MEASUREMENT OF INPLANE VIBRATION BY USING AN IMPROVED LASER SPECKLE INTERFEROMETER WITH THE DOUBLE-APERTURE METHOD

This paper describes the measurement of in-plane vibration using a laser speckle interferometer with the double-aperture method. A new optical detecting system with an additional cylindrical lens is proposed to transform two-dimensional interference fringes in a speckle into a line image on a CCD linear image sensor. From several experiments to measure the static displacement of a specimen, it is revealed that the cylindrical lens has the similar effect as that the interference fringes are detected two-dimensionally, similarly as a scanning measurement. Also, the measuring accuracy is improved through the reduction of local phase variations in the interference fringes. The interferometer is then applied to measure the flexural vibration of a cantilever, and the obtained measuring accuracy is 0.5 mu m.