Showing papers on "Speckle imaging published in 1994"
TL;DR: Experimental results are presented that demonstrate the validity of the principle and Unlike conventional moiré techniques the proposed technique permits the objects to have discontinuous height steps and/or surfaces spatially isolated from one another.
Abstract: An interferometric technique for automated profilometry of diffuse objects has been proposed. It is based on the Fourier-fringe analysis of spatiotemporal specklegrams produced by a wavelength-shift interferometer with a laser diode as a frequency-tunable light source. Unlike conventional moire techniques the proposed technique permits the objects to have discontinuous height steps and/or surfaces spatially isolated from one another. Experimental results are presented that demonstrate the validity of the principle.
227 citations
09 Jun 1994
TL;DR: In this paper, a new phase screen generation technique which uses low frequency subharmonic information to correct the problem of inaccurate model low-frequency turbulence characteristics is introduced. But the structure functions for this new method match very closely the structure function of Kolmogorov turbulence theory.
Abstract: Standard FFT-based phase screen generation methods do not accurately model low-frequency turbulence characteristics. This paper introduces a new phase screen generation technique which uses low frequency subharmonic information to correct the problem. We compare our technique to two other subharmonic methods. The structure functions for this new method match very closely the structure functions of Kolmogorov turbulence theory.
119 citations
TL;DR: A double-pulse electronic-speckle-interferometry system that uses three directions of illumination and one direction of observation to record at the same time all the information necessary for the reconstruction of the three-dimensional deformation vector.
Abstract: We describe a double-pulse electronic-speckle-interferometry system. Two separate speckle patterns of an object being tested are recorded within a few microseconds with a CCD camera. Their two images are stored in a frame grabber. The fringes obtained from subtraction are quantitatively analyzed by the spatial-carrier phase-shift method. Using three directions of illumination and one direction of observation, one can record at the same time all the information necessary for the reconstruction of the three-dimensional deformation vector. Applications of this system for measuring the rotating objects are discussed for the case for which a derotator needs to be used. Experimental results are presented.
97 citations
TL;DR: Electronic speckle photography offers a simple and fast technique for measuring in-plane displacement fields in solid and fluid mechanics and random errors are mainly dependent on the effective ƒ-number of the imaging system and Speckle decorrelation introduced by object displacement.
Abstract: Electronic speckle photography offers a simple and fast technique for measuring in-plane displacement fields in solid and fluid mechanics Errors from undersampling, illumination divergence, and displacement magnitude have been analyzed and measured The nature of the systematic error is such that a drift toward the closest integral pixel value is introduced Because of the finite extent of the sensor area, considerable undersampling is tolerable before systematic errors occur The random errors are mainly dependent on the effective ƒ-number of the imaging system and speckle decorrelation introduced by object displacement When sampling at a rate of ~ 70% of the Nyquist frequency, we avoided systematic errors and minimized random errors
85 citations
TL;DR: An interferometer with a computational system has been developed to record three phase-stepped interferograms simultaneously and to calculate displacements, which can be measured with an accuracy exceeding λ/55 if filtering is applied.
Abstract: Surface point displacements can be measured by using standard phase-stepping speckle interferometry, but the measured data are vulnerable to disturbances during the interferogram recordings. To overcome this an interferometer with a computational system has been developed to record three phase-stepped interferograms simultaneously and to calculate displacements. This system is evaluated by measurements of the out-of-plane rotation of a flat surface. The surface displacement is calculated at a rate of 25 times/s. If one reduces noise by filtering, hardware limitations decrease the speed to 12.5 displacement calculations/s. With this system displacements can be measured with an accuracy exceeding λ/55 if filtering is applied.
80 citations
Journal Article•
TL;DR: Lucy's algorithm is iteratively applied in a blind deconvolution method as mentioned in this paper, which permits the reconstruction of a greatly extended object from one speckle frame using a single image of the solar photosphere.
Abstract: Lucy's algorithm is iteratively applied in a blind deconvolution method This new approach permits the reconstruction of a greatly extended object from one speckle frame Speckle images of extended object may lie partly outside the active region of the detector Likewise, objects close to the boundary of the detector, but outside of the field of view, may contaminate the image The blind deconvolution method is adapted to deal with these situations Repeated use of the blind deconvolution method is also proposed Computer simulations are conducted and the effectiveness of the proposed method is demonstrated The method is applied to an image of the solar photosphere
69 citations
30 Sep 1994
TL;DR: In this paper, a phase-diverse speckle data set was collected at the Swedish Vacuum Solar Telescope on La Palma to overcome the effects of atmospheric turbulence and restore a fine-resolution image of solar granulation.
