Diffraction

Wednesday, September 2, 2009

Diffraction is an interference effect which leads to the scattering of strong beams of radiation in specific directions. Diffraction usually refers to various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Diffraction from crystals is described by the Bragg Law: n λ= 2 d sin θ; where n is an integer (the order of scattering), λ is the wavelength of the radiation, d is the spacing between the scattering entities (e.g. planes of atoms in the crystal) and θ is the angle of scattering.

Electron and X-ray diffraction are both particularly powerful because their wavelengths are smaller than the typical spacings of atoms in crystals and strong, easily measurable, diffraction occurs. The effects of diffraction can be regularly seen in everyday life. The most colorful examples of diffraction are those involving light; for example, the closely spaced tracks on a CD or DVD act as a diffraction grating to form the familiar rainbow pattern we see when looking at a disk.