Showing papers in "Optical Engineering in 1982"
TL;DR: In this paper, the surface displacement components in laser speckle metrology were measured using a digital image scanner interfaced to a computer. Butt et al. used a boundary integral equation method to calculate surface traction in the contour.
Abstract: Digital imaging techniques are utilized as a measure of surface displacement components in laser speckle metrology. An image scanner which is interfaced to a computer records and stores in memory the laser speckle patterns of an object in a reference and deformed configuration. Subsets of the deformed images are numerically correlated with the references as a measure of surface displacements. Discrete values are determined around a closed contour for plane problems which then become input into a boundary integral equation method in order to calculate surface traction in the contour. Stresses are then calculated within this boundary. The solution procedure is illustrated by a numerical example of a case of uniform tension.
1,617 citations
TL;DR: The mathematics of the technique are described, some computer simulations which involve both point sources and extended objects are shown and it is shown that the method provides an interesting challenge to designers of optical devices.
Abstract: Wavefront sensing by phase retrieval implies extraction of the Fourier transform of a complex signal based on observation of the modulus of the signal Only the image intensity from a system's focal plane array is required to estimate the phase aberrations These estimates are used to derive control signals to align (or to maintain alignment of) the optical system The concept can be used in both a predetection and postdetection mode In the former, the control system labors to keep the optics in a diffraction-limited mode all the time In the latter, the control system induces a phase or wavelength diversity that allows successive images to be restored to nearly diffraction-limited quality by postprocessing of the image This second mode is particularly interesting because it will reduce the design effort for both the optical system and the control system How the phase or wavelength diversity is achieved is not clear at this time If the method has utility, it provides an interesting challenge to designers of optical devices In this paper we describe the mathematics of the technique and show some computer simulations which involve both point sources and extended objects
639 citations
TL;DR: Shearography as mentioned in this paper is an interferometric method which employs an image-shearing camera to produce two laterally sheared images in the image plane, which depicts the surface displacement gradients.
Abstract: This paper presents a new optical method referred to as shearography. Shearography is an interferometric method which employs an image-shearing camera. It permits full-field measurement of derivatives of surface displacements. The object under study is illuminated by laser light, and it is imaged by an image-shearing camera. The image-shearing camera produces two laterally sheared images in the image plane. When a photographic film in the image plane is doubly exposed with the object being deformed between the exposures, the processed photograph yields a fringe pattern which depicts the surface displacement gradients. Theory of the method as well as its applications to strain meausrements and nondestructive testing are presented.
370 citations
TL;DR: In this paper, the authors review and explore the field, provide a historical perspective, analyze several of the nonlinear interactions useful for the generation of phase-conjugate replicas, and conclude with a brief survey of potential applications and suitable nonlinear media.
Abstract: The real-time information processing and manipulation of electromagnetic waves using nonlinear Qptical techniques has resulted in a myriad of new applications in diverse fields such as quantum electronics, image processing, optical computing, adaptive optics, and nonlinear spectroscopy. In this paper, we review and explore the field, provide a historical perspective, analyze several of the nonlinear interactions useful for the generation of phase-conjugate replicas, and conclude with a brief survey of potential applications and suitable nonlinear media.
251 citations
TL;DR: The article resumes the theory in a unifying approach and presents a comprehensive list of applications ofOptical methods of shadow and projection moire for mapping the absolute shape of a given surface or the difference between that surface and a master one or its accidental shape change.
Abstract: Optical methods of shadow and projection moire are particularly suitable for mapping the absolute shape of a given surface or the difference between that surface and a master one or its accidental shape change. Essentially, product moire fringes are obtained on an image plane where a "filter" grating analyzes the image of the test surface which has been "coded" by projecting a master grating on it. The article resumes the theory in a unifying approach and presents a comprehensive list of applications.
135 citations
TL;DR: The performance of this algorithm when applied to enhance typical undegraded images, images with large shaded areas, and also images degraded by cloud cover will be illustrated by way of examples.
Abstract: In this paper, we develop an image enhancement algorithm that modifies the local luminance mean of an image and controls the local contrast as a function of the local luminance mean of the image. The algorithm first separates an image into its lows (low-pass filtered form) and highs (high-pass filtered form) components. The lows component then controls the amplitude of the highs component to increase the local contrast. The lows component is then subjected to a nonlinearity to modify the local luminance mean of the image and is combined with the processed highs component. The performance of this algorithm when applied to enhance typical undegraded images, images with large shaded areas, and also images degraded by cloud cover will be illustrated by way of examples.
110 citations
TL;DR: In this article, a review of the progress in high-sensitivity moire interferometry is presented, with a comparison of the theoretical limit of X/2 displacement per fringe in one demonstration.
