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Showing papers on "Speckle imaging published in 2009"


Journal ArticleDOI
TL;DR: The cerebral hemodynamic response observed through the thinned and intact skull are more pronounced in the dLSI images as compared to the standard speckle contrast analysis, and the proposed method also yields benefits with respect to the quality of theSpeckle images by suppressing contributions of non-uniformly distributed specular reflections.
Abstract: Laser speckle imaging (LSI) based on the speckle contrast analysis is a simple and robust technique for imaging of heterogeneous dynamics. LSI finds frequent application for dynamical mapping of cerebral blood flow, as it features high spatial and temporal resolution. However, the quantitative interpretation of the acquired data is not straightforward for the common case of a speckle field formed by both by moving and localized scatterers such as blood cells and bone or tissue. Here we present a novel processing scheme, we call dynamic laser speckle imaging (dLSI), that can be used to correctly extract the temporal correlation parameters from the speckle contrast measured in the presence of a static or slow-evolving background. The static light contribution is derived from the measurements by cross-correlating sequential speckle images. In-vivo speckle imaging experiments performed in the rodent brain demonstrate that dLSI leads to improved results. The cerebral hemodynamic response observed through the thinned and intact skull are more pronounced in the dLSI images as compared to the standard speckle contrast analysis. The proposed method also yields benefits with respect to the quality of the speckle images by suppressing contributions of non-uniformly distributed specular reflections.

160 citations


Journal ArticleDOI
TL;DR: The Differential Speckle Survey Instrument (DSI) as discussed by the authors was designed to take speckle data in two filters simultaneously with two independent CCD imagers, allowing for subdiffraction-limited separations to be measured reliably.
Abstract: First results of a new speckle imaging system, the Differential Speckle Survey Instrument, are reported. The instrument is designed to take speckle data in two filters simultaneously with two independent CCD imagers. This feature results in three advantages over other speckle cameras: (1) twice as many frames can be obtained in the same observation time which can increase the signal-to-noise ratio for astrometric measurements, (2) component colors can be derived from a single observation, and (3) the two colors give substantial leverage over atmospheric dispersion, allowing for subdiffraction-limited separations to be measured reliably. Fifty-four observations are reported from the first use of the instrument at the Wisconsin-Indiana-Yale-NOAO 3.5 m Telescope9The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories. in 2008 September, including seven components resolved for the first time. These observations are used to judge the basic capabilities of the instrument.

139 citations


Journal ArticleDOI
TL;DR: An algorithm based on shrinkage in the curvelet domain to attenuate speckles in optical coherence tomography (OCT) images shows significant improvement of image quality.
Abstract: We describe an algorithm based on shrinkage in the curvelet domain to attenuate speckles in optical coherence tomography (OCT) images. The algorithm exploits the curvelet transform's sparse representation of edge discontinuities that are common in OCT images and its ability to map signals and noise into different areas in the curvelet domain. The speckle attenuation is controlled by a single parameter that determines the threshold in the curvelet domain. Applying the algorithm to OCT images shows significant improvement of image quality.

85 citations


Journal ArticleDOI
TL;DR: A method to measure the shape and deformation of 3D objects from the sequential intensity measurements of volume speckle field and phase retrieval based on angular-spectrum propagation technique is described here.
Abstract: Shape and deformation measurement of diffusely reflecting 3D objects are very important in many application areas, including quality control, nondestructive testing, and design. When rough objects are exposed to coherent beams, the scattered light produces speckle fields. A method to measure the shape and deformation of 3D objects from the sequential intensity measurements of volume speckle field and phase retrieval based on angular-spectrum propagation technique is described here. The shape of a convex spherical surface was measured directly from the calculated phase map, and micrometer-sized deformation induced on a metal sheet was obtained upon subtraction of the phase, corresponding to unloaded and loaded states. Results from computer simulations confirm the experiments.

