| 摘要 |
PURPOSE:To prevent optical parts such as a lens, etc. from being damaged by a laser beam, by providing a shielding plate having a thin slit or a small hole, between a lens and a mask plate. CONSTITUTION:A shielding plate 10 is provided between a lens 4 and a mask 5, and the shielding plate 10 consists of a thin metal, has a thin slit or a small hole 11 which is pierced in the center, and it is provided on a position where a laser beam is condensed most by the lens 4. In such a way, a laser beam 9 which is emitted from a laser oscillator 1 scarcely returns to the lens 4. Also, even if said beam has returned to the lens 4 through the thin slit or small hole 11 which has been pierced in the shielding plate 10, the laser beam 9 is in a divergent direction, therefore, the intensity of the laser beam 9 is feeble. That is to say, by providing the shielding plate 10, it does not occur that optical parts such as a lens, etc. are damaged by the laser beam reflected by the mask plate 5. |
