The Radiation Tolerance of Chalcogenide Glasses

Chalcogenide glasses are compounded from chalcogen elements, such as sulphur, selenium, and tellurium. These glasses are applied to commercial applications, e. g., night vision, because they transmit infrared in the spectral range of 0.8-16 mu m. Chalcogenide glasses have greater advantages over germanium (Ge), i.e., their wide spectral range of high transmissivity and their small temperature dependence of the refractive index. We have developed the Compact Infrared Camera (CIRC) with an uncooled infrared array detector (microbolometer) for space applications. The CIRC has been scheduled to launch in 2013 to demonstrate the usability of a microbolometer as a space application. The optics of the CIRC adopts two different kinds of materials for athermal optics. One is germanium, and the other is GASIR1 (R) which is a chalcogenide glass (Ge22As20Se58) developed by Umicore. However, the radiation tolerance of GASIR (R) has not been investigated in the past. We carried out irradiation tests to investigate the radiation tolerance of GASIR1 (R). We irradiated GASIR1 (R) with gamma-rays (Co60, 1.17 MeV and 1.33 MeV) up to 3Mrad. We measured the transmissivity and refractive index in the infrared range before and after irradiation. In this paper, we report the results of the irradiation tests of GASIR1 (R).