The laser is a highly advanced light source. The light is intense, monochromatic, and coherent. The light beam can be manipulated, controlled, and detected easily. With additional optical elements the beam can be directed, turned off-and-on, and the intensity varied continuously at will. All of these attributes make the laser a promising component for writing on emulsions and films, character recognition, non-impact printing, and quite recently, video recording and play-back. This all leads us into areas of infor-mation processing, storage, and handling never before thought possible.
Although laser scanning is a relatively new technology, it has already found many applications in recording systems, OCR, film readers and data digitizers. A primary reason is that the monochromaticity and coherence of the laser beam makes it possible to focus the wavefront to a diffraction limited point image which then becomes the recording or analyzing spot.
The announcement for this Seminar noted that the expanding technology of laser recording has already pene trated many diverse fields. With a few modifications, these applications are listed in Table 1. Table 1: LASER RECORDING APPLICATIONS Facsimile Reconnaissance Systems Image Processing Computer Output Microstorage Mass Memories Video Storage of Television Electronic Motion Pictures Graphics and Pattern Generation Phototypesetting and Platemaking Micropublication Aesthetics
The world has witnessed startling developments, in recent years, in the realm of unconventional imaging media. Numerous topical conferences have been held and volumes of text have been written on this wide ranging subject. Hence, today, in the few minutes avail-able to us, I feel the best we can do is take a bird's eye view of the subject matter, discuss in some depth one or two specific examples, and conclude with a few personal observations which need further exploration and understanding.
Early in the laser era, a wide variety of laser beam deflection techniques were explored. The most enduring among these have been acousto-optical and driven-mirror methods, which have been successfully applied in many electro-optical systems and are generally preferred for new systems. Some progress has also been made in electro-optical deflectors, which have produced deflection resolutions of hundreds of lines in both digital and phased-array embodiments. These methods are reviewed with respect to resolution. and scanning frequency capabilities now attainable.
The intent of this paper is to summarize the state-of-the-art of acousto-optic devices (A/0 devices) and discuss some of the appli-cations. The paper deals primarily with acousto-optic deflectors and modulators; however, a unique application of using A/0 devices to generate a "traveling lens" is described in Section II.
Most laser scanning systems require that the angular position of the laser beam be controlled by a pivoted mirror with a diameter of several millimeters. The requirements of speed and accuracy with which this function must be fulfilled in most systems have led to the development of compact servo-actuated galvanometers of a novel design. Such devices are capable of rotating mirrors 7.5 to 30mm in diameter, through steps of 20 degrees, in times of less than 0.5 to 4 milliseconds, respectively. They have a positional linearity in excess of 0.1%, excellent shock and vibration resistance characteristics, and will operate free of maintenance for over 10" scan cycles. Current uses in newspaper photo transmission, engraving of printing plates, resistor trimming of thick film circuits, label marking and other scanning applications are described briefly.
Recent advances in the technology of dielectric optical waveguides have resulted in the production of fast efficient optical switches and modulators which operate at voltages and powers consistent with those available from integrated circuits. The frequency capabilities of these devices extend well into the microwave region.
As communication and data transmission systems become more and more sophisticated, anticipated exploratory development objectives for wide-band recording go far beyond the capabilities of current data handling equipment. Typical characteristics include digital rates of 200 MBPS, 300 MBPS and even 1 GBPS (gigabit per second) with error rate requirements not to exceed 1 bit in 105, or 1 bit in 106 and analog rates in excess of 100 MHz with typical mission times of 5 to 10 minutes. The objective of this presentation is to briefly present the state-of-the-art in wideband recording, how RADC and the Air Force technology programs have impacted on this art and in what direction our future programs will be oriented. Wideband laser recording technology supports, and in some instances, is an integral part of systems and concepts which deal with sensors, communications and computerized data handling. The recorder, then, forms an important interface between the sensor and the data transmission system; and between the data transmission and the processor, analyst or user. Information collected by the advanced sensors must be stored in some appropriate form and be ready for rapid readout when the time comes to either transmit the data to other vehicles and/or ground stations or be available for further in-depth analysis. It follows, that if one is to collect and transmit these amounts of data in a timely manner, a sophisticated recording and playback capability is also required. Characteristics for these recorders include: (1) very wide bandwidths; (2) high-packing densities to reduce the total volume of recording media required; (3) large dynamic range for handling analog signals (a lesser range is required for digital recording); (4) low distortion; and (5) very good time base stability.
Storage of data using holographic techniques continues to hold the interest of researchers here and abroad even though the development of practical computer oriented holographic systems has been progressing at a slow rate. Several read/write demonstration systems have been built recently but further significant progress awaits the development of advanced page composers and materials or a more novel way of using presently available technology. The application of holographic techniques to data recording on photographic film has been more successful since the materials technology, as well as the page composer technology, are well in hand. This paper reviews the recent progress in holographic data storage and discusses a number of ways of utilizing holographic techniques in recording data.
