Radiation entrance windows for CCD detectors

A prototype spectral filter was developed to be used as a radiation entrance window for a satellite borne CCD (Charge coupled device) X-ray imaging detector, which is presently under development within the EOBB (Electro-Optical-Breadboard) phase of ESA's XMM project. The unsupported filter has an effective size of 30 mm X 10 mm and is composed of multi-layered thin films of parylene N, aluminum, and carbon with mass densities of 25, 30 and 25 (mu) g/cm 2 respectively. CCD's have a broad spectral response ranging from the X-ray to the NIR (Near Infrared) range. For X-ray observations the filter being located in front of the detector must suppress the radiation of VIS (Visible) and UV (Ultraviolet) stars by more than 6 orders of magnitude and be highly transparent at energies above 0.1 keV. The technique to manufacture the windows and the measurements of the spectral transmittance as well as the environmental testing is described. The performance data are given.