| 摘要 |
PURPOSE:To perform adaptive control at the optimum value, by arranging a polarizing optical device consisting of a liquid crystal plate on an optical path in which a reading light beam is made incident on an analyzer, comparing a synthesis signal with a reference value, and controlling the polarizing optical device corresponding to a compared result. CONSTITUTION:The polarizing optical devices 21 and 22 consisting of the liquid crystal plates are arranged on the optical path in which the reading light beam LA7 is made incident on the analyzer 8, and the synthesis signal is compared with the reference value, and the polarizing optical devices 21 and 22 are controlled corresponding to the compared output. And by adjusting the polarizing optical characteristics of the polarizing optical devices 21 and 22, the detecting signals S9A-S9D and S10A-S10D of first and second optical detectors 9 and 10 are controlled. In such a way, it is possible to adaptively control the polarizing characteristic of the reading light beam LA7 to be made incident on the analyzer 8 at the optimum condition.
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