| 摘要 |
PURPOSE:To prevent the noise due to crosstalk and to improve S/N by leading two light beams different in wavelength emitted from an optical system part and shielding the center part of the optical path with a light shielding member. CONSTITUTION:Laser light 12a and 12b obtained by reflecting the reflected light from a medium 10 by splitters 3a and 3b are led to the same optical path, whose center part is shielded by a light shielding plate 5, and reach a condenser lens 6. Light 12a and 12b are converged on the optical axis by the lens 6, and a focus 13b of light 12b having a shorter wavelength is before a focus 13a of light 12a having a long wavelength. Further, since the center part of the optical path is shielded, the light 12a is converged on a small-diameter photodetector 9 and the light 12b is spread and thrown to a large-diameter photodetector 11. Consequently, light 12a and 12b are completely separated. Thus, the noise due to crosstalk is prevented to improve S/N of a signal. |
