N112-105 TITLE: Reduced-Cost Grinding and Polishing of Large Sapphire Windows

TECHNOLOGY AREAS: Air Platform, Materials/Processes, Sensors

ACQUISITION PROGRAM: F-35, Joint Strike Fighter

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports):  This topic is "ITAR Restricted."  The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data.  Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop methods of grinding and polishing to reduce the cost of a finished sapphire sensor window with dimensions of 12 x 18 x 0.25 inches by at least one-third of that of current windows.

DESCRIPTION: There is a need for precisely figured sapphire sensor windows with dimensions of 12 x 18 x 0.25 inches operating in the 1- to 5-micron wavelength range. The purpose of this topic is to demonstrate improved methods of grinding and polishing to reduce the cost of the finished window by at least one-third. The sapphire must have optical and mechanical properties at least as good as those of today�s commercially available material.

PHASE I: Develop improved methods of grinding and polishing sapphire to reduce the cost by at least one-third without degrading mechanical or optical properties. Demonstrate the selected method by grinding and polishing a 4- x 4- x 0.25-inch a-plane sapphire plate to obtain a root-mean-square transmitted wavefront error of one-tenth of a wavelength measured at 0.63 micron over a clear aperture extending to 0.01 inch from the perimeter of the plate. Estimate the cost of grinding and polishing 12- x 18- x 0.25-inch finished windows and define a path forward to produce such windows.

PHASE II: Continue to develop and optimize grinding and polishing procedures. Produce finished plates with geometries and tolerances to be provided by the government at the time the Phase II plan is written. Extract at least 10 disks from each of 2 finished plates to make mechanical test specimens with a diameter of 3 inches and thickness of 0.25 inch. Measure the ring-on-ring flexure strength with a load diameter of 1.25 inches. Estimate production costs for sapphire blanks and define a path forward to produce window blanks.

PHASE III: Scale up for commercial production of window blanks and transition into applicable platforms.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: There is a large market for bulletproof windows for armored vehicles if cost per unit area can be decreased.

REFERENCES:
1. Bashe, J. R., Dempsey, G., Akwani, I. A., Jacoby, K. T., & Hibbard, D. L. (2007). "Critical parameters for grinding large sapphire window panels." Proceedings of SPIE 2007, 6545, 654517.

2. Hallock, B., & Shorey, A. (2009). "Technologies for precision manufacture of current and future windows and domes." Proceedings of SPIE 2009, 7302, 73020V.

KEYWORDS: Sapphire Polishing; Optical Finishing; Polishing; Sapphire; Window; Electro-Optic Window

** TOPIC AUTHOR (TPOC) **

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