Showing papers on "Speckle imaging published in 1996"
Book•
18 Mar 1996TL;DR: In this article, Fourier and Statistical Optics Fourier Optics statistical Optics Turbulence Effects on Imaging Systems Index of Refraction Fluctuations in the Atmosphere Statistics of Index of Reconstant Fluctuation Wave Propagation through Random Media First-Order Turbulences Effects on Incoherent Imaging Modal Expansions of Phase Perturbation Phase Screen Generation Speckle Imaging Techniques Introduction Overview of Speckles Imaging SpeckLE Interferometry Fourier Phase Estimation Techniques Image Reconstruction for Specksle Imaging Conclusion Adaptive Optical Imaging Systems Introduction Factors
Abstract: Introduction Overview of the Problem Area Historical Overview of Imaging Through Turbulence Overview of the Book Background: Fourier and Statistical Optics Fourier Optics Statistical Optics Turbulence Effects on Imaging Systems Index of Refraction Fluctuations in the Atmosphere Statistics of Index of Refraction Fluctuations Wave Propagation through Random Media First-Order Turbulence Effects on Incoherent Imaging Modal Expansions of Phase Perturbation Phase Screen Generation Speckle Imaging Techniques Introduction Overview of Speckle Imaging Speckle Interferometry Fourier Phase Estimation Techniques Image Reconstruction for Speckle Imaging Conclusion Adaptive Optical Imaging Systems Introduction Factors that Degrade AOI Systems Performance Adaptive Optical System Components and Models AOI System Performance Modeling Summary Hybrid Imaging Techniques Introduction Deconvolution from Wavefront Sensing Methods Involving Adaptive Optics Conclusion Index
853 citations
TL;DR: Three different image-processing methods based on the time-averaged technique were compared by the electronic speckle pattern interferometry (ESPI) technique for vibration measurement to increase the fringe pattern's visibility without additional image and/or signal processes.
Abstract: Three different image-processing methods based on the time-averaged technique were compared by the electronic speckle pattern interferometry (ESPI) technique for vibration measurement The three methods are the video-signal-addition method, the video-signal-subtraction method, and the amplitude-fluctuation method Also, errors introduced by using the zero-order Bessel function directly into the analysis of the fringe pattern were investigated The video-signal-addition method has been the most generally used ESPI technique for vibration measurement However, without additional image and/or signal-processing procedures, the fringe pattern obtained directly by the video-signal-addition method is rather difficult to observe The reason for poor visibility of the experimentally obtained fringe pattern with this method is explained To increase the fringe pattern's visibility without additional image and/or signal processes, we tried two video-signal-subtraction methods One of the two methods is the video-signal-subtraction method that has normally been used in the static applications The other method, called the amplitude-fluctuation method, and its associated theory are reported here
156 citations
125 citations
TL;DR: It is hypothesized that tissue viability could be assessed by an analysis of the spatial modulation of near-field laser speckle by flowing blood and suggested that the thickness of PTFE may be suitable for burn depth detection in vivo.
Abstract: A quantitative method for determining the depth of burn eschar would aid surgeons in determining whether to excise and subsequently graft a burn wound. We hypothesize that tissue viability could be assessed by an analysis of the spatial modulation of near-field laser speckle by flowing blood. A feasibility study of the technique was performed with two-layer tissue phantoms used to simulate a burn wound. A sheet of polytetrafluoroethylene (PTFE) was used to simulate nonperfused burn eschar, and tissue perfusion within deeper layers was represented by Brownian motion from a scattering solution. A low-power He–Ne laser was focused onto the target, and the resulting speckle image was captured with a CCD camera and stored on a computer for further processing. The diameter of the speckle pattern was found to be directly proportional to the thickness of the overlying layer. These data suggest that the thickness of PTFE can be determined to ±100-μm accuracy with 95% confidence and may be suitable for burn depth detection in vivo.
119 citations
TL;DR: Phase and amplitude information obtained from phase-shifting interferometry may be combined, to be a complex-valued phasor for every pixel of the image.
Abstract: Phase and amplitude information obtained from phase-shifting interferometry may be combined, to be a complex-valued phasor for every pixel of the image. Phasor image processing is presented as a simple yet effective concept for filtering, visualization, masking, and unwrapping interferometric phase maps. The results from two electronic speckle pattern interferometry data sets illustrate the new method.
81 citations
TL;DR: The first diffraction limited, 0.05s resolution images on the W. M. Keck Telescope have been obtained at a wavelength of 2.2 micrometers as mentioned in this paper.
