Optical Engineering is a journal with a purpose. It is designed to serve a special group of people called -optical engineers- as their professional journal. As the new editor. I am concerned with what has been a major problem for Optical Engineering: many optical engineers do not publish.

Optical metrology is in current use in most industrial plants throughout the world. Optics offers a simple, noncontacting, accurate approach to such problems as quality control, on-line process control, and performance monitoring.

The paper reviews a series of experimental stress analysis methods using moire fringe and laser speckles. An analogy is drawn between the two groups of methods showing that moire methods are special cases of speckle methods. Difference between the two approaches are also pointed out. The experimental methods discussed include the analysis of plane stress and general three-dimensional problems, static and dynamic bending of plates, steady state vibration and transient stress problems.

A multipurpose optical moire processor is described whereby one can introduce mismatches fringes, perform fringe multiplication and shifting, and separate u- and v-field isothetics. These functions can be done individually, sequentially, or simultaneously.

A technique for real-time measurement of interferograms is described which circumvents the common sources of error in traditional methods of analysis. By nulling the interferometer and simultaneously measuring the phase over a rectilinear grid, error due to geometric distortion in the interferometer (which produces apparent coma terms in the analysis of straight line interferograms), uneven pupil illumination (which shifts the apparent location of the fringe peaks), and the difficulty in fitting and interpolation of polynomials to unevenly sampled pupil functions are eliminated. Data are not interpolated or artificially smoothed, so localized irregularities in the wavefront are visible in the results. Because on-line computer processing is used, contour and isometric plots are displayed less than two minutes after data taking is completed. A unique interface design permits utilization of virtually all of the information present in the input video signal. By taking thousands of measurements per minute at each point in the wavefront, and extending the measurements over several minutes, the effects of vibration and turbulence are averaged out of the data. With a reasonably stable interferometer, the effective instrument bandwidth can be reduced to .01 Hz providing worst point peak-to-peak repeatabilities of successive measurements of better than A/100. For repeatabilities of A/20, data taking times can be reduced below two seconds. Interferometry plays a central role in the fabrication, alignment, and testing of precision optics at Tropel. From the time of our initial commitment to the manufacture of complex precision optics, we have realized the need for extreme precision in the surfacing and alignment of the individual elements. In recent years as optical systems with significant glass paths have been designed, we have begun measuring and selecting glass for homogeneity. As the requirements have become more severe, the resolution of conventional interferometry has become inadequate.

The interferometer described in this article combines a number of principles known for a long time in a system of unusual versatility. The operation modes range from classical interferometry for visual or photographic evaluation of apertures up to 150 mm diameter, to programmed scan heterodyne interferometry with fringe counting and to time- and space-resolved subfringe measurement with better than 10 nm resolution. The instrument is primarily intended as a diagnostic tool in adaptive optics to monitor the deformable corrector mirror during operation.

We have developed an automated technique for interferogram interpretation using a PDP-12 minicomputer, Cohu television camera and Hughes scan converter. A digitized image of the interferogram is stored on disc, and a small area is read into central memory. The fringe density in that region is estimated based on the number of peaks found in several line scans across the area under study. This calculation is repeated for successive small areas until a map of fringe density covering the entire part is compiled. If the fringe density map falls within an acceptance profile, the part is accepted. Experimental results demonstrate that this technique works well on interferograms having substantial variations in intensity and fringe contrast.

A method is described for performing noncontact optical gaging of complex parts in a production environment. The operational concept of the system, known as Gaging by Remote Image Tracking, relies upon an optical triangulation technique. A spot of light is projected from a gage head onto the surface of the part being gaged; an image of this spot is focused on the center of a tracking photodetector, mounted within the gage head. If the part is translated in a direction perpendicular to the projection axis, the focus spot on the surface of the photodetector will move as the surface curvature of the part changes. As a result of this movement, voltage signals are generated which provide: (1) a measure of the spot displacement on the photodetector, and (2) a signal for driving the optical head in a direction which recenters the image spot on the photodetector. The first signal, with appropriate scaling, provides virtually an instantaneous measure of the dimensional change of the part. The second signal is used to drive the system to a known distance from the part (system null). By monitoring the motion of the entire system with a linear encoder and adding this measurement to the instantaneous measure of surface curvature, the result is a fast, noncontact optical gaging system with large dynamic range.

A step-by-step process for aligning an unequal path interferometer is given. The interferometer as an optical test tool is discussed, as are configurations for evaluating a variety of optical components and systems.

Microdensitometers have already solved the problem of maintaining high speed and high accuracy across large regions of space. Modifications are needed to operate with much higher speed and in the reflection mode. Experimental results confirm accuracies better than 0.1 um over areas over 40 cm.

A 1024 x 1024 pixel image digitizer has been developed that provides high speed electro-optical scanning of image transparencies. The system consists of a linear diode array mounted on a stepping motor assembly to produce a 1024 x 1024 pixel array. An optical system projects image transparencies onto the detector at variable scales. One design utilizes a 5:1 zoom lens with 1.0x and 2.4x channels for selection of image sample spacing from 1.3 to 16 pm. Another optical design utilizes projection optics to enable sample spacing above 16 pm. In this paper, we examine the design considerations applied to this type of instrument.

