Patent ID: 8482855

Claim:
A reflection metallic diffraction grating ( 6 ) having a very high diffraction efficiency for diffracting laser pulses in the femtosecond regime, said grating comprising: a substrate ( 2 ) with a set of lines ( 1 ) having a pitch Λ, said substrate ( 2 ) being covered with a metallic layer ( 2 ′), and said grating ( 6 ) comprising a thin layer ( 4 ) of a dielectric material having a thickness e, said thin dielectric layer ( 4 ) covering the metallic surface ( 12 ) of the lines of the grating, wherein said grating ( 6 ) is suitable for receiving a pulsed electromagnetic lightwave in the femtosecond regime, wherein the thickness e of the thin dielectric layer ( 4 ) is lower than 50 nm, the thickness e being suitable for reducing by at least a factor three the maxima of the square of the electric field of the electromagnetic lightwave on the metallic surface ( 12 ) and in the metallic layer of the substrate ( 2 , 2 ′) compared with the square of the electric field at the surface of a metallic grating ( 5 ) having no thin dielectric layer, in order to improve the laser flow resistance of the diffraction grating in the femtosecond regime; wherein the metallic layer ( 2 ′) is a gold metallic layer ( 2 ′).