| 摘要 |
PROBLEM TO BE SOLVED: To uniformly cool the whole surface of a lens and to prevent the generation of distortion of the lens owing to a temperature difference by making a cooling liquid flow through at least one face of each composing lens. SOLUTION: A biconvex lens 3, a plano-concave lens 4 and a plano-convex lens 5 are arranged in a lens holder 2. Also, a cylindrical flow passage 7 is provided in the lens holder 2, a cooling water inlet 6a is provided in the upper part of the cylindrical flow passage 7 and a cooling water outlet 6b is provided in the lower part of the same. A flow passage 9 between lenses is composed of a space between the lenses, and the flow passage 9 between lenses and the cylindrical flow passage 7 are connected with a branched flow passage 8. The branched flow passage 8 is radially arranged, and the cooling liquid is made to flow through the whole surfaces of the lens. In such a manner, the cooling liquid is fed from the cooling water inlet 6a and discharged from the cooling water outlet 6b, whereby the cooling liquid is made to flow as shown with a hatched part, and the cooling liquid is made to flow over one face of the biconvex lens 3 and the plano-convex lens 5 and both faces of the plano-concave lens 4.
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