The winner of the Rudolf Kingslake Medal and Prize for 1979 is Dr. J. R. Fienup of the Environmental Research Institute of Michigan. His award-winning paper on "Space Object Imaging through the Turbulent Atmosphere" appeared in Optical Engineering 18(5), 529 (1979). This work, begun with his 1975 thesis work at Stanford, developed in several papers prior to this one, and was summarized by him in Optical Engineering 19(3), 297 (1980). Fienup showed that an iterative computer process can reconstruct an object scene from a noisy record of the modulus of its Fourier transform. Since speckle interferometry can be used to derive a diffraction-limited modulus of the Fourier transform, application of Fienup's analysis to the retrieval of diffraction-limited images in speckle interferometry proved quite promising.
Instant High-Speed Motion Analysis System. I don't expect many readers of this column to disagree with my observation that the diffusion-transfer-reversal (DTR) process perfected by Edwin Land in the late 194Os has revolutionized instrumentation "still" photography in the laboratory, plant, and field by virtue of its instant imaging capability. Through simple trial-and-error methods using media based on this technology, scientists and engineers with little or no background or interest in the theory or practice of photography have been able to experiment. more efficiently aud freely in their chosen fields, of research, unhindered by delays and inconveniences associated with conventional wet-procesing methods of photography. In fact, these and ensuing developments in instant imagery have actually conditioned many technical workers - and the general public as - to fully expect to see a recorded image of an experiment within a matter of seconds after it is exposed onto film. Instant photography has become accepted as a way of life!
We thought it was time to bring the readers of Optical Engineering up to date on the new developments in holography, as was done exactly five years ago with the September/October 1975 special issue. The seeds for this special issue were sown during the 1978 Gordon Conference on Coherent Optics and Holography held at the Miramar Hotel in Santa Barbara, California. The conference clearly demonstrated, through the discussion of many interesting research and development applications, that holography is alive and well. For example, artists have discovered holography as a new medium and there is a museum for displaying new holographic developments and inventions. In addition to the opening of the New York museum where artists and patrons are thoroughly enjoying holography, the past five years have witnessed the publication of the Handbook of Optical Holography, continuing issues of the Acoustical Holography proceedings, the gathering of scientists to exchange ideas at three Gordon Conferences in 1976, 1978, and 1980, and the SPIE conference on holography held in Los Angeles in February 1980.
The fact that further progress in holographic techniques depends to a great extent on improvements in recording materials has now gained recognition. Silver halide photographic emulsions are still the most widely used recording medium, and work continues to improve their characteristics as well as to optimize processing techniques. However, other materials are being used to an increasing extent for specific applications for which they are better adapted. Recent developments in this field as well as some of the advantages and drawbacks of currently available recording materials for holography are reviewed.
Dichromated gelatin holograms, properly recorded and processed, have so little scattering and absorption that they are nearly indistinguishable from clear glass plates. Dichromated gelatin is the best material today for the fabrication of holographic optical elements and certain reflection type image holograms because of its low scattering, large refractive index modulation capacity, moderate exposure level, high resolution capacity, good environmental stability with a cover plate, and other unique properties such as reprocessibility and relatively easy hologram thickness control. We first review the mechanism of hologram formation in dichromated gelatin and holographic characteristics and then discuss several promising applications of dichromated gelatin holograms such as holographic optical elements (or holographic optics components) and information storage and display.
A thin lens analogy between holographic optical elements, including transmission, reflection, flat, and curved holographic optical elements, and conventional optical elements is discussed. Examples show that a thin lens model of a holographic optical element can be used with a conventional optical design program such as ACCOS V for designing holographic optical elements.
Three examples of recent developments in the field of holographic interferometry are discussed. The first is the use of optical derotators to form double-exposure and real-time stroboscopic holographic interferograms of high-speed rotating objects. The second is the use of holographic interferometry as a diagnostic method in the automotive industry, and the third is the use of an iterative computation procedure to make possible the measurement of strongly refracting boundary layers.
