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Current status of very large sapphire crystal growth for optical applications

Sapphire is an ideal visible-MWIR window due to its excellent optical and mechanical properties and its availability in large sizes up to 340-mm diameter boules. Anticipated applications for new, high performance optical systems call for even larger, 450-750 mm diameter, windows. The present effort has focused on producing 500-mm diameter sapphire boules using the Heat Exchanger Method. Three experimental growth runs demonstrated the feasibility of producing 500-mm diameter sapphire boules. Completely crack- free boules have not been grown, but large size sapphire pieces up to 400 mm by 280 mm have yielded from these experimental runs.