Diffraction

prefLabel
  • Diffraction
definition
  • Bending and spreading of the propagating wave around obstacles, openings, and regions of varying refractive index.
altLabel
  • Df
topConceptOf
inScheme
Abstract from DBPedia
    Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660. In classical physics, the diffraction phenomenon is described by the Huygens–Fresnel principle that treats each point in a propagating wavefront as a collection of individual spherical wavelets. The characteristic bending pattern is most pronounced when a wave from a coherent source (such as a laser) encounters a slit/aperture that is comparable in size to its wavelength, as shown in the inserted image. This is due to the addition, or interference, of different points on the wavefront (or, equivalently, each wavelet) that travel by paths of different lengths to the registering surface. If there are multiple, closely spaced openings (e.g., a diffraction grating), a complex pattern of varying intensity can result. These effects also 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 – all waves diffract, including gravitational waves, water waves, and other electromagnetic waves such as X-rays and radio waves. Furthermore, quantum mechanics also demonstrates that matter possesses wave-like properties, and hence, undergoes diffraction (which is measurable at subatomic to molecular levels). The amount of diffraction depends on the size of the gap. Diffraction is greatest when the size of the gap is similar to the wavelength of the wave. In this case, when the waves pass through the gap they become semi-circular.

    回折(かいせつ、英: diffraction)とは、媒質や空間を伝わる波が、障害物の背後など、一見すると幾何学的には到達できない領域に回り込んで伝わっていく現象のことを言う。 1665年にイタリアの数学者・物理学者であったフランチェスコ・マリア・グリマルディにより初めて報告された。 障害物に対して波長が大きいほど回折角(障害物の背後に回り込む角度)は大きい。 回折は音波、水の波、電磁波(可視光やX線など)を含むあらゆる波について起こる。単色光を十分に狭いスリットに通しスクリーンに当てると回折によって光のあたる範囲が広がる。また、スリットが複数の場合や単一でも波長より広い場合、干渉によって縞模様ができる。この現象は、量子性が顕著となる粒子のビーム(例:電子線、中性子線など)でも起こる(参照:物質波)。

    (Source: http://dbpedia.org/resource/Diffraction)