An icaroscope is a telescope-like

nonlinear optical Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typicall ...

device that enables viewing of both very bright and dark objects in the same image simultaneously. The problem the icaroscope was designed to solve was observing enemy aircraft approaching with the sun behind them, when the bright sun in a clear sky dazzles the observer and masks aircraft near the sun's disc. In the icaroscope, the scene is not viewed directly; instead it is briefly projected onto a screen coated with a special

phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or ...

, and this screen is then shown to the viewer. The specific silver-activated zinc-cadmium sulphide phosphor has a short afterglow even in areas saturated by the full brightness of the sun. By rapidly exposing the phosphor, allowing it to decay for around 5 ms, and showing it to the viewer, the effect is to attenuate the brightness of the sun's disc by about 500 times, allowing details near it to be clearly seen. The icaroscope repeats this process at a rate of 90 Hz, permitting continuous observation. Development of the icaroscope was carried out during the

Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

at the Institute of Optics by Brian O'Brien, Franz Urbach, and other researchers. The device is named for

Icarus In Greek mythology, Icarus (; , ) was the son of the master craftsman Daedalus, the architect of the labyrinth of Crete. After Theseus, king of Athens and enemy of King Minos, escaped from the labyrinth, Minos suspected that Icarus and Daedalu ...

, the mythological figure known for flying too close to the sun.

References

{{Reflist Nonlinear optics Science and technology during World War II Telescope types