Over the past several years, considerable progress has been made in the art and science of hologram recording and in the application of this technique to a variety of problems. Commercial display holography at long last appears to be securing a firm footing with the recent success of embossed holography and impressive sales activity in large-scale reflection and rainbow holograms, particularly in Europe and Japan. Technical, scientific, and industrial applications in special optical systems and in metrology have been holography's mainstay for several years, however. This side of holography often does not have the glamour of the display hologram, but the value of holography in a great variety of technical applications is widely recognized, and innovative techniques are being developed at a significant rate.

Holographic optical elements and computer-generated holograms (CGHs) offer many attractive properties and uses. In this review, we consider the use of holography in pattern recognition, with specific attention to recent work with CGH elements.

A holographic optical processor has been built for efficient, fast, wide-field detection of submicrometer defects in repetitive subject formats such as integrated circuit photomasks. This paper describes the advantages gained by combining holography with standard optical processing techniques and presents results obtained on a 2 in. field-of-view prototype and 7 in. field-of-view fully automated mask inspection system.

A truly noninvasive measurement technique for plasma velocity has not been demonstrated. Plasma velocities have been inferred using laser Doppler anemometry or photographic analysis of the position of smoke or small particles. This paper describes an alternative method based on the refractive index change created in a plasma by a gaseous probe material injected into the plasma. This disturbance of the refractive index can be monitored using interferometry. A multipass real-time holographic interferometry system was used to follow the changes of the interferometric pattern, and the data were recorded using high speed cinematography. A transparent model of an industrial plasma torch was employed in these studies, and a number of different types of trace gas materials were used to track the plasma flow. Using a combination of multipass interferometry and a laser line absorbing gas, sufficient interferometric sensitivity was obtained to determine plasma velocities in the 100 m/s range. Based on these results, a working plasma torch was constructed. Further studies are planned using this torch and actual plasmas.

Vertex detectors with good spatial resolution are ideal devices for the detection of short-lived particles (mean lifetime > 10-13 s; mean distance traveled before decay- um) produced in high energy interactions. The bubble chamber equipped with high resolution photography is one such vertex detector. However, improving the resolution in photography results in a very rapid decrease of the depth of field, thereby rendering most of the chamber optically inaccessible. Using holography instead of photography remedies this problem by decoupling resolution and depth of field. This paper reports on our recent work in the use of a two-beam holographic technique for a large Freon bubble chamber (80 cm in diameter and 100 cm deep). The results reported here are for a full-scale setup in air with test targets to simulate bubble chamber tracks and in some cases a full-scale 28 cm thick glass plate to simulate chamber windows. This bubble chamber is the vertex detector for a hybrid spectrometer system that will be used for two of our forthcoming experiments at the Fermi National Accelerator Laboratory: the first to search for the short-lived charmed particles and the second to establish the existence of the T neutrino by observing the decay of the T lepton. We demonstrate that a 30 resolution can be achieved throughout the entire volume of the chamber. Specific details pertinent to achieving this resolution are also discussed. We also report on the construction of a semiautomated high precision measuring apparatus that will be used to scan and measure bubble chamber holograms.

The three-dimensional imaging capability, enormous information storage capacity, and the related very high resolution of images when they are correctly reconstructed combine to make holography an inspection tool of immense power and utility in capital-intensive industries. This paper describes work in the U.K. electricity-generating industry aimed at enabling high grade holograms to be routinely recorded in a wide range of industrial situations where high speed acquisition of visual data is desirable. Specific applications to be described are holography of nuclear reactor cores and of irradiated fuel elements for inspection after withdrawal from the reactor. Accurate recon-struction of images and precise, three-dimensional measurement of recon-structed images in a laboratory environment are then undertaken with computer-controlled micronlanipulator equipment traversing a television camera within the real image. Measurements of a 1 m long fuel element to within 0.1 mm have been demonstrated and resolutions of 50 line pairs/mm have been obtained on the reconstructed object. The paper describes work on in-reactor inspection in which the pulsed ruby laser used to record the holograms is routinely aligned to a 15 m beam relay and remote holographic head. Three-dimensional reconstruction and hologrammetry are described, and plans for automated measurement and inspection using image enhancement techniques are discussed.

This paper presents an improved technique that eliminates the ambiguity in holographic fringe interpretation. The technique is based upon generating a high density linear phase carrier. Introduction of the carrier results in the formation of a fringe pattern that has monotonically increasing fringe orders. Any deformation of the object under study produces a corresponding perturbation of the carrier pattern. If the carrier dominates, the perturbed pattern continues to have monotonically increasing fringe orders and thus allows the fringe order to be determined at any point without ambiguity. The phase change due to deformation alone is obtained by subtracting the known linear carrier from the modulated fringe pattern. The process of data reduction is so straightforward that skillful human interpretation is no longer required. This simplification of the fringe interpretation process will pave the way for automatic data acquisition in holographic interferometry.

