Fresneldiffraktsioon

Fresneldiffraktsioon, also known as near-field diffraction, describes the diffraction of light when the observation screen is relatively close to the diffracting aperture or object. In this regime, the distance between the aperture and the screen is not sufficiently large for the Huygens-Fresnel principle to simplify into the Fraunhofer approximation. This means that the wavefronts originating from different points on the aperture are not considered planar at the screen.

The Fresnel diffraction pattern is characterized by its complex and detailed structure, which changes significantly with distance. Unlike Fraunhofer diffraction, where the pattern is independent of distance (beyond the far-field condition), Fresnel patterns exhibit variations in size, shape, and intensity distribution as the observer moves closer to or further from the diffracting object. The curved nature of the wavefronts plays a crucial role in shaping these intricate patterns.

The mathematical description of Fresnel diffraction involves integrating the contributions from each point on the wavefront, taking into account both the amplitude and phase of the diffracted light. This integration typically leads to Fresnel integrals, which are complex functions. Observing Fresnel diffraction requires a light source with a small spatial extent and a coherent wavefront, such as a laser, and careful control of the distances involved. It is often observed with small apertures or edges where the distance to the observation point is comparable to the size of the aperture.