Designing a cryogenic camera is a good strategy to miniaturize and simplify an infrared camera using a cooled detector. Indeed, the integration of optics inside the cold shield allows to simply athermalize the design, guarantees a cold pupil and releases the constraint on having a high back focal length for small focal length systems. By this way, cameras made of a single lens or two lenses are viable systems with good optical features and a good stability in image correction. However it involves a relatively significant additional optical mass inside the dewar and thus increases the cool down time of the camera. ONERA is currently exploring a minimalist strategy consisting in giving an imaging function to thin optical plates that are found in conventional dewars. By this way, we could make a cryogenic camera that has the same cool down time as a traditional dewar without an imagery function. Two examples will be presented: the first one is a camera using a dual-band infrared detector made of a lens outside the dewar and a lens inside the cold shield, the later having the main optical power of the system. We were able to design a cold plano-convex lens with a thickness lower than 1mm. The second example is an evolution of a former cryogenic camera called SOIE. We replaced the cold meniscus by a plano-convex Fresnel lens with a decrease of the optical thermal mass of 66%. The performances of both cameras will be compared.

Date Published: 17 May 2016
PDF: 12 pages
Proc. SPIE 9822, Advanced Optics for Defense Applications: UV through LWIR, 982214 (17 May 2016); doi: 10.1117/12.2223588

Published in SPIE Proceedings Vol. 9822:
Advanced Optics for Defense Applications: UV through LWIR
Jay N. Vizgaitis; Bjørn F. Andresen; Peter L. Marasco; Jasbinder S. Sanghera; Miguel P. Snyder, Editor(s)