Electronic holographic imaging, as developed at the MIT Media Laboratory's Spatial Imaging Group, is a truly 3D real-time digital imaging medium. Recent progress in holographic video has demonstrated that the crucial technologies--computation, electronic signal manipulation, and optical modulation and scanning--may be scaled up to produce larger, more interactive, full-color holographic images. The overcoming of communication bottlenecks relies on the use of newly-developed 'diffraction-specific' computational algorithms to produce encoded holograms that are compressed by factors of about twenty to one. Here we describe progress in the very rapid 'decompression' of the holograms with stream-processor hardware built for the Cheops video processing system. The result is that 36-MB holographic images may be updated over a SCSI link in about six seconds, approaching truly interactive speed.

There is increasing interest in real-time autostereoscopic 3D displays. Such systems allow 3D objects or scenes to be viewed by one or more observers with correct motion parallax without the need for glasses or other viewing aids. Potential applications of such systems include mechanical design, training and simulation, medical imaging, virtual reality, and architectural design. One approach to the development of real-time autostereoscopic display systems has been to develop real-time holographic display systems. The approach taken by most of the systems is to compute and display a number of holographic lines at one time, and then use a scanning system to replicate the images throughout the display region. The approach taken in the ICVision system being developed at the University of Alabama in Huntsville is very different. In the ICVision display, a set of discrete viewing regions called virtual viewing slits are created by the display. Each pixel is required fill every viewing slit with different image data. When the images presented in two virtual viewing slits separated by an interoccular distance are filled with stereoscopic pair images, the observer sees a 3D image. The images are computed so that a different stereo pair is presented each time the viewer moves 1 eye pupil diameter (approximately mm), thus providing a series of stereo views. Each pixel is subdivided into smaller regions, called partial pixels. Each partial pixel is filled with a diffraction grating that is just that required to fill an individual virtual viewing slit. The sum of all the partial pixels in a pixel then fill all the virtual viewing slits. The final version of the ICVision system will form diffraction gratings in a liquid crystal layer on the surface of VLSI chips in real time. Processors embedded in the VLSI chips will compute the display in real- time. In the current version of the system, a commercial AMLCD is sandwiched with a diffraction grating array. This paper will discuss the design details of a protable 3D display based on the integration of a diffractive optical element with a commercial off-the-shelf AMLCD. The diffractive optic contains several hundred thousand partial-pixel gratings and the AMLCD modulates the light diffracted by the gratings.

The holography is a useful technology for 3D images. There are two types of the hologram in the reconstruction; one is a transmission-type and the other is a reflection-type. Especially, the reflection-type hologram that can be hanging on the wall is convenience because it needs no space. Mark Shires presented a flat panel real-time holographic stereogram in his paper. However, his display is unquestionably a transmission-type. In this paper, a 3D real-time display with a holographic optical element (HOE) is described. This display is realized both the transmission-type and the reflection-type. The diffraction efficiency becomes better because this display has a single HOE. This simple 3D display is ideal for both consumer and industrial use.

To realize an interactive holographic 3D display system, the system falls into three processes: the first is the generation of original 3D object data; the second is the computation of hologram patterns; the third is the modulation of electro-holographic display devices. These must be executed fast and continuously for 3D display. In these processes, the fast computation of holograms is the most important process. We investigate this process using a fast computation algorithm with a fast computing system, and fabricated a prototype of the interactive holographic 3D display system. We discuss the fast computation algorithm using a transform from frequency domain to spatial domain compared with the traditional computation method of the Fresnel hologram, reduction of calculation time using our fast computing system.

I calculate the modulation transfer function (MTF) characteristics of image-plane holographic stereograms and describe how the MTF behaves with respect to factors such as image depth, resolution, and perspective window size. I then use this expression for the MTF to determine the optimum stereogram parameters and compare the results of the analysis with those derived from a geometrical model.

Sequential perspective views have been generated from a single 2D image to synthesize holographic stereograms (HS). First, an image of a building photographed with a 35mm camera was recorded on a photo-compact-disk read-only memory (photo-CD-ROM). Second, the relative size of the building was reconstructed using a shape reconstruction technique, and subsequently, texture mapping data were extracted from the single building image. Then, rotating a viewpoint and a projection screen around a reconstructed building model, 100 frames of perspective views were calculated using the ray-tracing method. After HS synthesis using these data, a reconstructed image was observed from the HS with laser light illumination. Moreover, the stereoscopic effect which should be obtained in image reconstruction has been verified by means of computer simulation.

