Cryogenic cooling systems for thermal imaging equipment

For maximum sensitivity in the 8-12 micron waveband, thermal imaging devices which employ cadmium mercury telluride detectors for conversion of the thermal signal to electrical form (for further amplification, conditioning, and display) must be cooled and maintained at a steady 80-85 K. Commonly employed cooling engines are the Stirling cycle and the Joule-Thomson effect types. The former use pressurized He gas and, in the sizes used in existing thermal imagers, consume 100 watts. The latter avoid the mechanical vibration and cyclic cooling problems of the Stirling cycle devices, but require a compressed gas bottle supply. Attention is presently given to the elimination of the gas bottle requirement by feeding the Joule-Thomson cooler from a small, high pressure compressor that is driven by a low power electric motor.