Shearing speckle interferometry using the wedge arrangement yields displacement derivative fringes that are modulated by in-plane displacement fields. In this paper, it is found that using a biprism instead of a wedge suppresses the in-plane displacement modulation effect without affecting the visibility of the displacement derivative fringes.

The transmission function of a double-exposure shearing specklegram consists of fringe- bearing and non-fringe bearing components. To obtain interference fringes, spatial filtering is performed on the processed specklegram to allow only the fringe-bearing components to pass. The spatial frequency for filtering is often determined on a trial-and-error basis. In this paper, a technique is presented to obtain a spectral distribution from which the optimum spatial filtering frequency can be deduced. Knowledge of the optimum spatial filtering frequency to recording aperture relationship enables better selection of image recording conditions.

Optical detection of disbonds in aluminum composites is demonstrated using electronic speckle pattern interferometry combined with synchronized pressure stressing. The surface on the test specimen is periodically pressure stressed in synchronization with the image acquisition rate of an image processor. This is achieved by using a two-port, low volume, transparent vacuum chamber mounted on the specimen. One of the ports of the vacuum chamber is connected to a constant vacuum source, and the other is connected to the ambient via a solenoid valve that is periodically opened and closed in synchronization with the image acquisition. Furthermore, illumination of the specimen is also synchronized with the stressing. Speckle images of the surface of the specimen undergoing high and low pressure stressing are combined with a reference speckle image and acquired at the image acquisition frequency of the detecting CCD camera. Every two consecutive images are then subtracted in the image processor and displayed in real-time. In this manner, excellent noise reduction is achieved, rejecting the effects of low frequency noise contributions such as slow object drift, air current, and thermal gradients in/around the specimen found in typical industrial environments.

The use of phase-stepping technique in speckle interferometry allows a quantitative evaluation of the interference phase with high accuracy and offers the possibility of automated interferogram processing. In this paper, an automated measuring system based on this technique is described. The effects of system parameters on the phase extraction are discussed, some applications in the fields of transient event analysis, in-plane deformation measurement, vibration analysis and nondestructive testing are presented.

This paper addresses the use of holographic and computational methods to study coupled vibrations of thin wall channel cantilever beams. Holographic methods employed were time- average hologram interferometry and stroboscopic heterodyne hologram interferometry. The computational method was based on the finite element approach. The use of these methods emphasizes determination of the resonance frequencies and mode shapes as functions of geometry of the channel beams. Comparison of the experimental and computational results shows good correlation.

The identification of a defect and the ability to determine its impact on the structure provides the information needed to determine the resulting integrity of the structure. Electronic Speckle Pattern Interferometry (ESPI) is used to help find defects. One shortcoming of ESPI is the inability to determine the impact of the defect on the overall structural integrity. Displacement and strain data from ESPI measurements can be used to determine the parameters of a structure, thus providing a quantifiable means of determining the structural integrity. Parameter estimation techniques provide the means to bring ESPI data and structural models together. An example of the integration of parameter estimation and ESPI displacement output on a fixed-free supported beam will be discussed in this paper.

A fringe evaluation system for a vibration measurement is presented, which is based on the phase-stepping technique in stroboscopic double-exposure holographic interferometry. Vibration amplitude and bias deformation distributions can be derived directly from the phase- stepped patterns. Phase errors caused by the time integration during light pulses are investigated, and the selection of optimum system parameters is discussed. Digital image processing techniques are used to improve the signal-to-noise ratio in fringe patterns and provide high quality phase maps. Experimental results with out-of-plane resonant vibration objects are presented.

An absolute-ranging interferometer will be described that is suitable for dimensional gaging and surface profiling in manufacturing applications. The interferometer has a two-frequency source and a continuously tuned or 'chirped' synthetic wavelength. The fiber-coupled experimental system uses an eye-safe 25 (mu) W, 0.25 mm diameter collimated probe beam; and has an absolute distance measurement accuracy of 3 micrometers over a 150 mm dynamic range.

