Authors are the most important contributors to the quality of a technical journal, but referees are not far behind. Unfortunately, the delicate nature of their job prevents me from giving them public thanks by name for the work they do. I do appreciate their hard work and I love to see them mentioned in the acknowledgments of revised papers. To all of you who have helped by refereeing--thank you.

Review of the Sixth (1980) Annual SPIE Seminar on Modern Utilization of Infrared Technology My column this month is a review of the sixth annual seminar on Modern Utilization of Infrared Technology, which was held at the Town & Country Hotel, San Diego, on 31 July to 1 August 1980. The seminar was divided into four sessions:

This special issue on novel interferometry results from a suggestion by John DeVelis, over a year ago, that we attempt to find a number of papers on novel interferometers. This sounded intriguing, but what is a "novel interferometer"? Novelty implies uniqueness, which in turn leads to finding new interferometers that are somehow different from the commonplace interferometers widely used today. Of course, we would have to search out not one, but many "novel interferometers" to fill this special issue. Seeing this as a formidable task, we decided to broaden the scope of this special issue to include: unique applications of interferometry, truly novel interferometric instrumentation, and the integration of interferometry with other technologies. Thus we could pursue developments which incorporate new technology to the now familiar interferometers developed through the years, as well as informing the reader of new applications of interferometry in other disciplines. In keeping with the purpose of Optical Engineering, our intent was to seek papers stressing instrumentation and application as opposed to purely analytical treatments.

An instrument is described for measuring the thickness of thin liquid films by measurements of the irradiance in the reflected interference close to the central dark fringe. Variations in thickness can be measured by scanning a focused spot across the sample or an aperture across its image. The instrument has been tested on thin wedges.

Three recently developed methods are described and their capabilities discussed. Each of these methods is applicable for the accurate determination of the thickness, refractive index and absorption of thin films.

This paper describes a method by which recorded moire interferog rams of diffuse, nonoptical surfaces may be processed using the principle of optical phase measurement by heterodyne interferometry. In this method, a moire interferogram is recorded and processed as a transparency. The resulting interferogram is equivalent to a low spatial frequency optical hologram. An optical wavefront whose phase variations are proportional to the original surface height variations can be reconstructed from a plane wavefront and interfered with a second coherent plane wavefront of slightly different optical frequency, resulting in an interferogram appropriate for measurement by temporal electronic phase measurement. The results compare favorably to direct contact measurements.

Recently there has been increased interest in the measurement of the microtopography of optical surfaces. The information generated may be used either to predict the scattering characterisitics of a particular surface or to relate surface quality to damage thresholds. Previously, surface profiles have been measured by a variety of techniques including electro-mechanical profilometry and multiple beam interferometry. Surface profiles may also be measured using a scanning Fizeau interferometer. The instrument is similar to conventional Fizeau interferometers, with the exception that the interference pattern is temporally modulated by vibrating the test sample. A detector scanned across the modulated interference pattern produces an ac signal, with a phase that is directly proportional to the profile of the surface under test. An instrument based on this principle has been constructed and is capable of generating profiles of surfaces with rms roughnesses of approximately 20 A. The advantages and limitations of the instrument are discussed. Experimental results are presented.

This paper presents a study of scatterplate interferometry from a "user-oriented" standpoint. A review and clarification of past work as well as some of the author's own research on the subject are discussed. A wide range of areas concerning the scatterplate is covered including fabrication, basic principles of operation, advantages and limitations, and modifications for its use in null testing.

In the Omega laser fusion system, multiple laser beams are split from a single master oscillator. These beams are focused onto a reflective sphere which retroreflects the light back toward the beamsplitter. Any two of these beams can be operated as arms of an interferometer. With ac interferometry, the path lengths can be equalized to within one picosecond.

Any two rectilinear light vibrations A and B whose angle is given by u always have a time-average direction. They are thus able to induce an anisotropy in a silver-silver chloride photographic emulsion H. Here we show that when they are incoherent, their linear combination may be retrieved by observation of H between crossed polarizers after exposure. In the case they are coherent, H exhibits an interferogram whose black fringes characterize the value of angle u.