53 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented results for 607 speckle interferometric observations of double stars, as well as 222 measures of single stars or unresolved pairs, using the 2.5 m Hooker telescope.
Abstract: Results are presented for 607 speckle interferometric observations of double stars, as well as 222 measures of single stars or unresolved pairs. All data were obtained in 2006 and 2007 at the Mount Wilson Observatory, using the 2.5 m Hooker telescope. Separations range from 0.06 to 6.31, with a median of 0.34. These three observing runs concentrated on binaries in need of confirmation (mainly Hipparcos and Tycho pairs), as well as systems in need of improved orbital elements. New orbital solutions have been determined for 35 systems as a result.

47 citations


Journal ArticleDOI
TL;DR: The new oriented-couple partial differential equation (PDE) models based on the variational methods for filtering in electronic speckle pattern interferometry phase fringe patterns are derived and quantitatively evaluated with a comparative parameter, named the image fidelity.
Abstract: We derive the new oriented-couple partial differential equation (PDE) models based on the variational methods for filtering in electronic speckle pattern interferometry phase fringe patterns. In the filtering methods based on the oriented PDE models, filtering along fringe orientation for the entire image is simply realized through solving the PDEs numerically, without having to laboriously establish the small filtering window along the fringe orientation and move this filtering window over each pixel in an image. We test the proposed models on two computer-simulated speckle phase fringe patterns and an experimentally obtained phase fringe pattern, respectively, in which the fringe density is variable, and compare our models with related PDE models. Further, we quantitatively evaluate the performance of these PDE models with a comparative parameter, named the image fidelity. We also compare the computational time of our method with that of a traditional filtering method along the fringe orientation. The experimental results demonstrate the performance of our new oriented PDE models.

43 citations


Journal ArticleDOI
TL;DR: A digital speckle pattern interferometer that applies a binary diffractive optical element (DOE) to generate double illumination and radial in-plane sensitivity shows clearly that radial in -plane sensitivity increased when the red laser was changed by the green one.
Abstract: We report on a digital speckle pattern interferometer that applies a binary diffractive optical element (DOE) to generate double illumination and radial in-plane sensitivity. The application of the DOE ensures independence on the wavelength of the laser used as an illumination source. Furthermore, in-plane sensitivity only depends on the grating period of the DOE. An experimental setup was built allowing the measurement of a set of radial in-plane displacement fields either using a red laser as a light source or a green one. When displacement fields computed from the measured optical phase maps obtained with a red or a green laser were compared, two main results were observed: (a) deviations between mean values ranged only up to 7 nm and (b) phase maps presented the same amount of fringes. In addition, phase maps measured with the red laser were processed as they were obtained with green light. For this case, deviations have ranged only up to 0.5 nm. On the other hand, a set of measurements performed changing the DOE by a conical mirror showed clearly that radial in-plane sensitivity increased when the red laser was changed by the green one.

43 citations


Journal ArticleDOI
TL;DR: This work is actually an attempt to elaborate a phase extraction procedure which exploits all the reliable information in 3D, - two space and one time coordinates -, to endeavor to make the most of SI raw data.
Abstract: In a wider and wider range of research and engineering activities, there is a growing interest for full-field techniques, featuring nanometric sensitivities, and able to be addressed to dynamic behaviors characterization. Speckle interferometry (SI) techniques are acknowledged as good candidates to tackle this challenge. To get rid of the intrinsic correlation length limitation and simplify the unwrapping step, a straightforward approach lies in the pixel history analysis. The need of increasing performances in terms of accuracy and computation speed is permanently demanding new efficient processing techniques. We propose in this paper a fast implementation of the Empirical Mode Decomposition (EMD) to put the SI pixel signal in an appropriate shape for accurate phase computation. As one of the best way to perform it, the analytic method based on the Hilbert transform (HT) of the so-transformed signal will then be reviewed. For short evaluation, a zero-crossing technique which exploits directly the extrema finding step of the EMD will be presented. We propose moreover a technique to discard the under-modulated pixels which yield wrong phase evaluation. This work is actually an attempt to elaborate a phase extraction procedure which exploits all the reliable information in 3D, – two space and one time coordinates –, to endeavor to make the most of SI raw data.

