Improved performance in many optical instruments has been achieved by considering coherence effects in the design of the optical instrument. In this paper such improvements are reviewed by heuristically describing the fundamental principles of partial coherence which are required in the design of such instruments. Furthermore, these coherence effects, which arise from both coherent and incoherent sources of radiation, are illustrated by discussing a selected set of instruments in which improved performance has been achieved. These examples include high-resolution recording and analyzing instruments which use incoherent sources, as well as imaging and mensuration instruments which use coherent sources. A set of guidelines for determining when coherence effects influence system performance with respect to linearity, resolution, and noise is also presented.
Laser recording has penetrated still another field, the storage and retrieval of widebandwidth, high volume digital information. Initiated in the 1960s, matured in the 1970s, optical recording is now embarking on technology breakthroughs aimed at addressing requirements dictated by theexplosion of information now available for recording, storage, analysis, and dissemination. The capture and retention of this high volume, widebandwidth and highly volatile information can now be made possible largely through the successful maturity of advanced wideband laser recording methods.
One of the earliest practical applications of lasers was in the field of recording. The laser provides a source of radiation that is convenient to modu-late and sufficiently intense to affect permanent changes in materials (recording). Both signal and image recording systems have been built using silver halide film as the storage media. Now under development are optical disc techniques that ablate special coatings on the disc surface. The laser work has been funded in general because the requirements at hand could not be met by more conventional technology. The engineering of these systems has resulted in working with the ultimate in mechanical precision, the highest optical quality available, and at electrical bandwidths that push the state of the art. This paper describes the early work in laser signal recording, the significant accomplishments in image recording, and the current efforts in optical disc recording.
This article describes a laser beam image recorder, which has been designed and fielded for a minimum amount of flexibility for the operator and a maximum amount of control by a remote sensor minimizing the operator duties and requirements. It is also designed for the shelter environment of a tactical and field operation, where the environment is not so benign. With the advent of recent electronic sensors, the capability for data linking information directly to ground with immediate image production is now feasible. The laser beam recorder, which RCA chose to call the Tactical Laser Beam Recorder because of its application, has been designed to meet three general types of applications which are somewhat similar. They are systems with electronic sensors and data link capability, where images can be immediately produced, all in high resolution. The information from an Air Force remote sensor system is directed to the Tactical Laser II earn Recorder which records a latent image, immediately processes the film on a continuous in-line basis, and slides the film automatically across the photo-interpreter's tables. Simultaneously, a tape recorder records the information in the airborne reconnaissance plane in the event that a data link is not maintained,
The High Resolution Film Recording System (HRFRS), recently delivered to NASA/Goddard Space Flight Center by RCA, is uniquely characterized by full flexibility in: resolution (1,000 to 20,000 pixels/scan), line rate (15-350' lines/sec), data rate (0.5 to 20 Mbit/sec), optical spot size (10 itaM to 200 pm), pixel aspect ratio (0.5 to 2.0), and frame aspect ratio (0.5 to 2.0). This flexibility is designed to accommodate the specific characteristics of all NASA's satellite, imaging sensors of the 1970s and 1980s. RCA renamed this system Operation Laser Beam Recorder (OLBR) to reflect the production environment in which this versatile, high performance image recorder must operate. Design tech niques and objectives are presented which meet the required flexibilities while maintaining simplicity of design, repeatability, quality of performance, and operability in an image production environment. Human factors, careful partitioning of subsystems, and innovative design techniques are successfully employed to yield a versatile film recording system with a minimum of operational complexity..
A high resolution laser image recorder/processor for reconnaissance applications has been designed with an integral wet film processor providing rapid access to the imagery. This system operates over a wide range of film velocities with nearly instant film velocity change capability. The laser recorder/processor system is described. Specific details are given on the film and processing against a five-second development requirement. The method of obtaining consistent density over a 7 to 1 range of film velocities is explained in detail. A linear or definable density over a range of three density units is achieved with the equipment. Examples of product output are shown, demon-strating its high resolution, high quality, low grain, and large density range.
