Large aperture (20-inch diameter) sapphire optical windows have been identified as a key element of new and/or upgraded airborne electro-optical systems. As has been recently reported, Crystal Systems continues in the development of the technology to grow 20-inch diameter, single crystal sapphire boules to meet this need. Owing to the spatial variations in the optical index of refraction potentially anticipated within 20-inch diameter sapphire crystals, computer controlled optical finishing has been identified as a key technology that may be required to enable achievement of transmitted wavefront errors of much less than 0.1 wave rms. BFGoodrich has developed this technology and has previously applied it to finish 8-inch- diameter sapphire optical windows to a transmitted wavefront error of at least four times better than the above requirement. As a key step in the scaling of these critical window technologies to produce 20-inch-diameter sapphire windows, BFGoodrich and Crystal Systems collaborated to apply these technologies to produce a 13-inch-diameter sapphire window having a transmitted wavefront error of 0.059 wave rms. Optical testing of this 13-inch sapphire crystal revealed that it possessed excellent refractive index homogeneity; far better than had previously been encountered in finishing 8-inch sapphire windows. This improvement in material quality implied that conventional optical finishing could potentially have been employed to finish this window to the 0.059 wave rms error. However, due to our desire to demonstrate the process technology for potential future application to 20-inch diameter sapphire windows, it was fabricated using computer controlled optical finishing. This paper addresses the results of this effort, the lessons learned, and the implications associated with the scaling of these technologies to 20-inch-diameter sapphire optical windows.

High strength edge bonds between individual sapphire components have been developed as a means to produce affordable large area windows. Several bonding methods have been demonstrated, with bond fracture strengths ranging from 100-200 MPa. When polished, the bonded windows show excellent transmittance with no degradation in transmitted wavefront quality. The bonding processes have recently been scaled up to 355mm wide, 10mm thick bond lines and multipane windows. Using singly-curved sapphire components for the individual panes, doubly-curved bonded sapphire components have also been produced and polished with excellent results. The edge bonding approach shows promise for fabricating affordable sapphire windows up to 750mm diameter. In addition, recent developments with index-matching glass coatings show the feasibility of substantial cost reductions in optical finishing of sapphire windows, particularly for transparent armor.

The Sapphire Statistical Characterization and Risk Reduction Program tested 1400 4-point flexure bars with different crystal orientations at different temperatures to establish a mechanical strength database for engineering design. Sapphire coupons were selected to represent surfaces on two different missile windows and a missile dome. Sapphire was obtained from the same suppliers used for the windows or dome and, as much as possible, coupons were fabricated in the same manner as the corresponding part of the window or dome. For one missile window, sapphire from one fabricator was 50% stronger than sapphire made to the same specifications from the same blanks by another fabricator. In laser thermal shock tests, sapphire performed better than predicted from flexure tests. Of several nondestructive methods evaluated for their ability to identify mechanically weak specimens, only x-ray topography was correlated with strength for a limited set of specimens.

Neutron irradiation of sapphire with 1 x 10²² neutrons(<EQ MeV)/m² increases the c-axis compressive strength by a factor of 3 at 600 degree(s)C. The mechanism of strength enhancement is the retardation of r-plane twin propagation by radiation-induced defects. ^1-B and Cd shielding was employed during irradiation to filter our thermal neutrons (<EQ1 eV), thereby reducing residual radioactivity in the sapphire to background levels in a month. Yellow-brown irradiated sapphire is nearly decolorized to pale yellow by annealing at 600 degree(s)C with no loss of mechanical strength. Annealing at sufficiently high temperature (such as 1200 degree(s)C for 24 h) reduces the compressive strength back to its baseline value. Neutron irradiation decreases the flexure strength of sapphire at 600 degree(s)C by 0-20% in some experiments. However, the c- plane ring-on-ring flexure strength at 600 degree(s)C is doubled by irradiation. Elastic constants of irradiated sapphire are only slightly changed by irradiation. Infrared absorption and emission and thermal conductivity of sapphire are not affected by irradiation at the neutron fluence used in this study. Defects that might be correlated with strengthening were characterized by electron paramagnetic resonance spectroscopy. Color centers observed in the ultraviolet absorption spectrum were not clearly correlated with mechanical response. No radiation-induced changes could be detected by x-ray topography or x-ray diffraction.

