yksireikädiffractionin

Yksireikädiffractionin, commonly called single-slit diffraction, is the diffraction pattern produced when coherent light of wavelength λ passes through a slit of width a that is comparable to λ. The light from different parts of the slit interferes, producing a characteristic intensity distribution on a distant screen rather than a simple geometric shadow.

In the Fraunhofer (far-field) regime, the intensity I(θ) is proportional to (sin β / β)², where β = π a sin θ / λ. The principal minima occur at a sin θ = m λ for m = ±1, ±2, ..., while the central maximum sits at θ = 0. The width of the central maximum is approximately 2λ/a in small-angle approximation; on a screen at distance L its width is about 2L λ / a.

Physically, the pattern arises from interference of waves emitted across the slit. The distribution can be understood as the Fourier transform of a rectangular aperture. As a decreases, diffraction broadens and the pattern spreads; as a increases, diffraction features narrow and the pattern approaches the geometric shadow. Energy is redistributed among the bands, and total transmitted intensity decreases with smaller a.

Single-slit diffraction is a basic consideration in optics and spectroscopy. It sets a fundamental limit on the angular resolution of slit-based instruments and is used to measure wavelength and slit dimensions. The phenomenon is closely related to diffraction effects in circular apertures, which produce an Airy pattern.