| 摘要 |
PURPOSE:To prevent a rear mirror and a front mirror from being contaminated by a method wherein a plurality of optical members, each having a laser beam transmission region, are provided at positions adjacent to each of the front and rear mirrors in a laser chamber and each laser beam transmission region is movably designed on the optical axis of laser beam. CONSTITUTION:A plurality of protective members 12 are mounted on a rotatable discal protective member holder 10 at positions, where are located at the same distance from the center of rotation of the holder 10. The incidences of laser light to a rear mirror 6 and a front mirror 8 are all performed through the members 12 as shown by an arrow FA. Accordingly, it follows that the laser medium and contaminants due to the sputtering and so on of a reserve electrode and so on adhere to said protective members 12 and the mirrors 6 and 8 are protected by the members 12. Thereby, it is almost eliminated for the mirrors 6 and 8 themselves to be contaminated. |
