| 摘要 |
PURPOSE:To decrease the probability of dropout generation and to detect a moving speed with high accuracy from a slow speed to a high speed by varying a detection area on the surface of a moving body when scattered light from the surface of the moving body is detected. CONSTITUTION:Speed information on the body 7 is detected according to the shift in the frequency of the scattered light from the moving body 7 where luminous flux with wavelength lambda is made incident. At this time, laser light from a laser 1 is made into parallel luminous flux 3 and diffracted light beams 5a and 5b which are diffracted at an angle theta1 o diffraction by a diffraction grating 10 which rotates at a constant peripheral speed are reflected by reflecting mirrors 6a and 6b which are parallel to the cylindrical shaft 10a of the grating 10. Then they are made incident on the surface of the body 7 at the same angle theta1 of incidence in crossing relation in mutually different directions. In this constitution, the angle theta of incidence on the body 7 varies with the wavelength lambda and the current ratio sintheta/lambda is made nearly constant. Then a driving part 12 puts a condenser lens 8 and a photodetector 9 in linear reciprocal motion in parallel to the cylindrical shaft 10a and then the area of detection by a detector 9 is thus varied and adjusted. |
