Two IBM 1350 units are scheduled for mid-1967 delivery to the Atomic Energy Commission at Livermore and at Berkely for use with bubble chamber data. Other techniques of reading and writing with electron beams are explained by Herbert." (Van Dam and Michener, 1967, p. 205).

6.29 "Results of basic theoretical studies conducted at the NCR research laboratories have indicated that CW lasers of relatively low power should be capable of permitting very high resolution real-time thermal recording on a variety of materials in the form of thin films on suitable substrates. Subsequent laboratory studies have shown that such thermal recording is indeed possible. This recording technique has been termed heat-mode recording." (Carlson and Ives, 1968, p. 1).

"The recording medium is coated on a 5- by 7-inch glass plate, a quarter of an inch thick. The plate carrier mechanism is capable of stepping in the horizontal and vertical directions to form matrices of up to 5,000 images at an overall reduction of 150 to 1." (Carlson and Ives, 1968, p. 5).

"The results of the studies described in this paper have established laser heat-mode recording as a very high resolution real-time recording process capable of using a wide variety of thin film recording media. The best results were obtained with images which are compatible with microscope-type optics. The signals are in electronic form prior to recording and can receive extensive processing before the recording process occurs. In fact, the recordings can be completely generated from electronic input. For example, Figure 6 shows a section of a heat-mode microimage with electronically generated characters, produced by the Engineering Department in our Division. The overall image is compatible with the 150-to-1 PCMI system (less than 3 mm field), and consists of 73 lines of characters, 128 characters per line. Although this image was recorded in 1.6 seconds, faster recordings are anticipated. A description of this work will be published in the near future." (Carlson and Ives, 1968, p. 7).

6.30 "Another scheme for storing digital information optically is the UNICON system, under development at Precision Instrument Company. This system uses a laser to write 0.7-microndiameter holes in the pigment of a film. Information is organized in records of at most a million bits; each record is in a 4-micron track extending about a meter along the film. Individual tracks are slanted slightly so that they extend diagonally across the film. (The amount of slant and the width of the film determine the length of the records.) Each record is identified by information stored next to the beginning of that record, in an additional track at the edge of the film. Readout of a particular record involves scanning the identifier track for the proper code and then scanning the track with a laser weaker than that used for writing. It is predicted, on the basis of an experimental working

model, that one UNICON device with 35 mm film could store a trillion bits on 528 feet of film, with an average access time to a record of 13 seconds." (Van Dam and Michener, 1967, p. 205). (See also note 6.14).

6.31 "Considerable experimentation in modulation and transmission is needed before optical communication by laser can be said to be really useful except in very specialized cases." (Bloom, 1966, p. 1274).

6.32 "At first sight a laser communication system with its extremely wide information carrying capacity would appear to be a natural choice for an interplanetary communication system. However, among other things, the acquisition and tracking problems are considered to be so severe that such a system is not thought to be realistic at the present time. This may be indicative of an information technology utilization gap." (Asendorf, 1968, p. 224).

6.33 "In general, earthbound laser-ranging systems are limited by local atmospheric conditions. A typical value of range routinely measured is 20 km or less." (Vollmer, 1967, p. 68).

"Earthbound applications of coherent optical radiation for communications appear to be severely limited for two reasons. The first, and most significant, is the effect of atmospheric turbulence on the coherence of the radiation. The second is the effect of small vibrations on the coherent detection efficiency and signal-to-noise ratio. This can be minimized by careful design, but the first factor is beyond the designer's control. Although coherent optical detection has been demonstrated over some useful paths, the vulnerability of the link to atmospheric variations makes practical application somewhat doubtful." (Cooper, 1966, p. 88). 6.34 "Is the enormous increase in bandwidth offered by light as a carrier frequency in communications needed? For transmission in space the acquisition and aiming of the light beams pose formidable problems. In the atmosphere, rain, smog, fog, haze, snow, etc., make light a poor competitor of microwaves. Can a system of enclosed tubes with controlled atmosphere and light repeater stations be built on a technologically sound and economically feasible basis?" (Bloembergen, 1967, p. 86).

6.35 "Information Acquisition, Sensing, and Input", Sect. 3.1.1. Some additional references are as follows:

"Since the first laser was demonstrated in 1960, considerable interest has developed in its possibilities for use in communication systems. The basic sources of this interest are the coherent nature of the radiation obtained as compared with all previously known extended sources of optical radiation, and the laser's short wavelength. This latter characteristic provides the potential ability to achieve bandwidths, or information capacities, that are orders of magnitude greater than anything obtained heretofore. A more realistic advantage, in terms of presently available information sources,

results from the combination of high coherence and short wavelength. It is the ability to generate a highly collimated beam (limited by diffraction phenomena), which leads to the ability to achieve communications over great distances. Of equal importance is the fact that with a coherent signal, coherent detection of the information can be obtained with greatly improved immunity to natural incoherent noise sources such as the sun." (Cooper, 1966, p. 83).

