Optical design for a hyperspectral imager from 1 to 12 μ m

An hyperspectral imager capable of sensing from 1 to 12 micrometers with three (3) possible field-of-views (FOV) steerable within a field-of-regard eight (8) times larger than the FOV is presented. This level of flexibility imposes several constraints on the front-end optics especially when the maximum etendue of the spectrometer must be maintained for all configurations. This paper presents the design approach and trade-offs leading to a high performance optical design. Other constraints such as mass and volume are also considered. An important limiting factor is the size of the window and its minimum distance to the primary mirror of the telescope. The design has been optimized by re-imaging the aperture stop on each component that are critical in size: the interferometer corner cubes, the steering mirror and the primary mirror of the telescope. A set of two (2) telescopes and two (2) afocal relays are interchanged to produce 3 FOVs with optimized etendue and minimum size on critical components.