Pre-treatment for preventing degradation of measurement accuracy by speckle noise in speckle interferometry

Abstract

The deformation measurement method by using only two speckle patterns has been proposed in ESPI (electronic speckle pattern interferometry) by using Fourier transform. Furthermore, three-dimensional deformation of the object was able to be measured with the same sensitivities in each direction of three-dimensional axis. However, the measurement results of a complex shape deformation are not always a smooth distribution of phase map. It can be thought that this trouble is caused from the effect of speckle noise which is included in speckle pattern. In this paper, the solution of the problem concerning the speckle noise is investigated. The degradation of measurement accuracy in speckle interferometry is caused by some speckle noise. The speckle noise influences the bias component and the amplitude of the speckle pattern. Furthermore, the spatial movement of speckles of speckle-pattern during the deformation process also influences into the measurement accuracy. In this paper, the pre-treatment for the speckle interferometry is proposed in order to reduce such influence by speckle noise. In the experimental results, it is confirmed that the influence of speckle noise can be reduced by using the features of the reference and the object beams’ intensity distributions in interference measurement process. The proposed method can reduce the influence of speckle noise to 1/1000 in comparing with the results of conventional method. The validity of the proposed method in the practical operation is confirmed from the experiments.