Fraunhofer diffraction

Summary

Fraunhofer diffraction, or far-field diffraction, is the diffraction pattern of an aperture observed very far away, or in the focal plane of a lens. In this regime the field is, up to a phase factor and a scaling, the Fourier transform of the field in the aperture. It applies when the Fresnel number is much smaller than $1$, and it is the limiting case of Fresnel diffraction. Its patterns include the single-slit fringes, the Airy disk of a circular aperture and the orders of a diffraction grating.