The slow crack growth parameters, fracture toughness, and inert strength of the r-and a-planes of sapphire were measured in water in order to perform a life prediction on a pressurized sapphire window. The window is being considered for use in a combustion chamber on the International Space Station. Sapphire is relatively susceptible to stress corrosion in water despite a large strength in the absence of humidity. Two life prediction approaches were considered: a deterministic fracture mechanics approach and a Weibull based reliability approach. Preliminary results indicate that the window is feasible if a short finish is avoided. Fractography and additional predictions are being performed.

A complete and independent method is used to measure the infrared refractive index of sapphire, both e-ray and o-ray, as a function of temperature and frequency. The technique combines single frequency and broadband measurements. The refractive index at the wavelength 3.39micrometers is measured using a prism and the minimum deviation method. A laser interferometer and an etalon of the material are then used to measure the thermo-optic coefficient also at 3.39micrometers . A broadband FTIR spectrometer is used to measure the transmittance spectrum of the etalon and then a fringe counting method is applied to obtain the frequency dependent refractive index. The technique is applied to sapphire over the temperature range from room temperature to 600 degree(s)C and wavelength range from 1 to 5micrometers . High accuracy is demonstrated. The errors of this experimental approach are analyzed.

BaO-Ga₂O₃-GeO₂(BGG) glasses have the desired properties for window applications in the 0.5-5micrometers wavelength region. These glasses are low cost alternatives to the currently used window materials and are being scaled- up to large sizes for various Department of Defense (DoD) applications. Fabrication of a high optical quality 6.5' x 8.5' x 0.5' rectangular BGG glass window has already been demonstrated. A transmitted wave front error of about (lambda) /15 at 632nm has been achieved in polished BGG glasses. Recently a 20' round glass window blank has been cast. Although the mechanical properties of BGG glass are acceptable for various window applications, it is demonstrated here that they can be further improved significantly either by the glass-ceramization process or by forming a composite. Neither process adds any significant cost to the final window material. The glass composite transmits in the 0.5-5micrometers region while the crystallite size in the glass-ceramic currently limits its transmission to the 2-5micrometers region.

Aluminum Oxynitride or ALON optical ceramic is transparent material, developed and patented by Raytheon, which is very similar to sapphire, being comprised mostly of Al₂O₃ with a small amount of additional nitrogen. This nitrogen addition has the effect of producing a cubic material whose optical and mechanical properties are isotropic. Importantly, this means that it can be produced by powder processing methods, which are scalable to larger sizes, and at lower prices than can be achieved by the single crystal growth techniques that are used to grow sapphire. Furthermore, its isotropic properties make it much easier to grind and polish than sapphire. Recently, the interest in ALON optical ceramic has grown substantially following impressive results in ballistic testing. Ballistic laminates, containing ALON layers, have demonstrated protection against armor piercing rounds, at half the areal density and thickness of conventional ballistic laminates. ALON plates as large as 14x20in are being produced, under Air Force funding, for evaluation as IR windows and transparent armor, using conventional powder processing techniques. The production processes themselves are now being scaled to produce large pieces and large quantities of ALON optical ceramic.

There are difficult points such as lowering of the detection or recognition capability of some targets by aerodynamic heating with speedup of the aircraft and missile and restriction of the operation by the raindrop in rainfall time on the conventional ZnS infrared window application used for missile seeker and FLIR equipment. Therefore, in this study, the promising polycrystal GaAs which has low infrared radiations in high temperature was produced using HB method (Horizontal Boat method) and VG method (Vertical Boat method) as a new infrared window material expected the durability for rain erosion. As the result, 70mm² windows by the HB method and 100mm diameter windows by VB method were realized. Moreover, their optical characteristics, mechanical properties and thermal shock durabilities were measured and they were confirmed to be about 56% in average transmittance in the wavelength of 10micrometers bands, 530~630kg/mm² in their hardness and thermostable at 300 degree(s)C.

Ion implantation and diffusion have been used to create conductive layers in germanium windows while maintaining high LWIR transmission. We have reduced the sheet resistance to below 5 ohms/square while limiting transmission losses to less than 9% in the 8-12 micron range.

