Metamaterial Negative Refraction — Snell–Veselago
When both ε<0 and μ<0 (double-negative metamaterial), the refractive index n=−√(εμ) is negative — refracted ray bends to the SAME side as incident ray
Veselago (1968): Maxwell's equations permit ε<0, μ<0 simultaneously. The wavevector k, electric field E, and magnetic field H form a left-handed triplet (backward wave). Snell's law n₁sinθ₁ = n₂sinθ₂ still holds, but with n₂<0, θ₂ is negative — refracted ray is on the same side of the normal as the incident ray. Energy flow (Poynting vector) and phase velocity are anti-parallel. A flat slab with n=−1 acts as a perfect lens (Pendry 2000), amplifying evanescent waves to reconstruct sub-wavelength features.