| 摘要 |
PROBLEM TO BE SOLVED: To provide a diffraction optical element having desired wavelength characteristics and polarization characteristics by reducing wavelength dependence and polarization dependence.SOLUTION: A diffraction optical element 1 comprises: a first diffraction grating (21) including a first grating surface (21a) and a first grating wall surface (21b); a second diffraction grating (31) including a second grating surface (31a) and a second grating wall surface (31b); and a thin film (11) provided between the first grating wall surface and the second grating wall surface, and in contact with both the first grating wall surface and the second grating wall surface. An extinction coefficient of the thin film for a wavelength λ in a used wavelength band is 0.0005 or less. For the wavelength λ, respective refractive indices of materials of the thin film, the first diffraction grating and the second diffraction grating, a relative refractive index difference between the thin film and the first diffraction grating, and the width of the thin film between the first grating wall surface and the second grating wall surface satisfy predetermined conditions.SELECTED DRAWING: Figure 2 |