"The first enthusiastic suggestions that laser technology potentially provides many orders of magnitude more communication capability than RF technology, and that it might, therefore, offer the only solution to the problem of general wideband communications with deep-space probes, needs to be more carefully assessed." (Dimeff et al., 1967, p. 104).

"For deep-space, wide-band communication ... another factor may be . . . important - namely, the size of the transmitting aperture. A very large aperture, as would undoubtedly be required by a microwave channel, is likely to prove an obstruction to the sensors of the aircraft and will, therefore, reduce the time available for collecting information or transmitting it. In this respect, the laser has an important advantage over microwave." (Brookner et al., 1967, p. 75).

"Several optical links which use GaAs injection lasers as transmitters have been constructed. One of them has been demonstrated to be capable of transmitting 24 voice channels over 13 km." (Nathan, 1966, p. 1287).

6.36 "If we classify our communication requirements on the basis of range, we find that lasers can be helpful at the range extremities - that is, for distances less than about 15 km and for those greater than 80 million km.” (Vollmer, 1967, p. 66). 6.37 "An electronic system that transmits military reconnaissance pictures from Saigon to Washington in minutes via satellite may soon enable news media to dispatch extremely highquality photographs and type around the world. for instant reproduction.

"Potential benefits are also foreseen for medicine, earth resources surveys and industry.

"The high-performance system was developed for the U.S. Air Force Electronics Systems Divisions by CBS Laboratories, a division of Columbia Broadcasting System, Inc. It combines electrooptical and photographic techniques to relay highresolution aerial photographs of ground activity in Vietnam to the President and Pentagon officials. Pictures seen by the President are many times sharper than the best pictures shown on home television sets.

similar receiving and recording station there reconstructs the photographs to their original form for immediate inspection." (Spie Glass 5, No. 2, 9 (Aug. 1969).)

"According to Air Force officials, pictures produced by the CBS Laboratories Image Scanning and Recording System contain the highest resolution ever reported in the transmission of aerial reconnaissance photographs. High-altitude photographs processed by the system show such detailed information as identification numbers of ships in port, planes on runways and troop movements . . .

"In operation, the lightweight system uses a precisely controlled laser beam to scan rapidly across photographic film. The laser converts each picture frame to an electronic video signal. The signal is then fed to a transmitting device for satellite relay, said John Manniello, CBS Laboratories Vice President for Government Operations, who conceived the system application. Once the signals contact the satellite, they are flashed to a receiving station in Washington within seconds, he added.

"The receiving station - which has related photoscanning, recording and developing equipment reconstructs the video signal to the original film image and produces high-quality photographic prints.

"Because of the laser-scanning technique involved, no photographic resolution is lost between recording and transmission from the original film taken in Vietnam." (Spie Glass 5, No. 2, 9 (Aug. 1969).)

6.38 "Superficially, it appears attractive to have fast switching, high storage density, direct visual display. Such developments would depend heavily on the availability of cheap, small, high-quality semiconductor lasers. If these were available, the entire organization of computers using them would probably be different." (Bloembergen, 1967, p. 86).

6.39 "The power and efficiency available from lasers at the desired wave lengths (particularly ultraviolet) must be improved, and adequate laser deflection techniques must be developed before laser displays will be feasible for widespread use." (Hobbs, 1966, p. 1882).

"Since lasers don't require vacuums, there is a significant convenience relative to electron beams. But there is a severe penalty compared to electron beams due to problems in deflecting, modulating, and focusing." (Gross, 1967, pp. 7-8).

"Lasers offer great promise for future implementation of display systems - particularly largescreen displays. The ability of a laser to deliver highly concentrated light energy in a coherent beam of very small spot size is well known. Several different approaches to laser displays are being investigated. Since they all require some means for deflecting and modulating the laser beam, considerable development efforts are being expended on deflection techniques. Digital deflection of lasers by crystals has been satisfactorily demonstrated for 256 positions in each direction, but at

least 1024 positions in each direction are needed for a practical large-screen display system." (Hobbs, 1966, p. 1881).

