| 摘要 |
PURPOSE:To stabilize a focus pulling-in to a recording film by detecting a laser output increase caused by a sudden increase of a laser return light quantity and outputting a focus ON signal, when a laser beam is focused to the recording film. CONSTITUTION:The back light of a laser 1 is received by a solar battery 15, a feedback signal 19 is inputted to a driving circuit 16, and also, a focus ON signal 14 is outputted from a comparator 18. Among reflected light beams from the recording film of the laser 1, a light beam not separated by a beam splitter is returned to the laser 1, brought to feedback coupling and the power is increased. Accordingly, by an instantaneous signal 19 focused by the recording film, an abnormal value is detected. On the other hand, when it is focused to a substrate, the reflected light quantity does not increase suddenly, by the spherical aberration of a diaphragming lens. The abnormal value of the signal 19 is detected by the circuit 18, and the focus ON signal 14 is outputted. In such a way, a stable focus pulling-in to the recording film can be executed.
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