Theoretical basis for real-time shearography

Abstract

The principle behind the formation of high resolution live fringe patterns by real-time shearography is presented. It is shown that linear and nonlinear photographic recordings both yield instantaneous fringe patterns which depict the instantaneous surface displacement gradient of the object. However, in theory, nonlinear photographic recording results in lower fringe visibility compared with linear photographic recording. In either case, real-time shearography requires a simple optical setup and eliminates the need for Fourier filtering during fringe read-out. It is also found that the fringe characteristics of real-time and double exposure methods differ by a phase angle of 180 degrees.