| 摘要 |
PURPOSE:To detect stably a signal by placing transparent ceramics in front of a signal detecting photodiode, and feeding back a voltage corresponding to the variation of a luminous amount caused by an uneven reflectivity of a medium, etc., to a transparent ceramics plate. CONSTITUTION:A laser light which has been emitted from a semiconductor laser 1 is made parallel by a collimator lens 2, converted to a circularly polarized light by a 1/4 wavelength plate 4 through a beam splitter 3, stopped down by an objective lens 5, and reflected by a medium 6. Thereafter, its reflected light is made incident on the 1/4 wavelength plate 4 again, returned to a linearly polarized light and reflected by the beam splitter 3, made incident on a transparent ceramics plate 10, stopped down by a condensing lens 7 after erasing the variation of the luminous amount due to an uneven medium by said plate, and made incident on a photodiode 8. |
