How Do Infrared Cameras Work - FLIR PathFindIR User Manual

8 – Infrared Technology
converter and the photon detector. At first, the image converter received
the greatest attention by the military, because it enabled an observer for
the first time in history to literally 'see in the dark'. However, the
sensitivity of the image converter was limited to the near infrared
wavelengths, and the most interesting military targets (i.e. enemy soldiers)
had to be illuminated by infrared search beams. Since this involved the
risk of giving away the observer's position to a similarly-equipped enemy
observer, it is understandable that military interest in the image converter
eventually faded.
The tactical military disadvantages of so-called 'active' (i.e. search beam-
equipped) thermal imaging systems provided impetus following the 1939–
45 war for extensive secret military infrared-research programs into the
possibilities of developing 'passive' (no search beam) systems around the
extremely sensitive photon detector. During this period, military secrecy
regulations completely prevented disclosure of the status of infrared-
imaging technology. This secrecy only began to be lifted in the middle of
the 1950's, and from that time adequate thermal-imaging devices finally
began to be available to civilian science and industry.

8.2 How do Infrared Cameras Work?

Infrared energy is part of a complete range of radiation called the
electromagnetic spectrum. The electromagnetic spectrum includes gamma
rays, X-rays, ultraviolet, visible, infrared, microwaves (RADAR), and radio
waves. The only difference between these different types of radiation is
their wavelength or frequency. All of these forms of radiation travel at the
speed of light (186,000 miles or 300,000,000 meters per second in a
vacuum). Infrared radiation lies between the visible and RADAR portions
of the electromagnetic spectrum. Thus infrared waves have wavelengths
longer than visible and shorter than RADAR.
8
334-0001-00-10, version 100 04/07 33