"The laser is an efficient light source, and its output can be focussed to small sizes and high power densities. There is confidence that laboratory means for modulating lasers and deflecting their beams will be found practical." (Bonn, 1966, p. 1869).

"More rapid progress would be made in utilizing laser recording if better means of deflecting laser beams at the desirable speeds and resolutions existed or were clearly foreseeable." (Smith, 1966, p. 1297).

"An experimental device that can switch the position of a light beam more than a thousand times faster than the blink of an eye could become an important part of computer memories of the future. The device, a digital light deflector, was developed at the IBM Systems Development Div. laboratory in San Jose, Calif.

"The experimental deflector changes the location of a beam in 35 millionths of a second by a unique method of moving a glass plate in and out of contact with a prism.

"High-speed deflectors of this type are potentially useful in future optical memories to randomly position a laser beam for data recording and reading. Such beam addressable memories are expected to be many times faster than present magnetic storage methods because of the relative speed of relocating a light beam in comparison to moving a bulky recording head." (Computers & Automation 18, No. 5, 68 (May 1969).)

6.40 "Another attractive approach is the use of a laser beam to write directly on a large luminescent screen. This is somewhat equivalent to an ‘outdoor' cathode-ray tube in which the laser beam replaces the electron beam and the luminescent screen replaces the phosphor face plate of the tube. It offers advantages over a CRT in that a vacuum is not required and a large-screen image can be generated directly. One feasibility system has been developed using a 50 milliwatt neon-helium gas laser, a KDP crystal modulator, a piezoelectric crystal driven horizontal deflecting mirror, and a galvanometer driven vertical deflecting mirror to provide a television rastor scan image projected onto a 40 inch screen. Brightness of 50 foot-lamberts, contrast ratio of 100 to 1 (dark environment), resolution of 1,000 to 2,000 lines, and update time of 33 milliseconds are anticipated for direct view laser systems." (Hobbs, 1966, p. 1882).

"Electron-beam devices, including those which use photographic emulsions and thermoplastic films, operate in a vacuum, which is a nuisance." (Bonn, 1966, p. 1869).

6.42 "By definition, phototropy is the photochemical phenomenon of changing some physical property (color) on exposure to electromagnetic radiation (light) and returning to its original (colorless) state after removal of the activating source

and under a de-activation condition and/or at a later time." ("Investigation of Inorganic Phototropic Materials . . .", 1962, p. 1).

"The property of certain dyes and other chemical compounds to exhibit a reversible change in their absorption spectrum upon irradiation with specific wavelengths of light has been termed phototropism, or photochromism. The emphasis in this definition is on reversibility, because, upon removal of the activating radiation the systems must revert to their original states to be considered photochromic." (Reich and Dorion, 1965, p. 567).

"By definition, photochromic compounds exhibit reversible spectral absorption effects - color changes, resulting from exposure to radiant energy in the visible, or near visible, portions of the spectrum. For example, one class of photochromic materials consists of light-sensitive organic dyes. NCR photochromic coatings consist of a molecular dispersion of these dyes in a suitable coating material. Photochromic coatings are similar to photographic emulsions in appearance and with respect to certain other properties. Coatings can be made to retain two-dimensional patterns or images which are optically transferred to their surface." (Hanlon et al., 1965, p. 7).

"Photochromic film, a reusable UV sensitive recording media has progressed to the point where prototype equipment is being designed." (Kesselman, 1967, p. 167).

6.43 "Photochromic coatings exhibit excellent resolution capabilities. In addition, both positiveto-negative and direct-positive transfers are possible. . . The coatings are completely grain-free, have low gamma (excellent gray scale characteristics), and exhibit inherently high resolution. Further, because the coatings are reversible, the information stored can be optically erased and rewritten repeatedly." (Hanlon et al., 1965, p. 7).

"Photochromism may be defined as a change in color of a material with radiation (usually near ultraviolet) and the subsequent return to the original color after storage in the dark. Reversible photochromism is a special case of this phenomenon in which a material can be reversibly switched by radiation between two colored states. Photochromic compounds may be valuable for protection from radiation; reversibly photochromic materials are potentially valuable for data storage and display applications." (Abstract, talk on photochromic materials for data storage and display, by U. L. Hart and R. V. Andes, UNIVAC Defense Systems Division, at an ONR Data Processing Seminar, May 4, 1966, See also Hart, 1966).

6.44 "Most of the systems so far reported are only partially, or with difficulty, reversible, or are subject to fatigue-a change in behavior either with use or with time in storage." (Smith, 1966, p. 40).

"Organic photochromic materials fatigue with use." (Bonn, 1966, p. 1869).