In normal double-exposure holography with impulse loading, it is very difficult to locate defects because fringe clutter, which is due to random motion between exposures, often dominates the fringe shifts caused by the presence of subsurface defects (cracks, disbonds, etc.). We attempted to simplify the defect location problem by developing a concept more amenable to automatic readout techniques. Our approach to incorporate this change is quite simple. We swing the object beam between the two exposures, which adds a linear fringe to the reconstructed image. Proper selection of the fringe frequency (angle of object beam swing) and the loading force creates a reconstructed image laced with linear fringes that have fringe shifts at the defect locations that are highly visible. We describe the theory of the process. Experiments performed with static load illustrate that the defect is seen as fringe shifts on a linear carrier. Both through cuts and rear-surface cuts in a metal test plate were used to simulate defects. We further show that the defects have characteristic Fourier signatures different from those of the carrier.

Reflection holograms of the volume-phase type fabricated with dichromated gelatin have the advantages of achieving efficiencies very close to 100%, very low noise, and, due to their wavelength selectivity, a chromatic dispersion that can be acceptable in many applications. For several years, the production of these holograms has been investigated with the goal of controlling their processing and achieving high quality and good repeatability. Holographic spherical mirrors with dimensions larger than 82 cm were used in the holographic Pancake Window optical simulator suitable for the training of pilots. These holographic spherical mirrors were also built as compound holograms providing a "white". spectral response very similar to that of conventional mirrors. Pro totypes of holographic combiners were fabricated and analyzed. Holographic mirrors were also manufactured for use as notch filters, which selectively reflect very narrow spectral frequencies, for example, laser radiation. They offer the advantages of high optical densities with large field-of-view coverage and high photopic transmission.

The manufacturing technique and experimental results for a narrowband holographic reflection filter that is linearly tunable over the 1.2 to 1.6 um wavelength region are described. The filters have greater than 90% reflection efficiency with spectral bandwidths less than 20 nm at full width at half maximum (FWHM). One application of this component is as a single-channel selector for wavelength-multiplexed optical fiber systems.

An optical system containing multifaceted holographic optical elements (HOEs) was constructed to correct for aberrations introduced by a nonflat window in NASA laser Doppler velocimetry (LDV) experiments in an internal combustion engine. For these experiments, two green beams separated by 82 mm in a vertical plane and two blue beams separated by 82 mm in a horizontal plane were brought into coincident focus inside a thick walled sapphire cylinder. The focal power needed to bring these beams to a common focus and the aberration correction required by the presence of the cylinder were built into the holographic elements. A modular optical breadboard system was configured to fabricate, test, and use the custom-made HOEs. Additional HOEs were also fabricated to provide aberration correction and color separation for the multi-spectral output waves emerging from the focal volume. Compensation for the birefringence of a thick sapphire cylindrical window in the experiments was also accomplished. A general system such as we have built is useful wherever high efficiency, localized optical correction of wavefront errors is needed in LDV or other optical experiments.

By combining advances in lithography and electromagnetic grating theory, we recently have demonstrated the ability to produce highly efficient binary gratings and binary lenses for use at 10.6 um. Electromagnetic theory predicts that binary gratings with the proper parameters can achieve a first-order diffraction efficiency of nearly 100%. If the periodicity of the grating is on the order of the radiation wavelength, all of the orders become evanescent except for the zero and positive first orders. By choosing the depth-to-period ratio and duty cycle properly, the zero order can be suppressed, placing virtually all of the incident radiation into the first diffracted order. Theoretical calculations have been done only for constant period gratings. However, assuming a lens pattern to be a minor perturbation of a grating, we succeeded in producing an f/5 binary lens with a diffraction efficiency of 96% at 10.6 um. Furthermore, because of the high efficiency of these elements, it becomes practical to consider using more than a single diffractive element in a system. We have constructed a simple afocal telescope from two binary lenses. The telescope has a 2 in. entrance aperture and a magnification of 5. A final point to be considered is the wavefront quality of these elements. Electron beam machines, which are used to write the lens patterns, are designed to draw the pattern in a raster fashion. This quantization sets a limit on the quality of the lens pattern.

