Mainstream Engineering fabricates transparent optical windows in the infrared spectrum for high-temperature applications such as hypersonic vehicles. Our patented cooling method (US Patents 11,022,378, 11,015,874, and 10,914,529) passes single-phase or two-phase coolant through internal passages that are formed within the window. Our equipment allows us to produce windows made from a wide variety of materials (e.g., ZnS and SiC) using various processes, such as chemical vapor deposition and physical vapor deposition.