better quality reconstructions. This allows the possibility of recording wave fields from larger test objects.

193 citations


Journal ArticleDOI
TL;DR: The algorithms applied to quantifying the strain response of a mechanically inhomogeneous, bi-layered polyvinyl alcohol tissue phantom that is subjected to either small or large dynamic compressive forces while being imaged with a spectral domain OCT system performed well.
Abstract: We present two approaches to speckle tracking for optical coherence tomography (OCT)-based elastography, one appropriate for small speckle motions and the other for large, rapid speckle motions. Both approaches have certain advantages over traditional cross-correlation based motion algorithms. We apply our algorithms to quantifying the strain response of a mechanically inhomogeneous, bi-layered polyvinyl alcohol tissue phantom that is subjected to either small or large dynamic compressive forces while being imaged with a spectral domain OCT system. In both the small and large deformation scenarios, the algorithms performed well, clearly identifying the two mechanically disparate regions of the phantom. The stiffness ratio between the two regions was estimated to be the same for the two scenarios and both estimates agreed with the expected stiffness ratio based on earlier mechanical testing. No single numerical approach is appropriate for all cases and the experimental conditions dictate the proper choice of speckle shift algorithm for OCT-based elastography studies.

150 citations


Journal ArticleDOI
TL;DR: Experimental results are presented that demonstrate the validity and the performance of the proposed optical vortex metrology with nano-scale resolution.
Abstract: As an alternative to correlation-based techniques widely used in conventional speckle metrology, we propose a new technique that makes use of phase singularities in the complex analytic signal of a speckle pattern as indicators of local speckle displacements. The complex analytic signal is generated by vortex filtering the speckle pattern. Experimental results are presented that demonstrate the validity and the performance of the proposed optical vortex metrology with nano-scale resolution.

140 citations


Journal ArticleDOI
TL;DR: Spatio-temporal analysis of LSI data is investigated, in conjunction with diffusion theory and Monte Carlo modeling of light transport, to estimate fibrous cap thickness in NCFAs, which is an important predictor of plaque stability.
Abstract: Necrotic-core fibroatheromas (NCFA) with thin, mechanically weak fibrous caps overlying lipid cores comprise the majority of plaques that rupture and cause acute myocardial infarction. Laser speckle imaging (LSI) has been recently demonstrated to enable atherosclerotic plaque characterization with high accuracy. We investigate spatio-temporal analysis of LSI data, in conjunction with diffusion theory and Monte Carlo modeling of light transport, to estimate fibrous cap thickness in NCFAs. Time-varying laser speckle images of 20 NCFAs are selected for analysis. Spatio-temporal intensity fluctuations are analyzed by exponential fitting of the windowed normalized cross-correlation of sequential laser speckle patterns to obtain the speckle decorrelation time constant, tau(rho), as a function of distance rho from the source entry location. The distance, rho', at which tau(rho) dropped to 65% of its maximum value is recorded. Diffusion theory and Monte Carlo models are utilized to estimate the maximum photon penetration depth, zmax(rho'), for a distance equal to rho', measured from LSI. Measurements of zmax(rho') correlate well with histological measurements of fibrous cap thickness (R=0.78, p<0.0001), and paired t-tests show no significant difference between the groups (p=0.4). These results demonstrate that spatio-temporal LSI may allow the estimation of fibrous cap thickness in NCFAs, which is an important predictor of plaque stability.

108 citations


Journal ArticleDOI
TL;DR: Experimental results for translational and rotational displacement measurements are presented that demonstrate large dynamic range and high spatial resolution of the proposed optical vortex metrology.
Abstract: A new technique for displacement measurement is proposed that makes use of phase singularities in the complex signal generated by a Laguerre-Gauss filter operation applied to a speckle pattern. The core structures of phase singularities are used as unique fingerprints attached to the object surface, and the displacement is determined by tracing the movement of registered phase singularities with their correspondence being identified by the fingerprints. Experimental results for translational and rotational displacement measurements are presented that demonstrate large dynamic range and high spatial resolution of the proposed optical vortex metrology.

106 citations


Journal ArticleDOI
TL;DR: In this article, optical configurations for DSPI and DS with a double aperture mask in front of the imaging lens for spatial phase shifting are proposed for the measurement of out-of-plane displacement and its first order derivative (slope) respectively.
Abstract: Digital speckle pattern interferometry (DSPI) and digital shearography (DS) are well known optical tools for qualitative as well as quantitative measurements of displacement components and its derivatives of engineering structures subjected either static or dynamic load. Spatial phase shifting (SPS) technique is useful for extracting quantitative displacement data from the system with only two frames. Optical configurations for DSPI and DS with a double aperture mask in front of the imaging lens for spatial phase shifting are proposed in this paper for the measurement of out-of-plane displacement and its first order derivative (slope) respectively. An error compensating four-phase step algorithm is used for quantitative fringe analysis.

