Bi-directional displacement measurement by speckle interferometry immune to random vibration

Abstract

A bi-directional in-plane displacement measurement by speckle interferometry using an optimum image extraction under environmental disturbances as random vibrations is investigated. A compact speckle interferometer which has 4 laser beams for bi-directional sensitivity is constructed on a tripod. The polarizations of laser beams of each sensitive direction are arranged orthogonal and diffuse reflected laser beams from an aluminum target can be separated by a polarizing beam splitter in front of digital cameras. The bi-directional in-plane displacement measurement is made possible by a simultaneous capturing of the speckle images for each sensitive direction. An in-plane rotation of the target is measured by the proposed method in a presence of the random vibration. A lot of images are captured at the initial and the rotated state. Then, optimum images which can make interference fringes are extracted. A phase analysis by random phase-stepping method using extracted images is performed. As a result, the analyzed phase difference maps show a good agreement with the given rotation angle. Therefore, it is validated that the bi-directional displacement measurement by speckle interferometry under environmental disturbance is possible.