SIMULTANEOUS MEASUREMENT OF WHOLE INPLANE DISPLACEMENT USING PHASE-SHIFTING ESPI

A novel method for simultaneously measuring whole field in-plane displ acements by using optical fiber phase-shifting electronic speckle patt ern interferometry (ESPI) is presented in this paper. A 1 x 4 single m ode optical fiber beamsplitter is employed to split the laser beam int o four beams of equal intensity. One pair of fibers is utilized to ill uminate the diffuse target at equal angles in the horizontal plane so it is sensitive only to horizontal in-plane displacement. Another pair of optical fibers is set to be sensitive only to vertical in-plane di splacement. The polarization directions of light emitted by fibers are the same for each pair, but are at a right angle between pairs. The o ptical fibers are equal in length for each pair, but are not equal bet ween two pairs. In this case the speckles are interference between eac h pair of fibers, thus the horizontal and vertical displacement compon ents can be obtained simultaneously. By means of a fiber phase shift t echnique we can obtain the quantitative data of whole field displaceme nts. This method has made it possible to study the in-plane displaceme nt of a thin metal plate, and the examples of the results are shown to demonstrate the novel method. (C) 1997 Elsevier Science Ltd.