A technique is described that uses radiation and a gas-phase species to produce a protective carbon coating on extreme ultravioles, (EUV) optics. A specific example is given in which a similar to5 Angstrom carbon coating is deposited on EUV Mo/Si optics via coexposure to radiation (EUV photons, electrons) and ethanol vapor. Auger electron spectroscopy, sputter Auger depth profiling, and EUV reflectivity measurements are presented that suggest a carbon coating that is substantially void free and protects the optic from water-induced oxidation at the water partial pressures used in the tests (similar to2 X 10(-7) Torr). The coating is also resistant to atmospheric degradation, and to gasification by the combination of electrons and molecular oxygen. The protective coating reduces the relative reflectivity (DeltaR/R-0) of an optic by similar to0.5%.