Conformal optics are defined as optics that deviate from conventional form to best satisfy the contour and shape needs of system platforms. Precision Conformal Optics Technology (PCOT), a comprehensive 48 month program funded by the Defense Advanced Research Program Agency (DARPA) and the U. S. Army Missile Research, Development, and Engineering Center (MRDEC), assessed the potential benefits achieved by use of conformal optics on a variety of U.S. weapon systems. Also addressed were all barriers impeding conformal optics use. The PCOT program was executed by a consortium of organizations ranging from major U.S. defense prime contractors, to small businesses, and academia. The diversity of organizations encouraged synergy across a broad array of skills and perspectives. Smooth team interaction was made possible by the 845 contractual structure of the program. Benefits identified by the PCOT consortium included major reductions in aerodynamic drag (by as much as 50%), reduced time-to-targets (by as much as 60%), and reduced weapon signatures. Impediments addressed included inadequacies in optical design tools, optical manufacturing methods and equipment, optical testing, and system integration. The PCOT program was successfully completed with a demonstration of a highly contoured missile dome, which reduced overall missile drag by 25%, and led to a predicted twofold increase in missile range.

This paper describes the computer-controlled machines and deterministic processes developed by the Center for Optics Manufacturing (COM) at the University of Rochester to produce conformal windows and domes that have non-traditional optical surface geometry and unusual shapes. COM's DMG (deterministic microgrinding) technology produces aspheric and conformal (freeform) surfaces in minutes, versus the weeks that are required to produce the surfaces conventionally. The demonstrated techniques and equipment provide a predictable and repeatable optical production process for just about any IR, visible, or UV material. The DMG process, in concert with newly developed CNC machining equipment, typically yields 1.0 wave peak-to-valley form accuracy, 150 Angstroms rms surface finish, and subsurface damage levels low enough that some of the infrared materials do not require additional polishing.

Recently precision replication of flat, spherical and aspheric surfaces was demonstrated in ZnS by a chemical vapor deposition (CVD) process. Two-inch size ZnS parts were replicated successfully down to a fraction of a wave in the visible and finish of 20-180 Angstroms RMS. The replication technology was then extended to produce six best-fit-sphere ZnS corrector elements of diameter 2.4-inch by replicating on Al₂O₃ and SiO₂ coated, highly polished and diamond turned ZnS mandrels. These replicated corrector elements measured an inside surface figure of 0.14-0.27 Angstroms RMS and smoothness of about 41 Angstroms RMS. Mandrel reusability was then demonstrated by replicating on several previously used corrector element mandrels which were minimally refurbished (mandrel surface was cleaned with acetone). These replicas and mandrels measured essentially same surface figure and smoothness after second replication as before. After replication, analysis was performed on a few mandrels, which did not release from the replicas. Cause of this adherence was determined to be presence of 10-20 micron size pinholes in the release coating. Very good replication was achieved on those areas where no pinholes were present. The integrity of the release coating determines the durability of the replication mandrel.

A conformal optic is typically an optical window that conforms smoothly to the external shape of a system platform to improve aerodynamics. Conformal optics can be on-axis, such as an ogive missile dome, or off-axis, such as in a free form airplane wing. A common example of conformal optics is the automotive head light window that conforms to the body of the car aerodynamics and aesthetics. The unusual shape of conformal optics creates tremendous challenges for design, manufacturing, and testing. This paper will discuss fabrication methods that have been successfully demonstrated to produce conformal missile domes and associated wavefront corrector elements. It will identify challenges foreseen with more complex free-form configurations. Work presented in this paper was directed by the Precision Conformal Optics Consortium (PCOT). PCOT is comprised of both industrial and academic members who teamed to develop and demonstrate conformal optical systems suitable for insertion into future military programs. The consortium was funded under DARPA agreement number MDA972-96-9-08000.

The principle of Offner's refractive null lens has been extended to test the transmission wavefront through conformal window optics and provide feedback during surface fabrication. First, the basic theory of the refractive null lens is reviewed followed by design examples for conformal optics. Second, given a specific window shape, the results and interpretation of a conformal widow test are described. Finally, a method of data analysis to reduce the transmission wavefront map to a more useful sag table is presented.

