| 摘要 |
PROBLEM TO BE SOLVED: To provide a diffraction optical element in which wavelength characteristics of diffraction efficiency of a grating including influences of a grating side face are controlled to be approximately uniform.SOLUTION: A diffraction optical element 10 comprises layers of a plurality of diffraction gratings 1, 2 formed of different materials. Each material for the plurality of gratings shows such a property that in a range 2/3 or more of the use wavelength band of the diffraction optical element, &Dgr;Φ(λ) defined by the following formula increases with the shorter wavelength. In the formula, λ represents a wavelength included in the use wavelength band; ni represents a refractive index at the wavelength λ of the material for an i-th grating in the plurality of gratings; di represents a grating height of the i-th grating; and m represents a diffraction order used. |
