22 October 1999 Spectral function of an optical filter for the pn-CCD camera on board the German astronomy satellite ABRIXAS
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Abstract
We have provided optical filters developed at the Max-Planck Institut fuer extraterrestrische Physik to the German x-ray astronomy observatory ABRIXAS. Specific Si-PN CCDs will be serving as focal plane camera. Since this detector is sensitive to radiation from the x-ray to the near IR spectral range, for observation in x-ray astronomy it must be protected from visible and UV radiation. This is achieved by an optical filter which combines a high transmittance for photon energies in the soft x-ray range and a high transmittance for photon energies in the soft x-ray range and a high absorptance for UV and visible radiation. With respect to the mission goal in orbit a spectral transmittance function is required attenuating radiation below photon energies of 10 eV by more than 7 orders of magnitude and transmitting soft x-ray photon energies above 1000 eV by more than 90 percent. This was realized by a 0.80 micrometers thick polypropylene film coated with approximately 60 nm aluminum on both sides. The filter has an effective diameter of 73 mm without any support structure. Environmental test have been performed and proved the filters to be resistant against acoustic nose and vibrational load during the launch. Synchrotron radiation in the photon energy range from 60 eV to 2000 eV was used to characterize the spectral transmittance in the center and the transmittance topography across the filter. The thickness of the surface oxide layer was determined by x-ray reflectance measurements on an Al-layer in order to study longterm variations of transmittance caused by oxidation effects. We present the resulting performance data.
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Karl-Heinz Stephan, Karl-Heinz Stephan, Frank Haberl, Frank Haberl, Jan Friedrich, Jan Friedrich, } "Spectral function of an optical filter for the pn-CCD camera on board the German astronomy satellite ABRIXAS", Proc. SPIE 3765, EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy X, (22 October 1999); doi: 10.1117/12.366506; https://doi.org/10.1117/12.366506
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