Optical design information was generated for commercially available, injection moldable acrylic molding pellet formulations. Detailed spectrophotometric transmittance curves were prepared for the ultraviolet, visible, and infrared regions. Comprehensive refractive index and dispersion data were obtained using novel compression molding techniques to produce optically superior specimens for measurement. Uniformity of the acrylic material within a production lot and among several lots was examined in detail. ND, NF, and NC values indicated a refractive index uniformity of ±0.00010, ±0.00013, and ±0.00012, respectively. Dispersion was calculated as v=61.4. The critical aspects of specimen preparation for precision refractive index measurements to ±0.00005 is given particular emphasis. Other mechanical properties of acrylic molding formulations are listed as well as special characteristics useful in optical design considerations. Advantages of acrylic optics compared to conventional glass systems are discussed.
The properties of polymeric materials are related to certain physical and chemical structural characteristics such as molecular weight, polarity, crystallinity and others. This paper will discuss some general effects and, in particular, the relation of optical behavior to polymer structure.
Wilkerson: As we begin the panel discussion on the Current Status of Plastics for Optics, the panel members will be considering both the present status and what they expect to occur in the next two to three years. On our panel we have Brian Welham, Vice-President of U.S. Precision Lens. They are certainly one of the largest, if not the largest, plastic fabricators, and they specialize in plastics only. Brian was Director of Engineering at Bausch & Lomb Special Products Division and he spent 16 years there before joining U.S. Precision Lens. Then there is Joe Berg from Berg Industries, John Lytle from M.U. Engineering and Mfg., Bob Jans of Rohm and Haas, and Richard Griskey of the University of Wisconsin at Milwaukee. I am Gary Wilkerson of Wilkerson Associates.
Most elements can be used as constituents of inorganic glasses. Oxides of the elements are most widely used because of their stability, economic availability, and important contributions to physical properties of the glasses. Silicate glasses contain substantial amounts of Si02 in combination with other oxides such as B203, PbO, Al203, CaO, and so on. These have received the most extensive use in products. A review of the nature of silicate glasses and their property behavior serves well as an introduction to all types of oxide glasses. These glasses are products of fusion. They can be cooled to room temperature without crystallizing and are characterized as supercooled materials. Their properties, therefore, are determined by time-temperature conditions during their formation as well as chemical composition and temperature at the time properties are measured. Glasses are essentially solids at room temperature with high elastic constants and useful dielectric constants. As temperature is increased they take on more and more the behavior of viscous liquids; their dielectric constants increase and they become electrolytic conductors. These characteristics of glasses are reviewed in terms of selected electromagnetic, mechanical, and thermal property data.
The current status of gradient index optical systems is reviewed. Particular emphasis is placed on the design of optical systems embodying gradient index elements, fabrication of suitable materials, the measurement of their optical properties, and the fabrication of finished lens components.
The extended x-ray absorption fine structure (EXAFS) is the oscillation in the absorption coefficient extending a few hundred eVs on the high energy side of an x-ray absorption edge. This mode of spectroscopy has recently been realized to be a powerful tool in probing the local atomic structure of all states of matter, particularly with the advent of intense synchrotron radiation. More importantly is the unique ability of EXAFS to probe the structure and dynamics around individual atomic species in a multi-atomic system. In this paper, the physical processes associated with the EXAFS phenomenon will be discussed. Experimental results obtained at the Stanford Synchrotron Radiation Laboratory on some oxide and metallic glasses will be presented. The local structure in these materials are elucidated using a Fourier transform technique.
Alumina and lanthana glasses in ternary systems containing BaO and SiO2 are useful for the vacuum deposition of thin film lightguides.1 Evaporated with an electron gun they produce low-loss films of refractive index 1.64-1.66. These can serve as the interconnecting lightguide for components of an integrated optics system. Understanding the refraction process at the boundaries of refracting components is vital. This paper describes experimental studies of refraction at a straightline boundary between evaporated glass lightguides and evaporated thin film overlays of Sb203 with index 2.10. In the guide the angle of incidence on the boundary was 60°. Refraction was measured versus overlay thickness. As an example, for lowest order modes, a lightguide optically 2.4 quarterwaves thick with a 1.8 quarterwave overlay refracts a HeNe beam 7° in TM polarization and 11° in TE. The overlay edge was tapered a width of 1 mm. The refraction process is a continuous direction change through the taper. Snell's law gives the total change if mode indices on each side of the boundary are used. The work was supported by the Air Force Office of Scientific Research (AFSC), The United States Air Force, and the Army Research Office, United States Army.
