Showing papers on "Speckle imaging published in 1985"
TL;DR: One application of phase-shifting techniques to speckle interferometry is finding the phase of deformations, where up to ten waves of wavefront deformation can easily be measured.
Abstract: Speckle patterns have high frequency phase data, which make it difficult to find the absolute phase of a single speckle pattern; however, the phase of the difference between two correlated speckle patterns can be determined. This is done by applying phase-shifting techniques to speckle interferometry, which will quantitatively determine the phase of double-exposure speckle measurements. The technique uses computer control to take data and calculate phase without an intermediate recording step. The randomness of the speckle causes noisy data points which are removed by data processing routines. One application of this technique is finding the phase of deformations, where up to ten waves of wavefront deformation can easily be measured. Results of deformations caused by tilt of a metal plate and a disbond in a honeycomb structure brazed to an aluminum plate are shown.
740 citations
TL;DR: Tests were performed on synthetic aperture radar images which show that the algorithm reduces speckle noise in images favorably with a 3 × 3 median filter.
Abstract: An algorithm is described which reduces speckle noise in images. It is a nonlinear algorithm based on geometric concepts. Tests were performed on synthetic aperture radar images which show that it compares favorably with a 3 × 3 median filter.
248 citations
TL;DR: Digital speckle-pattern interferometry systems for automatic measurement of deformations of a diffuse object are presented, which are based on a fringe scanning method with phase-shifted Speckle interferograms.
Abstract: Digital speckle-pattern interferometry systems for automatic measurement of deformations of a diffuse object are presented, which are based on a fringe scanning method with phase-shifted speckle interferograms. A digital speckle pattern before deformation of an object is recorded in the mass storage device of a computer facility. After deformation, four digital speckle patterns are recorded as changing the phase of reference light such as 0, π/2, π, and 3π/2, respectively. Four speckle interferograms, whose phases are shifted by 0, π/2, π, and 3π/2, are generated by calculating the square of the differences between speckle patterns before and after deformation. These interferograms are low-pass filtered to reduce speckle noise. The calculation of the arctangent with four phase-shifted speckle interferograms gives the optical path difference which is proportional to the deformation. A correction of the discontinuity of the calculated phase gives the numerical data of the deformation in the whole object area. Some experimental results for the measurement of out-of-plane, in-plane, and 3-D deformations are presented.
201 citations
TL;DR: It is shown that the macroscopic surface profile may be determined from the phase differences if the effective wavelength Λ = λ1λ2/|λ1−λ2| is sufficiently larger than the standard deviation of the microscopic profile of the illuminated surface, and the statistical error is reasonably small if the phase measurements are obtained from speckles of sufficient intensity.
Abstract: If a rough surface is illuminated by a coherent lightwave of wavelength λ1, it is not possible to determine the surface profile from the phases of the speckle field formed by the scattered light. If the rough surface is illuminated, however, by an additional coherent wave of wavelength λ1, the phase differences between the two speckle fields do contain information about the macroscopic surface profile even if subject to a statistical error. It is shown that (1) the macroscopic surface profile may be determined from the phase differences if the effective wavelength Λ = λ1λ2/|λ1−λ2| is sufficiently larger than the standard deviation of the microscopic profile of the illuminated surface, and (2) the statistical error is reasonably small if the phase measurements are obtained from speckles of sufficient intensity. Using a heterodyne interferometer we demonstrate the feasibility of this technique. In the first experiment we determine the radius of curvature of a rough spherical surface. In the second experiment the macroscopic surface contour on two ophthalmic lenses of the same power variation, one with a grounded surface and the other with a polished surface, was determined.
123 citations
TL;DR: In this article, a new method of observing vibration fringes is presented and compared with existing techniques as well as some variations on them, which involves continuously subtracting a reference frame containing only self-interference terms and no cross interference term from the time-averaged data frames of the vibrating object.