Abstract: The first diffraction limited, 0.05s resolution, images on the W. M. Keck Telescope have been obtained at a wavelength of 2.2 micrometers. These images were part of an experiment to test the suitability of the Keck Telescope for speckle imaging. In order to conduct this test, it was necessary to modify the pixel scale of the Keck facility Near Infrared Camera (NIRC) to optimally sample the spatial frequencies made available by the Keck telescope. The design and implementation of the external reimaging optics, which convert the standard fl25 beam from the secondary mirror to fl182, are described here. Techniques for reducing speckle data with field rotation on an alt-az telescope are also described. Three binary stars were observed in this experiment with separations as small as 0.05s. With only 100 frames of data on each, a dynamic range of at least 3.5 mag was achieved in all cases. These observations imply that a companion as faint as 14.5 mag at 2.2 micrometers could be detected around an 11th magnitude point source.
80 citations
Book•
01 May 1996
TL;DR: The first chapter of this book provides an introduction to optical holography and speckle interferometry, but while the explanation is sound and thorough it lacks clarity and it is doubtful that it will be understood by any reader who is not an expert in modern optics.
Abstract: The first chapter of this book provides an introduction to optical holography and speckle interferometry. While the explanation is sound and thorough it lacks clarity and it is doubtful that it will be understood by any reader who is not an expert in modern optics. The second and third chapters are devoted, respectively, to holographic interferometry and speckle interferometry. The treatment of both topics is rigorous, there are good discussions of experimental errors and experimental techniques and comprehensive bibliographies. Holographic and speckle interferometry, unlike Moire, do not require any special surface preparation and dispense with the use of gratings, but the fringe patterns produced are difficult to interpret. The mapping out of the displacement field from the experimental data and the derivation of strains are discussed in chapter 4, where the problem presented by steep changes in displacement near strain raisers is addressed. While mathematical techniques for differentiation of experimental data are presented, no mention is made of modern computer software used to automate the process. More than half of the book consists of a number of examples from many different fields: shell structures, fracture mechanics, low cycle fatigue, contact problems, residual stress measurements by the hole drilling method and other practical cases. These examples are taken from the Russian scientific literature. Apart from their interest to the specialist, they illustrate experimental techniques not commonly used in the western world. C Ruiz
73 citations
TL;DR: The use of the bispectrum as a tool to handle the phase-retrieval problem associated with speckle interferometry is examined, and a simple recipe to predict the success of bispectral imaging is given.
Abstract: The use of the bispectrum as a tool to handle the phase-retrieval problem associated with speckle interferometry is examined. The basic concepts and equations involved in bispectral imaging are discussed. Based in signal-to-noise ratio considerations, a simple recipe to predict the success of bispectral imaging is given. Because of their higher noise tolerance, two least-squares minimization schemes are used to reconstruct the object Fourier phase encrypted in the bispectral phase. The error-reduction algorithm for phase retrieval is applied in conjunction with the minimization procedures to overcome stagnation at local minima. Examples with simulated and real astronomical data are presented, including a comparison of the outcome of bispectral processing applied to both adaptively compensated and uncompensated data. The resulting diffraction-limited reconstructions are very similar.
50 citations
TL;DR: A decrease in the spatial frequency of the mosaic with the eccentricity and an important intersubject variability is found, in agreement with anatomical studies.
Abstract: A new system for the recording of high-resolution images of the cone mosaic in the living human fovea has been developed. The experimental method is inspired by stellar speckle interferometry, used in astronomy to resolve binary stars. Series of short-exposure images of small areas of the fovea are registered under coherent illumination. These images show speckle patterns that have some correlation with the topography of the cone mosaic and retain high-resolution information. Such correlation is better revealed in the power spectrum (square modulus of the Fourier transform). The signal-to-noise ratio is increased, without loss of high frequencies, by averaging the power spectra of a number of such speckle patterns. The average power spectra show, in most of the cases, an elliptical ring (or hexagon), whose mean radius corresponds to the characteristic spatial frequency of the cone mosaic (or the inverse of the mean row-to-row cone spacing) at a given retinal location. Good results are obtained in the five normal observers tested, at various retinal eccentricities, up to 1 visual degree, including the center of the fovea for two eyes. We find a decrease in the spatial frequency of the mosaic with the eccentricity and an important intersubject variability, in agreement with anatomical studies.
45 citations
TL;DR: The experiment resulted in a mean carrier-to-noise ratio increase of 1.8, which is within 1% of the theoretical predictions, when the two signals were phase locked, versus no increase without phase locking.
