Optical Interference

Double-slit & multi-slit diffraction — wave superposition

Wavelength λ (nm)550 nm

Slit Separation d (μm)10 μm

Slit Width a (μm)3 μm

Screen Distance L (cm)30 cm

Num Slits N2

I(θ) = I₀ · [sinc(πa·sinθ/λ)]² · [sin(N·πd·sinθ/λ)/sin(πd·sinθ/λ)]²

Light passing through slits diffracts and interferes. The intensity pattern combines single-slit diffraction (envelope) with multi-slit interference (fringes). At maxima: d·sin(θ) = mλ. This is the principle behind diffraction gratings and X-ray crystallography.