Optical material, and, optical element, optical system and laminated diffractive optical element using it

An optical element of which diffraction efficiency hardly varies with wavelength is provided by using an optical material satisfying the conditions that n_d-;6.66710^-;3v^d+1.70 and _g,F-;210^-;3_d+0.59 where n_d is a refractive index at d-line, _d is an Abbe number at the d-line, and _g,F is a second order dispersion at d-line, whereby diffraction efficiency is improved in any working visible wavelength region and more precise chromatic aberration correction is obtained.