A proposed method for the precise realization of an absolute standard of dc voltage requires, inter alia, the measurement of a number of spacings, of order 2 to 5 mm, between a horizontal reflecting mercury surface and an upper semitransparent film. The accuracy with which these measurements are made will largely determine the overall accuracy of the voltage realization. An interferometry system is being developed in which the spacings are measured by white-light optical multiplication with respect to scanning Fabry-Perot measuring interferometers having nominal spacings of about 0.66 mm. The Fabry-Perot interferometers are calibrated using a stabilized He-Ne laser and are capable of measurements having an accuracy of the order of 10-4 fringe (X = 633 nm). The design and performance of the interferometers and the other major components of the optical system are discussed. Those uncertainties which can be assessed at this stage seem likely to amount in total to less than 10-3 fringe in spacing, or less than one part in 106 of voltage.

Described is a technique for accurately measuring the radius of curvature of very long radius concave optical surfaces in a relatively short working length. Presented is the basic theory of the technique and the detailed information necessary to provide for its practical application. Using the technique, radii of up to 175 meters can be measured to an accuracy of better than 0.01 percent with a one-meter long scale and slide, and in an overall working length of less than 5 meters. Generalizations of the technique allow for the measurement of convex surfaces and even longer radius concave surfaces. Photographs, interferograms, calculations, and an error analysis illustrate the technique.

The effects of pulse number, separation, width, and shape on holographic interferometry for objects subject to both uniform and vibrational motion are considered. The reconstructed irradiance for uniformly moving objects holographed by means of rectangular pulse shapes or narrow multiple pulses contains fringes that are contours of constant velocity. Fringes that are contours of constant vibrational amplitude are formed in the case of combined uniform and vibrational motion for which the vibrational period is much less than the pulse width and for which the uniform velocity is sufficiently small. Situations are identified in which narrow multiple-pulse and long single-pulse holographic techniques could be advantageous for the interferometric study of object motion.

Many tend to underestimate the extent of the science of particle sizing. Every field of science and virtually all industries encounter critical phases where particles become a part of a product or by-product.

Optical techniques for particulate analysis have inherent and significant advantages over those conventional methods which involve batch sampling and subsequent analysis. Optical particle diagnostic techniques can be divided into three broad categories: ensemble methods which analyze the integrated optical properties of an assembly of particles; single particle counters (SPC) which analyze individual particles; and, finally, imaging techniques based on photography or holography. This paper is primarily concerned with laser-based single particle counters applicable to in situ sizing of particles and droplets in the diameter range 0.1 um to 1 mm. Theoretical principles of the various single particle counter designs are discussed with emphasis on comparing performance characteristics and relative advantages. The effects of size-dependent sample space, nonspherical particles, unknown particle composition, and applicable size ranges are considered.

The precise knowledge of particle size and particle size distribution is fundamental to the control of a wide variety of industrial processes. Processing steps as diverse as crystallization, grinding, emulsification, and atomization, produce particles in the size range .1 to 1000 micrometers in diameter. While the object of some processes may be the production of particles of specified sizes, e.g., abrasives and glass beads, other processes may require particle size control for process efficiency, e.g., crystallization, and still others for control of final product quality, e.g., minerals, cement, and ceramics. In many processes more than one of these reasons may be important. A line of instruments has been developed using light scattering to measure various parameters of particulate distributions. These instruments employ laser illumination of a flowing stream of particles, producing Fraunhofer diffraction patterns which are processed both optically and electronically with unique, proprietary techniques. Various parameters of the particle size distribution are measured. The measurement is both rapid and precise. This paper will cover the importance of particle size measurements in various processes, different types of measurement methods, and the application of light scattering technology to size determinations in wet slurries and dry powders. A number of specific applications will be discussed encompassing minerals grinding, Portland cement, and rolling mill emulsions. Some references will be made to energy savings through automation.

A near-forward and a wide scattering angle optical particle counter were carefully calibrated and aligned, using monosized latex particles. Good correlation was obtained both for number concentration and particle size response. Systematic differences, however, were found when the two instruments were then used to observe laboratory air. Different concentration data were produced by the two instruments in their equivalent size ranges, indicating that ambient air particles are sized differently than are latex particles; the differences vary in extent over the overall size ranges of the two instruments.

