Single-Slit Diffraction

Physics: Fraunhofer diffraction: I(θ) = I₀·[sin(β/2)/(β/2)]², where β = 2π·a·sinθ/λ. First minimum at sinθ = λ/a; central maximum width Δθ = 2λ/a. Huygens (1678) postulated every wavefront point is a secondary source; Fresnel (1818) added interference between secondary sources; Young (1801) demonstrated two-slit interference. A single photon diffracts through the slit — the pattern is a probability distribution. Resolving power of a lens: θ_min = 1.22λ/D (Rayleigh criterion).