title: Cryogenic optical testing of sandwich-type silicon carbide mirrors.
abstract: The experimental cryogenic performance of 160-mm-diameter silicon carbide (SiC) mirrors, one of which, a 700-mm-diameter mirror, is to be used as a primary mirror of the Japanese Infrared Astronomical Satellite ASTRO-F, is described. The mirrors are made from a sandwich-type SiC material that comprises a light porous core and a dense chemical-vapor-deposited coat of SiC. Three mirrors were manufactured consecutively, and changes in their surface contours related to temperature were measured with an interferometer when the mirrors were placed in a liquid-helium cryostat. Owing to significant improvements in manufacturing, the third SiC mirror showed only slight deformation as the temperature decreased from 300 to 6 K, which indicates high thermal strain homogeneity for a well-controlled sandwich-type SiC mirror.
authors.affiliation: Institute of Space and Astronautical Science, Kanagawa 229-8510, Japan. kaneda@ir.isas.ac.jp
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Kaneda
authors.forename: Takashi
authors.initials: T
authors.lastname: Onaka
authors.forename: Mitsunobu
authors.initials: M
authors.lastname: Kawada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Murakami