For the past three years, the Precision Conformal Optics Consortium has been developing a revolutionary new class of optics. These optics are characterized by outer window elements that conform to aerodynamic rather than optical requirements. Conformal optical elements can greatly improve the aerodynamic performance of the host platform. To make conformal optics a reality, challenges had to be overcome in design, fabrication, and testing. This was accomplished in October 1999 when Raytheon demonstrated the world's first conformal optical system. This fineness ratio one system was a risk reduction effort to develop technology for later systems. It is comprised of a calcium fluoride conformal optical dome, a TI-1173 aspheric corrector, and a calcium fluoride solid catadioptric telescope. The design involved overcoming large amounts of aberration that varied with gimbal look angle. Efforts also included aligning the system to tight tolerances and testing highly aspheric optical elements. Overall, the actual system performance compared very favorably with the design model. With the proven success of this risk reduction demonstration, the path was cleared for new higher performance conformal optical systems.

Design, fabrication, and testing were demonstrated for a conformal window imaging system. The conformal window is sapphire and has a toroidal shape. A pair of axially translating cylindrical lenses were constructed to correct the astigmatism introduced by the window across the full field of regard. A telephoto camera lens was used with the system for imaging objects at infinity. Images of some distant targets were collected, and they compare favorably to those images taken with the camera alone.

A calculation is presented for meridional rays of the ray path deviation in a conformal dome in which both the shape of the inner and outer surfaces are specified in detail so as to examine under what conditions the ray path deviation might be minimized by independently adjusting the shape of the inner surface. Specific results are given for the case that both surfaces are ellipsoidal in shape.

Sophisticated electro-optic sensors are employed on aircraft and missiles, and it is essential to protect them from relatively high-speed impacts with airborne dust particles. A loss in transmission caused by such an event can impair guidance, and catastrophic failure may occur. Protection is afforded by the installation of a hard cover that is transparent in the relevant regime. Diamond is potentially by far the most attractive window material due to excellent optical and mechanical properties, but it is difficult to shape. Chemical vapor deposited (CVD) diamond is a polycrystalline synthetic with properties that approach those of single crystal diamond, and it can be more easily shaped. The aims of the present research were to quantify the erosion and transmission losses, and to understand the material removal mechanisms involved. Steady-state erosion rates were obtained for CVD diamond of different grain sizes, using 300-600 micrometers quartz erodent at velocities between 60 and 140 m/s. Images of CVD diamond at various stages of erosion, obtained using an optical microscope and an environmental scanning electron microscope (ESEM), reveal that erosion initially occurs at grain boundaries and that so-called micro-features also have some influence on erosion.

Chemical Vapour Deposited (CVD) Diamond can now be fabricated in the form of large planar windows (up to 120mm in diameter and 2mm thick) and hemispherical domes (up to 70mm in diameter) suitable for operation as ultra-robust, aero-space infrared (IR) apertures. This paper describes the optical and IR properties of such components, reporting in detail on the short wavelength IR properties and the variation in optical properties with sample temperature. Flat CVD diamond windows are currently being used with great success in a number of long wavelength infrared (LWIR) applications. The paper discusses how the optical properties, such as absorption and scatter, differ when operating at shorter wavelengths and speculates on the usefulness of CVD diamond as a multi-spectral window. Aerospace windows and domes are often required to perform at elevated temperatures and thus the change in IR properties under these conditions is of interest. The paper describes a series of studies into the transmission, emission and absorption of CVD diamond as a function of temperature, using spectroscopic techniques. The extension of the CVD diamond growth and processing technologies to geometries other than flats is at an advanced stage of development and data on the IR properties of state-of-the-art, high geometrical tolerance diamond domes will be presented, including MTF assessment at 10.6micrometers .

CVD diamond optics are now available for far infrared airborne applications in both flat plate and dome geometries. For many applications, these require durable coatings for antireflection and/or oxidation protection. With a high characteristic modulus, diamond may allow the use of relatively weaker materials for such coatings provided that the coatings are well-adhered to the substrate. Single layer and two-layer designs have been assessed based on yttria, ytterbia and silicon. Magnetron sputtered examples have been assessed with single layer coatings reducing single surface reflectivities by 12%, whilst maintaining transmission to 13.5 micrometers . The erosion properties of these coated optics, assessed by water jet impact testing (MIJA), are found to be exceptional, with damage thresholds > 350 ms^-1 achieved, with a 0.8 mm jet size. The pre-deposition treatment of the diamond has been found to influence the strength of the diamond/coating interface and thus the durability of the coatings. The nature of the diamond surface and the effects of oxidizing pre-deposition treatments have been investigated by X-ray electron spectroscopy (XPS). Strong oxidizing etches conventionally used to clean diamond can leave the surface rich in chemisorbed oxygen with a range of valence states evident in XPS data. In comparison, the valence states of the carbon atoms at hydrogen terminated surfaces have a much narrower distribution. The type of carbon oxygen bonding on the surface of the diamond is critical to adhesion of transition metal oxide based coatings.

