 |
|
| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
|
|
diffraction
The spreading or bending of waves as they pass round the edge of an obstacle or through an opening whose size is about that of the light's wavelength. The disturbed waves then interfere to produce ripple-patterns. Diffraction is a property that distinguishes between wavelike and particlelike behavior.
Diffraction effects are classified into either Fresnel or Fraunhofer types. Fresnel diffraction is concerned mainly with what happens to light in the immediate neighborhood of a diffracting object or aperture, so is only of concern when the illumination source is close by. Fraunhofer diffraction is the light-spreading effect of an aperture when the aperture (or object) is lit by plane waves, i.e. waves that effectively come from a source that is infinitely far away. Because of Fraunhofer diffraction, a telescope can never form a perfect image. A point-like source, for example, will be seen as a small disk surrounded by a series of rings; a thin line on a planet will become widened into a band, which decreases in intensity on both sides. The only way to overcome the limitations of diffraction is to use a telescope of larger aperture.
Related categories
• OPTICS AND OPTICAL PHENOMENA
• WAVES AND WAVE PHENOMENA
Also on this site:
Encyclopedia of Alternative Energy & Sustainable Living
Encyclopedia of History
Transport Concepts & Designs (partner site)