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Electronic speckle pattern interferometry (ESPI) is a full-field measurement technique, capable of displaying vibrational mode shapes. A simple optical set-up for an ESPI system using a holographic optical element (HOE) is presented. The HOE is designed to create a speckled reference beam in the interferometer. A partially reflective glass plate provides illumination of the object along the normal to its surface, ensuring that the system is sensitive only to out-of-plane displacement of the object. It is demonstrated that the HOE-based system can be used for vibration measurements. Phase shifting can be implemented for fringe analysis. A big advantage of the system is its simplicity. It requires a small number of components: a coherent light source, a holographic optical element, a glass plate and a CCD camera. Introducing holographic optical elements in ESPI gives the advantage of large aperture optical elements at relatively low cost.
Mihaylova, E., Bavigadda, V. & Jallapuram, R. (2008). Whole field out-of-plane vibration analysis with a HOE-based ESPI system, Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, Ed. E. P. Tomasini, Proc. of SPIE, 7098, 70980M. doi:10.1117/12.803004