Optical design and performance of MIRIS near-infrared camera

Multi-purpose Infra-Red Imaging System (MIRIS) is a near-infrared camera onboard on the Korea Science and Technology Satellite 3 (STSAT-3). The MIRIS is a wide-field (3.67 degrees x 3.67 degrees) infrared imaging system which employs a fast (F/2) refractive optics with 80 mm diameter aperture. The MIRIS optics consists of five lenses, among which the rear surface of the fifth lens is aspheric. By passive cooling on a Sun-synchronous orbit, the telescope will be cooled down below 200 K in order to deliver the designed performance. As the fabrication and assembly should be carried out at room temperature, however, we convert all the lens data of cold temperature to that of room temperature. The sophisticated opto-mechanical design accommodates the effects of thermal contraction after the launch, and the optical elements are protected by flexure structures from the shock (10 G) during the launch. The MIRIS incorporates the wide-band filters, I (1.05 mu m) and H (1.6 mu m), for the Cosmic Infrared Background observations, and also the narrow-band filters, Pa alpha (1.876 mu m) and a specially designed dual-band continuum, for the emission line mapping of the Galactic interstellar medium. We present the optical design, fabrication of components, assembly procedure, and the performance test results of the qualification model of MIRIS near-infrared camera.