For future space IR missions, such as SPICA, it is crucial to establish an experimental method for eval- uating the performance of mid-IR detectors. In particular, the wavelength dependence of the sensitivity is important but difficult to be measured properly. We are now preparing a testing system for mid-IR Si:As/Si:Sb detectors on SPICA. We have designed a cryogenic optical system in which IR signal light from a pinhole is collimated, passed through an optical filter, and focused onto a detector. With this system, we can measure the photoresponse of the detector for various IR light using optical lters with different wavelength properties. We have fabricated aluminum mirrors which are adopted to minimize thermal distortion effects and evaluated the surface figure errors. The total wavefront error of the optical system is 1.3 μm RMS, which is small enough for the target wavelengths (20-37 μm) of SPICA. The point spread function measured at a room temperature is consistent with that predicted by the simulation. We report the optical performance of the system at cryogenic temperatures.

ABSTRACT
1. INTRODUCTION
2. METHOD
    2.1. Surface figure errors of mirror
    2.2. Optical alignment at a room temperature
3. RESULT AND DISCUSSION
    3.1. Surface figure error of the mirror
    3.2. Imaging performance at a room temperature
    3.3. Imaging performance at 6 K
4. SUMMARY
REFERENCES

• Miho Nishiyama(Graduate school of Science, Nagoya university)
• Hidehiro Kaneda(Graduate school of Science, Nagoya university)
• Daisuke Ishihara(Graduate school of Science, Nagoya university)
• Shinji Oseki(Graduate school of Science, Nagoya university)
• Nami Takeuchi(Graduate school of Science, Nagoya university)
• Takahiro Nagayama(Graduate school of Science and Engineering, Kagoshima university)
• Takehiko Wada(Institute of Space and Astronautial Science)