Diffraction of electromagnetic radiation refers to various phenomena that occur when an electromagnetic wave encounters an obstacle or passes through an opening.

  • Diffraction and interference are phenomena associated with all kinds of waves. Electromagnetic waves are a special case however because of their unique behaviour.
  • Diffraction of electromagnetic waves deals with the way light bends around the edges of obstacles into regions that would otherwise be in shadow.
  • Interference deals with the way that electromagnetic waves behave during the diffraction process.
  • Diffraction can be produced by the edges or by a hole (aperture) in any opaque surface or object.
  • Diffraction causes a propagating electromagnetic wave to produce a distinctive pattern as waves interfere with one another. The resulting pattern becomes visible if diffracted light subsequently strikes a surface.
  • Diffraction produces a circular pattern of concentric bands when a narrow beam of electromagnetic waves passes through a small circular aperture and then strikes a flat surface.
  • Diffraction and interference of electromagnetic waves are not limited to visible light but occur across the entire electromagnetic spectrum, including radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
Diffraction in classical physics
  • In classical physics, an explanation of the diffraction of electromagnetic waves treats each point at which a propagating wavefront encounters the edge of an obstacle as a site at which a new spherical wavelet is generated, which modifies the original waveform.
  • Separate spherical wavelets bend independently of one another beyond the site at which an obstacle is encountered. However, interference between them alters the way they bend and the distance they must travel before striking a surface.
  • Explanations that describe the process of diffraction and interference patterns belong to Wave Theory and are the result of more than two centuries of study in the field of optics.
Diffraction in quantum mechanics
  • In modern quantum mechanics, diffraction is explained by referring to the wave function and probability distribution of each photon of light as it encounters the corner of an obstacle or the edge of an aperture.
  • Wave functions and probability distributions are part of mathematical formulations of the outcomes of all possible measurements of a photon’s behaviour in the course of diffraction.