EFFECTS OF INTERFERENCE AND OXIDATION ON THE UV VISIBLE REJECTION PROPERTIES OF FILTERS FOR SOFT-X-RAY DETECTORS/

We report on UV/Visible transmission measurements of aluminum coated L exan filters designed as UV blocking filters for soft x-ray detectors. Transmission of the filters in the 2300 - 8000 A wavelength range is significantly higher than expected. It cannot be accounted for applyin g a simple slab model of the transmission and adopting material proper ties reported in the literature. We show that this is due to interfere nce effects which are strongly dependent on the filter geometry, and t o oxidation of exposed aluminum surfaces and/or chemical interaction w ith the plastic support. The results of this work have led to the rede sign of the Advanced X-ray Astrophysics Facility High Resolution Camer a UV blocking filters.