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.
Publ. No. 1 557 544 Rev. a121 – ENGLISH (EN) – October 6, 2005
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