Single-Slit Diffraction

Explore how slit width and wavelength shape the diffraction intensity pattern

Single-slit diffraction arises from Huygens' principle: every point within the slit acts as a secondary wavelet source. At the central maximum (θ = 0) all wavelets arrive in phase, producing maximum intensity. At the first minimum, the slit can be divided into two halves whose wavelets cancel pairwise. The condition a·sinθ = mλ locates all minima (m ≠ 0). The central bright fringe is twice as wide as the side maxima and carries most of the light energy. Narrowing the slit increases diffraction (wider central maximum) — a direct consequence of Heisenberg's uncertainty principle at the quantum level. When two slits are present, the single-slit envelope modulates the double-slit interference fringes, producing missing orders wherever a diffraction minimum coincides with an interference maximum.