Simultaneous measurement of x, y, z components of displacement in holographic interferometry using a four-mirror technique

Abstract

A technique of simultaneously measuring all three Cartesian components of displacement in holographic interferometry is proposed. A single camera is used to record four interferograms of different sensitivities on a single video frame with the aid of mirrors mounted behind the holographic plate. A transformation algorithm has been developed to transform the two-dimensional fringe centres on the interferograms onto the object surface in spatial coordinates. The transformation takes into account perspective distortion and lateral inversion of the images. The accuracy of the transformation is verified by transferring grid points on a graph paper fixed around a cylinder. The measurement technique has been verified by measuring the surface displacement of a thermally deforming cylinder and the results are compared with the prediction of a finite element model of the cylinder.