Rain erosion is a critical problem in the use of conventional Zinc Sulfides as infrared window and dome. In this study, the diamond-ZnS composite, which dispersed diamond particles into a zinc sulfide matrix, was fabricated for improved durability against rain erosion. It was found that mechanical properties, such as hardness, fracture strength and Young modulus of the diamond-ZnS composite improved with the increase in diamond particles. Furthermore the diamonds-ZnS composite consisted of two layers, a diamond dispersed layer and a pure ZnS layer. They have a 280-350kg/mm² hardness, which is 1.5 times higher than conventional ZnS, while maintaining about 55~70% in average transmittance at the wavelength of 10micrometers bands.

Temperature dependent infrared transmittance measurements and room temperature BSDF measurements are collected on 1.5mm thick CVD diamond samples produced by De Beers Industrial Diamond Division. The transmittance measurements are from 2 to 20 micrometers covering the temperature range from room temperature to 400 degree(s)C. The BSDF measurements are conducted at wavelengths of 0.6328, 3.39, and 11 micrometers and as a function of the incidence angle. The total integrated scatter is obtained by integrating the BSDF function over all the reflection angles.

High quality measurements of the refractive index of Cleartran Zinc Sulfide at different temperatures over a wide frequency range are reported. The simplest expression of temperature dependence is the derivative of refractive index with respect to temperature, i.e. the thermo-optic coefficient. A convenient method for determining refractive index is measuring constructive or destructive interference between surfaces of a thick lamina that produce transmission peaks. Such transmittance measurements, made at several temperatures, along with knowledge of the sample thickness provide a comprehensive picture of the temperature-dependent refractive index. Results from these measurements show that ZnS has a dn/dT between 3x10^-5 and 5.5x10^-5 depending on temperature and wavelength. In addition, photoelastic measurements on both thin and thick samples in the visible and mid-IR region show ZnS to have a relative photoelastic constant of about 1.2x10^-11m²/N.

The use of energetic electrons to modify the optical and mechanical properties of several window materials was examined. The materials were exposed to fields of high-energy electrons (5 MeV at a dose of 1,000 MRad). In this paper, we will report on the electron irradiation effects on the following materials: alumina, ALON, ZnSe and ZnS. Alumina irradiated under these conditions revealed little if any changes in flexure strength at room temperature. Irradiation changes in ALON hardness were measured. The hardness fracture toughness of electron beam irradiated ZnS and ZnSe was examined by both indentation and known flaw methods. Toughness measured by both methods were then compared and contrasted to ascertain the effects induced by the irradiation. The electron irradiation produced changes in the fracture toughness of both the ZnS and the ZnSe. The optical properties of the ZnSe and ZnS were measured by FTIR indicated minor changes in the absorption spectra.

For the purpose of assessing the strength of engineering ceramics, it is common practice to interpret the measured stresses at fracture in the light of a semi-empirical expression derived from Weibull's theory of brittle fracture, i.e., ln[-ln(1-P)]=-mln((sigma) _N)+mln((sigma) ), where P is the cumulative failure probability, (sigma) is the applied tensile stress, m is the Weibull modulus, and (sigma) _N is the nominal strength. The strength of (sigma) _N, however, does not represent a true measure because it depends not only on the test method but also on the size of the volume or the surface subjected to tensile stresses. In this paper we intend to first clarify issues relating to the application of Weibull's theory of fracture and then make use of the theory to assess the results of equibiaxial flexure testing that was carried out on polycrystalline infrared-transmitting materials. These materials are brittle ceramics, which most frequently fail as a consequence of tensile stresses acting on surface flaws. Since equibiaxial flexure testing is the preferred method of measuring the strength of optical ceramics, we propose to formulate the failure-probability equation in terms of a characteristic strength, (sigma) _C, for biaxial loadings, i.e., P=1-exp{-(pi) (r_o/cm)²[(Gamma) (1+1/m)]^m((sigma) /(sigma) _C)^m}, where r_o is the radius of the loading ring (in centimeter) and (Gamma) (z) designates the gamma function. A Weibull statistical analysis of equibiaxial strength data thus amounts to obtaining the parameters m and (sigma) _C, which is best done by directly fitting estimated P_i vs i data to the failure-probability equation; this procedure avoids distorting the distribution through logarithmic linearization and can be implemented by performing a non-linear bivariate regression. Concentric- ring fracture testing performed on five sets of Raytran materials validates the procedure in the sense that the two parameters model appears to describe the experimental failure-probability distributions remarkably well. Specifically, we demonstrate that the wide divergence in published CVD-diamond strength data reflects the poor Weibull modulus of this material and must be attributed to the size effect rather than the quality of the deposits. Finally, the problem of obtaining correct failure stresses from the measured failure loads is examined in the Appendix.

