Imaging Infrared Seekers 

A more common approach is to use an infrared waveband where there is a large amount of ambient light from the thermal emission of the
background.
There are three main infrared bands:
- Near Infrared: 0.7 µm to about 2 µm.
• Little thermal emission in this band, but can be used with laser illumination systems.
- Mid-wave Infrared: 3 µm to 5 µm.
• The mid-wave band is good for hot objects because thermal emission peaks in this waveband for aircraft and missile plumes.
- Long wave Infrared: 8 µm to 14 µm.
• The long wave band is good for room temperature scenes since the thermal emission peaks in this band for 300K.
Infrared imagers are used in each of these bands, but there are a number of problems associated with their use and manufacture.
- Silicon photodetectors do not work (CdHgTe).
- The focal planes often require cooling to 77K.
- Few are sold, and therefore need to be made to order, and are far more expensive that visible systems.