A method is described for ordering the fringes in an ordinary moire topogram. It requires no a priori shape information and resolves "hill-or-valley" ambiguities using local surface reflectance properties. The theoretical and practical constraints of this method are discussed, and analyzed examples are presented as experimental evidence.
A NASA laboratory for evaluating linear detector arrays for remote sensing applications from the visible to shortwave infrared is described. Nominal requirements for acceptable sensor performance are presented for the critical parameters of signal-to-noise ratio, modulation transfer function, response linearity, dynamic range, and detector-to-detector response uniformity. Results of tests are presented for a custom-developed multispectral linear array from RCA and two commercial arrays from Texas Instruments and Reticon for the visible and near infrared. The custom array was clearly superior to its off-the-shelf counterparts in signal-to-noise ratio and dynamic range. All the arrays were found to have somewhat less than desirable modulation transfer functions but excellent response linearity.
Thermal imaging system performance is described by the minimum resolvable temperature difference (MRTD), which is the spatial-frequency-dependent thermal sensitivity. Three different MRTD models are presented. Two are based on the adaptive matched filter concept in order to describe the human eye-brain combination. The third uses the limited synchronous integrator concept. In all three models the usual assumptions of periodicity and of one-dimensional targets are replaced by two-dimensional and more realistic representations of the targets. MRTD expressions are derived for these three models, and the values calculated from them are compared with the Ratches-Lawson model predictions and with measured results for two different systems with known parameters. It is shown that the limited synchronous integrator model results in a more accurate functional dependence of the MRTD on the spatial frequency. The prediction error commonly found in the low frequency region is reduced, and the overall accuracy is enhanced throughout the frequency range of the system in comparison to the Ratches-Lawson model.
A new integral equation is presented and solved by a matrix method based on iterative procedures to obtain information about the transmission and reflection of light (scalar field) in inhomogeneous media. The method, which may be applied to a wide category of arbitrary x,y,z-varying refractive index profiles, is used to study the holographic lens/ SELFOC optical fiber coupling system. The properties of the spatial transfer function for invariant linear systems are used.
An automated image-shearing microscope for measuring the lengths of the gaps in magnetic recording heads is discussed. A model, developed for a manual measurement system, is used to identify sources of measurement error. The architecture of an automated measurement system is described in detail. Algorithms for automating the measurement process are presented, and the model is extended to analyze their performance. These algorithms include a method of finding a clean site, of automatic focusing, and of automatic measurement based on image shearing. The effects of system parameters such as illumination bandwidth, focus error, and transducer resolution are investigated, and it is shown that gap lengths as narrow as 0.5 µm may be measured reliably. Performance tests show that the system can measure gap lengths to better than 0.01 µm (lo) reproducibility in less than 4 s.
The optical and electronic design of the Halogen Occultation Experiment (HALOE) elevation sun sensor is described. The HALOE instrument is a gas-correlation radiometer now being developed by NASA Langley Research Center for the Upper Atmosphere Research Satellite (UARS). The system uses a Galilean telescope to form a solar image on a linear silicon photodiode array. The array is a self-scanned monolithic charge-coupled device. The addresses of both solar edges imaged on the array are used by the control/pointing system to scan the HALOE science instantaneous field of view (IFOV) across the vertical solar diameter during instrument calibration and then to maintain the science IFOV 4 arcmin below the top edge during the science data occultation event. Vertical resolution of 16 arcsec and a radiometric dynamic range of 100 are achieved at the 0.7 µm operating wavelength. The design provides for loss of individual photodiode elements without loss of angular tracking capability.
Combining the concepts of phase-only filtering and multiple-exposure holography, we propose a method for making a phase-only composite filter using a plane reference wave as the carrier. We used this filter for the optical recognition of four kinds of hardware items, and the results of a computer simulation are presented. The characteristics and possible applications of this correlation recognition method are discussed.
Alternating bismuth/selenium multilayered films prepared by thermal evaporation show an exceptionally high optical recording sensitivity energy threshold of 0.5 nJ for 50 ns pulses because the absorbed light heats the film until it begins to melt, at which time an exothermic reaction between the Bi and Se releases more energy. Electron microscopy reveals that the bits written on the multilayered Bi/Se films are very clean. The intrinsic signal-to-noise ratio, corrected for the substrate defects, of a digital signal recorded in these films was about 55 dB and was the same as or slightly better than that of a 300 A pure Te film on a glass substrate. An earlier study by AT&T Bell Laboratories showed exceptionally good environmental stability of the Bi/Se bilayers; some Bi/Se bilayer films deposited more than 10 years ago still show little sign of degradation. For write pulse energies below those required to form a hole, the write beam causes the reflectivity of the film to increase because of Bi2Se3 formation. The thermal annealing of the film at 220°C for 1 min results in a similar reflectivity increase. This reflectivity increase effect could be used to write format information, and hole formation could then be used to record user data.
