The invention is directed to highly reflective optical elements having an amorphous MgAl2O4−SiO2 coating with fluoride enhancements inserted and sealed by dense smooth SiO2 layers, and to a method for preparing such elements using energetic deposition techniques and the spinel crystalline form of MgAl2O4 as the source of the amorphous MgAl2O4 coating, The coating and the method described herein can be used to make highly reflective mirrors, and can also be applied to beamsplitters, prisms, lenses, output couplers and similar elements used in