^ "Fraunhofer, Joseph von (1787-1826) - from Eric Weisstein's World of Scientific Biography".As the spread of wavelengths is increased, the number of "fringes" which can be observed is reduced. If the spread of wavelengths is significantly smaller than the mean wavelength, the individual patterns will vary very little in size, and so the basic diffraction will still appear with slightly reduced contrast. it consists of a range of different wavelengths, each wavelength is diffracted into a pattern of a slightly different size to its neighbours. In all of the above examples of Fraunhofer diffraction, the effect of increasing the wavelength of the illuminating light is to reduce the size of the diffraction structure, and conversely, when the wavelength is reduced, the size of the pattern increases. If the aperture is in x ′y ′ plane, with the origin in the aperture and is illuminated by a monochromatic wave, of wavelength λ, wavenumber k with complex amplitude A( x ′, y ′), and the diffracted wave is observed in the unprimed x,y-plane along the positive z Non-monochromatic illumination In Cartesian coordinates Diffraction geometry, showing aperture (or diffracting object) plane and image plane, with coordinate system. The Fraunhofer diffraction equation is an approximation which can be applied when the diffracted wave is observed in the far field, and also when a lens is used to focus the diffracted light in many instances, a simple analytical solution is available to the Fraunhofer equation – several of these are derived below. The Kirchhoff diffraction equation provides an expression, derived from the wave equation, which describes the wave diffracted by an aperture analytical solutions to this equation are not available for most configurations. When a beam of light is partly blocked by an obstacle, some of the light is scattered around the object, and light and dark bands are often seen at the edge of the shadow – this effect is known as diffraction.
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