| 摘要 |
Since the focal distance of the collective lens varies according to a temperature change, when resuming irradiation after laser irradiation is stopped, a long time is required until the cooled lens reaches a predetermined temperature, which lowers the work efficiency. A first mirror (5) and a second mirror (6) are arranged between the collective lens (2) and an irradiation object (4). The first mirror (5) can be set to a reflection position (I) for reflecting laser "a" by cutting off the optical path. The second mirror (6) reflects the laser "a" reflected by the first mirror (5). When the first mirror (5) is set to the reflection position (I), the laser "a" passing through the collective lens (2) is successively reflected by the first mirror (5) and the second mirror (6). The intensity of the laser "a" reflected again by the first mirror (5) is matched with the intensity of the laser "a" reflected from the irradiation object (4) when passing through the collective lens (2), so that the collective lens (2) is heated in the same way as when the laser " a" is applied to the irradiation object (4).
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