| 摘要 |
PURPOSE:To enable a higher measuring accuracy of particle speed by providing a concave section with a specified shape at the part of the inner wall surface facing an optical window irradiated with a laser light to restrain reflected lights from the wall of a passage to a very low level. CONSTITUTION:An optical window 3 is provided on a wall 1 composing a passage where particles flow and a concave section 6 is provided at a part of the inner wall surface 1B facing it in such a manner as to be in noway narrowed depthwise while the inlet thereof is broader than the part irradiated with a laser light 5 while the bottom 6C is formed spherical. The laser light 5 from a laser light source 4 is focused at the point F and dispersed by particles to be detected with a photodetector whereby the particle speed is determined utilizing a Doppler effect. Here, the laser light 5 reaching the inner wall surface 1B penetrates into the concave section 6 and damped with the repetition of reflections several times. This restrains reflected lights to a very low level to enable a high measuring accuracy. |
