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Removal of a protective coating on Al by ion etching for high reflectance in the far ultraviolet.

The effect of ion etching on the reflectance of Al coatings in the far ultraviolet is investigated. Ion etching of an overlayer grown on Al was performed by applying 100-300 eV Ar(+) ions using an ion gun. Ion etching was employed to remove the oxide naturally grown on an Al film that had been in contact with atmosphere. Ion etching was also used to remove part or all of the protective MgF(2) film on Al. The reflectance at 121.6 nm, H Lyman alpha line of the overlayer-removed Al surface was monitored after protecting it with a MgF(2) layer. Ion etching on both types of coatings resulted in an excellent reflectance value at 121.6 nm, whereas a reflectance loss was observed at longer wavelengths.