A honeycomb close-packed microstructure can be recorded in a positive photoresist layer by a simultaneous exposure of three coherent laser beams. A close-packed square structure results from a simultaneous four-beam exposure. The structure consists of parabolic-shaped depressions in the surface. By replication and embossing techniques, it is possible to impress the mirror image of the microstructure into plastic, such that the top surface consists of parabolic-shaped posts, or microlenses. The size of each microlens can be varied from around one micrometer to a millimeter or more. There are wide-ranging applications for such regularly spaced and precise structures, extending from solar concentrators to three-dimensional imaging devices.

We report here the development of an integrated capability for writing computer-generated holograms (CGHs) using either of two commercially available electron-beam lithography systems. These binary, chrome-on-glass holograms have been used extensively for aspheric optical testing and also have applications to the interferometric recording of holograms. Algorithms are described for encoding CGHs for drawing by e-beam systems. Limitations of e-beam CGH fabrication are discussed. A self-contact lithography and ion milling process is described for con-verting chrome-on-glass holograms into 40% efficient, environmentally durable all-glass holograms.

Holography with a new photopolymer system, Polaroid DMP-128, is described. Films of DMP-128 from an aqueous solvent are coated on either solid or flexible substrates. The resulting films, when stored dry, have a shelf life that exceeds nine months. The dry films are inactive and must be incubated for a few minutes in an environment of approximately 50% RH before laser expo-sure. Recording is possible with either blue (442 nm, 488 nm), green (514 nm), or red (633 nm, 647 nm) laser light. Exposure of 5 mJ/cm2 is sufficient for high diffraction efficiency (80% to 95%) transmission holograms, while 30 mJ/cm2 is required for bright reflection holograms. It is not necessary to exclude atmospheric oxygen during hologram recording. Refractive index modulation of 0.03 is routinely achieved. After laser exposure a uniform white-light illumination is used to complete the photopolymerization. A single processing bath yields holograms with good environmental stability. An additional processing bath yields images with exceptional resistance to high humidity.

A review of color holographic imaging techniques utilizing a white-light source is presented. These techniques consist of reflection holography, rainbow holography, spatial encoding, coherent and white-light speckle encoding, double-aperture encoding, a dual-beam encoding principle, incoherent spatial encoding, source encoding, and white-light Fourier holography. The holographic construction and reconstruction processes of these techniques are explained, and experimental demonstrations of the techniques are given.

This special issue of Optical Engineering, which includes the five papers that appeared in the previous (July/August 1985) issue as well as the six papers contained here, com-memorates the 20th anniversary of holographic interferometry. As such, it is dedicated to all the known and unknown inventors, coinventors, scientists, researchers, workers, students, and others who have contributed to the development of holographic interferometry.

Holographic interferometry is increasingly being used in industry to detect defects in large structures (holographic nondestructive testing) and to measure the deformation of an object subjected to nondestructive stressing (static or dynamic). Applied forces often lead to a large parasitic object motion that forbids the exploitation of the interferograms. Several methods allow compensation of object motion (sandwich holography, for example) but no one method is able to correct a general displacement (three translations plus three rotations). We propose a new method, simple in principle, that allows compensation for any motion with any amplitude, in the limit of the coherence length of the laser. Basic ideas of this method are given. Experimental checking has been done with both real-time and double-exposure holographic interferometry. The diffuse test object was subjected to various displacements: in-plane translation of 5 mm, out-of-plane translation of 1 mm, and rotation of 30' around an axis located in its plane. With these amplitudes no interference fringes are visible, but in spite of this fact the compensation is possible: interference fringes progressively appear, and finally the infinite fringe is obtained. Moreover, when used with a computer this method should allow the measurement of the different components of the motion even if its amplitude is greater than the dimensions of the object.

The use of heterodyne and quasi-heterodyne techniques in holographic interferometry allows a quantitative evaluation of the interference phase with high accuracy and offers the possibility of automated interferogram processing. In this paper, the fundamentals of these electronic methods are reviewed, the possibilities and limitations are discussed, and some applications in the field of displacement and strain measurement are presented. Heterodyne holographic interferometry is well suited for scientific applications in which very high accuracy (1/1000 of a fringe) is needed. Quasi-heterodyne holographic interferometry with video processing is adequate for industrial applica-tions in which high speed and medium accuracy (1/100 of a fringe) are required.

Principles of pulsed laser double-exposure hologram interferometry are discussed. In this presentation, emphasis is placed on biomedical applications of the method. Procedures for quantitative interpretation of images obtained during reconstruction of holograms are presented and illustrated with representative examples. The procedures for quantitative interpretation of holograms allow determination of translations, rotations, and strains of an object, including determination of and compensation for the object's rigid-body motions. A system for automated interpretation of holograms is also discussed. The results shown relate to in vitro and in vivo studies of tooth and bone motions.