A review of current testing methods used in the characterization of parabolic reflector headlamps is presented. Analysis of these tests reveal detectable figure errors in the reflectors' surfaces. These errors are related to the Zernike polynomial aberrations and then traced to their source in the manufacturing process. Two possible optical methods are discussed as substitutes to the current testing procedures.

Inspection for contaminant particles on surfaces is of major interest in the semiconductor industry as well as many others. We have developed an optical inspection instrument which detects particles as small as 65 nm and give information about the refractive index as well. Such information can be used to identify contaminant particles leading to more rapid identification of the source. The instrument is based on a scanned laser Nomarski interferometer, and measures differential phase and amplitude over an inspected area. We have previously shown that the forward scattered light from a small particle (in this case in liquid) interferes with the incident beam to produce a phase shift and amplitude change (extinction) dependent on the particle size and refractive index. This method is also applicable to surfaces by using a reflection mode. Similar to ellipsometry, plotting phase shift against extinction can provide information on both size and refractive index. We have analyzed particles on a silicon surface for a range of compositions, and found that particles can be sorted into refractive index classes such as low index, moderate index and metals.

Many wood products manufacturing processes require a 3-dimensional measure of surface roughness to determine processing parameters and product grades and values. Currently, on- line measurement of wood surface roughness is limited to visual inspection and single-point laser-based triangulation or ultrasonic systems, while most off-line analysis is based on stylus tracing. Wood has unique characteristics that complicate surface texture measurement and analysis such as the need to separate distinct causes of error of form, waviness, and roughness as well as to correlate visual grades of processing standards with 1-dimensional (1-D), 2-D, and 3-D measures. This paper discusses the performance characteristics of a laser scatter/optical imaging system for wood roughness measurement and compares them to those of a stylus tracing system. The abilities of both approaches to capture the types of roughness information required in wood manufacturing processes are discussed as well as the functionality of 1-D, 2-D, and 3-D roughness descriptors.

The scanning electron microscope (SEM) has long been recognized as a tool to give a visual image of a surface. Because of the SEM's wide magnification range both macro and micro structure can be recorded. A method which uses the SEM to record topography and provide an understanding of surface structure is described in this paper. This method is especially useful when surface gloss measurement tools do not agree with visual perception. High gloss, depth of gloss, or icy gloss are better visualized with this new procedure. A review of how macro and micro structure effects gloss, how typical gloss measurement tools can be misleading, and how the human eye differs in its perception from these tools will be made. Normal SEM operation optimizes for resolution, whereas the new method sets the sample angle to be the complement of the gloss measurement tool angle. Photomicrographs will highlight the advantages the new SEM method offers.

The primary limitation of the conventional techniques of surface roughness measurement is that the stylus has to traverse perpendicular to the machine lay always. The present research looks at the non contact, fiber optics based methodology using solid state lasers, which evaluates surface finish independent of the machine lay and surface orientation. The basic principle involves using diffracted laser light and digitizing the information to measure surface irregularities. The research has wide applications in manufacturing industries. One typical application described is the measurement of surface irregularities of a contoured turbine blade root attachment area as used in Aerospace industry. The paper outlines the optimization of the instrument using Design of Experiments or Robust Design procedure. The paper explains the steps involved in achieving reliable and quality design by taguchi experimentation.

A noncontact surface profiling technique based on active-stabilized interferometry is described. Direct frequency monitoring by the reference interferometer connected parallel to the sensing interferometer provides high accuracy in nanometer resolution measurement.

Electronic speckle pattern interferometry is elaborated in such a way that also spatially resolved image decorrelation can be measured. While retaining the typical ESPI setup for deformation measurements, a speckle correlation formalism is implemented based on the phase-shift method. In many practical situations decorrelation is directly related to surface microstructure changes of a test specimen. Feasibility and restrictions of the method are illustrated by measurements of water-induced changes at the surfaces of natural stones and by monitoring microbiological activity on stones.

