单缝衍射 / Single Slit Diffraction
第一暗纹角 θ₁ = —
中央明纹宽: —
亮纹 Bright
暗纹 Dark
狭缝 Slit
λ 颜色
光源 / Light
狭缝与屏 / Slit & Screen
演示要点 / Key points
⊙
惠更斯原理 / Huygens Principle
波前上每一点都是次级子波源，子波包络面形成新波前，解释衍射现象。
⏺
中央明纹最宽（2倍）
Central max is twice as wide as secondary maxima: Δθ₀ = 2λ/a vs Δθₙ = λ/a.
⇔
单缝 vs 双缝：衍射包络 × 干涉条纹
Single slit diffraction envelope modulates double-slit interference fringes in real experiments.
a
缝越窄，衍射越明显
Narrower slit → wider diffraction. When a ≫ λ, diffraction is negligible (geometric optics).