Although photoconductor-thermoplastic devices have been considered for holographic applications in the past, they suffered from limited recording bandwidth and poor noise characteristics; as a consequence, they were confined to recording holograms of relatively small objects. In this paper techniques for improving the spatial bandwidth to 1500 lines/mm are described. Furthermore, the frost formation mechanism was investigated, and means for suppressing the frost were determined, thereby leading to improved signal-to-noise ratios. These results, together with high exposure sensitivity (50 ergs/cm2) and the improvement in sample fabrication, have led to an operable device which may be incorporated into most holographic nondestructive systems.
A one-step rainbow holographic process implemented with an imaging lens is presented. The generation of color hologram images by this one-step technique is illustrated. The applications of this one-step technique for the archival storage of color films and the generation of pseudocolor holographic imaging are presented. One of the most interesting and important applications of the one-step process is in holographic interferometry. Demonstrations of double exposure, time averaging, and contour generation by this one-step process are included. As compared with the conventional holographic interferometry, the one-step rainbow holographic process is a very simple and versatile technique which yields the advantages of white light readout. The one-step process offers a brighter image, less speckle noise, and better fringe visibility. For multiwavelength and multislit rainbow holographic interferometry, the techniques enable different physical holographic fringe patterns to be displayed in different colors.
A computer-generated hologram is a geometric pattern that can be used as a precise reference in an optical test. Computer-generated holograms can be used to make reference wavefronts that would be very difficult and expensive to make by other methods. This paper reviews the development of computer-generated holograms for optical testing. Various encoding methods are discussed. Examples are given to demonstrate some of the properties of such holograms. A review of interferometer design leads to a discussion of how the hologram functions as part of the interferometer and of the limitations to the computer-generated hologram as used in optical testing.
Three-dimensional holographic images are becoming more widely enjoyed as more practical white-light illumination techniques are developed, more varied types of images are represented, and lower production costs are attained.
The cylindrical holographic stereogram, invented by Lloyd Cross, is one of the most significant developments of the last decade in commercial holography. This hologram has several technical problems, however, which have limited its application in the commercial marketplace. Two of these problems are its limited vertical viewing range and rainbow colored rather than natural colored images. This paper reviews the general problem of color holography and discusses the specific requirements for generating color images in Cross holograms. Several optical techniques are described, and experimental results obtained with one especially promising technique are presented.
360° holograms can be used for directly viewable image display both in information retrieval systems and in static displays. Images can be displayed with modest sized viewers that use a small section of the hologram for individual observers and with the capability for rapid interchange of holograms. Static displays that use the entire hologram are also realized in this concept. Holographic projector systems are also possible which can form two-dimensional images on a flat screen with parallax change along two dimensions. The design of viewers and projectors involves consideration of many parameters and tradeoffs that involve image quality, design complexity, appearance, and cost. Virtual image display units can use either laser or arc lamp light sources, while a laser beam is needed for projectors. Projectors require special design considerations related to the fact that the hologram con-tains the images in their original size and depth. Coherent speckle of projected images can be eliminated by use of fluorescent paints on the pro-jection screen. Several design examples of display units are described and shown.
Since the early euphoria enveloping acoustical holography, considerable progress has been made in both application and technique. The major use for this imaging mode is in flaw characterization in thick structural materials such as used in the nuclear industry. Most recent advances derive from the development of piezoelectric arrays and microprocessors. The former allows data to be gathered at high speed and the latter allows the image to be reconstructed without the necessity of optics. In this paper, we describe some of these advances and offer experimental evidence for the optimism expressed by researchers in this field.
We combine the scan flexibility of computer-generated holographic laser beam scanners with the high diffraction efficiency of volume phase holograms to produce a new type of "holo-scanner." The scanner-hologram consists of numerous, small, volume hologram facets recorded in dichromated gelatin films and produces an arbitrary output pattern with greater than 90% light efficiency. Experimental results for discrete point, continuous line, and 3-D scanners are shown. Multiwavelength and materials processing scanners are also considered.
A coherent optical pattern recognition system using a frequency plane correlator with weighted matched spatial filter synthesis is described. The case study chosen to describe this application of holography is the determination of all pages in a microfilm data base on which a given key word is present.