A considerable effort has been expended over the past ten years to develop high resolution, wide bandwidth, and wide dynamic range recorders. In the earlier years, the effort was concentrated on flying spot CRT recorders. These devices have good performance at low bandwidth, limited dynamic range, and medium to low resolution. The advent of the laser opened new dimensions in the recording and readout fields. The properties which make the laser a unique light source are its high collimation, monochromaticity, and power density. It can be used to form near diffraction-limited spots with very high power densities. The availability of laser light sources has been matched by the development and availability of high perform-ance (diffraction-limited) optical components tailored to the available lasers, modulation schemes operating from a video bandwidth of a few hundred kilohertz to tens of megahertz, spinner/moving mirror schemes operating from a speed of a few hundred rpm to tens of thousand rpm, variable speed film transport system(s) compatible to the spinner speed, and necessary ancillary circuit designs/ components to permit the required control and synchronization of the recorder. The available operational recorders, of the continuous strip and frame form(s), can be improved in future developments by the incorporation of the HoloFacetTM type spinner. This device will minimize the line start (jitter) and line-to-line disturbance (banding) in the recording due to geometrical errors in the fabrication of the spinner/moving mirror unit, including the bearing assembly.
In the past few months numerous articles have been published that describe optical video disc systems. (Refs.1-12). In reading through these articles it soon becomes evident that a principle of convergent technical evolution has been at work: the majority of systems under development are remarkably alike in their basic aspects. This convergent evolution is no accident, of course; the criteria for survival have been common to almost all systems. They are cost, simplicity and durability so as to gain acceptance in the consumer market. In less insipid terms: the evolutionary goal that has to be reached is to mass produce an optical read only memory with a capacity of 11 about 10 bits for under $500. The 1011 bits approximately represent the information content of a half-hour T.V. program and the $500 the average cost of a color T. V. set.
Optical spectral analysis is finding wider application in data processing. The major advantages of the technique are very high speed and high resolution (Refs. 1,2,3). As an example, the laser beam system considered in this paper can continuously record a signal of several MHz bandwidth with no loss of data. The laser beam recorder may be considered as the input channel of a computer. The data are stored on film in a compact raster format in analog form and can place about a half million samples in the aperture of the optical computer. Because the optical analyzer or computer produces output based upon this large data sample, the resolution of the system is greatly enhanced.
The ability to image large terrestrial areas from space with high spatial resolution and radiometric fidelity gives rise to unprecedented requirements for handling, storing, and displaying such information. These requirements, expected during the next decade, are discussed in this paper as they apply to pictorial image recording on the basis of total system consideration, and the user end product. In this context, there are two types of users: the image recording system user and the end product user, both of whom must be taken into consideration in the process of developing and implementing image recording systems. Thus, requirements for image recording systems are viewed from the standpoints of system perfor-mance, system operation, product type, and product quality.
In the course of evolving a completely new news picture distribution system for the Associated Press, we have developed a facsimile system using laser scanners and dry silver paper. It is believed that a substantial improvement in cost/performance ratio has been achieved. The system features feedback intensity control of a modulatable He-Ne laser, a flat-bed double pass optical system, a galvanometer-driven mirror for horizontal scanning, paper motion for vertical scanning, and oven pro-cessing of the exposed paper. The tone scale is controlled with stable processing conditions and a non-linear amplifier to compensate for the D log E characteristic.
A significant revolution in printing plate-making technology has been developing for the last few years -- a revolution which could mark a major step in the transformation of printing technology from the mechanical basis of the 19th century to the electronic techni-ques of today. The revolution is changing some old concepts -- both in newspaper press-rooms, and in high-technology development laboratories. New languages are being learned as engineers familiar with the world of coherent optics learn the world of Goss presses, ink, paper and the deadline. After years of development, the laser platemaker is now emerging as a practical production tool.
Transparent electrophotography is a technology which has demonstrated photographic quality. It has the versatility to sup-port many of the diverse needs of image recording, storage, retrieval and up-date.
A laser beam recorder for analog data has been constructed having recording precision adequate for Fourier readout with 30 to 40 dB suppression of all spurious signal-like effects that could be caused from recording inaccuracies. It has been shown by Baker and Corcor-an (Ref. 1) that to attain such a high ratio of spurious effect suppression requires recording accuracies in terms of a small fraction of a recording spot dimension. Furthermore, the required spatial precision in line straightness, line parallelism, line spacing, vertical line alignment, scan velocity along lines, and other factors, must have an accuracy equivalent to 2 to 3 phase angle degrees of the highest recording frequency or 1 to 2 percent of a spot dimension. For the 6 micrometer spot employed, this spatial accuracy requirement amounts to 70 to 100 nanometers or 3 to 4 microinches.
A real-time, non-photographic, high-resolution Laser Microprinter without photographic film and processing is presented. It produces permanent 35 millimeter slides of special metallic thin-films, by means of laser scanning of 81/2" x 9" half-tone pictures. Laser scanning occurs with a rotating drum system. Transfer of the original picture content takes place by means of AM/PDM conversion of the backscattered reading laser intensity, to pulse-duration modulation of the printing laser. Actual Laser Microprinting comprises 20 linear density steps of 0.1, by means of changing the "hole" size in the metal thin-film of the microprint.
We may now take a look at the other end of the scale, after dis-cussing the relatively low resolution applications such as TV and facsimile, perhaps we can consider the reconnaissance quality pictures and imagery which may be considered to have started laser scanning and recording as a technology about ten years ago. I wonder if Sam Bousky, Carmine Masucci and Al Jamberdino, who are among the best representatives of that technology, might express themselves as to what directions are being taken in that field.