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) toimprove 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 structuresetched 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 foranti-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 thebandwidth 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 toimprove spectral performance of the THAAD system or any kill vehicle utilizing the IR part of the spectrum. It is anticipated that GaAs as an IR window material which incorporates the sub-wavelength d