Diffraction - a certain set of phenomena that occur when light waves moving through a medium with a pronounced inhomogeneities (small holes, opaque screens, etc.).They are associated with a deviation from the principles of geometrical optics.The essence of this concept is the ability of electromagnetic radiation bend around any obstacles.Fraunhofer diffraction in optics is significantly more practical value than the diffraction phenomenon Frankel.
Because of this, electromagnetic waves of light bending around obstacles, fall within the so-called geometric shadow and penetrate into the holes of a small diameter.Passing through them, the waves break up into components, which opens up opportunities for learning and spectral analysis of the nature of light studies.This Fraunhofer diffraction involves matching the size of the holes wavelength.
This phenomenon can also be explained by the principle of Huygens - Frenkel.It is used to solve some problems related to the researches in the field of distribution of light intensity and distribution in different environments with obstacles.The discovery of the phenomenon of diffraction at the time was the key evidence of the wave nature of light.The first quantitative theory of this phenomenon belongs to the French physicist Frenkel.However, it postulates still have substantially the theoretical value.
A Fraunhofer diffraction has a practical exercise in which the light source is placed in the focus of the lens.It is not required if the source is a laser, because it emits a parallel beam of radiation.Fraunhofer diffraction occurs on any obstacle in the way prescribed by light rays passing through the lens.The picture of the optical phenomena observed in the focal plane of the lens another placed behind an obstacle.
yet simple calculations and is extremely important for practical optics case is the Fraunhofer diffraction on one slit of long rectangular cross-section.In this case, the hole falls monochromatic plane wave.The light field behind the slit is constructed according to Huygens' principle as a result of the interference of coherent secondary wave.All the waves of this type come from different parts of the wavefront.The main feature of the diffraction pattern is that the secondary waves emitted wavefront strip, folding after passing obstacles form a single cylindrical wave whose axis serves as the band.
diffraction pattern in this case is an alternation of light areas with dark and is characterized by a bright spot in the center, where the geometric shadow zone.It is significant that for white light picture will be painted.Central band will then be light, and the rest will alternate in color from purple to red.Fraunhofer diffraction at the slit creates a blurred image of the light source, which is divided by dark stripes.The diffraction pattern of small holes to give the system of concentric circles with a dark spot in the center of the Poisson.Light bands emerging on the screen, called the diffraction maxima, and the dark - at least.
phenomenon of diffraction is used to accurately measure the wavelength of light.Also, it is taken into account when designing the various optical devices, since this phenomenon imposes some limitations on their resolution.