Key Terms Related to 'Cold' in Thermal Infrared Imaging Systems

1.    What does “cold” mean in thermal infrared imaging systems?

In thermal infrared imaging systems, 'cold' specifically refers to the low-temperature operating state of the detector maintained through active cooling (such as liquid nitrogen cooling or Stirling cooling), typically at a temperature of 77K. This low-temperature environment is essential for high-sensitivity detection in cooled infrared detectors, such as HgCdTe and InSb focal plane arrays, and can significantly reduce thermal noise of the detector.

2.    What is cold shield?

The cold shield is a cooled aperture that limits the detector's field of view to the desired scene radiation and blocks unwanted background radiation from outside the intended field.

3.    What is cold stop efficiency?

Cold stop efficiency is a parameter that measures how well the cold stop matches the detector's field of view. It is defined as the proportion of radiation received by the detector that passes through the cold stop. Ideally, the cold stop efficiency is 100%, indicating that the detector only receives radiation from the target scene, with no stray radiation from outside the cold stop. Imperfect matching between the cold stop and detector FOV reduces efficiency and increases background noise.

4.    What is cold finger?

The cold finger serves as a thermal link between the cryocooler and the detector, ensuring efficient heat extraction to maintain the detector at cryogenic temperatures. The cold finger must possess both high thermal conductivity and mechanical stability.

5.    What is cold reflection?

Cold reflection refers to a phenomenon in cooled infrared systems where thermal radiation from low-temperature components (such as the cold shield, cold finger, or the detector itself) is reflected by optical surfaces (lenses or mirrors) back onto the detector, resulting in image artifacts. Since the intensity of low-temperature radiation is lower than that of scene radiation, the artifacts typically appear as dark spots, though bright spots may also occur when reflections involve high-temperature paths.