This PDF file contains the front matter associated with SPIE Proceedings Volume 12518, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

We present a scalable approach capable of manufacturing high-precision three-dimensional (3-D) GRIN nanocomposites based on multi-component bulk glass-ceramics where we spatially modulate the concentration of high refractive index nanocrystals within a glass matrix. Previously demonstrated in homogeneous thin films and bulk glasses containing large scale liquid-liquid phase separation, this work expands on our efforts to optimize processing protocols employing a near single-phase bulk glass starting material enabling true 3-D modification. Sub-bandgap laser exposure generates Pb-rich amorphous phases within a Ge-As-Pb-Se glass matrix, which undergo crystallization resulting in the formation of highindex nanocrystals upon controlled heat treatment. Nanocrystal density is modulated in both radial and axial geometries by the laser dose, providing spatially tailorable changes in index and dispersion.

Gallium Lanthanum sulphur-oxide (GLSO) glass is an excellent candidate for a window/dome material ought to its wideband transmission window from visible to MWIR. The suitable optical transmission from 0.45-8 microns is supplemented by its superior thermal and mechanical properties to contemporary materials, such as Cleartran™ zinc sulphide. In this work, the properties of GLSO were enhanced by doping with small concentrations of silicon nitride (≤ 0.5 M%), which expanded the transmission window to encompass all the visible spectra. Nano-indentation demonstrated that the hardness and elastic modulus slightly improved. Overall, the improvements demonstrated here make this glass an even better solution when compared to the state-of-the-art for use in single-optic windows and domes.

Active transition metal ion (TM) doped infrared transparent chalcogenide glasses are a promising class of solid-state materials which can be drawn into a new generation of optical fibers for efficient sources of mid-infrared (MIR) lasers. This work evaluates a candidate glass matrix system of As-S-Se chalcogenide glass as a host for iron (Fe) doped ZnSe crystals. Despite good refractive index match between the chalcogenide glass and the Fe²⁺:ZnSe particles, the stability of the dopant is critically impacted by the melt temperature conditions. To address this issue, Fe²⁺:ZnSe particles were coated with a conformal shell of Al₂O₃, via Atomic Layer Deposition (ALD), to improve the stability of the dopant in the chalcogenide glass matrix melt environment. An ozone pretreatment of the ZnSe powders prior to ALD also improved particle stability, resulting in significant reduction in dissolution of coated powders. Moreover, an improvement in the drying protocol of the glass resulted in significantly lower impurity concentrations. The broadband optical emission of the composites in the 3520-5200 nm region was measured using Er (III):YAG pump laser. Improved ALD coating and drying protocol resulted in a bulk optical composite with higher emission signal compared to previous composite fabricated without these protocols, for the same loading levels.

Advanced ceramics require well defined stoichiometries to exhibit their optimal electronic and optical behaviors. The CaS-La₂S₃ solid solution exhibits promising optical and thermoelectric properties but is also venerable to sulfur loss during processing. The characterization of this sulfur loss is difficult using traditional methods due to sample preparation, long acquisition times, and error bars which limit the usefulness of the measurement. In this paper, we show that our material system undergoes sulfur loss during processing and that this sulfur loss goes on to impact material physical properties. We access sulfur loss through the use of Raman spectroscopy and the evaluation of the full width at half maximum (FWHM) of the A1 peak of the system. We then correlate this Raman analysis and XRD to trends in the material properties as a function of sulfur loss.

Multispectral zinc sulfide (MS-ZnS) is a gold-standard window material for applications requiring broadband transmission from the visible to the LWIR. This work investigates a vapor transport process to diffuse Ga₂S₃ into the subsurface of MS-ZnS and improve on the durability of this polycrystalline material. After solid-state diffusion, the presence of gallium in the host is confirmed by secondary ion mass spectroscopy and its concentration is quantified by x-ray diffraction. We show that, under optimized conditions, one can double the Vickers microhardness of MS-ZnS without precipitation of wurtzite and significant degradation of transmission.

Conformal windows and freeform optics are becoming more widely used. Conformal window/freeform optics have a geometry that is non-rotationally symmetric. These optics improve aerodynamic performance by matching the mold line of the design, enabling more complex systems, and reducing the optical system footprint. Freeform and conformal window geometries are becoming more complex to increase their design benefits and, with tighter tolerances on the surface geometries, new challenges in manufacturing are being realized. From part design to the manufacturing process to metrology of the surfaces, each stage plays a role in whether the part is made successfully. In design, a good datum structure should be chosen for repeatably and accurately locating the part in the manufacturing and metrology machines. Careful consideration to stresses being induced in the part during the fixturing process is required to minimize part springing and the associated form error changes when removing the part after machining is complete. As part geometries have evolved in complexity and sensitivity to error map alignment has increased, a 3D error map is crucial to making error alignment easier and less prone to mistakes. Just as important as the freeform surfaces, but often not focused on as much, is the quality of the edges of the part. High quality edges are critical to prevent breakage and chippage propagating out from the edges. This paper presents keys and best practices for manufacturing freeform and conformal geometries to ensure the greatest chance of meeting the required tolerances.