Abstract: Phase-diverse speckle imaging is a novel imaging modality that makes use of both speckle-imaging and phase-diversity concepts. A phase- diverse speckle data set consists of one conventional image and at least one additional image with known phase diversity for each of multiple atmospheric phase realizations. We demonstrate the use of a phase-diverse speckle data set collected at the Swedish Vacuum Solar Telescope on La Palma to overcome the effects of atmospheric turbulence and to restore a fine-resolution image of solar granulation. We present preliminary results of simultaneously reconstructing an object and a sequence of atmospheric phase aberrations from these data using a maximum-likelihood parameter- estimation framework. The consistency of the reconstructions is demonstrated using subsets of the sequence of images pairs. The use of different phase-aberration parameterization schemes and their affect on parameter estimates are discussed. Insight into the desired number of atmospheric realizations is provided.
60 citations
TL;DR: In this paper, a laser speckle shearing interferometric technique is used for measuring the temperature profile inside a gaseous flame and the experimental results are compared with the values obtained by a thermocouple and also by speckel photography.
Abstract: A laser speckle shearing interferometric technique is used for measuring the temperature profile inside a gaseous flame. The experimental results are compared with the values obtained by a thermocouple and also by speckle photography. Good agreement is seen among the temperatures measured by speckle shearing interferometry, speckle photography, and the thermocouple. Speckle shearing interferometry is easier to implement than speckle photography. This is because in speckle shearing interferometry the accurate positions of the fringes can be known without point-by-point analysis and correction for the halo effect.
59 citations
TL;DR: An optical-fiber-based speckle shearing interferometer for an out-of-plane displacement derivative measurement is described.
Abstract: An optical-fiber-based speckle shearing interferometer for an out-of-plane displacement derivative measurement is described. The technique uses a highly birefringent optical fiber to illuminate a test object with equal amounts of orthogonally polarized light, and the interferometer is readily phase stepped, without mechanical movement of components, by strain modulation of the relative phase of the polarization states in the fiber. A Wollaston prism is used to produce two sheared images with adjustable shear.
28 citations
TL;DR: In this paper, the authors considered the mechanism of the speckle interlerometer output signal formation for biovibration measurements and the factors creating amplitude-phase modulation of the output signal are investigated.
Abstract: We consider the mechanism of the speckle interlerometer output signal formation for biovibration measurements. Statistical characteristic analysis of the output signal amplitude is carried out. The factors creating amplitude-phase modulation of the output signal are investigated. The possibility of a differential homodyne speckle interferometer application in Tibetan pulse diagnostics is demonstrated.
27 citations
TL;DR: An iteration algorithm for the analysis of speckle interference patterns is presented and theoretical study shows that the iterated phase converges to a perfect result under ideal conditions.
Abstract: An iteration algorithm for the analysis of speckle interference patterns is presented. First, four digitized phase-shifted patterns are locally averaged. The phase information is then extracted by the usual phase shift algorithm. The wrapped phase is in turn used to reconstruct four new phase-shifted patterns. These three steps form a cycle. Repetition of the three steps has a great effect on suppressing speckle noise. Theoretical study shows that the iterated phase converges to a perfect result under ideal conditions. In general, the iteration causes little error but improves the phase information a great deal. The signal-to-noise ratio rises when additional iterations are performed.
TL;DR: The method has better fringe visibility than can be obtained with purely additive ESPI and also does not suffer from the fringe distortions that can occur with subtractive ESPI in the presence of high-frequency noise.
Abstract: Fringe-visibility issues of additive–subtractive phase-modulated (ASPM) electronic speckle pattern interferometry (ESPI) are explored. ASPM ESPI is a three-step method in which additive-speckle images are acquired rapidly in an analog fashion in every frame of a video sequence, a speckle phase modulation is intentionally introduced between frames, and a digital subtraction of consecutive pairs of additive-speckle images is performed. We show that this scheme has the good high-frequency noise immunity associated with additive-ESPI techniques as well as the good fringe visibility associated with subtractive-ESPI techniques. The method has better fringe visibility than can be obtained with purely additive ESPI and also does not suffer from the fringe distortions that can occur with subtractive ESPI in the presence of high-frequency noise. We show that even if full speckle decorrelation were to occur between the two additive speckle images that are to be subtracted, the visibility of ASPM ESPI fringes can be made to approach unity by suitable adjustment of the reference-to-object beam-intensity ratio.