Electronic Speckle Pattern Interferometry (ESPI) has been used for many years in nondestructive testing applications in laboratories. Field applications of ESPI systems have been limited by the need to restrict the amount of light, sunlight and other sources, during operation. Interference filters and other techniques have been tried to increase the applicability of ESPI systems in daylight environments. Each of these attempts have been moderately successful. The FADOF (Faraday Anomalous Dispersion Optical Filter) is a revolutionary filter that improves throughput, field-of-view, and the signal-to-noise ratio of the laser signal returning from the test object. This paper describes the basics of a FADOF and how the filter can be incorporated into an ESPI system.

An improved processing technique is described which reliably produces high quality holograms of uniform brightness.

This paper presents the use of holographic optical elements for the measurement of slope and curvature by video techniques. the curvature fringes occur as moire between two speckle slope patterns. A good agreement between theory and experimental results is demonstrated.

Large building quantitative inspection needs both automatic correction of perspective distortion and precise air and surface temperature measurement. Unfortunately these operations are heavily time consuming if performed manually by a human operator. We present a dedicated algorithm devoted to this task. The procedure first of all detects suitable reference structures put in the field of view, by means of a visual image processing and identifies the 3D position of the wall. The second step matches the thermogram with the visual image of the object. The third step performs an inverse perspective projection applying a thermal camera model, the output is a corrected radiance field. The fourth step measures the air temperature on the reference and the surface temperature map. The surface temperature can be obtained by absolute, relative or differential methods mainly depending on object emissivity value and its spatial distribution.

Considerable progress has been achieved recently in the development of new ellipsometric and polarimetry sensors that meet the requirements of an industrial environment. In particular, multidetector instruments, such as the four-detector photopolarimeter (FDP or Stokes meter), are particularly suited for fast, on-line, and real-time monitoring of industrial processes because of their simplicity, ruggedness, and absence of moving parts. We review some of these recent developments with reference to the semiconductor, steel-making, and optical- coating industries as examples.

Based on the theory of partially coherent light, an analytical scheme is established to determine the radiative properties of multilayer thin films. An accurate knowledge of the magnitude of interference effects is absolutely indispensable when measurements of the spectral transmissivity and reflectivity of thin films are used to derive optical constants of the film material. As illustrated by experiments, in many cases of practical interest neither a geometrical nor a wave optics model gives satisfactory results. A general formulation is introduced that covers this intermediate, partially coherent regime as well as the limiting cases of geometrical and wave optics. The complex degree of coherence provides a direct measure of the varying influence of interference effects on spectral measurements. An analytical approximation of the numerical approach is developed that gives a good physical understanding of the occurring phenomena. Experiments on the transmissivity of one- and two-layer films using a Fourier-transform infrared spectrometer in the medium infrared range ((lambda) equals 2 - 20 micrometers ) confirm the theoretical approach and the relevance of the addressed issue.

Moire techniques can be a powerful tool to determine deviation of a manufactured shape from a desired shape. In a traditional moire system, distorted gratings on an object are viewed through an undistorted grating. The moire contours that result represent equal depth contours over the entire viewed surface. By generating the moire patterns in video, it is possible to view the distorted gratings on a test object through a set of gratings that has been distorted by a similar but perfect object. The output is then a set of moire contours that corresponds to the differences between the two surfaces. This difference or error map eliminates much of the unnecessary information generated in traditional moire inspection and thus becomes a valuable tool for comparisons between an imperfect test object and a manufacturing standard. We have developed a variable resolution video system for creating this error map using a Michelson interferometer to generate the gratings. We have successfully applied this system to damage detection on a long, continuous lengths of pipe by having two side-by-side cameras looking at different sections of pipe and also by having one camera's view filtered with a video-taped recording of an undamaged section of the pipe.