The enthusiastic introduction of laser light techniques into the area of particle field diagnostics has prompted the further development of increasingly sophisticated instrumentation. Laser light scatter methods offer online, in situ, nonintrusive evaluation of droplet and particle fields. Recent advances in this area have greatly extended the range of applications. Holographic techniques allow in-depth analysis of particle field phenomena never previously available. These optical techniques have been proven successful in applications ranging from spray diagnostics to combustion studies with numerous additional applications only now being considered.

To view and align Shiva laser targets, two telemicroscopic instruments have been designed; one is a single field instrument and the other a multiple field instrument. Each instrument is integral with a TV camera and HeNe laser illuminator. The common feature of the instruments is the capability of imaging both the large surrogate target (5 mm diameter) and the laser fusion target (0.250 mm diameter) with the same resolution (better than 7 um). Both instruments have an optical relay which images the targets on a fixed reference reticle so that both the surrogate target and the fusion target can be centered on the same reference point. The single field instrument reimages the reticle plane onto the TV detector using a zoom arrangement. The TV camera zoom assembly can be translated in three axes and is thereby capable of exploring an object-space volume of 1cm3 without moving either the relay optical train or the reference reticle. In the multiple field instrument the reticle plane is reimaged by a zoom lens and this enlarged image is relayed to the TV detector by a cluster of five lenses. Four lateral lenses image the periphery of the surrogate target and the reticle for coincidence. The central objective images the center of the reticle and the fusion target when it is centered.

The evaluation of the interactive nonlinear performance of an electro-optical system is often best achieved by exercising the system in the context of a simulated environment which provides more complex and realistic stimuli than bench tests at less than field testing. The systematic behavior of an electro-optical device, test goals, and simulator resources jointly constrain an appropriate simulation environment. It is the responsibility of the simulation specialist to recognize the peculiar qualities of the object system and to provide for it an environment which, in its relevant characteristics, is practically indistinguishable from the real world, and which is sufficient to exercise the system over its entire stimulus domain. To illustrate this thesis, the location of a hypothetical missile seeker/tracker in the context of a hardware-in-the-loop simulation will be established and the manipulable features of its environment illustrated. Some aspects of such a device's response to its environment which have required special attention will be discussed.

Afocal systems are frequently used in thermal imagers to match the field of view required by the user to that required for high scan efficiency. The limitation on performance of such telescopes due to chromatic aberrations and field curvature as a function of magnification, field angle, and f/number is discussed together with some methods for reducing these aberrations. A detailed scheme is given for the analytical correction of the primary monochromatic aberrations in telescope systems. Aberrations of the pupil in such telescope systems, and their control, are discussed with respect to the radiometry of thermal imagers. Finally a number of designs of telescope systems of various magnifications are discussed in some depth, from design philosophy to performance values. The designs include refracting and reflecting systems employing both spherical and aspheric surfaces.

Two-dimensional x-y addressed mosaic arrays of more than 12,000 lead-sulfide detectors each (64 by 192 detectors in an active area slightly larger than 6.4 by 19 mm) have been successfully developed and demonstrated at Aerojet ElectroSystems Company. This paper describes the pulse-bias modulation concept used to operate the detectors and multiplex their outputs and the design and fabrication techniques used to implement this concept. The measured performance of an array which was independently verified by the Naval Ocean Systems Center in San Diego is described, and data for an additional 10 modules (a total of more than 105 detectors) are summarized

The power requirements for acousto-optic devices increase with wavelength as X2, so it becomes extremely important for infrared operation to have very high figure-of-merit materials available. Potentially important infrared applications include scanners for laser radar, choppers for surveillance satellites, and acousto-optic tunable filters for a variety of systems. Higher efficiency materials are also important as thin films for integrated optic devices, such as the spectrum analyzer, and several bulk acoustic wave-optical waveguide concepts. A large number of materials of the sulfosalt class have been identified as having very desirable acousto-optic properties, and will find use in a number of these applications. More development of these materials is required to make them of suitable quality, and new compositions must be examined to achieve high performance.

The properties of fine grain films are related to their use in moire photography. Dimensional instability due to creep, changes in humidity, and processing effects can be avoided or corrected by a simple camera modification and the use of a reference target. Compensation for fading of the image has also been examined.

