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  1 Chapter-1 INTRODUCTION Holography is the method we use to record patterns of light. These patterns are reproduced as a three dimensional image called a hologram. While Hungarian physicist Dennis Gabor invented the hologram in 1947. Development in this field was stifled during the 1950’s light  because the light sources were not coherent. In 1960, the invention of the laser overcame the non-coherent light problem Coherent light is light that is monochromatic and of a single wavelength. In 1962 Emmett Leigh and Juries realized that holography could be used as a 3-D visual medium. From their work, they used a laser to create the first hologram in history, which of a toy train and bird. Hologram is from the Greek word holes, meaning whole and gamma meaning message. Because a holograph is a complete image of an srcinal object. Holography captures both light intensity and phase, distinguishing it from photography, which can only record intensity. A photograph lacks the parallax that a holograph can display. Holography is able to record the phase of light waves from an object by interfering two light waves out of phase. The human eye cannot determine phase, but it can detect the phase difference between these two  beams of light. The srcinal object can be reproduced with a reconstruction beam used on the hologram, creating an apparently 3-D image. This image is really just focused light. It is an advanced form of photography that allows an image to be recorded in three dimensions. Holography   is the process or technique   of making holograms, which are three-dimensional images. A hologram is produced    by the interaction of two beams of laser light (light composed all of the same   color, or wavelength), which have been split from a single beam by a mirror. Holography   is   lens less photography in which an image is captured not as an image   focused on film, but as an   interference pattern   at the film .  The technique of holography can also be used to optically store, retrieve, and process information. Today’s new technology provides some outstanding advantages to not only everyday consumers but also large business corporations and governments. Holographic projection is the new wave of technology that will change how we view things in the new area. It will have tremendous effects on all fields of life including business, education, science, art and  2 healthcare. Holography is a much broader field than most people have perceived. Recording and display in truly three-dimensional images are only small parts of it. A hologram is a recording in a two- or three-dimensional medium of the interference  pattern formed when a point source of light (the reference beam) of fixed wavelength encounters light of the same fixed wavelength arriving from an object (the object beam). When the hologram is illuminated by the reference beam alone, the diffraction pattern recreates the wave fronts of light from the srcinal object. Thus, the viewer sees an image indistinguishable from the srcinal object. Holographic memory is a promising technology for data storage because it is a true three dimensional storage system, data can be accessed an entire page at a time instead of sequentially, and there are very few moving parts so that the limitations of mechanical motion are minimized. Holographic memory uses a photosensitive material to record interference patterns of a reference beam and a signal beam of coherent light, where the signal beam is reflected off of an object or it contains data in the form of light and dark areas. The nature of the  photosensitive material is such that the recorded interference pattern can be reproduced by applying a beam of light to the material that is identical to the reference beam. The resulting light that is transmitted through the medium will take on the recorded interference  pattern and will be collected on a laser detector array that encompasses the entire surface of the holographic medium. Many holograms can be recorded in the same space by changing the angle or the wavelength of the incident light. The interest in 3D viewing is not new. The public has embraced this experience since at least the days of stereoscopes, at the turn of the last century. New excitement, interest, and enthusiasm then came with the 3D movie craze in the middle of the last century, followed  by the fascinations of holography, and most recently the advent of virtual reality. Recent developments in computers and computer graphics have made spatial 3D images more  practical and accessible. The computational power now exists, for example, for desktop workstations to generate stereoscopic image pairs quickly enough for interactive display. At the high end of the computational power spectrum, the same technological advances that  permit intricate object databases to be interactively manipulated and animated now permit large amounts of image data to be rendered for high quality 3D displays.  3 1.1 History of Holography   Holography dates from 1947, when British (native of Hungary) scientist Dennis Gabor developed the theory of holography while working to improve the resolution of an electron microscope. Gabor coined the term hologram from the Greek words holos, meaning whole, and grammar, meaning message . Further development in the field was stymied during the next decade because light sources available at the time were not truly coherent (monochromatic or one-color, from a single point, and of a single wavelength). This barrier was overcome in 1960 by Russian scientists N. Bassov and A. Prokhorov and American scientist Charles Towns with the invention of the laser, whose pure, intense light was ideal for making holograms. In that year the pulsed-ruby laser was developed by Dr. T.H. Maimam. This laser system (unlike the continuous wave laser normally used in holography) emits a very powerful burst of light that lasts only a few nanoseconds (a billionth of a second). It effectively freezes movement and makes it possible to produce holograms of high-speed events, such as a bullet in flight, and of living subjects. The first hologram of a person was made in 1967, paving the way for a specialized application of holography: pulsed holographic portraiture. In 1962 Emmett Leith and Juris Upatnieks of the University of Michigan recognized from their work in side-reading radar that holography could be used as a 3-D visual medium. In 1962 they read Gabor's paper and simply out of curiosity decided to duplicate Gabor's technique using the laser and an off-axis technique borrowed from their work in the development of side-reading radar. The result was the first laser transmission hologram of 3-D objects (a toy train and bird). These transmission holograms produced images with clarity and realistic depth but required laser light to view the holographic image. Their pioneering work led to standardization of the equipment used to make holograms. Today, thousands of laboratories and studios possess the necessary equipment: a continuous wave laser, optical devices (lens, mirrors and beam splitters) for directing laser light, a film holder and an isolation table on which exposures are made. Stability is absolutely essential  because movement as small as a quarter wave- length of light during exposures of a few  4 minutes or even seconds can completely spoil a hologram. The basic off-axis technique that Leith and Upatnieks developed is still the staple of holographic methodology. Also in 1962 Dr. Yuri N. Denisyuk from Russia combined holography with 1908 Nobel Laureate Gabriel Lippmann's work in natural color photography. Denisyuk's approach  produced a white-light reflection hologram which, for the first time, could be viewed in light from an ordinary incandescent light bulb. Another major advance in display holography occurred in 1968when Dr. Stephen A. Benton invented white-light transmission holography while researching holographic television at Polaroid Research Laboratories. This type of hologram can be viewed in ordinary white light creating a rainbow image from the seven colors which make up white light. The depth and  brilliance of the image and its rainbow spectrum soon attracted artists who adapted this technique to their work and brought holography further into public awareness. Benton's invention is particularly significant because it made possible mass production of holograms using an embossing technique. These holograms are printed by stamping the interference pattern onto plastic. The resulting hologram can be duplicated millions of times for a few cents apiece. Consequently, embossed holograms are now being used by the  publishing, advertising, and banking industries. In 1972 Lloyd Cross developed the integral hologram by combining white-light transmission holography with conventional cinematography to produce moving 3-dimensional images. Sequential frames of 2-D motion-picture footage of a rotating subject are recorded on holographic film. When viewed, the composite images are synthesized by the human brain as a 3-D image. In 70's Victor Komar and his colleagues at the All-Union Cinema and Photographic Research Institute (NIFKI) in Russia, developed a prototype for a projected holographic movie. Images were recorded with a pulsed holographic camera. The developed film was projected onto a holographic screen that focused the dimensional image out to several points in the audience. Holographic artists have greatly increased their technical knowledge of the discipline and now contribute to the technology as well as the creative process. The art form has become international, with major exhibitions being held throughout the world.
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