Abstract: Vibration observation is a major application of digital speckle-pattern interferometry (DSPI), which is a variation on electronic speckle-pattern interferometry (ESPI). DSPI processes speckle patterns in a computer rather than with a frame grabber and analog electronics as in ESPI. A new method of observing vibration fringes is presented and compared with existing techniques as well as some variations on them. Fringe contrast and signal-to-noise ratio are used as a means of comparison since these quantities are dependent on the techniques used. This new technique involves continuously subtracting a reference frame containing only self-interference terms and no cross interference term from the time-averaged data frames of the vibrating object. This reference frame is created by vibrating a reference mirror at a high amplitude while the object is at rest. Comparisons of calculated fringe contrast with four other observation methods show that this method yields extremely good fringe contrast. Experimental results are shown for this new technique as well as for the most commonly used vibration-observation technique. These results show that the new technique is far superior to all the other methods for moderately unstable objects, which may slowly drift or deform in time.
110 citations
TL;DR: In this paper, the influence of photon noise on the bispectrum of an image-intensity distribution is discussed, and it is shown theoretically that bispectral analysis in speckle masking should yield true, diffraction-limited images in all those cases in which the specckle-interferometry process has been successful in reconstructing the object autocorrelation.
Abstract: The bispectrum is the Fourier transform of the triple correlation, sometimes also referred to as the triple-product integral. The influence of photon noise on the bispectrum of an image-intensity distribution is discussed. As an example, the astronomical speckle-masking method is considered. Speckle masking is a method to overcome image degradation that is due to the turbulent atmosphere. It is shown theoretically that bispectral analysis in speckle masking should yield true, diffraction-limited images in all those cases in which the speckle-interferometry process has been successful in reconstructing the object autocorrelation.
101 citations
TL;DR: Technical details on the PAPA (precision analog photon address) detector are presented and some of the laboratory and astronomical results which demonstrate the detector's capabilities are included.
Abstract: A new 2-D photon-counting camera, the PAPA (precision analog photon address) detector has been built, tested, and used successfully for the acquisition of speckle imaging data. The camera has 512 x 512 pixels and operates at count rates of at least 200,000/sec. In this paper, technical details on the camera are presented and some of the laboratory and astronomical results are included which demonstrate the detector's capabilities.
58 citations
TL;DR: In this paper, a survey on the formation of the fringe patterns observed in these methods is presented, which helps in deriving dependences of their shape and visibility on object deformation parameters and optical systems by starting from the correlation properties of the light scattered from diffuse objects.
Abstract: Publisher Summary This chapter focuses fringe formations in deformation and vibration measurements using laser light. The chapter discusses a survey on the formation of the fringe patterns observed in these methods. The chapter helps in deriving dependences of their shape and visibility on object deformation parameters and optical systems by starting from the correlation properties of the light scattered from diffuse objects, and discuss the mutual relationships and features of each method by putting physical interpretations on derived mathematical relations. In holographic interferometry and speckle interferometry, the fringe shape represents the distribution of the phase change of the scattered light caused by object deformation, while the fringe visibility depends on the overlap of the corresponding speckle pair, therefore, on speckle displacement and speckle size. In speckle photography, on the other hand, the fringe shape represents the speckle displacement, while the fringe visibility is affected by the speckle decorrelation accompanying the displacement. In addition the relations derived in the present chapter would deliver a quantitative basis for selecting an adequate method of measurement and the optimum manner of signal processing in these modem interferometric techniques.
56 citations
TL;DR: Electronic speckle pattern interferometry with a cw laser has been used to study objects at very high temperatures, and examples on how the technique can be used toStudy deformations, oxidation shell growth, and melting zones are presented.
Abstract: Electronic speckle pattern interferometry with a cw laser has been used to study objects at very high temperatures. Interference patterns were observable to 1700°C, while high contrast interference fringes could be recorded up to 1550°C. These temperature limits were mainly set by the onset of surface reactions and melting of the objects. Examples on how the technique can be used to study deformations, oxidation shell growth, and melting zones are presented.
48 citations
TL;DR: In this article, the amplitude modulation of the information-carrying cosine fringes is controlled by three factors: a decorrelation factor γ, a displacement factor Ω, and a displacementgradient factor ψ.