TL;DR: In this paper, the effects of the generated turbulence on optical propagation are directly measured by sensing the perturbed wavefront phase using a shearing interferometer, and statistical properties of the turbulence are then characterized by means of estimating the phase structure function from the wavefront measurements.
Abstract: The resolution achieved by an optical imaging system in the presence of the random effects of the atmosphere is severely degraded from the theoretical diffraction limit. Techniques exist for recovering near diffraction-limited performance of an imaging system in the presence of atmospheric turbulence. These image enhancement techniques include speckle imaging, deconvolution, and adaptive optics. A turbulence chamber has been designed and built for laboratory testing of current and future adaptive optics and image enhancement techniques. The turbulence is produced within a chamber consisting of two small fans and a heating element. The effects of the generated turbulence on optical propagation are directly measured by sensing the perturbed wavefront phase. The wavefront phases are measured using a shearing interferometer. The statistical properties of the turbulence are then characterized by means of estimating the phase structure function from the wavefront phase measurements. We found that the estimate of the phase structure function depends only on the magnitude of the separation between two points on the optical wavefront and follows the Kolmogorov 5/3 power law.
TL;DR: The DWFS method provides an alternative to speckle imaging that uses simple postprocessing at the cost of a wave-front sensor measurement but with no loss of SNR performance for extended objects.
Abstract: One method for improving the quality of astronomical images measured through a atmospheric turbulence uses simultaneous short-exposure measurements of both an image and the output of a wave-front sensor exposed to an image of the telescope pupil. The wave-front sensor measurements are used to reconstruct an estimate of the instantaneous generalized pupil function of the telescope, which is used to compute an estimate of the instantaneous optical transfer function, which is then used in a deconvolution procedure. This imaging method has been called both deconvolution from wave-front sensor (DWFS) measurements and self-referenced speckle holography. We analyze the signal-to-noise ratio (SNR) behavior of this imaging method in the spatial frequency domain. The analysis includes effects arising from differences in the correlation properties of the incident and the estimated pupil phases and the fact that the object-spectrum estimator is a randomly filtered doubly stochastic Poisson random process. SNR results obtained for the DWFS method are compared with the speckle-imaging power-spectrum SNR for equivalent seeing conditions and light levels. It is shown that for unresolved stars the power-spectrum SNR is superior to the DWFS SNR. However, for extended objects the power-spectrum SNR and the DWFS SNR are similar. Since speckle imaging uses a separate Fourier phase-reconstruction process not required by the DWFS method, the DWFS method provides an alternative to speckle imaging that uses simple postprocessing at the cost of a wave-front sensor measurement but with no loss of SNR performance for extended objects.
TL;DR: In this article, speckle interferometry was used to detect and quantify damage in fatigued carbon fibre-reinforced plastic laminates via its effect on surface displacements.
Abstract: A recently reported new technique renders speckle interferometry applicable for measuring high local displacement gradients. This paper reports how the technique is used to detect and quantify damage in fatigued carbon fibre-reinforced plastic laminates via its effect on surface displacements. Moreover, the measured displacement fields are used to verify a finite element damage model. The accuracy of the delamination measurement is confirmed by ultrasonic results.
Patent•
04 Apr 1994TL;DR: In this article, a displacement measuring method and device is disclosed in which speckle amplitude interferometry within a single feature or a small number of features of a pattern is used to achieve sub-fringe accuracy with a single detector and to measure displacement of the object under investigation with sub-wavelength accuracy at measurement speeds consistent with real-time control of manufacturing processes.
Abstract: A displacement measuring method and device is disclosed in which speckle amplitude interferometry within a single speckle feature or a small number of features of a speckle pattern is used to achieve sub-fringe accuracy with a single detector and to measure displacement of the object under investigation with sub-wavelength accuracy at measurement speeds consistent with real-time control of manufacturing processes. The same technique applied to multiple spots on a sample with optical means for causing interference between different combinations of scattered fields, including fields from different illuminated spots, permits measurements of the total sample motion.
TL;DR: The first results, to the authors' knowledge, of compensated-speckle-imaging experiments, conducted at a compensated telescope operated by the U.S. Air Force, that confirm predictions that improved power-spectrum estimation results from application of speckled imaging postprocessing to compensated astronomical images.
Abstract: Previous analyses have predicted that improved power-spectrum estimation results from application of speckle-imaging postprocessing to compensated astronomical images. We report the first results, to our knowledge, of compensated-speckle-imaging experiments, conducted at a compensated telescope operated by the U.S. Air Force, that confirm these predictions. The power-spectrum signal-to-noise ratio is used as the metric for evaluating the performance. We report the results of power-spectrum estimation for a single star and three binary stars, and we reconstruct images of the binary stars using the bispectrum method to obtain the Fourier phase of the object. Compensated and uncompensated results are compared. A previously derived expression that expresses the power-spectrum signal-to-noise ratio in terms of the compensated optical transfer function statistics and object parameters is verified by experimental data.
