A wave property of light which allows it to curl around obstacles whose size is
about that of the wavelength of the light. As a → wavefront
of light passes by an opaque edge or through an opening, secondary weaker wavefronts
are generated, apparently originating at that edge. These secondary wavefronts will interfere
with the primary wavefront as well as with each other to form a
→ diffraction pattern.
From Fr. diffraction, from Mod.L. diffractionem, from L. diffrac-, stem of diffringere "break in pieces," from → dis- "apart" + frangere "to break."
Parâš "dispersion, scattering," variant of pâš, pâšidan, → dispersion.
turi-ye parâš (#)
Fr.: réseau de diffraction
An optical device containing thousands of very fine parallel grooves which produce interference patterns in a way which separates out all the components of the light into a spectrum.
olgu-ye parâš (#)
Fr.: tache de diffraction
A series of concentric rings of dark and light color produced by interference.
Olgu, loanword from Turkish; parâš→ diffraction.
Fr.: aigrette de diffraction
One of several light rays emanating from a bright light source in images taken with → reflecting telescopes. They are artifacts caused by light diffracting around the support or → spider vanes of the → secondary mirror.
karânmand bé parâš
Fr.: limité par la diffraction
parâš-e elekroni (#)
Fr.: diffraction des électrons
A diffraction phenomenon resulting from the passage of electrons through matter, analogous to the diffraction of visible light. This phenomenon is the main evidence for the existence of waves associated with elementary particles; → de Broglie wavelength.
parâš-e Fresnel (#)
Fr.: diffraction de Fresnel
The diffraction effects obtained when either the source of light or observing screen, or both, are at a finite distance from diffracting aperture or obstacle. → Fraunhofer diffraction.
Named after Jean Augustin Fresnel (1788-1827), French physicist, a key figure in establishing the wave theory of light. His earlier work on interference was carried out in ignorance of that of Thomas Young (1773-1829), English physician and physicist, but later they corresponded and were allies; → diffraction.
parâš-e partow-e iks
Fr.: diffraction de rayons X
The diffraction of X-rays by the atoms or ions of a crystal. The wavelength of X-rays are comparable to the size of interatomic spacings in solids. Since the atoms in a crystal are arranged in a set of regular planes, crystals serve as three-dimensional diffraction gratings for X-rays. Planes of repetition within the atomic structure of the mineral diffract the X-rays. The pattern of diffraction thus obtained is therefore used to identify minerals by bombarding them with X-rays.