In my editorial that appeared in the November/December 1985 issue of Optical Engineering, I indicated that a number of changes were in store for the journal in 1986. Most of those changes have now been implemented, the most significant of which is the increase of the publication frequency from bi-monthly to monthly. I believe that SPIE took a major step forward when the Society's Board of Governors authorized this change.

Astronomy from Stonehenge to Quasars-Reviewed by Edwin B. Weston; Optical Fiber Communications: Principles and Practice-Reviewed by Virginia Ormiston; Lightwave Communications Technology: Part D: Photodetectors-Reviewed by Robert H. Kingston; Pulsed Laser Processing of Semiconductors-Reviewed by George K. Celler; Introduction to Microlithography: Theory, Materials, and Processing-Reviewed by John Melngailis; Pulsed Light Sources-Reviewed by S. Goldberg

A novel family of germania-modified cordierite ceramics has been developed for the fabrication of precision optical components. Compositions in this family possess zero average coefficient of thermal expansion (CTE) over selected temperature regions. Moreover, the zero CTE can be tailored to a desired temperature range of operation by varying the relative proportions of Ge02 and Si02 in the modified cordierite structure. Thermal diffusivity of these ceramics is more than twice that of the ULE glass, a current state-of-the-art material for precision mirror substrates. In addition, germanium-cordierites possess high specific stiffness and low thermal-moment/rigidity ratio. Control-lable fine-grained structure enables good polishability and offers the potential for an optical quality surface. These thermal and mechanical properties make Ge-cordierites an excellent family of materials for optical and structural applications. The theoretical basis for germania substitution for silica in the pure cordierite structure has been examined. Material characteristics including solid solubility and sinterability have been considered. All the germanium-cordierite compositions presented in this study are morphologically single-phase and microstructurally homogeneous materials. These properties along with tailorable zero CTE characteristics offer the potential of employing cordierites for high precision optics.

The presence of a solid window at the entrance aperture of an air-borne FLIR can degrade the signal-to-noise ratio as a result of (a) the reduction in target signal-caused by the absorption of radiation by the window and (b) the loss in system detectivity caused by additional quantum noise generated by window-emitted photons. It is also known that, in order to avoid a degradation of the resolution at spatial frequencies of current interest, the window must satisfy specific requirements in terms of its modulation-transfer characteristics. The purpose of this paper is to consider some relevant properties of chemically vapor-deposited ZnS and ZnSe prior to assessing how windows made from these materials may impact the performance of state-of-the-art FLIRs. The degradation in signal-to-noise ratio occurring in the presence of a ZnS window reflects a substantial increase in absorptance/emittance at the long-wavelength end of the FLIR bandpass (8 to 12 iim) and must be attributed to lattice absorption processes, thus imposing intrinsic limitations on the performance, particularly at elevated temperatures. With ZnSe there is essentially no degradation to be anticipated, but since this material is soft, ZnSe windows cannot cope with rain/ice/dust erosions occurring in an operational environment. This emphasizes the need to develop a "new-generation" FLIR window that combines adequate erosion resistance and ZnSe-type optical properties. The present investigation confirms that ZnS/ZnSe laminates represent a highly attractive solution from the point of view of eliminating the loss of sensitivity encountered with ZnS windows in high speed flight.

The effective veiling glare has been measured in a linear, 64 element Si(Li) detector of 5 mm thickness and 0.5 mm center-to-center spacing between adjacent sensitive areas. Each elemental contact was 6 mm high and 0.4 mm wide. The measurement was made in two different ways, both employing a 33 keV beam of synchrotron x-rays at the Stanford Synchrotron Radiation Laboratory. In one method, a lead phantom in the shape of an isosceles triangle was illuminated across its width with a fan beam of 33 keV x-rays 0.5 mm high by 20 mm wide. The x-ray flux passing by the phantom was measured in each channel of the Si(Li) detector. In the second method, a highly collimated beam of 33 keV x-rays (0.5 mm high by 0.025 mm wide) was scanned across 15 channels of the detector in 0.01 mm steps. The measured intensity in each channel of the detector was recorded at each position of the beam. The photon flux fell to less than 0.1% at a distance of 3 mm from the edge of the beam. The results of both measurements were in agreement. They were also compared to calculated results based on the known total x-ray cross sections for Compton scattering and photoelectric absorption. To within the experimental error, the observed and calculated results were found to be in good agreement.

