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- Arago_spot abstract "In optics, an Arago spot, Fresnel bright spot, or Poisson spot is a bright point that appears at the center of a circular object's shadow due to Fresnel diffraction. This spot played an important role in the discovery of the wave nature of light (see history section below) and is a common way to demonstrate that light behaves as a wave for example in undergraduate physics laboratory exercises. The basic experimental setup is shown in the figure on the right. The light must come from a "point source" such as an illuminated pinhole, or a diverging laser beam. The dimensions of the setup must comply with the requirements for Fresnel diffraction. Namely, the Fresnel number must satisfy where d is the diameter of the circular object l is the distance between the object and the screen λ the wavelength of the sourceFinally, the edge of the circular object must be sufficiently smooth. These conditions together explain why the bright spot is not encountered in everyday life. However, with the abundance of laser sources available today it is easy to perform an Arago spot experiment (see for example here). In astronomy, the Arago spot can be also easily observed in the strongly defocussed image of a star in a Newtonian telescope. There the star provides an almost ideal point source at infinity and the secondary mirror of the telescope constitutes the circular obstacle.The presence of the Arago spot can be easily understood. When light shines on a circular obstacle, Huygens' principle says that every point in the plane of the obstacle acts as a new point source of light. The light coming from points on the circumference of the obstacle, and going to the center of the shadow, travels exactly the same distance; so all the light passing close by the object arrives at the screen in phase and constructively interferes. This results in a bright spot at the shadow's center, where geometrical optics and particle theories of light predict that there should be no light at all.".
- Arago_spot thumbnail Poissonspot_setup_treisinger.jpg?width=300.
- Arago_spot wikiPageExternalLink PoissonSpot.html.
- Arago_spot wikiPageExternalLink 047.PDF.
- Arago_spot wikiPageID "44665".
- Arago_spot wikiPageRevisionID "605167843".
- Arago_spot hasPhotoCollection Arago_spot.
- Arago_spot subject Category:Diffraction.
- Arago_spot subject Category:History_of_physics.
- Arago_spot comment "In optics, an Arago spot, Fresnel bright spot, or Poisson spot is a bright point that appears at the center of a circular object's shadow due to Fresnel diffraction. This spot played an important role in the discovery of the wave nature of light (see history section below) and is a common way to demonstrate that light behaves as a wave for example in undergraduate physics laboratory exercises. The basic experimental setup is shown in the figure on the right.".
- Arago_spot label "Arago spot".
- Arago_spot label "Poisson-Fleck".
- Arago_spot label "Punto de Arago".
- Arago_spot label "Пятно Пуассона".
- Arago_spot label "アラゴスポット".
- Arago_spot label "泊松光斑".
- Arago_spot sameAs Poisson-Fleck.
- Arago_spot sameAs Punto_de_Arago.
- Arago_spot sameAs アラゴスポット.
- Arago_spot sameAs m.0c55f.
- Arago_spot sameAs Q1807778.
- Arago_spot sameAs Q1807778.
- Arago_spot wasDerivedFrom Arago_spot?oldid=605167843.
- Arago_spot depiction Poissonspot_setup_treisinger.jpg.
- Arago_spot isPrimaryTopicOf Arago_spot.