Probably the most severe obstacle in the widespread use of holographic interferometry has been the methodology for extracting the data from the hologram in a timely fashion. Holography technology makes possible the recording of more data than can normally be used because of this limitation. In recent years great strides have been made toward solving the problem of automated data reduction. Available com-puter power, new codes, and detector arrays have played key roles. This paper summarizes the current state of the art in automated data reduction of holographic interferograms.

This paper deals with the quantitative interpretation of time-average holograms of vibrating objects. It is shown that the images obtained during reconstruction of such holograms are modulated by a system of fringes described by the square of the zero-order Bessel function of the first kind. A procedure for quantitative interpretation of these fringes is described and illustrated with examples. The experimental results, obtained directly from the time-average holograms, show good agreement with the exact solution of the differential equation of motion based on the beam theory and with the mode shapes determined by the finite element modeling of the vibrating beam.

Heterodyne hologram interferometry was used to study load-deformation characteristics of computer microcomponents that were surface mounted on a printed circuit board. The board was assembled as a cantilever plate and subjected to cyclic flexure loading according to industry standards. The flexure loading was sinusoidal at 0.1 cps with an amplitude of 1.25 mm (0.050 in.) at the tip of the board. Double-exposure heterodyne holograms were recorded under a number of conditions specified by the magnitude of deflection at the board's tip and the number of accumulated flexure cycles. Data obtained during reconstruction of heterodyne holograms were used to compute displacements and strains along the leads connecting the component to the printed circuit board. The experimental results show that lead displacements were on the order of 1.2 um, while strains were up to 0.054%. The results obtained in this study will be used as input to finite element models of computer microcomponents.

It is well known that detector response nonuniformity results in pattern noise with staring sensors that is a severe problem in the infrared due to the low intrinsic contrast of IR imagery. The pattern noise can be corrected by electronic processing; however, the ability to correct for pattern noise is limited by the interaction of interscene and intrascene variability with the dynamic range of the processor (number of bits) and, depending upon the algorithm used, by nonlinearities in the detector response. This paper quantifies these limitations and describes the interaction of detector gain nonuniformity and detector nonlinearities. Probabilistic models are developed to determine the maximum sensitivity that can be obtained using a two-point algorithm to correct a nonlinear response curve over a wide temperature range. Curves that permit a prediction of the noise equivalent differential temperature (NEAT) under varying circumstances are presented. A piecewise linear approach to dealing with severe detector response nonlinearities is presented and analyzed for its effectiveness.

An in situ instrument designed to measure the spectral attenuation coefficient of seawater and the ocean remote-sensing reflectance from 400 to 750 nm is in the test and development stage. It employs a 256 channel, charge-coupled type of linear array measuring the spectral intensities diffracted by a grating. Examples of the types of data delivered by this instrument have been simulated using a breadboard laboratory instrument and an above-water, solid-state radiometer. Algorithms developed using data from these instruments provide measures of chlorophyll a plus phaeophytin a concentrations from less than 0.1 to 77.0 mg/m3, gelbstoff spectral absorption coefficients, and detrital spectral backscattering coefficients for waters of the west Florida shelf.

In this paper we discuss a method to achieve expansion of a fiber optic bus on the base of a distributed star configuration. Also, we demonstrate the fundamentals of a fiber optic network with commutation properties that handles high traffic and a large number of subscribers.

Thermal (2.0 to 5.6 um) measurements of the normal emissivity EN of several diathermanous materials having slightly different refractive indices were made at 15.2 °C, 4.9 °C, and -5.6 °C. Calculations of the total hemispherical emissivity EH were made from EN and plotted against the optical depth PyaxX. A comparison of these data with a model proposed by R. Gardon [J. um. Ceram. Soc. 39(8), 278 (1956)] indicates that at near-ambient temperatures they agree very closely. This comparison presumes that the narrow range of refractive indices about n = 1.5 associated with these specimens would not preclude them from being treated as having a value of 1.5. It has been observed that EN > EH by 5% for both weakly and strongly absorbing materials. This is attributable to phase differences in the multiply reflected internal radiation attempting to exit the specimen throughout r steradians. Other radiation properties of the materials, i.e., diffuse transmittance TD, absorption coefficient Thx, and absorption index k, were calculated.

Multiplexing, as applied to interferometry, is the combination of separate interferometric tests to yield additional information about test object deformation. This paper details the multiplexing of moire interferometry to yield additional information through (1) object test comparison, (2) comparison of directional components of test object displacement, and (3) zero-order fringe location through secondary moire pattern analysis.

