Negative Refraction

Veselago lens · reversed Snell's law · phase vs group velocity

n₁ = 1.50
n₂ = −1.50
θ₁ = 35°
Physics: Snell's law with n < 0: n₁sinθ₁ = n₂sinθ₂; for n₂ < 0, the refracted ray bends to the same side of the normal as the incident ray. Veselago (1968) predicted this and showed n < 0 materials also have reversed Doppler effect and reversed Cherenkov radiation. Phase velocity antiparallel to group velocity (energy flow). Perfect lens (Pendry 2000): slab with n = −1 focusses propagating waves with no aberrations AND amplifies evanescent waves to restore near-field information, achieving sub-diffraction resolution. Shelby, Smith & Schultz demonstrated the first n < 0 metamaterial at microwave frequencies in 2001.