Visualization of 3D information or 3D displays are important subjects. We have been researching 3D displays using computer-generated holograms (CGHs). We set our sights on making large and high quality 3D displays. In this paper we present an approach to making large CGHs relatively easily, and at low cost, which are binary Fresnel holograms and are recorded by using a high resolution laser printer (an image setter). By using the image setter it is possible to draw large CGH patterns very easily. Furthermore, we found it was possible to reconstruct CGHs with light-emitting diodes or miniature light bulbs. Making good use of this advantage we propose a method of making larger 3D displays by the multiple comstruction using plural light sources and CGHs.

The word 'grating image' was first named by Toppan Printing Company, Ltd. It means that an image consists of grating dots. In 1988, we presented this new technology at the Optical Security Systems Symposium, in Switzerland. Then it was improved and applied in display application. Recently, it was further applied in 3D video systems. In this report, the development history and the recent situations of grating image technology are described.

The use of holograms for security and authentication accounts for around half of all optical holograms produced. This sector is crucial to the hologram industry. Yet it is under threat, as holograms become the target of criminals around the world who wish to counterfeit the documents and products the holograms protect. It is possible to produce holograms using techniques and security procedures which raise the barriers to the counterfeiters, but the hologram industry appears to be complacent and inadequately prepared to deal with this threat to its future. This requires the production of appropriate holograms for each application, awareness, education, and policing. A suitable vehicle for the implementation of these tasks now exists in the International Hologram Manufacturers Association and its Hologram Image Register.

Using the rainbow holographic technique, a color or an achromatic image can be obtained from the superposition of various rainbow holograms. In the present work, an analysis of the reconstruction process of a multiple rainbow hologram using a simulation program that includes Kogelnik's theory is performed. The objective of the analysis performed in this work is the searching of adequate recording conditions to improve the luminance of the final reconstructed image. Comparison between experimental data and calculations are shown. The effects of shrinkage and hologram tilting on the diffraction efficiency of the holograms in function of the wavelength are evaluated quantitatively.

In this paper, we propose a new synthesis process for true-color holographic stereogram to enhance the image resolution and compensate color distortion errors that occur when recording wavelengths are different between master and final hologram. An anamorphic projection algorithm for CG images, a special image processing for real object, and a simple way to synthesize master stereogram is combined in the process. Experimental results show the process is avalable for high quality true-color holographic stereogram.

DuPont has developed full color holographic photopolymer films with high sensitivity across the visible spectrum, which can be used to produce high performance full-color volume holograms and holographic optical elements. In addition, three color mastering films have been developed to produce high quality full color master holograms. Methods and results of holographic color recording and mastering in these materials are discussed. Examples of full- color display holograms and simple holographic optical elements are presented.

Methylene blue sensitized dichromated gelatin (MBDCG) is a suitable recording material for full color hologram in a single layer. Such a hologram has the possibility of being used as the advanced display devices and optical elements. However, the process of drying in an ammonia atmosphere is necessary for making the MBDCG. This process is troublesome and instable. A new method for preparing the MBDCG has been developed. The sensitized solution is composed of MB, ammonium dichromate, and gelatin in alkaline state. The MBDCG does not need to dry in an ammonia atmosphere when the concentration of MB and ammonium dichromate is properly controlled. The limits of the most suitable concentration of these agents are studied. Some experimental results of Lippmann color holograms using this MBDCG are presented.

The limited efficiency of diffractive optical elements is an important consideration in their design and application. These elements, fabricated using lithographic techniques, have very high theoretical diffraction efficiencies when analyzed using first-order scalar analysis. However, assumptions made in this scalar approach limit its accuracy for high frequency diffractive structures, such as those encountered in fast diffractive lenses. Fabrication limitations also reduce the physically achievable diffraction efficiency. This paper will discuss alternatives to the conventional scalar analysis technique and review how fabrication constraints can be incorporated into the design approach to realize improvements in diffraction efficiency.

