Fresnelbegrensningen

Fresnelbegrensningen, often translated as Fresnel diffraction or Fresnel boundary, refers to a phenomenon in optics where light waves bend around the edges of obstacles or openings. This bending causes the light to spread out, creating a diffraction pattern that deviates from the simple geometric shadow one might expect. Unlike Fraunhofer diffraction, which occurs when both the source and observation point are effectively at infinity, Fresnel diffraction deals with situations where either the source or the observation point, or both, are at a finite distance.

The key characteristic of Fresnel diffraction is that the wavefronts are considered to be curved. This curvature is taken into account when calculating the interference of light rays arriving at the observation point from different parts of the diffracting object. The resulting diffraction pattern is typically more complex than Fraunhofer patterns and varies significantly with the distance from the diffracting object. The shape and intensity distribution within the Fresnel diffraction pattern depend on the geometry of the obstacle or aperture and the wavelength of the light.

This effect is observed in everyday phenomena such as the blurring of shadows' edges and is crucial in understanding the behavior of light in various optical systems, including imaging, microscopy, and holography, especially when dealing with close-range interactions or small apertures. The mathematical treatment of Fresnel diffraction involves the Fresnel integrals, which describe the amplitude and phase of the diffracted light.