Abstract: A description is given of the design, operation, and test over a 2-km path (roundtrip) of a continuous wave, coherent laser array receiver that uses two independent aperture-receivers whose intermediate frequencies are electro-optically co-phased in real time and then added as a proposed way to overcome effective aperture limitations imposed by atmospheric turbulence and to mitigate signal fading associated with atmospheric turbulence and speckle effects. The experiment resulted in a mean carrier-to-noise ratio increase of 1.8, which is within 1% of the theoretical predictions, when the two signals were phase locked, versus no increase without phase locking. Further, the carrier fading strength, or normalized carrier-to-noise ratio variance, was reduced by a factor of 0.53, which is within 2% of the theoretical prediction. The bandwidth of the electro-optic phase-locked loop was measured to be of the order of 600 Hz, which is adequate to compensate for atmospheric refractive turbulence fluctuations.
43 citations
TL;DR: In this article, the statistical distribution of the background intensity and the modulation is derived for an arbitrary number n of speckles per pixel, for both the speckle and the smooth reference wave setup.
TL;DR: Electronic speckle-shearing pattern interferometry is applied to yield whole-field phase maps corresponding to the curvature and twist distributions of a deformed specimen.
Abstract: Electronic speckle-shearing pattern interferometry is applied to yield whole-field phase maps corresponding to the curvature and twist distributions of a deformed specimen.
TL;DR: In this article, different arrangements for double-pulsed holographic and speckle interferometry for vibration analysis are described, and the phases of the two reconstructed wave fields are calculated from the complex amplitudes.
Abstract: Different arrangements for double-pulsed holographic and speckle interferometry for vibration analysis will be described. Experimental results obtained with films (classical holographic interferometry) and CCD cameras (digital holographic interferometry) as storage materials are presented. In digital holography, two separate holograms of an object under test are recorded within a few microseconds using a CCD camera and are stored in a frame grabber. The phases of the two reconstructed wave fields are calculated from the complex amplitudes. The deformation is obtained from the phase difference. In the case of electronic speckle pattern interferometry (or image plane hologram), the phase can be calculated by using the sinusoid-fitting method. In the case of digital holographic interferometry, the phase is obtained by digital reconstruction of the complex amplitudes of the wave fronts. Using three directions of illumination and one direction of observation, all the information necessary for the reconstruction of the 3-dimensional deformation vector can be recorded at the same time. Applications of the method for measuring rotating objects are discussed where a derotator needs to be used.
TL;DR: The application of a scale-space filter to reduce speckle noise in ESPI fringes is reported and results obtained using both computer-simulated and experimental fringe patterns are used to test the scale- space filter.
Abstract: Processing of correlation fringes obtained from electronic speckle pattern interferometry (ESPI) requires the use of a digital filter to reduce the speckle noise. Even though smoothing algorithms based on the Fourier transform significantly suppress speckle noise, they do not preserve the image characteristics. The application of a scale-space fil- ter to reduce speckle noise in ESPI fringes is reported. Results obtained using both computer-simulated and experimental fringe patterns are used to test the scale-space filter and they are also compared with those obtained by Fourier, convolution, and median filtering. © 1996 Society of Photo-Optical Instrumentation Engineers.
TL;DR: The phase-stepping technique is demonstrated with a three-step algorithm to measure out-of-plane strain on a f lat metal plate with wavelength modulation of the optical source.
Abstract: Phase stepping by wavelength modulation of the optical source is demonstrated in a path-length unbalanced shearing interferometer. A magnification difference, which accompanies the path-length imbalance in the interferometer, introduces an unwanted radial shear, which is shown to be compensated by inclusion of a block of high-refractive-index material in the longer interferometer arm. The block also increases the phase shift obtained for a given wavelength change. The phase-stepping technique is demonstrated with a three-step algorithm to measure out-of-plane strain on a flat metal plate.
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TL;DR: In this article, the fundamental statistics of bio-speckles are discussed and a promising way is to observe the bio speckle fluctuations in detail and to establish experimentally and empirically the relation between the fluctuations and the necessary information to be extracted.