Abstract: Recent progress in high-sensitivity moire interferometry is reviewed. Interference patterns reveal full-field contour maps of in-plane displacements. Sensitivity corresponds to moire with 1200 lines/mm (30,480 //in.) for most examples, but approaches the theoretical limit of X/2 displacement per fringe in one demonstration. Techniques for producing cross-line phase gratings on specimens are described, as well as use of real and virtual reference gratings. Carrier patterns and optical filtering are used to cancel initial or no-load patterns. Diverse applications are illustrated.
101 citations
TL;DR: An automatic computer analysis system for interferometric patterns is developed, and the least-square interpolation method is applied to determine the fractional fringe orders of pixels between fringe skeletons.
Abstract: An automatic computer analysis system for interferometric patterns is developed A digital interferogram is stored on disk memory, and fringe skeletons of the interferogram are extracted, based on the two-dimensional gray level fringe peak detection method Extracted fringe skeletons are thinned, and then their fringe orders are determined, during which process the fringe pattern is visually inspected The least-square interpolation method is applied to determine the fractional fringe orders of pixels between fringe skeletons All the procedures of analyzing fringe data, except for the fringe order determination, are automatically performed A man-machine interactive method with a light pen is used to inform the determined fringe orders to the computer A representative example of the fringe pattern analysis is presented
86 citations
TL;DR: Electronic speckle pattern interferometry (ESPI) as mentioned in this paper enables static and dynamic surface displacements to be measured in real time to an accuracy of the order of a wavelength of light.
Abstract: Electronic speckle pattern interferometry (ESPI) enables static and dynamic surface displacements to be measured in real time to an accuracy of the order of a wavelength of light. The principles of the technique are outlined and the different configurations of interferometers described. Some applications of the technique are discussed.
80 citations
TL;DR: In this paper, a two-dimensional polynomial expansion of the wavefront coefficients is used to optimize the performance of an optical system containing a holographic Fourier transform lens with the aid of a computer-generated hologram.
Abstract: Holographic optical elements (HOEs) recorded with arbitrary aspheric wavefronts can now be analyzed with a holographic ray-tracing design program The recording wavefronts are defined by analytical phase functions, for example, a two-dimensional polynomial expansion The coefficients of the functional representations of the HOE recording wavefronts are used as parameters to optimize the performance of an optical system containing the HOE The optimum recording wavefronts are then produced with the help of computer-generated holograms Several useful arbitrary wavefront phase functions are discussed Design predictions and experimental results are presented for a holographic Fourier transform lens recorded with the aid of a computer-generated hologram
80 citations
TL;DR: In this paper, a review of various nonlinear optical mechanisms that may be used for DFWM, as well as the various DFWM and related "transient grating" experiments that have been performed for application to phase conjugation and to carrier dynamics studies are presented.
Abstract: Semiconductors appear to have excellent potential as materials for phase conjugation via degenerate four-wave mixing (DFWM) because of the large variety of nonlinear optical mechanisms that may be invoked in them. When the optical wavelength is near or above the band gap, mobile particles such as free electrons and holes or free excitons may be created; in such cases, DFWM itself provides a powerful contact-free and nondestructive technique for the study of carrier transport and decay parameters, such as ambipolar diffusion coefficients and recombination times. In this article, we briefly review the various nonlinear mechanisms that may be used for DFWM, as well as the various DFWM and related "transient grating" experiments that have been performed for application to phase conjugation and to carrier dynamics studies.
TL;DR: In this paper, the basic principle of the white light speckle method for strain analysis is reviewed with a theoretical analysis of the recording and reconstruction processes of specklegrams including the effect of defocus.
Abstract: The basic principle of the white light speckle method for strain analysis is reviewed with a theoretical analysis of the recording and reconstruction processes of specklegrams including the effect of defocus. Ways to increase the sensitivity are proposed. The method's a-plicability to measuring inplane displacement, out-of-plane displacement, surface strain on a curved object, interior strain in a 3-D object, and large deformation is exemplified.
TL;DR: In this article, a review article summarizes applications of the interferometric strain/displacement gage (ISDG), which measures in-plane surface deformation between two small reflecting surfaces by monitoring the interference fringe pattern motion.
Abstract: This review article summarizes applications of the interferometric strain/displacement gage (ISDG). The laser-based ISDG measures in-plane surface deformation between two small reflecting surfaces by monitoring the interference fringe pattern motion. The short gage length (100 micrometers) and noncontacting nature are especially attractive in certain laboratory situations. Following a discussion of the measurement procedures, applications in dynamic loading, fatigue and fracture, and high temperature environments are reviewed.
