This special issue of Optical Engineering deals with the progress currently being made in the synthesis of new and perhaps revolutionary materials that can perform novel functions or make possible improved performance in modern optical devices. During the past five years, SPIE has sponsored a series of conferences focusing on the state of the art of emerging optical materials for passive as well as active applications. Over 200 papers have been presented in these conferences and published in the conference proceedings.
The fabrication of IR optical fibers for the 2- to 14-µm region is described. Both cylindrical and square fibers fabricated from rods and tubes are discussed. The physical properties of the GeSbSe glasses and optical fibers are reviewed. Fabrication of different fiber bundles is also reported. The applications of IR optical fibers and bundles are described, and system performance and parametric analyses are developed for some applications, including thermal imaging, IR sensors, CO2 laser power guide, and low-loss optical fibers.
The development of laser glass is reviewed. The fluorescence and laser effect of numerous glass compositions have been investigated over the past 20 years, but the industrial applications are few compared to the volume of research: only 20 to 30 glass types are available commercially today. Phosphate glasses are in the foreground because they exhibit a large laser effect and because it is possible to produce them in large volume and with high damage threshold. They are used in both high power lasers and lasers for machining and measurement.
In glasses, the largest observed value of nonlinear refractive index n2 is currently about 0.1 X10-11 esu. Changes in n2 are dependent on the third-order electronic polarization, which can be estimated from the linear electronic polarizability or from the refractive index and Abbe number. Theoretical calculations of n2 have been made for some glasses with potentially high nonlinear refractive indexes. Glasses are likewise useful for the matrix of some organic compounds and semiconductors with high optical nonlinearity.
Results obtained recently demonstrate that many organic molecules can be designed to provide nonlinear susceptibilities far larger than those of lithium niobate. These molecules may be attached to polymer chains to create films of large area with good mechanical properties as well as the required optical performance. Applications that have been predicted include second-harmonic generation, optical modulation, optical switching, and memories. For these hopes to reach fruition, highly ordered polymer films incorporating these molecules must be fabricated. Among the most promising techniques being pursued is Langmuir-Blodgett deposition, in which monolayers can be extracted from a water subphase onto a substrate. The interleaving of film materials permits the creation of multiple-layer systems between 5 A and 5000 A thick. In this paper we review both the research directed toward molecular design and the efforts to grow multilayer crystalline polymer films.
Improvements in crystal growth technology have made it possible to grow crack- and twin-free boules of AgGaS2 and AgGaSe2 in comparatively large dimensions, AgGaS2 to 28 mm diameter by 100 mm length and AgGaSe2 to 37 mm diameter by 100 mm length. Although the crystals grow with optical defects (micrometer-size scattering centers), postgrowth heat treatment procedures have been used to successfully eliminate the defects and produce material of near-theoretical transparency. High optical quality, oriented single crystals of AgGaS2 1 cm in cross section and more than 2 cm in length and of AgGaSe, 1 cm in cross section and more than 3.5 cm in length have been produced and are leading to new advances in IR frequency generation. The optical and phase equilibrium studies as well as details of the crystal growth technology that led to this advance in materials technology are described.
Infrared properties and electro-optic effects of nematic liquid crystals are reviewed. Physical origins and characterization techniques of infrared birefringence and rotatory power are described. Advantages and disadvantages of three device configurations--parallel, twisted, and perpendicular alignments--are analyzed. Among them, parallel alignment shows the best potential for long-wavelength applications. Several methods for improving the response times of nematic liquid crystals with emphasis in the infrared region are briefly discussed.
The symmetry arguments that predict the existence of ferroelectricity in chiral smectic liquid crystals are presented. The structures of the ferroelectric liquid crystals in the thin and the thick cell configurations are reviewed. The techniques to align these liquid crystals are briefly described. Finally, the effect of electric fields on these liquid crystals is discussed.
An illustrative, device-systems-level desirability optimization analysis is performed for a number of important electro-optic materials that are candidates for use in high-speed guided-wave optical devices. Ferroelectric materials with high and low transition temperatures, cubic crystals, organic crystals, and alloy semiconductors are considered. The simple bulk (lumped-type) guided-wave phase modulator is taken as the initial screening device. Performance measures such as electrical power supply constraints and the device's maximum operating speed are analyzed as a function of system variables that include material properties and electrode architectures. A desirability analysis is presented as a composite mathematical function that describes two or more indepen-dent performance measures in terms of all relevant system variables. This function is displayed graphically to identify those sets of system variables that jointly optimize the performance measures of greatest interest. The initial screening analysis ignores propagation loss and less-than-ideal overlap between electrical and optical fields. Potassium niobate, barium titanate, and lithium niobate are found to be among the more desirable electro-optic materials. The use of dielectric buffer layers, several thousand angstroms thick, is found necessary to isolate the modulator electrodes from materials of high dielectric constant, high electro-optic strength such as potassium niobate. Buffer layers, however, are generally unnecessary when the lower permittivity and lower electro-optic strength materials such as lithium niobate are used.
