| 摘要 |
PURPOSE:To prevent a contaminant from sticking to a mirror surface by blowing clean gas to the mirror surface. CONSTITUTION:In a mirror holder 17 for a reflecting mirror 18 which reflects a laser beam 16, etc., a nozzle hole 21 is formed and the surface of the mirror 18 is held invariably at constant pressure higher than the atmospheric pressure by the clean gas supplied through the hole 21. Thus, a contaminant is prevented from sticking on the surface of the mirror 18, improving the durability of the reflecting mirror. |