99 citations


Journal ArticleDOI
TL;DR: In this article, a fast readout mode was developed to take short exposures of stellar images corrected by adaptive optics at ground-based UCO/Lick Observatory, with integration times of 5 ms and a time between successive frames of 14.5 ms (λ = 2.2 μm).
Abstract: Imaging observations are generally affected by a fluctuating background of speckles, a particular problem when detecting faint stellar companions at small angular separations. These speckles can be created by both short-lived atmospheric aberrations and slowly changing distortions in the optical system. Over the course of a long-exposure image, the combination of many independent realizations of speckle patterns forms a halo in the point-spread function (PSF) of characteristic scale Δθ ~ λ/r0 (where r0 is the coherence length in the pupil). While adaptive optics can increase the achievable image contrast, speckle noise remains a major source of random error, which decreases the sensitivity of companion detection observations near the diffraction limit. Knowing the distribution of the speckle intensities at a given location in the image plane is therefore important for understanding the noise limits of companion detection. The speckle noise limit in a long-exposure image is characterized by the intensity variance and the speckle lifetime. In this paper we address the former quantity through the distribution function of speckle intensity. Previous theoretical work has predicted a form for this distribution function at a single location in the image plane. We developed a fast readout mode to take short exposures of stellar images corrected by adaptive optics at the ground-based UCO/Lick Observatory, with integration times of 5 ms and a time between successive frames of 14.5 ms (λ = 2.2 μm). These observations temporally oversample and spatially Nyquist sample the observed speckle patterns. We show, for various locations in the image plane, that the observed distribution of speckle intensities is consistent with the predicted form. In addition, we demonstrate a method by which Ic and Is can be mapped over the image plane. As the quantity Ic is proportional to the PSF of the telescope free of random atmospheric aberrations, this method can be used for PSF calibration and reconstruction.

98 citations


Journal ArticleDOI
TL;DR: A technique for the reduction of speckle noise in digital holography is introduced, not based on classical filtering techniques such as median filters, but instead utilizes the shift theorem of the Fourier transform.
Abstract: Speckle pattern decorrelation reduces the accuracy of interferometric shape and deformation measurements. We introduce a technique for the reduction of speckle noise in digital holography. The method is not based on classical filtering techniques such as median filters. Instead it utilizes the shift theorem of the Fourier transform. For this method several holograms of the same object under test are recorded. The reconstruction leads to a set of object wave fields with different speckle patterns. A proper averaging procedure, taking into account the properties of the wrapped phases, leads to an improvement of the accuracy in the resulting phase difference. The theory of the applied method is described and our first results for technical components with an improvement of accuracy up to 1/57 of the wavelength are presented.

93 citations


Journal ArticleDOI
TL;DR: Factors within the simulation include rate of change of phase within individual speckle transitions, low-pass filtering to match the frequency range of experimental data with which comparison is to be made, a track-and-hold facility for periods of low signal amplitude, and wavefront curvature effects.
Abstract: The fundamental mechanism by which speckle noise is generated in laser vibrometry before describing a new numerical simulation for prediction of speckle noise level in a real measurement is considered. Factors within the simulation include rate of change of phase within individual speckle transitions, low-pass filtering to match the frequency range of experimental data with which comparison is to be made, a track-and-hold facility for periods of low signal amplitude, and wavefront curvature effects. The simulation data provide real insight into the phase and amplitude modulation of the Doppler signal, and good agreement is found in the final comparison with experimental data from a measurement on a rotating target.

Journal ArticleDOI
TL;DR: The experimental results show that the surface roughness contained in the surface speckle pattern texture images has a good monotonic relationship with their energy feature of the gray-level co-occurrence matrices.
Abstract: Surface speckle pattern intensity distribution resulting from laser light scattering from a rough surface contains various information about the surface geometrical and physical properties A surface roughness measurement technique based on the texture analysis of surface speckle pattern texture images is put forward In the surface roughness measurement technique, the speckle pattern texture images are taken by a simple setup configuration consisting of a laser and a CCD camera Our experimental results show that the surface roughness contained in the surface speckle pattern texture images has a good monotonic relationship with their energy feature of the gray-level co-occurrence matrices After the measurement system is calibrated by a standard surface roughness specimen, the surface roughness of the object surface composed of the same material and machined by the same method as the standard specimen surface can be evaluated from a single speckle pattern texture image The robustness of the characterization of speckle pattern texture for surface roughness is also discussed Thus the surface roughness measurement technique can be used for an in-process surface measurement

Journal ArticleDOI
TL;DR: In this article, the influence of the speckle noise on the measured data quality is investigated, which is an unavoidable phenomenon occurring when a coherent light beam is scattered back from an optically rough surface.

