Proton-induced contaminant film effects on ultraviolet reflecting mirrors

The effects of thin, polymer contaminant films on the reflectance and scattered light properties of far ultraviolet reflecting mirrors were studied. Deposition of the contaminant films was induced by irradiating the mirrors with 10-keV protons in a high vacuum environment containing hydrocarbon molecules. Contaminant films were deposited using integrated fluxes up to 10(16) protons-cm(-2), and a flux of about 1.4 x 10(11) protons-cm(-2) sec(-1). Contaminant film effects were studied on mirror coatings of evaporated aluminum coated with MgF(2), aluminum coated with LiF, and platinum. Results of experiments showed that a film as thin as 4-5 nm produced large reflectance degradation in selected wavelength bands as a result of interference-type effects. Radiation-induced degradation of MgF(2), LiF, and Al film was shown to be negligible. An oxidation cleaning technique was developed that successfully removed the contaminant film and restored reflectance to nearly preirradiation values.