This paper discusses aspects of wideband RF photorecorder design from the standpoint of equipment operation in an aircraft environment, at the advanced development model (ADM) level. Fundamental issues associated with photorecorder operation include selection of laser source, Bragg cell, and film type. In addition to fundamental or functional issues, operation in the aircraft environment imposes further constraints. This paper will outline design issues from each of these topics, and discuss approaches that presently are being incorporated in an ADM Bragg Photorecorder.
Expansion of computer managed, digitally stored image data coupled with improved sensors, expanding information sources, and needs, have increased demands for higher performance image generators with increased image sample (pixels) and higher geometric accuracies. This paper addresses a design approach which meets the next generation requirements for computer managed image generators/recorders.
A high resolution laser film printer is being developed for the United States Air Force. The printer is a high speed black and white image recorder, the Fire 240, which is being highly modified by the manufacturer, MacDonald Dettwiler and Associates, Ltd. (MDA). The printer will output 40,000 picture elements (pixels) and 40,000 lines on a film format of 9" x 9". To preserve the high quality of the digital aerial imagery inputs, the printer must meet stringent radiometric and geometric specifications.
A brief summary is given of the results of the full scale development of the Tactical Digital Facsimile, its planned and potential applications, and consideration for design improvements based on modifications within the state-of-the-art. The unique electro-optical design is described which includes a laser scanner and a laser recorder which is capable of two hundred lines per inch resolution and sixteen shades of grey. The application of TDF to the INTRA-THEATRE IMAGERY TRANSMISSION System (IITS) is described.
An optical disk recording and playback system was developed for mass data storage which utilizes 14 inch diametyy disks permanently housed in cartridges. Sixty-eight disks with a storage capacity of 10 user bits per side per disk are located in storage and may be accessed within six seconds or less. To access a disk, a cartridge is cycled from storage, through a transport position and then onto a load station. From this position, the disk is loaded onto a turntable where digital data may be accessed at a ratelof 100 Mb/s. The enhanced approach utilizes the previously reported upon jukebox concept , however, with an optimized system approach. All optical elements, as well as the translation stage, which dynamically positions the focusing head, are located above the optical table for ease of accessibility and maintainability. The disk itself is suspended and sealed in a .32 inch thick cartridge. The profile of the cartridge is ideally suited for mass storage applications, where volume growth of stored cartridges is only limited by practical considerations. The active area of the disk is completely enclosed, except during data access times, when the dust seals are removed from actual disk contact. The spindle that rotates the disk is supported on porous graphite air bearings while the disk itself is held in place via vacuum. The optical table, which supports all of the recorder's critical static and dynamic components, was designed to be isolated from external perturbations, as well as from on-table generated and then transmitted vibrations. The paper describes mechanism design, dynamic test results obtained in the handling of optical disks i cartridges, as well as the growth potential to a double-sided disk and write/read rates significantly beyond 100 Mb/s.
Design, analysis and implementation of an optical test channel device in the laser scanned visual system for use in 2B33 helicopter simulator. Device capabilities include: lateral and angular color convergence monitoring for the multi-laser system; monitoring of the laser transmission system alignment between the laser table (source) and the scanner subsystem located on a three axis dynamic gantry; measurement of transmitted laser beam pupil size and divergence; and laser beam power analysis up to the scanner subsystem.
Beam deflectors used in laser scanners and printing systems cause cross axis spot placement errors due to mechanical wobble of the deflecting mirror in oscillating mirror scanners and due to facet to facet and bearing noise errors in spinners. Small errors become objectionable for high resolution printing and scanning systems. The usual techniques for measuring cross axis wobble and scan amplitude stability are laborious and the data obtained is difficult to interpret. A method based on real time signal analysis is presented which quantifies the scanner performance quickly and accurately.
Scan velocity variation in a flying spot laser scanner is a major contributor to pixel placement errors. Two sources of scan velocity variation are Motor Hunt and Polygon Signature. Since the incremental change in frequency needed to correct scan velocity variation may be very small, a highly accurate method is required to both measure the facet-dependent velocity differences and correct them.' An all-digital system which has the required high accuracy has been successfully demonstrated for the correction of these effects. The system employs a crystal time base and adjusts the frequency of a bit clock by fractional control of its phase. The accuracy of the measurements of the polygon characteristics is augmented by averaging many measurements.
