Design of a compact off-axis two-mirror freeform infrared imager with a wide field of view.

With the development of modern precision optical fabrication and measurement technologies, optical freeform surfaces have been widely employed in different applications, especially in off-axis reflective optical systems. For an infrared optical system operating in the long-wavelength spectrum, compactness, brightness, and a wide field of view are key requirements for military surveillance or scene sensing. In this paper, we present an off-axis two-mirror freeform infrared imager with compactness and brightness. It has a large pupil of size 12 mm and a fast focal ratio of 2.2 over a wide 23° diagonal field of view, as well as good image quality. XY-polynomial freeform surfaces are applied to the viewing mirror and focusing mirror. The multiple degrees of freedom of optical freeform surfaces are very helpful for off-axis aberration correction and improving the optical performance over the entire pupil across the full field of view. The overall dimension of our designed freeform infrared imager is about 30 mm by 30 mm by 30 mm, which is elegantly miniaturized. The final designed results of a reflective freeform infrared imager are demonstrated and discussed in detail. [ABSTRACT FROM AUTHOR]