TOPICS: Image processing, Laser systems engineering, Digital imaging, Systems modeling, Image resolution, Data modeling, Image enhancement, Digital recording, Image acquisition, Digital image processing
This article is meant to provide the digital image recording community with an overview of digital image processing and recording. The Digital Interactive Image Processing System (DIIPS) was assembled by ESL for Air Force Systems Command under Rome Air Development Center's guidance. The system provides the capability of mensuration and exploitation of digital imagery with both mono and stereo digital images as inputs. This development provided for system design, basic hardware, software, and operational procedures to enable the Air Force's Systems Command photo analyst to perform digital mensuration and exploitation of stereo digital imagery. The engineering model was based on state-of-the-art technology and, to the extent possible, off-the-shelf hardware and software. A laser recorder was also developed for the DIIPS Systems and is known as the Ultra High Resolution Image Recorder (UHRIR). The UHRIR is a prototype model that will enable the Air Force Systems Command to record computer enhanced digital image data on photographic film at high resolution with geometric and radiometric distortion minimized.
Three electrophotographic films from James Rivers Graphics, Eastman Kodak, and Coulter Information Systems were evaluated for application to high performance data recording. An evaluation breadboard, designed to provide basic characterization of image quality and image stability parameters, included the recommended processing stations for each film supplied by the film manufacturers for high resolution toner particle deposition. The results of the sensitometric, holographic, and microimage investigations are presented. The sensitometric evaluation discusses the D log E curves, Dmin, Dmax, and contrast, the effects of processing on sensitometric properties, and high intensity reciprocity law failure. Covered in the holographic evaluation are discussions on diffraction efficiency of Fresnel holograms, latent image decay, image stability to temperature and relative humidity as well as extended and high intensity readout. The microimage evaluation section discusses RMS granularity and contact printing.
The complex optical index of refraction for evaporated films of tellurium has been measured using ellipsometry over the wavelength range 439 to 633 nm. Values of n and k as a function of wavelength and as a function of thickness are presented. The transmittance and reflectance of single layers of tellurium, as well as multilayer structures to be used for optical data recording media, are shown as a function of wavelength. Oxide formation of these films has also been measured, and a model for the role of oxides in altering adhesion of the films is presented.
Vanadium dioxide undergoes a semiconductor-metal phase transition at temperature of 340 K. When prepared as a thin film on a suitable substrate, the transition exhibits hysteresis, i.e. the curve describing the state of the film versus temperature is double valued. Here the material is capable of existing in equilibrium in either of two states at the same temperature. Both high writing speed and high spatial resolution are possible, contrary to what one might normally expect from a thermal process. The writing speed is limited by the time taken to deliver the latent heat of transition, and the resolution is limited by the diffusion time during which written and unwritten adjacent areas are out of thermal equilibrium. Both of these times are connected, and they along with the latent heat dictate the exposure. Experiments thus far have produced writing times as small as 30 nanoseconds and stored spots of a few microns in size. They by no means represent limits, and writing times of a few nanoseconds and spot sizes down to a few thousand angstroms appear feasible. A discussion will be given detailing the material as a high density recording medium including laser beam writing requirements, spot sizes, stored contrast, and signal-to-noise ratio. In addition, information on optical constants, latent heat and other physical parameters will be given along with some past results concerning long term storage, cycling, lifetime, and reciprocity.
Amorphous materials can be used in a variety of configurations for optical recording and storing of information. Focused laser beams yield changes in state between cystalline and amorphous, giving high quality images without ablation or post processing of the film. Tailoring material compositions to a particular application results in films that can be read in reflection or transmission, and store information in a read-only or erasable form. The materials inherently provide permanence of storage, even in the case of erasable films, due to threshold imaging mechanisms. Films can be coated on a variety of substrates, including flexible plastic, sheet plastic, and glass depending on reading and writing system requirements.
