Integral Sub-Wavelength Microstructures For Enhanced, Long-Life Sunshade Light Control

Low reflectivity or, ‘black” surfaces are currently employed to reduce stray light in optical systems such as the telescope housings and sunshades for MDA missile seekers and kill vehicles (KV), as well as other space based optical instruments such as Star Trackers. Baffle or light shade assemblies are designed to restrict a sensor’s field of view through absorption, obscuration or diffusion of incident light outside the sensor’s spectral range. Surface treatments of the baffle and sunshade assemblies can include a variety of black paints, black coatings, and appliqués. Although appliqués may provide lower scattering levels, disadvantages include lower laser damage thresholds, adhesive issues, and outgassing properties, making them unacceptable for many of these applications. State of the art black coatings and paint such as the Martin Black series are currently used on beryllium sunshades and baffles and has been the selected choice for many BMDS programs. These scattering surfaces are designed to diffuse the incoming light, however, this leads to issues in which the energy is absorbed thus generating heat in the black surface treatment. Issues with Martin Black (and other) black coatings include scattering off the treated surface, emissivity issues due to the absorption of shorter wavelengths and the emitting of longer wavelengths, and, perhaps most importantly, issues arising with delamination of the surface treatment. TelAztec has developed a series of sub-wavelength, anti-reflective microstructures that can be applied to virtually any material, eliminating the need for traditional black coatings. Such AR microstructures have been successfully fabricated in many types of IR, visible, and UV transmitting materials providing ultra high AR performance with the microstructures fabricated directly into surface of the optic material. These surface relief microstructures fabricated directly into the sunshade housing material, completely eliminate the limitations due to stress, thermal mismatch, adhesion, radiation damage, complexity, narrow-band performance, polarization splitting, and cost associated with conventional light control coatings. This Phase I project will build upon the success of the preliminary demonstration, and will deliver an AR treatment fabrication process that is cost effective and can consistently produce high transmission diamond windows with an extended operational lifetime in the presence of proton and ionizing radiation. A successful Phase II effort will see the incorporation of an AR micro-structured sunshade in the IDA of an MDA kill vehicle.