36 citations


Journal ArticleDOI
TL;DR: Using the linear canonical transform and ABCD ray matrix techniques to describe general optical systems, analytical formulas for determining axial and lateral speckle sizes are derived and the correlation properties of nonaxial speckles can be considered.
Abstract: Correlation properties of speckle fields at the output of quadratic phase systems with hard square and circular apertures are examined. Using the linear canonical transform and ABCD ray matrix techniques to describe these general optical systems, we first derive analytical formulas for determining axial and lateral speckle sizes. Then using a numerical technique, we extend the analysis so that the correlation properties of nonaxial speckles can also be considered. Using some simple optical systems as examples, we demonstrate how this approach may be conveniently applied. The results of this analysis apply broadly both to the design of metrology systems and to speckle control schemes.

31 citations


Journal ArticleDOI
TL;DR: In this article, a laser speckle microinterferometer incorporated with optoelectronic devices for a stroboscopic illumination and a synchronization of the signals between excitation and illumination is described and demonstrated.

29 citations


Journal ArticleDOI
TL;DR: The possibility of obtaining comparable, setup-independent results in blood perfusion monitoring can contribute to better applicability of LASCA.
Abstract: In laser speckle contrast analysis (LASCA) used for imaging of blood flow, besides the moving blood cells, the speckle pattern is also influenced by the imaging system and scattering properties of the laser-illuminated static surface. A latex microsphere (650 nm size) emulsion was covered with scattering semitransparent materials (Teflon foils, tracing paper). Speckle images were recorded with different exposure times (0.2 ms-500 ms), and correlation times were determined by parameterizing the theoretical contrast-exposure time function. The correlation times obtained for covered and uncovered microsphere emulsions were in good agreement. The possibility of obtaining comparable, setup-independent results in blood perfusion monitoring can contribute to better applicability of LASCA.

Journal ArticleDOI
TL;DR: Low-speckle laser projection is demonstrated using a broad-area vertical-cavity surface-emitting laser emitting at 840 nm wavelength as the illumination source and quantitatively model the speckle contrast reduction based on polarization scrambling and the reduced temporal and spatial coherence of the VCSEL.
Abstract: We demonstrate low-speckle laser projection using a broad-area vertical-cavity surface-emitting laser (VCSEL) emitting at 840 nm wavelength as the illumination source. By driving the source in a nonmodal emission regime, we were able to achieve speckle contrast values as low as 3.5% in a realistic projection setup. This was done by driving the VCSEL with specific current pulses without using any additional or mechanically moving components to destroy the coherence of the laser beam. We quantitatively model the speckle contrast reduction based on polarization scrambling and the reduced temporal and spatial coherence of the VCSEL.

Journal ArticleDOI
TL;DR: In this paper, the authors present some recent development of super-resolution digital speckle photography with the emphasis on micro/nano measurements with the focus on micro and nano measurements.

Journal ArticleDOI
TL;DR: It is shown that this approach can effectively recover phase distributions in time series of speckle interferograms that are affected by sets of adjacent nonmodulated pixels.
Abstract: We propose an approach based on a 3D directional wavelet transform to retrieve optical phase distributions in temporal speckle pattern interferometry. We show that this approach can effectively recover phase distributions in time series of speckle interferograms that are affected by sets of adjacent nonmodulated pixels. The performance of this phase retrieval approach is analyzed by introducing a temporal carrier in the out-of-plane interferometer setup and assuming modulation loss and noise effects. The advantages and limitations of this approach are finally discussed.

