Increased Infrared (IR) Sensor Angle of Regard for Conformal/Special Operations Force

ABSTRACT: Optical sensors are extensively used in aircraft for a variety of purposes. The majority of these sensors are situated behind windows, which provide the interface between the aircraft interior and the outside world. The window must be transparent in the spectral bands of interest, and this requirement generally mandates materials that tend to have a large refractive index. Without surface treatment, each window surface reflects a significant amount of light (up to 30%, depending on material) destined for the sensors. The reflection problem is greatly exacerbated at larger angles of incidence, where the window can cause polarization changes and ghosting due to internal reflections. Conformal aircraft windows have curvatures that make conventional surface treatment techniques complex. There is a need for optical window surface treatments that reduce reflections over broad regions of the electromagnetic spectrum, and for large incident angles, while maintaining the structural, mechanical, optical, and environmental qualities associated with the interface between aircraft interior and exterior. Nanohmics proposes to develop and demonstrate broad-spectral, high-angle, anti-reflection surface treatments for conformal infrared windows by producing nanoscale structures into the window surface. Computational modeling has demonstrated that surface structures reduce optical reflections over wide spectral ranges and for angles exceeding 70 degrees . BENEFIT: Nanohmics will be producing transparent optical window components with low surface reflection and low scattering losses over broad ranges of the visible and infrared spectrum. The windows will maintain low surface reflectivity even at large angles of incidence. Furthermore, the surface treatment and materials involved make the windows rugged and resistant to erosion by rain and sand. These qualities will find application in numerous markets beyond airborne sensor systems, such as security and surveillance, environmental process windows in chemical plants, advanced night-vision optics, and chemical and biological detection equipment.