The two types of diffractive optical elements capable of compensating chromatic aberration in MO data storage optics have been developed. One is a diffractive element that has little optical power, and is used in cooperation with an aspherical objective lens separated from each other. The other is an aspherical singlet with a diffractive grating on its surface. Both have a diffraction efficiency of 100% for the first order diffraction.

Reported in this paper are our experimental studies which were made to ensure the feasibility of applying a diffractive lens element to a lithographic projection lens. The studies include lens design, diffractive element fabrication and the method, exposure experiments and the results, and some analysis of the results. It can be concluded from the results that the application is possible although improving the diffraction efficiency of the diffractive element is a significant issue for practical use.

We propose a new signal detection method for optical encoders. Two diffraction gratings whose periods are slightly different from eachother are irradiated by a collimated beam to make an interference fringe. This encoder system has a simple structure while the performance is not influenced by the wavelength change, theoretically. A quasi sine curve of period 0.5 micrometers was detected by a fundamental experiment.

A binary phase grating that has a 2D periodic phase structure is useful to generate the directional diffuser. Recent analysis and computation for the periodically phase distributed plate will give the most optimized characteristics of the diffuser. This binary phase grating is successfully obtained, large enough, by a planar fabrication technique such as photolithography. Typical application of the phase grating for a clear and high efficiency focusing screen of the viewer is presented.

The phase optimization of a quantized kinoform by the genetic algorithm is discussed. Because the genetic algorithm inherently deals with discrete values, the quantized phase of the kinoform can be easily estimated. The periodicity of the discrete Fourier transform for the 2D Fourier kinoform enables us to perform the crossover process, which is one of the processes in genetic algorithms, without concern of a spatial bandwidth of the kinoform. We introduce a step-quantization method for the multilevel kinoform. Improvements are shown to be significant with this method in computer simulations. The optically reconstructed image agrees well with the calculated one.

A new type of wavelength division demultiplexer (DEMUX), which consists of a pair of diffractive optical elements integrated on one substrate, is presented. The 3 dB-resolution of the DEMUX is about 2 nm and the measured losses are about -3.5 db at 1.55-micrometers wavelength. To simplify the fabrication process of the integrated diffractive optical elements, a new 3D structure replication technique is proposed.

We designed a new type of array illuminator based on the Talbot effect to optimize the optical throughput of large-aperture phase-only spatial light modulators. The illuminator consists of a three-level phase relief and produces an intensity distribution with a duty cycle of 80%. To investigate both near and far field, we formulated an algorithm using the Fresnel-Kirchhoff diffraction formula and computed intensity and phase patterns. A tolerance analysis on typical fabrication errors and their effects on the optical throughput is presented.

In this paper, a kind of diffractive optical element (DOE) was designed and fabricated. For the design, an improved Gerchberg-Saxton algorithm and an approach of aperture division are presented. The DOE was generated by means of photolithogrpahy and ion etching techniques with 16 phase levels. The experimental results of quenching processing of steel parts by inserting the DOE into CO₂ laser beam are satisfactory. The DOE is of an advantage of that applicable to a variety of multimode laser beams.

A real-time read/write motion picture has been demonstrated by hole-burning holography using cryogenic Eu³⁺:Y₂SiO₅ crystal. In a holographic configuration, the laser frequency was continuously scanned within the ⁷F₀-⁵D₀ absorption line while the object was in motion. Since this movie does not have any picture frames, it is temporary continuous. This feature might realize high-speed and high-time- resolution motion recording.

The distribution and dynamics of aggregates in the aquatic environment play an important role in the modeling of biogeochemical processes. Previous work on aggregates in the ocean (e.g. sedimentary 'marine snow' particles), which vary in size from tens of microns to several millimeters, has used electronic counting or conventional photogrpahy coupled with image analysis. Here we describe a nondestructive in situ approach by use of holographic mensuration, hologrammetry, that affords greater scope and higher accuracy for the enumeration, sizing, and spatial distribution determination of aggregate particles. By means of two complimentary techniques, in-line and off-axis transmission holography, we present the initial experiments conducted in our laboratory and discuss the preliminary results from real image analysis.

