Diffraction

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  • Diffraction
definition
  • Bending and spreading of the propagating wave around obstacles, openings, and regions of varying refractive index.
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  • Df
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Abstract from DBPedia
    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. 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.

    回折(かいせつ、英語:diffraction)とは媒質中を伝わる波(または波動)に対し障害物が存在する時、波がその障害物の背後など、つまり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り、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)。電子線や中性子線などを結晶などに当てて得られる回折図形から結晶構造の解析を行うことができる。これは電磁波であるX線でも同様な結晶構造の解析を行うことができる。それぞれ電子回折法、中性子回折法、X線回折法として結晶構造の解析手法が確立されている。写真撮影においても、絞りを小さく絞ると光の回折現象により画像の鮮明さが低下する。この現象については小絞りボケの項を参照されたい。

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