| 摘要 |
PROBLEM TO BE SOLVED: To manufacture an optical device of high accuracy by joining a plurality of optical elements. SOLUTION: The optical unit is manufactured by joining diffraction optical elements 41, 42 each as extremely thin as about 1 mm thick to about 120 mm diameter and having diffraction grating patterns 41a, 42a, respectively, in such a manner that the diffraction grating patterns are aligned to be adjacent to each other on the border and that the diffraction grating patterns 41a, 42a posses the center region and peripheral region, respectively. When the optical axis is aligned along the vertical direction, the unit acts as one diffraction optical device having the diffraction grating patterns 41a, 42a overlapped and having a sealed space 43. The optical unit 34 has an 8-step form in the center region in the diffraction grating pattern 41a and has a 4-step form in the peripheral region in the diffraction grating pattern 42a by superimposing effect of the diffraction grating patterns 41a, 42a.
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