An optical technique for measuring surface stress in chromium-doped sapphire windows is reported. The approach utilizes the well-known effects of temperature and stress on the spectral profile of chromium ion fluorescence in crystalline sapphire. In this study, the sapphire samples were selectively doped with a surface concentration of chromium ions, which provided a direct measure of the stress and temperature in the surface region of the window. A series of fluorescence measurements were performed to calibrate the effects of temperature and mechanical stress on the spectral characteristics of the surface fluorescence. The results of this laboratory study are currently being developed into a dynamic, non-contact probe of stress in infrared seeker windows while under simulated conditions of flight.

With the advent of common aperture systems comes a requirement for substrates and coatings that are transparent in both the visible and IR bands. While there are many suitable bulk materials there are surprisingly few coatings available that offer both antireflecting properties and substrate protection. Materials that need little environmental protection tend to be costly to fabricate and machine while others are far too soft to be of any great use. It is for this reason that particular attention has been given to multispectral zinc sulfide which is a relatively cheap material and has good transparency both in the visible and the IR up to -13micrometers . Although it is a soft material (~150kg.mm^-2) it may be protected by a range of coatings. This paper will look at two main materials, ZrN deposited by RF reactive sputtering and YF₃ by ion assisted deposition (IAD) which when used in conjunction offer both increased durability to the substrate and good tri-color transmittance for practical window applications.

Plasma Assisted Chemical Vapor Deposition (PACVD) boron phosphide (BP) has long been established in service on materials such as germanium and FLIR grade zinc sulfide as a protective coating. As airborne systems are required to fly at higher speeds either coatings must become more protective or substrates must become more durable. For MWIR only systems it is logical to use silicon as a window or dome material as the natural hardness of the substrate provides good resistance to particle and rain erosion. The optical transmittance of uncoated silicon is not particularly good (~53% over the 3-5micrometers for a 5mm substrate and normal incidence, Pol=R, room temperature). Applying low energy multilayers on each surface boosts the transparency but offers no resistance to harsh environmental conditions. Although generally the silicon substrate is unaffected due to its hardness, the coating is eroded on the external surface and the transparency drops. With the deposition of boron phosphide by the improved PACVD process the adhesion is so great that not only does the BP not get removed by the erosion, but it protects the substrate at higher speeds. This paper presents data collected by several methods relating to airborne erosion by solid impact of an IR coating/substrate system.

Thin films of selected amorphous and nano-crystalline compositions from the ternary phase diagram made up of carbon, silicon, and nitrogen, with a significant oxygen impurity, have been grown by chemical plasma reactions, ion beam deposition and plasma CVD. Characterization has focused on optical and mechanical properties to determine the compositions best suited for erosion resistant infrared (IR) optical coatings. The most desirable film compositions for the goal application are located in a compositional region around the C/Si atom ratio = 0.2 and C/N = 0.3. The most durable films have no apparent midwave infrared (IR) absorptions, an optical index of refraction ranging from 2 to 2.1, and indent hardness near 40 GPa. Thin film compositions nearer to carbon nitride show significant midwave absorption bands and lower hardness. Ambient thermal oxidation resistance increases with film nitrogen content, with the most durable films being stable at 700 degree(s)C in air.

