Fringespalt

Fringespalt, literally "fringe slit," is a term used in optics to describe a narrow aperture through which light passes, producing a pattern of bright and dark fringes on a distant screen. The concept arises from diffraction and interference of waves and appears in German- and Dutch-language literature as a standard description of single-slit and multi-slit experiments.

Principle: When coherent light of wavelength λ shines through a slit of width a, the emitted wavefronts interfere across the aperture. This results in a diffraction pattern, with intensity I(θ) approximately I0 (sin β / β)^2, where β = π a sin θ / λ. Minima occur where a sin θ = m λ (m ≠ 0).

Variants include the single-slit continuum and the multi-slit configurations. A double-slit arrangement produces evenly spaced bright fringes at angular positions given by d sin θ = m λ, where d is the center-to-center slit separation; a diffraction envelope from the finite slit width modulates the pattern. A diffraction grating yields a series of sharp maxima at y such that m λ = d sin θ.

Applications and history: The fringespalt arrangement played a key role in the development of the wave theory of light and in early wavelength measurements. In modern labs, it remains a standard demonstration and calibration tool in teaching and optical metrology. In English-language literature the term is uncommon; the patterns are usually described as single-slit diffraction, double-slit interference, or diffraction gratings.

See also: Diffraction, Interference, Diffraction grating, Single-slit diffraction, Double-slit interference.