Abstract: Publisher Summary
This chapter discusses bio-speckles. Laser light scattered from diffuse objects produces granular interference patterns, which are well known as “speckle phenomena.” If the diffuse object moves, the speckle grains also move and change their shape. The speckle pattern thus, becomes time dependent. This property can be applied to measurements of velocity, vibration, and displacement. The dynamic statistical properties of speckles have been extensively studied by theory and experiment, especially for velocity measurements. This chapter discusses the fundamental statistics of bio-speckles. They can be used for analyzing bio-speckle dynamics and extracting useful information from living objects. Bio-speckles show various aspects depending on the living objects to be measured, and methods of their analysis and applications can be changed accordingly. Thus, general theoretical approaches to analysis of bio-speckles seem to be considerably difficult. A promising way is to observe the bio-speckle fluctuations in detail and to establish experimentally and empirically the relation between the fluctuations and the necessary information to be extracted. The field of bio-speckle techniques covers all the subjects of speckles obtained from various living objects: (1) short- and long-range temporal fluctuations, (2) spatial fluctuations, (3) intensity and phase fluctuations, (4) their statistical properties and fundamental modeling, and (5) applications, including the design of measuring apparatus. The field can also be combined with conventional speckle metrology, such as speckle photography and speckle interferometry.
TL;DR: In this article, the phase and gradient of displacement amplitude of a vibrating object using continuous wave illumination in a path length imbalanced speckle shearing interferometer was measured using laser diode emission wavelength modulation.
Abstract: Laser diode emission wavelength modulation is demonstrated as a technique for measuring the phase and gradient of displacement amplitude of a vibrating object using continuous wave illumination in a path length imbalanced speckle shearing interferometer The unwanted mismatch in the magnification of the two images in the shearing interferometer and sensitivity to radial shear introduced by a path length imbalance is overcome by the use of a transparent block of high refractive index in one path in the interferometer
TL;DR: In this method an object point is viewed symmetrically with respect to surface normal and combined coherently at the image plane of the imaging system, which extends the range of measurement.
Abstract: An optical configuration for measurement of in-plane displacement and for contouring is reported. In this method an object point is viewed symmetrically with respect to surface normal and combined coherently at the image plane of the imaging system. Because the beams are combined by small apertures at the image plane, decorrelation sets in rather slowly. Owing to low decorrelation, fringes have been obtained for large in-plane deformations and large angular tilts. The method is simple to implement, and its sensitivity can be varied over a wide range. The configuration, therefore, extends the range of measurement.
TL;DR: In this article, a technique for accurate phase measurement based on additive-subtractive speckle pattern interferometry is presented, which requires five frames of additive specckle patterns S0, S1,..., S4, where S0 is taken with the laser illumination pulsed at instants when the vibration reaches its two zero amplitude positions within one harmonic vibration cycle of the object, and the remaining four (S1 through S4) are taken with illumination pulses arranged at times when the vibrations reached their maximum and minimum amplitudes.
Abstract: A technique for realizing accurate phase measurement based on additive-subtractive speckle pattern interferometry is presented. Ad- ditive fringe patterns corresponding to two deformation states of an ob- ject vibrating sinusoidally are first obtained and these are then sub- tracted from that with zero deformation. The technique requires five frames of additive speckle patterns S0, S1, ... , S4, where S0 is taken with the laser illumination pulsed at instants when the vibration reaches its two zero amplitude positions within one harmonic vibration cycle of the object, and the remaining four (S1 through S4) are taken with the illumination pulses arranged at times when the vibration reaches its maximum and minimum amplitudes. During the acquisition of S1 through S4, the phase of the reference beam is appropriately shifted between the two pulses within each vibration cycle. The phase shifts are synchro- nized with the pulses. Speckle patterns S1 through S4 are then sub- tracted from S0 to generate four correlation fringe patterns with relative phase shifts of 0, p/2, p and 3p/2, respectively. These fringe patterns are then utilized to derive a phase map using a four-step phase calcula- tion algorithm and quantitative vibration amplitudes can be readily ob- tained from the phase map. Results obtained from electronic speckle pattern interferometry and shearography are presented, and the ability of the technique to perform in relatively severe noisy environments is dem- onstrated. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: additive-subtractive fringes; phase measurement in noisy condi- tions; laser pulsing/strobing; speckle interferometry and shearography.
TL;DR: The disk-growing algorithm presented allows the inner and the outer propagation of the unwrapping from a growing disk and so avoids the main problem of anisotropic error propagation for noisy phase maps.
Abstract: Interferometric techniques combined with phase shifting allow computation of the phase that is linked to the displacement of the object under study. The phases before and after displacement are computed from three or more interferograms (called specklegrams when speckle is used as the information carrier). Subtraction of these two phase patterns leads to a raw phase map. Phase unwrapping restores the 2π discontinuities and gives a continuous phase map. The disk-growing algorithm presented allows the inner and the outer propagation of the unwrapping from a growing disk and so avoids the main problem of anisotropic error propagation for noisy phase maps. It works successfully in speckle interferometry.
