Patent ID: 7710651

Claim:
A diffractive optical element, comprising: two diffraction gratings made of a first material and a second material, respectively, the two diffraction gratings each having a grating surface and being in contact with each other at the grating surfaces, wherein the first and second materials satisfy all of the following conditions, and the second material is a material obtained by mixing a resin material with a first particulate material satisfying all of the following conditions: nd1≧1.48 νd1≧40 (−1.665 E− 07 ×νd 1 3 +5.213 E− 05 ×νd 1 2 −5.656 E− 03 ×νd 1+0.675)≦θ g,F 1≦(−1.665 E− 07 ×νd 1 3 +5.213 E− 05 ×νd 1 2 −5.656 E− 03 ×νd 1+0.825) (−1.687 E− 07 ×νd 1 3 +5.702 E− 05 ×νd 1 2 −6.603 E− 03 ×νd 1+1.400)≦θ g,d 1≦(−1.687 E− 07 ×νd 1 3 +5.702 E− 05 ×νd 1 2 −6.603 E− 03 ×νd 1+1.580) nd2≦1.6 νd2≦30 θ g,F 2≦(−1.665 E− 07 ×νd 2 3 +5.213 E− 05 ×νd 2 2 −5.656 E− 03 ×νd 2+0.675) θ g,d 2≦(−1.687 E− 07 ×νd 2 3 +5.702 E− 05 ×νd 2 2 −6.603 E− 03 ×νd 2+1.400) nd 1 −nd 2>0 ndb2≧1.70 νdb2≦20 where ng1, nF1, nd1, and nC1 are refractive indexes of the first material for g-line, F-line, d-line, and C-line, respectively, ng2, nF2, nd2, and nC2 are refractive indexes of the second material for g-line, F-line, d-line, and C-line, respectively, and nFb2, ndb2, and nCb2 are refractive indexes of the first particulate material for F-line, D-line, and C-line, respectively, and ν d 1=( nd 1−1)/( nF 1 −nC 1) ν d 2=( nd 2−1)/( nF 2 −nC 2) θ g,F 1=( ng 1 −nF 1)/( nF 1 −nC 1) θ g,d 1=( ng 1 −nd 1)/( nF 1 −nC 1) θ g,F 2=( ng 2 −nF 2)/( nF 2 −nC 2) θ g,d 2=( ng 2 −nd 2)/( nF 2 −nC 2) ν db 2=( ndb 2−1)/( nFb 2 −nCb 2).