| 摘要 |
An apparatus for decreasing stray radiation incident upon an infrared detector includes a concavely curved lens surface adjacent the detector, the center of curvature of which concave surface is located on the surface of the detector. This arrangement limits stray radiation originating rearward of the concave lens surface to black-body radiation emitted forward from the surface on which the detector is mounted, and the detector itself. That stray radiation may be reduced to a low value by decreasing the temperature and/or increasing the emissivity of the detector mounting surface and the detector itself. Stray radiation out of a desired wavelength band and originating forward of the rear concave lens surface may be attenuated by means of a spectrally selective filter. In a preferred embodiment, the spectrally selective filter comprises a multi-layer dielectric coating on the concave rear lens surface, the coating having high transmissivity for in-band radiation and high reflectivity for out-of-band radiation, thereby reflecting out-of-band radiation forward, away from the detector.
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