Automatic Evaluation Of Holographic Interferograms By Reference Beam Phase Shifting

In most cases experimental investigations in fracture mechanics using holographic interferometry demand a spatial resolution better than a fraction of the wavelength of light. High accuracy can be achieved by phase measurements rather than mere fringe counting. A variation of the phase is performed by heterodyne techniques using a frequency shift of the reference waves or by phase shifting of the reference waves during reconstruction. A method was proposed to determine the three dimensional deformation field of object surface points by solving three systems of equations, each one defined by the data of four phase shifted fringe patterns. By means of this method fringe pattern disturbances can be eliminated, an accurate determination of interference phases, even between fringe maxima, is performed, and the sign of the deformation vector can be achieved. Furthermore, this method is well suitable to be automated in the data generation, recording, and evaluation processes, respectively. These aspects will be discussed and for the first time results of an experimental application of this method in practice, containing all the necessary intermediate steps, are presented.