Diffractive optical element and manufacturing method thereof

production method of a diffractive optical element, comprising:

• a step of providing a body being composed of a first optical material containing a first resin, and having a diffraction grating on a surface thereof;
• a step of placing on the body a raw material of a second optical material containing a raw material of a second resin, so as to cover the diffraction grating;
• and
• a step of curing the raw material of the second resin to form an optical adjustment layer composed of the second optical material, wherein,
• the first optical material has a refractive index which is smaller than a refractive index of the second optical material;
• the refractive index of the first optical material has a wavelength dispersion which is greater than a wavelength dispersion of the refractive index of the second optical material;
• a difference in solubility parameter between the first resin and the raw material of the second resin is no less than 0.8 [cal/cm3]1/2 and no more than 2.5 [cal/cm3]1/2;
• and
• the second resin has an OH group.