Proceedings Article | 21 May 2011
Proc. SPIE. 8012, Infrared Technology and Applications XXXVII
KEYWORDS: Mirrors, Optical design, Cameras, Off axis mirrors, Infrared imaging, Aspheric lenses, Imaging systems, Monochromatic aberrations, Indium oxide, Wavefronts
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 27.70 (H) x 48.70 (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.