TL;DR: To obtain the minimum phase-measurement error, it is found that the mean speckle intensity ought to be adjusted to be 0.058 times the saturation intensity of the camera and the beam ratio is to be 5.7.
Abstract: In a real phase-shifting interferometer the camera (i.e., a photodetector plus an analog-to-digital converter) cuts off intensities above some saturation level and provides a limited number of digitization steps. Owing to the intensity statistics of speckle fields, this might severely influence the accuracy of the calculated speckle phase. The optimum beam ratio and the modulation of the camera are computed. To calculate the standard deviation of the phase difference, first, we derive a relation that shows that the variances of the two measured phase frames are equal and that they must be added with the decorrelation-dependent variance. To obtain the minimum phase-measurement error of 25.1 mrad, it is found that the mean speckle intensity ought to be adjusted to be 0.058 times the saturation intensity of the camera and that the beam ratio is to be 5.7. The results are confirmed by computer simulation of a two-wavelength speckle interferometer.
TL;DR: Digital speckle pattern interference (DSPI) is an optical nondestructive testing method allowing the visualization of the defects or the deformations of an object submitted to static deformation or to vibration.
TL;DR: Analyses of the power spectra of both the speckle noise and of the measured surface profiles of different substrates suggest that the paper surface granularity can be approximated by a white Gaussian noise process, thus confirming the assumption of the theoretical model.
Abstract: We present a theoretical model and its experimental verification for speckle-induced noise in laser-based bar-code-scanner systems. We measured the dependence of the signal-to-speckle-noise ratio on distance, spot size, and detector size. Analyses of the power spectra of both the speckle noise and of the measured surface profiles of different substrates suggest that the paper surface granularity can be approximated by a white Gaussian noise process, thus confirming the assumption of the theoretical model.
TL;DR: In this article, a brief overview of techniques developed for the analysis of blood microcirculation in vivo is presented, including speckle interferometry and focused Gaussian beam diffraction.
Abstract: This paper presents a brief overview of several techniques developed for the analysis of blood microcirculation in vivo. Both theoretical and experimental investigations have been performed using focused Gaussian beams, which are diffracted by blood capillaries with diameters slightly larger than the erythrocyte. Speckle interferometry, utilizing the diffraction of a focused Gaussian beam, was used for the analysis of lymph circulation in native microvessels. The spectra of scattered intensity fluctuations produced by diffraction in such capillaries are analysed, and variations in the envelope of the spectra induced by the influence of drugs on the lymph vessels have also been studied.
TL;DR: In this article, the authors present a real-time analysis of TV-Holography, also called electronic speckle interferometry (ESPI), and double or multipulse (three or four) holography.
TL;DR: In this paper, an optical technique for shape measurement that works satisfactorily in relatively severe noisy conditions by using additive - subtractive phase-modulated electronic speckle pattern interferometry (AS-ESPI) is described.
Abstract: This paper describes an optical technique for shape measurement that works satisfactorily in relatively severe noisy conditions by using additive - subtractive phase-modulated electronic speckle pattern interferometry (AS-ESPI). Through repetitively altering the illumination angle of one interfering beam at a frequency much higher than the video frame rate, and by simultaneously locking the beam tilting via laser strobing, random noises that normally are of much lower frequency than that of the repetitive tilting can be removed by frame averaging of the AS-ESPI correlation fringe patterns. A procedure of phase shifting that is synchronized with the repetitive tilting is utilized to perform data reduction. Quantitative experimental results obtained under rather noisy conditions are presented to show the validity of the principle.
TL;DR: Real-time optical image subtraction and edge enhancement based on a speckle modulation technique is carried out by using ferroelectric liquid-crystal polarization switches and a ferro Electric spatial light modulator as a real-time and multiple-exposure optical device.
Abstract: We carried out real-time optical image subtraction and edge enhancement based on a speckle modulation technique by using ferroelectric liquid-crystal polarization switches and a ferroelectric liquid-crystal spatial light modulator. A ferroelectric liquid-crystal spatial light modulator is employed as a real-time and multiple-exposure optical device, and successful results are obtained from three-exposure images modulated by speckles. Thus, image subtraction and edge enhancement are realized in real time. The whole operation is performed within several milliseconds with modest operating conditions. Because the spatial light modulator has a high resolution of greater than 100 line pairs/mm and can store fine speckle patterns, the image qualities we obtained are quite satisfactory.