Soft x-ray transmission of optical blocking filters for the x-ray CCD camera onboard Astro-E2

摘要

We measured optical and soft X-ray transmission of Optical Blocking Filters (OBFs) for Charge Coupled Device (CCD) cameras, which will be launched as focal plane detectors of X-ray telescopes onboard the Japanese 5th X-ray astronomical satellite, Astro-E 2. The filters were made from polyimide coated with AL. The X-ray absorption fine structures (XAFSs) at the K edges of C, N, O and K and L edges of Al were measured. The depth of the absorption edge of O was deep, compared to the other elements of polyimide. This is evidence of the oxidation of Al. The optical transmission is roughly less than 10~(-6) except for a peak around the wave length of 550nm. Long term change of the soft X-ray transmission was measured. No significant change of the thickness of the oxidation layer was found during half year.