Observation of the Poisson Spot

The first-time observation of Poisson’s (or Arago’s) spot in 1818 constituted one of the most relevant experiments in the history of optics, helping discard the (at the time) favoured position of attributing a corpuscular nature to light. When Fresnel presented his theory of diffraction before the French Academy of Sciences, Poisson, a member of the committee, scoffed at the fact that Fresnel’s approach predicted a bright spot in the shadow of a circular obstacle placed in the way of a beam of light. And sure enough, as fellow committee member Arago demonstrated, this spot could be observed experimentally.