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Infrared (IR) windows and domes for use with electro-optic (EO) systems operating in the 8- to 12-micrometer region are currently fabricated from the following limited number of materials: germanium (Ge), zinc sulfide (ZnS), and a zinc selenide (ZnSe) sandwich. A multiyear development effort at Texas Instruments (TI) has been produced another such material: gallium arsenide (GaAs). A novel crystal growth process has been developed that allows for economical growth of either high-resistivity (107 ohm-cm) or conductive [> 1 (ohm-cm)-1] GaAs crystals of various thicknesses in sizes up to 12 by 12 inches. This unique growth process permits production of GaAs, which is highly uniform or has a tailored electrical conductivity. With high IR transparency from approximately 1 to 14 micrometers, the high resistivity and conductive GaAs remain operationally useful to 400 degree(s) and 200 degree(s)C, respectively. The low resistivities allow for effective electromagnetic interference (EMI) shielding of 60 dB or more in the gigahertz region in highly transmissive IR windows made of this conductive GaAs. Besides fabrication of traditional precision optical components like lenses and prisms, TI has developed precision fabrication techniques for domes, windows, and segmented windows made of GaAs. These same techniques have also been designed to lower the mean size and distribution of the traditional optical component fabrication flaws, thereby increasing the strength and Weibull modulus of GaAs to 19.1 Kpsi and 4.7, respectively. These high strengths and the corresponding survival probabilities are comparable to those of chemical vapor deposition grown ZnS. TI has also developed techniques to further toughen GaAs, specifically for window and dome applications, in terms of increased strength through increasing the critical stress intensity factor (KIC) by changing the GaAs microstructure. Toughening in terms of impact resistance to rain during aerodynamic flight has also been developed by means of a protective coating. Antireflective coatings for surface-impedance matching have also been developed. This paper describes the properties of these various GaAs technologies.
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