Transparent ceramics are materials of choice for high temperature IR window applications: they are a compromise between transparency, thermal shock resistance and processing costs. Alumina, AlON and spinel-type ceramics have been developed for the 3-5 μm atmospheric transparency band. Nevertheless, these compounds show a degradation of their optical properties (transparency and emissivity) at high temperature (above 500°C), limiting their use in that wavelength range. MgO and Y₂O₃ have a broader transparency window up to 9 μm and they are transparent enough in the 3-5 μm range even at high temperature but their thermomechanical resistance is weak. Authors have combined these compounds into a nanocomposite ceramic to improve this while keeping good IR transparency. To reach such properties, porosity ratio must be close to zero and the average grain size must stay as small as possible (< 200 nm). Throughout this study, Pechini’s esterification sol-gel route was chosen in order to process the Y₂O₃-MgO nanocomposite powder. Then, a two-step sintering and low temperature profiles (700‡C) were performed by the Spark Plasma Sintering technique. Post treatments, air annealing and Hot Isostatic Pressing at 400MPa, improved the quality of the ceramics. Finally, structural, microstructural and optical characterizations were carried out. Samples with different nanostructures were obtained. The best samples have average grain diameters below 200 nm with almost no porosity. Good mid-IR transparency, up to 80% for a thickness of 1 mm, was obtained in band II. The material showed a loss of transparency at 5μm below 15% at 1000°C.

ALON^® Transparent Ceramic (ALON) consists primarily of aluminum and oxygen, similar to that of alumina, with a small amount of nitrogen added to help stabilize its cubic phase. Importantly, materials with cubic symmetry are optically isotropic, and consequently, transparent in their polycrystalline form. This allows ALON to be manufactured by conventional powder processing methods. Surmet has implemented an extremely robust manufacturing process for ALON optics blanks in very large flat as well as curved shapes. Spinel (MgAl₂O₄) is a cubic material, that transmits further into the infrared than ALON. Spinel is also produced via powder processing techniques similar to those used to produce ALON. Spinel’s superior transmission at wavelengths beyond 4.5um, make it the preferred option for certain MWIR sensor applications. ALON’s superior physical and mechanical properties combined with its superior producibility/manufacturability make it the material of choice for most other applications, including very large sensor windows and transparent armor. Powder processing provides the flexibility to produce both ALON and spinel components in a wide range of shapes and sizes, including complex dome shapes, such as hyper-hemispherical and tangent ogive, as well as conformal shapes for aerospace and automotive applications. To this end, Surmet has developed inspection polishing techniques applicable to conformal optics and curved transparent armor. Examples of inspection polished windows with complex curvature will be presented. Surmet has consolidated its manufacturing operations for large ALON and Spinel windows into our 75,000 square foot facility in Buffalo NY. The facility now houses new production furnaces and custom-built ceramics processing equipment that is the largest of its kind in the US. This expansion has established a vertically integrated capability to manufacture transparent ceramic products at this facility.

ALON^® Transparent Ceramic (ALON) consists primarily of aluminum and oxygen, similar to that of alumina, with a small amount of nitrogen added to help stabilize its cubic phase. Importantly, materials with cubic symmetry are optically isotropic, and consequently, transparent in their polycrystalline form. This allows ALON to be manufactured by conventional powder processing methods. ALON is deployed in several Vis-MWIR Sensor Window applications and provides outstanding environmental durability. Further, ALON windows are available in very large sizes as required for Defense reconnaissance systems. The conventional approach for predicting how the strength of a ceramic material scales from the small strength coupons (~1” diameter), to full sized sensor windows, which may be orders of magnitude larger, is to use Weibull scaling as is described by Harris et al in reference 1. Weibull scaling assumes that as the window gets larger and larger, the strength controlling flaws get larger too. However, this ignores the microstructure of the window material, and the role that the microstructure may have in limiting the size of strength controlling flaws. All materials, amorphous, single crystal and polycrystalline are therefore treated as equivalent. Jeff Swab et al2 measured strength in ALON samples over a range of sizes. The largest strength samples measured were <11-in diameter. These ALON samples were purchased from Surmet with our standard commercial polish. We have the average strength and Weibull modulus data for samples produced with the same surface. Scaling the strength from coupons (~350MPa, and Weibull modulus m=3.11) to the largest samples broken by Swab et.al, predicts a strength of only 53 MPa. However, the actual strengths measured by Swab et.al. was 152+/-28 MPa, 3x higher than predicted. The potential role of ALON’s microstructure in this higher than predicted strength will be discussed, and future experiments will be proposed to determine an improved approach to scaling strength with area.

AmeriCOM has partnered with the DoD Industrial Base and Sustainment (IBAS) to create a Defense Precision Optics Consortium (DPOC). This presentation reports on a project of interest to the DoD, that is being executed by the consortium. The DoD perception is that the extreme accuracy requirements and immaturity of some of the measurement techniques for HEL components have caused challenges and disruptions in the DoD HEL supply chain. The HEL supply chain is being asked to increase their rate capability and any problems with low manufacturing readiness levels are a disruption to the on-time delivery of systems to the warfighter. A gage repeatability and reproducibility study in a round robin format is being used to determine the industry wide uncertainties for measurements of key optical characteristics, such as coating and substrate absorption. Participating organizations will use their systems, built in-house or procured instruments, to measure components supplied.

In this research, a novel hybrid lens consisting of a metallic circular symmetry and a diffractive optical element (DOE), whose combined diffraction distribution is very similar to a single DOE, is proposed as an alternative to a hybrid lens consisting of Frequency Selective Surface (FSS) and a DOE. The hybrid lenses are simulated by using optical wave propagation in optical bands and simulated with CST Studio Suite in RF bands. Simulation results are reported for both RF and optical bands. The results indicate that the novel hybrid circularly symmetric lens has almost the same shielding effectiveness (SE) in the RF band compared to the hybrid FSSs. Furthermore, circular symmetry minimizes the spectral components specified in the Abbe-Porter experiment. Consequently, due to the circular symmetry, the combined amplitude distribution of the hybrid lens is close to the amplitude distribution of only one lens. As a result of this research, the proposed hybrid lens will contribute to the development of these structures, entitled FSDOE in this study.