| 摘要 |
<P>PROBLEM TO BE SOLVED: To uniformize waveform characteristics of diffraction efficiency in diffraction light of designed order. <P>SOLUTION: A diffractive optical element 10 is formed by tightly sticking a first diffractive grating 1 and a second diffractive grating 2 to each other, each of which has a blazed structure. At least one of the first and second diffractive gratings 1 and 2 is made of a material having a refractive index distribution in a plane normal direction. The diffractive optical element satisfies the following expressions with respect to an arbitrary wavelength λ in a visible wavelength range: ΔΦ1(λ)=1-än22(λ)-n11(λ)}d/mλ, ΔΦ2(λ)=1-än21(λ)-n12(λ)}d/mλ, ΔΦ1(λ)×ΔΦ2(λ)<0, where n11(λ) and n12(λ) are refractive indices for light having the wavelength λ of a base section 11 and an apex section 12 of the first diffractive grating respectively, n21(λ) and n22(λ) are refractive indices for the light having the wavelength λ of a base section 21 and an apex section 22 of the second diffractive grating, respectively, d is an absolute value of a grating height of the first or second diffractive grating, and m is a designed order. <P>COPYRIGHT: (C)2013,JPO&INPIT |
