M. Wang, F. Châteauneuf, C. Proulx "Optical designs of compact multichannel and all-reflective system for infrared imaging " Proc. of SPIE, 8012, art. no. 801226, 2011
Résumé: In space infrared (IR) optics, to achieve better observation of ground target, a common aperture all-reflective telescope, working at fast focal-ratio with multi-channel to cover different waveband and wide field-of-view (FOV), is a most wanted optical system. The remarkable imaging properties of the fast focal-ratio, flat-field, anastigmatic, rotationally symmetric Schwarzschild telescope have been well recognized historically, but suffer strong central obscuration and limited FOV in the conventional axis-symmetric design. Our solution is to use an eccentric system evolved from the Schwarzschild axially symmetric system, adding a tertiary off-axis mirror, to optimize the off-axis performance with the appropriate system parameters and specs, as required by most space IR optical systems. The optical design system consists of three powered mirrors, in which the primary (M1) is convex and secondary (M2) is either convex or concave, with a tertiary (M3) always in concave shape respectively. Both secondary and tertiary mirrors have their size larger than that of the primary. The entrance pupil of the system is projected behind M1. Dichroic filters can be used after the tertiary mirror to achieve separation of multi-spectral channels. In the designs the mirrors with optimized aspherical shapes, which are all in even-asphere warped up to 10th asphericities, are used for achieving the final image quality. The final corrected wavefront in the system can result in the good optical performance with an encircled energy of better than 80% per pixel for all channels, working at F/1.66 to correct a wide FOV up to 27.7° (H) x 48.7° (V). The design is scalable for different image scales, as usually required for different optical systems targeting different applications. The broad spectral range from mid-wave infrared (MWIR) up to Far IR can be fully covered by this design. Multiple focalplane- arrays (FPAs) can be used with respect to different spectral channels in the optical systems.
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