Uses beam branching optical system the laser Doppler vibrometer

摘要

PURPOSE:To make it possible to measure speed so that the difference between the lengths of the light paths of substance light and reference light is made small by connecting a probe part and an optical-system part with an optical fiber. CONSTITUTION:The laser beam from an output tube 12 is condensed at the end surface of an optical fiber C whose polarization plane is preserved through a polarization beam splitter (BS) 13, a Farady rotor 14, a lambda/2 plate 15, a mirror 16, a polarization BS 17 and a lens 18. The beam is split into the transmitted light and the reflected light (reference light) through a half mirror 26 which is in close contact with the other end surface. The transmitted light is projected on a material to be measured W through a lambda/4 plate 27 and a lens 28. The light is reflected and becomes the object light. The object light and the reference light are transmitted through the fiber C in the reverse direction. At this time, the polarization planes of the object light and the reference light are perpendicular to each other and split into two light paths through the BS 17. The light beams advance through the respective light paths and combined again. The light is inputted into a signal processing part 21. At this time, one of the object light and the reference light is optically modulated 22 and inputted into the processing part 21 so that the polarization planes are directed in the same direction and the frequencies are different. Thus the beat is detected, and the moving speed of the material to be measured W can be operated.