The optical/UV filters for the EPIC experiment

The European Photon Imaging Cameras (EPIC) is an experiment based on cooled CCDs on board the ESA X-ray Multi Mirrors (XMM) satellite due to be launched in 1999. Since the CCDs 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 the target source. Here we report on the medium and thin filters developed by MOXTEK Inc. in Orem, Utah. The two filters, here described, have a 1600 Å polyimide substrate coated with 400 A 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 on or are in progress at one of the EPIC Institutes (Osservatorio Astronomico di Palermo)