Unlike fused silica and oxyfluoride glasses that cannot survive in some harsh environments, a new transparent ceramic for high-energy laser (HEL) systems developed at the US Naval Research Laboratory (NRL; Washington, DC) can withstand impact from rain droplets at 600 mph and sand particles at speeds up to 460 mph with no change in transmission parameters.
The transparent magnesium aluminate spinel (MgAl2O4) ceramic, developed as a window and dome material for protecting sensors operating from the UV to the mid-IR region to 5 µm, was designed with optimized low absorption loss of 6 ppm/cm to minimize the beam distortions and loss of output power that are measured as optical-path distortions in HEL systems. The ceramic spinel was made by hot-pressing ball-milled spinel powders at 1400–1650ºC for 2–4 hours using a uniform coating of a small amount of lithium fluoride sintering aid that was eliminated by evaporation prior to full densification. The NRL spinel powder (synthesized by an aqueous process) had crystallites 100–200 nm in size with excellent phase purity based on x-ray diffraction and chemical analysis, with an impurity content several orders of magnitude lower than commercially available spinel powders. Contact Jas Sanghera at email@example.com.