| 摘要 |
PROBLEM TO BE SOLVED: To precisely and easily position plural diffraction grids. SOLUTION: In (a), a die 1 is arranged in a sleeve 2 to form a diffraction surface on its surface and in addition, a die 3 for forming an optical surface opposed to the diffraction surface is fitted freely movable in the sleeve 2. Then, water glass G is poured from a pouring port 5 into a cavity 4 formed in the sleeve 2 by the dies 1, 3 and hardened to prepare a diffraction optical device X. Next, in (b), the obtained device X is moved with the die 3 to form a cavity 6 between the die 1 and the device X. Water glass G' of a kind different from the water glass G is poured from the port 5 into this cavity 6 and hardened to obtain a two-layered diffraction optical device.
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