| 摘要 |
PURPOSE:To eliminate thermal damage to an expensive optical modulator by guiding part of a light beam to a photodetector by a mirror, and closing a shutter when the output of the photodetector exceeds a specific value and preventing the light beam from striking on the optical modulator. CONSTITUTION:The projection light beam A of a laser 4 for recording is split by a mirror 19 into the 1st and the 2nd light beams A1 and A2. The mirror 19 is so selected that the intensity of the 2nd light beam A2 is about 1/100 time as large as that of A. This 2nd light beam A2 is incident on the photodetector 20, whose output is applied to a comparator 21. The output of the comparator 21 is applied to the shutter 22. When the light intensity of the 2nd light beam A2 increases and the output of the photodetector 20 exceeds a specific value, that is detected by the comparator 21 and shutter 22 is closed, so that the 1st light beam A1 does not strike on the optical modulator 5 any more. |
