Development in EFG sapphire at II-VI Optical Systems

Large sapphire crystals are currently being grown at II-VI Optical Systems with dimensions of approximately 12 " x 36 " x 0.300 " thick via an Edge Defined Film Fed Growth (EFG) method. These crystals are being used to make large sapphire windows for aerospace applications which require high strength and optical performance in the visible to mid-wave infrared regions. In the following paper, II-VI OS will present material data for their EFG sapphire and compare it to that for sapphire grown via the HEM approach, a method which is also used at II-VI OS. Reported data includes index homogeneity evaluated over the entire grown crystal. Other properties to be presented are equibiaxial flexural strength, index of refraction, Knoop hardness, thermal expansion coefficient and modulus of elasticity. The results presented herein will demonstrate that the material performance of sapphire grown at II-VI OS by either method is entirely comparable.