Hologrammetry has many advantages over conventional imaging techniques for subsea visual inspection. Holograms recorded underwater can be replayed in the laboratory to provide an optical replica of the original subject. Real-image reconstruction allows planar 'optical sections' to be isolated and measured directly. However, these advantages can be removed by poor optimization of the reconstructed image. Furthermore, recording the hologram in water and replaying in air increases the magnitude of the optical aberrations which may be apparent. Such aberrations can be minimized using index compensation whereby the hologram is replayed in air with a wavelength which is equivalent to the effective wavelength of the beam in water. To monitor the influence of these effects and to establish the validity of the index compensation method, reconstruction takes place in a micrometer-controlled plate holder to allow precise positioning about all three rotational axes and the three translational axes. The image is viewed using a lensless TV camera or measuring microscope which is accurately moved through the image volume to provide dimensional information. Index compensation has been shown to work well for both back-lit and front-lit off-axis holograms and is effective over a wide range of field angles. Typically an on-axis resolution of around 1 1p/mm for a front-lit hologram replayed at the recording wavelength will increase to over 20 1p/mm when reconstruction takes place at the compensation wavelength. The corresponding astigmatic difference reduces from around 100 mm to less than 2 mm on employing compensation.

In a previous study, a mathematical model relating surface and bulk behaviors of metals in aqueous solutions has been developed. The model was established based on principles of holographic interferometry for measuring dissolution, i.e. mass loss, and on those of electrochemisty for measuring the bulk electronic current, i.e. corrosion current. In the present work, an optical corrosion-meter was built based on the above model. The corrosion- meter consists of an electrochemical cell in which the sample is immersed in aqueous solution. Furthermore, the corrosion-meter has a holographic camera with a thermoplastic film for in- situ processing holograms in order to obtain real time holographic interferoms of the sample in the electrochemical cell. Results of measuring the corrosion current density of different alloys in aqueous solutions. In addition, the corresponding corrosion potential for each corrosion current density was measured by a potentialmeter. As a result, the corrosion current density of Aluminium, stainless steel, and low carbon steel in 1M KCl, 1M NaCl, and 1M NaOH solutions were obtained. A comparison between the corrosion data of samples showed that the corrosion current density of the stainless steel in 1M NaCl is nearly three folds higher than that of the Aluminium in 1M KCl and the low carbon steel in 1M NaOH.

The phase-shifting holographic interferometry combined with the blind-hole method for measuring residual stresses was introduced in this paper. The relationship between the out-of- plane displacements and the residual stresses relieved from blind-hole drilling was examined. Combining this relationship and the theory of holographic interferometry, it is found that full- field out-of-plane displacements can be measured by taking one interference fringe pattern even when the illumination and viewing directions are arbitrary. By using this measured displacement field, it is sufficient to determine the residual stresses with three relative out-of- plane displacements measured along the radial directions. Adopting this newly developed technique to measure a known residual stress in an aluminum specimen, good agreement between the experimental data and the known values were found to agree well with respect to eachother.

Theoretical and experimental investigation into the use of the holographic blind-hole method to measure residual stress is presented in detail. Under the specific optical configuration proposed in this paper, both maximal and minimal out-of-plane displacements can be directly obtained with a single axisymmetric measured fringe pattern. To increase the displacement measurement accuracy in order to facilitate the residual stress measurements of high strength/high stiffness materials, a phase-shifting technique was introduced into the hologrpahic setup. After careful data analysis and error analysis, the residual stress obtained experimentally was found to agree well with the theoretical residual stress results.

The recorded results of the statical model 'detail--cutter' by double-exposure holographic interferometry method which was under load in an isothermal condition have been shown. A deformations field at the contact 'detail--cutter' was studied, depending on the applied weight, the angle of contact between the cutter and the bronze and steel disks. Recording on the photothermoplastics with the aid of the 'memory' effect was carried out in the simultaneous regime. Pseudo-three-dimensional images of absolute values of cutter's deformation were obtained.

We demonstrate that by using diffuse object illumination, deformation measurements with hologrpahic interferometry can be performed on a specularly reflecting object without the use of any additional coating of the object surface. An expression for the secondary fringe formation is found, and the system is found only to be sensitive to deformations along the surface. The fringe visibility is studied for a rigid rotation of the object by using the theory of speckle decorrelation. It is found that maximum fringe visibility is obtained if the recording camera is focused on the surface of the object. Agreement between the theory and the experimental results are found.