Near field approximation to Kirchhoff's diffraction formula, i.e. when the plane of observation is near the object diffracting.
Articles by others on the same topic
Fresnel diffraction is a type of wave diffraction that occurs when a wavefront encounters an obstacle or aperture with dimensions comparable to its wavelength. It is named after the French engineer and physicist Augustin-Jean Fresnel, who developed the theory to better understand the behavior of light.