| 摘要 |
PURPOSE:To perform stable detection of the titled angle with easy constitution by providing a light source, a single polarizing plate fitted to a movable mirror, a divided light detector, etc. and obtaining an error signal corresponding to a turning angle of the movable mirror. CONSTITUTION:Since a combined polarizing plate 5 is a combination of two polarizing plates 5a and 5b whose mutual deviated axial directions go straight on a parting line 6, when the light from the light source 1 is transmitted through the polarizing plates 4 and 5, and the polarizing plates 4 and 5a, a difference takes place on the quantities of the transmitted light beams. These quantities of the transmitted light beams are detected respectively by a two-divided-light beam detector 7 and the error signal is obtained by amplifying differentially an output of the light detector 7 with a differential amplifier 9. Since the error signal is indicated by Sin2thetam (thetam is the turning angle of the movable mirror 3), the turning angle displacement of the movable mirror 3 can be detected.
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