Patent ID: 7268947

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 λ1 satisfying the relationship: 0.35 μm≦λ1≦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 λ2 satisfying the relationship: 0.6 μm≦λ2≦0.7 μm is incident, wherein the diffraction efficiency of the first order diffracted light with the second wavelength λ2 is 30% or higher.