Patent ID: 6987615

Claim:
A diffractive optical element comprising a substrate and a grating portion formed on the substrate, wherein the grating portion has a step-wise cross section with substantially any one of levels selected from four levels, five levels and six levels, and the diffractive optical element emits substantially zero-order diffracted light that has been transmitted through the grating portion when light with a first wavelength λ 1 satisfying the relationship: 0.35 μm≦λ 1 ≦0.45 μm is incident and emits substantially first-order diffracted light that has been transmitted through the grating portion when light with a second wavelength λ 2 satisfying the relationship: 0.6 μm≦λ 2 ≦0.7 μm is incident, wherein the diffraction efficiency of the first order diffracted light with the second wavelength λ 2 is 50% or higher.