A mounted x-ray window 10 and 20 can include an x-ray window 18 mounted on the flange 11f of a housing 11. The x-ray window 18 can include the following layers: a top strong layer 17, a stress-relief layer 16, a bottom strong layer 15, an adhesive layer 14 then a support ring 13. These layers can have a material composition and thickness for optimizing x-ray window low gas permeability, low outgassing, high strength, low visible and infrared light transmission, high x-ray flux, low atomic number materials, corrosion resistance, high reliability, and low-cost.