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study was the conclusion that lasers are capable of satisfying all the requirements for digital devices. It was shown that, in addition to the neuristor-type logic, lasers in form of resonators and amplifiers can have input-output characteristics that resemble those of conventional logic circuits such as gates or flipflops." (Reimann, 1965, pp. 250-251).

“Fiber-optic elements, with appropriate concentrations of active emissive ions and passive absorptive ions, are the basic components of this system. The computer is powered by being in a continuous light environment that provides a constant pump power for maintaining an inverted population of the emissive ions. Among the potentially attractive features of such a system are the freedom from power-supply connections for individual circuits, the possibility of transmission of signals without actual connections between certain locations, and a promise of high-speed operation.” (Reimann and Kosonocky, 1965, p. 182).

6.16 “The feasibility of machining resistive and capacitive components directly on thin film metallized substrates with a laser has been demonstrated. Tantalum films can be shaped into resistor geometries and trimmed to tolerance by removing metal. These films also can be oxidized to value using the laser beam as the heat source. Resistors can be made with tolerances in value of less than +0.1 per cent. ...

"Pattern generation by laser machining has been demonstrated on various thin films as well as on electroplated films. Vaporized lines as fine as 0.25 mil are readily attainable in thin films, as are 0.4 mil lines in plated films. Much narrower lines may be obtained under particularly wellcontrolled conditions. Uniform lines as fine as 1 micron have been scribed in thin films on sufficiently flat substrates. These films have been removed with minimum effect to the substrate surface." (Cohen et al., 1968, p. 403).

"Semiconductor laser digital devices offer an improvement in information processing rates of one to two orders of magnitude over that expected from high-speed integrated transistor circuits. Data processing rates of 10 to 100 gigabits per second may be possible using semiconductor lasers. However, the technology for fabricating low-power laser circuits is still undeveloped and low-temperature operation may be required." (Kosonocky and Cornely, 1968, p. 1).

“Laser digital devices may be used for generalpurpose logic circuits in very much the same way that transistors are now used, except that all of the processing is done with optical rather than electric signals.” (Reimann and Kosonocky, 1965, p. 183).

"Semiconductor current-injection lasers are most attractive for digital devices because of their small size, high pumping efficiency, and high speed of operation.” (Reimann and Kosonocky, 1965, p. 194).

“The utility of a laser as a tool for fabricating thin

film circuits results primarily from the spectral purity and degree of collimation of the laser light. These characteristics allow the beam to be focused to a very fine and intense spot. The high heat flux which occurs when the light is absorbed by the target material, and the sharp definition and localized nature of the working region allow heating, melting, or vaporizing minute amounts of material, with minimum effect to adjacent material or components.” (Cohen et al., 1968, p. 386).

6.17 See Hobbs, 1966, p. 42.

6.18 “A new laser data storage/retrieval system that provides a 1000-time increase in packing density over conventional mag tape, an error rate of 1x 108 better, permanent (nonerasable) storage, a transfer rate of 4 megabits/sec., and instantaneous read-while-write verification has been developed by Precision Instrument Co., Palo Alto, Calif.

“A working demonstrator of the 'Unicon' system uses a l-watt argon gas laser, which makes a hole in the metallic coating of a mylar-base tape wrapped around a drum. The current system, using 5-micron holes, offers a packing density of 13 million bits/sq. in.

“Readout is accomplished by reducing the laser power; beam reflection or non-reflection indicates nonholes or holes. The tape being used on the current system offers storage equivalent to 10 2400-ft. reels of 800 bpi tape. The system can serve on- and off-line, and is capable of recording analog, FM or video data, all of which require high speed." (Datamation 14, No. 4, 17 (Apr. 1968)).

6.19 “By early 1968, Precision Instrument Co. had developed a massive-scale laser recorder/ reader storage system, but the first order for the device was not received until this year. Ed Gray, the chief engineer on the UNICON (Unidensity Coherent Light Recorder/Reproducer) Laser Mass Memory System, said that convincing the first potential customers that they should acquire a $500K to $1 million memory system was not easy, especially when you had to 'tell someone that you were not going to store data with magnetics like God intended.' Now that the first order has been placed, by Pan American Petroleum Corp. of Tulsa, Oklahoma, Mr. Gray feels that the systems will move a little faster in the marketplace.

“The $740K system placed with Pan American is to be installed with all requisite software about March of 1970. Four other potential customers, including some government agencies and a private credit-reporting firm, are also expected to place orders." (Datamation 15, No. 3, 116 (Mar. 1969).)

6.20 "The National Archives and Records Service has begun a cost-effectiveness study of archival storage systems in an effort to shrink its mag tape library, which contains one million plus reels. The study, due for completion next month, is using the capabilities of Precision Instruments Unicon device as a model. The Unicon employs a

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laser-etched aluminum strip with a 30-year shelf life.” (Datamation 14, No. 10, 171 (Oct. 1968)).

