Arago spot
In
optics, an
Arago spot is a bright point which, owing to
diffraction, appears at the center of the
shadow of a circular object in
light from a point source. The diffraction pattern of a circular object has considerable interest due to the historical part it played in the
wave theory of light.
SimÃÂéon Poisson deduced from
Augustin Fresnel's theory the necessity of a bright spot at the centre of the shadow of a circular opaque obstacle. With this counterintuitive result Poisson hoped to disprove the wave theory; however
Dominique Arago experimentally verifed the prediction and today the demonstration goes by the name "Poisson's (Arago's) spot".