Optical/UV filters for the EPIC experiment

The European Photon Imaging Cameras (EPIC) is an experiment based on cooled CCD's on board the ESA X-ray Multi Mirrors satellite due to be launched in 1999. Since CCD's are sensitive to radiation other than X-rays, namely optical and UV light, filters are necessary to prevent this radiation from reaching the detector sensitive area. Three types of filters were developed, to be used alternatively depending on target source. Here we report on the medium and thin filters developed by MOXTEK Inc. in Orem, Utah, while the thick ones, developed at the Max-Planck-Institut fuer Extraterrestrische Physik (MPE, Germany) have been described elsewhere. The two filters, here described, have a 1600 angstroms Polyimide substrate coated with 400 angstroms and 800 angstroms aluminum for the thin and medium filter, respectively. After manufacturing, the filters have been submitted to an intensive qualification and calibration programme at MOXTEK. Further calibrations, transmission measurements and performance stability, have been carried on or are in progress at one of the EPIC Institutes (Osservatorio Astronomico di Palermo).