Low Cost Fabrication of IR Windows for Hypervelocity Interceptors

There are presently three materials (sapphire, ALON and spinel) which are considered suitable for IR windows in severe hypervelocity environments. Of these materials spinel is presently the least developed, but offers optical performance advantages and asignificantly lower fabrication cost than either sapphire or ALON. In the proposed development effort, the hot pressing process presently utilized will be optimized for producing large plates of thick sectioned spinel in a single step. Additional costreduction approaches in the finishing operations will be investigated and their effect on the optical and mechanical performance of spinel quantified. Optical quality spinel will be fabricated with a variety of grain sizes and the optical, and thermalshock performance will be established. The fabrication approach will be developed for 11' diameter parts and the optical properties determined at both room temperature and 500¿C. This work will establish spinel as a low cost, high performance opticalmaterial. Development of this spinel plates will provide an alternative material to sapphire with improved optical properties and at considerably reduced cost. These spinel components are presently being developed and tested as lenses, IR windows, domes,hypersonic windows and as armor for a number of defense applications. Commercial applications such as security windows, IR lenses, fuses and IR windows are also being pursued.