30 May 2013 Large-size spinel windows and domes
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Excellent transmission in the Mid IR wavelength range coupled with good mechanical properties make the use of spinel ceramics very attractive for high performance windows and domes. MER has concentrated its current development efforts in the scale up to windows as large as 25”x32” and domes/hyperdomes as large as 10” in diameter. The MER spinel technology allows producing complex 3-D shape parts like hyper-hemispherical domes and other aspheric lenses. The thickness can reach 1" and above. MER has shown the feasibility of producing several windows 25”x32” and 18”x22” per run. Optimization of transmittance and strength, minimization of the stress birefringence, keeping the variation of the index of refraction to a minimum, has been the main objective. MER also pursued edge bonding technology, where large, thick, panes were edge bonded into a final large window. High optical and IR transparency in the 0.3 – 5.5 μm wavelength range is obtained. Optical metrology measurement of a polished 18”x22”x0.86” window indicated tolerable levels of high frequency variation in the index of refraction homogeneity as well as acceptable low values of residual stress birefringence. MER is also scaling up production to several 7" diameter hemispherical domes blanks per run. After rendering, polishing, and coating, defect free domes in conformance with optical, mechanical, and dimensional specifications have been produced. Details of MER’s technology achievements to produce low cost, high strength, transparent magnesium aluminum spinel windows and domes are described. Optical and mechanical properties were measured and are provided.
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Juan L. Sepulveda, Juan L. Sepulveda, Raouf O. Loutfy, Raouf O. Loutfy, Sharly Ibrahim, Sharly Ibrahim, Simon Bilodeau, Simon Bilodeau, "Large-size spinel windows and domes", Proc. SPIE 8708, Window and Dome Technologies and Materials XIII, 870806 (30 May 2013); doi: 10.1117/12.2016442; https://doi.org/10.1117/12.2016442

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