Poisson's spot

Poisson's spot

also called  Arago's spot 

      diffraction pattern produced by a small spherical object in the path of parallel light rays. French physicist Augustin-Jean Fresnel (Fresnel, Augustin-Jean) presented much of his work on diffraction as an entry to a competition on the subject sponsored by the French Academy of Sciences (Sciences, Academy of) in 1818. The committee of judges included a number of prominent advocates of Isaac Newton (Newton, Sir Isaac)'s corpuscular model of light, one of whom, Siméon-Denis Poisson (Poisson, Siméon-Denis), pointed out that Fresnel's model predicted a seemingly absurd result: If a parallel beam of light falls on a small spherical obstacle, there will be a bright spot at the centre of the circular shadow—a spot nearly as bright as if the obstacle were not there at all. An experiment was subsequently performed by the French physicist François Arago, and Poisson's spot was seen, vindicating Fresnel and giving support for the wave model of light.

Glenn Stark
 

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Universalium. 2010.

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