Abstract: The use of laser speckle for displacement and deformation measurement has found wide applications in mechanics and metrology. Traditionally, a deterministic approach has been adopted to analyze the process. In this paper a statistical approach is utilized, resulting in a better understanding of the limitations and potentials of one-beam subjective laser-speckle interferometry (or speckle photography). We find that the amplitude modulation of the information-carrying cosine fringes is controlled by three factors: a decorrelation factor γ, a displacement factor Ω, and a displacement-gradient factor ψ. We introduce the concept of an ambiguity factor that sets a critical value for the product γΩψ. We then propose a criterion for fringe discernibility from which the upper limit of measurement is established.
32 citations
TL;DR: Speckle and speckle-shearing interferometer geometries have been combined into a single setup by the use of a small ground glass reference diffuser on the lens pupil to obtain the moire curvature pattern.
Abstract: Speckle and speckle-shearing interferometer geometries have been combined into a single setup by the use of a small ground glass reference diffuser on the lens pupil. Sheared fields are obtained with a split lens arrangement. Judicious aperturing results in separated diffraction halos at the FT plane. Fringe patterns corresponding to out-of-plane displacement and slope are obtained by filtering via the appropriate halos. A four-aperture arrangement coupled with shearing elements extends the method to obtain the moire curvature pattern.
TL;DR: Speckle interferometry of 532 Herculina performed on January 17 and 18, 1982, yields triaxial ellipsoid dimensions of (263 + or - 14) x (218 + or 12) × (215 + or 13) km, and a north pole for the asteroid within 7 deg of RA = 7h47min and DEC = -39 deg (ecliptic coordinates lambda = 132 deg beta = -59 deg).
TL;DR: The simple shift-and-add method was applied to reconstruct a binary star, α Com, which was ob served with wide bandwidth light and examined the performance of this method for wideband speckle images, and the effecive bandwidth of the recording system was defined by the spectral response of the Recording system.
Abstract: Naoshi Baba, Syuzo Isobe, Youji Norimoto, and Motokazu Noguchi Naoshi Baba is with Hokkaido University, Department of Applied Physics, Faculty of Engineering, Sapporo 060, Japan; the other authors are with University of Tokyo, Tokyo Astronomical Observatory, Mitaka 181, Japan. Received 27 November 1984. 0003-6935/85/101403-03$02.00/0. © 1985 Optical Society of America. The shift-and-add method proposed by Bates and Cady is a simple reconstruction technique for true imaging of stellar objects. This method can be regarded as an extension of the technique invented by Lynds et al. , which, however, needs complicated procedures. Lynds et al. applied their technique to reconstruct α Ori. There are some variations of the shiftand-add method. Bagnuolo used his version of it to in vestigate α Aur. We applied the simple shift-and-add method to reconstruct a binary star, α Com, which was ob served with wide bandwidth light. The simple shift-and-add method is stated as follows: the brightest point in each speckle image is shifted to the center of image space, and the translated image is added to all other speckle images that have been similarly processed. The theoretical analysis of this method has been described by Bagnuolo and by Hunt et al. Speckle interferometric observations were carried out at the Okayama Astrophysical Observatory on the night of 17 Feb. 1984: α Com was observed with our speckle camera combined with the ƒ/13.0 Cassegrain focus of the 91-cm tele scope. The speckle camera we developed contains a Philips XX1500 image intensifier and a l0× microscope objective. Speckle data were recorded on Tri-X film. Bates and Caddy showed in their simulation experiments that the shift-and-add method is applicable to white light speckle images. We examined the performance of this method for wideband speckle images, and we recorded speckle images without a filter, namely, the effecive bandwidth of the recording system was defined by the spectral response of the
TL;DR: A technique applicable to double-exposure speckle interferograms obtained from processing twoSpeckle patterns is described, which utilizes a computer-controlled stepping motor to tilt the object illumination, which is repeatable to lambda/100.
Abstract: Speckle-fringe quality can be improved by averaging many statistically independent interferograms together, which are generated by shifting the object’s illumination angle. A technique applicable to double-exposure speckle interferograms obtained from processing two speckle patterns is described. It utilizes a computer-controlled stepping motor to tilt the object illumination, which is repeatable to λ/100. Results are shown for double-exposure interferograms corresponding to mechanical deformations and vibrations. A significant increase in the fringe visibility is gained.
