Patent ID: 10670875

Abstract:
A diffractive optical element 10 includes a first diffraction grating 4, a second diffraction grating 5, films 6 formed between the first diffraction grating 4 and the second diffraction grating 5. The DOE 10 satisfies a conditional expression of n2<n1<nha, where nha is an average refractive index of films 6b formed between grating wall surfaces 4b and grating wall surfaces 5b at a wavelength of 550 nm, n1 is a refractive index of the first diffraction grating 4 at a wavelength of 550 nm, and n2 is a refractive index of the second diffraction grating 5 at a wavelength of 550 nm. The films 6b and films 6a that are formed between grating surfaces 4a and grating surfaces 5a satisfy a predetermined relationship.