EUV transmission of Optical Blocking Filter and Optical Blocking Layer for Soft X-ray Imager (SXI) onboard Astro-H

摘要

We have developed the X-ray CCD camera system for the Soft X-ray Imager (SXI) which will be launched as focal plane detectors of X-ray telescope onboard the Japanese 6th X-ray astronomical satellite, Astro-H. The X-ray CCD is back-illuminated (BI) CCD which has an Optical Blocking Layer (OBL) directly coating its X-ray illumination surface with Aluminum-Polyimide-Aluminum instead of Optical Blocking Filter (OBF). The X-ray CCD is affected by large doses of extreme ultraviolet (EUV) radiation from Earth sun-lit atmosphere (airglow) in orbit. To evaluate the performance of polyimide that cut off EUV, we measured the EUV transmission of both OBL and OBF at various energy range between 15-72 eV by utilizing beam line located at the Photon Factory in High Energy Accelerator Research Organization (KEK-PF) in this March and June, and obtained the EUV transmission to be 3% at 41 eV which is as same as expected transmission from the designed thickness of polyimide layer.