🌀 Huygens' Principle & Wave Diffraction
Every point on a wavefront is a source of secondary spherical wavelets. Their superposition forms the next wavefront — and when a barrier interrupts them, diffraction occurs. Adjust wavelength, slit width, and preset to see single-slit, double-slit (Young's experiment) and circular aperture patterns. Click the canvas to add point sources.
Preset
Parameters
Stats
Huygens' Principle
Proposed by Christiaan Huygens in 1678: every point on a propagating wavefront acts as a point source of secondary spherical wavelets. The new wavefront is the envelope of all those wavelets. When part of the wavefront is blocked by a barrier with an aperture, the remaining secondary sources radiate into the geometric shadow — producing diffraction.
Single-Slit Diffraction
A slit of width a diffracts light so that the intensity minima occur at angles where an integer number of half-wavelengths fit across the slit:
Intensity: I(θ) = I₀ · sinc²(β/2), where β = (πa sinθ) / λ
Central maximum half-width: θ₁ = arcsin(λ/a)
Double-Slit (Young's Experiment)
Two slits separated by distance d produce bright fringes (constructive interference) where the path difference is an integer multiple of λ:
Dark fringes: d · sinθ = (m + ½)λ
Fringe spacing (small θ): ∆y = λL / d
Applications
CD/DVD grooves act as diffraction gratings — the groove spacing (~1.6 µm) is comparable to visible-light wavelengths, separating colours. X-ray crystallography (Bragg diffraction) uses the periodic atomic lattice as a 3D grating to determine crystal structure. Radio telescopes use aperture synthesis to overcome single-dish diffraction limits. Even the human iris sets a limit on visual acuity through diffraction (Rayleigh criterion: θ ≈ 1.22 λ/D).