A novel class of complex metal oxides that have potential as transparent conducting oxides (TCOs) for the electromagnetic-interference (EMI) shielding on IR-seeker windows and missile domes has been identified. These complex metal oxides exhibit the rhombohedral (R3m) crystalline structure of naturally occurring delafossite, CuFeO₂. The general chemical formula is ABO₂ where A is a monovalent metal (Me⁺¹ such as Cu, Ag, Au, Pt or Pd, and B is a trivalent metal (Me³⁺) such as Al,Ti,Cr,Co,Fe,Ni,Cs,Rh,Ga,Sn,In,Y,La,Pr,Nd,Sm or Eu. By adjusting the oxygen content, the conductivity can be varied over a wide range so that the delafossites behave as insulators, semiconductors or metals. This paper presents results for films of p-type Cu_xAl_yO_z and n-type Cu_xCr_yO_z deposited by reactive magnetron co-sputtering from high-purity-metal targets. Films have been deposited using conventional RF- and DC-power supplies, and a new asymmetric-bipolar-pulsed- DC-power supply. Similar to the high-temperature-copper- oxide superconductors, the presence of Cu-O bonds is critical for the unique properties. Fourier transform infrared (FTIR) and electron spectroscopy for chemical analysis (ESCA) are used to understand the relationship between the optoelectornic properties and the molecular structure of the films. For example, FTIR absorption bands at 1470 and 1395cm^-1 are present only in Cu_xAl_yO_z films that exhibit enhanced electrical conductivity. When these bands are absent, the Cu_xAl_yO_z films have high values of resistivity. In addition to the 1470 and 1395cm^-1 bands observed in Cu_xAl_yO_z films, another pair of bands at 1040 and 970cm^-1 is present in Cu_xCr_yO_z films.

Aluminum nitride (AIN) has the potential to meet the requirements of hypersonic-seeker windows that operate in the visible to mid-wave infrared and rf frequencies. With dielectric properties and thermal-shock resistance similar to those of hot-isostatic-pressed silicon nitride, but with a thermal conductivity eight times higher, AIN is a primary candidate for high-power-microwave windows and for high- speed radomes. The true potential of AIN has yet to be demonstrated because single crystals of AIN with purities high enough to be considered intrinsic have never been fabricated. Carbon and oxygen are the two most significant impurities and are the most difficult to eliminate. Impurities and voids present in AIN fabricated from nanocrystalline powders degrade the thermal-mechanical properties and produce optical scatter that limits the useful wavelength range. A large amount of scatter could be removed by eliminating the carbon and oxygen impurities and by reducing the crystallite size in polycrystalline AIN to sub-micron and nanometer sizes. Oxygen incorporation has yet to be avoided using conventional powder processing techniques because the newly formed AIN powders react spontaneously with trace amounts of oxygen. Over the past 50 years, the solid-state-chemistry approach has been used by several research groups and has produced useful material for electronic heat-sink applications but never the high- optical-quality material needed for 2-mm-thick missile domes and windows. This suggests that research aimed at producing high-quality-microcrystalline-AIN coatings and freestanding films would be productive. This paper will present results for films of AIN deposited using reactive asymmetric- bipolar-pulsed-dc-magnetron sputtering.

Using well proven boron phosphide (BP) technology, Thales Optronics (formally Barr & Stroud Ltd.) have expanded the range of IR materials successfully protected to include gallium arsenide. BP has already been used as part of a dual band coating for FLIR grade ZnS which performs well environmentally and is currently used on several prototype dome systems. Having a hardness lower than germanium, gallium arsenide is perhaps not the first choice for applications required to perform well in harsh conditions however there are some other useful properties, among these is the recently reported ability to create low resistivity material for stealth applications and low free-carrier absorption at elevated temperatures. This paper will look at some of the measured optical and physical characteristics of this new substrate/coating system including rain erosion tested by whirling arm and solid particle erosion. In addition some attention will be given to the actual vs. theory performances and envisaged practical applications.

Dual band transparent conductive coatings for the visible and 3-5 micrometers range have been developed on sapphire substrates. The conductive layer consists of indium oxide, deposited in reactive oxygen ion plasma. The typical average transmission of a coated element is about 72% 3.6-4.2 micrometers and about 82% 0.5-0.9 micrometers . Sheet resistance is about 40 ohm/square. The coatings are highly durable and withstand MIL-C-675C tests. Coating transmission in both spectral ranges remains constant in the temperature range -140 degree(s)C - +160 degree(s)C . Sheet resistance increases by about 30% when heating from room temperature to 250 degree(s)C.