Fresnel diffraction

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In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of the Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near field. It is used to calculate the diffraction pattern created by waves passing through an aperture or around an object, when viewed from relatively close to the object. In contrast, the diffraction pattern in the far field region is given by the Fraunhofer diffraction equation. The near field can be specified with the Fresnel number, F = a 2 L λ {\displaystyle F={\frac {a^{2}}{L\lambda }}} , of an optical arrangement under consideration, where a {\displaystyle a} is the characteristic size (e.g. radius) of the aperture,...

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