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Proceedings Paper

Scalable MWIR and LWIR optical system designs employing a large spherical primary mirror and small refractive aberration correctors
Author(s): David A. Beach
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Paper Abstract

Design variants of a recently developed optical imaging system have been computed for the thermal infrared spectral bands, which offer some advantages for long-range surveillance and astronomy. Only the spherical primary mirror has the full pupil diameter, all other components being sub-diameter, so scaling is possible up to relatively large pupils. Low-cost fabrication is enabled by the prevalence of spherical optical surfaces. Both MWIR and LWIR spectral transmissions are enabled by the choice of corrector materials, the examples given employing germanium and sapphire for 3.5 - 5.5 micrometers and germanium and zinc selenide for 3.5 - 5.5 micrometers and 8 - 12 micrometers passbands. Diffraction at these wavelengths is the main contributor to resolution constraints, so high numerical aperture values are preferred to enable a better match of blur spot diameter to generally available pixel dimensions. The systems described can routinely be designed to have speeds of f/0.8 or faster, while maintaining diffraction-limited performance over useful angular fields. Because the new design system employs a relayed catadioptric, it is possible to make the aperture stop of the system coincident with the window of the detector cryostat, enabling precise radiometric geometry. The central obscuration provides a convenient location for a calibration source, and both this and a mask for secondary spider supports can be included within the detector cold screen structure. Dual-band operation could be enabled by inclusion of a spectral beam splitter prior to a dual relay/imager system.

Paper Details

Date Published: 5 December 2001
PDF: 9 pages
Proc. SPIE 4441, Current Developments in Lens Design and Optical Engineering II, (5 December 2001); doi: 10.1117/12.449561
Show Author Affiliations
David A. Beach, Industrial Research Ltd. (New Zealand)

Published in SPIE Proceedings Vol. 4441:
Current Developments in Lens Design and Optical Engineering II
Iain A. Neil; Robert E. Fischer; Takanori Yamanashi; R. Barry Johnson; Warren J. Smith, Editor(s)

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