närdiffraktion

Närdiffraktion, often translated as near-field diffraction, refers to the phenomenon of wave diffraction that occurs very close to the diffracting object. Unlike far-field diffraction, where the distance between the observer and the aperture is large enough for approximations to simplify analysis, near-field diffraction considers the more complex wave patterns that exist in the immediate vicinity of the diffracting structure. This region is also known as the Fresnel diffraction zone.

In near-field diffraction, the wavefronts are still significantly curved as they propagate from the diffracting object. The mathematical description typically involves the Fresnel integrals, which account for these curved wavefronts. The resulting diffraction pattern is highly dependent on the precise distance from the aperture and the shape of the aperture itself. As the distance increases, the near-field pattern gradually transitions into the Fraunhofer or far-field diffraction pattern, where the wavefronts can be approximated as planar.

Applications of understanding near-field diffraction can be found in various optical and electromagnetic systems. It is important in the design and analysis of optical components, such as lenses and gratings, especially when considering their performance at short distances. In microscopy, near-field techniques can be used to achieve resolutions beyond the diffraction limit, as seen in near-field scanning optical microscopy (NSOM). Similarly, in antenna theory, near-field measurements are crucial for characterizing antenna performance and radiation patterns close to the antenna itself. The complex wave behavior in the near-field region requires more detailed computational methods for accurate prediction and analysis compared to the simplified models used for far-field diffraction.