Diffraction grating of the reflective-type

摘要

Reflection-type diffraction grating (1), the cross-section of which having an asymmetrical triangular-shape, the diffraction grating comprising a first layer (3) formed on the cross-section having the asymmetrical triangular shape, of which a material is a metal (Al) for reflecting light; and a second layer (4) formed on said first layer in a surface of a long side of the triangular-shape, of which a material is a dielectric (e.g. MgF₂), wherein the thickness of the second layer is, in nanometers, lower than or equal to 15.38 x (n - 1)^-0.65 where n denotes the refractive index of the dielectric.