6.45 "Photochromic films permit the storage

of images containing a wide contrast of gray scale because they are inherently low gamma and grain-free." (Tauber and Myers, 1962, p. 409). 6.46 "It is recorded that Alexander the Great discovered a substance, whose composition has been lost in the obscurity of antiquity, that would darken when sunlight shone upon it. He dipped a narrow strip torn from the edge of his tunic into a solution of the material and wore this strip wrapped about his left wrist. Many of his soldiers did the same. By observing the changes of color during the day, they could tell the approximate hour. This became known as Alexander's rag time-band. (I am sorry that I cannot identify, and hence cannot give proper credit to the author of this delightful footnote to history.)" (Smith, 1966, p. 39).

6.47 "1. Photochromic films provide very high resolution with no grain.

"2. Photochromic films permit the storage of images containing a wide contrast of gray scale because they are inherently low gamma and grain-free. "3. Photochromic films provide immediate

visibility of the image upon exposure. No development process is required. "4. Photochromic films provide both erasing and rewriting functions. This permits the powerful processes editing, updating, inspection, and error correction to be incorporated into systems.

"5. The PCMI process incorporates the
ability to effect a bulk-transfer read-out
of micro-images at the 200:1 reduction
level by contact printing.

"6. Use of high-resolution silver halide
films provides both permanency for
the storage of micro-images and eco-
nomical dissemination of duplicates.
"7. The very high density of 200:1 micro-

images offers the possibility of using
some form of manual retrieval tech-
niques for many applications. This
eliminates the normal requirement in
systems of this size for expensive and
complex random access hardware."
(Tauber and Myers, 1962, p. 266).

In the photochromic micro-image (PCMI) microform process developed by the National Cash Register Company there have been achieved "linear reductions from 100-to-1 to greater than 200-to-1, representing area reductions from 10,000to-1 to greater than 40,000-to-1, [which] have been successfully demonstrated by using a variety of image formats, such as printed materials, photographs, drawings, and even fingerprints." (Hanlon et al., 1965, p. 1).

"NCR has developed a number of research prototype readers for viewing PCMI transpar[including] a miniaturized microimage

ences

reader . . . which was designed specifically for possible use aboard a manned space vehicle. The reader would have a self-contained, fixed reference file of up to 50,000 pages of information, such as navigational charts, planetary and space data, and checkout, maintenance, and emergency procedures." (Hanlon et al., 1965, p. 13).

"Current design emphasis by NCR has been toward the development of low cost PCMI readers for commercial applications." (Hanlon et al., 1965, p. 19).

6.48 "The information glut threatening to swamp the engineer and the scientist is being eased by a British organization called Technical Information on Microfilm. The medium of the 'message' is the National Cash Register Company's PCMI process. This makes possible the storage of over 3000 printed pages of information on a single 4-by-6-inch transparency. The system used by TIM enables the engineer to locate the data he wants in a matter of seconds. He simply selects the proper transparency and immediately locates the appropriate page images with an NCR reader which displays the selected pages on an illuminated viewing screen. TIM points out that one of the most valuable sources of information to engineers and scientists is manufacturers' literature. The problem has been that this is produced in an extraordinary variety of forms. These are difficult to catalogue comprehensively and they also create an enormous bulk. The NCR-developed PCMI technology involves a photochromic coating which produces an image that is virtually grain-free. The process permits a microscopic-size reduction which is not practical with conventional microfilm processes. NCR is producing the transparencies for TIM in its Dayton, Ohio processing center from 35-millimeter microfilm supplied by the British firm. All data is updated every six months." (bema News Bull., Dec. 9, 1968, p. 8).

6.49 "Information stored on photochromic coatings is semipermanent . . . This is a result of the reversible nature of the photochromic coating. The life of the photochromic micro-image is dependent upon the ambient temperature of the coating. At room temperature, image life is measured in hours, but as the temperature is lowered, life can be extended very rapidly to months, and even years." (Hanlon et al., 1965, p. 8).

6.50 "The temperature-dependent decay of image life obviously prohibits the use of photochromic micro-images in their original form for archival storage. To overcome this problem, means have been developed for contact-printing the photochromic micro-images to a high-resolution photographic emulsion, thereby producing permanent micro-images." (Hanlon et al., 1965, pp. 8-9).

"The entire contents of the photochromic microimage plate are then transferred (as micro-images) in one step, by contact-printing onto a high-resolution silver halide plate . . . Micro-image dissemi

nation (duplicate) films are prepared in a similar manner, using the silver masters to contact-print onto high-resolution silver halide film." (Hanlon et al., 1965, p. 9).

