Diffractive optical element, optical system, and optical apparatus

A diffractive optical element made by adhering a first diffractive grating and a second diffractive grating to each other, each of the first diffractive grating and the second diffractive grating comprising a blazed structure in which a plurality of gratings each having a sawtooth shape are arranged in a grating period direction,

• wherein at least one of the first diffractive grating and the second diffractive grating is made of a material having a refractive index distribution in a plane normal direction perpendicular to the grating period direction, and the following expressions are satisfied for an arbitrary wavelength λ in a visible wavelength range,
• ΔΦ1(λ)=1−{n22(λ)−n11(λ)}d/mλ
• ΔΦ2(λ)=1−{n21(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 of the sawtooth shape of the first diffractive grating and an apex section of the sawtooth shape 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 of the sawtooth shape of the second diffractive grating and an apex section of the sawtooth shape 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.