Dual-Band Electro-Optic (EO)/Infrared (IR) Multifunctional Pod Windows

Aluminum Oxide (sapphire) windows are a critical element Electro Optical (EO) and infrared (IR) imaging systems. As the demand for an increase in the performance of these optical systems rises, so must the quality of the sapphire windows. One of the most technically challenging aspects of producing high quality sapphire optics is achieving the required surface figure while maintaining a stress free optical surface with good surface finish (or micro-roughness). The desired surface figure error is now < 0.03 waves rms as tested at 632.8 nm for a 22” diagonal sapphire window. Even with extremely skilled opticians, the conventional fabrication process to achieve this surface figure on sapphire optics while maintaining tight wedge specifications and high surface quality can be very slow and costly with the quality of the results being unpredictable. The purpose of the research proposed here is to develop a complete fabrication process (from blank to final shape) that will produce high quality sapphire windows by incorporating magnetorheological finishing (MRF) as the final step of the process. The research will show that by combining the MRF process with the proper CNC grinding and pre-polishing processes, low-cost, high-quality sapphire windows can be deterministically fabricated to repeatedly meet the desired specifications. Phase I of the research has demonstrated the ability of the deterministic MRF process to meet and exceed the surface figure requirement of 0.03 waves rms. Phase II will build upon these initial activities to scale up our process to meet the U.S. Navy's requirements.