Diffractively Structured Multi-Spectral GaAs EO Seeker Windows for Kill Vehicles

Strategic missile defense will benefit directly by increasing the operational IR bandwidth from the mid-wavelength to a multi-bandwidth capability. Increasing bandwidth performance will allow on-board processing (target acquisition and discrimination) to improve range performance, tracking, and hit-to-kill. Increasing bandwidth to include the near IR to the long wavelength IR also allows for incorporation of active sensing (LADAR) in addition to passive sensing. Sub-wavelength diffractive structures etched onto gallium arsenide (GaAs) present tremendous performance enhancement potential for missile applications. Employing gray scale lithography to etch the sub-wavelength diffractive structures onto both surfaces of the GaAs eliminates the need for anti-reflective coatings and allows for discreet sub-bandwidths of operation over a broadband operational window with very high performance, improved field-of-regard, and increased fracture toughness. Employing GaAs as the bulk IR window opens the bandwidth from the mid-wavelength region (sapphire) to include the near IR to the far long wavelength IR. It also provides a cutoff temperature of nearly 460°C. GaAs and the sub-wavelength diffractive structures present a significant opportunity to improve spectral performance of the THAAD system or any kill vehicle utilizing the IR part of the spectrum. Relatively large area diffractively structured GaAs windows (T>85%) will be demonstrated.