6.21 “Honeywell scientists are investigating a method that uses a laser for mass storage and retrieval of information in computer memory. Although emphasizing that development is still in the research stage and may be several years away from practical application, the researchers believe the discovery is a possible key to inexpensive mass storage of data for the enormous computer networks envisioned for the 1970's. (Commun. ACM 11, 66 (Jan. 1968)).

6.22 “The system ... uses a modulated laser beam to inscribe data onto photosensitive discs . . Each disc contains 3, 100 tracks with a capacity of 67,207 bits per track, including error corrections bits. The storage unit holds 2, 600 discs, stored on edge, in four (or eight] trays ... two auxiliary disc banks can be added to achieve the maximum memory capacity . of 150 billion characters. The reader reaches any piece of information on the 3, 100 tracks (per disc) within 15 milliseconds ...” (Business Automation 12, No. 6, 84 (1965)).

A CW helium-neon laser is used to "achieve real-time writing of information on the system's photosensitive memory discs." (Connolly, 1965,

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P. 4).

“Such a system could be used with a matrix containing alphabetical or other symbols. The laser would be used as a print-out device, projecting the various symbols onto a recording medium.

"The Air Force Systems Command at WrightPatterson AFB is interested in IBM's work on a variable frequency laser which might be used in conjunction with

color-sensitive computer. This type of setup is said to have a potential capacity of a hundred million bits per square inch of photographic material.” (Serchuk, 1967, p. 34).

p 6.25 "Instead of recording a bit as a hole in a card, it is recorded on the file as a grating pattern of a certain spacing . . . A number of different grating patterns with different spacings can be superposed and when light passes through, each grating bends the light its characteristic amount, with the result that the pattern decodes itself . The new system allows for larger areas on the film to be used and lessens dust sensitivity and the possibility of dirt and scratch hazards." (Commun. ACM 9, No. 6, 467 (June 1966).)

6.26 “Recently Longuet-Higgins modeled temporal analogue of the property of holograms that allows a complete image to be constructed from only a portion of the hologram. In the present paper a more general analogue is discussed and two two-step transformations that imitate the recording-reconstruction sequence in holography are presented. The first transformation models the recall of an entire sequence from a fragment while the second is more like human memory in that it provides recall of only the part of the sequence that follows the keying fragment.” (Gabor, 1969, abstract, p. 156).

6.27 “A new recording mechanism ... sists of the switching of magnetization under the influence of a stress resulting from a heat gradient introduced by a very narrow light or electron beam. The mechanism is assumed to be magnetostriction with a rotation of the anisotrophy. The model presented and the criteria for recording are supported, at least in part, by experimental observations. (Kump and Chang, 1966, p. 259).

6.28 “In attempts to provide computers with previously unavailable amounts of archival (readonly) storage, various techniques involving optical and film technology have been employed to utilize the high information capacity of film (approximately 106 bits/in. ?) and the high resolution and precision of lasers and electron beams. The trillion-bit IBM 1350 storage device, an offshoot of the 'Cypress' system, . uses 35 mm x 70 mm silver halide film 'chips.'

“A total of 4.5 million bits are prerecorded on each chip by an electron beam. For readout, a plastic cell containing 32 film chips is transported to a selector, which picks the proper chip from among the 32; average access time to any of the 1012 bits is 6 seconds. After a chip is positioned, information is read using a flying-spot CRT scanner.

6.23 “A method for producing erasable holograms may enable an optical memory to store 100 million bits in a film one inch square.

“The memory could be read out, erased and reused repeatedly, according to Dr. William Webster, vice president in charge of RCA Labora. tories.

"Information can be written into the magnetic film in 10 billionths of a second, and erased in 20 millionths of a second. Laser light split into two beams, one going directly to the film and the other going to the information bit pattern, interferes constructively to produce heat and consequently a realignment of atoms.

"Where the two beams interfere destructively, nothing happens.” (Data Proc. Mag. p. 21 (Sept. 1969)).

6.24 In the IBM-laser system developed for Army Electronics Command and installed at Fort Monmouth, it is noted that: “Through employment of a deflection technique, the shaft of light can be focused on 131,072 distinct points within a space smaller than a match head. ... To provide a readout in printed form, the laser beam can scan through a mask inscribed with the alphabet and other symbols and through the action of light-bending (deflection) crystals - turn out the final product on photo-sensitive paper.” (Commun. ACM 9, 467 (1966)).

"At International Business Machines Corp. . .. one method, devised for the Army Electronics Command, Fort Monmouth, N.J., makes use of a high-speed switching arrangement with electronically controlled crystals.

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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

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

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,