Optical warm stop with fresnel type reflective surface

Abstract

An infrared imaging system (10) has a detector assembly (12) positioned for viewing infrared radiation from a subject (20), and a housing (18) enclosing the detector assembly for maintaining the detector assembly at a temperature lower than a temperature of an environment outside the housing, the housing having a window (42) for transmission of radiation from the subject to the detector assembly. A cold stop (46) is located within the housing and a warm stop (48) is located outside the housing for transmitting radiation via their respective apertures (50, 52) from the subject to the detector assembly. The warm stop has a planar retroreflective surface (62) for reflecting rays from the detector assembly back to the detector assembly, thereby to minimize thermal noise. The retroreflective surface is profiled with grooves (66) arranged in a configuration for directing the rays of radiation back to the detector assembly, the configuration of grooves being a Fresnel configuration (62) or a kinoform configuration (62A) or a binary configuration (62B). Any desired location of the warm stop may be employed, even within a lens assembly (26), and any desired configuration of the shape of the aperture may be employed such as a rectangular or square shaped aperture.

Dependencies are inferred from the claim text.