There are many high density optical recording systems that require storage media capable of high recording and playback performance. In this paper, the general requirements which govern the selection, design, and optimization of the recording media are described. The use of a high power diode laser as the recording and playback source is also described.
Continuing advances in the technologies supporting wideband communications and information handling are leading to extremely large volume digital data systems. Until recently, conventional storage techniques, through evolutionary product improvements, have been able to keep pace with this growth. The point has been reached, however, where incremental improvements are becoming technically and economically impractical for these demands. Recognizing the limitations of conventional data storage and retrieval techniques, Rome Air Development Center (RADC) has actively pursued devel-opment of alternate techniques for this rapidly expanding field and their application to the areas of mass storage, archivability, and rapid access. An overview is provided of RADC efforts in the data storage and retrieval area which encom-passes high density magnetic, laser spot, laser holographic, and optical disk technologies with data bandwidths ranging up to 1000 megabits per second (MBPS) and total data storage capacities in the 1011 to 1012 bit region.
The optical disc has become a viable candidate for mass digital data storage. Its unique characteristics make it suitable for archival, wideband, high density record and playback applications, as well as those requiring fast access to a large data base. RCA has been pursuing the development of such systems for government mass data storage and retrieval requirements. This work is centered around a unique "tri-layer" optical disc structure, which offers high sensitivity and signal-to-noise (SNR) at very high packing densities. The two major areas of pursuit are record and playback at data rates of 200 Mb/s or more and multiple-disc record and playback units for very large on-line capacities. Record and playback at high data rates are achieved through simultaneous multiple, parallel-channel operation. Single-channel rates of 50 Mb/s and multiple-channel rates of 150 Mb/s have been demonstrated on laboratory breadboard equipment. Concept designs for multiple disc record and playback systems are centered around two "jukebox" configurations, which can provide fast automatic access to large on-line data stores. A feasibility design for a reader unit with an access time of three seconds to 1013 bits (100 discs) has been performed. A second concept provides a capability of both record and playback of 50 Mb/s with an access time of seven seconds to 1013 bits.
The transition of digital optical mass storage technologies from the laboratory to an integrated deliverable system is a challenge whose time has come. Harris Corporation has accepted the challenge and will deliver a 1013 bit Archival Mass Memory (AMM) System. AMM provides: variable data ingest rates up to 50 Mbits/sec accommodating sources as diverse as telephone links, computer links, and satellite downlinks; Reed-Solomon error detection and correction (EDAC) coding to preserve better than a 10 -9 bit error rate (BER) for up to 10 years of operation without rerecording; real time optical spot recording of 109 user bits on each 148 X 148 mm diskette; storage and automatic on-line retrieval of data from 1024 diskettes housed in each storage and retrieval unit; less than 15 second access time to any record in the archive; simultaneous data recording and readout; forward file management for rapid user-oriented access down to the byte level; simultaneous access to multiple modular storage and retrieval units; and variable output rates up to 50 Mbits/second direct or interleaved for multiple variable rate users tied to the fiber-optic distribution bus. This paper outlines the system design and performance including the complex electro-optic technologies employed to provide high-speed high-density optical spot recording and readout.
From extensive measurements of diffracted power distributions from binary-data-page holograms, the probabilities of bit error are calculated to be as low as 5 x 10-8 for volume Fourier transform holograms in iron-doped lithium niobate. Results are determined as a function of reference beam angular position for different diffraction efficiencies, for the angularly multiplexed superposition of holograms with dif-ferent angular separations, and for different displacements of the Fourier transform plane from the electro-optic crystal.
