Electro-optical imaging has extended man's capability to observe his world beyond the dreams of science fiction writers of just one generation ago. Man has placed his eyes on the surface of the moon, Venus, and Mars-spacecrafts took fascinating closeup pictures of Mercury and Jupiter. Who was not awed by seeing the earth rising above the rugged mountain ranges of the moon?
Solid-state imagers will displace electron-beam scanned imagers in applications which conventional TV does not satisfy. These are imaging from a moving platform like a weather satellite, imaging requiring very large intrascene dynamic range, imaging of very low contrast scenes and imaging in the infrared. In very low light level imaging, "photon counting" techniques with an ICCD can eliminate problems of dark current and preamplifier noise to provide high signal-to-noise ratio for improved radio-metric accuracy. At present, solid-state imagers lead for large effective dynamic range, maximum signal-to-noise ratio, free-dom from lag, geometric fidelity and metricity, and stability of characteristics, as well as for compactness, long life, and low operating voltages. Tubes lead for the greatest number of resolvable elements per frame, for producing images with better element-to-element uniformity, and for maximum output data rate on a single terminal.
A direct coupling experiment between a 5-micrometer photo-voltaic mercury-cadmium telluride detector and a CCD multiplexer is reported. No detectable degradation in signal-to-noise ratio was experienced and D*x peak = 1.6 x 1011 cm Hz1/2/W (BLIP) was obtained after the CCD multiplexer, when the photodiode at 77°K was irradiated by the 300 K background with 180-degree field of view, chopped at 723 Hz.
Detection of 1.5 to 2.3-micrometer radiation is important for a number of earth resource and military applications. Hgi_xCdxTe photodiodes have recently been developed which offer substantial improvement in operating temperature for detection of 1.5 to 2.3-micrometer radiation. For example, arrays of Hg1-xCdxTe photodiodes with cutoffs in the 2.0 to 2.3-micrometer spectral range have achieved detectivities of 1.0 x 1012 - 4.0 x 1012 cm Hz1/2/W at an operating temp-erature of 193 K. In this paper we present results on these (Hg,Cd)Te photodiode arrays.
The fundamental question in determining radiometric accuracy in a Forward Looking Infrared (FLIR) system is "What does the detector see?" The answer is that it "sees" with thermal radiation originating from emitting surfaces in a completely enclosed surround by virtue of the various transfer mechanisms -reflection, refraction, and scattering. To achieve high radiometric accuracy, the detector ideally would "see" only the object. However, due to effects such as lens emission, lens surface reflection, mirror surface emission, calibration source reflection (emissivity less than unity), and vignetting, the detector "sees" many other points in the field of view which are interpreted as part of the target itself. Other factors could contribute, e.g., cosn falloff, distortion, and pupil aberrations. From the viewpoint of the detector, all of these are closely related to vignetting, where the detector is partially "seeing" walls and lens mounts together with reduced intensities of radiation from the object scene. The approach here is to determine radiometric accuracy across the field of view on the basis of contributions from geometrically-defined sources outside of the object. Such a spatial spread of detector view must be combined with the temperature distribution to determine the radiometric accuracy of the system as well as image effects such as shading and narcissus. What the detector "sees" is determined by a computerized backward trace of many rays from the detector. To determine the variation across the field of view, this computation is made for a number of rotations of the scan mirrors. In the case of a FLIR designed for imaging and display, a high relative radiometric accuracy is required. For a FLIR used as an absolute radiometer, absolute radiometric accuracy close to the noise equivalent temperature difference of the system is achievable.
Ground-based astronomy has been carried out for thousands of years using the human eye and, in the last century, photographic film. The recent addition of orbiting platforms has forced the development of new image sensors, several of which have already seen use or are in advanced stages of development. In this paper, we will discuss the use of electro-optical image sensors for spaceborne astronomy. Several aspects of the spaceborne imaging problem will be examined, including the astronomical phenomenology and the reasons for the use of electro-optical devices for stellar imaging. The problem of detection and measurement of stellar objects will be discussed in terms of photo-electron statistics and image quality of the optics and image detector. Astronomical and device parameters will be used to give typical sensitivity limits within the context of the Space Telescope Program. A detailed model for the sensitivity limit is given.
The Return Beam Vidicon (RBV) is a high performance electronic image sensor and electrical storage component. It can accept continuous or discrete exposures. Information can be read out with a single scan or with many repetitive scans for either signal processing or display. Resolution capability is 10,000 TVL/Height, and at 100 1 p/mm, performance matches or exceeds that of film, particularly with low contrast imagery. Electronic zoom can be employed effectively for image magnification and data compression. The high performance and flexibility of the RBV permit wide application in systems for reconnaissance, scan conversion, information storage and retrieval, and automatic inspection and test. This paper summarizes the characteristics and performance parameters of the RBV and cites examples of feasible applications.