Journal Article•
TL;DR: In this article, the authors deal with solutions to overcome or correct for the defects of photon-counting detector for the purpose of speckle interferometry and show how to cope with strong image distortion in the photon counting case and with the so-called photon counting hole.
Abstract: This paper deals with solutions to overcome or to correct for the defects of photon-counting detector ― intensified CCD (ICCD) in particular ― for the purpose of speckle interferometry. Among others, we show how to cope with strong image distortion in the photon-counting case and with the so called photon-counting hole. The latter is due to the incapacity to detect any pair of close photon-events in the short exposure images. Our photon-counting detector, the CP40 camera (Blazit 1987; Foy 1988a), consists in an ICCD and centroiding electronics. Nevertheless, other photon-counting detectors present a defect similar to the photon-counting hole due to the limited shortest time delay between two consecutive photon-events
TL;DR: In this article, the performance characteristics of commercially available CCD cameras adapted to standard television signal transmission have been analyzed for use in video speckle interferometry and the selection criteria for the different camera systems that are offered are discussed.
Abstract: Commercially available CCD cameras adapted to standard television signal transmission have been analyzed for use in video speckle interferometry. Their relevant performance characteristics are described and the selection criteria for the different camera systems that are offered are discussed. It is shown that the requirements that are specific for video speckle interferometry often favor the use of cameras based on the interline transfer principle rather than frame transfer devices, especially when pulsed lasers are applied.
01 Feb 1994
TL;DR: Laser speckle, originally regarded as a nuisance because of the image degradation it caused when laser light was used, has now found a number of uses and been used in biomedical research.
Abstract: Laser speckle, originally regarded as a nuisance because of the image degradation it caused when laser light was used, has now found a number of uses. Many of these can be applied to biomedical systems. This review paper describes six such techniques and some of the ways they have been used in biomedical research.
TL;DR: In this paper, a simple tip-tilt adaptive optics system was proposed to improve the peak intensity of the corrected image in the infrared by a factor of 2 to 3 compared with that of the uncorrected image.
Abstract: A simple tip–tilt adaptive optics system can improve the peak intensity of the corrected image in the infrared by a factor of 2 to 3 compared with that of the uncorrected image. With conventional methods this performance cannot be achieved in the visible unless flexible mirrors are used. A method of improving the peak intensity in the visible by a factor of 8 to 10 compared with that of the uncorrected image by use of a simple tip–tilt mirror is presented. To achieve this improvement, the effective wave aberration, that is, the aberration modulo 2π, is used to obtain tilt and defocus of the turbulent wave front. It is shown that correcting the effective aberration is the equivalent in Fourier space of shift-and-add in image space, that is, moving the brightest speckle to the image center. Christou [ Pub. Astron. Soc. Pac.103, 1040 ( 1991)] has demonstrated the potential of a tip–tilt system when using shift-and-add. Operating in Fourier space rather than in image space offers the advantage of being independent of the type of object to be used for the correction. Additionally, this method is applied to the correction of defocus by determination of the brightest speckle in the three-dimensional image space. Thus the full potential of a rigid-mirror adaptive optics system is demonstrated.
Journal Article•
TL;DR: In this article, the authors used the speckle imaging technique to analyze time series of high angular resolution images of solar small scale structure at a wavelength of 585 nm in active regions with the 76 cm diameter vacuum tower telescope at NSO/Sac Peak.
Abstract: The speckle imaging technique which is described in the first paper of this series (von der Luhe 1993) was used to analyze time series of high angular resolution images of solar small scale structure at a wavelength of 585 nm in active regions with the 76 cm diameter vacuum tower telescope at NSO/Sac Peak. Two sets of reconstructed images with a field of 4 by 4 arcsec which cover a period of 36 min and 83 min were generated and analyzed. The image reconstructions are supplemented with simultaneous large field photographs taken within a 15 A passband centered on the Ca II K (3933) line. The prime objective of the observing program was the study of the structure and the dynamics of the continuum wavelength counterpart of facular points which appear with high contrast in the Ca pictures, i.e., continuum bright points (CBPs)
08 Sep 1994
TL;DR: Digital speckle pattern interference (DSPI) is a non destructive testing optical method allowing the visualization of the defects of the deformations of an object submitted to static deformation or to vibration as mentioned in this paper.
