The optical/UV filters for the EPIC experiment

EPIC, the European Photon Imaging Cameras is an experiment based on cooled CCDs 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 fur Extraterrestrische Physik (MPE, Germany) have been described elsewhere. The two filters, described here, have a 1600 Å Polyimide substrate coated with 400 Å and 800 Å aluminium 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 out or are in progress at one of the EPIC Institutes (Osservatorio Astronomico di Palermo)