Journal ArticleDOI
TL;DR: In this paper, the 3D full-field deformation of a carbon fiber/epoxy composite pressure vessel was studied using a 3D digital speckle correlation method, which is suitable for deformation measurement of composite pressure vessels in real engineering practice.

Journal ArticleDOI
TL;DR: The SNR of the system was sufficiently high to provide an image pixel per acoustic burst without signal averaging, and the use of intense acoustic bursts is a promising signal enhancement strategy for UOT.
Abstract: Biophotonic imaging with ultrasound-modulated optical tomography (UOT) promises ultrasonically resolved imaging in biological tissues. A key challenge in this imaging technique is a low signal-to-noise ratio (SNR). We show significant UOT signal enhancement by using intense time-gated acoustic bursts. A CCD camera captured the speckle pattern from a laser-illuminated tissue phantom. Differences in speckle contrast were observed when ultrasonic bursts were applied, compared with when no ultrasound was applied. When CCD triggering was synchronized with burst initiation, acoustic-radiation-force-induced displacements were detected. To avoid mechanical contrast in UOT images, the CCD camera acquisition was delayed several milliseconds until transient effects of acoustic radiation force attenuated to a satisfactory level. The SNR of our system was sufficiently high to provide an image pixel per acoustic burst without signal averaging. Because of the substantially improved SNR, the use of intense acoustic bursts is a promising signal enhancement strategy for UOT.

Journal ArticleDOI
TL;DR: In this paper, a detailed analysis of laser speckle effects in scanning laser Vibrometer measurements on rotors is presented in the form of a speckles repeat map, together with experimental data quantifying the dramatic reduction in speckhe noise found in tracking measurements.

Journal ArticleDOI
TL;DR: The results of 1657 speckle interferometric observations of double stars, made with the 26 inch (66 cm) refractor of the US Naval Observatory, are presented in this article.
Abstract: The results of 1657 speckle interferometric observations of double stars, made with the 26 inch (66 cm) refractor of the US Naval Observatory, are presented. Each speckle interferometric observation of a system represents a combination of over 2000 short-exposure images. These observations are averaged into 1111 mean relative positions and range in separation from 016 to 1699, with a median separation of 165. This is the 12th in a series of papers presenting measurements obtained with this system and covers the period 2005 January 3-December 29. Included in these data are 30 older measurements whose positions were previously deemed possibly aberrant but are no longer classified this way following a confirming observation. Sixteen of these systems have new orbital elements, which are presented here as well. For η Coronae Borealis (STF 1937) we determine masses of 1.207 and 1.077 M⊙ and an orbital parallax of 54.95 mas.

Journal ArticleDOI
TL;DR: Compared to the traditional approach, both dynamic range and signal-to-noise ratio can be increased by a factor of up to five times, which demonstrates considerable promise for a possible eventual clinical implementation.
Abstract: Phase contrast magnetic resonance velocity imaging is a powerful technique for quantitative in vivo blood flow measurement. Current practice normally involves restricting the sensitivity of the technique so as to avoid the problem of the measured phase being ‘wrapped’ onto the range −π to +π. However, as a result, dynamic range and signal-to-noise ratio are sacrificed. Alternatively, the true phase values can be estimated by a phase unwrapping process which consists of adding integral multiples of 2π to the measured wrapped phase values. In the presence of noise and data undersampling, the phase unwrapping problem becomes non-trivial. In this paper, we investigate the performance of three different phase unwrapping algorithms when applied to three-dimensional (two spatial axes and one time axis) phase contrast datasets. A simple one-dimensional temporal unwrapping algorithm, a more complex and robust three-dimensional unwrapping algorithm and a novel velocity encoding unwrapping algorithm which involves unwrapping along a fourth dimension (the ‘velocity encoding’ direction) are discussed, and results from the three are presented and compared. It is shown that compared to the traditional approach, both dynamic range and signal-to-noise ratio can be increased by a factor of up to five times, which demonstrates considerable promise for a possible eventual clinical implementation. The results are also of direct relevance to users of any other technique delivering time-varying two-dimensional phase images, such as dynamic speckle interferometry and synthetic aperture radar.

Journal ArticleDOI
TL;DR: In this paper, the phase map is calculated by local inversion of the Bessel function and the phase is calculated using the time-averaged hologram for calculating the unwrapped vibration-related phase map.