Scanning with laser illumination is becoming increasingly utilized as a tool to inspect materials, parts and assemblies for a variety of features, including dimension, orientation, flaws, contamination, patterns and transit velocity. This method of acquiring an image has a number of technical advantages over more conventional vision systems. Improvements in resolution, depth of field, contrast, signal to noise ratio, speed and versatility can be realized when scanning laser light as a detection method. A typical inspection scanning system is described and a number of features are discussed. Trade-offs between alternative methods are given. One drawback previously facing users of laser scanning systems has been polygon deflector induced tracking errors in the scan. A. novel method of reducing such errors is described. Performance characteristics and typical in-practice advantages are listed.
Low power, air-cooled Argon lasers with internal mirrors are now replacing external mirror designs in most O.E.M. applications. This recent change in design philosophy has been driven by the laser needs of the rapidly growing laser graphics and image handling industries. While these users are now developing more sophisticated systems, they are also improving production and field service economies. For these reasons a need for low cost, Helium-Neon like dependability in O.E.M. Argon lasers has developed. Although the major benefits of this new technology are greatly improved life, reliability, and low cost; there are also improvements in warm-up characteristics, power and beam pointing stability, and reduced low frequency noise. Data illustrating these improved performance characteristics is presented.
Recently a new method of retinal imaging by laser scanning ophthalmoscopy was developed that overcomes the intensity problem of conventional fundus photography and promises further advantages. The laser scanning ophthal-moscope has been modified by incorporating an adaptive optical feedback system for laser beam control. For wave-front reconstruction maximum likelihood methods and the Gerchberg-Saxton-algorithm are applied. The system essentially provides an elimination of optical eye aberrations which diminish the fundus image quality. On the other hand by active focus control and/or wavefront sensing the aberrations of the human eye like astigmatism of the cornea and spherical aberration of the lens can be measured.
The image quality performance of laser printers can be enhanced through closed loop photoreceptor monitoring and control. The photoreceptor surface potential in an exposed area is maintained at a target value through control of the optical exposure. The control mechanisms of both the photoreceptor potential and the optical exposure which are specific to the Datapoint 9660 Laser Printer are presented.
A discussion of advances in computer driven laser scanners for graphic arts is given. Presented is a development history of the LASERITE Laser Scanner System. A detailed description of the patented pyramidal scanner is given. The Computer-to-Plate system which is being used in newspaper production is discussed. Various types of laser imaged output for other applications is illustrated.
Design and fabrication considerations for multi-electrode modulation in a single acousto-optic device operating in the near acoustic field are presented. In particular, topics including acoustic and electrical crosstalk and electrode apodization to control Fresnel effects of the sound column on diffracted light are discussed; a concept of nesting electrodes to create overlapping laser beams is introduced.
The guidance of remote bodies is increasing in importance. The use of wire, or similar, links has obvious drawbacks and radio frequency systems are prone to interference. The laser generates a low divergence beam, which may have a high power density, that may be transmitted into a pattern that can provide information to the guided body. Several systems exist which achieve this but most require a second synchronisation source. The scanned pattern described is self synchronising but is such that it can not easily be generated using a mechanical system. The scanner is a solid state acousto-optic system.
The tobacco industry has required a means of reducing tar content of inhaled smoke from cigarettes for some time now. One effective way of achieving this is to perforate the tipping paper (cork or plain) which wraps the cigaratte filter plug. Air is drawn into and mixed with the smoke as the smoker inhales resulting in two effects on the smoke. The first is that it is diluted and the second is that the air-smoke mixture is cooled. The dilution of the smoke probably has little significant effect since the total smoke inhaled per cigarette is always the same. The cooling of the smoke, however, causes the tar present to condense more readily on the filter plug and so represents a genuine reduction in tar content. In the light of increasing health consciousness both from popular movement or deliberate Government propaganda the importance of this method of tar reduction is well recognised in the industry.
A brief summary is given of a laser scanner system used for printed circuit board production. A patented pyramidal scanner is the essential element of the laser imaging system. Discussion of required optical corrections to meet accuracy requirements is given. Application to direct exposure of dry-film photoresist is discussed.
Acousto-optic techniques for the generation of spot matrix alphanumerics on continuously moving target material are described. The systems utilise a high p.r.f. Nd:YAG laser to mark the characters point by point. Two approaches are considered: a simple system using a single acousto-optic deflector is briefly discussed which relies on the movement of the target material to provide the necessary shift in the orthogonal direction; and a two axis system is described which enables a high utilisation of the available laser pulses, resulting in a high throughput rate of the marked target material.
