Patent ID: 8755119

Claim:
A diffractive optical element comprising: a first diffractive grating; and a second diffractive grating layered on the first diffracting grating, wherein each of the first and second diffractive gratings are made of two different materials, wherein a difference of an extinction coefficient to d-line between the two materials of each of the first and second diffractive gratings is larger than 0.0002 and smaller than 0.002, and the following conditional expressions are satisfied: 0.05 <|Δnd 1|<0.3; 0.05 <|Δnd 2|<0.3; 20 <|Δvd 1|<40; and |Δ vd 2|<15, where Δnd1 is a difference of a refractive index to the d-line between the two materials of the first diffractive grating, Δnd2 is a difference of a refractive index to the d-line between the two materials of the second diffractive grating, Δvd1 is a difference of an Abbe number between the two materials of the first diffractive grating, and Δvd2 is a difference of an Abbe number between the two materials of the second diffractive grating, and wherein at least one of the two materials of at least one of the first or second diffractive grating satisfies the following conditional expression: 0.35 <θgF <(−1.665 E− 07 ×vd 3 +5.213 E− 05 ×vd 2 −5.656 E− 03 ×vd+ 0.715), where θgF is a partial dispersion ratio of the at least one of the two materials, and vd is an Abbe number of the at least one of the two materials.