Several methods for generation of three dimensional surface shapes from variable resolution video moire contours are described. In a classical moire system, a physical grating is projected on a target and also used to view the target. The moire contours are generated in the plane of the viewing grating. An unambiguous surface shape can then be computed by processing a set of moire images where the grating, target, or both are moved. By using an interferometer to generate and project variable pitch gratings and video technology to generate the moire contours, a 3-D surface can be scanned at different resolutions and used on a wide range of object sizes. The elimination of the physical grating also leads to surface generation techniques that do not use moving parts, increasing reliability. From these video moire contours, it is possible to uniquely reconstruct the 3-D surface, making the distinction between concave and convex surfaces. In one technique, a computer is used to mix digitized images of distorted gratings projected on the object with computer generated gratings, creating the moire patterns. By shifting one grating, it is possible to reconstruct the surface without having to move the object being scanned.

A new technique for making high speed measurements of complete scenes of three- dimensional objects is described. The sensor has several advantages over Moire, time-of-flight and conventional structured-light systems including a data acquisition time of 0.1 milliseconds, a processing time of 100 milliseconds and a measurement standard deviation of 1/2000 of the field of view. It is robust to ambient lighting, able to measure across surface discontinuities, and capable of measuring moving objects. The technique uses a fan of laser planes to illuminate the scene and two solid-state video cameras to measure the stripes in the scene. The methods for disambiguating and triangulating the stripes into three-dimensional coordinates are given and an example reconstructed scene from a prototype sensor is presented.

Quality grading of natural materials such as fur, wood and cork has traditionally been done manually. Since the grading by humans is done by assessing the visual quality of the material it has been tempting to try to automate the process using some kind of image analysis. Much research has been devoted to solving this problem. Grading rules for natural materials usually consist of a description of which types of defects are allowed for each grade and how severe they may be. The complexity of these grading rules and the variability of natural materials taken into account makes expert system or artificial intelligence approaches infeasible. This paper proposes a method for automatic grating of natural materials using statistically based classification techniques. The method involves two classification steps: in the first step a pixel wise classification of defects is performed based upon a number of features generated from the original image; the second step utilizes the relative distribution of defects to perform a final grading assessment. The method is illustrated using the grading of beech wood slabs as an example.

Time-of-flight laser radar devices utilizing a single heterostructure semiconductor laser diode as a light source have a measurement spot diameter from a few millimeters to several centimeters depending on the optics and the required optical output power. Inhomogeneities in the reflectivity and surface profile of a target inside the area illuminated by the laser beam can be a source of error in distance measurement. If inhomogeneities, the intensity profile of the transmitter beam on the target surface and the shape of the received optical pulse in the time domain from a flat homogeneous surface are known, the shape of the received pulse from an non-homogeneous target surface can be calculated. As the measurement spot sweeps over the surface of the target its shape in the time domain varies, causing distance error. If the timing discrimination method used in a laser radar device is known, the distance error can be estimated by means of a numerical analysis. A simple method of estimating the error caused by the finite measurement spot size together with inhomogeneities of the target surface is presented here. A number of real measurement results obtained with a prototype of a commercial laser radar device are presented, together with simulation results. Both sets of results show that a spot size of several centimeters together with large variations in the reflectivity of the target surface can really cause an error of some centimeters in distance measurement.

In a steel bar rolling mill, billets are run through a series of rolling stands to produce steel bars with various cross-sectional shapes. An optical gauge is used to provide on-line measurements for the purpose of statistical process control of the mill operation. The orientation of the bar in the gauge must be determined in order to accurately infer critical dimensions. An algorithm is developed for aligning the optical image to remove any bar twist. Bar size determination from the aligned measurement sequence using an exact interpolation technique is also described.

The performance of range imaging devices is determined by many factors, but no common practice exists for testing and evaluating them. We describe in this paper a test method developed for our internal use which estimates certain specific performance factors such as resolution, repeatability and accuracy. The method is designed especially for range imaging devices having millimeter level accuracy and a large measurement range (1 m ... tens of meters).

To increase the functionality and complexity of microelectronic components, new packaging techniques such as multichip-modules (MCMs) are used. However, certain MCM manufacturing processes are limited by the yield and reliability of the electrical contacts formed by the solder interconnects or bumps. In this paper we describe an optical measurement system to detect defective electrical contacts before bonding occurs. By using a high-speed, laser-based point range sensor and a high speed part transport system, critical solder bump features such as volume, height and planarity can be measured.