The LTV Aerospace and Defense Company is currently developing a two dimensional infrared spatial modulator system. A laser projector using an 18 watt ND:YAG laser writes a raster on the modulator which is back illuminated by a blackbody source. Subsequently, the two dimensional infrared pattern is projected onto an IR sensor for viewing. The paper describes the optical and system design criteria of the laser projector which is used to write onto the spatial modulator. The laser projector employs a number of novel techniques to meet the performance specification of the system. In this application an acousto-optic modulation technique known as Scophony modulation is used. Scophony modulation was originally proposed at the beginning of this century for conventional television projection. For current laser projectors it has a number of inherent advantages which range from the ability to modulate high powered lasers with high temporal bandwidths, to improved spatial resolution which results from the coherent imaging process. The expected horizontal resolution is equivalent to 1325 line resolution in the visible region of the spectrum.
In the course of my work I have done information gathering towards technology assessment, given seminars within NCR Corp. on laser scanning applied to microimaging from which the following work evolved. It is therefore appropriate to give this paper the subtitle "Evolution of a laser-scanning system for Advanced R & D purposes".
This paper is an overview of electro-optical methods for generating a sequence of pixel clocks related to the angular rotation of a scanner excited in a sinusoidal motion. The emphasis is on the methods of synchronizing the clock generator to the scanner motion and the trade-offs between scanner frequency, pixel placement accuracy, and the total system resolution. The methods are applicable to data input and output applications. Both digital and analog implementations of a clock generator are explored, and the drift and stability issues examined. Scan field distortion correction capabilities are also detailed. The conclusion is that an electro-optical scanner system offers many of the features of a high quality spinner system at a lower cost.
Presented is a versatile precision digital encoding technique for mechanical resonant scanners. Described is it's application to electronic correction of the sinusoidal scan pattern traced. To contrast the flexibility of the electronic encoding technique a number of direct correction methods are described.
Ronchi rulings can serve as low cost, high precision position references in galvo-based, actively-stabilized laser deflection systems. An overview of beam position sensing principles is presented, including a comparison of the design trade offs between monotonic and periodic position sensors. Next, methods are described to use a Ronchi ruling as a mask to define a series of identical locations on a media. Each location is the gap between two bars of the Ronchi ruling. By focusing the beam onto the grating, and introducing a high frequency, low amplitude dither in the beam position, a position signal can be generated which is zero when the beam is centered between two grating bars. This signal is suitable for use in a position stabilization loop which keeps the beam centered at the particular location. A method of using a pair of quadrature signals (including the dither position signal) is described in which the beam position can be tracked while scanning across many locations. A dual mode demonstration system is described which accesses any of 63 positions with a settling time less than two milliseconds. The spot size is 50 microns, resolution 1 micron and drift is not measurable. Techniques for extending the one-dimensional deflection to two-dimensional (x-y) operation are presented.
The basis principles of holographic scanning will be reviewed. Topics will include - zone plate analysis, aberrations, scan multiplication, scan line straightening, recording media and manufacturing methods. Several applications will be discussed, with particular emphasis on bar code scanning.
A high resolution and high speed 2-D holorgaphic scanner is described. In addition to straight scan lines and good linearity, the scanner can be designed to be insensitive to mechanical eccentricity and wobble. This scanner can be readily extended for high resolution 3-D and double-raster scans. The latter has a large field of view (with lower resolution) and at the same time a high resolution in a small central area. This is similar to human's eyes and thus can be explored for robot's vision
Holographic deflectors of various designs have been reported in the literature for at least 15 years. SPIE Proc. 390 contains a description of an important design by Kramer and an adaptation of the same by Funato. Both systems use a surface relief grating structure in photo-resist; similar devices and performance have been obtained in DCG grating structures that are also rugged, environmentally stable, AR coated and highly efficient in both polarizations. Fabrication procedures and performance characteristics are given for the Kramer type deflectors in DCG.
A cost effective approach to accurate, automated Gaussian beam diameter measurements is described. The measurement system uses an inexpensive computer and interfacing to a moving slit beam scanner. The software is written in Basic and machine language. The choice of using either language at any point of the program is based on tradeoffs between speed and instruction compactness in memory. The operator is allowed to make other tradeoffs at data taking time. The algorithm, which interprets intensity data from the beam scanner, gives a beam diameter measurement that is invariant to ambient light and d.c. offsets in the electronic circuitry and is relatively immune to noise. Factors that influence the choice of program flow and hardware configuration are discussed. The choice is optimized for an operator who expects fast, reliable and accurate measurements from a simple and inexpensive measurement system.