Self-marking phase-stepping electronic speckle pattern interferometry (ESPI) for determining a phase map with least residues

Different from most of the electronic speckle pattern interferometry (ESPI) approaches, which involve the correlation fringe formulation followed by speckle noise elimination (or filtering), to develop a wrapped phase map, this study adopts the approach proposed by Creath in 1985 instead. However, Creath's approach is so critical of its applying interferograms, the influence of which is dependent on the robustness of the applied phase-shifting algorithm and the accuracy of the phase shifter. The self-marking technique proposed by Huang and Chou in 2000 is adopted herein to help overcome any unfavorable conditioning, including hysteresis, nonlinearity or plane tilting, of the pieozo-electrical transducer (PZT), to enable the successful implementation of the Creath's method. With its help, the whole phase stepping history of a practical work (i.e., an ESPI experiment for the present study) can be fully recorded and monitored. Thus, the required phase stepping frames can be accordingly decided and their further calculation will yield a phase map with least number of residues.