Journal ArticleDOI
TL;DR: A procedure that will reduce the number of frames required for the analysis of the time-averaged fringe pattern of TV holographic system used and the experimental results obtained on an edge-clamped, sinusoidally excited square aluminium plate sample are discussed.
Abstract: Time-average TV holography is widely used method for vibration measurement. The method generates speckle correlation time-averaged J0 fringes that can be used for full-field qualitative visualization of mode shapes at resonant frequencies of an object under harmonic excitation. In order to map the amplitudes of vibration, quantitative evaluation of the time-averaged fringe pattern is desired. A quantitative evaluation procedure based on the phase-shifting technique used in two beam interferometry has also been adopted for this application with some modification. The existing procedure requires a large number of frames to be recorded for implementation. We propose a procedure that will reduce the number of frames required for the analysis. The TV holographic system used and the experimental results obtained with it on an edge-clamped, sinusoidally excited square aluminium plate sample are discussed.

Journal ArticleDOI
TL;DR: In this paper, the virtual speckle pattern is applied to the measurement of dynamic events including a complex deformation distribution, which includes the increase and the decrease distributions. And the optical system of the method is improved in order to deal with the complex deformed distribution.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed optical vortex behavior in dynamic speckle patterns with the boiling phenomenon and found that vortices exhibit a Brownian motion in pure boiling patterns.
Abstract: Optical vortex analysis has become an important tool in optical metrology. It has been shown to be able to measure small displacements with up to nanometric precision. We analyze optical vortex behavior in dynamic speckle patterns with the boiling phenomenon. We first study translational patterns with boiling and we find the limitations of the optical vortex metrology. Pure boiling patterns are also evaluated and we find a quantitative descriptor for the activity. We also observe that vortices exhibit a Brownian motion in pure boiling patterns. Numerical and experimental results are shown.

Journal ArticleDOI
TL;DR: In this article, the authors used speckle imaging to place the components of binary star systems on the H-R diagram, and a best-fit isochrone was determined for each system, yielding both masses of the components as well as an age range consistent with the system parameters.
Abstract: Magnitude differences obtained from speckle imaging are used in combination with other data in the literature to place the components of binary star systems on the H-R diagram. Isochrones are compared with the positions obtained, and a best-fit isochrone is determined for each system, yielding both masses of the components as well as an age range consistent with the system parameters. Seventeen systems are studied, 12 of which were observed with the 0.6 m Lowell-Tololo Telescope at Cerro Tololo Inter-American Observatory and six of which were observed with the WIYN 3.5 m Telescope (The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories) at Kitt Peak. One system was observed from both sites. In comparing photometric masses to mass information from orbit determinations, we find that the photometric masses agree very well with the dynamical masses, and are generally more precise. For three systems, no dynamical masses exist at present, and therefore the photometrically determined values are the first mass estimates derived for these components.

Proceedings ArticleDOI
15 Jun 2009
TL;DR: In this article, a digital speckle interferometer was used to measure residual stresses in a gas pipeline in a risky area, where a small blind hole was drilled on the surface to be measured.
Abstract: Digital speckle pattern interferometry is potentially capable to solve a large variety of measurement and inspection demands in industrial applications. However, it is not so widely used in industry due to some special requirements that are not easily fulfilled on the shop floor. This paper presents some reflections about what would be necessary for an interferometer to be successfully applied in industrial environments: it must be robust, flexible, compact, stable, friendly and cooperative. Next, a case study, that fulfills those requirements, is presented in details. It involves a digital speckle interferometer designed to measure residual stresses in-field. It was developed using an axis-symmetrical diffractive optical element in such a way that it is not sensitive to the laser wavelength at all. It produces radial in-plane sensitivity on a circular region. The interferometer was accommodated in a compact construction that made it robust enough for infield applications. A magnetic kinematic mounting base is used to firmly attach the interferometer to the surface where residual stresses have to be measured. The same kinematic base is used for positioning an ultra-high speed pneumatic drilling unit. In order to measure residual stresses, a reference phase pattern is first acquired from a sequence of four 90° phase-shifted images. After that, a small blind hole is drilled on the surface to be measured. The residual stresses are then relieved at the borders of the blind hole, what produces a local displacement filed. A second phase pattern is then acquired. The radial displacement filed is computed from the phase difference and it is fitted to a mathematical model. The principal residual stresses are then determined. The interferometer was used outside of the laboratory for residual stresses measurement in a gas pipeline in a risky area. The goal was to investigate the effectiveness of a repair.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the speckle interferometer of the BTA 6m telescope of the SAO RAS based on a new detector with an electron multiplication CCD.
Abstract: The description is given for the speckle interferometer of the BTA 6-m telescope of the SAO RAS based on a new detector with an electron multiplication CCD. The main components of the instrument are microscope objectives, interference filters and atmospheric dispersion correction prisms. The PhotonMAX-512B CCD camera using a back-illuminated CCD97 allows up to 20 speckle images (with 512$\times$512 pix resolution) per second storage on the hard drive. Due to high quantum efficiency (93% in the maximum at 550 nm), and high transmission of its optical elements, the new camera can be used for diffraction-limited (0.02$''$) image reconstruction of $15^{m}$ stars under good seeing conditions. The main advantages of the new system over the previous generation BTA speckle interferometer are examined.