Journal ArticleDOI
TL;DR: This work presents the simultaneous measurement of three-dimensional deformations by electronic speckle pattern interferometry using five object beams and three colors to validate out-of-plane and in-plane deformation measurements and demonstrate sensitivity on the order of 10 nm.
Abstract: We present the simultaneous measurement of three-dimensional deformations by electronic speckle pattern interferometry using five object beams and three colors. Each color, corresponding to an orthogonal direction of displacement, is separated through dichroic filtering before being recorded by a separate CCD camera. Carrier fringes are introduced by tilting the beam path in one arm of each of the three interferometers. The measured deformation modulates these carrier fringes and is extracted using the Fourier-transform method to achieve high displacement sensitivity. The field of view is on the order of a millimeter, making the system suitable for study of microstructural deformations. We compare experimental results with calculated values to validate out-of-plane and in-plane deformation measurements and demonstrate sensitivity on the order of 10 nm.

Journal ArticleDOI
TL;DR: In this article, the authors present an implementation of the extended Knox-Thompson (EKT) speckle reconstruction algorithm dedicated to solar observations, which yields nearly diffraction-limited images from bursts of short exposure solar observations under a wide range of seeing conditions.
Abstract: We present an implementation of the extended Knox-Thompson (EKT) speckle reconstruction algorithm dedicated to solar observations. EKT speckle imaging yields nearly diffraction-limited images from bursts of short exposure solar observations under a wide range of seeing conditions. Our implementation supports field dependent amplitude calibration to permit analyzing data obtained with a partially compensating adaptive optics systems. The principles of the method and some technical details of our implementation are discussed. We have performed various tests using simulated data of representative solar scenes. The simulations include the effects of seeing and noise with the exception of anisoplanatism. The expected photometric error of a reconstructed image amounts to a few percent of the mean intensity under seeing conditions ranging from poor to excellent. We also present sample reconstructions of real data and discuss issues arising from anisoplanatism.

Journal ArticleDOI
TL;DR: In this paper, Kumar et al. investigated and implemented a new filtering scheme on digital speckle pattern interferometric fringes to enhance the signal-to-noise ratio (SNR) in the speckLE interferograms.

Journal ArticleDOI
TL;DR: In this article, the authors used dynamic speckle techniques to study the drying process of a spray paint with relatively long drying times, and developed alternative speckles contrast methods to characterize faster processes.
Abstract: The short drying times of spray paints are of great benefit in some applications, and this property allows for painting over almost immediately. However, this fast-drying process precludes following it using conventional techniques. In a previous article, we used the dynamic speckle to follow the drying process of solvent-based and water-based paints with relatively long drying times, and recently we developed alternative speckle contrast methods to characterize faster processes. This article presents the application of these methods using dynamic speckle techniques to study the drying of a spray paint. Activity image display is also included.

Journal ArticleDOI
TL;DR: A simple correction is proposed that minimizes the experimental error committed in positioning the CCD and that diminishes the error to 0.43%.
Abstract: We present and evaluate two corrections applicable in determining the modulation transfer function (MTF) of a charge-coupled device (CCD) by the speckle method that minimize its uncertainty: one for the low frequency region and another for the high frequency region. The correction at the low-spatial-frequency region enables attenuation of the high power-spectral-density values that arise from the field and CCD response non-uniformities. In the high-spatial-frequency region the results show that the distance between the CCD and the aperture is critical and significantly influences the MTF; a variation of 1 mm in the distance can cause a root-mean-square error in the MTF higher than 10%. We propose a simple correction that minimizes the experimental error committed in positioning the CCD and that diminishes the error to 0.43%.

Journal ArticleDOI
TL;DR: This work extends the OFRT analysis to more general LCT systems with a single limiting aperture and demonstrates the benefits of using an LCT approach to metrology design by showing that by varying the curvature of the illuminating field, it can effectively change the output domain.
Abstract: Digital speckle photography can be used in the analysis of surface motion in combination with an optical linear canonical transform (LCT). Previously [D. P. Kelly et al. Appl. Opt.44, 2720 (2005)] it has been shown that optical fractional Fourier transforms (OFRTs) can be used to vary the range and sensitivity of speckle-based metrology systems, allowing the measurement of both the magnitude and direction of tilting (rotation) and translation motion simultaneously, provided that the motion is captured in two separate OFRT domains. This requires two bulk optical systems. We extend the OFRT analysis to more general LCT systems with a single limiting aperture. The effect of a limiting aperture in LCT systems is examined in more detail by deriving a generalized Yamaguchi correlation factor. We demonstrate the benefits of using an LCT approach to metrology design. Using this technique, we show that by varying the curvature of the illuminating field, we can effectively change the output domain. From a practical perspective this means that estimation of the motion of a target can be achieved by using one bulk optical system and different illuminating conditions. Experimental results are provided to support our theoretical analysis.

