2 September 2015 Homogeneity of material and optical properties in HEM grown sapphire
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Sapphire crystal boules, approximately 34 cm in diameter and 22 cm tall, grown by the Heat Exchanger Method (HEM) are currently being sliced, ground and polished for use as window substrates in a variety of aerospace applications. As the need for larger volumes of higher quality material increases, it is necessary to evaluate and understand the homogeneity of optical and material properties within sapphire boules to ensure the needs of the industry can be met. The optical homogeneity throughout the full useable thickness of a representative sapphire boule was evaluated by measuring the transmitted wavefront error of multiple thin slices. This approach allowed the creation of a full-volume three-dimensional homogeneity map. Additionally, the uniformity of other critical characteristics of the material was evaluated at multiple locations within a boule. Specific properties investigated were equibiaxial flexural strength, index of refraction, Knoop hardness, coefficient of thermal expansion and modulus of elasticity. The results of those evaluations will be reported.
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M. Stout, M. Stout, D. Hibbard, D. Hibbard, } "Homogeneity of material and optical properties in HEM grown sapphire", Proc. SPIE 9574, Material Technologies and Applications to Optics, Structures, Components, and Sub-Systems II, 95740I (2 September 2015); doi: 10.1117/12.2187136; https://doi.org/10.1117/12.2187136


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