Degenerate four-wave mixing of picosecond light pulses in polydiacetylene dissolved in toluene has been observed. Phase conjugate reflectivities of over 100% were obtained. The origin of the non-linear interaction was found to be a thermal refractive index change.

A method is presented for the routine fabrication and testing of freestanding wire grids with large apertures for the Cosmic Back-ground Explorer (COBE) Far Infrared Absolute Spectrophotometer (FIRAS) experiment. Design criteria and performance specifications are discussed. Test and characterization results are also included that indicate that these wire grids are quite rugged and can withstand the rigors of qualification for spaceflight use.

The Hubble Space Telescope (HST) will be subjected to charged particle strikes in its space environment. HST's onboard fine guidance sensors utilize photomultiplier tubes (PMTs) for attitude determination. These tubes, when subjected to charged particle strikes, generate "spurious" photons in the form of Cerenkov radiation and fluorescence, which can give rise to unwanted disturbances in the pointing of the telescope. This paper presents a stochastic model for the number of these spurious photons that strike the photocathode of the photomultiplier tubes, which in turn produce the unwanted photon noise. Based on thousands of simulated charged particle strikes, the probability distribution of Cerenkov radiation and fluorescence was obtained. The results of the simulation demonstrate that the Cerenkov noise and fluorescence noise are not statistically dependent to the degree that the Cerenkov pulse amplitude could be used as reliable warning of the fluorescence. This finding prompted an engineering hardware change that will eliminate the possibility of telescope pointing disturbances caused by charged particles. The model that has been programmed, complete with three-dimensional graphics of the charged particle/PMT window interaction, allows for easy adaption to a wide range of charged particles and different phototube parameters.

A wind tunnel study was performed to determine the size spectra produced by spray atomization systems currently in use by the U.S. Forest Service. The atomization systems were assessed dynamically using a remote sensing laser particle spectral analyzer (LPSA) developed by Aerosol Science Laboratory personnel at the Colorado State University. The LPSA system, which is mounted on a traverse having three degrees of freedom, is capable of in-situ remote measurement of the size distribution of particles from 1 to 200 micrometers traveling inside a wind tunnel. Performance of the LPSA system was analyzed, and an absolute calibration method was developed. Two types of spray nozzles were placed in a high speed wind tunnel in an effort to establish droplet spectra under actual aircraft flight conditions. Size distributions of droplets produced by the two nozzles were characterized at two different wind speeds using the LPSA system.

Three-dimensional data derived from sensors utilizing a single point of view exhibit a high degree of nonlinearity. This nonlinearity, in the form of interrelated range, or radiometric, and geometric distortions, is corrected in real time without imposing any severe restrictions on the type of distortion laws to which the particular sensor adheres. This general correction technique is experimentally verified and shown to produce accurate 3-D images for a very broad class of distortion. A simple hardware implementation is also proposed.

A polarization photometer has been developed for rapidly determining the bidirectional, polarized, and diffuse light-scattering properties of individual leaves illuminated and measured in vivo at an angle of 55° (approximately Brewster's angle) in six wavelength bands in the visible and near-infrared wavelength regions. The optical performance and data quality of the system are evaluated to estimate the magnitude of the variation in the data attributable to the instrument system and to measurement procedures. The potential to discriminate between three species of oak is demonstrated using data acquired by the polarization photometer. The instrument is being used to increase understanding of the radiation transfer process in plant canopies and specifically to determine how agronomic information of the physical and chemical processes in leaves, plants, and plant canopies is expressed in these light-scattering properties.

We have examined an experimental acousto-optical computing system based on multiplication by binary convolution. Although this technique has previously been discussed, there are few reports regarding its experimental implementation. In our studies, we find several disadvantages in the proposed system configurations and report a simple yet powerful improvement that makes this technique much more practical. The paper includes a description of earlier designs, as well as the improved design, and gives experimental results.