Evaluation of the quality of cylindrical optical elements has always presented severe difficulties. Previous techniques have depended on either indirect methods or methods providing relatively poor resolution. A new basic interferometric technique makes possible direct figure characterization for cylindrical optics utilizing conventional interferometric equipment. Several variations are possible for different test conditions for both cylindrical mirrors and cylindrical lenses. This measurement technique has been applied successfully to cylindrical mirrors and lenses. The basic technique and several variations are presented and discussed. Examples of the results of actual tests are included with test conditions specified, and a complete listing of necessary conventional interferometric equipment is given.
Two-dimensional transforms of the chrominance components of the National Television Systems Committee (NTSC) color video signal are studied. The effects of interlace and subcarrier modulation on the spatial frequency spectra are treated in detail. Multidimensional sampling theorems for the NTSC signal are presented. The relation of interlacing and decimation-in-space for a two-dimensional fast Fourier transform (FFT) algorithm is discussed.
The fringes produced by a wedge with partially reflecting faces placed in the input plane of a coherent processor are shown to provide a conveniently tunable spatial carrier. This carrier is tunable in frequency and orientation and has a controllable fringe profile. This encoding scheme is ideal for a number of optical processing techniques. Its use for density slicing, an example of a nonlinear operation, is demonstrated.
The transformation relating two different views of a two- or three-dimensional object scene is derived as a function of the displacement of the camera, relative to the scene, between the taking of the two views. It is shown how this transformation can be used to place the two views into exact area registration, as required for interframe processing operations such as frame addition, frame subtraction, frame comparison, etc. It is also shown, for the case of a two-dimensional object scene, how the transformation relating the two views can be derived from the images themselves, without knowledge of the camera displacement. A practical example of this action is given, illustrating automatic exact area registration of the different views. The algorithm used is based upon a generalization of classical cross correlation in which the dimensionality of the correlation surface is extended from two to eight, corresponding to the eight degrees of freedom existing between any two views of a common object scene.
An absolute laser power meter based on the momentum ex-changed between the incident beam and a movable mirror is described. The force exerted by the beam on the mirror is proportional to the incident power. Thus, from the measurement of the force value, we can deduce the incident power carried by the beam. But, generally speaking, the coefficient linking the exerted force and the incident power contains parameters which cannot be known with precision. The conceived device we describe cancels these parameters.
The advantages and properties of InGaAsP laser diodes in the 1.0 to 1 .7 um spectral region are discussed. The structure, growth (both vapor and liquid phase epitaxy), and operating principles of these devices are briefly reviewed. State-of-the-art device results from 1.3 and 1 .55 um devices are then presented. The modal, thermal, and reliability properties of these devices, as well as their commercial availability, are also discussed, and possible directions for future applications are considered.
Shadows can add significant edge and surface detail to imagery and thus substantially increase the performance of automated correlation guidance systems. A shadow-generation algorithm was implemented to increase the accuracy of synthetic imagery used to simulate visible, near-infrared, and far-infrared sensors. Initially, a data base was established in which all surfaces were represented by a list of vertices and material codes and arranged according to a scheme of a priori masking priority. Each surface was then clipped against updated clipping polygons representing the silhouette of all previous surfaces that had higher masking priorities as viewed from the position of the light source. The resulting hidden surface was inserted into the data base and flagged as a shadow for gray-scale prediction by the appropriate sensor model. Because each surface is compared to a union of polygons rather than to individual surfaces, this algorithm is computationally efficient for use with large data bases.
Development and test work in the laboratory frequently requires variation of the size and radiative characteristics of a source which is used to provide the radiant power for effects or detection studies. To provide this capability, a system of multiple moving mirrors has been designed for use in optical beam shaping and image manipulation arrangements applied in optical diagnostic procedures and testing of optical sensor systems. Its particular features are a zoom capability of 30:1 and a total scaling range of 800:1, so that approaching or receding sources can be simulated in the laboratory. In addition, the effective source area and with it the accepted radiative flux can be varied over a range of five magnitudes. A detailed analysis of the system and its in-herent wavefront aberrations is given; the dynamic requirements, and methods to improve the optical performance of the mirror system are discussed.
