Läheisdiffraktion

Läheisdiffraktion, also known as near-field diffraction, describes the wave phenomenon that occurs when light interacts with an object or aperture at a very short distance. Unlike far-field diffraction (Fraunhofer diffraction) where the observation point is far away, in near-field diffraction, the detector is placed close to the diffracting element. This proximity means that the light waves are still significantly curved and have not yet propagated into plane waves.

The mathematical description of near-field diffraction is more complex than far-field diffraction. It often involves the Fresnel integrals and requires considering the Huygens-Fresnel principle in its full form, taking into account the phase and amplitude of the wavefronts at every point on the diffracting surface. The resulting diffraction patterns in the near field are highly dependent on the exact distance between the object and the observation plane. They are typically intricate and do not show the simple characteristic patterns seen in far-field diffraction.

This effect is important in applications where high resolution is required at short distances, such as in microscopy, holography, and in the design of optical elements for specific near-field interactions. Understanding and controlling near-field diffraction is crucial for manipulating light at the micro and nanoscale.