Practical considerations for particle and flow diagnostic holography are described. These begin with simple rules for determining if holography is advantageous over other methods. Design equations for determining system and hologram requirements and properties of the resulting image are presented. Finally, practical effects which are often encountered but rarely mentioned in the literature are illustrated and explained. These include hologram masking, nonlinear recording, and phase effects in multiple exposure recording.
Far-field holography is now a well-developed technique that has been applied to a variety of problems. Thus a significant number of systems have been engineered. Nevertheless, there are still several important questions that have needed further study. Progress has been made in optimizing the resolution, particularly as it relates to particle shape and noise. Preliminary results are also reported on the effect of semitransparent and fully transparent objects.
The effect of shape on the fall velocity of silt-size mineral particles was investigated by recording sequential transmission holograms of settling particles. Particles with similar densities and settling speeds varied in their sphere-equivalent radii by a factor of 5. The large particles were edgewise-settling thin flakes while the smaller particles were much more compact. Variations of the Stokes' settling equation for thin disks accurately described the settling data for large thin flakes. The fall velocities for small, compact, fast-settling particles were much greater than for volume-equivalent spheres and were adequately described by the Stoke's equation for elliptical cylinders. An unresolved problem remains in that the theoretical drag on thin disks is about four times that on flat elliptical cylinders of the same surface area.
To utilize the real-time two-dimensional coherent imaging devices for antenna data processing, the properties of a raster-scanned wideband signal are studied. To extend the processed bandwidth-duration product widely over the recording capability of a single line on the imaging device, the time signal is displayed on several lines of the raster. The time-Doppler ambiguity function of the resulting 2-D signal is defined, leading to the possibility of two-dimensional processing. For a 2-D or 3-D phased-array antenna with any geometry, the received signals from each channel can be raster scanned and spatially multiplexed in the full aperture of the imaging device, enabling the performance of the array-pattern synthesis in every direction simultaneously, with the theoretical directivity of the antenna. Holographic filters are designed to perform either the matched filtering of a rastered signal with many Doppler replicas, or the array-pattern synthesis, or these two operations simultaneously (complete processing) with a single hologram. The complete processing is demonstrated experimentally for the case of a sonar-Doppler circular-array antenna, with correlation detection and extraction of the three target parameters' range, Doppler, direction.
A method is described whereby the field performance of an all-germanium triplet, as used for imaging radiation in the 8 to 13 µm waveband, can be improved. The principle of the method, which could also be used to improve the performance of achromatic triplets or aspherized doublets, involves the use of a field flattener lens which replaces the germanium window of the detector. The curvature of this lens can be optimized to minimize field curvature, which together with chromatic aberration is one of the most serious residuals of thermal imaging systems with relative apertures of around f/0.7. It is also shown that for such relative apertures, and for typical fields of less than 15 degrees, at 100 mm focal length, the location of the aperture stop is not a significant design parameter. This arises as a result of the intrinsic optical properties of germanium.
To utilize the full performance advantages of staring infrared imaging systems currently under development, it is necessary to compensate for the characteristic fixed pattern "noise" which is present at the output from these infrared focal planes. Since many of the applications for staring sensor systems require low power dissipation configurations, it is necessary to develop automatic nonuniformity compensation electronics which have much lower power dissipation requirements than conventional digital compensation techniques. This paper discusses the sources of the nonuniformities and describes the typical characteristics of elevated temperature staring arrays. An analysis is given which shows how detector/charge-coupled device electrical coupling techniques strongly influence the compensation implementation, and finally a review of circuit configurations for the compensation function will be given which shows that very low power dissipation circuitry can be developed which meets the performance power dissipation requirements.
Preprocessing that enables accurate matching of two images taken by sensors located at different points in space is presented. Separation between the sensors results in perspective changes that appear as geometric distortion. Two methods for removing the distortion are described. One method applies to sensors that measure range. The second method applies to sensors that do not measure range. Descriptions of the applicable sensor data formats, rationale for the preprocessing approaches, and transformations used to implement the approaches are included. Examples comparing images before and after preprocessing are shown.