An introduction to the computer image pattern recognition guidelines for accurately locating an object are presented in this paper. The accurate measurement of three-dimensional position requires a camera calibration process as well as the determination of corresponding image points in two images. The accuracy of the three-dimensional measurement depends upon the accuracy of the image matching solution. Since there is a variety of image matching techniques, the pattern recognition guidelines are reviewed which indicate that the optimum features are nonlinear, a posteriori probabilities of the measurements. These optimum features also maximize the trace of the between-class scatter matrix normalized by the mixture scatter matrix. However, the theoretical guidelines do not indicate how to determine simple measurement methods for the optimum features. Therefore, some experimental examples are presented which illustrate some practical solutions to the problem.
This paper discusses the capabilities and limitations of a pyroelectric vidicon camera used to profile 10 ,usec CO2 laser pulses. Points examined include dynamic range, signal-to-noise ratio capabilities, spatial resolution capabilities, uniformity of sensitivity, maximum faceplate irradiance, and required electro-magnetic (EM) and radio frequency (RF) shielding. The relationship between camera performance and pulse length is also discussed. Samples of data acquired and requirements of an adequate data processing system are presented.
Pyroelectric detectors have been developed at Los Alamos National Laboratory (LANL) for use with high-frequency applications such as laser fusion. Less than 50-ps total response time devices have been measured. The voltage responsivity with a 50-0 load is about 5 to 10 V/MW, requiring 10 to 20 mJ/cm2 to produce 1 -V, 1-ns pulses. The latter are 1 mm2 in area. High-speed devices with up to 1 cm2 area have been developed. A novel method of fabrication now permits voltage responsivities up to 50 V/MW with a 50-0 load. This improved sensitivity detector is slower than the fastest design but is still suitable for measuring 1-ns pulses.
In this paper, several techniques to reduce speckle noise (more generally signal independent multiplicative noise) in images are studied. The techniques include gray scale modification, frame averaging, low-pass filtering in the intensity and density domains, and application of the short space spectral subtraction image restoration technique in the density domain. Some discussions on the theoretical basis of the techniques studied are given and their performances are illustrated by way of examples.
The history of Badoz's principle of linear detection of fringes having a potential precision of 5 X 10-6 orders and its applications to the measurement of birefringence, to ellipsometry, and to interferometry are given. The application of the principle to a servo-scanning interferometer (Twyman-Green configuration) for the calibration of the instrument, the analysis of the data, and the determination of the absolute contour of small plates is described. The problems of the interferometry and the determination of absolute contours, and the prospects for improving the precision from that attained, 1 /70 fringe, to the very much greater potential of Badoz's principle are discussed.
The methods of computerized tomography (CT), developed for medical x-ray applications, can be adapted for use in studying plasma x-ray emissivity distributions in tokamaks and other magnetic confinement devices. Current generation CT scanners reconstruct maps of x-ray absorptivity on body cross sections by processing transmission data from a number of fan-shaped beams of x rays. Analogous fan beam emission data can be obtained from confined plasmas by collimating emitted soft x rays with a "pin hole" or slit and detecting them with a linear array of solid-state detectors. Data from a number of such one-dimensional views of the plasma can be used to reconstruct a two-dimensional "photograph" of the absolute x-ray emission in cross section. No a priori assumptions about the nature of the emissivity distribution are necessary. In this paper we demonstrate the feasibility of the technique by reconstructing test patterns with data simulated for a number of different types of detector arrangements. We also use the technique with real data to reconstruct a rotating emissivity feature on a cross section of Massachusetts Institute of Technology's Alcator A tokamak.
With this issue we revive a practice once common in Optical Engineering-the inclusion of tutorial material in the SPIE Reports. This offers me a chance to say what I hope these tutorials can accomplish and to seek reader assistance in finding topics and authors for future tutorials.