Compact, high cold shield efficiency optical system

Abstract

An optical system is disclosed for use with a radiant energy receiver which provides high cold shield efficiency and is compact; further the optical system is temperature tolerant to maintain focus with changes in temperature and wavelength without operator intervention. The optical system has primary utility in the infrared region of the spectrum and where a two dimensional array of detectors senses the infrared radiant energy or flux from the scene of interest. The optical system is comprised of a window for environmental protection and two objective mirrors for folding and focusing the scene of interest on a first focal plane. Relay optical means, which may be comprised of one or more optical elements, relays and relocates the first focal plane to a second focal plane which is coincident with the surface of the two dimensional detector array; the relay optical means also forms an exit pupil (the image of the aperture stop) around which the aperture of a cold shield is positioned to minimize extraneous radiant energy falling on the detector array. Using a positive and negative refractive lens and judicious selection of materials allows the relay optical means to automatically compensate for variation in its index of refraction as a function of temperature and wavelength.