80-mm EFG Sapphire Dome Blanks Yield High-Quality Low-Cost Single-Crystal Domes

Close attention to crystal growth parameters and characterization of the crystal's thermal environment during growth has led to improvement in the crystal structure of EFG grown dome blanks. These near net shape 80 mm sapphire blanks have been fabricated to produce high quality finished domes. New measurements of the coefficient of thermal expansion (CTE), thermal conductivity, optical scatter, rain erosion and the thermal coefficient of refractive index (dn/dT) as a function of wavelength have been performed and the data are presented.

It presents dynamic 3D finite element simulation of stress and deformation of growing thin-walled, polygonal tubes. As an example, the growth of octagonal silicon tubes by the edge-defined film-fed growth (EFG) method is chosen. In tubes with wall thickness in the order of several 100 μm the increasing strain energy during growth is periodically reduced by deflections of the walls at regular intervals. The influence of various temperature profiles on the deflection behavior is studied. The applicability of this model to the EFG growth of silicon octagons is discussed by means of experimental observations.


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