TECHNOLOGY AREA(S): Materials/Processes, Weapons

ACQUISITION PROGRAM: PMA-259 Air-to-Air Missiles

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a method for applying an antireflection coating to the inside of a deep concave surface such as a tangent ogive infrared dome.

DESCRIPTION: Future infrared-guided missiles could use an aerodynamically shaped seeker dome, instead of a hemispheric dome, to reduce drag, increase range and/or speed, and permit increased field of regard for the seeker. Aerodynamic domes require an antireflection coating to reduce unwanted reflections that create stray light. Polycrystalline alumina is a promising material for an aerodynamic dome because its physical, and most of its optical, properties are similar to those of sapphire, and polycrystalline alumina can be formed in near net shape for a dome.

The antireflection coating should be designed to reduce the average of s- and p-polarized reflectance from a single surface of sapphire (a surrogate for alumina) at a wavelength of 4 microns to <1% at normal incidence, <3% at 55 degrees, and <5% at 60 degrees.

The coating process should be capable of producing at least one coated dome for a tangent ogive dome with a base diameter of 5 inches and a height of 7.5 inches per 10-hour workday. The tip of the ogive can be cut off and so can serve as an inlet or outlet for gas flow during the coating process.

The coated dome must undergo subsequent high-temperature processing steps. The coating should withstand temperatures of 1000�C in air without degrading, cracking, or delaminating during heating or cooling.

Proposers must have expertise in thin-film design and optical coating fabrication and characterization. Proposals must include calculated reflectance and transmittance spectra for the proposed coating design on sapphire for wavelengths from 3 to 5 microns at angles of incidence of 0, 30, 45 and 60 degrees. Detailed information including thicknesses and refractive index values for the different layers in the coating design must be included in the proposal.

PHASE I: Design and develop a coating to be deposited onto flat sapphire wafers and supply at least three coated wafers to the Government for evaluation. The coated wafers will be tested to measure the transmittance at normal incidence and the reflectance at angles of incidence up to 60 degrees before and after heating the coated wafers to 1000�C in air. After demonstrating that performance requirements have been met on flat sapphire wafers, develop a detailed task plan to coat the inside of the tangent ogive dome using a process that can coat at least one dome during a 10-hour day. Any remaining time in Phase I should be used to construct hardware for dome coating and begin coating experiments. Develop plans for an antireflection coating application method to be developed in Phase II.

PHASE II: Construct a fixture that replicates the shape of an ogive dome (to be defined by the Government) and that has mounting holes for flat disks of sapphire or polycrystalline alumina at different levels between the base and tip of the dome. Use the proposed application method to coat polycrystalline alumina disks at different locations inside the fixture (dome) for the Government to evaluate. Measure the transmittance at normal incidence and the reflectance at angles of incidence up to 60 degrees before and after heating the coated disks to 1000�C in air. The coating process should be capable of grading the coating thickness so it is optimized for the probable angle of incidence that varies along the length of the dome from the tip to the base. Guidance will be provided on most probable angles of incidence. Demonstrate the capability to deposit coatings with graded thickness from the tip to the base of the dome. Deliver coupons coated inside the dome fixture to demonstrate that the coating thickness varies as intended with distance from the base of the dome. Develop a detailed plan and cost analysis on how the coating process will be implemented in a production environment.

PHASE III DUAL USE APPLICATIONS: Implement a commercial process capable of coating aerodynamic domes on the internal and external surfaces. The external coating must be resistant to erosion as well as providing antireflection performance. Transition developed technology to appropriate platforms and commercial entities.

The ability to coat a small spherical lens uniformly and economically would be an important commercial application. Coating application technology developed in this SBIR effort has potential in the application of heat-resistant coatings where durability and stability at high temperature is required. Commercial applications include: (1) Medical-lighting systems that use hot mirrors, cold mirrors, and ultraviolet-blocking filters that need to withstand high temperature and high ultraviolet flux. Coatings that have better heat and ultraviolet radiation resistance and that could be deposited uniformly onto the interior and exterior of the bulbs would extend the lifetimes of these medical-lighting systems. (2) Ball lenses for fiber-optic interconnects that are used in the telecommunications industry�antireflection coating uniformity is an issue on these types of lenses. (3) Products such as solar reflectors, infrared- and ultraviolet-curing filters, optical-projection systems, and satellite and space-based optical systems that are subjected to high thermal loads.

REFERENCES:

1. Baumeister, P. �Optical coating technology�. SPIE Press, Bellingham, Washington, 2004. doi: 10.1117/3.548071

2. Parish, M., Pascucci, M., and Rhodes, W. �Aerodynamic IR domes of polycrystalline alumina�. Proceedings, Defense and Security, Orlando, Florida, 2005, Volume 5786, 195-205. doi: 10.1117/12.604596

3. Rancourt, J. �Optical thin films: User handbook�. SPIE Press, 1996, Bellingham, Washington. doi: 10.1117/3.242743

KEYWORDS: Anti-reflection Coating; Aerodynamic Missile Dome; Spatially Variable Coating; Optical Coating; Infrared Dome; Thin Film