The number and variety of digicon-type devices has been increasing at a rapid rate in the last year. This paper describes most of those which are new either in type of array used, design of electron optics, photocathodes, faceplates, or unusual applications. New parallel output digicons have been built using large two-dimensional arrays for UV and visible photometry. and spectrophotometry. An intensified charge coupled device with 10,000 channels will be described and test results given. Single photoelectron pulse height distributions for CCDs used in the electron bombardment mode will be shown and the first data on the use of avalanche diodes to detect photoelectrons will be given.
Charge coupled imagers present special problems not encountered with beam-scanned sensors. This paper describes some of the instrumentation, procedures, and analyses used to evaluate charge coupled imagers. A simple analog technique for extracting signals from noise is discussed. Techniques are given for measuring and interpreting MTF (modulation transfer function), limiting resolution, temporal and spatial noise, image spreading, and image lag. Effects peculiar to CCDs (charge coupled devices) and CIDs (charge injection devices), such as aliasing and image smearing, are discussed.
Possible system applications of Infrared Charge Transfer Devices are reviewed. It is found that this device technology can have a very significant systems impact. Analyses are performed to calculate the quantum efficiency, quantum yield, frequency response, photoconductive gain, operating temperature, noise and the distinction between longitudinal and transverse bias configurations of silicon detectors. Tables of silicon detector properties are included. Approaches to the interface circuitry which couples the detectors and the CTD multiplexer are examined. Examples of existing low background and high background IRCTD detector arrays are given.
Single-ended laser radars using discretely tunable infrared gas lasers have been demonstrated to be capable of high-sensitivity remote measurement of gases. Two systems have been investigated: (1) a deuterium fluoride laser was used for remote measurement of the integrated concentration of HC1, CH4, and N20 between the lidar system and a topographic target; and (2) a CO2 laser was used for range-resolved measurement of water vapor using radiation backscattered from naturally occurring aerosols in the atmosphere. Calculations indicate that range-resolved concentration profiles can be obtained for many gases at a range of 10 km using commercially available components.
Dichroic iodine polarizers with light transmissions over 50% approach the critical range of applicability in Liquid Crystal Displays (LCD) because of fading and polarization loss on environmental exposure. This degradation and the development of edge bubbles with adhered polarizers are two of the major problems encountered in constructing the display. The manufacture and properties of LCD polarizers are described in order to understand the sources of and solutions to these problems. Other required properties, such as UV resistance, heat and chemical stability, are obtained by proper material selection and rigorously controlled manufacturing conditions. Selection of adhesives for bonding polarizing elements to the LCD cell is critical as the adhesive can become the major factor in determining the life of the polarizer. Accelerated environmental exposure of several commercially available adhesive systems indicates a wide range of stability.
A device utilizing a fluoroscent screen was fabricated to assist in the evaluation of x-ray beam alignment of fluoroscopic systems. This device is employed for routine equipment checks and adjustments of the following physical factors: (1) alignment of the x-ray beam with respect to the image intensifier (and television chain), (2) field size congruence with the spot filming device and/or the image intensifier, and (3) source-to-tabletop distance (STD). The description and operational procedure of this device are demonstrated in detail.
This paper describes a development program which uses sunlight concentration techniques to effect an immediate reduction in cost-per-unit power for photovoltaic systems in which solar cell cost dominates the total system cost. Current examples of concentrator solar cell technologies are single crystal silicon and gallium arsenide. Implementation of cost reductions by the use of sunlight concentration is not dependent on the development of low-cost, mass-production cell technologies but emphasizes high cell efficiency and low-cost concentrator systems.
The potential advantages of the Mach-Zehnder Heterodyne Interferometer as a rotation sensing device are discussed. Recently, a Mach-Zehnder Heterodyne Interferometer was described which allowed the direct reading of changes in the relative phase between the two beams. This was achieved by the use of a phase comparator that develops a voltage which is linear with increasing relative phase. The purpose of this note is to point out the potential advantages that such a device could have as a rotation sensor. Of course, the capability of a passive interferometer to sense rotations has been known since Sagnac's work. More recently, interest has centered on the ring laser gyro as an active interferometer. Both devices have disadvantages that limit their usefulness. The Sagnac Interferometer reflects rotational motion by a fringe shift which is proportional to the rate of rotation.
The Influence of Other Sciences on Optics Since, at least in my contention, optics per vades nearly all facets of science, I make no apology here when describing the life of a man known primarily for his contributions to mathematics. I refer to Joseph Louis Lagrange. (1736-1813). The comments presented here dwell primarily on his character and on the influence he had on his contemporaries, and has on present-day scientists. It is hoped that the relationship of this man's life to education in optics will become clear without delineating the details.