TL;DR: In this paper, major advances in using coherent and incoherent speckle patterns for displacement and strain measurements are reviewed, including the laws of spatial movement of laser speckles, the halo functions of coherent and coherent speckLE patterns, decorrelation factors and their effect on the fringe visibility and the upper limit of measurement, new techniques of holospeckle interferometry, real-time and electron microscopic speckler photographies, and automatic processing of Young's fringes.
Abstract: Major advances in using coherent and incoherent speckle patterns for displacement and strain measurements are reviewed. Topics include the laws of spatial movement of laser speckle, the halo functions of coherent and incoherent speckle patterns, decorrelation factors and their effect on the fringe visibility and the upper limit of measurement, new techniques of holospeckle interferometry, real-time and electron microscopic speckle photographies, and the automatic processing of Young's fringes.
TL;DR: Two extensions of the previously reported ‘crude phase estimation’ procedure are developed, which serve to provide starting phases (for Fienup's iterative algorithms) which are ‘improved’ in the sense that rates of convergence of these algorithms are accelerated.
Abstract: Two extensions of our previously reported ‘crude phase estimation’ procedure are developed. They both serve to provide starting phases (for Fienup's iterative algorithms) which are ‘improved’ in the sense that rates of convergence of these algorithms are accelerated. The theory is illustrated by examples of phase retrieval from phaseless Fourier data. Images are reconstructed from Fourier magnitudes which were either computer-generated or measured in our optical laboratory, set up to simulate Labeyrie's speckle interferometry.
25 Nov 1985
TL;DR: In this article, the phase of the difference between two correlated speckle patterns can be determined by applying phase-shifting techniques to the interferometry, which will quantitatively determine the phase.
Abstract: Speckle patterns have high-frequency phase data, which make finding the absolute phase of a single speckle pattern difficult. However, the phase of the difference between two correlated speckle patterns can be determined by applying phase-shifting techniques to speckle interferometry, which will quantitatively determine the phase of double-exposure speckle measurements. The technique uses computer control to take data and calculate phase without an intermediate recording step. The randomness of the speckle causes noisy data points that are removed by data processing routines. A study of the phase errors attributable to decorrelation of the speckle patterns shows a 33° rms error for 10 waves of tilt. One application of this technique is finding the phase of deformations, where up to 10 waves of wavefront deformation can easily be measured. Results of deformations caused by tilt of a metal plate and a disbond in a honeycomb structure brazed to an aluminum plate are shown.
TL;DR: A number of methods to obtain in-plane displacement, out of plane displacement and slope data using holographic optical elements are presented, all of which are as good as those obtained with conventional optical systems.
Abstract: This paper presents a number of methods to obtain in-plane displacement, out of plane displacement and slope data using holographic optical elements. The results obtained with a hololens and a holoshear lens are as good as those obtained with conventional optical systems.
TL;DR: The reconstructed cardiac displacement patterns, obtained by this new noncontact and noninvasive technique, provide information on the functioning of various parts of the heart in cardiac disorders which are in qualitative agreement with that of two-dimensional echocardiography.
Abstract: Laser speckle interferometry has been used to determine the displacement pattern on the chest wall produced by the heart action during the systolic phase of the cardiac cycle. The time averaged specklegram, recorded in the image plane, is scanned by the pointwise method. From the values of the spacings of Young's fringes, measured at various points, the corresponding displacement pattern in the form of a 40 × 30 matrix, equal to that of the cardiac region, is reconstructed and color-coded by a PDP 11/23 image processor. This pattern shows significant variations in displacements at various locations. Depending on the clinical status of the subjects, further changes in the pattern are observed. The reconstructed cardiac displacement patterns, obtained by this new noncontact and noninvasive technique, provide information on the functioning of various parts of the heart in cardiac disorders which are in qualitative agreement with that of two-dimensional echocardiography.
TL;DR: It is shown that the 2-D cross-correlation function between the level-crossing maps obtained from two speckle patterns before and after displacement is equal to the occurrence-rate histogram of the distances between the levels.
Abstract: It is shown that the 2-D cross-correlation function between the level-crossing maps obtained from two speckle patterns before and after displacement is equal to the occurrence-rate histogram of the distances between the level-crossing points. On the basis of this fact, the displacement vectors of speckles produced in both diffraction and image planes are successfully measured. The analysis for measurements of the speckle displacement in a vectorial form is performed on line using digital processing by means of a TV–computer system.