The requirements of high-energy laser systems have stimulated the development of low-refractive index, low-dispersion optical glasses, thus extending the range of available glasses in the Abbe diagram. Fluorophosphate glasses are the prime candidates to meet these requirements, but their preparation is complicated by fluorine volatilization on melting and devitrification and cracking on casting. The latter difficulties are caused by low viscosity at the crystallization temperature and by high thermal expansion. Exploration of glassforming regions and simultaneous optimization of the optical properties has led to the identification of compositions with commercial potential. A representative 100-gram melt contained 60 mol % RF2 (R = Mg, Ca, Sr, Ba), 36.7 mol % A1F3' 3.3 mol % Al(P03)3' with nD = 1.439 and vD = 95. After annealing it was optically homogeneous and strain-free.
A tutorial review of refractive index, absorption, birefringence, the electro-optic effect and the photoelastic effect in crystalline materials is presented. Tensorial relationships are presented and related to the symmetry classes of crystals.
Absorption coefficients smaller than 0.001 cm 1 can, with more or less difficulty, be measured by several techniques. All methods can be refined to permit measurement of absorption coefficients as small as 0.00001 cm -1. Spectral data are most readily obtained by transmission (spectrophotometric) methods, using multiple internal reflection to increase effective sample length. Emissivity measurements, requiring extreme care in the elimination of detector noise and stray light, nevertheless afford the most accessible spectral data in the 0.0001-0.00001- 1cm-range. Single-wavelength information is most readily obtained with modifications of laser calorimetry. Thermocouple detection of energy absorbed from a laser beam is convenient, but involves dc amplification techniques and is susceptible to stray-light problems. Photoacoustic detection, using ac methods, tends to diminish errors of these types, but at some expense in experimental complexity. Laser calorimetry has been used for measurements of absorption coefficients as small as 0.000005 cm-1. Both transmission and calorimetric data, taken as functions of intensity, have been used for measurement of nonlinear absorption coefficients.
In recent years, work on chemically vapor-deposited zinc sulfide (CVD ZnS) has resulted in the development of a material that shows much promise for infrared systems applications involving windows (or domes) and operating in the 8- to 12-μm region. This paper summarizes measurements and calculations carried out in the context of assessing relevant features of CVD ZnS, particularly with regard to: (a) Spectral Transmittance /Emittance. We show that CVD-ZnS windows capable of satisfying structural requirements stemming from the mechanics of high-speed flight exhibit transmittance and emittance characteristics which do not seriously affect the system sensitivity, over the range of anticipated thermal loads. And (b) Image Spoiling Properties. Line-spread function data demonstrate that small-angle scattering, index inhomogeneities, and other potential image-spoiling features do not inject any detectable degradation in system MTF, at spatial frequencies of interest for high-resolution thermal imaging.
A literature survey of refractive indices, thermo-optic constants and photoelastic constants has been conducted for materials of potential use in high-power ultraviolet applications. The limiting ultraviolet wavelength for which data exist is given for twenty alkali-halides, sixteen other crystalline solids, and three glasses. The bulk of the materials selected for the survey have band gaps that exceed 7 eV which is twice the photon energy of the XeF laser. There are large gaps in the available data for most of the materials.
In selecting an optical material, the instrument designer's first consideration is optical properties, especially transmission region but also homogeneity, freedom from birefringence, perhaps refractive index and dispersion. Next in his hierarchy are the other physical properties: mechanical, thermal, and chemical (solubility, for example). In this review article, the several properties are listed, and data sources are given. No single compilation or handbook contains all the desired data, so many references are quoted. This review covers materials useful in the ultraviolet and esuecially the infrared spectral regions; it does not include the standard glasses used in the visible region.
Segmented composite panes are proposed to improve the durability of infrared windows for high-speed aircraft. Prototype designs using silicon and zinc selenide are outlined. Effects on system MTF, mechanical reliability and erosion resistance are discussed.
The properties of new and weathered samples of low cost, high volume glasses have been studied to determine their usefulness for solar energy applications. Glasses of varying compositions produced by float, drawn, rolled, fusion, and twin ground techniques were examined. Spectral transmittance and reflectance were measured and solar weighted values calculated. Laser raytrace techniques were used to evaluate surface parallelism and bulk homogeneity. Compositional changes were examined with scanning electron microscopy, X-ray fluorescence, and Auger electron spectroscopy. These techniques were used in conjunction with ellipsometry to study the surface effects associated with weathering.