Fresneltilnærmingen

Fresneltilnærmingen refers to a method used in optics and wave physics to approximate wave phenomena in regions where the wavefronts are not necessarily plane or spherical, but can be described by more general surfaces. It is particularly useful for analyzing diffraction effects, such as the Fresnel diffraction pattern, which occurs when the distance between the diffracting object and the observation screen is comparable to the wavelength of the light and the dimensions of the object.

The core idea behind the Fresneltilnærmingen is to divide the wavefront into small regions, often called Fresnel zones or half-period zones. The contribution of each zone to the total wave amplitude at a specific point on the observation screen is calculated. These contributions are then summed up, taking into account their relative phases. The phase difference between successive zones is approximately pi radians, which leads to an alternating constructive and destructive interference as more zones are considered.

This approximation is valid when the distance to the observation point is not so large that the wavefront can be considered planar (which would lead to Fraunhofer diffraction) nor so close that higher-order approximations are needed. The Fresneltilnærmingen provides a more accurate description of diffraction patterns than simpler models but is less computationally intensive than full wave simulations. It is a fundamental concept in understanding the behavior of light and other waves in various optical instruments and phenomena.