Abstract: Digital Speckle Pattern Interferometry (DSPI) is a non destructive testing optical method allowing the visualization of the defects of the deformations of an object submitted to static deformation or to vibration. This method can be applied to a lot of cases within a range of displacements between tens of nanometers and tens of micrometers. DSPI can be applied to detect the natural frequencies and to visualize the mode shapes of a vibrating object. It is very convenient to study small and weak objects because no contact is required comparing the classical modal analysis using accelerometers. DSPI was successfully applied to study a cantilever aluminum plate (5 cm X 10 cm X 1 mm). The experimental iso-displacement fringe maps are compared to computational results using a finite element method.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
12 Dec 1994
TL;DR: In this article, the phase shifted electronic speckle interferometry (SSEI) was used to detect various types of fatigue damage in carbon fiber reinforced plastics (CFRP).
Abstract: This paper demonstrates the advantages of a recently reported improved technique of phase- shifted electronic speckle interferometry. The improvement extends the range and enhances the accuracy of measurements and thus unlocks many new applications. One of these is detecting various types of fatigue damage in carbon-fiber-reinforced plastics (CFRP). The optical measurements of surface matrix cracks and of delaminations agree very well with the results of other non-destructive testing (NDT) methods. We also demonstrate an improved contouring technique and present the theory behind the experimental procedure, leading to the improved results reported here.
TL;DR: The use of a diffraction-grating technique to process simultaneously the three or more required viewpoints of a digital holography experiment is reported.
Abstract: Digital speckle pattern interferometry provides information on deformations equivalent to that given by image holography. Thus more than one viewpoint is necessary for the description of three-dimensional deformation vectors. We report the use of a diffraction-grating technique to process simultaneously the three or more required viewpoints of a digital holography experiment.
TL;DR: A stellar speckle spectrometer with increased performance and flexibility has been newly developed and a stellar spectrum with the diffraction-limited spatial resolution of a telescope is obtained by referring to specklegrams that are simultaneously recorded with dispersed Speckle patterns.
Abstract: A stellar speckle spectrometer with increased performance and flexibility has been newly developed. In this new spectrometer two synchronized detectors are used to observe a dispersed speckle pattern and a specklegram. A reflection grating is employed as a disperser. We obtained a stellar spectrum with the difiraction-limited spatial resolution of a telescope by referring to specklegrams that are simultaneously recorded with dispersed speckle patterns. A preliminary observational result is also shown.
TL;DR: In this article, an experimental method based on the application of speckle interferometry is proposed in order to determine the dynamic elastic constants of an isotropic material, where a broad frequency spectrum impact is applied to a cylindrical sample and, when this vibrates freely, a heterodyne laser interferometer is used to detect the displacement of a point of the material.
Abstract: An experimental method based on the application of speckle interferometry is proposed in order to determine the dynamic elastic constants of an isotropic material. A broad frequency spectrum impact is applied to a cylindrical sample and, when this vibrates freely, a heterodyne laser interferometer is used to detect the displacement of a point of the material. Once the sample is suitably excited, the displacement component of interest, either in‐plane or out‐of‐plane, is detected in order to determine its frequency content. A spectral analysis allows the determination of the longitudinal, transverse, and torsional natural frequencies. From this the elastic constants are calculated. The measurement precision is checked experimentally using the same method by means of a third detection.
TL;DR: In this article, the authors have adapted the digital shearing speckle interferometry for whole-field modal analysis, and experimental verification is performed on a thin square plate fully constrained and subjected to a steady-state excitation.
01 Jan 1994-Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology
TL;DR: In this paper, an optical fiber sensor system based on dual beam speckle interferometry is presented, which takes advantage of simple optical components and fibers through a signal processing technique capable of measuring vibration displacement components.
Abstract: An optical fiber sensor system based on dual beam speckle interferometry is presented. The system provides a noncontact method of very small vibration displacement real-time measurement. It takes advantage of simple optical components and fibers through a signal processing technique capable of measuring vibration displacement components. The theoretical analysis and experimental systems are described. Experimental results show that the in-plane vibration spectrum can be easily established.
28 Jun 1994
TL;DR: In this article, the prospective for medical diagnostics schemes of speckle-interferometers and the application of differential specckle interferometer and coherent optical analyzers for skin vibration and structure investigations is shown.
Abstract: The description of coherent optical methods including speckle-optics and speckle-interferometry techniques with respect to laser diagnostics methods development is made. The prospective for medical diagnostics schemes of speckle-interferometers and the application of differential speckle- interferometers and coherent optical analyzers for skin vibration and structure investigations is shown.