Optimum beam ratio of speckle deformation interferometry using only two speckle patterns

Abstract

The speckle interferometry is a useful deformation measurement method. The speckle interferometry has been improved to the electronic speckle pattern interferometry and the high resolution deformation measurement method by introducing TV and fringe scanning technologies. However, when the method is employed to the deformation measurement of a large object, the intensity of the object beam in optical system has to be forced to use a dark object beam. Then, a problem concerning unresolved speckles happens in the fringe analysis process in the case of a low ratio between object and reference beams’ intensities. In this paper, the process of occurrence of this problem is discussed concerning the ratio of these beams. Under results of discussion, the solution of the problem has been proposed. The deformation by bending a mechanical beam is analyzed under the condition that happens to the trouble concerning unresolved speckles. The validity of the new method is confirmed by the experimental results.