Proceedings ArticleDOI
TL;DR: By leveraging the custom, reconfigurable nature of the FPGA, this work has achieved performance twenty times faster than a modern desktop PC, in a form-factor that is compact, low-power, and field-deployable.
Abstract: While imaging over long distances is criti cal to a number of security and defense applications, such as homeland security and launch tracking, current optical systems are limited in resolving power. This is largely a result of the turbulent atmosphere in the path between the region under observation and the imaging system, which can severely degrade captured imagery. There are a variety of post-processing techniques capable of recovering this obscured image information; however, the computational complexity of such approaches has prohibited real-time deployment and hampers the usability of these technologies in many scenarios. To overcome this limitation, we have designed and manufactured an embedded image processing system based on commodity hardware which can compensate for these atmospheric disturbances in real-time. Our system consists of a reformulation of the average bispectrum speckle method coupled with a high-end FPGA processing board, and employs modular I/O capable of interfacing with most common digital and analog video transport methods (composite, component, VGA, DVI, SDI, HD-SDI, etc.). By leveraging the custom, reconfigurable nature of the FPGA, we have achieved performance twenty times faster than a modern desktop PC, in a form-factor that is compact , low-power, and field-deployable. Keywords: bispectral speckle imaging, FPGA , embedded, atmospheric compensati on, real-time image processing

Journal ArticleDOI
TL;DR: In this paper, relative astrometric measurements of visual binaries made during the first semester of 2007, with the Pupil Interferometry Speckle camera and COronagraph (PISCO), at the 102-cm Zeiss telescope of Brera Astronomical Observatory, in Merate, were presented.
Abstract: We present relative astrometric measurements of visual binaries made during the first semester of 2007, with the Pupil Interferometry Speckle camera and COronagraph (PISCO) at the 102-cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our sample contains orbital couples as well as binaries whose motion is still uncertain. We obtained 226 new measurements of 214 objects, with angular separations in the range 0.15-4.5 arcsec, and an average accuracy of 0.013 arcsec. The mean error on the position angles is . Most of the position angles could be determined without the usual 180° ambiguity with the application of triple-correlation techniques and/or by inspection of the long integration files. We also present the new orbits we have computed for ADS 7871, 7982 and 8128, for which our measurements lead to large residuals and/or for which the revision is justified by the significant number of observations made since the publication of the previous orbit.

Journal ArticleDOI
TL;DR: It is shown that depth information about in-plane phase gradients can be determined in two planes using reconstructed speckle fields from four different depths.
Abstract: A technique to gain depth information from an image-plane digital holographic recording of a transient phase object positioned between a diffuser and an imaging system is demonstrated. The technique produces telecentric reconstructions of the complex amplitude throughout the phase volume using numerical lenses and the complex spectrum formulation of the diffraction integral. The in-plane speckle movements as well as the phase difference between the disturbed field and a reference field are calculated in a finite number of planes using a cross-correlation formulation. It is shown that depth information about in-plane phase gradients can be determined in two planes using reconstructed speckle fields from four different depths. In addition, the plane of optimum reconstruction for calculating the phase difference with maximum contrast is detected from the technique. The method is demonstrated on a measurement of a laser ablation process.