TL;DR: The Cosmic Background Explorer (COBE) satellite as mentioned in this paper was the first satellite to map the spectrum and the angular distribution of diffuse radiation from the universe over the entire wavelength range from 1 micron to 1.3 cm.
Abstract: The Cosmic Background Explorer (COBE) satellite, under study by NASA since 1976, will map the spectrum and the angular distribution of diffuse radiation from the universe over the entire wavelength range from 1 micron to 1.3 cm. It carries three instruments: a set of differential microwave radiometers (DMR) at 23.5, 31.4, 53, and 90GHz, a far infrared absolute spectrophotometer (FIRAS) covering 1 to 100 per cm, and a diffuse infrared background experiment (DIRBE) covering 1 to 300 microns. They will use the ideal space environment, a one year lifetime, and standard instrument techniques to achieve orders of magnitude improvements in sensitivity and accuracy, providing a fundamental data base for cosmology. The instruments are united by common purpose as well as similar environmental and orbital requirements. The data from all three experiments will be analyzed together, to distinguish nearby sources of radiation from the cosmologically interesting diffuse background radiations. Construction is planned to begin in 1982 for a launch in 1988.
TL;DR: In this paper, a modification of the optical setup is proposed to change the observed fringe patterns by modifying the optical configuration of the holographic interferometry system, and well-known procedures of the moire method can be applied to holographic Interferometry.
Abstract: In conventional holographic interferometry, the observed fringe patterns are determined by the object displacement and deformation, and by the illumination and observation configurations. The obtained information may not be in the most convenient form for further data processing. To overcome this problem, and to create new possibilities, holographic fringe patterns can be changed by modifying the optical setup. As a result of these modifications, well-known procedures of the moire method can be applied to holographic interferometry. Components of displacement and components of the strain tensor can be isolated and measured separately. Surface contours and slopes can also be determined.
TL;DR: In this paper, a real-time and point-by-point method for measuring surface strain by electro-optical techniques is described, in which a specimen surface is illuminated by a thin laser beam and the displacements of the speckle pattern resulting from the surface deformation are detected by linear image sensors followed by a microcomputer.
Abstract: An automatic method of measuring surface strain by electro-optical techniques is described. It is a real-time and point-by-point method in which a specimen surface is illuminated by a thin laser beam and the displacements of the speckle pattern resulting from the surface deformation are detected by linear image sensors followed by a microcomputer. The displacements are calculated as the peak positions of the cross-correlation functions of image sensor signals before and after the deformation. By adopting a differential system consisting of two image sensors positioned symmetrically about the surface normal we can eliminate the effect of rigid body motion. The sensitivity depends on the surface to sensor distance, while the gauge length is given by the diameter of the laser spot. These relations derived from physical optics are verified by experiments using a metal plate specimen subject to tensile strain that is monitored by an electrical resistance strain gauge. The minimum strain value measured was a few ten microstrains with a gauge length of 1 mm. We could also measure thermal strain by this method.
TL;DR: In this article, a summary of experiments which show how retrodirective arrays have been used to approximate phase conjugation is presented, along with a detailed discussion of the experiments and their results.
Abstract: A summary of experiments is presented which show how retrodirective arrays have been used to approximate phase conjugation.
TL;DR: Various techniques that are used to print, record, and analyze grids are discussed, and the types of problems to which the grid method has been applied are presented.
Abstract: Determining strain with grids is one of the oldest and simplest methods of experimental stress analysis. Here, the method is reviewed. Various techniques that are used to print, record, and analyze grids are discussed, and the types of problems to which the grid method has been applied are presented.
TL;DR: In this paper, the basic principles of the subjective laser speckle method are reviewed with an analysis of its sensitivity and limitation, focusing on the method's application to various solid mechanics problems.
Abstract: The basic principles of the subjective laser speckle method are reviewed with an analysis of its sensitivity and limitation Emphasis is on the method's application to various solid mechanics problems Examples cited include stress concentration due to discontinuities, determination of thermal stresses, flexure of plates, vibration of composites, fracture of aluminum, interior strain determination, impact stresses, nondestructive testing of debond in lavprpri nnmnncitpc atom
TL;DR: Moire fringe maps represent in detail the three-dimensional displacements that have occurred in engineering structures measured by applying a fine grid pattern to the surface and photographing this in white light with a specially modified 35 mm camera.
Abstract: Deformations of engineering structures are measured by applying a fine grid pattern to the surface and photographing this in white light with a specially modified 35 mm camera. The processed negatives are analyzed in a spatial filtering system to produce moire fringe maps which represent in detail the three-dimensional displacements that have occurred. Measurements have been obtained from brick built and concrete structures, from steel surfaces heated to 600°C, and from plastic and composite materials.