A new indirect ophthalmoscope has been developed that combines a viewing lens and a compact illumination system in a small, prealigned, easy-to-use package. Undesirable back reflections are eliminated by admitting the illumination behind the viewing lens via beamsplitter, and by using polarized light. The conditions for stereoscopic viewing are discussed.

We describe the basic principle and geometry of certain simple catadioptric magnifiers which have been designed and fabricated. These magnifiers are made of spherical reflecting surfaces of moderate curvature and they are capable of producing visual magnifications of sixteen to twenty times with reasonable eye relief. They are useful for reading microfiche having nominal frame sizes of 16 mm x 12 mm and 12 mm x 9 mm.

A simple and concise method of depicting the relative competition of third order coma and astigmatism as a simultaneous function of field angle and f/number is presented, using a mirror and a thin lens as examples.

A sensor has been designed to provide real-time detection and recognition of 3 mm wires at range of 300 meters during nighttime helicopter flight operations. An Army-sponsored program to demonstrate such automatic wire detection and warning for Nap-of-the-Earth (NOE) helicopter missions is currently in progress. Wire or wirelike objects are electro-optically detected and then recognized by a pattern recognition technique. The recognition algorithm is accomplished within 50 msec of the first wire detection indication. A flyable exploratory development wire obstacle warning system model, consisting of a scanning laser transmitter, electro-optical receiver, real-time processor, and display unit is described.

We describe the mathematical procedures needed to generate three-dimensional phantoms and corresponding simulated radiographic data for an arrangement of cone-beam x-ray sources and two-dimensional detector arrays. The techniques described here are being used to test fully three-dimensional cone-beam reconstruction algorithms for application to dynamic spatial reconstructor type machines.

Many Anger scintillation cameras are equipped with microprocessors for live correction of field nonuniformities. The purpose of this study was to evaluate the corrected flood field uniformity after varying count rate, analyzer window size, analyzer window position, and scatter. A 2.54 cm thick Tc-99m disk source was used with large and small field Anger cameras under conditions simulating clinical usage. Uniformity was evaluated quantitatively by computing the location and percentage of cells in a 64X64 matrix that were within ±5% of the mean cell count; it was judged qualitatively by examination of the computer thresholded image. The corrected 2.54 cm thick Tc-99m disk flood image showed virtually no change in uniformity as scatter medium was increased from 0 cm to 8.9 cm. When count rate was varied from 5K to 44K cps as much as a 13% decrease in field uniformity was observed. Changing the analyzer window size produced a 5-21% decrease in uniformity while changing the window position resulted in even more significant image degradation. Knowledge of these camera characteristics is important in improving clinical images.

The gray level or intensity distribution of an image is frequently inadequate to select a good threshold for image segmentation. Considerable improvement can be achieved by a histogram transformation based on second-order gray-level statistics. This paper describes an approach using the co-occurrence matrix. Results are shown for target extraction in forward looking infrared (FLIR) images.

Significant advances have been made in the development of high-performance diode laser sources and photodiode detectors that will be essential for future optical signal processing systems. AIG aAs/G aAs diode lasers for 0.8 to 0.9 um wavelengths are now commercially available and GalnAsP/InP for 0.9 to 1.7µm should soon become available. Recent achievements include long lifetime lasers (>10,000 hours) in both materials systems, single longitudinal and transverse mode operation, high speed pulse modulation (1Gbit/sec), and mode-locked operation with <20 psec pulses. High performance avalanche photodiodes have been developed in Si for wavelengths up to 0.9 uM and modest-performance diodes in Ge up to 1.5 um. For wavelengths beyond 1 uM, III-V compounds, especially the GaInAsP/InP system, show promise for fast, highly sensitive diodes that could be integrated into optical waveguide circuits along with diode lasers.

A review of recent work on diode laser spectroscopy is presented. Special emphasis is placed on measurement techniques and calibration methods. Different types of spectroscopy and analytical applications are discussed. A comprehensive listing of references since early 1976 is also included.

An optical sight apparatus is described which consists of a beamsplitter and a corner retroreflector. This sight is very easily assembled from stock items and permits a beam of light, such as from a laser, to be aimed where no aiming clues normally exist.