Journal ArticleDOI
TL;DR: A postdetection correction method is reported on that seeks to correct for the effects of space-variant aberrations, with the goal of reconstructing near-diffraction-limited imagery.
Abstract: Space-variant blur occurs when imaging through volume turbulence over sufficiently large fields of view Space-variant effects are particularly severe in horizontal-path imaging, slant-path (air-to-ground or ground-to-air) geometries, and ground-based imaging of low-elevation satellites or astronomical objects In these geometries, the isoplanatic angle can be comparable to or even smaller than the diffraction-limited resolution angle We report on a postdetection correction method that seeks to correct for the effects of space-variant aberrations, with the goal of reconstructing near-diffraction-limited imagery Our approach has been to generalize the method of phase-diverse speckle (PDS) by using a physically motivated distributed-phase-screen model Simulation results are presented that demonstrate the reconstruction of near-diffraction-limited imagery under both matched and mismatched model assumptions In addition, we present evidence that PDS could be used as a beaconless wavefront sensor in a multiconjugate adaptive optics system when imaging extended scenes

Journal ArticleDOI
TL;DR: In this article, a new residual stress determination method in two directions simultaneously is presented, which is based on stresses relaxation in a groove that is machined incrementally, and the residual stresses relaxation occurs simultaneously from both the depth and the length of the groove.
Abstract: In this study a new residual stress determination method in two directions simultaneously is presented. This method is based on stresses relaxation in a groove that is machined incrementally. The residual stresses relaxation occurs simultaneously from both the depth and the length of the groove. Thus, measuring the surface strain field generated by the relaxation enables to determine the stress gradient both along the depth and the length of the groove. To measure the surface strain in a direction perpendicular to the groove, a digital speckle pattern interferometer is used. This method is suitable when the residual stress field in the structure varies in the depth as well as along the surface of the part, like for example in a welded structure. The method is tested here on an aluminium plate in which a central band has been shot peened.


Journal ArticleDOI
TL;DR: In this article, a simple optical technique is described that allows for the direct whole-field visualization of anti-nodal patterns in noisy environments, which requires no reference beam and is tolerant of environmental noise.

Journal ArticleDOI
TL;DR: Theoretical derivations show that Gaussian speckle contrast as a functional of optical aberrations exhibits a stationary point for the aberration free condition, where apparently contrast does not achieve a local maximum.
Abstract: Optical aberration effects up to the second moment of Gaussian laser speckle are theoretically investigated for both partially and fully developed speckle. In the development, a plane-wave illuminated diffuser generates a phase-perturbed random field in the object plane that creates speckle in the image plane. Theoretical derivations show that image field statistics are generally non-circular Gaussian due to aberrations. Speckle statistics are not affected by odd-functional aberrations, such as coma, and dependency of aberrations is asymptotically ignorable for very weak or strong diffusers. Furthermore, Gaussian speckle contrast as a functional of optical aberrations exhibits a stationary point for the aberration free condition, where apparently contrast does not achieve a local maximum. Calculations of speckle contrast for several aberration conditions are also presented.

Proceedings ArticleDOI
02 Jun 2009
TL;DR: In this paper, a cheap, compact and generic approach for suppressing speckle effect, allowing laser illumination for fast imaging is proposed, which is obtained by angular diversity using MEMS.
Abstract: We propose a cheap, compact and generic approach for suppressing speckle effect, allowing laser illumination for fast imaging. The speckle reduction is obtained by angular diversity using MEMS.

Journal ArticleDOI
TL;DR: In this paper, a new anisotropic partial differential equation noise-reduction algorithm based on fringe orientation for interferometric fringe patterns was proposed. But it does not consider the effect of the diffusion along the two directions of fringe gradient and isophote line.