Transparent spinel (MgAI2O4) ceramic has become the material of choice for numerous naval and other defence applications. Representing a cubic crystalline material, it is increasingly being used for all aspects of ship protection, including sensors, protective and smart materials, and weapons. In addition to a high degree of ruggedness, spinel ceramic possesses an excellent transmission from the ultraviolet (0.2μm) to the mid-IR (5μm) region. The US Navy's (USN) VIRGINIA-class nuclear-powered fast attack submarine uses a single window made of spinel on its photonic mast, which enhances survivability and significantly reduces maintenance and life-cycle costs. Previously, the photonic mast produced by L-3 KEO was equipped with silica glass and crystalline germanium for transmission of visible and mid-IR light, respectively. Both these materials, however, have been shown to be weak and prone to damage, despite the fact that they are more than 3.8cm thick. The challenge is how to make thick spinel windows. According to research, 3.8cm thick spinel ceramic comes with very good optical quality, based on a hot-press process.
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