THEORETICAL BASIS FOR REAL-TIME SHEAROGRAPHY

The principle behind the formation of high resolution live fringe patt erns by real-time shearography is presented. It is shown that linear a nd nonlinear photographic recordings both yield instantaneous fringe p atterns which depict the instantaneous surface displacement gradient o f the object. However, in theory, nonlinear photographic recording res ults in lower fringe visibility compared with linear photographic reco rding. In ei ther case, real-time shearography requires a simple optic al setup and eliminates the need for Fourier filtering during fringe r ead-out. It is also found that the fringe characteristics of real-time and double exposure methods differ by a phase angle of 180 degrees.