To eliminate difference in diffraction efficiency caused by difference in the pitch, in diffractive optical element having a grating or a plurality of grating areas with different pitch.
The diffractive optical element has gratings (grating areas) 4a, 4b with different pitch. In the diffractive optical element, with the ratio of the width A of grating projections to the pitch Λ of the gratings defined as the duty (A/Λ) of the gratings, the gratings (grating areas) 4a, 4b with different pitch are designed to be different in the duty. In other words, in the diffractive optical element, the duty is made variable so that the diffraction efficiency becomes equal in the gratings (grating areas) 4a, 4b with different pitch or, to be concrete, the duty is set for the purpose of making the diffraction efficiency equal in the gratings with different pitch.
KAWASAKI TOSHIYUKI
SUZUDO TAKESHI
MORI KOJI
Shogo Honda