Practical, compact time-of-flight (TOF) laser distance meters have been constructed for many industrial applications using a semiconductor laser as the light source. The optical pulse power of such devices has varied in the range of 1 to 30 W, rise times between 1 and 3 ns and pulse widths between 5 and 10 ns. The lasers have usually been DH lasers at low pulse powers (< 5 W) and SH lasers with 1 to 3 stripes at higher powers (5 - 30 W). A capacitor discharged by an avalanche transistor has been widely accepted as the pulser circuit for producing fast electric current pulses for lasers. Improvement of the timing resolution of the measurement result requires an increase in the slew-rate of the received light pulse or a decrease in the noise level. Use of a commercial non-pigtailed 1-stripe SH laser and a commercial power transistor in the avalanche operation mode yielded an optical pulse, the rise time of which was clearly less than 1 ns (rise time of the electric pulse was 3.5 ns). It was noticed in the tests that the rise time of the light pulse varied according to the measurement angle of the received light and the temperature of the laser. In order to obtain fast laser pulses it is necessary to control the temperature and the space angle in which the radiation is collected. There are also big differences in the shape of the optical pulse between different items of the same laser type and for this reason selection of the laser items is needed.

Active fibers, i.e. optically pumped doped fibers, have been developed and studied intensively during the last few years, and an optical amplifier based mainly on erbium-doped fibers has just been launched on the expanding telecommunications market. Fiber lasers have a market of their own in the sensor applications. The use of fiber lasers as pulse sources in laser rangefinder applications is studied here. The main advantages with respect to high energy pulses and a small emitting area are listed, the problems and disadvantages are discussed and some practical solutions to these problems are given. Possible Q-switching techniques for obtaining short, powerful pulses (> 10 W) of about 10 ns are studied as are liquid-crystal, PLZT crystal, acousto-optic and Pockels Cell modulators. Finally, the practicability of these modulators for laser pulsing in industrial environments is discussed.

Nowadays several techniques are available for the inspection and crack detection in internal cylindrical surfaces as, for instance, those of heat exchanger pipes, being miniaturized optical probes (endoscopes, CCD cameras, etc..) and eddy current probes the most commonly used in industrial applications. Both techniques, however, present strong limitations. To overcome these limitations a new approach, based on the use of an optical fiber linear array, has been explored by our group, for which a specifically designed fiberoptic probe has been exhaustively tested in order to evaluate the possibilities of this technique.

Laser triangulation range sensors mounted in coordinate measuring machines are finding increasing use for dimensional measurement applications. These applications include confirming that part dimensions are within tolerances and, in some cases, providing the dimensional database needed to reverse engineer products. This paper summarizes the results of recent studies on the performance characteristics of triangulation probes, describes certain effects which are not commonly understood, and presents concepts for improved designs and data analysis.

A novel automated inspection technique to recognize, locate, and quantify damage is developed. This technique is based on two already existing technologies: video moire metrology and artificial neural networks. Contour maps generated by video moire techniques provide an accurate description of surface structure that can then be automated by means of neutral networks. Artificial neural networks offer an attractive solution to the automated interpretation problem because they can generalize from the learned samples and provide an intelligent response for similar patterns having missing or noisy data. Two dimensional video moire images of pipes with dents of different depths, at several rotations, were used to train a multilayer feedforward neural network by the backpropagation algorithm. The backpropagation network is trained to recognize and classify the video moire images according to the dent's depth. Once trained, the network outputs give an indication of the probability that a dent has been found, a depth estimate, and the axial location of the center of the dent. This inspection technique has been demonstrated to be a powerful tool for the automatic location and quantification of structural damage, as illustrated using dented pipes.

The departure from flatness of a steel plate after rolling, including center buckle and edge wave undulations, is an important parameter indicative of product quality. By monitoring the flatness of steel plates during manufacturing, information can be fed to the rolling press to control the process. A quantitative, three dimensional technique for measuring the surface structure of objects is moire interferometry. This paper presents the results of a project to demonstrate the feasibility of using moire interferometry to monitor the flatness of steel plates. This project involved the design and construction of a demonstration moire optical head, the coding of a fringe interpretation algorithm, and a performance evaluation of each.

