Demand for larger aperture sapphire IR windows is increasing. To withstand the higher dynamic and pressure forces exerted on them these larger windows require thicker material. Edge Defined Film-fed Growth (EFG)TM Sapphire crystals have traditionally been grown with a thickness of ≤ 11 mm, then finished and polished to a nominal thickness of 5.5 mm. We present optical characteristics data here for Class225(R) EFGTM sapphire sheet that is being grown up to 22 mm thick and finished at 16.8 mm.
EFG sapphire sheet measuring 305 x 510mm and 225 x 660mm have been produced in quantity. The average optical transmission of 6.15 mm thick uncoated polished panels is 84.0% ± 0.5 at 700 nm. This value assures good transmission throughout the 500 to 5000 nm spectral range. Effective absorption coefficients for this spectral range and thickness are calculated and presented. An average index inhomogeneity of 6 ppm ± 2 has been measured and is the requirement for panels polished to 0.1λ at this thickness (@633 nm).
Edge Defined Film-fed Growth (EFGTM) Saphikon® sapphire crystals have been grown as large, thick sheet. The sheet is then precision-polished and coated into an infrared or laser transmission compatible window. The sapphire windows are subsequently assembled into a multi-panel configuration for advanced targeting, navigation, or reconnaissance applications. As future aerospace programs will require windows with larger apertures, material characteristics and uniformity such as refractive index homogeneity will increase in importance. Optical measurements, x-ray topography data and rocking curve analysis are presented The crystalline properties as they relate to refractive index inhomogeneity and wave front distortion are discussed.
EFG sapphire sheet measuring 305 x 510mm and 225 x 660mm have been produced in quantity. The average optical transmission of 6.15 mm thick uncoated polished panels is 84.0% ± 0.5 at 700 nm. This value assures good transmission throughout the 500 to 5000 nm spectral range. Effective absorption coefficients for this spectral range and thickness are calculated and presented. An a verage index inhomogeneity of 6 ppm ± 2 has been measured and is the requirement for panels polished to 0.1λ at this thickness (@633 nm).
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