Absorption of light by extremely shallow metallic gratings: metamaterial behavior.

Extremely shallow lamellar metallic gratings are shown to totally absorb incident light inside a wide angular interval. The full absorption still holds at the homogeneization limit when the period tends toward zero. It is shown that a lamellar grating, illuminated in normal incidence and in transerve magnetic polarization with a period lower than 1/, of the vacuum wavelength behaves like a dielectric one with a high refractive index. The full absorption is then not due to the excitation of surface plasmon but either to Fabry-Perot resonance or Brewster effect, depending on the corrugated layer thickness.