TL;DR: It is shown theoretically and experimentally that the use of a single aperture is essential for obtaining the proper value of the deflection slope of an object: the single-aperture method enables us to obtain the proper slope distribution regardless of the direction of displacement.
Abstract: The difference in the information obtained by the single-aperture and the double-aperture methods in speckle shearing interferometry is discussed. It is shown theoretically and experimentally that the use of a single aperture is essential for obtaining the proper value of the deflection slope of an object: the single-aperture method enables us to obtain the proper slope distribution regardless of the direction of displacement. With the double-aperture method, however, proper distribution can be obtained only for displacement in a particular direction, and this introduces an error into the slope measurement.
TL;DR: In this paper, two methods of identifying fringe positions in speckle patterns were proposed, one using local directional averaging to track fringes, while the second using standard image processing techniques to connect the patterns into a form where the fringes can be identified.
Abstract: This paper two methods of identifying fringe positions in speckle patterns. The first uses local directional averaging to track fringes, while the second uses standard image processing techniques to connect the patterns into a form where the fringes can be identified.
TL;DR: In this article, the use of a simple tilt procedure in electronic speckle pattern interferometry (ESPI) for rapid mapping of in-plane vibration modes is explained and demonstrated.
Abstract: The use of a simple tilt procedure in electronic speckle pattern interferometry (ESPI) for rapid mapping of in-plane vibration modes is explained and demonstrated.
TL;DR: In this article, first-order statistics of the speckle phase were studied on an axis of the imaging system under the assumption of Gaussian statistics for the formation of the sparse field.
Abstract: First-order statistics of the speckle phase are studied on an axis of the imaging system under the assumption of Gaussian statistics for the formation of the speckle field. It is found that the speckle phase is most widely distributed at the image plane owing to the noncircularity of the speckle field. Asymmetry of the probability-density distribution of the speckle phase also appears to be due to the inclination of the joint probability density of the complex speckle amplitude. These statistical characteristics of the speckle phase are enhanced for relatively small values of the optical roughness of the object.
TL;DR: Application de l'interferometrie speckle aux essais non destructifs de la statue de Marco Aurelio as mentioned in this paper, a statue of the famous sculptor.
Abstract: Application de l'interferometrie speckle aux essais non destructifs de la statue de Marco Aurelio. Etude des deformations mecaniques
25 Nov 1985
TL;DR: The zero-and-add technique as discussed by the authors can be extended to two dimensions by appealing to the theory of image reconstruction from projections, which can be used to reconstruct any object viewed through severely distorting media (corresponding to one-dimensional speckle images).
Abstract: Recent partially-published and previously unpublished extensions of the shift-and-add principle are summarised. An up-to-date bibliography of shift-and-add is included. A new technique, potentially capable of imaging any object viewed through severely distorting media, is presented and illustrated with computer generated data (corresponding to one-dimensional speckle images). The technique, which is called zero-and-add, can be extended to two dimensions by appealing to the theory of image reconstruction from projections.
TL;DR: In this paper, the normal model of light propagation through a turbulent atmosphere is used to investigate the telescope-atmosphere transfer function in stellar speckle interferometry, and the effect of the finite bandwidth of a spectral filter on the transfer function is considered.
Abstract: The normal model of light propagation through a turbulent atmosphere is used to investigate the telescope–atmosphere transfer function in stellar speckle interferometry. The effect of the finite bandwidth of a spectral filter on the transfer function is considered. The permissible focusing errors for successful processing in stellar speckle interferometry are obtained based on the normal model. Some observational results are presented and compared with theory. The normal model leads to an analytically simple solution and properly describes light scattering from turbulent atmosphere. The results for the normal model are compared with those for the log-normal model.
TL;DR: An optical method of generating high-constrast contours by using speckle interferometry has been proposed and the conventional dual-index immersion method has been adopted.
Abstract: An optical method of generating high-constrast contours by using speckle interferometry has been proposed. To demonstrate the use of this technique the conventional dual-index immersion method has been adopted.