TL;DR: In this paper, the concept of carrier-mean-frequency-selective convolution is introduced to solve the undersea problem of passive acoustic surveillance (PAS) and compared with the conventional notion of difference-frequency Doppler-corrected correlation.
Abstract: The concept of carrier-mean-frequency-selective convolution is introduced to solve the undersea problem of passive acoustic surveillance (PAS) and compared with the conventional notion of difference-frequency Doppler-corrected correlation. The former results in the cross-Wigner distribution function (WD), and the latter results in the cross-ambiguity function (AF). When the persistent time of a sound emitter is more important than the characteristic tone of the sound emitter, WD will be more useful than AF for PAS activity detection, and vice versa. Their mutual relationships with the instantaneous power spectrum (IPS) show the importance of the phase information that must be kept in any 2-D representation of a 1 -D signal. If a square-law detector is used, or an unsymmetric version of WD or AF is gener-ated, then one must produce the other 2-D representations directly, rather than transform one to the other.
TL;DR: A rapidly convergent adaptive algorithm based upon iteratively estimating the inverse of the covariance matrix was developed, which lends to a simplified hardware structure because it eliminates the matrix inversion process.
Abstract: This paper presents some theoretical analysis and applications of adaptive filtering techniques for the detection of dim targets in the presence of highly structured background clutter. The computer algorithms carry out spatial, temporal, and multispectral filtering processes of forward looking infrared (FLIR) images taken at various times and in different spectral bands. These images were obtained from the Air Force TABILS data base. The basic criterion to drive these adaptive processes is based upon the minimum-mean-square error algorithm. The solution to the problem is to find a set of filter coefficients that will achieve the minimum mean square error at the output of the adaptive filter. The resulting Wiener-Hopf equation involves inverting the covariance matrix. Direct inversion of the covariance matrix, however, is a time-consuming process. To relax the computation complexity, a rapidly convergent adaptive algorithm based upon iteratively estimating the inverse of the covariance matrix was developed. The filtering operation consists of updating the inverse matrix in a sample-by-sample manner. This algorithm lends to a simplified hardware structure because it eliminates the matrix inversion process.
TL;DR: In this article, the use of resonantly enhanced four-wave mixing to generate high reflectivity phase-conjugate waves is discussed and a physical understanding of the mechanisms underlying the nonlinear response for a simple two-level system is presented followed by a discussion of the complicating effects of pump absorption, pump depletion, unbalanced pumps, and thermal motion.
Abstract: The use of resonantly enhanced four-wave mixing to generate high reflectivity phase-conjugate waves is discussed. A physical understanding of the mechanisms underlying the nonlinear response for a simple two-level system is presented followed by a discussion of the complicating effects of pump absorption, pump depletion, unbalanced pumps, and thermal motion. Modifications of the theory to describe four-level behavior are presented and compared with experiments. The application of nearly degenerate four-wave mixing to narrow-band filtering complicated by the A. C. Stark effect is dis-cussed along with examples of experimental observations.
TL;DR: In this article, a general purpose fringe pattern processing facility was developed in order to analyze moire photographs used for scoliosis diagnoses and interferometric patterns in optical shops, where a TV camera reads a fringe profile to be analyzed, and peaks of the fringe are detected by a microcomputer.
Abstract: A general purpose fringe pattern processing facility was developed in order to analyze moire photographs used for scoliosis diagnoses and interferometric patterns in optical shops. A TV camera reads a fringe profile to be analyzed, and peaks of the fringe are detected by a microcomputer. Fringe peak correction and fringe order determination are performed with the man-machine interactive software developed. A light pen facility and an image digitizer are employed for interaction. In the case of two-dimensional fringe analysis, we analyze independently analysis lines parallel to each other and a reference line perpendicular to the parallel analysis lines. Fringe orders of parallel analysis lines are uniquely determined by using the fringe order of the reference line. Some results of analysis of moire contourograms, interferometric testing of silicon wafers, and holographic measurement of thermal deformation are presented.
TL;DR: The paper discusses in some depth the major facets of preperceptual visual processing and their interaction with instrumental image quality and noise, and highlights the statistical nature of visual performance before going on to consider a number of specific mathematical models of partial visual function.