The measurement of part diameters is an important factor in metal turning operations, increased production demands have suggested the use of methods that adjust subsequent cuts depending on the previous operations. This paper describes the design of a laser based gage made specifically for measuring parts on the machine tool to a high accuracy. The tri-beam gage uses three beams of light to measure the local curvature of the part in a manner similar to a V-block gage. The diffraction of the light beams that touch the sides of the part are sensed by a detector array. The distinctive diffraction pattern is correlated to locate the edge of the shadow to a very high precision. The properties of this design include: calibration that is independent of the machine tool scales, non-contact damage free operation, high speed of measurement, low cost of the gage, and the ability to measure parts in motion. This paper will describe the design considerations of this gage including issues of design angle of the V, light source coherence, thermal drift, noise effects, stability, and accuracy.

Several applications require agile and accurate positioning of a high power laser beam. Agile positioning is generally accomplished via manipulation of some jointed support apparatus such as a robot arm. The size and weight limitations of high power lasers prevent placement of the laser at the final node of the robot arm. Hughes has developed a continuous, automatic, closed loop, alignment system for robot arm propagation of a high power laser beam based on conical scan tracking. The Hughes design employs a low power, continuous, HeNe laser for control purposes which is co-aligned with the high power beam. The control system receives its continuous feedback from a retro-reflective annulus located at the final node of the robot arm. The system includes a coelostat at each joint enabling complete angular coverage. The type II control system operates with a 30 Hz bandwidth ensuring precise alignment over typical arm velocities and accelerations.

Laser material processing is becoming more and more important for high precision applications. This precision is often not keepable in laser machines with 'flying optics' because of the varying distance between laserresonator and focussing optics, the distance between focussing optics and 'TCP' (focal point) varies too; and because of moving mirrors along the beam propagation path, the angle between beam axis and machine axis is fluctuating during the process. These effects have an impact on the result of the process and diminue the effectiveness and precision of laser material processing. We have developed and tested a system, consisting of an active mirror and a sensor that is positional directly in the 'flying optics' before the focussing optic. The active mirror can be tilted in both directions perpendicular to the beam axis and is spherically deformable. The sensor couples out a minute of the laser beam by a hole grating and measures the important beam parameters. A control unit drives the adaptive mirror with regard to the sensor signals. The system makes the 3-D on-line control of the focal point possible.

An innovative anthropomorphic robot laser is described. The beam is transmitted from the source to the sensorized focusing head by a chain of flat high reflective mirrors, located inside the robot structure. This machine can be joined to whatever laser source up to 8 kW and is able to perform cutting, welding and heat treating processes mainly by changing the final optical head. In order to obtain constant and repeatable results, during laser processing, it was necessary to develop suitable sensorized systems. The paper treats the activity and results obtained in the first phase of the research where the feasibility of a new sensorized head, for controlling hardening process, has been experimentally tested. The statistical methodology 'Parameter Design' was used in order to obtain an accurate analysis over the process field. Several tests have been performed both in oven and with laser beam. A good correlation between sensor signals and case depth was found. A prototype of optical head will be presented.

The ability to measure in-plane displacement on the surface of a rotating structure under service conditions and real-time analysis to provide component strain distributions would form the ideal experimental optical technique. Pulsed Laser ESPI which can display interference patterns for in-plane displacement in conjunction with the Fourier transform method of fringe analysis is one attractive approach which is coming closer to this ideal. The optical system used enables a wide range of rotational speeds to be covered with tangential velocities up to 300 ms^-1. The paper describes how the fringe analysis may be carried out using a 80486 desk top computer.

