The following paper submitted by Dr. Barhydt on the effect of various parameters on the performance of nearly-BLIP search and surveillance systems is divided into two parts. In the first part, he discusses the noise equivalent target equation and radiometric performance of these sensor systems. The second part, to be presented in the next issue, will cover scanning sensor optimization, the filter mismatch coefficient, and staring mosaic sensors. From a sensor performance optimization point of view, I believe that the filter mismatch coefficient concept Dr. Barhydt presents should be of interest to sensor design engineers.
Modern high technology is somewhat taken for granted by most people. To those who have witnessed and participated, even to a limited extent, in the tremendous and rapid changes in electronics since the 1940s, the times have caused some confusion and consternation, but always with a sense of excitement and urgency to get on with the next development. Optics and its related technologies have been a part of this upheaval and have moved so far to the forefront that today the line between electronics and optics has all but faded out. Consider the implications of such disciplines as quantum optics, electro-optics, and opto-electronics. It was only a short time ago that the national determination to enter the space age and the advent of the laser accelerated optics toward its present place in high technology, with spinoffs into countless other fields. A listing of SPIE symposiums over the years indicates the extent of this penetration of optics.
Organic materials have been used for volume phase holographic recording media and for integrated optical devices. A summary of the chemical and physical properties of the organic materials which we have investigated is presented. We discuss the relationship of the optical properties of the materials to the device parameters and show how concurrent physical measurements including interferometry, EPR, and absorption and emission spectroscopy, have led to a consistent model for the mechanism of hologram formation, which involves the production of free radicals by hydrogen abstraction.
The photoelastic constants describe the effect of stress or strain on the refractive indices of materials. These coefficients are important in several applications. They are required for the computation of stress-induced optical distortion in optical systems such as high-power laser systems and they are needed for computing figures of merit for materials to be used in acousto-optic devices. Interferometric and polarimetric techniques are described for measuring piezo-optic coefficients under static load-ing conditions. Acousto-optic and Brillouin scattering techniques are described for measuring elasto-optic constants.
The propagation of intense optical beams through dielectric media induces changes in the refractive index which cause self-focusing and beam breakup in high-power laser systems. After a brief discussion of the origin and spatial anisotropy of refractive-index nonlinearities, methods for measuring the nonlinear refractive index coefficient are reviewed. The use of time-resolved interferometry is described in detail. Nonlinear indices for optical glasses and crystals measured at 1064 nm by this technique are tabulated. From these data, an empirical expression is given which, using the linear refractive index and partial dispersion, provides a good estimate of the nonlinear index of optical materials in the long-wavelength limit.
The optically induced change of the refractive index of electro-optic crystals, which was discovered over ten years ago in LiNb03, is now referred to as the photorefractive effect (by analogy with photochromism). Progress in our understanding of the microscopic mechanisms which has led to the development of optical recording sensitivities comparable to that of silver halide emulsions is reviewed. Possibilities for application of the effect to optical memories, holographic interferometry, and integrated optics are considered.
In the visible and ultraviolet regions of the spectrum the dominant source of scattered light from optical components is surface scattering by microirregularities. They are typically only a few nanometers in height but cover the entire optically polished surface. Since microirregularity scattering is inversely proportional to the square of the wavelength, the dominant source of scattering in the infrared is often macroscopic defects such as scratches or digs. Pitting of the surface by sand or rain erosion also contributes to defect scattering. Dust particles and other particulates are a third important source of scattered light in the near infrared. When specifying the surface quality of optical components to be used in low scatter applications, at least the rms microroughness of the surface and the scratch/dig specification should be given. (An improved scratch standard would be most helpful here.) Better yet is a functional test of the scattering performance of the component. The most direct functional test is total integrated scatter. A prototype instrument utilizing a Coblentz sphere and a HeNe laser operating at 3.39 p.m, where the dominant source of scattering is scratches and other macro-scopic defects; at 1.15 p.m, where particulates such as dust may be important; and at 0.6328 pm, where microirregularity scattering dominates, has been constructed to perform this functional test. A simple theory allows us to extrapolate the results at these wavelengths to obtain a reasonably complete picture of the total integrated scattering behavior of the component at any wavelength. Additional data are required to understand the angular dependence of the scattered light since the angular dependence of scattered light is related to the slopes as well as the heights of the surface defects. Such data can be measured experimentally and analyzed to give a more complete picture of the surface than is obtainable from total integrated scattering measurements alone.
