Reflection of light at various interfaces: (a) A semi-infinite PEC metal milled with subwavelength square holes behaves like an effective medium (λ ≫ d) with a resonant impedance (the hole width is a, the period is d, and the permittivity of hole filling medium is set as ε_h = 25); (b) A semi-infinite PEC metal milled with periodic slits (the slit width is a and the period is d) can induce the diffracted evanescent waves at the interface (λ ~ d); (c) Light reflection by a dielectric slab (with a thickness h) sandwiched between two semi-infinite media. The reflection efficiency and phase shift for the case (a)–(c) are shown in (d)–(f) respectively. We set in (d) and (e) a = d/2 and in (f), n₁ = 1, n₂ = 2, and n₃ = 1.5.