2D Huygens' Principle — Wavelet Diffraction

Scenario

Parameters

Wavelength λ 550 nm

Slit width 3.0 λ

Huygens' construction: every unobstructed point of a wavefront is treated as an independent point source of spherical wavelets. Their coherent sum — real interference, not a drawn envelope — reconstructs the next wavefront. Where a barrier blocks part of the front, the remaining wavelets still radiate sideways, bending the wave into the geometric shadow: diffraction.

Single slit: 1st minimum at sinθ = λ/a. Narrower slit (smaller a/λ) → wider spreading.

Wavelength
550 nm

a / λ ratio
3.00

Diffraction angle θ₁
19.5°