Laboratory erosion data, estimates of the rain environment, and the desired capabilities of the aircraft or missile can be utilized with a rain erosion damage model to provide a fairly reliable estimate of environmental degradation of infrared-transmitting windows and radomes throughout a flight trajectory. If water drop interactions with the flow field around the vehicle are ignored, the suggested approach will provide an upper bound on the extent of the water drop impact damage associated with a particular mission. The design philosophy is that if this level of damage can be tolerated, the actual impact conditions will not be detrimental. A wide range of flight scenarios can be examined on this basis. If the upper bound computation indicates that the resulting level of damage will be well beyond the tolerable limit, then aerodynamic analyses of water drop interactions with the flow field around the vehicle and a more complete statistical analysis of the impact damage will have to be undertaken.
Westinghouse Hanford Company has designed and constructed a nuclear fuel fabrication process line for the U.S. Department of Energy. This process line includes a system that remotely inspects the cylindrical surface of nuclear fuel pellets for surface spots, flaws, or discoloration. The pellets are inspected on a 100% basis after pellet sintering. A feeder delivers the pellets directly to a fiber optic inspection head, which views one pellet surface at a time and images it to a closed-circuit color televison camera (CCTV). The output signal of the CCTV is input to a digital imaging processor that stores approximately 25 pellet images at a time. A human operator visually examines the images of the pellet surfaces on a high resolution monitor and accepts or rejects the pellets based on visual standards. The operator uses a digitizing tablet to record the location of rejected pellets, which are then automatically removed from the product stream. The system is expandable to automated disposition of the pellet surface image.
A theoretical model is presented that predicts the output response of a thinned CCD to soft x-ray spectra. The model simulates the four fundamental parameters that ultimately limit CCD performance: quantum efficiency, charge collection efficiency, charge transfer efficiency, and read noise. Simulated results are presented for a wide variety of CCD structures, and general conclusions are presented about achieving a practical balance of sensitivity, energy, and spatial resolution for an Advanced X-ray Astrophysics Facility (AXAF) instrument. We compare the results of the analysis to existing state-of-the-art CCDs and project improvements that will be made in the near future.
When in-plane surface deformations are measured using white-light speckle photography, errors arise if an out-of-plane displacement is present. Stereoscopic photography resolves this problem and makes possible the measurement of true in-plane displacements. A rigid-body translation is introduced to determine unambiguously the direction of the displacement.
Measurements are always subject to errors resulting from the interaction of the measurement device with the quantity being measured. Electro-magnetic fields are typically detected with an antenna that must be electrically connected to a recording instrument, and the antenna and its electrical connection can significantly perturb the field being measured. The use of fiber optics in the detection process minimizes the perturbation of the microwave fields since most of the probe and its associated connections are dielectric. This paper presents preliminary results obtained using a commercially available fiber optic thermometer in the measurement of microwave power. A small amount of slightly conductive material is placed in contact with the fiber optic sensor. In the presence of a microwave field, currents are induced in the conductive material, which in turn produces joule heating. It is shown experimentally that under certain conditions the probe temperature is linearly related to the power level present. Experimental results are presented for power measurements at 2.45 and 94 GHz. Probe design criteria and limitations are also discussed.
Ionized cluster beams (ICBs) are widely used to deposit metal, semi-conductor, and insulating films. This paper describes the current state of this technology in both fundamental and applications areas. One important ambi-guity in the theory of metal cluster formation is addressed. Rutherford back-scattering is used to measure the extent of any displacement of surface atoms caused by ICBs. The minimal amount of such surface damage is confirmed by the close-to-ideal values measured for Schottky barrier height on an Al/Si interface. Several examples of ICBs are described.
About a year ago I wrote an editorial* in which I expressed my opinion that too many SPIE Proceedings papers were being submitted for publication in Optical Engineering. In that editorial I revealed my bias that papers previously published in the Proceedings should not, in general, be reprinted in Optical Engineering--at least not without substantive revision. I am pleased to say that we are now receiving far fewer such papers than we were at the time I wrote that editorial.
This is another useful book in the Springer Series in Optical Sciences. It contains discussions of grating formation and detection, the phenomena that can be probed with grating techniques, and a large number of applications such as real-time holography, phase conjugation, and four-wave mixing. As is often the case with multiple-author books, some subjects are treated more than once, style and notation vary from section to section*there is a useful symbol index, however, so that multiple use of the same symbol is not especially confusing), and the authors' specialties receive more comprehensive treatment than some other subjects.