RADIATION-DAMAGE EFFECTS IN FAR-ULTRAVIOLET FILTERS, THIN-FILMS, AND SUBSTRATES

Advances in vacuum ultraviolet thin-film filter technology have been m ade through the use of filter designs with multilayers of materials su ch as Al2O3, BaF2, CaF2, HfO2, LaF3, MgF2, and SiO2. Our immediate app lication for these filters will be in an imaging system to be flown on a satellite where a 2 x 9 RE orbit will expose the instrument to appr oximately 250 krad of radiation. Because to our knowledge no previous studies have been made on the potential radiation damage of these mate rials in the thin-film format, we report on such an assessment here. T ransmittances and reflectances of BaF2, CaF2, HfO2, MgF2, and SiO2 thi n films on MgF2 substrates, Al2O3 thin films on fused-silica substrate s, uncoated fused silica and MgF2, and four multilayer filters made fr om these materials were measured from 120 to 180 nm before and after i rradiation by 250 krad from a Co-60 gamma radiation source. No radiati on-induced losses in transmittance or reflectance occurred in this wav elength range. Additional postradiation measurements from 160 to 300 n m indicates 2-5% radiation-induced absorption near 260 nm in some of t he samples with MgF2 substrates. From these measurements we conclude t hat far-ultraviolet filters made from the materials tested should expe rience less than 5% change from exposure to up to 250 krad of high-ene rgy radiation in space applications.