Abstract: Based on a wide variety of fragmentary evidence taken from psycho-physics, neurophysiology and electron microscopy, it has been possible to put together a very widely applicable conceptual model of photopic visual threshold performance. Such a model is so complex that a single comprehensive mathematical version is excessively cumbersome. It is, however, possible to set up a suite of related mathematical models, each of limited application but strictly known envelope of usage. Such models may be used for assessment of a variety of facets of visual performance when using display imagery, including effects and interactions of image quality, random and discrete display noise, viewing distance, image motion, etc., both for foveal interrogation tasks and for visual search tasks. The specific model may be selected from the suite according to the assessment task in hand. The paper discusses in some depth the major facets of preperceptual visual processing and their interaction with instrumental image quality and noise. It then highlights the statistical nature of visual performance before going on to consider a number of specific mathematical models of partial visual function. Where appropriate, these are compared with widely popular empirical models of visual function.
TL;DR: This pattern recognition algorithm is verified using multi-sensor imagery, and the results are found to compare favorably to those obtained using other candidate techniques.
Abstract: Concepts, measures, and models of image quality are shown to be quite important in pattern recognition applications. Pattern recognition of imagery subjected to geometrical differences (such as scale and rotational changes) and intensity differences (such as arise in multispectral imagery) are considered. After modeling these image differences as a stochastic process, the optimal filter is derived. This filter is shown to be the principal component of the data. This pattern recognition algorithm is verified using multi-sensor imagery, and the results are found to compare favorably to those obtained using other candidate techniques.
TL;DR: In this paper, a set of conditions has been developed under which a sequence is uniquely specified by the phase or samples of the phase of its Fourier transform, which are applicable to both one-dimensional and multi-dimensional sequences.
Abstract: Recently, a set of conditions has been developed under which a sequence is uniquely specified by the phase or samples of the phase of its Fourier transform. These conditions are distinctly different from the minimum or maximum phase requirement and are applicable to both one-dimensional and multi-dimensional sequences. Under the specified conditions, several numerical algorithms have been developed to reconstruct a sequence from its phase. In this paper, we review the recent theoretical results pertaining to the phase-only reconstruction problem, and we discuss in detail two iterative numerical algorithms for performing the reconstrucction.
TL;DR: The average air-broadening coefficient for the vi and v3 ozone lines is 0.077 and 0.083 cm-1/atm, respectively as mentioned in this paper, and the measured line strengths are typically 10% to a factor of two larger than those given in the Air Force Geophysics Laboratory compilation.
Abstract: Air-broadening coefficients and line strengths are reported for selected ozone lines in the 8.8 to 10 um spectral region. These parameters were obtained from a least squares fit of the Voigt line shape to experimental ozone absorption spectra obtained with a tunable diode laser. Analysis of 11 lines in the vi and 18 lines in the v3 band suggest a transition-dependent coefficient although no definitive relationship was identified. The average air-broadening coefficient for the vi and v3 ozone lines is 0.077 and 0.083 cm-1/atm, respectively. The measured line strengths are typically 10% to a factor of two larger than those given in the Air Force Geophysics Laboratory compilation.
TL;DR: A real-time optical synthetic aperture radar (SAR) processor is described that utilizes an acousto-optic device as the input electronic-to-optical transducer and a CCD camera that serves as the optical detector and simultaneously performs the focusing of the SAR image in the azimuth direction.
Abstract: A description is given of a real-time optical synthetic aperture radar (SAR). The processor employs an acoustooptic device as the input electronic-to-optical transducer and a CCD camera that serves as the optical detector and simultaneously performs the focusing of the SAR image in the azimuth direction. The performance criteria of the optical processor that are discussed include azimuth resolution, image size in azimuth, range resolution, image size in range, flexibility, and dynamic range.
TL;DR: In this paper, the authors proposed two families of isodynes related to two characteristic directions of a plane stress field and additional redundant information, which can be applied to determine all three stress components in photoelastic models and in original machine or structural parts using isodyne coatings.
Abstract: The term "isodynes" has been proposed by Pindera and Mazurkiewicz to denote a new family of characteristic lines of plane stress fields. These lines carry information on total normal forces acting on related cross sections and yield the distribution and values of related normal and shear stress components. Two families of isodynes related to two characteristic directions yield the values of all three components of a plane stress field and additional redundant information. Isodyne photoelasticity methods can be applied to determine all three stress components in photoelastic models and in original machine or structural parts using isodyne coatings. The term "gradient photoelasticity" has been proposed by Pindera and Hecker to denote a new method of photoelasticity which utilizes relationships between the curvature of light paths in a photoelastic object and the gradients of symmetrical and distortional parts of stress/strain tensors. Utilizing a basic mathematical model of photoelastic effect presented by Ramachandran and Ramaseshan, gradient photoelasticity yields the momentary values of absolute and relative photoelastic coefficients. Both methods can be applied to determine the values of stress intensity factors for arbitrary cracks and all stress components in composite structures.