With the rising importance of powerful lasers in the scientific and industrial communities, material failure by interaction with intense laser radiation is today also a common event. In this status report we review the understanding of the physical processes that lead to laser-induced breakdown in bulk materials and on their surfaces. The roles and interplay of various mechanisms, which depend on material properties and the laser light intensity and frequency, are discussed. The experimental basis for electron avalanche behavior at optical frequencies is discussed in detail. Multiphoton ionization is briefly described. Tabulations of measured breakdown thresholds for transparent solids (bulk and surfaces), metal surfaces, liquids, and gases, and of multiphoton absorption coefficients, are presented. Experiments needed for further progress are discussed.
The unique and demanding requirements on mirrors for use in synchrotron-radiation beams are discussed in the light of recent experience with current mirror technology. The crucial role played by optical scattering from real mirror surfaces is discussed along with scattering and roughness measurement results on available mirrors. Mirror-cooling requirements and implications are reviewed. The prospects for future mirrors with smoother substrates, larger sizes, greater stability against spontaneous or thermally generated distortions, and more complex optical figures are discussed as well.
Internal-reflection spectroscopy has found considerable use in the infrared for studying vibration-band properties, optical constants, surface electromagnetic waves, and guided modes in thin-film channels. This paper discusses the principal ideas, including the forms of the evanescent waves and the effects of refractive indices and absorption coefficients of various magnitudes, for various prism-sample combinations--for example, prism pressed against bulk sample, prism separated slightly from sample and prism with thin film. Also discussed are examples of applications of the techniques to the studies of (a) vibration bands in opaque materials and thin films, (b) molecules adsorbed to surfaces, (c) Raman scattering in thin films, (d) fluorescence in thin films and (e) surface plasmons on bulk metal surfaces and on thin films.
The measurement of very low optical absorption coefficients in bulk materials is described with emphasis on adiabatic laser calorimetry with long rod samples. Bulk absorption coefficients lower than 10-5 cm-1 have been achieved in both crystals and glasses using this technique. At extremely low levels, both sensitivity and discrimination between surface and bulk sources of absorption is required. The technique described is perhaps the best way at the present time of studying such low level absorptions.
Electroabsorptive phenomena such as the Franz-Keldysh effect have prompted a considerable number of new device concepts which have potential application in electro-optic systems. The fundamental physical processes underlying these phenomena along with the special material requirements needed to design such new devices are reviewed in this article. Emphasis is placed on the design of electroabsorption modulators, detectors, and filters as well as the latest state of the art of these devices.
Ferrous chloride is an antiferromagnet (AF) below its Neel temperature TN, but it may be driven into a saturated paramagmetic (SP) state by an external magnetic field applied along the c-axis. This AF-SP transition is first order below and continuous above a tricritical temperature Tc, a classic example of metamagnetism. With a pulsed dye laser, piezoelectric modulator, and a unique gated amplifier, we monitored the scattering of circularly polarized light by the mixed AF-SP phase below Tc. Above Tc the optical density of a sharp absorption line changes with the spin ordering; because the transition couples to spin fluctuations, the optical density maximizes in the SP phase. We have used these optical techniques to map the thermodynamic phase diagrams of FeC12 and FeC12 doped with cadmium, which to our knowledge is the first study of a randomly disordered critical system.
Techniques for resolving small transverse distances are compared with those for resolving small longitudinal displacements. As the desired resolution becomes finer, there comes a point where both problems are best solved by switching to the transform domain. Techniques for measuring displacement can be divided into those used for nonoscillatory versus oscillatory motions. Examples are described for achieving X/105 for the former and X/109 for the latter. Fundamental limitations are discussed.
Many complex optical and electro-optical systems are currently operating in the space environment, and other more sophisticated systems are being planned for future development and operation. Assurance of the survivability of these systems is typically provided by ground-based testing which simulates those aspects of the space environment considered most serious. Such testing, however, has not prevented occasional anomalous behavior and unexplained failures. To properly explain the degradation mechanisms affecting these systems and to obtain the engineering and testing data necessary for the development of improved systems, in situ testing in the space environment is required. The Long Duration Exposure Facility (LDEF) can provide this capability. Several of the experiments being developed for the first LDEF mission will seek to determine the ef-fects of the space environment on components which will form the key elements of future electro-optical systems, and a considerable number of related experiments have been proposed. The engineering and scientific community is encouraged to be-come aware of this activity and to participate in the planning and experiment development for future LDEF missions.
Tomography is the common technique used in nuclear medicine for obtaining information about the three spatial dimensions of a radioactive source. In this paper the advantages of using stereoscopy instead are demonstrated. Three systems are described for obtaining undistorted stereoscopic images of gamma ray sources. One of the systems described has been constructed and tested using four radioactive wires as sources.
In the course of developing a portable holo-camera for field use, a small battery powered ruby laser, based on an electronic flash unit, was built. In this letter we describe the laser in sufficient detail to allow others to build one for themselves.