Mitsunobu Kawada

Cryogenic optical testing of sandwich-type silicon carbide mirrors

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.

Flight performance of the Near-Infrared Spectrometer

The near-infrared spectrometer (NIRS) is one of the focal plane instruments of the infrared telescope in space (IRTS). The NIRS is a simple grating spectrometer with two element InSb linear arrays, and was designed to measure the absolute sky brightness at the wavelengths from 1.4 to 4.0 micrometer with a spectral resolution of 0.13 micrometer and a beam size of 8 feet by 8 feet. The IRTS was launched on 1995 March 18. The NIRS worked well throughout the observation period from March 29 to April 25, and scanned about 7% of the entire sky. Multiple passage of bright stars through the NIRS field of view enabled us to reconstruct the beam pattern and to calibrate the sensitivity. Those flight data confirmed good performance of the NIRS on the orbit as was expected from the preflight measurements.

Development of a far-infrared Ge:Ga monolithic array detector for SPICA (space infrared telescope for cosmology and astrophysics)

We are developing a far-infrared Ge:Ga monolithic array detector for the future space telescope SPICA. We demonstrate the performance of our detector by showing the test results of 5×5 pixel prototype detectors. These detectors worked properly and they showed the expected performance.

DEVELOPMENT OF NEW STITCHING INTERFEROMETRY FOR THE SPICA TELESCOPE

The telescope to be onboard SPICA (Space Infrared Telescope for Cosmology and Astrophysics) has an aperture diameter of 2.5 m and its imaging performance is to be diffraction-limited at a wavelength of 20 μm at the operating temperature of <8 K. Because manufacturing precise autocollimating flat mirrors (ACFs) with sizes comparable to the SPICA telescope is not technically feasible, we plan to use sub-aperture stitching interferometry through ACFs for optical testing of the telescope. We have verified the applicability of the sub-aperture stitching technique to the SPICA telescope by performing stitching experiments in a vacuum at a room temperature, using the 800-mm telescope and a 300-mm ACF. We have also developed a new method to reduce uncertainties possibly caused by cryogenic and gravitational deformations of ACFs.

Astronomical Far-Infrared FTS of the FIS Instrument onboard the ASTRO-F satellite

The far-infrared Fourier transform spectrometer is developed for an application of the astronomical satellite ASTRO-F. FIS-FTS is the unique instrument which covers 50 - 200 μm wavelength range with spectral resolution of 0.3cm-1.