Patent ID: 8520304

Claim:
A diffractive optical element comprising: a diffraction grating portion including a first diffraction grating and a second diffraction grating, the first diffraction grating and the second diffraction grating being formed of different materials and being stacked so that grating surfaces thereof are in contact with each other, wherein the first diffraction grating is formed of a first grating material having at least three kinds of materials mixed therein, and the following conditions are satisfied: nd 1< nd 2; vd 1 <vd 2; θ gF 1<(−1.665 E −07 ×vd 1 3 +5.213 E −05 ×vd 1 2 −5.656 E −03 ×vd 1+0.715); θ gF 1>(+4.80 E −03 ×vd 1+0.33); and θ gF 1>(−4.73 E −02 ×vd 1+1.31), where nd1, vd1, and θgF1 represent a refractive index, an Abbe number, and a partial dispersion ratio, respectively, of the first grating material with respect to a d-line, and nd2 and vd2 represent a refractive index and an Abbe number, respectively, of a second grating material forming the second diffraction grating with respect to the d-line.