The performance of coherent optical receivers is affected by the phase noise of the laser transmitter and the laser local oscillator and by the shot noise due to the detectors employed in the receiver. In this paper, the performance of coherent optical receivers is discussed, taking into account both noise sources. Further, the maximum permissible laser linewidth AP for coherent optical communications systems is reported. Both heterodyne and homodyne systems are considered. It is shown that the value of AP depends on the system bit rate Rb and on the modulation/demodulation technique employed: for heterodyne receivers with noncoherent postdetection processing [used in conjunction with amplitude-shift keying (ASK) or frequency-shift keying (FSK) modulation formats], Av_0.09 Rb; for heterodyne receivers with coherent postdetection processing [used in conjunction with the phase-shift keying (PSK) modulation format], Av< 2.26 X 10-3 Rb; and for PSK homodyne receivers, Av 3.1 X 10-4Rb. This paper presents the main results only; details of the mathematics involved have been published elsewhere. The purpose is to give a user a set of simple laser linewidth requirements without forcing him to analyze the research results scattered among several publications.

Three new fiber-optic components are described: an in-line filter, an optical switch, and an in-line attenuator. The in-line filter inserts an optical filter into any fiber line containing a connector while imposing very little additional power loss. The optical switch allows a single out-put fiber to transmit input from either of two fibers and permits switching back and forth between the input fibers as needed. The in-line attenuator attenuates signals in fiber lines over a range of about -30 dB with infinite variability. All three components are rugged, reliable, accurate, and inexpensive. They were developed for the prompt diagnostics used on underground nuclear tests and have successfully performed in this harsh. demanding environment.

Wavefront sensors that can operate at low light levels, be built from present technology components, and provide accurate wavefront phase estimates in real time are required for use with adaptive optics systems. The use of estimation theory makes possible the evaluation of wavefront sensors without specification of the wavefront phase estimation algorithms. The Cramer-Rao method was used to find a lower bound on integrated rms wavefront sensor estimation error. In addition to an analysis of the general case, the error lower bound was numerically evaluated for the shearing interferometer wavefront sensor. Computer simulations of the atmosphere and wavefront sensor measurements including noise were performed. Using an appropriate algorithm, the phase was estimated and the resulting phase error was compared with the lower bound. The results support the validity of using the Cramer-Rao lower bound to evaluate wavefront sensor performance.

When compact mirror telephoto lenses are used with light tri-pods, a major source of image blur is shutter-induced camera vibration. The impulsive torque about the center of mass of the camera-lens system, produced by the sudden shutter motion, generates an angular velocity that sweeps the optical axis across the object during the exposure. The antivibration mount, by means of an adjustable counterweight, relocates the system's center of mass to coincide with the shutter plane, thus reducing the impulsive torque to zero. Because the optical axis now maintains a fixed direction during the exposure, a sharp image is registered on the film. Tests with an 800 mm lens demonstrate that this simple mount permits very light tripods to be used with very long focal lengths.

The methodology for inferring temperature from optical radiation exitent from an opaque surface is described. Beginning with the measurement equation, the output of the radiation thermometer is related to radiant flux reaching the detector. Characteristics of blackbody radiators are reviewed, and the effects of surface emissivity, reflected irradiances, and the atmosphere are presented. Applications to a reheat furnace and a direct-fired process heater illustrate the practical importance of these effects and point out the need for a firm understanding of the physics of thermal radiation to properly interpret radiation thermometer observations.

The search for improved optical fiber glasses with the potential for losses lower than those of fused silica-based composition could be expedited if the relevant optical parameters could be calculated. This is particularly important for the magnitude and wavelength of the minimum in the loss curve, since these values have been experimentally established only for fused silica. Details are given of a way of estimating such data. A summary is also given of a way of calculating the wavelength at which the material dispersion parameter is zero and of calculating the material dispersion slope at that wavelength. A listing is given of calculated and some experimental values of the material dispersion slope. The availability of these parameters should expedite the search for new and improved glasses.