An empirical TV range performance prediction methodology is described that depends on only two TV camera merit functions. These merit functions are the MRS, or minimum resolvable signal, and Ir, the background reference current. Both can be measured. This methodology differs from other TV system performance models in that it does not require detailed knowledge of the camera design characteristics, nor does it require extensive measurement of merit functions. The described methodology removes the need to rely heavily on incomplete theoretical models and replaces them with a largely empirical method more likely to yield reliable results. The simplified approach allows many camera designs to be optimized for application requirements and evaluated without an extensive modeling effort.

An example of a physical system whose mechanical accuracy can be improved by feedback control is a motor-driven spindle. Such a system is being used as a test-bed to study measurement and actuation systems as well as control algorithms. The specific apparatus reported utilizes an eddy-current probe for runout error measurement, a piezo-electric crystal to move the spindle to reduce the error, and a minicom-puter using a FORTRAN program for the feedback controller. The spindle runout before correction is in the 2.5 itm (100 gin.) range; with the error correction system in place, this error is reduced to less than 0.25 um (10 pin.)-an order of magnitude improvement. While the corrected runout figures for this spindle are still above those of a precision air-bearing spindle, the technique presents new possibilities for precision spindle performance including correction for wear, thermal deformations, and unbalanced loads.

The medical motivation for interactive manipulation of 3D data via a 2D display device is presented. Four specific topics are described: (i) interactive orientation specification, (ii) 3D83, a program currently being used in clinical practice, (iii) directed-contour-based display and manipulation, and (iv) binary-array-based display and manipulation. Timings are reported for medical exam-ples. Advantages and disadvantages of the various approaches are discussed.

In image-forming optical systems the image of a three-dimensional object consists of a superposition of focused and defocused object layers. For a quantitative evaluation of the object it is necessary to decompose the superposi-tion image into different images corresponding to single object layers. For this purpose the object radiation is measured with different optical transfer func-tions of the imaging system, for example, by simply changing the focus plane. Each image contains focused and defocused parts of the object and can be described as a linear equation of the object layers, assuming linear space-invariant imaging properties. From these images the real object distribution can be calculated by the evaluation of the resulting linear system of equations in the Fourier domain. Due to noise in the detected images it is only possible to get an estimate of the true object distribution. In our case this estimate is based on an integral minimal mean square error in the reconstructed object. The algorithm is presented and demonstrated by simulation experiments and reconstructions of real human cell images in optical microscopy.

The generation of subnanosecond dye laser pulses from an excimer pumped dye laser, using a saturable absorber, is investigated. Subnanosecond pulses from rhodamine 610 and rhodamine 640 dye lasers, using cresyl violet as a saturable absorber, are reported. Self-pulse modulation was also observed.

An analysis of the detector size effects on the performance of a bulk acousto-optic spectrum analyzer is presented. The performance is measured in terms of peak-to-sidelobe ratio, which is a measure of the analyzer's dynamic range. The numerical results suggest that the system's performance is significantly affected not only by the detector's size but also by the location of the sidelobe within a detector element. These numerical results can be used to guide the choice of detector sizes in practical applications.

An unusual experiment is described for determining what influence infrared presensitization has on the spectral sensitivity of a film.

In order to maintain fragments of fractured bones in a state of immobilization, the use of an external rigid frame has proved to be very advantageous. Confronted by contradictory requirements, the conception of external fixation has, however, been a difficult task. The present paper aims to show, through three examples of varied bearings, the interest of holographic interferometry in external osteosynthesis. The first example deals with the mechanical behavior of a key element of the fixation device the ball joint submitted to realistic loads. The last two examples compare two models of ball joints as to their characteristics of rigidity and of resistance to slipping. Whereas in the former case holographic interferometry primarily fulfills the function of a prelude to the modelization work, in the latter cases it serves to formulate an engineering diagnostic. The findings relate to the remarkable elastic behavior of the ball joint, to the effectiveness of a lightened bowl design, and to the fact that cousin models may behave quite differently as to their resistance to slipping rotations of the bar. In comparison with other experimental methods, holographic interferometry appears to be very competitive and result-oriented and, as such, is expected to multiply applications in similar evaluation tasks.

I suppose it is rather obvious that without authors there would be no journal to publish, and without readers there would be no need to publish it. What Its perhaps less obvious is that without a solid corps of qualified referees as well, it would be highly unlikely that a journal of high quality could be published at all. Because of the importance of the review process, I have chosen it as the subject for this editorial column.

I suppose it is rather obvious that without authors there would be no journal to publish, and without readers there would be no need to publish it. What is perhaps less obvious is that without a solid corps of qualified referees as well, it would be highly unlikely that a journal of high quality could be published at all. Because of the importance of the review process, I have chosen it as the subject for this editorial column.