S. Thibault, Q. Cui, M. Poirier, P. Vallée, R. Doyon, P. Rabou, D. A. Salmon "Optical design of WIRCAM, the CFHT wide-field infrared camera" Proc. of SPIE, 4841 : 932-944, 2003
Résumé: In this paper, we present the final design of the optical train of WIRCAM, a wide-field infrared camera to be installed in early 2004 at the prime focus of CFHT. This cryogenic camera, optimized for J, H and K operating region, used a 4kX4k IR detector mosaic fed by a single optical train. The sky will be imaged onto the focal plane at an optical speed of F/3.5 yielding an image scale of 0.3 arcsecond per 18 µm pixel. The design image quality is 0.30 arcsecond 50% diffraction encircled energy over the central 20 arcmin field and no images worse than 0.35 arcsecond over the 29.7 arcminute diameter camera field. The optical design distortion at the corners is less than 1%. The WIRCAM camera have a lyot stop at the telescope image pupil in order to mask background radiation coming from external structures. The image of the pupil is sufficiently sharp for background elimination and impose not more than 2% loss of light from the sky in the K spectral band. We also present an optimization of AR coating for IR based camera weighted by MK atmospheric transmission. We discuss the impact of this coating design method on various camera throughput. We include an efficient technique for ghost analysis based on the detector image. We demonstrate that our design meets the performance requirements from an optical and practical point of view.
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