6.51 Further, "a more realistic assessment . . so that spillover, halation, and registration restrictions would not be impossibly severe, still results in a contiguous bit density of 10"/cm2." (Reich and Dorion, 1965, p. 572).

6.52 "Transparent silicate glass containing silver halide particles darkens when exposed to visible light, and is restored to its original transparency when the light source is removed. These glasses have been suggested for self-erasing memory displays, readout displays for air traffic controls, and optical transmission systems. . .

"Photochromic glass appears to be unique among other similar materials because of its non-fatiguing characteristics. No significant changes in photochromic behavior have resulted from cycling samples with an artificial 3600A black light source up to 30,000 cycles. There were also no apparent solarization effects causing changes in darkening or fading rates after accelerated UV exposure equivalent to 20,000 hours of noon-day sunshine." (Justice and Leibold, 1965, p. 28).

"Another potentially important application of photochromic materials is in the display of information. Data can be recorded in photochromic glass in two ways: by darkening the glass with shortwavelength light in the desired pattern; or by uniformly darkening the glass and bleaching it, in the desired pattern, with longer wavelength light." (Smith, 1966, p. 45).

6.53 "To produce a display, patterns of varying optical density are written on photochromic film with a deflected ultraviolet light beam. The film so exposed forms the 'object' in a projection system. Visible light is projected through the film onto a screen. This display has mechanical simplicity, controllable persistence, and a brightness comparable to conventional film-projection displays." (Soref and McMahon, 1965, p. 62).

6.54 "For dynamic applications such as target tracking, this technique not only permits a realtime target track, but also provides target track history in the form of a trace with intensity' decreasing with time. The time period covered by the visible target track history is a function of the photochromic material. At the present time, the speed of photochromic materials limits the character generation rate to less than 100 characters per second. Successful development of faster photochromic materials will provide an attractive electro-optical dynamic large-screen display with no mechanically moving parts." (Hobbs, 1966, p. 1879).

6.55 "One of the technological trends which will give us mass memories at a viable price is photochromic microimagery. Photochromic techniques-by which as many as 2,000,000 words can be stored on a film transparency only 4 inches

by 6 inches-can now be used to store a pattern of bits instead of images of pictorial or alphabetical information. Photochromic high-resolution films coupled with proper light sources and optical systems can provide the storage of millions of bits to the square inch. A micro-holographic indexing system used with such storage devices may revolutionise data storage and retrieval." ("R and D for Tomorrow's Computers," 1969, p. 53).

6.56 "The breadth of the sensitivity characteristics of the photochromic films in conjunction with the width of the spectral characteristics of the available phosphors present a potential systems designer with a choice of a number of component parts ... Future improvements in CRT-photochromic film display systems are dependent upon the capabilities of each of the components. The basic parameters which enter into the cathode ray tube efficiency are the fiber optic plate and phosphor. An increase in the fiber optic efficiency is doubtful except through the use of higher numerical aperture fibers. Increasing the numerical aperture has the disadvantage of requiring a higher degree of control on the film-CRT gap. An improvement in basic phosphor efficiency is difficult to foresee although several military agencies are now or will be sponsoring programs to achieve this goal.

"An advance of the state-of-the-art of phosphor technology should be possible by a factor of 4, but probably not beyond. By careful optimization of the phosphor deposition with respect to particular applications some improvement is possible. At the same time an increase in the efficiency of the photochromic film by a factor of 2 is theoretically possible. Of more importance to the system designer is the understanding and optimization of writing and rewriting rates as they affect phosphor efficiency and life and in the matching of the CRT with the photochromic film." (Dorion et al., 1966, p. 58).

6.57 "Wavefront reconstruction was invented by Gabor and expounded by him in a series of classic papers [1948-1951]." (Armstrong, 1965, p. 171).

"The wavefront reconstruction method of image formation was first announced by Gabor in 1948.”

6.58 Stroke gives a derivation of the term: "Hence, the name 'hologram' from the Greek roots for 'whole' and 'writing'." (Stroke, 1965, p. 54). And also defines it: "A hologram is therefore an interference pattern between a reference wave and the waves scattered by the object being recorded." (Stroke, 1965, p. 53). 6.59 See also the following: "Arbitrary objects . . . are illuminated by parallel laser light. In the general case, the light reflected by these objects will be diffuse and the reflected wavefronts will proceed to interfere in the photosensitive medium where the interference pattern can be recorded. After the photosensitive medium has been exposed and processed it is