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Refractive index homogeneity TWE effect on large aperture optical systems

Sapphire windows are routinely being used in demanding aerospace applications due to their high strength and desirable optical and material properties. Sapphire is particularly useful in addressing the increasing need for systems that provide a wider range of capabilities in a single package. In general, refractive index homogeneity of the component materials can have a significant impact on overall optical system performance. This leads to the need for a deeper understanding of the shape and magnitude of index inhomogeneity in large sapphire windows to ensure predictable, high quality operation. Thin, sapphire slices from a sapphire crystal boule grown via the Heat Exchanger Method (HEM) have been previously evaluated for refractive index homogeneity over a 25.4cm (10.0”) aperture. The resultant transmitted wavefront error (TWE) from those measurements has now been used to model typical optical systems to quantify the effects on system-level performance attributed to representative amounts of index inhomogeneity in the sapphire window. The results of this modeling effort are presented in the following paper.