Some more information on infrared sensors and the use of liquid nitrogen.
From
www.FreePatentsOnline.com
"An infrared detector includes an outer cylinder having an infrared permeable window and an inner cylinder accommodated in the outer cylinder. The inner cylinder has an end surface, a cylindrical side surface, and an annular tapering surface formed between the end surface and the cylindrical side surface. The annular tapering surface has a diameter continuously decreasing toward the end surface. A multiple element type infrared sensor is mounted on the end surface of the inner cylinder, the infrared sensor having a plurality of output electrodes. A cryogenic cooling arrangement is provided for cooling the infrared sensor to low temperatures, and a signal fetching arrangement is provided for carrying a signal detected by the infrared sensor, the signal fetching arrangement including wiring patterns formed on the end surface, the tapering surface and the cylindrical side surface of the inner cylinder. The tapering surface of the inner cylinder is mirror-finished, and the wiring patterns are formed by laser-cutting a gold thin film deposited on the inner cylinder."