| 摘要 |
PURPOSE:To measure excellently a speed even when a body to be measured and a laser oscillation sources are distant from each other to some extent by providing a polarization beam splitter, quarter-wavelength plate, irradiation lens, and a photodetector which obtains a Doppler component. CONSTITUTION:A laser beam 12 emitted from a laser 11 in split by a partial reflecting mirror 13 into about 100:1 intensity proportion. The intense light beam is passed through the polarization beam splitter 14 which transmits only a polarized light beam to illuminate the body 17 to be measured. At such a time, a scattered beam is generated by particles in the object body 17 and returns as a circular polarized beam 12C, but reflected by the polarization beam splitter 14 without being transmitted to change its optical path b6 90 deg.. This vertical polarized light beam 12D and the other weak reference light 12E split by the partial reflecting mirror 13 are photodetected by a photodetector 20 through a partial reflecting mirror 19, then the difference frequency between the vertical polarized beam 12D and reference light 12E, i.e. Doppler frequency is known. Consequently, even when the speed of the object body is measured at a distant point, intense scattered light is obtained, so an accurate measurement is taken. |
