Diffraktion

Diffraktion, or diffraction, is the bending and spreading of waves as they encounter an obstacle or pass through an aperture. While the effect is most familiar with visible light, it also occurs with sound, water waves, and matter waves such as electrons.

The phenomenon can be understood through the Huygens-Fresnel principle and the superposition of waves. Each point of a wavefront acts as a source of secondary wavelets; the sum of these contributions yields interference patterns. Constructive and destructive interference produce characteristic bright and dark regions in the resulting intensity distribution.

Common forms include single-slit diffraction, double-slit diffraction, and diffraction gratings. In single-slit diffraction the intensity varies with angle according to I(θ) ∝ [sin(β)/β]², where β ∝ a sin(θ)/λ and a is the slit width. For a pair of slits, the pattern is modulated by a cosine factor, while a grating produces a series of sharp maxima. Fraunhofer (far-field) and Fresnel (near-field) diffraction describe different observational regimes.

Diffraction imposes fundamental limits on resolution in optical instruments and is essential to many techniques. It underpins spectroscopic dispersion with gratings, X-ray crystallography, and electron diffraction in materials science and biology. In practice, diffraction patterns reveal information about apertures, structures, and the wavelength of the illuminating wave. The term has historical roots in early wave-theory experiments that established the wave nature of light.