The process by which the direction of radiation is changed so that it spreads into the geometric shadow region of an opaque or refractive object that lies in a radiation field. </dd>
Diffraction is an optical edge effect.
Reference to Huygens' principle is a common means of explaining diffraction. Analysis of the interference between individual Huygens wavelets which originate in the vicinity of the edge of an irradiated body reveals that detectable amounts of radiant energy must invade the nominal shadow zone of the object, and there, by interference, set up characteristic energy distributions known as diffraction patterns. The amount of diffractive bending experienced by a ray is a function of wavelength; thus dispersion occurs, although dispersion is in the opposite sense to that produced by refraction. </dd>
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use