The 3D vision system described in this paper has been developed to calculate the 3-D surface patches of objects illuminated by a projected grid. In order to exploit the parametrization offered by the projected grid, we have to extract the imaged grid as a network of curves, rather than a graph, so the 2D and 3D processings are based on the curve idea. One difficulty in this approach is to establish the correspondence between the original grid and the imaged grid. Different from other published methods, the correspondence is done curve per curve without any ambiguity by using geometrical and global constraints. The 3D projected grid is calculated per curves by triangulation, to obtain 2 independent families of 3D curves allowing to calculate the shape parameters.

An optical non-contact profilometer is presented for in-process measurement of super-smooth surfaces, applying a common-path interferometer and signal correlation processing technique. Environmental disturbation and laser amplitude noise, which commonly exist in similar instruments are overcome in the system. The overall simplicity of the optics and electronics, the low cost of components and the ease of alignment make this a convenient system to implement.

Progress in development of the advanced optical materials for window applications requires the necessity of creating non-contact optical methods to characterize properties of thin film materials and their structures. Many existing systems for scanning control such optical thin films structures have limited spatial resolution as laser shift interferometers or need to be calibrated as methods of the intensivity distribution registration in diffraction orders. Some attempts and demonstrations to increase spatial resolution of the phase microscopes have been made. However the field amplitude-phase methods of surface/structure registration contain from theoretical point much more possibilities. The necessity of creating direct real time scanning methods to control thin films structures in the mode of registration coinciding with operation mode of their industrial application with appropriate for this application spatial resolution has stimulated preparing of this paper.

This paper reviews a patented technique for measuring (or monitoring) XYZ coordinate positions. Unlike theodolites, which depend on a well-established instrument position for measurement accuracy, this system relies on mechanical accuracies that are easily built into custom targets. The targets consist of several elements organized to create coordinate systems within the camera field of view. These systems are related to one another by software to produce the desired measurements. Target elements may be active (LED's, integrating diffuse sources) or passive (retro-reflective circles). Position changes as small as 0.002 inches at distances over 20 feet are repeatably detected. In principle the stand off distance can be increased to over 100 feet. Several applications are discussed in addition to system specifications.

In this paper, fundamentals of electronic shearography and electronic holography are outlined. Equations for quantitative interpretation of the electronically generated interferograms are discussed and their implementation is presented and illustrated by representative examples. These examples were obtained by operating the shearographic and holographic systems side by side. Responses of the object to static and dynamic loads were recorded using double-exposure and time-average interferograms. Comparison of the electronically generated shearographic and holographic results shows good correlation with each other and also with the theoretical results.

Vibration characteristics of a submillimeter cantilever beam of variable cross section are investigated using computational and hologram interferometry methods. The computational method is based on the finite element approach. The hologram interferometry methods are based on the time-average and stroboscopic heterodyne hologram interferometry approaches. Mode shapes and resonance frequencies of the beam are determined as a function of its length. Comparison between the finite element results and the holographic results shows good correlation.

A virtual image superposing comparator is described which can be used to classify scratch widths, dig diameters and dig densities when verifying the surface quality of optical components. The magnified virtual image of an apparent defect is visually superposed anywhere on the viewing plane of a complete set of large scale standards in a common visual field. By positioning the virtual image of a defect next to or between any corresponding standard, it is possible to make direct, comparative measurements. The density of digs is verified by visually superposing the circular array of the standards over separated digs or groups of digs and summing the classes of digs appearing within the array. Unlike the current, full scale, scratch and dig surface quality standards, the large scale scratch and dig standards can be objectively calibrated by conventional methods and can be accurately and inexpensively reproduced. A derivation of infinity for the 'standard' eye; a coefficient for system scale factor and system magnifying power; an analysis of the effect of relative object spacing, tilt and contrast on comparative measurement; and two surface defect slide charts for expediting the scratch and dig area density computations specified in Military standard specifications are described.

The conditions of obtaining an aberration-free image of a point source formed by an aspherical diffraction grating with straight-line nonequidistant grooves are investigated theoretically. As shown, a perfect geometric image can be obtained, if a radiation source and its image lie on a straight line passing perpendicular to the grating normal and being a rotation axis of a grating surface.