| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a diffractive optical element in which high diffraction efficiency and high transmittance can be easily obtained and the grating thickness in a grating portion of a diffractive grating can be made thin. <P>SOLUTION: The diffractive optical element includes a diffractive grating portion comprising layers of a first diffractive grating and a second diffractive grating formed of different materials from each other, with the respective grating faces in contact with each other. A first grating forming material constituting the first diffractive grating comprises a mixture of three or more kinds of materials. The first grating forming material and the second grating forming material satisfy conditions represented by nd1<nd2, νd1<νd2, θgF1<(-1.665E-07×νd1<SP POS="POST">3</SP>+5.213E-05×νd1<SP POS="POST">2</SP>-5.656E-03×νd1+0.715), θgF1>(+4.80E-03×νd1+0.33) and θgF1>(-4.73E-02×νd1+1.31), where nd1, νd1 and θgF1 denote the refractive index, the Abbe number and the partial dispersion ratio of the first grating forming material for the d-line, respectively, and nd2 and νd2 denote the refractive index and the Abbe number of the second grating forming material for the d-line, respectively. <P>COPYRIGHT: (C)2012,JPO&INPIT |
