| 摘要 |
The diffractive optical element includes two diffraction gratings made of different materials and being in contact with each other at their grating surfaces. The materials satisfy the following conditions, and the second material is obtained by mixing a resin material with a particulate material satisfying the following conditions: nd1≧1.48, &ngr;d1≧40, (−1.665E−07×&ngr;d13+5.213E−05×&ngr;d12−5.656E−03×&ngr;d1+0.675)≦̸&thetas;g,F1≦̸(−1.665E−07×&ngr;d13+5.213E−05×&ngr;d12−5.656E−03×&ngr;d1+0.825), (−1.687E−07×&ngr;d13+5.702E−05×&ngr;d12−6.603E−03×&ngr;d1+1.400)≦̸&thetas;g,d1≦̸(−1.687E−07×&ngr;d13+5.702E−05×&ngr;d12−6.603E−03×&ngr;d1+1.580), nd2≦̸1.6, &ngr;d2≦̸30, &thetas;g,F2≦̸(−1.665E−07×&ngr;d23+5.213E−05×&ngr;d22−5.656E−03×&ngr;d2+0.675), &thetas;g,d2≦̸(−1.687E−07×&ngr;d23+5.702E−05×&ngr;d22−6.603E−03×&ngr;d2+1.400), nd1−nd2>0, ndb2≧1.70, &ngr;db2≦̸20. The element achieves a high diffraction efficiency in a specific diffraction order over a wide wavelength range.
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