A radiation shield 40 is mounted to an uncooled portion, such as an outer case 14, of an IR detector assembly 10 such that it surrounds a thermoelectric cooler 16 and a radiation detector 18. The shield 40 has a curved reflective upper surface 42 having the shape of a toric segment and cylindrical or rectangular reflective sidewalls 46 for imaging the detector 18 and the upper cooler stage upon the tops and sides of lower and warmer cooler stages. This beneficially reduces the heatload upon the coldest stage by excluding warmer surfaces from its view. An aperture 46 defines the effective coldstop for the detector 18.
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