DoppelspaltSetup

DoppelspaltSetup is an experimental arrangement used to demonstrate interference patterns arising when waves pass through two closely spaced openings. It is most commonly associated with light but can be applied to other matter waves, illustrating wave–particle duality and coherence.

A typical setup includes a coherent light source, such as a laser, a barrier containing two narrow slits separated by distance d, and a detection screen or photographic plate positioned at a distance L from the slits. The slits must be narrow relative to the wavelength to produce well-defined fringes, and the light should be spatially coherent to create stable interference. The observable result is a series of alternating bright and dark fringes on the screen, with fringe spacing approximately Δy ≈ λL/d for small angles, where λ is the wavelength.

The observed intensity pattern can be described by an interference term modulated by a single-slit envelope: I(θ) ≈ I0 cos^2(π d sinθ / λ) · sinc^2(π a sinθ / λ), where a is the slit width. This captures both the two-slit interference and the finite width of each slit.

Variations of the DoppelspaltSetup have used electrons, neutrons, atoms, or molecules as the projectiles, demonstrating that interference is not limited to light but is a general feature of quantum waves. The setup also serves to explore which-path information and complementarity: acquiring path data typically reduces or destroys the interference pattern.

Historically, the double-slit experiment traces to Thomas Young in the early 19th century and remains a foundational demonstration of quantum mechanics and wave behavior.