High resolution airborne or vehicular imaging systems are often limited in performance by mechanical vibrations. High vibration frequency MTF is known. Low vibration frequency MTF is a random process analyzed here. Average and ideal maximum spatial frequency limitations are calculated. Plots are presented to describe the number of independent images of the same object required so that at least one "lucky shot" with a given spatial frequency requirement is obtained with a given probability. Examples for short and long relative exposures are included. These data can be used to statistically define expected performance of high resolution systems and to aid accordingly in sensor selection. The probability of achieving higher resolution improves noticeably as relative exposure time is decreased.
This paper presents a new temperature sensor that utilizes multimode optical fibers for light transmission and a thermochromic transducer for temperature sensing. The working principle of the transducer, technical data on the optoelectronic system, and experimental results are presented.
The results of a research program on the delivery of high-peak-power laser light via fiber optics are presented. We discuss the influence of the host medium and the optical signals on the choice of fiber materials, complemented by a consideration of the measurement environment's effects on the quality of the data. We pay close attention to the choice of input/output beam/fiber coupling optics, nonlinear processes in the core, measurement system noise, and baseline drifts. Useful discussions of pulsed laser damage to optical fibers and data for optimization of a given fiber optic laser beam delivery system are given. As an example, details are given of the optical and instrumentational aspects of a particular fiber optic system developed for remote sensing of pressures and temperatures of UF6 gas in an operating advanced gas centrifuge.
We report the results of an experimental study of optical power losses due to lateral offset of the input aperture of a step-index optical fiber used to scan a point source. Data were taken with hard-clad silica and plastic-clad silica fibers having core diameters ranging from 200 to 1000 µm. These results will be useful in establishing alignment criteria for the optical components used in our laser-based remote thermometry research program.
A concept is described for phasing the outputs of a multiple telescope array used as a laser transmitter. The technique uses samples of the transmitted beams to control optical path lengths through the separate telescopes so that the beams add constructively at the receiver. The phasing concept is applicable both to systems that provide inputs to the multiple telescopes by dividing a single laser beam and to systems in which the inputs to the telescopes are multiple, phase-locked laser beams. The approach is also compatible with single line and multiline lasers and does not entail stringent alignment requirements. The concept uses a three-step procedure to find the zero optical path difference condition and to effect fine control of the optical path lengths through the different telescopes. Algorithms are described for estimating the phase mismatch from focal plane measurements. The technique is susceptible to errors induced by local aberrations within the individual telescopes. The errors and one possible solution, the use of redundant measurements, are discussed. Performance requirements for a phased-array laser transmitter are described.
With this issue, I have completed my second year as Editor of Optical Engineering. I'm certain that this disclosure has elicited a big "ho hum" from a number of you, unless you happen to be among those who are eagerly anticipating my retirement. The bad news-particularly for those who do not appreciate my editorial style-is that I have agreed to stay on as Editor at least through June 1989. However, the good news is that Martha Stockton, my Associate Editor, has agreed to stay in her position as well. One last comment before getting on to the main topic of this editorial; May 311,1987, is rapidly approaching, and I am still wondering what event will occur that might have the same sort of impact on my life as the events of May 31 of the two preceding years (see my Editorial in the June 1986 issue). In a recent conversation with Eric Pepper, the Managing Editor of Optical Engineering, I learned that the circulation of the journal has nearly reached 10,000 copies per issue and that each press run now exceeds 10,000 copies. Thus was born the topic for this editorial, which contains some information I think might be of interest to readers of the journal.
Over the years, beginning with the observation of one- and two-magnon light scattering in FeF2 by Fleury et al., light scattering has proved very fruitful in investigating excitations in magnetic systems. While many fine reviews of the subject have appeared, including a chapter in the book by Hayes and Loudon, none has been as comprehensive as this volume, in which scattering from ferromagnets, antiferromagnets, impure systems, and surfaces is treated in great detail. An indication of the overage provided is the chapter one one-magnon scattering in antiferromagnets, in which there are three detailed and well-organized subdivisions on simple antiferromagnets, canted systems, and metamagnets. The authors have been active contributors to experimental and theoretical develpments in the field.