Speckle interferometry: three-dimensional deformation field measurement with a single interferogram

An electronic speckle interferometer, arranged for out-of-plane sensitivity and with an off-axis reference beam to produce spatial phase bias, is used for three-dimensional deformation field measurements. The complex amplitud e of the object wave is calculated by application of a Fourier-transform me thod to a single interferogram. The change in phase after object deformatio n yields the out-of-plane component of the displacement field. The two in-p lane components are obtained by cross correlation of subimages of the recon structed object wave's intensity, a method that is also referred to as digi tal speckle photography. The Fourier-transform algorithm is extended and mo dified, leading to random measurement errors that are below widely accepted theoretical limits and also to an extended measuring range. These properti es and the mutually combined information improve the accuracy of both metho ds compared with their usual single implementation. The performance is eval uated in experiments with pure out-of-plane, pure in-plane, and combined de formations and compared with theoretical values. An example of a practical application is given. (C) 2001 Optical Society of America.