N112-115 TITLE: Durable Multispectral Sensor Window

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: Produce an aircraft multispectral sensor window that can replace sapphire with a target cost that is less than two-thirds that of a finished sapphire window. The alternative material must meet requirements for strength, stiffness, and spectral transmission.

DESCRIPTION: There is a need for durable, precisely figured multispectral (1- to 5-micron wavelength) sensor windows with dimensions of approximately 30 x 46 x 6 cm (12 x 18 x 0.25 inches). Sapphire provides an expensive solution to the window requirement. The purpose of this topic is to demonstrate an alternate material that can produce finished windows at less than two-thirds the cost of sapphire. The alternative material must be strong and stiff enough to replace sapphire without being excessively thicker than sapphire. The alternative material must not sacrifice spectral transmission and must have low optical scatter.

The desired strength is at least 450 mega pascals (MPa), with a Weibull modulus of at least 5 when tested in ring-on-ring flexure with a 16-mm-diameter load ring. The desired Young�s modulus is at least 300 giga pascals (GPa). Spectral absorption at wavelengths of 4 to 5 microns should not be greater than that of sapphire. Total integrated optical scatter for a thickness of 5 mm should not exceed 1 percent in the wavelength range of 1 to 5 microns and be preferably less than 0.5 percent. Refractive index homogeneity should not exceed 10 parts per million so that the window can be finished to a high degree of optical precision.

Off-the-shelf materials other than sapphire do not satisfy the requirements. A fine-grain spinel might be strong enough but is not likely to be stiff enough. Aluminum oxynitride has the desired mechanical properties but absorbs too much radiation near 5 microns. Experimental materials such as fine-grain yttrium aluminum garnet (YAG) or, possibly, nanograin composites might meet the requirements. Composite material might have too much optical scatter at short wavelengths.

PHASE I: Demonstrate on a coupon scale the optical and mechanical properties of a selected material that meets requirements for optical transmission, optical scatter, mechanical strength, and Young�s modulus. Estimate the cost of producing finished 30- x 46- x 6-mm windows and define a path forward to produce such windows.

PHASE II: Produce finished windows of a practical size and geometry determined by mutual agreement with the government. Measure mechanical and optical properties of material taken from large panels. Properties to be measured will be determined by mutual agreement with the government. Estimate production costs for windows and define a path forward to produce such windows.

PHASE III: Scale up for commercial production of finished windows and transition technology to applicable platforms.

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

REFERENCES:
1. Huie, J. C., Dudding, C. B., & McCloy, J. (2007). "Polycrystalline yttrium aluminum garnet (YAG) for IR transparent missile domes and windows." Proceedings of SPIE 2007, 6545, 65450E.

2. Stefanik, T, Gentilman, R., & Hogan, P. (2007). "Nanocomposite optical ceramics for infrared windows and domes." Proceedings of SPIE 2007, 6545, 65450A.

KEYWORDS: Window; Sensor Window; Transparent Ceramic; Yttrium Aluminum Garnet; YAG; Nanocomposite Optical Ceramic

** TOPIC AUTHOR (TPOC) **

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