Fresnel Diffraction
Near-field wave diffraction where source or observation screen is close to the diffracting aperture, requiring spherical wavefront curvature analysis.
Governing formula
Fresnel Number F = a² / (λ L) ≳ 1
SI unit
N/A
In depth
Accounted for using Fresnel half-period zones. Produces complex fringe patterns whose center can alternate between bright and dark as screen distance changes.
Examples in the real world
The bright Poisson spot (Arago spot) forming in the center of the shadow cast by a small circular disk.