Journal ArticleDOI
TL;DR: An approach of phase extraction from a single fringe pattern is tested for computer-simulated and experimentally obtained fringe patterns and works well under a high noise level and limited visibility and can extract accurate phase values.
Abstract: The ordinary differential equation (ODE) and partial differential equation (PDE) image- processing methods have been applied to reduce noise and enhance the contrast of electronic speckle pattern interferometry fringe patterns. We evaluate the performance of a few representative PDE denoising models quantitatively with two parameters called image fidelity and speckle index, and then we choose a good denoising model. Combining this denoising model with the ODE enhancement method, we make it possible to perform contrast enhancement and denoising simultaneously. Second, we introduce the delta-mollification method to smooth the unwrapped phase map. Finally, based on PDE image processing, delta mollification and some traditional techniques, an approach of phase extraction from a single fringe pattern is tested for computer-simulated and experimentally obtained fringe patterns. The method works well under a high noise level and limited visibility and can extract accurate phase values.

Journal ArticleDOI
TL;DR: The deformation field showed clearly the difference between the thermal expansions of the stainless steel and ceramic and it was revealed that the boundary of materials and its vicinity suffer very large thermal strain due to the significantly large difference in the linear coefficient of thermal expansions.
Abstract: A dynamic electronic speckle pattern interferometry method is applied to investigate thermal expansion of a joint material (ceramic-stainless steel) as a practical industrial object. The speckle interference signal is considered in the temporal domain and the phase is analyzed by the Hilbert transform method. Errors caused by the bias and modulation variations over the phase values are first examined by numerical simulation. Two experiments are performed with in-plane and out-of-plane sensitive systems to study the 3D deformation field thoroughly. The deformation field showed clearly the difference between the thermal expansions of the stainless steel and ceramic. It was also revealed that the boundary of materials and its vicinity suffer very large thermal strain due to the significantly large difference in the linear coefficient of thermal expansions.

Journal ArticleDOI
TL;DR: A reflection-based optical implementation of two simultaneous scale-invariant fractional Fourier transforms is used to develop a novel compact speckle photographic system that allows the independent determination of both surface tilting and in-plane translational motion from two sequential mixed domain images captured using a single camera.
Abstract: A reflection-based optical implementation of two simultaneous scale-invariant fractional Fourier transforms (FRTs) is used to develop a novel compact speckle photographic system. The system allows the independent determination of both surface tilting and in-plane translational motion from two sequential mixed domain images captured using a single camera.

Journal ArticleDOI
TL;DR: In this article, a method that combines finite element analysis and genetic algorithms was proposed to determine the elastic properties of materials from the full-field measurement of the surface displacements of plates under flexural loads.
Abstract: The article describes a method that combines finite element analysis and genetic algorithms in order to determine the elastic properties of materials from the full-field measurement of the surface displacements of plates under flexural loads. An optimizing process updates the elastic constants in a numerical model until the calculated displacements fit the experimental data. The unknown parameters are identified simultaneously by a single test and without damaging the structure. An original method is also proposed for optimizing the loading and constraining conditions of the specimen with a view to obtaining faster and more stable solutions. The procedures were applied to a steel specimen whose displacement field was detected by speckle interferometry.

Journal ArticleDOI
TL;DR: In this article, the authors describe the development of optical fiber low-coherence speckle interferometers capable of 3D surface profiling with a resolution of 10-20 µm and a depth range of typically tens of centimetres.
Abstract: This paper describes the development of optical fibre low-coherence speckle interferometers capable of three-dimensional surface profiling with a resolution of 10–20 µm and a depth range of typically tens of centimetres The technique is absolute, enabling the measurement of steps and through holes The inclusion of optical fibres enables compact, flexible configurations to be realized, alleviating the experimental difficulties encountered with bulk interferometers, particularly when using long path lengths for measurements on large test objects Sources including light-emitting and superluminescent diodes and multimode laser diodes are compared, and the use of a multimode laser diode source in pulsed mode is shown to improve depth resolution Fibre-based systems using both single mode and polarization-maintaining fibre are described, and the results of experimental measurements on a stepped test object, a tilted plate and a coin are presented A depth resolution of ±20 µm is obtained for the standard fibre system and ±14 µm for the system based on polarization-maintaining fibre