A computer control algorithm utilizing the modern control theory and the heuristic artificial intelligence approach has been developed to control the MIT Scheinman electric arm. The control algorithm is task-oriented with the capabilities of accepting visual input coordination and discrete word voice commands in addition to the linguistic commands typed in by an operator at the remote terminal. The motion of the arm is considered to be composed of motion of the wrist and orientation of the hand. A human operator, always present in the control loop and interacting with the system, generates linguistic task-directed commands at the remote terminal. A task-directed command is recognized, interpreted, and decoded into sequence of subtasks. The first subtask corresponds to the motion of the wrist which is controlled by the suboptimal feedback controller. The remaining four subtasks are further broken down into combinations of six primitive movements which govern the position/orientation of the hand. The objective of the visual recognition algorithm is to identify ob-jects and their locations surrounding the arm from its environmental library or model. The library is then updated to initiate the arm to complete its execution of task. Areas and circumferences of the objects are the two features chosen for recognition. The recognition of an object is then based on the threshold value of the weighted sum of area and circumference of the object. The set of weights is trained again when a new object is introduced to the arm and incorporated into the library. The real-time implementation of the algorithm on AARL MIT arm connected to a PDP 11/45 computer shows that it can recognize the objects surrounding the arm within 50 seconds.

Diffraction pattern sampling was introduced by Lendaris and Stanley in the late 1960s for the analysis of transparency material. In the decade since the introduction of diffraction pattern sampling there have been numerous applications of the technique to imagery analysis. This paper describes several industrial applications in which the diffraction pattern is formed directly from the object without an intervening transparency. Each application is described by a different diffraction model and utilizes a different optical configuration. A specific algorithm for each application relates the diffraction data to the desired measurement or go/no-go decision. In general, diffraction pattern sampling systems are most effective when the inverse relationship between space and frequency domains yields high effective magnification so that fewer samples are required in the diffraction domain than would be required to directly sample the image. This generally results in a faster, lower cost system realization than conventional video analysis.

This paper describes the investigations of various techniques employed to compensate the degradation in the modulation transfer function as a direct consequence of charge-transfer inefficiency in charge-transfer device applications where the inefficiency cannot be neglected, then describes these techniques in applications using CCD delay lines and imaging arrays.

An Optical Parallel Logic (OPAL) device which performs Boolean algebraic operations on two binary images has been developed. This device consists of a photoconductor and an electro-optic light modulating material appropriately arranged to bring about an in-teraction between the input signals. Two such OPAL devices have been interconnected to form a half-adder circuit (one of the essential components in the CPU of a futuristic digital optical processor). Operation of an 8 x 8 OPAL device containing CdS (photoconductor) and twisted nematic liquid crystal (electro-optic light modulating material) is reported. A contrast ratio of 20:1 was obtained. A circuit composed of two such devices is shown to perform addition of two 8 x 8 binary images generating SUM and CARRY images.

A coherent optical method capable of performing arbitrary two-dimensional linear transformations has recently been studied, in which transform coefficients are given by two-dimensional inner products of the input image and a set of basis functions. Since the inner product of two functions is equal to the value of their correlation when there is zero shift between the functions, it is possible to use an optical correlator to solve for the coefficients of the transform. By using random phase masks in the input and the filter planes of the correlator, we have been able to pack many coefficients close together in the output plane, and thus take better advantage of the space-bandwidth product of the optical system. Both the input random phase mask and the spatial filter are computer-generated holographic elements, created by a computer-controlled laser beam scanner. The system can be "pro-grammed" to perform arbitrary two-dimensional linear transformations. For demonstration, the set of two-dimensional Walsh functions was chosen as a transform basis. When the resolution of the Walsh functions was limited to 128 x 128, up to 256 transform coefficients were obtained in parallel. The signal-to-noise and accuracy of the transform coefficients were compared to the theory.

Laboratory measurements were made of the sizes, shapes, and settling speeds of microscopic ocean-type particles by recording sequential transmission holograms of clay aggregates and glass shot in a settling chamber. Density values for particles that were approximate spheroids were determined using a modified Stokes settling equation. The successful application to this problem of inexpensive, off-the-shelf components and low power, HeNe lasers improves the feasibility of remote, in situ measurements of ocean particle settling dynamics.

A simple method is described to obtain a linearly variable frequency sine-wave grating. The method consists of using the wedged glass plate the back surface of which was given a suitable curvature.

For telescopes operating at optical wavelengths, the turbulence of the atmosphere limits the resolution of space objects to about one second of arc, although the diffraction limit of the largest telescopes is many times as fine. We discuss an image processing technique that uses interferometer data (the modulus of the Fourier transform) to reconstruct diffraction limited images. Data from a stellar speckle interferometer or from an amplitude interferometer can be used. The processing technique is an iterative method that finds a real, non-negative object that agrees with the Fourier modulus data. For complicated two-dimensional objects, the solutions found by this technique are surprisingly unique. New results are shown for simulated speckle interferometer data having realistic noise present.

We describe the operation and performance of two Schottky infrared charge-coupled device (IRCCD) staring sensors. Both sensors are monolithic and are fabricated from conventional integrated circuit grade silicon. The devices include a 256 element linear array and a 25 x 50 element area array of PtSi Schottky photodiodes which are sensitive from 1.1 to 4.6 pm. The 1250 element mosaic incorporates an interline transfer architecture. Signal readout for both devices is via a 4-phase buried channel charge-coupled device network and an on-chip amplifier. The focal plane may be operated between 20°K and 100°K; optimum performance is observed between 50°K and 90°K. We present examples of human thermal imaging against ambient backgrounds as well as photoresponse, thermal transfer, and resolution characteristics. Measured results are compared to theoretical predictions of performance and future developments for this class of sensor are projected.

In the early 1960s farsighted astronomers recommended a study of a very large optical telescope that would provide a major advance in light-gathering power over the Palomar 5-meter telescope. Large telescopes are expensive, however, and for a time, great gains in performance were more easily obtained by developing better detectors, or more efficient diffraction gratings or high performance reflective mirror coatings. Computers came into vogue and enabled better data extraction and analysis as well as increasing the number of observations that could be made in a given period of time. Daytime usage of telescopes for infrared astronomy became commonplace, thus extending the available observing time.