Baron Siméon Denis Poisson FRS FRSE was a French mathematician and physicist who worked on statistics, complex analysis, partial differential equations, the calculus of variations, analytical mechanics, electricity and magnetism, thermodynamics, elasticity, and fluid mechanics. Moreover, he predicted the Arago spot in his attempt to disprove the wave theory of Augustin-Jean Fresnel.
Siméon Denis Poisson
Poisson in 1804 by E. Marcellot
Poisson's equations for electricity (top) and magnetism (bottom) in SI units on the front cover of an undergraduate textbook.
Title page to Recherches sur le Mouvement des Projectiles dans l'Air (1839)
In optics, the Arago spot, Poisson spot, or Fresnel spot is a bright point that appears at the center of a circular object's shadow due to Fresnel diffraction. This spot played an important role in the discovery of the wave nature of light and is a common way to demonstrate that light behaves as a wave.
Arago spot experiment. A point source illuminates a circular object, casting a shadow on a screen. At the shadow's center a bright spot appears due to diffraction, contradicting the prediction of geometric optics.
Numerical simulation of the intensity of monochromatic light of wavelength λ = 0.5 μm behind a circular obstacle of radius R = 5 μm = 10λ.
Notation for calculating the wave amplitude at point P1 from a spherical point source at P0.
The on-axis intensity at the center of the shadow of a small circular obstacle converges to the unobstructed intensity.
