The 80021 InSb detector exhibits superior performance over its operating range and approaches the maximum theoretical limit of sensitivity for background-limited applications. This detector requires liquid nitrogen cooling. Liquid nitrogen holding time is eight hours. A preamplifier is integrated into the design, which reduces the effects of background radiation. It is matched with the detector, allowing the detector to function at its ideal operating point. A manually adjustable iris is included with the 80021. Its diameter range is from 0.8" to 1.4" (2 to 36 mm). The iris can act as a Jacquinot Stop. By decreasing the effective source size and reducing the spot size on the detector, resolution is increased. The iris uses standard Oriel^® 1.5-Inch Series male and female flanges, allowing it to be easily integrated into the FT-IR system, if desired.