In studying the performance of any matching technique for image registration it is important to select an appropriate reference image. In this paper a set of a priori probabilities of detection based on explicit information about the materials which surround the edges is used in a strategy for reference selection. This set of a priori probabilities of detection is obtained by finding the frequency of occurrence of material edges. The correlation results for three edges, each belonging to a different material class, are presented. The results of two criteria for optimum reference selection, namely the Neyman-Pearson and the ideal observer, are used to show that the best choice appears to be a compromise. This minimizes the total probability of error while giving a higher probability of correct acquisition for a fixed probability of false alarm.
The photodichroic silicate glass surface is a direct-read-after-write laser recording material which permits instant optical recording without processing of any kind. The required writing energy density at mega Hz rate and higher is 40 mj/cm2. An even better writing sensitivity is expected for a preconditioned glass surface which is yet to be demonstrated at mega Hz rates. The inherent resolution capability of this material is better than 2000 cycles/mm, which is consistent with the fine grain structure of the photodichroic silicate glass surface (grain size <0.02 pm). The photodichroic silicate glass surface can be pre-recorded with tracks of width 1µm or less. It is potentially a pinhole-free recording material due to the inherent homogeneity of the silicate glasses, and to the very small sizes of the photosensitive crystals, relative to the wavelength of light and the thickness of the photosensitive glass sur-face layer. The physical effect of recording is irreversible; yet the recorded spots or bits are erasable. The erased 1-bit can be distinguished easily from the 0-bit (of course, not distinguishable in the normal read mode), when necessary. There is also a mechanism to prevent erasing after recording and error corrections are completed. The writing is done with a polarized red light, and nondestructive read is done using a near infrared beam, with the recorded bits between crossed polarizers. The erasure is to re-expose with the write beam whose polarization direction has been rotated 45° with respect to the initial polarization exposure direction. In this manuscript, the physical effect of recording is discussed in detail, including the intensity dependent writing sensitivity, the threshold effect, and the relationships among observed spot size, contrast and the writing energy density. Recording in mega Hz rates as well as write-erase cycling are demonstrated.
The design of an instrument which measures particulate size and loading of the off gas from a fluidized-bed combustor is discussed. This noninvasive technique is based on the use of Fraunhofer diffraction. Experimental results are presented for three size fractions of synthetic diamond dust in water which approximates the refractive index of coal dust in air.
Experimental procedures and current state-of-the-art are presented for laser surface treating methods such as alloying, cladding, grain refining, and transformation hardening using a cw CO2 laser. Microstructural and x-ray analyses of the treated surfaces indicate that a laser beam can locally enhance surface properties. Laser alloying offers the possibility to selectively modify a low cost workpiece surface so that it has the desired high quality surface properties characteristic of high performance alloys. Laser cladding offers feasibility to apply high melting cladding alloys on low melting workpieces, to reduce the amount of dilution of cladding alloy with the workpieces, and the potential to apply dense ceramic claddings to metallic workpieces. Laser grain refining offers potential to either minimize or eliminate surface defects such as inclusions, intermetallic compounds, and pores, and to provide a refined grain structure. Laser transformation hardening provides the treated workpieces with a hard martensitic surface that has compressive stresses for enhanced fatigue life; in addition, reduction in wear rate of treated surfaces is achieved. This experimental study indicates that the use of lasers for surface treatment has several limitations. Further studies will provide better understanding for maximum utilization of laser surface treating processes.
An optical method for measuring the percent of open area of perforated sheet materials is presented. The technique, which is based on Fourier optics, uses a detector to measure a small central portion of the light in the Fraunhofer diffraction pattern of the perforated sheet. This approach offers accuracy and speed while avoiding diffraction problems associated with arrays of small holes. In addition it can be used with translucent materials. A brief theoretical analysis is presented as well as results obtained with a laboratory system. The system is being developed to inspect perforated materials fabricated for use on noise suppression systems for aircraft engines, however, it should be useful in the general noncontact determination of the open area of perforated materials.