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The Collaborative International Dictionary

Diffraction \Dif*frac"tion\, n. [Cf. F. diffraction.] (Opt.) The deflection and decomposition of light in passing by the edges of opaque bodies or through narrow slits, causing the appearance of parallel bands or fringes of prismatic colors, as by the action of a grating of fine lines or bars.

Remarked by Grimaldi (1665), and referred by him to a property of light which he called diffraction.

Diffraction grating. (Optics) See under Grating.

Diffraction spectrum. (Optics) See under Spectrum.

Douglas Harper's Etymology Dictionary

1670s, from French diffraction (17c.) or directly from Modern Latin diffractionem (nominative diffractio), noun of action from past participle stem of Latin diffringere "break apart in pieces," from dis- "apart" (see dis-) + frangere "to break" (see fraction).


n. (context quantum mechanics English) The breaking up of an electromagnetic wave as it passes a geometric structure (e.g. a slit), followed by reconstruction of the wave by interference.


n. when light passes sharp edges or goes through narrow slits the rays are deflected and produce fringes of light and dark bands


Diffraction refers to various phenomena which occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle. In classical physics, the diffraction phenomenon is described as the interference of waves according to the Huygens–Fresnel principle. These characteristic behaviors are exhibited when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. Similar effects occur when a light wave travels through a medium with a varying refractive index, or when a sound wave travels through a medium with varying acoustic impedance. Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, X-rays and radio waves.

Since physical objects have wave-like properties (at the atomic level), diffraction also occurs with matter and can be studied according to the principles of quantum mechanics. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1660.Francesco Maria Grimaldi, Physico mathesis de lumine, coloribus, et iride, aliisque annexis libri duo (Bologna ("Bonomia"), Italy: Vittorio Bonati, 1665), page 2:

Original : Nobis alius quartus modus illuxit, quem nunc proponimus, vocamusque; diffractionem, quia advertimus lumen aliquando diffringi, hoc est partes eius multiplici dissectione separatas per idem tamen medium in diversa ulterius procedere, eo modo, quem mox declarabimus.

Translation : It has illuminated for us another, fourth way, which we now make known and call "diffraction" [i.e., shattering], because we sometimes observe light break up; that is, that parts of the compound [i.e., the beam of light], separated by division, advance farther through the medium but in different [directions], as we will soon show.

While diffraction occurs whenever propagating waves encounter such changes, its effects are generally most pronounced for waves whose wavelength is roughly comparable to the dimensions of the diffracting object or slit. If the obstructing object provides multiple, closely spaced openings, a complex pattern of varying intensity can result. This is due to the addition, or interference, of different parts of a wave that travels to the observer by different paths, where different path lengths result in different phases (see diffraction grating and wave superposition). The formalism of diffraction can also describe the way in which waves of finite extent propagate in free space. For example, the expanding profile of a laser beam, the beam shape of a radar antenna and the field of view of an ultrasonic transducer can all be analyzed using diffraction equations.

Usage examples of "diffraction".

Lang and Bresson and Deren but the anti-New Wave abstracters like Frampton, wacko Nucks like Godbout, anticonfluential directors like Dick and the Snows who not only really belonged in a quiet pink room somewhere but were also self-consciously behind the times, making all sorts of heavy art-gesture films about film and consciousness and isness and diffraction and stasis et cetera.

The colored beryllium metal of the wall had been ruled with 20,000 lines to the inch, mere scratches, but nevertheless a diffraction grating.

Luna is a silvery iridescent sphere, planed smooth down to micrometer heights, luminous with diffraction patterns.

Outer Kingdom, from a variety of sources, but all of it contributed to the same purpose: It surveyed the microscopic world through X-ray diffraction, electron microscopy, and direct nanoscale probing, and synthesized all of the resulting information into a single three-dimensional view.

In realistic situations, this diffracted starlight is much stronger than the light from planets around the star, and because of diffraction effects a circular disk is not useful as an occulter in searching for extrasolar planets.

This is done by the smoothing or tapering of the sharp edge of the occulter in such a way that the waves from different regions tend to cancel and diffraction is suppressed.

Moreover, even if the occulter developed many pinholes, the diffraction effects would spread the penetrating light over an area much larger than the images of interest, reducing its effect.

If so, the logical step for us is to go back to the beginning of our tests and rerun our diffractions to see if we can refine our measurements of positron frequencies.

CHAPTER 16 T~tE DEFIANT'S ~ viewer showed the speckled plasma field, complete with flares and clusters and rippling diffractions of every scientific description.

We isolated, and even crystallized the virus, got X-Ray diffractions, did epidemiological studies, all in strictest secrecy.

The real was only probably real, a nexus in endlessly expanding diffractions of the could-be.

The machine's computer began loading the diffraction data into the GeneDyne net, where it was sent across a dedicated land line at 110,000 bits per second to the GeneDyne supercomputer in Boston.

At one moment it would be as flat and featureless as polished steel then it would become flooded with iridescent, rainbow colors, behaving like a giant diffraction grating.

Its metallic limbs gleamed with the rainbow iridescence of a diffraction grating.

I saw that a shaft of red light, split out and deflected by his prism, shone through a diffraction grating and cast an angular pattern of dots and lines on a scrap of smooth plastic behind.